Patent Publication Number: US-2004054014-A1

Title: Method and pharmaceutical compositions forthe treatment of cancer

Description:
[0001] This application is a continuation-in-part of PCT/IL02/00750, filed Sep. 10, 2002, which claims the benefit of priority from U.S. patent application Ser. No. 09/948,621, filed Sep. 10, 2001. 
    
    
     
       FIELD AND BACKGROUND OF THE INVENTION  
       [0002] The present invention relates generally to the field of oncology, and to methods and pharmaceutical compositions for enhancing the activity of a cancer chemotherapeutic agent. More particularly, the present invention concerns the use of a 3-aryloxy-3-phenylpropylamine such as fluoxetine [(N-methyl 3-(p-trifluoromethylphenoxy)-3-phenylpropylamine] as a chemosensitizer for enhancing the cytotoxicity of a chemotherapeutic agent, especially in drug-resistant tumors and more particularly in the case of inherent and/or acquired Multidrug Resistance (MDR). Methods and compositions are provided for the treatment of cancers such as, but not limited to, leukemia, lymphoma, carcinoma and sarcoma (including glioma) using a 3-aryloxy-3-phenylpropylamine, fluoxetine in particular, as a chemosensitizer.  
       [0003] Many of the most prevalent forms of human cancer resist effective chemotherapeutic intervention. Some tumor populations, especially adrenal, colon, jejunal, kidney and liver carcinomas, appear to have drug-resistant cells at the outset of treatment (Barrows, L. R., “Antineoplastic and Immunoactive Drugs”, Chapter 75, pp 1236-1262, in: Remington: The Science and Practice of Pharmacy, Mack Publishing Co. Easton, Pa., 1995). In other cases, a resistance-conferring genetic change occurs during treatment; the resistant daughter cells then proliferate in the environment of the drug. Whatever the cause, resistance often terminates the usefulness of an antineoplastic drug.  
       [0004] Clinical studies suggest that a common form of multidrug resistance in human cancers results from the expression of the MDR1 gene that encodes P-glycoprotein. This glycoprotein functions as a plasma membrane, energy-dependent, multidrug efflux pump that reduces the intracellular concentration of cytotoxic drugs. This mechanism of resistance may account for de novo resistance in common tumors, such as colon cancer and renal cancer, and for acquired resistance, as observed in common hematologic tumors such as acute nonlymphocytic leukemia and malignant lymphomas. Although this type of drug resistance may be common, it is by no means the only mechanism by which cells become drug resistant. MDR is effected via an extrusion mechanism (Tan B, Piwnica-Worms D, Ratner L., Multidrug resistance transporters and modulation. Curr. Opin. Oncol, 2000 September;12(5):450-8). The influx of chemotherapeutic drugs into cells is mainly by passive diffusion across the cell membrane, driven by the drug&#39;s electrochemical-potential gradient. In multidrug resistance cells there are energy-dependant extrusion channels that actively pump the drug out of the cells, reducing its intracellular concentration below lethal threshold. The first pump identified was named Pgp (for P-glycoprotein), the second was named MRP (for Multidrug Resistant associate Protein) and several more have been identified in recent years (Tan et al. 2000, ibid.). All of them are naturally occurring proteins, and their physiological roles are assumed to involve detoxification of cells. In multidrug resistance cells they are present, for reasons yet unknown, in a significantly higher number of copies than in other non-multidrug resistance cells. Hereinafter, these proteins acting as extrusion pumps or channels in multidrug resistance cells are referred to, interchangeably, as “MDR pumps”, “MDR extrusion pumps”, “extrusion pumps”, “MDR channels”, “MDR extrusion channels” and “extrusion channels”.  
       [0005] Chemical modification of cancer treatment involves the use of agents or maneuvers that are not cytotoxic in themselves, but modify the host or tumor so as to enhance anticancer therapy. Such agents are called chemosensitizers. Pilot studies using chemosensitizers indicate that these agents may reverse resistance in a subset of patients. These same preliminary studies also indicate that drug resistance is multifactorial, because not all drug-resistant patients have P-glycoprotein-positive tumor cells and only a few patients appear to benefit from the use of current chemosensitizers.  
       [0006] Chemosensitization research has centered on agents that reverse or modulate multidrug resistance in solid tumors by modulating the activity of the MDR extrusion pumps. Chemosensitizers known to modulate the function of MDR extrusion pumps, e.g., P-glycoprotein, include: calcium channel blockers (Verapamil, indicated for the treatment of hypertension), calmodulin inhibitors (trifluoperazine), indole alkaloids (reserpine), quinolines (quinine), lysosomotropic agents (chloroquine), steroids, (progesterone), triparanol analogs (tamoxifen), detergents (cremophor EL), and cyclic peptide antibiotics (cyclosporines, indicated to prevent host vs. graft disease) (DeVita, V. T., et al., in Cancer, Principles &amp; Practice of Oncology, 4th ed., J. B. Lippincott Co., Philadelphia, Pa., pp 2661-2664, 1993; Sonneveld P, Wiemer E. Inhibitors of multidrug resistance., Curr Opin Oncol 1997 November;9(6):543-8).  
       [0007] A review of studies where chemosensitizing agents were used concluded the following: (i) cardiovascular side effects associated with continuous, high-dose intravenous Verapamil therapy are significant and dose-limiting; (ii) dose-limiting toxicities of the chemosensitizers, trifluoperazine and tamoxifen, was attributed to the inherent toxicity of the chemosensitizer and not due to enhanced chemotherapy toxicity; (iii) studies using high doses of Cyclosporin A as a chemosensitizer found hyperbilirubinemia as a side effect; and (iv) further research is clearly needed to develop less toxic and more efficacious chemosensitizers to be used clinically (DeVita et al., 1993, ibid.).  
       [0008] For example, while Verapamil is effective in hypertension treatment at the 2-4 μM range, for MDR reversal it requires the dose range of 10-15 μM, while at 6 μM it is already in the toxic domain.  
       [0009] Tumors that are considered drug-sensitive at diagnosis but acquire an MDR phenotype at relapse, pose an especially difficult clinical problem. At diagnosis, only a minority of tumor cells may express proteins such as P-glycoprotein, which act as extrusion pumps and treatment with chemotherapy provides a selection advantage for the few cells that are, for example, P-glycoprotein positive early in the course of disease. Another possibility is that natural-product-derived chemotherapy actually induces the expression of MDR1, leading to P-glycoprotein-positive tumors or other MDR pump-positive tumors at relapse. Using chemosensitizers early in the course of disease may prevent the emergence of MDR by eliminating the few cells that are MDR-pump positive at the beginning. In vitro studies have shown that selection of drug-resistant cells by combining Verapamil and Doxorubicin does prevent the emergence of P-glycoprotein, but that an alternative drug resistance mechanism develops, which is secondary to altered topoisomerase II function (Dalton, W. S., Proc. Am. Assoc. Cancer Res. 31:520, 1990).  
       [0010] More efficacious and less toxic chemosensitizers are urgently needed to improve the outcome of chemotherapy. Clinical utility of a chemosensitizer depends upon its ability to enhance the cytotoxicity of a chemotherapeutic drug and also on its low toxicity in vivo. The present inventors have addressed these problems and provide herein a new class of chemosensitizers that permit new approaches in cancer treatment.  
       [0011] 3-Aryloxy-3-phenylpropylamines and their use to treat depression are described in, for example, U.S. Pat. Nos. 4,018,895 and 6,258,853. Fluoxetine [(N-methyl 3-(p-trifluoromethylphenoxy)-3-phenylpropylamine], known better by its commercial name Prozac, is a well-known approved drug, indicated for psychiatric treatments (Cookson J, Duffett R., Fluoxetine: therapeutic and undesirable effects. Hosp Med 1998 August;59(8):622-6). It is known to be an SSRI (Selective Serotonin Reuptake Inhibition) agent, and this activity is considered to be related to its mechanism of action in its capacity as a psychiatric drug (Cookson et al., 1998, ibid.).  
       [0012] WO 94/18961, WO 92/11035, and U.S. Pat. Nos. 5,798,339 and 5,859,065, which are incorporated by reference as if fully set forth herein, disclose methods of treating cancer using histamine antagonists followed by chemotherapy. Specifically, the methods described in these documents are directed at increasing the cytotoxicity and inhibiting the adverse side effects of a chemotherapeutic agent used in chemotherapy, and are effected by administering the chemotherapeutic agent following the administration of a histamine antagonist. WO 94/18961 teaches in this respect that histamine antagonists inhibit normal cell proliferation, while promoting malignant cell proliferation and further teaches DPPE analogs as preferred compounds that act as histamine antagonists that affect cell proliferation as described. WO 94/18961 recites fluoxetine amongst other psychiatric agents which can also act as histamine antagonists, but further states that this group of compounds, at their effective histamine antagonizing concentration, cause adverse side effects, such as cardiac arrhythmia.  
       [0013] In the experiments described in WO 94/18961, doses equivalent to 20-40 mg/M 2  of fluoxetine were employed. These experiments show that at this dose range, fluoxetine promotes the proliferation of fibrosarcoma cells and inhibits the proliferation of concavalin A-stimulated normal lymphocytes. It will be appreciated in this regard that the known, acceptable safety limit of fluoxetine is 80 mg/M 2 , while the safe, substantially side effect-free, daily dose range of fluoxetine is below 10-15 mg/M 2 .  
       [0014] According to WO 94/18961 and WO 92/11035, the histamine antagonists are administered prior to the administration of the chemotherapeutic agent. WO 92/11035 clearly indicates that the antagonist compound is administered about 15 to about 90 minutes, preferably, about 30 to about 60 minutes, prior to the administration of the chemotherapeutic agent, in order to permit the antagonist to inhibit the binding of intracellular histamine to its receptor in normal cells and thereby, in effect, inhibit the proliferation of normal cells and hence provide chemoprotection to such cells.  
       [0015] Although WO 94/18961 teaches the use of fluoxetine in a method of treating cancer, as a compound which is administered in combination with a chemotherapeutic drug, WO 94/18961 does not teach the use of fluoxetine as a chemosensitizer used for enhancing the cytotoxic effect of a chemotherapeutic agent in the treatment of multidrug resistance cancer cells.  
       [0016] Rather, WO 94/18961 teaches that fluoxetine acts as a compound that inhibits proliferation of normal cells while promoting the proliferation of cancer cells, when administered prior to the chemotherapeutic drug, at a dose which causes adverse side effects. Both WO 94/18961 and WO 92/11035 do not address the issue of multidrug resistance cancer cells and fail to indicate the use of the methods disclosed therein for treating multidrug resistance cancer. In fact, the methods taught in these publications, employ, as is described in the Examples section thereof, cancer cells that are known to be susceptible to chemotherapeutic treatment, such as S-10 and fibrosarcoma cells. Furthermore, U.S. Pat. Nos. 5,798,339 and 5,859,065, which correspond to these international publications, specifically recite methods of treating cancer cells which are susceptible to chemotherapy treatment. Based on the mechanism of action of histamine antagonists disclosed in these publications, one would be reluctant from administering fluoxetine at its histamine antagonizing dose to a cancer patient not only because of its associated side effects, but also because it is said and shown to enhance the proliferation of cancer cells at these concentrations.  
       [0017] Hence, 3-Aryloxy-3-phenylpropylamines in general and fluoxetine in particular have not hitherto been indicated as chemosensitizers for the treatment of multidrug resistance cancer.  
       SUMMARY OF THE INVENTION  
       [0018] While reducing the present invention to practice it was unexpectedly found that fluoxetine, a member of the 3-aryloxy-3-phenylpropylamines family of compounds, induces a significant enhancement of the cytotoxic effect of conventional chemotherapeutic drugs, acting via totally different cytotoxic mechanisms, at a dose range well below fluoxetine&#39;s toxicity limits and further well below fluoxetine&#39;s side effect-free limit. Such an enhancement of the cytotoxic effect of chemotherapeutic drugs is particularly advantageous in the treatment of multidrug resistance cancer cells.  
       [0019] Hence, the present invention provides methods, pharmaceutical compositions and kits for chemosensitization using a 3-aryloxy-3-phenylpropylamine as a chemosensitizing agent.  
       [0020] As used herein, the term “chemosensitization” means an increase or an enhancement of the measured cytotoxicity of a chemotherapeutic agent on multidrug resistance cells in the presence of a chemosensitizing agent, as is compared to the level of cytotoxicity exerted by the chemotherapeutic agent in the absence of the chemosensitizing agent.  
       [0021] As shown herein, 3-aryloxy-3-phenylpropylamines act as chemosensitizing agents, rendering inherent and acquired multidrug resistant cancer cells more sensitive to chemotherapy.  
       [0022] Hence, in one aspect, the present invention provides a method of treating a subject suspected of having, or having, a multidrug resistance (MDR) cancer. The method comprises administering to the subject a chemotherapeutically effective amount of a chemotherapeutic agent and a chemosensitizing effective amount of a 3-aryloxy-3-phenylpropylamine. The cancer may be leukemia, lymphoma, carcinoma or sarcoma.  
       [0023] In a preferred embodiment, the chemotherapeutic agent and the 3-aryloxy-3-phenylpropylamine are administered substantially at the same time.  
       [0024] In another preferred embodiment, the chemosensitizing dose of the 3-aryloxy-3-phenylpropylamine is within its safety range, and moreover, it is within its side effect-free range, so as to avoid adverse side effects. Preferably the range used is between about 0.1 mg/M 2  and about 10 mg/M 2 .  
       [0025] As used herein, the term about indicates ±20%.  
       [0026] The phrases “side effect-free range” and “side effect-free limit” indicate a dose range and a maximal dose, respectively, that are within the safety limit and are further below the minimal dose that substantially induces adverse side effects. In other words, these phrases indicate safe, substantially free of side effects, range and limit, respectively. As is demonstrated hereinabove, fluoxetine, for example, induces side effects even at concentrations that are within its safety limit. As the safety limit of fluoxetine is a daily dose of 80 mg/M 2 , fluoxetine induces side effects such as cardiac arrhythmia at a dose range of 20-40 mg/M 2 . Hence, the side effect-free range of fluoxetine includes daily doses that are below its side effect-free limit, namely, below 15 mg/M 2 , preferably, below 10 mg/M 2 .  
       [0027] In another aspect of the invention, 3-aryloxy-3-phenylpropylamines may be used as topical chemosensitizers. For example, Table 2 below indicates that 5-fluorouracil is used topically in the treatment of premalignant skin lesions. The inventors of the present invention envision the use of 3-aryloxy-3-phenylpropylamines to enhance the cytotoxicity of chemotherapeutic agents formulated applicable for topical administration.  
       [0028] A method for selecting a chemotherapeutic agent for which 3-aryloxy-3-phenylpropylamine acts as a chemosensitizer is a further aspect of the present invention. The method comprises (i) assaying cytotoxicity of a candidate chemotherapeutic agent in the presence and in the absence and optionally at different concentrations of a 3-aryloxy-3-phenylpropylamine; and (ii) selecting a candidate chemotherapeutic agent as a chemotherapeutic agent for which 3-aryloxy-3-phenylpropylamine is a chemosensitizer when the cytotoxicity of the candidate agent is greater in the presence of 3-aryloxy-3-phenylpropylamine than in the absence of 3-aryloxy-3-phenylpropylamine. A presently preferred in vitro assay is the MTT cytotoxicity assay which is described in the examples section. An exemplary in vivo assay is described in, for example, U.S. Pat. No. 5,776,925, which is incorporated herein by reference.  
       [0029] Preferably, the method according to this aspect of the present invention is performed with inherent or acquired multidrug resistant cells, with a dose of 3-aryloxy-3-phenylpropylamine that ranges between about 1 μM and about 15 μM, preferably, about 1 μM and about 12 μM and/or while administering the 3-aryloxy-3-phenylpropylamine and the candidate chemotherapeutic agent substantially at the same time.  
       [0030] According to further aspects of the present invention, there are provided pharmaceutical compositions and pharmaceutical kits.  
       [0031] In one embodiment, the pharmaceutical composition of the invention comprises a 3-aryloxy-3-phenylpropylamine as a chemosensitizing agent and a chemotherapeutic agent.  
       [0032] The pharmaceutical composition is preferably packaged in a packaging material and is identified in print in or on the packaging material for use in the treatment of inherent and acquired multidrug resistance cancer.  
       [0033] In another embodiment, the pharmaceutical composition of the invention comprises a 3-aryloxy-3-phenylpropylamine and the pharmaceutical composition is packaged in a packaging material and is identified in print in or on the packaging material for use in chemosensitization.  
       [0034] The pharmaceutical kit of the present invention comprises a 3-aryloxy-3-phenylpropylamine as a chemosensitizing agent and a chemotherapeutic agent, which are individually packaged in the kit.  
       [0035] A 3-aryloxy-3-phenylpropylamine used as a chemosensitizer in accordance with the teachings of the present invention is preferably of the formula:  
                 
 
       [0036] wherein each R′ is independently hydrogen or methyl;  
       [0037] R is naphthyl or  
                 
 
       [0038] R″ and R′″ are halo, trifluoromethyl, C 1 -C 4  alkyl, C 1 -C 3  alkoxy or C 3 -C 4  alkenyl; and  
       [0039] n and m are 0, 1 or 2; and acid addition salts thereof formed with pharmaceutically acceptable acids.  
       [0040] In the above formula when R is naphthyl, it can be either alpha-naphthyl or beta-naphthyl. R″ and R′″ when they are halo, C 1 -C 4  alkyl, C 1 -C 3  alkyloxy or C 3 -C 4  alkenyl represent, illustratively, the following atoms or groups: fluoro, chloro, bromo, iodo, methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, t-butyl, methoxy, ethoxy, n-propoxy, isopropoxy, allyl, methallyl, crotyl and the like. R thus can represent o, m and p-trifluoromethylphenyl, o, m and p-chlorophenyl, o, m and p-bromophenyl, o, m and p-fluorophenyl, o, m and p-tolyl, xylyl including all position isomers, o, m and p-anisyl, o, m and p-allylphenyl, o, m and p-methylallylphenyl, o, m and p-phenetolyl(ethoxyphenyl), 2,4-dichlorophenyl, 3,5-difluorophenyl, 2-methoxy-4chlorophenyl, 2-methyl-4-chlorophenyl, 2-ethyl-4-bromophenyl, 2,4,6-trimethylphenyl, 2-fluoro-4-trifluoromethylphenyl, 2,4,6-trichlorophenyl, 2,4,5-trichlorophenyl and the like.  
       [0041] Also included within the scope of the present invention are the pharmaceutically acceptable salts of the amine bases represented by the above formula formed with non-toxic acids. These acid addition salts include salts derived from inorganic acids such as: hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrobromic acid, hydriodic acid, nitrous acid, phosphorous acid and the like, as well as salts of non-toxic organic acids including aliphatic mono and dicarboxylates, phenyl-substituted alkanoates, hydroxy alkanoates and alkanedioates, aromatic acids, aliphatic and aromatic sulfonic acids etc. Such pharmaceutically-acceptable salts thus include: sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, nitrate, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide, iodide, fluorodide, acetate, propionate, decanoate, caprylate, acrylate, formate, isobutyrate, caprate, heptanoate, propiolate, oxalate, malonate, succinate, suberate, sebacate, fumarate, maleate, butyne-1,4-dioate, hexyne-1,6-dioate, benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate, hydroxybenzoate, methoxybenzoate, phthalate, terephthalate, benzenesulfonates, toluenesulfonate, chlorobenzenesulfonate, xylenesulfonate, phenylacetate, phenylpropionate, phenylbutyrate, citrate, lactate, beta-hydroxybutyrate, glycollate, malate, tartrate, methanesulfonate, propanesulfonates, naphthalene-1-sulfonate, naphthalene-2-sulfonate, mandelate and the like salts.  
       [0042] Compounds illustrative of the scope of this invention include the following:  
       [0043] 3-(p-isopropoxyphenxoy)-3-phenylpropylamine methanesulfonate;  
       [0044] N,N-dimethyl 3-(3′,4′-dimethoxyphenoxy)-3-phenylpropylamine p-hydroxybenzoate;  
       [0045] N,N-dimethyl 3-(alpha-naphthoxy)-3-phenylpropylamine bromide;  
       [0046] N,N-dimethyl 3-(beta-naphthoxy)-3-phenyl-1-methylpropylamine iodide;  
       [0047] 3-(2′-methyl-4′,5′-dichlorophenoxy)-3-phenylpropylamine nitrate;  
       [0048] 3-(p-t-butylphenoxy)-3-phenylpropylamine glutarate;  
       [0049] N-methyl 3-(2′-chloro-p-tolyloxy)-3-phenyl-1-methylpropylamine lactate;  
       [0050] 3-(2′,4′-dichlorophenoxy)-3-phenyl-2-methylpropylamine citrate;  
       [0051] N,N-dimethyl 3-(m-anisyloxy)-3-phenyl-1-methylpropylamine maleate;  
       [0052] N-methyl 3-(p-tolyloxy)-3-phenylpropylamine sulfate;  
       [0053] N,N-dimethyl 3-(2′,4′-difluorophenoxy)-3-phenylpropylamine 2,4-dinitrobenzoate;  
       [0054] 3-(o-ethylphenoxy)-3-phenylpropylamine dihydrogen phosphate;  
       [0055] N-methyl-(2′-chloro-4′-isopropylphenoxy)-3-phenyl-2-methylpropylamine maleate;  
       [0056] N,N-dimethyl 3-(2′-alkyl-4′-fluorophenoxy)-3-phenylpropylamine succinate;  
       [0057] N,N-dimethyl 3-(o-isopropoxyphenoxy)-3-phenyl-propylamine phenylacetate;  
       [0058] N,N-dimethyl 3-(o-)bromophenoxy)-3-phenyl-propyl amine beta-phenylpropionate;  
       [0059] N-methyl 3-(p-iodophenoxy)-3-phenyl-propylamine propiolate;  
       [0060] N-methyl 3-(3-n-propylphenoxy)-3-phenyl-propylamine decanoate; and preferably,  
       [0061] N-methyl 3-(p-trifluoromethylphenoxy)-3-phenylpropylamine.  
       [0062] The present invention successfully addresses the shortcomings of the presently known configurations by identifying new chemosensitizers which efficiently act at concentrations well below their toxicity and which are of particular efficacy in chemosensitizing multi drug resistant (MDR) cancer cells. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0063] The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.  
     [0064] In the drawings:  
     [0065]FIG. 1 is a bar graph demonstrating the increase in death of C6 cells and, separately, PANC-1 cells (% from untreated control) as a function of treatment media, at 24 hours post administration. CS—15 μM fluoxetine alone, CT—0.1 μg/ml Doxorubicin alone, CT+CS—combination of the two. Each bar is an average of 32-64 repeats, and the error bars represent the standard deviations. The star (*) indicates statistical significance P&lt;0.001 (two-tails student t-test) compared to the treatment with the chemotherapeutic drug alone.  
     [0066]FIG. 2 is a bar graph demonstrating the increase in death of C6 cells and, separately, PANC-1 cells (% from untreated control) as a function of treatment media, at 24 hours post administration. CS—15 μM fluoxetine alone, CT—30 μg/ml Mitomycin C alone, CT+CS—combination of the two. Each bar is an average of 32-64 repeats, and the error bars represent the standard deviations. The star (*) indicates statistical significance P&lt;0.001 (two-tails student t-test) compared to the treatment with the chemotherapeutic drug alone.  
     [0067]FIG. 3 is a dose response curve for the effects of fluoxetine on the survival of PANC-1 cells treated with 0.1 μg/ml Doxorubicin or, separately, 0.3 μg/ml Vinblastine, 48 hours post administration. The points are experimental, each an average of 32-64 repeats (sd levels which are similar to those in FIGS. 1 and 2, are not shown in order to reduce symbol crowding). The solid curves are non-theoretical, drawn to emphasize the trends in the data.  
     [0068]FIG. 4 is a bar graph demonstrating LD 50  doses of fluoxetine effect in potentiating tumor treatment by the chemotherapeutic drugs Doxorubicin and, separately, Vinblastine, for five different cell lines. Data was taken from analysis of dose response curves similar to those shown in FIG. 3, for each of the cell lines, obtained under the same drug species, drug dose and treatment period listed in the legend to FIG. 3.  
     [0069]FIGS. 5 a - b  are bar graphs demonstrating the effect of various concentrations (1-20 μM) of fluxetine on the survival of P388/WT (denoted WT) non-resistant cell line (FIG. 5 a ) and P388/ADR (denoted ADR) DOX-resistant cell line. Each bar is an average of 64 wells and the standard deviation (sd) is expressed by the error bar.  
     [0070]FIGS. 6 a - b  are bar graphs demonstrating the effect of various concentrations (0.5, 1 and 5 μg/ml) of doxorubicin (denoted as DOX) with and without 5 μM fluoxetine on the cells death of non-resistant cell line P388/WT (FIG. 6 a ) and the superior chemosensitizing effect of fluoxetine, as compared with Verapamil and Cyclosporin A (denoted as CsA), on MDR-acquired cells (P388/ADR) treated with various concentrations (1, 5 and 10 μg/ml) of DOX (FIG. 6 b ). Each bar is an average of 64 wells and the standard deviation (sd) is expressed by the error bar.  
     [0071]FIG. 7 is a scheme illustrating the MDR mechanism. The chemotherapeutic drug, denoted CT, usually gains entry into the cell by self-diffusion, this influx driven by the electrochemical gradient of the drug across the cell membrane. The intracellular drug concentration is reduced below lethal threshold, by ATP-dependant extrusion through the MDR pumps embedded in the cell membrane.  
     [0072]FIG. 8 demonstrates the efflux of intracellular doxorubicin (DOX) from C6 cells, under unidirectional flux conditions. The efflux is expressed as f(t), the cumulative quantity of DOX that diffused out of the cells at time t, normalized to the total intracellular DOX concentration at time=0. The points are the experimental data, open squares—for cells loaded with 0.1 μg/ml DOX and open circles for cells loaded with 0.1 μg/ml DOX together with 15 μM fluoxetine. The solid curves are non-theoretical, drawn to emphasize the trends in the data.  
     [0073]FIG. 9 demonstrates the efflux of intracellular doxorubicin (DOX) from P388/ADR cells, under unidirectional flux conditions. The efflux is expressed as the cumulative quantity of DOX that diffused out of the cells at time=t, normalized to the total intracellular DOX concentration at time=0. The points are the experimental data, each an average of ten determinations with the sd represented by the error bars, filled squares—for cells loaded with 0.1 μg/ml DOX, open squares—for cells loaded with 0.1 μg/ml DOX together with 5 μM Verapamil, open triangles—for cells loaded with 0.1 μg/ml DOX together with 5 μM Cyclosporin A (CsA) and open circles for cells loaded with 0.1 μg/ml DOX together with 5 μM fluoxetine. The solid curves are non-theoretical, drawn to emphasize the trends in the data.  
     [0074]FIG. 10 is a bar graph demonstrating the chemosensitizer-induced intracellular accumulation of Rhodamine-123 in C-26 cells, expressed in Rhodamine-123 intracellular fluorescence. Each bar is an average of three independent experiments and the standard deviation (sd) is expressed by the error bar.  
     [0075]FIG. 11 is a bar graph demonstrating the chemosensitizer-induced intracellular accumulation of Rhodamine-123 in P388/ADR cells, expressed in Rhodamine-123 intracellular fluorescence. Each bar is an average of three independent experiments and the standard deviation (sd) is expressed by the error bar.  
     [0076]FIGS. 12 a - c  present confocal microscopy images demonstrating the intracellular accumulation of Rhodamine-123 in monolayers of C-26 cells incubated with 5 μM Rhodamine-123 alone (FIG. 12 a ), 5 μM Rhodamine-123 and 15 μM Verapamil (FIG. 12 b ) and 5 μM Rhodamine-123 and 15 μM fluoxetine (FIG. 12 c ).  
     [0077]FIGS. 13 a - b  present confocal microscopy images demonstrating the intracellular accumulation of Doxorubicin in monolayers of P388/ADR cells incubated with 5 μg/ml Doxorubicin alone (FIG. 13 a ) and 5 μg/ml Doxorubicin and 5 μM fluoxetine (FIG. 13 b ).  
     [0078]FIG. 14 presents comparative plots demonstrating an increase in a solid tumor volume with time, in each of the tested groups in in vivo studies of a solid tumor model. Each point in the plots represents an experimental measurement and is an average of 5 animals. The error bars represent the SEM and the curves are non-theoretical, indicating the trends in the data. The results presented in the left-hand side plots were obtained with Mitomycin C (MMC) as the chemotherapeutic drug and the results presented in the right-hand side plots were obtained with Doxorubicin (DOX) as the chemotherapeutic drug.  
     [0079]FIG. 15 presents the survival data in each of the tested groups in the solid tumor model of FIG. 14.  
     [0080]FIGS. 16 a - b  are bar graphs demonstrating the increase in lung weight (FIG. 16 a ) and the number of tumor metastasis (FIG. 16 b ) in different mice groups injected with B16F10 cells. Each bar is an average of all the animals in the group and the sd is represented by the error bars.  
     [0081]FIG. 17 presents the survival data obtained in each of the tested groups in the lung metathesis model of FIGS. 16 a - b.    
     [0082]FIGS. 18 a - b  present comparative plots demonstrating the change in body weight with time, in each of the tested groups in the acquired MDR model: open squares—saline; open circles—doxorubicin; open triangles—fluoxetine; and filled circles—a combination of doxorubicin and fluoxetine. FIG. 18 a  presents the data obtained in mice transplanted with non-resistant P388/WT and FIG. 18 b  presents the data obtained in mice transplanted with MDR-acquired P388/ADR. Each point in the plots represents an experimental measurement and is an average of 5 animals. The error bars represent the standard deviation and the curves are non-theoretical, indicating the trends in the data.  
     [0083]FIGS. 19 a - b  presents the survival data in each of the tested groups described in FIG. 18. FIG. 19 a  presents the data obtained in mice transplanted with non-resistant P388/WT and FIG. 19 b  presents the data obtained in mice transplanted with MDR-acquired P388/ADR. Each line in the plots connects the symbols representing the daily survival state of the group, the symbols themselves were omitted in order to avoid cluttered drawings.  
     [0084]FIG. 20 presents plots demonstrating the effect of fluoxetine on the pharmacokinetics of doxorubicin (DOX) in mice bearing B16F10.9 lung tumors. Each point in the plots represents an experimental measurement and is an average of 10 animals. The error bars represent the standard deviations and the curves are non-theoretical, indicating the trends in the data.  
     [0085]FIG. 21 presents bar graphs demonstrating the effect of fluoxetine on the biodistribution of doxorubicin (DOX) in mice bearing B16F10.9 lung tumors. Each bar is an average of 5 animals and the error bars represent the standard deviations. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0086] The present invention is of methods and pharmaceutical compositions which can be used in chemosensitization. Specifically, the present invention can be used to render cancer cells and, in particular inherent and/or acquired multidrug resistant cancer cells, more sensitive to chemotherapeutic agents, hence increase the cytotoxic effect of such agents on cells.  
     [0087] The principles and operation of the methods and pharmaceutical compositions according to the present invention may be better understood with reference to the drawings and accompanying descriptions.  
     [0088] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.  
     [0089] The present invention results from the discovery that 3-aryloxy-3-phenylpropylamines act as efficient chemosensitizers on multidrug resistance cells at non-toxic concentrations. Chemosensitization using a 3-aryloxy-3-phenylpropylamine refers to an enhancement of cytotoxicity on the part of a chemotherapeutic agent when that agent is administered to multidrug resistance cells in conjunction with administering a 3-aryloxy-3-phenylpropylamine.  
     [0090] Hence, the invention relates to a novel treatment for effecting tumor (both solid and non-solid) chemotherapy, based on the combination of at least one chemotherapeutic drug that are used in, for example, standard therapy protocols in the clinic such as, but not limited to, Doxorubicin, Vinblastine and Mitomycin C; and at least one 3-aryloxy-3-phenylpropylamine, preferably fluoxetine (also known as Prozac), a drug approved and widely used for psychiatric situations such as depression.  
     [0091] It is shown herein that a combined treatment of at least one chemotherapeutic drug and at least one 3-aryloxy-3-phenylpropylamine leads to significant increases in efficacy of the cytotoxic drugs, up to 5-fold for a single dose, and at doses well below safety limits and side effect-free limits known for 3-aryloxy-3-phenylpropylamines. Moreover, the novel treatment is especially effective in tumors that are resistant to the chemotherapeutic drugs, i.e., inherent and acquired multidrug resistance tumors.  
     [0092] It will be appreciated in this respect that other multidrug resistance reversal agents, such as Verapamil and Cyclosporin A, are not used in the clinic due to their toxicity at the required dose levels.  
     [0093] In addition, 3-aryloxy-3-phenylpropylamines, such as fluoxetine, can be administered orally, which is easier on the patient, and its presently indicated effect of mood improvement will also be beneficial to the cancer patient.  
     [0094] According to the present invention the chemotherapeutic agent may be, for example, one of the following: an alkylating agent such as a nitrogen mustard, an ethylenimine and a methylmelamine, an alkyl sulfonate, a nitrosourea, and a triazene; an antimetabolite such as a folic acid analog, a pyrimidine analog, and a purine analog; a natural product such as a vinca alkaloid, an epipodophyllotoxin, an antibiotic, an enzyme, a taxane, and a biological response modifier; miscellaneous agents such as a platinum coordination complex, an anthracenedione, an anthracycline, a substituted urea, a methyl hydrazine derivative, or an adrenocortical suppressant; or a hormone or an antagonist such as an adrenocorticosteroid, a progestin, an estrogen, an antiestrogen, an androgen, an antiandrogen, or a gonadotropin-releasing hormone analog. Specific examples of alkylating agents, antimetabolites, natural products, miscellaneous agents, hormones and antagonists, and the types of cancer for which these classes of chemotherapeutic agents are indicated are provided in Table 2. Preferably, the chemotherapeutic agent is a nitrogen mustard, an epipodophyllotoxin, an antibiotic, or a platinum coordination complex. A more preferred chemotherapeutic agent is Bleomycin, Vinblastine, Doxorubicin, Paclitaxel, etoposide, 4-OH cyclophosphamide, or cisplatinum.  
     [0095] Presently preferred chemotherapeutic agents are Doxorubicin, Mitomycin C and/or Vinblastine, which are the chemotherapeutic drugs employed in the in vitro and/or the in vivo experiments described in the Examples section that follows, yet the use of other chemotherapeutic drugs in context of the present invention is also applicable.  
     [0096] As is well known in the art, Vinblastine, Mitomycin C and Doxorubicin are cytotoxic drugs toward which many tumors exhibit drug resistance and therefore serve as representative examples for the chemosensitization effect of 3-aryloxy-3-phenylpropylamine.  
     [0097] Furthermore, as is delineated in Table 1 below, these drugs differ from one other by their chemical structure, mechanism of action and the location of their cellular targets. For example, Vinblastine acts in the cytosol, via depolymerization of microtubules, Mitomycin C acts in the nucleus via DNA alkylation and Doxorubicin acts in both the cytosol and the nucleus, as well as in the cell membrane, having different effects in each of these locations.  
                       TABLE 1                           Intracellular               location of drug       Cytotoxic drug   target   Mechanisms of action                  Vinblastine   The cytosol   Depolymerization of Microtubules       Mitomycin C   The nucleus   DNA alkylation       Doxorubicin   The nucleus   DNA intercalation, blocking synthesis               of DNA and RNA           The cytosol   DNA strands scission by affecting               topoisomerase II           The cell   Altering membrane fluidity and ion           membrane   transport               Generation of semiquinone free radicals               and oxygen radicals                  
 
     [0098] Hence, as these drugs act via different pathways, the present inventors envision that 3-aryloxy-3-phenylpropylamines may be used as chemosensitizers for enhancing the cytotoxicity of a variety of chemotherapeutic agents having different mechanisms of action.  
     [0099] A listing of currently available chemotherapeutic agents according to class, and including diseases for which the agents are presently indicated, is provided as Table 2 below. Each of these exemplary chemotherapeutic agents can be used in the context of the present invention.  
               TABLE 2                          Chemotherapeutic Agents Useful in Neoplastic Disease 1                               Class   Type of Agent   Name   Disease 2                 Alkylating   Nitrogen   Mechlorethamine   Hodgkin&#39;s disease, non-Hodgkin&#39;s       Agents   Mustards   (HN 2 )   lymphomas               Cyclophosphamide   Acute and chronic lymphocytic               Ifosfamide   leukemias, Hodgkin&#39;s disease,                   non-Hodgkin&#39;s lymphomas,                   multiple myeloma,                   neuroblastoma, breast, ovary,                   lung, Wilms&#39; tumor, cervix,                   testis, soft-tissue sarcomas               lphalan   Multiple myeloma, breast, ovary               lorambucil   Chronic lymphocytic leukemia,                   primary macroglobulinemia,                   Hodgkin&#39;s disease, non-                   Hodgkin &#39;s lymphomas               Estramustine   Prostate           Ethylenimines   Hexamethyl-   Ovary           and   melamine           Methylmelamines   Thiotepa   Bladder, breast, ovary           Alkyl   Busulfan   Chronic granulocytic leukemia           Sulfonates           Nitrosoureas   Carmustine   Hodgkin&#39;s disease, non-Hodgkin&#39;s                   lymphomas, primary brain                   tumors, multiple myeloma,                   malignant melanoma               Lomustine   Hodgkin&#39;s disease, non-Hodgkin&#39;s                   lymphomas, primary brain                   tumors, small-cell lung               Semustine   Primary brain tumors, stomach,                   colon               Streptozocin   Malignant pancreatic insulinoma,                   malignant carcinoid           Triazenes   Dacarbazine   Malignant melanoma, Hodgkin&#39;s               Procarbazine   disease, soft-tissue sarcomas               Aziridine       Antimetabolites   Folic Acid   Methotrexate   lymphocytic leukemia,           Analogs   Trimetrexate   choriocarcinoma, mycosis                   fungoides, breast, head and                   neck, lung, osteogenic sarcoma           Pyrimidine   Fluorouracil   Breast, colon, stomach,                   pancreas,           Analogs   Floxuridine   ovary, head and neck, urinary                   bladder, premalignant skin                   lesions (topical)               Cytarabine   Acute granulocytic and acute           Purine Analogs   Azacitidine   lymphocytic leukemias           and Related   Mercaptopurine   lymphocytic, acute           Inhibitors       granulocytic, and chronic                   granulocytic leukemias               Thioguanine   Acute granulocytic, acute                   lymphocytic, and chronic                   granulocytic leukemias               Pentostatin   Hairy cell leukemia, mycosis                   fungoides, chronic lymphocytic                   leukemia               Fludarabine   Chronic lymphocytic leukemia,                   Hodgkin&#39;s and non-Hodgkin&#39;s                   lymphomas, mycosis fungoides       Natural   Vinca Alkaloids   Vinblastine (VLB)   Hodgkin&#39;s disease, non-Hodgkin&#39;s       Products           lymphomas, breast, testis               Vincristine   Acute lymphocytic leukemia,                   neuroblastoma, Wilms&#39; tumor,                   rhabdomyosarcoma, Hodgkin&#39;s                   disease, non-Hodgkin&#39;s                   lymphomas, small-cell lung               Vindesine   Vinca-resistant acute lymphocytic                   leukemia, chronic myolocytic                   leukemia, melanoma, lymphomas,                   breast           Epipodophyl-   Etoposide   Testis, small-cell lung and other           Lotoxins   Teniposide   lung, breast, Hodgkin&#39;s                   disease, non-Hodgkin&#39;s                   lymphomas, acute granulocytic                   leukemia, Kaposi&#39;s sarcoma           Antibiotics   Dactinomycin   Choriocarcinoma, Wilms&#39; tumor,                   rhabdomyosarcoma, testis,                   Kaposi&#39;s sarcoma               Daunorubicin   Acute granulocytic and acute                   lymphocytic leukemias               Doxorubicin   Soft-tissue, osteogenic, and               4′-   other sarcomas; Hodgkin&#39;s               Deoxydoxorubicin   disease, non-Hodgkin&#39;s                   lymphomas, acute leukemias,                   breast, genitourinary, thyroid,                   lung, stomach, neuroblastoma               Bleomycin   Testis, head and neck, skin,                   esophagus, lung, and                   genitourinary tract;                   Hodgkin&#39;s disease, non-                   Hodgkin&#39;s lymphomas               Plicamycin   Testis, malignant hypercalcemia               Mitomycin   Stomach, cervix, colon, breast,                   pancreas, bladder, head and                   neck           Enzymes   Asparaginase   Acute lymphocytic leukemia           Taxanes   Docetaxel   Breast, ovarian               Paclitaxel           Biological   Interferon Alfa   Hairy cell leukemia, Kaposi&#39;s           Response       sarcoma, melanoma, carcinoid,           Modifiers       cell, ovary, bladder,                   non-Hodgkin&#39;s lymphomas,                   mycosis fungoides, multiple                   myeloma, chronic granulocytic                   leukemia               Tumor Necrosis   Investigational               Factor               Tumor-   Investigational               Infiltrating               Lymphocytes       Miscellaneous   Platinum   Cisplatin   Testis, ovary, bladder, head and       Agents   Coordination   Carboplatin   neck, lung, thyroid, cervix,           Complexes       endometrium, neuroblastoma,                   osteogenic sarcoma           Anthracenedione   Mitoxantrone   Acute granulocytic leukemia,                   breast           Substituted   Hydroxyurea   Chronic granulocytic leukemia,           Urea       polycythemia vera, essential                   thrombocytosis, malignant                   melanoma           Methyl   Procarbazine   Hodgkin&#39;s disease           Hydrazine           Derivative           Adrenocortical   Mitotane   Adrenal cortex           Suppressant   Aminoglutethimide   Breast       Hormones and           Acute and chronic lymphocytic       Antagonists   costeroids       leukemias, non-Hodgkin&#39;s                   lymphomas, Hodgkin&#39;s disease,                   breast           Progestins   Hydroxy-   Endometrium, breast               progesterone               caproate               Medroxy-               progesterone               acetate               Megestrol acetate           Estrogens   Diethyistil-   Breast, prostate               bestrol               Ethinyl estradiol           Antiestrogen   Tamoxifen           Androgens   tosterone               propionate               Fluoxymesterone           Antiandrogen   Flutamide   Prostate           Gonadotropin-   Leuprolide   Prostate, Estrogen-receptor-           Releasing   Goserelin   positive breast           hormone           analog                       #in particular for treatment protocols.                   
 
     [0100] 3-aryloxy-3-phenylpropylamine compounds, methods for making same and methods for using them are described in U.S. Pat. Nos. 4,018,895, 4,314,081, 5,166,437 and 6,258,853, which are incorporated by reference herein, and further below.  
     [0101] 3-Aryloxy-3-phenylpropylamines used as chemosensitizers may be administered before, together with or after administration of the chemotherapeutic agent. Preferably, the 3-aryloxy-3-phenylpropylamine and the chemotherapeutic agent are administered substantially at the same time.  
     [0102] The administration of a chemosensitizer and a chemotherapeutic agent substantially at the same time is a highly important and advantageous feature in the treatment of multidrug resistance (MDR) cells.  
     [0103] As is discussed in detail hereinabove, MDR is effected via an extrusion mechanism, which involves energy-dependant extrusion channels or pumps that actively pump the drug out of the cells, thereby reducing its intracellular concentration below lethal threshold. As is further discussed hereinabove, chemosensitizers in this respect are agents that reverse or modulate multidrug resistance in MDR cells by modulating the activity of the MDR extrusion pumps. It is therefore advantageous that the chemosensitizing agent and the chemotherapeutic agent would be administered substantially at the same time, in order to allow their combined action by their dual presence in the treated cell.  
     [0104] Hence, the phrase “substantially at the same time”, as used herein, means that the 3-aryloxy-3-phenylpropylamine and the chemotherapeutic agent are administered in such time intervals that would allow their dual presence in effective concentrations in the treated cells. The 3-aryloxy-3-phenylpropylamine and the chemotherapeutic agent can be administered by different or identical routes of administration.  
     [0105] The 3-aryloxy-3-phenylpropylamine may be administered as a single dose, or it may be administered as two or more doses separated by a time interval. Where the 3-aryloxy-3-phenylpropylamine is administered as two or more doses, the time interval between the 3-aryloxy-3-phenylpropylamine administrations may be from about one minute to about 12 hours, preferably from about 5 minutes to about 5 hours, more preferably about 4 to 5 hours. The dosing protocol may be repeated; from one to three times, for example. Administration may be intravenous, intraperitoneal, parenteral, intramuscular, subcutaneous, oral, or topical, with oral and intravenous administration being preferred, and intravenous administration being presently most preferred.  
     [0106] The 3-aryloxy-3-phenylpropylamine used in the method of the invention administered in a chemosensitizing effective amount.  
     [0107] As used herein the phrase “chemosensitizing effective amount” means that daily dose which results in an enhanced toxicity by a chemotherapeutic agent, without adverse side effects. The specific daily dose will vary depending on the particular 3-aryloxy-3-phenylpropylamine used, the dosing regimen to be followed, and the particular chemotherapeutic agent with which it is administered. Such a daily dose can be determined without undue experimentation by methods known in the art or as described herein.  
     [0108] As is exemplified in the Examples section that follows, a presently preferred chemosensitizing effective amount, according to the present invention, ranges between 0.05 mg/M 2  and 20 mg/M 2 , preferably between 0.1 mg/M 2  and 10 mg/M 2 , more preferably between 0.1 mg/M 2  and 7 mg/M 2 , more preferably between 0.1 mg/M 2  and 5 mg/M 2  and most preferably between 0.4 mg/M 2  and 4 mg/M 2 .  
     [0109] The chemosensitizing effect of fluoxetine as a representative example of a 3-aryloxy-3-phenylpropylamine, was tested in vitro by administering fluoxetine, in combination with different chemotherapeutic drugs, at doses that range between 2 μM and 15 μM, administered every two days. These in vitro doses correspond to human daily doses that range between about 0.45 mg/M 2  and about 3.5 mg/M 2 , respectively.  
     [0110] The conversion of these in vitro doses to in vivo human daily doses is performed by first converting the μM fluoxetine concentrations to units of mg/ml, and thereafter estimating the corresponding human daily dose in mg/Kg body weight, taking into account that an average human weight is about 70 Kg, an average human height is about 1.75 m and that the human blood volume is 5 liters, and further taking into account that the in vitro treatment in the experiments conducted included a single dose every two days. The obtained results are then converted into mg/M 2  surface area units, assuming that an individual weighting 70 Kg and of a height of 1.75 m has 1.85 M 2  skin surface.  
     [0111] In the in vivo studies, which are also described in detail in the Examples section that follows, the daily doses of fluoxetine were about 0.04 mg/kg body, which correspond to 2.8 mg per 70 Kg body or to 1.5 mg/M 2 , according to the conversion index described hereinabove.  
     [0112] The chemosensitizing effective amount of fluoxetine as a representative 3-aryloxy-3-phenylpropylamine, as is demonstrated by the in vitro and in vivo studies described herein, is therefore well below fluoxetine doses that are used in its classical, psychiatric indications, and are well below both its safety limit and its side effect-free limit. As is further shown in these in vitro and in vivo studies, at this low dose, fluoxetine has no anticancer effect and no adverse side effects.  
     [0113] The fact that fluoxetine exerts chemosensitizing effect in the treatment of multidrug resistance cancer at such low doses is novel and highly advantageous.  
     [0114] As is discussed in detail hereinabove, a method that involves administration of fluoxetine for treating cancer is described in WO 94/19861.  
     [0115] The fluoxetine is used in this method as a compound that inhibits proliferation of normal cells, while promoting the proliferation of cancer cells, via histamine receptor antagonism mechanism. The fluxetine dose required to achieve these effects, according to the teachings of WO 94/19861, is 20-40 mg/M 2 , which is about 10-20 fold higher than the dose used in context of the present invention and about 2 fold higher than the side effect-free limit determined for fluxetine. As is further indicated in WO 94/18961, at this dose range, fluoxetine promotes the proliferation of cancer cells, and is further accompanied by adverse side effects such as cardiac arrhythmia. Also, administration of fluoxetine according to the teachings of WO 94/18961 should precede the administration of a chemotherapeutic agent in order to be effective. In sharp contrast, the administration of fluoxetine and the chemotherapeutic agent, according to the present invention, should be substantially at the same time, for reasons set forth hereinabove.  
     [0116] Hence, the present invention provides a method of treating cancer that is superior over to the presently known methods, as it involves the administration of the chemosensitizing agent at low concentrations, within its safety and side effect-free limits, and therefore does not results in adverse side effects.  
     [0117] A 3-aryloxy-3-phenylpropylamine for use as a chemosensitizer according to the teachings of the present invention may have structure I:  
                 
 
     [0118] wherein each R′ is independently hydrogen or methyl;  
     [0119] R is naphthyl or  
                 
 
     [0120] R″ and R′″ are halo, trifluoromethyl, C 1 -C 4  alkyl, C 1 -C 3  alkoxy or C 3 -C 4  alkenyl; and  
     [0121] n and m are 0, 1 or 2; and acid addition salts thereof formed with pharmaceutically acceptable acids.  
     [0122] In the above formula when R is naphthyl, it can be either alpha-naphthyl or beta-naphthyl. R″ and R′″ when they are halo, C 1 -C 4  alkyl, C 1 -C 3  alkyloxy or C 3 -C 4  alkenyl represent, illustratively, the following atoms or groups: fluoro, chloro, bromo, iodo, methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, t-butyl, methoxy, ethoxy, n-propoxy, isopropoxy, allyl, methallyl, crotyl and the like. R thus can represent o, m and p-trifluoromethylphenyl, o, m and p-chlorophenyl, o, m and p-bromophenyl, o, m and p-fluorophenyl, o, m and p-tolyl, xylyl including all position isomers, o, m and p-anisyl, o, m and p-allylphenyl, o, m and p-methylallylphenyl, o, m and p-phenetolyl(ethoxyphenyl), 2,4-dichlorophenyl, 3,5-difluorophenyl, 2-methoxy-4chlorophenyl, 2-methyl-4-chlorophenyl, 2-ethyl-4-bromophenyl, 2,4,6-trimethylphenyl, 2-fluoro-4-trifluoromethylphenyl, 2,4,6-trichlorophenyl, 2,4,5-trichlorophenyl and the like.  
     [0123] Also included within the scope of this invention are the pharmaceutically acceptable salts of the amine bases represented by the above formula formed with non-toxic acids. These acid addition salts include salts derived from inorganic acids such as: hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrobromic acid, hydriodic acid, nitrous acid, phosphorous acid and the like, as well as salts of non-toxic organic acids including aliphatic mono and dicarboxylates, phenyl-substituted alkanoates, hydroxy alkanoates and alkanedioates, aromatic acids, aliphatic and aromatic sulfonic acids etc. Such pharmaceutically-acceptable salts thus include: sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, nitrate, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide, iodide, fluorodide, acetate, propionate, decanoate, caprylate, acrylate, formate, isobutyrate, caprate, heptanoate, propiolate, oxalate, malonate, succinate, suberate, sebacate, fumarate, maleate, butyne-1,4-dioate, hexyne-1,6-dioate, benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate, hydroxybenzoate, methoxybenzoate, phthalate, terephthalate, benzenesulfonates, toluenesulfonate, chlorobenzenesulfonate, xylenesulfonate, phenylacetate, phenylpropionate, phenylbutyrate, citrate, lactate, beta-hydroxybutyrate, glycollate, malate, tartrate, methanesulfonate, propanesulfonates, naphthalene-1-sulfonate, naphthalene-2-sulfonate, mandelate and the like salts.  
     [0124] Compounds illustrative of the scope of this invention include the following:  
     [0125] 3-(p-isopropoxyphenxoy)-3-phenylpropylamine methanesulfonate;  
     [0126] N,N-dimethyl 3-(3′,4′-dimethoxyphenoxy)-3-phenylpropylamine p-hydroxybenzoate;  
     [0127] N,N-dimethyl 3-(alpha-naphthoxy)-3-phenylpropylamine bromide;  
     [0128] N,N-dimethyl 3-(beta-naphthoxy)-3-phenyl-1-methylpropylamine iodide;  
     [0129] 3-(2′-methyl-4′,5′-dichlorophenoxy)-3-phenylpropylamine nitrate;  
     [0130] 3-(p-t-butylphenoxy)-3-phenylpropylamine glutarate;  
     [0131] N-methyl 3-(2′-chloro-p-tolyloxy)-3-phenyl-1-methylpropylamine lactate;  
     [0132] 3-(2′,4′-dichlorophenoxy)-3-phenyl-2-methylpropylamine citrate;  
     [0133] N,N-dimethyl 3-(m-anisyloxy)-3-phenyl-1-methylpropylamine maleate;  
     [0134] N-methyl 3-(p-tolyloxy)-3-phenylpropylamine sulfate;  
     [0135] N,N-dimethyl 3-(2′,4′-difluorophenoxy)-3-phenylpropylamine 2,4-dinitrobenzoate;  
     [0136] 3-(o-ethylphenoxy)-3-phenylpropylamine dihydrogen phosphate;  
     [0137] N-methyl-(2′-chloro-4′-isopropylphenoxy)-3-phenyl-2-methylpropylamine maleate;  
     [0138] N,N-dimethyl 3-(2′-alkyl-4′-fluorophenoxy)-3-phenylpropylamine succinate;  
     [0139] N,N-dimethyl 3-(o-isopropoxyphenoxy)-3-phenyl-propylamine phenylacetate;  
     [0140] N,N-dimethyl 3-(o-)bromophenoxy)-3-phenyl-propylamine beta-phenylpropionate;  
     [0141] N-methyl 3-(p-iodophenoxy)-3-phenyl-propylamine propiolate;  
     [0142] N-methyl 3-(3-n-propylphenoxy)-3-phenyl-propylamine decanoate; and preferably,  
     [0143] N-methyl 3-(p-trifluoromethylphenoxy)-3-phenylpropylamine.  
     [0144] The 3-aryloxy-3-phenylpropylamines of this invention in the form of their free bases are high boiling oils, but white crystalline solids in the form of their acid addition salts. The compounds can be prepared in several ways. A particularly useful procedure for preparing compounds represented by the above formula (in which both R′ groups attached to the nitrogen are methyl) involves the reduction of beta-dimethylaminopropiophenone produced by a Mannich reaction to yield N,N-dimethyl 3-phenyl-3-hydroxypropylamine. Replacement of the hydroxyl group with a halogen, such as chlorine, yields the corresponding N,N-dimethyl 3-phenyl-3-chloropropylamine. Reaction of this chloro compound with a suitably substituted phenol, as for example o-methoxyphenol (guiacol), produces a compound of this invention in which both R′ groups are methyl. Treatment of the N,N-dimethyl compound with cyanogenbromide serves to replace one N-methyl group with a cyano group. Hydrolysis of the resulting compound with base yields a compound of this invention in which only one R′ group on the nitrogen is methyl. For example, treatment of N,N-dimethyl 3-(o-anisyloxy)-3-phenylpropylamine with cyanogen bromide followed by alkaline hydrolysis of the N-cyano compound yields directly N-methyl 3-(o-anisyloxy)-3-phenylpropylamine [N-methyl 3-(o-methoxy phenoxy)-3-phenylpropylamine].  
     [0145] An alternate preparation of the compounds of this invention in which only one of the R′ groups attached to the nitrogen is methyl is carried as follows:  
     [0146] 3-Chloropropylbenzene is reacted with a positive halogenating agent such N-bromosuccinimide to yield the corresponding 3-chloro-1-bromopropylbenzene. Selective replacement of the bromo atom with the sodium salt of a phenol, as for example, the sodium salt of o-methoxyphenol (guiacol) yields a 3-chloro-1-(1-methoxyphenoxy)-propylbenzene [also named as 3-chloro-1-(o-anisyloxy)propylbenzene]. Reaction of the 3-chloro derivative thus produced with methylamine yields the desired N-methyl 3-(o-anisyloxy)-3-phenylpropylamine.  
     [0147] 3-Aryloxy-3-phenylpropylamine compounds in which both R′ groups attached to the nitrogen in the above formula are hydrogen can be prepared from an intermediate produced in the previous preparation of the N-methyl compounds such as, for illustrative purposes, 3-chloro-1-(o-anisyloxy)-propylbenzene prepared by the reaction of 3-chloro-1-bromobenzene and sodium guiacol. This chloro compound is reacted with sodium azide to give the corresponding 3-azido-1-(o-anisyloxy)-propylbenzene. Reduction of the azide group with a metallo-organic reducing agent such as sodium borohydride yields the desired primary amine. Alternatively, the chloro compound can be reacted directly with a large excess of ammonia in a high pressure reactor to give the primary amine.  
     [0148] 3-Aryloxy-3-phenylpropylamine compounds in which the R′ group on the carbon atom alpha to the nitrogen is methyl can be prepared by reacting phenyl 2′-propenyl ketone with dimethylamine [See J. Am. Chem. Soc., 75, 4460 (1953)]. The resulting 3-dimethylaminobutyrophenone is reduced to yield the N,N-dimethyl 3-hydroxy-1-methyl-3-phenylpropylamine. Replacement of the hydroxyl with chlorine followed by reaction of the chloro-compound with the sodium salt of a suitably substituted phenol yields the N,N-dimethyl derivatives of this invention bearing an alpha methyl group on the propylamine backbone of the molecule. Production of the corresponding N-methyl derivative can be accomplished by the aforementioned reaction sequence utilizing cyanogen bromide. The N-methyl derivative can in turn be converted to the corresponding primary amine (in which both R′ groups on the nitrogen are hydrogen) by oxidation in neutral permanganate according to the procedure of Booher and Pohland, Ser. No. 317,969, filed Dec. 26, 1972. Compounds in which the R′ group attached to the beta-carbon atom is methyl are prepared by a Mannich reaction involving propiophenone, formaldehyde and dimethylamine. The resulting ketone, an alpha-methyl-beta-dimethylaminopropiophenone, is subjected to the same reduction procedure as before to yield a hydroxy compound. Replacement of the hydroxyl with chlorine followed by reaction of the chloro compound with the sodium salt of a phenol yields a dimethyl amine compound of this invention. Conversion of the dimethylamine to the corresponding monomethyl and primary amines is carried out as before.  
     [0149] Those 3-aryloxy-3-phenylpropylamine compounds in which the R′ group attached to either the alpha or beta-carbon is methyl have two asymmetric carbon atoms, the carbon carrying the R′ methyl and the gamma.-carbon carrying the phenoxy and phenyl groups. Thus, such compounds exist in four diastereomeric forms occurring as two racemic pairs, the less soluble pair being designated alpha-dl form and the more soluble the beta-dl form. Each racemate can be resolved into its individual d and l isomers by methods well known in the art, particularly, by forming salts with optically active acids and separating the salts by crystallization.  
     [0150] A 3-aryloxy-3-phenylpropylamine may be coupled to a site-directing molecule to form a conjugate for targeted in vivo delivery. “Site-directing” means having specificity for targeted sites. “Specificity for targeted sites” means that upon contacting the 3-aryloxy-3-phenylpropylamine-site-directing-conjugate with the targeted site, for example, under physiological conditions of ionic strength, temperature, pH and the like, specific binding will occur. The interaction may occur due to specific electrostatic, hydrophobic, entropic or other interaction of certain residues of the conjugate with specific residues of the target to form a stable complex under conditions effective to promote the interaction. Exemplary site-directing molecules contemplated in the present invention include but are not limited to: oligonucleotides, polyamides including peptides having affinity for a biological receptor and proteins such as antibodies; steroids and steroid derivatives; hormones such as estradiol, or histamine; hormone mimics such as morphine; and further macrocycles such as sapphyrins and rubyrins.  
     [0151] As used herein, a “site-directing molecule” may be an oligonucleotide, an antibody, a hormone, a peptide having affinity for a biological receptor, a sapphyrin molecule, and the like. A preferred site-directing molecule is a hormone, such as estradiol, estrogen, progesterone, and the like. A site-directing molecule may have binding specificity for localization to a treatment site and a biological receptor may be localized to a treatment site. A 3-aryloxy-3-phenylpropylamine oligonucleotide-conjugate, where the oligonucleotide is complementary to an oncogenic messenger RNA, for example, would further localize chemotherapeutic activity to a particularly desired site. Antisense technology is discussed in U.S. Pat. Nos. 5,194,428, 5,110,802 and 5,216,141, all of which are incorporated by reference herein.  
     [0152] A couple may be described as a linker, i.e., the covalent product formed by reaction of a reactive group designed to attach covalently another molecule at a distance from the 3-aryloxy-3-phenylpropylamine macrocycle. Exemplary linkers or couples are amides, amine, thiol, thioether, ether, or phosphate covalent bonds. In most preferred embodiments, site-directing molecules are covalently bonded to the 3-aryloxy-3-phenylpropylamine via a carbon-nitrogen, carbon-sulfur, or a carbon-oxygen bond.  
     [0153] Generally, water soluble 3-aryloxy-3-phenylpropylamines retaining lipophilicity are preferred for the applications described herein. “Water soluble” means soluble in aqueous fluids to about 1 mM or better. “Retaining lipophilicity” means having greater affinity for lipid rich tissues or materials than surrounding nonlipid rich tissues. “Lipid rich” means having a greater amount of triglyceride, cholesterol, fatty acids or the like.  
     [0154] Representative examples of useful steroids include any of the steroid hormones of the following five categories: progestins (e.g. progesterone), glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), androgens (e.g., testosterone) and estrogens (e.g., estradiol).  
     [0155] Representative examples of useful amino acids of peptides or polypeptides include amino acids with simple aliphatic side chains (e.g., glycine, alanine, valine, leucine, and isoleucine), amino acids with aromatic side chains (e.g., phenylalanine, tryptophan, tyrosine, and histidine), amino acids with oxygen and sulfur-containing side chains (e.g., serine, threonine, methionine, and cysteine), amino acids with side chains containing carboxylic acid or amide groups (e.g., aspartic acid, glutamic acid, asparagine, and glutamine), and amino acids with side chains containing strongly basic groups (e.g., lysine and arginine), and proline. Representative examples of useful peptides include any of both naturally occurring and synthetic di-, tri-, tetra-, pentapeptides or longer peptides derived from any of the above described amino acids (e.g., endorphin, enkephalin, epidermal growth factor, poly-L-lysine, or a hormone). Representative examples of useful polypeptides include both naturally occurring and synthetic polypeptides (e.g., insulin, ribonuclease, and endorphins) derived from the above described amino acids and peptides.  
     [0156] The term “a peptide having affinity for a biological receptor” means that upon contacting the peptide with the biological receptor, for example, under appropriate conditions of ionic strength, temperature, pH and the like, specific binding will occur. The interaction may occur due to specific electrostatic, hydrophobic, entropic or other interaction of certain amino acid or glycolytic residues of the peptide with specific amino acid or glycolytic residues of the receptor to form a stable complex under the conditions effective to promote the interaction. The interaction may alter the three-dimensional conformation and the function or activity of either or both the peptide and the receptor involved in the interaction. A peptide having affinity for a biological receptor may include an endorphin, an enkephalin, a growth factor, e.g. epidermal growth factor, poly-L-lysine, a hormone, a peptide region of a protein and the like. A hormone may be estradiol, for example.  
     [0157] For use as a chemosensitizer, 3-aryloxy-3-phenylpropylamines are provided as pharmaceutical preparations. A pharmaceutical preparation of a 3-aryloxy-3-phenylpropylamine may be administered alone or in combination with pharmaceutically acceptable carriers, in either single or multiple doses. Suitable pharmaceutical carriers include inert solid diluents or fillers, sterile aqueous solution and various organic solvents. The pharmaceutical compositions formed by combining a 3-aryloxy-3-phenylpropylamine of the present invention and the pharmaceutically acceptable carriers are then easily administered in a variety of dosage forms such as injectable solutions.  
     [0158] For parenteral administration, solutions of the 3-aryloxy-3-phenylpropylamine in sesame or peanut oil, aqueous propylene glycol, or in sterile aqueous solution may be employed. Such aqueous solutions should be suitably buffered if necessary and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous and intraperitoneal administration. In this connection, sterile aqueous media which can be employed will be known to those of skill in the art in light of the present disclosure.  
     [0159] The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases the form must be sterile and must be fluid to the extent that easy use with a syringe exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms, such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars such as mannitol or dextrose or sodium chloride. A more preferable isotonic agent is a mannitol solution of about 2-8% concentration, and, most preferably, of about 5% concentration. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.  
     [0160] Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof.  
     [0161] As used herein, “pharmaceutically acceptable carrier” includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, its use in the therapeutic compositions is contemplated. Supplementary active ingredients can also be incorporated into the compositions.  
     [0162] 3-Aryloxy-3-phenylpropylamines may be co-formulated with a chemotherapeutic agent. Methods of co-formulating more than a single active ingredient are well known in the art. Such co-formulation ensures co-administration of the chemotherapeutic agent and the 3-aryloxy-3-phenylpropylamine.  
     [0163] Hence pharmaceutical compositions that comprise a 3-aryloxy-3-phenylpropylamine, as a chemosensitizing agent, and a chemotherapeutic agent, are provided in accordance with the present invention. Such pharmaceutical compositions can be formulated as described hereinabove.  
     [0164] The pharmaceutical compositions of the present invention may be presented in a pack or dispenser device, such as a FDA approved kit, which may contain one or more unit dosage forms containing the active ingredients. The package may, for example, comprise metal or plastic foil, such as a blister package. The package or dispenser device may be accompanied by instructions for administration and indication. The package or dispenser may also be accompanied by a notice associated with the container in a form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals, which notice is reflective of approval by the agency of the form of the compositions or human or veterinary administration. Such notice, for example, may be of labeling approved by the U.S. Food and Drug Administration for prescription drugs or of an approved product insert.  
     [0165] The pharmaceutical compositions of the present invention can therefore be packaged in a packaging material and identified in print in or on the packaging material for use in the treatment of a multi drug resistance cancer.  
     [0166] The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.  
     [0167] Hence, additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.  
     EXAMPLES  
     [0168] Reference is now made to the following examples, which together with the above descriptions, illustrate the invention in a non limiting fashion.  
     In Vitro Studies Materials and Methods  
     [0169] Chemotherapies (CT):  
     [0170] Mitomycin C (MMC), Vinblastine (VIN) and Doxorubicin (DOX).  
     [0171] Chemosensitizers (CS):  
     [0172] Fluoxetine, Verapamil and Cyclosporin A.  
     [0173] Cell Lines:  
     [0174] MCF-7 (human breast carcinoma), HT1080 (human fibrosarcoma), U2OS (human osteosarcoma), PANC-1 (human pancreatic adenocarcinoma), C6 (rat glioblastoma), C26 (murine colon adenocarcinoma), B16F10 (murine melanoma), P388/WT (murine leukemia) and its MDR-acquired subline P388/ADR (obtained by selective growth of P388/WT in the presence of Doxorubicin, according to the procedure described in Johnson et al., Cancer Treat. Rep., 62: 1535-1547, 1978.  
     [0175] Cell Culture Growth and Maintenance Media:  
     [0176] Dulbecco&#39;s modified Eagle&#39;s medium (DMEM) supplemented with 10% fetal calf serum (FCS), Penicillin (10,000 units/ml), Streptomycin (10 mg/ml) and L-Glutamine (200 mM).  
     [0177] Cell Cultures:  
     [0178] Cells were grown in monolayers in 100×20 mm dishes, in the growth media listed above, at 37° C. in 5% CO 2 .  
     [0179] Cell Survival:  
     [0180] Cells were grown in monolayers as describe above and seeded onto 96 multiwell plates at a density of 1×10 4  cells/ml, 24 hours prior to an experiment. Twenty four hours later, the media was replaced by treatment media as is detailed in the Experimental Results section that follows. The experiments were terminated 24 or 48 hours post media replacement. The quantity of viable cells was determined by the MTT test, recording the absorbencies in a plate reader, at two wavelengths: 550 and 650 nm.  
     [0181] Drug Efflux Measurements:  
     [0182] Cells were grown in monolayers as described above. Several days prior to an experiment the cells (at a density in the range of 5×10 4 -5×10 5  cells/ml) were seeded into 24 multiwell culture plates. The experiments were performed when the cells reached semi-confluency. The efflux experiments were conducted according to the following protocol: Cells were loaded, by incubation for 10 hours, with either a non-lethal dose of DOX, or the same DOX dose combined with fluoxetine, Verapamil or Cyclosporin A. Control cells received media alone. At the end of the incubation, the media was removed, the cells washed with phosphate-buffered saline (PBS), and thereafter incubated with either efflux media (PBS) alone (for the wells incubated with DOX only) or efflux media with fluoxetine at the same dose as in the 10 hours incubation. At selected time points, the medium from every well was collected and replaced with a fresh similar medium. At the end of the experiment the cells in each well were dissolved by adding 5% Deoxycholate (DOC) to each well. Samples from the media collected at each time point, and samples from the final detergent-dissolved cells, were transferred to a 96 well plate suitable for a fluorimeter plate reader. Excitation and emission were at 480 nm and 530 nm, respectively. Calibration curves were run with each assay using DOX standards dissolved in the appropriate media (i.e., buffer or buffer/DOC).  
     [0183] Drug Uptake and Drug Efflux Measurements Using Rhodamine-123:  
     [0184] Rhodamine-123 is a well-known substrate of Pgp, the first MDR extrusion channel identified, and hence serves as a fluorescent indicator for the presence and activity of a chemosensitizer. As the accumulation of Rhodamine-123 in Pgp-containing multidrug resistance cells is increased significantly in the presence of a chemosensitizer, the effects of a molecule suspected to inhibit MDR pumps on the intracellular accumulation of Rhodamine-123 has become a classical test for chemosensitizers.  
     [0185] The effect of fluoxetine as a chemosensitizer was therefore measured by fluorescence measurements upon incubating a cell line with either a chemotherapeutic drug or Rhodamine-123 or with a combination of fluoxetine and a chemotherapeutic drug or Rhodamine-123. In the experiments conducted with Rhodamine-123 as a model, the chemosensitizing effect of fluoxetine was compared to the effect of the known chemosensitizer Verapamil and, in some experiments, also to the known chemosensitizer Cyclosporin A.  
     [0186] The intracellular accumulation of the chemotherapeutic agent or Rhodamine-123 was measured on C-26 cell line, which is known as Pgp-containing, inherent MDR cell line, and on the MDR-acquired cell line P388/ADR, in two different systems: In system I, suspensions of cells were used and the accumulation was measured by flow cytometry; In system II, adherent monolayers of cells were used and the accumulation was measured by confocal microscopy, according to the following protocols:  
     [0187] System I: Suspensions of cells in PBS (1×10 6  cells/ml) were incubated for 30 minutes, at 37° C., with 5 μM Rhodamine-123 alone and in combination with fluoxetine, at varying doses. For comparison, experiments were performed also with Verapamil or Cyclosporin A as a chemosensitizer, at a typical dose of 15 μM. The cells were thereafter analyzed for intracellular fluorescence, using a flow cytometer (Becton-Dickinson, USA). Excitation and emission were at 485 nm and 547 nm, respectively.  
     [0188] System II: Cells were grown as monolayers on cover slides, and were thereafter incubated for one hour at 37° C., with 5 μg/ml Doxorubicin or 5 μM Rhodamine-123, either alone or in combination with a chemosensitizer as described hereinabove. At the end of the incubation time, the cells were washed 6 times with PBS, fixed with a mounting medium (Mounting medium with anti-fading agents, Biomeda corp., CA, USA) and were analysed by Confocal microscopy (Zeiss LSM 510). Excitation was at 488 nm and emission was measured using a band pass filter of 505-550 nm.  
     Experimental Results  
     [0189] Testing the Response of Inherent MDR Cell Lines to a Single Fluoxetine Dose:  
     [0190] C6 and, in separate experiments, PANC-1 cells were seeded onto multiwell (96) culture plates, and the experiments were initiated when the cells reached semi-confluency. The serum-supplemented cell growth media was replaced by a treatment media, selected from: (i) the combination of a chemotherapeutic drug and fluoxetine dissolved in serum supplemented growth media; (ii) chemotherapeutic drug dissolved in serum supplemented growth media; (iii) fluoxetine dissolved in serum supplemented growth media; and (iv) serum supplemented growth media alone (untreated control). Drug species and dose were the same in (i) and (ii). Fluoxetine dose was the same in (i) and (iii). The experiment was terminated 24 hours later, and the number of viable cells was quantitated using the MTT method.  
     [0191] Typical results, showing the effects of the various treatment groups on cell death are shown in FIGS. 1 and 2, for both cell lines and for the chemotherapeutic drugs Mitomycin C (MMC) and Doxorubicin (DOX), respectively. The fluoxetine dose used in these experiments matches the highest safe dose used for accepted indications of fluoxetine. The data clearly shows that fluoxetine alone does not affect cell survival at all. At the drug doses applied (listed in FIGS. 1 and 2), treatment with drug alone was only mildly effective in causing cell death, at its best no more than 20%. In contrast, for the four cases studied (2 drugs, 2 cell lines), the combination treatment caused a significant enhancement in cell death, which was 3-4 fold, clearly showing the effectiveness of the combination treatment.  
     [0192] These experiments were similarly performed with B16F10 and C-26 cell lines, which are known as drug resistance cells. Mitomycin C and Doxorubicin were applied, at typical doses of 50 μg/ml and 1.0 μg/ml, respectively, with and without 15 μM of fluoxetine. The treatment with the drug alone generated cell death in the range of 10-15%, thus confirming the inherent-resistant nature of these cell lines. Treatment with a combination of the drug and fluoxetine increased the cell death to about of 80-90%, thus demonstrating the increased cell demise caused by the chemosensitizer.  
     [0193] Evaluating Fluoxetine Dose Response in Inherent MDR Cell Lines:  
     [0194] Studies similar in general to those outlined in the previous section, were conducted with five cell lines selected for this task (PANC-1, C6, MCF-7, U20S and HT1080), increasing the length of the experiment to 48 hours. The studies were performed with DOX and with Vinblastine (VIN or VLB). The treatment groups were similar to those listed in the previous sections, with the following additions: a series of fluoxetine doses were tested, alone and in combination with the cytotoxic drugs, covering a fluoxetine range of 0-15 μM.  
     [0195] As expected from the testing with 15 μM, fluoxetine alone was not toxic to the cells. For the drug species and respective doses tested—0.1 μg/ml DOX and 0.3 μg/ml VIN—drugs alone caused 50% and 10-20% reductions in cell survival, for the non-resistant and resistant cell lines, respectively. Normalizing, for each cell line, the survival of cells receiving the chemotherapeutic drug and fluoxetine, to the survival of the cells receiving the chemotherapeutic drug alone (i.e., zero fluoxetine) it was possible to construct fluoxetine dose response curves. A typical example is shown in FIG. 3, for the PANC-1 cell line, with both drugs. From such dose response curves, using computer-aided polynomial curve fitting, it was possible to determine for each drug and each cell line, an LD 50  for the fluoxetine potentiation effect. These LD 50  values, for all five cell lines, each with both drugs, are shown in FIG. 4.  
     [0196] Comparative Studies on the Response of a Non-Resistant Cell Line and an MDR-Acquired Cell Line to Fluoxetine:  
     [0197] Evaluating the response of non-resistant and MDR-acquired cells to fluoxetine alone: The effect of various concentrations (1-20 μM) of fluoxetine on the non-resistant P388/WT cell line and its MDR-acquired subline P388/ADR was tested by incubating the cells with increasing concentrations of fluoxetine for 4 hours and thereafter washing and re-incubating the cells with CS-free media for additional 20 hours. The number of viable cells was quantitated using the MTT method.  
     [0198] The obtained data, presented in FIGS. 5 a  and  5   b , clearly indicate that at the tested concentrations range, 1-20 μM, fluoxetine has no effect on cells viability in both non-resistant cells (FIG. 5 a ) and MDR-Acquired cells (FIG. 5 b ).  
     [0199] Testing the Response of MDR-Acquired Cell Lines to a Single Fluoxetine Dose:  
     [0200] P388/WT cells were seeded onto multi-well (96) culture plates, and the experiments were initiated when the cells reached semi-confluency. The serum-supplemented cell growth media was replaced by a treatment media, selected from: (i) various concentrations (0.5, 1 and 5 μg/ml) of a chemotherapeutic drug (DOX) dissolved in serum supplemented growth media; (ii) a combination of a chemotherapeutic drug (1, 5 or 10 μg/ml DOX) and a chemosensitizing agent selected from fluoxetine, Verapamil, and Cyclosporin A (5 μM) dissolved in serum supplemented growth media; and (iii) serum supplemented growth media alone (untreated control). After 4 hours incubation, the treatment media was replaced with CS- and CT-free media and the experiment was terminated 24 hours later. The number of viable cells was quantitated using the MTT method.  
     [0201] As is shown in FIG. 6 a , treatment with 0.5 μg/ml DOX was sufficient to generate about 50% cell death in the non-resistant cell line P388/WT, while 100% cell death was observed in these cells upon increasing the DOX concentration to 5 μg/ml. As expected for non-resistant cells, a combination treatment of a chemotherapeutic agent and fluoxetine had no effect on the level of cells death in this cell line.  
     [0202] Contrary to the data obtained with the non-resistant cell line, a well-demonstrated chemosensitizing effect of fluoxetine was observed with the MDR-acquired cell line P388/ADR. As is shown in FIG. 6 b , treatment with 5 μg/ml DOX, which was enough to kill all the cells in the non-resistant cell line, generated less then 20% cell death, while doubling the drug concentration increased the cell death only to about 30%, thus confirming the acquired resistance of this cell line. While a combined treatment of DOX and 5 μM Verapamil or Cyclosporin A (CsA) generated a modest increase in cell death, treatment with a combination of DOX and fluoxetine at the same concentration resulted in significant increase (about 2-3 fold as compared with Verapamil and CsA) in cell death, thus demonstrating the enhanced chemosensitizing effect of fluoxetine on MDR-acquired cells. Several features of these results are worthy of attention:  
     [0203] First, in all cases fluoxetine potentiates the cytotoxic effect of the chemotherapeutic drug.  
     [0204] Second, the LD 50  range, which spans from 7-10 μM fluoxetine and 6.5-8 μM fluoxetine, for DOX and VIN, respectively, is well below the highest safety limit of 15 μM fluoxetine. This is completely different than the cases of Verapamil and Cyclosporin, where the dose range for chemosensitization was well above their safety limit and hence impractical for clinical applications.  
     [0205] Third, taking into consideration that in the resistant cell lines the potentiation has to work on double the number of cells than in the non-resistant lines, yet the LD 50  range is quite similar—these data imply that the potentiation effect is more significant in the MDR lines.  
     [0206] Fourth, in the non-resistant lines, the effect of fluoxetine on a given line is not drug-sensitive while in the resistant lines, fluoxetine is more potent (lower LD 50 ) with VIN than with DOX.  
     [0207] Insights and Results with Respect to the Operating Mechanisms:  
     [0208] Without an intention to limit the present invention in any way, the data presented herein allows speculating some mechanistic insights with respect to the chemosensitization activity of 3-aryloxy-3-phenylpropylamine in general and fluoxetine in particular.  
     [0209] The finding that fluoxetine potentiates the cytotoxicity with different drugs, that have furthermore different killing mechanisms, rules out a drug-specific effect. Could fluoxetine be triggering a cell death mechanism that it totally independent of the presence of the chemotherapeutic drug in the cell? It is suggest this triggering option is unlikely in view of the finding that fluoxetine alone is not toxic to the cells—at the same dose level where it exerts its effect in the presence of a cytotoxic drug. Since the sites of action for the chemotherapeutic drugs are intracellular it is reasonable to assume that fluoxetine exerts its effect(s) inside the cell, also.  
     [0210] In general, nature has not planned for the introduction of foreign matter such as drugs, into living biological systems. Hence nature has made no specific efforts to assist drug entry into cells. That drugs do gain entry into cells is a fact of life. Drugs do it by at least two pathways that are not mutually exclusive: (i) by diffusion across the cell membrane, driven by the drug&#39;s electrochemical-potential gradient; and (ii) by “borrowing a ride” on natural transport systems designed (by nature) to transport molecules that are a normal component of a living system. Obviously both pathways can operate in both directions, namely influx and efflux. In addition, the interaction of the foreign entity with biological transport systems can take the form of blockage, where a foreign matter blocks the passage of other materials through the transporter.  
     [0211] The data presented herein reveal that fluoxetine acts on both MDR and non-multidrug resistance cells, but is more effective with the former type. This raises at least two possibilities for fluoxetine&#39;s mechanism(s) of action:  
     [0212] First: Fluoxetine inhibits extrusion channels that pump chemotherapeutic drugs out of the cells, reducing the intracellular drug doses below the lethal threshold. The fact that both MDR and non-multidrug resistance cells have been affected, but to different extent, fits with the extrusion pumps being natural proteins that can exist in all cells, but in significantly larger numbers (copies per cell) in multidrug resistance cells.  
     [0213] Second: Fluoxetine has two different activities: One is pump inhibition as above especially (and possibly only) in the multidrug resistance cells. The other is enhancement of the cellular response to the chemotherapeutic drug, without any change in the intracellular drug level. The latter could operate in the non-multidrug resistance cells alone, or in both types of cells.  
     [0214] An experimental method to support or refute the first mechanism, is the following:  
     [0215] Cells are loaded with non-lethal doses of a chemotherapeutic drug alone, or drug and fluoxetine. Upon completion of loading the extracellular fluid is replaced with buffer alone, and the efflux of drug into the external media is monitored for several hours. If fluoxetine inhibits efflux pumps, drug efflux in the systems receiving the combined treatment should be slower than in those receiving the drug alone. This expectation was met, as shown by the following:  
     [0216] The effect of fluoxetine on DOX efflux from inherent MDR C6 cells and from acquired MDR P388/ADR cells was studied as detailed under the Methods section above.  
     [0217] In the experiments conducted with C6 cells, the DOX and fluoxetine loading doses were 0.1 μg/ml and 15 μM, respectively, and the obtained data is presented in FIG. 8. The cumulative quantity of DOX that diffused out of the cells at time=t was normalized to the total intracellular concentration of DOX at time=0, and is denoted f(t). The magnitudes of f(t) as function of time are plotted in FIG. 8, for the cells that received DOX alone and for the cells that received DOX with fluoxetine.  
     [0218] The data presented makes it clear that 2 hours suffice for complete depletion of intracellular DOX from cells that were loaded with DOX alone. In contrast, DOX efflux was significantly slower in cells that received both DOX and fluoxetine. At 2 hours, loss of intracellular DOX (in the combined treatment) was under 40%, and complete depletion was 450% slower than in the absence of fluoxetine. The pattern of DOX efflux from the cells loaded with this drug alone fits dominance of a single pathway. Based on previous experience, were the efflux seen for the DOX-alone systems dominated by self diffusion of the drug through the lipid bilayer membranes, at 2 hours f(t) would range from 10-30%. This clearly indicates that the single efflux pathway, that provides 100% depletion at 2 hours, can be assigned to an extrusion pump.  
     [0219] DOX efflux from cells that received the combined treatment is at the least bi-phasic, which indicates that DOX diffuses out of those cells by at least two pathways. The pattern of the fastest pathway, which dominates efflux at the first 30 minutes and accounts for ≦20% of the total depletion, is quite similar to that of the DOX-alone case. The pattern of the remaining 80% fits one or more additional, significantly slower, pathways. These data imply a fluoxetine effect at the transport level, a major part of which is reduction in the number of active pumps, with possible minor effects of reduction in the rate constant of DOX efflux through this pump.  
     [0220] In the experiments conducted with P388/ADR cells, the effect of fluoxetine on drug efflux was compared with the effect of the known chemosensitizers Verapamil and Cyclosporin A (CsA). The DOX and chemosensitizer dose loadings were 1 μg/ml and 5 μM, respectively, and the obtained data is presented in FIG. 9. The cumulative quantity of DOX that diffused out of the cells at time=t is presented as its percentage from the total intracellular concentration of DOX at time=0.  
     [0221] As is shown in FIG. 9, in these cells one hour suffices for complete depletion of intracellular DOX from cells that were loaded with DOX alone. In contrast, and similarly to the results obtained with C6 cells, DOX efflux was significantly slower in cells that received both DOX and a chemosensitizer. However, the obtained data clearly show that in cells treated with fluoxetine as a chemosensitizer, a 11 fold increase of the time needed for complete depletion of the intracellular DOX was observed as compared with cells treated with DOX only, while an increase of only 3 and 5 fold was observed in cells treated with Verapamil and CsA, respectively, as chemosensitizers. These data indicate again the superior chemosensitizing effect of fluoxetine as compared with presently known chemosensitizers. Support for these data was found in the drug uptake measurements performed with either a chemotherapeutic agent or with Rhodamine-123 as an indicator for the effect of a molecule on MDR extrusion pumps. As is detailed hereinabove in the methods section, the chemosensitizing effects of fluxetine and Verapamil on the intracellular level of doxorubicin or Rhodamine-123 were measured in two different systems.  
     [0222] As is shown in FIG. 10, in the experiments performed in suspended C-26 cells, Verapamil, at the standard dose (15 μM), generated a minor increase of 23% of the intracellular fluorescence, as compared to the control, chemosensitizing-free cells, while fluoxetine, at the same dose generated an increase of 140% of the intracellular fluorescence. The experiments further showed a direct correlation between the fluoxetine dose and the fluorescence level. By comparing the results obtained with the known chemosensitizer Verapamil and with fluoxetine, it is clearly demonstrated that (i) fluoxetine acts as a chemosensitizer by exerting the same effect as Verapamil on the intracellular fluorescence level; and (ii) the chemosensitizing potential of fluoxetine in substantially higher than that of Verapamil.  
     [0223] The same enhanced chemosensitizing effect of fluoxetine, as compared with known chemosensitizers, was also observed in the MDR-acquired cell line. As is shown in FIG. 11, in the experiments performed in suspended P388/ADR cells incubated with Rhodamine-123, with or without Verapamil or Cyclosporin A at the standard dose (15 μM), an increase of about 60% and about 110%, respectively, of the intracellular fluorescence, as compared to the control, chemosensitizing-free cells, was observed, while fluoxetine, at the same dose, generated an increase of about 200% of the intracellular fluorescence.  
     [0224] Similar results were obtained in the experiments performed with monolayered cells. FIGS. 12 a - c  present confocal microscopy images of C-26 cells incubated with Rhodamine-123 and a chemosensitizer, which clearly demonstrate that while Verapamil generated an increase in the intracellular level of Rhodamine-123 (FIG. 12 b ), as compared with the control, chemosensitizer-free, cells (FIG. 12 a ), fluoxetine generated a substantially higher increase in the intracellular accumulation of Rhodamine-123 (FIG. 12 c ).  
     [0225]FIGS. 13 a - b  present confocal microscopy images of the MDR-acquired cell line P388-ADR, incubated with doxorubicin, with or without 5 μM fluoxetine, and clearly show that the intracellular accumulation of doxorubicin alone is quite poor (FIG. 13 a ) while adding to the incubation media a rather low dose of fluoxetine (5 μM) generated a substantial increase in the intracellular level of DOX.  
     [0226] Hence, the results obtained by the qualitative and quantitative measurements of drug uptake provide additional support for the inhibitory effect of fluoxetine on MDR extrusion pumps, which was suggested upon the efflux studies described hereinabove. These results further demonstrate the superior activity of fluoxetine over known chemosensitizers such as Verapamil and Cyclosporin A. The chemosensitizing activity of fluoxetine in both suspended and monolayered cells provides an indication for its in vivo chemosensitizing activity in both solid and non-solid tumors, as is further demonstrated hereinbelow.  
     In Vivo Studies in Inherent MDR Tumors Materials and Methods  
     [0227] The following in vivo studies were conducted in mice, in two tumor models: a solid tumor model (also referred to herein as model 1) and a lung metastasis model (also referred to herein as model 2).  
     [0228] Cells:  
     [0229] In the solid tumor model, MDR-inherent C-26 cells were injected into the animal&#39;s right-hind footpad.  
     [0230] In the lung metastasis model, MDR-inherent B16F10 cells were injected intravenously, into the tail vein.  
     [0231] Chemosensitizer (CS):  
     [0232] The chemosensitizer used in both models was fluoxetine.  
     [0233] In both models the chemosensitizer was administered orally, via the drinking water. Daily intake was 0.04 mg/kg body weight. This daily dose is equivalent to a daily dose of 2.8 mg for a human weighting 70 kg, whereas the approved (safe) range of daily dose of fluoxetine as an antidepressant is 20-80 mg for a human weighting 70 kg.  
     [0234] Chemotherapeutic Agents (CT):  
     [0235] In the solid tumor model, Mitomycin C (MMC) and Doxorubicin (DOX) were tested separately, each at a dose of 5 mg/kg body.  
     [0236] In the lung metastasis model, only Doxorubicin, at a dose of 10 mg/kg body, was tested.  
     [0237] In each model, the animals were divided into 4 groups, 5 animals per group. In the lung metastatic model, a fifth group of untreated, healthy animals (i.e., animals that were not inoculated with tumor cells), served as a control group for both models.  
     [0238] Each of the animal groups was treated with saline, chemosensitizer, chemotherapeutic agent or a combination of chemotherapeutic agent and chemosensitizer. The saline and the chemotherapeutic agent were injected into the tail vein (100 μl). The dosing regimen in the solid tumor model experiments was 3 injections, spaced a week apart and starting at day 5 from tumor inoculation. The dosing regimen in the lung metastatic model was also 3 injections, at days 1, 5 and 9 from tumor inoculation.  
     Experimental Results  
     [0239] The Solid Tumor Model:  
     [0240] The effective impact of the combined treatment of fluoxetine and a chemotherapeutic agent in the solid tumor model is demonstrated in FIGS. 9 and 10. FIG. 9 clearly demonstrates that the solid tumor increases fast and exponentially in the groups treated with saline, a chemosensitizer alone and a chemotherapeutic agent alone. These results indicate that the tumor retains its drug resistance nature in vivo. Contrary to that, in the animals receiving the combination therapy, the appearance of the tumor is delayed, as compared with the other groups, the tumors are substantially smaller and the tumor growth is significantly slower. FIG. 10 indicates the same trend, as it demonstrates that only the animals receiving the combination therapy were long survivors, namely, the survival of the animals treated with MMC+CS and DOX+CS was prolonged 2 and 3 fold, respectively, as compared with animals treated with saline, CS alone and the respective CT alone.  
     [0241] The Lung Metastasis Model:  
     [0242] The results presented in FIGS. 11 a  and  11   b  demonstrate the lung metastatic burden by two measures: the increase in the lung weight (FIG. 11 a ) and the number of lung metastasis (FIG. 11 b ). These results clearly indicate that, by both measures, animals treated with saline or a chemosensitizer alone had the highest metastatic burden. These results further demonstrate that treatment with Doxorubicin generated only a mild reduction in the metastatic burden, while the combination treatment of chemosensitizer and a Doxorubicin generated a substantial reduction thereof.  
     [0243] This encouraging effect of the combination treatment is reflected also in the survival results presented in FIG. 12. The survival data in FIG. 12 show the results obtained in a 75-days experiment. As is shown in FIG. 12, similar to the pattern of the solid tumor model (FIG. 10), animals treated with saline, CS alone or CT alone, died rather early and within short intervals of one another, while those treated with the combination treatment were long survivors.  
     [0244] Of the two tumor models tested, the B16F10 is a more aggressive tumor. This fact is evident by the shift in the survival data in FIG. 12, as compared with the data shown in FIG. 10, towards a shorter time span between the administration of the tumor cells to the animals and onset of animal demise.  
     [0245] The obtained results clearly demonstrate the advantageous features of fluoxetine, as a representative example of a 3-aryloxy-3-phenylpropylamine, as a chemosensitizing agent, as is delineated hereinbelow:  
     [0246] This chemosensitizing agent changes the course of the tumor response to chemotherapeutic drugs from poor to excellent, by all counts: tumor progression, metastatic burden, and survival;  
     [0247] As the chemosensitizing activity of the CS agent was demonstrated with two different chemotherapeutic drugs, acting via different pathways (as is discussed in detail hereinabove), this CS agent is not drug specific and therefore has the potential to resolve the drug resistance to additional drugs;  
     [0248] The chemosensitizer itself at the doses employed has no detrimental effects with respect to tumor progression;  
     [0249] The dose range required for chemosensitization is well below the safe dose in humans; and  
     [0250] Finally, the chemosensitizer is administerable orally, which is a patient-friendly route of administration.  
     In Vivo Studies in Acquired MDR Tumors  
     [0251] The following in vivo studies were conducted in mice, in two tumor models: a non-resistant model and an acquired MDR model.  
     [0252] Cells:  
     [0253] P388/WT (non-resistant) or P388/ADR (MDR-acquired) murine leukemia cells were propagated in the peritoneum of BDF 1  female mice by weekly transfer of 0.5 ml of peritoneal fluid containing 5×10 5  cells, to generate an intraperitoneal ascites model.  
     [0254] Chemosensitizer (CS):  
     [0255] The chemosensitizer used in both models was fluoxetine.  
     [0256] In both models the chemosensitizer was administered orally, via the drinking water. Daily intake was 0.04 mg/kg body weight, which is, as described hereinabove, well below the approved (safe) range of daily dose of fluoxetine as an antidepressant.  
     [0257] Chemotherapeutic Agents (CT):  
     [0258] In both models, Doxorubicin (DOX) was tested. Doses of 3 mg/kg body were injected into the lateral tail vain, 1, 5 and 9 days after tumor inoculation.  
     [0259] Evaluating the Effect of Fluoxetine on Animals Weight and Survival in Non-Resistant and MDR-Acquired Tumors:  
     [0260] Comparative experiments were run in parallel with the sensitive, non-resistant P388/WT model and the corresponding, MDR-acquired P388/ADR model. In each experiment, 20 animals were divided into four treatment groups (5 animals per group), each treated with either saline, a chemosensitizing agent (fluoxetine), a chemotherapeutic agent (DOX) or a combination of a chemotherapeutic agent and chemosensitizing agent (DOX and fluoxetine). A group of untreated healthy animals was served as a control group. The saline and the chemotherapeutic agent were injected into the tail vein (100 μl). The fluoxetine was given in the drinking water, from tumor inoculation and on. Doxorubicin was injected into the lateral tail vain 1, 5 and 9 days post tumor inoculation. The effects of the various treatments on tumor response were monitored through animals&#39; survival and animals&#39; body weight. The latter was monitored in order to assess the treatment toxicity.  
     Experimental Results  
     [0261] The Effect of Fluoxetine on Animals&#39; Body Weight:  
     [0262] The changes in animals body weight in the various treatment groups as compared with the control group, in mice induced with a non-resistant tumor and an MDR-acquired tumor are presented in FIGS. 18 a  and  18   b , respectively. The obtained data indicate that the nature of the tumor did not affect the body weight changes and further indicate no weight loss in the fluoxetine-only treatment groups and a minor weight decrease in the groups treated with DOX, either alone or in combination with fluoxetine. However, as is clearly shown in FIGS. 18 a  and  18   b , in both tumor models fluoxetine was found to positively modulate weight loss, thus indicating no reproducible enhancement of toxicity as a results of the combined, fluoxetine and DOX, treatment.  
     [0263] The effect of Fluoxetine on Animal&#39;s Survival:  
     [0264] The survival data of animals implanted with the non-resistant P388/WT tumor and the MDR-acquired P388/ADR tumor, as a result of the various treatments described hereinabove are presented in FIGS. 19 a  and  19   b , respectively.  
     [0265] As is shown in FIG. 19 a , in animals implanted with the non-resistant cells, the combined treatment of DOX and fluoxetine had no effect on animal&#39;s survival. However, as is shown in FIG. 19 b , in sharp contrast, in animals implanted with the MDR-acquired cells, treatment with a combination of fluoxetine and DOX generated a significant impact on the animals&#39; survival, resulting in more than 2-fold elongated life span.  
     [0266] These results further demonstrate the chemosensitizing efficacy of fluoxetine, as a representative of a 3-aryloxy-3-phenylpropylamine. As the chemosensitizing activity of fluoxetine was demonstrated with both MDR-inherent tumor and MDR-acquired tumor, this CS agent is not tumor specific and furthermore has the potential to resolve also acquired drug resistance of various tumors to chemotherapeutic drugs.  
     The Effect of Fluoxetine on Drug Pharmacokinetics and Biodistribution Materials and Methods  
     [0267] Cells:  
     [0268] B16F10.9 cells were injected intravenously into 12-weeks old male C57BL/6 mice.  
     [0269] Chemosensitizer (CS):  
     [0270] The chemosensitizer used was fluoxetine. The chemosensitizer was administered orally, via the drinking water. Daily intake was 0.04 mg/kg body weight.  
     [0271] Chemotherapeutic Agents (CT):  
     [0272] Doxorubicin (DOX), at a dose of 10 mg/kg body was injected into the lateral tail vain, 10 days after tumor inoculation.  
     [0273] Evaluating the Effect of Fluoxetine on Drug Pharmacokinetics and Biodistribution:  
     [0274] The animals were divided into two groups, 10 animals per group, one was treated with DOX only and the other with a combination of DOX and fluoxetine. Fluoxetine was given in the drinking water, as described above, from tumor inoculation and on. DOX was injected at day 10 from tumor inoculation. In an experiment designated for pharmacokinetics, blood samples were taken up to six hours post injection of the chemotherapeutic drug and were processed for assaying their DOX content by fluorescence measurements. In a parallel experiment, designated for biodistribution, animals were scarified one hour post injection of the chemotherapeutic drug, the lungs and other selected organs were removed and were viewed by a pathologist, weighed and thereafter processed for assaying their DOX content.  
     Experimental Results  
     [0275] The Effect of Fluoxetine on Drug Pharmacokinetics and Biodistribution:  
     [0276] The pharmacokinetics of doxorubicin in mice having inherent MDR lung tumor was evaluated by measuring the drug concentration in the mice blood as a function of time. The decrease in the DOX concentration was measured and compared in mice treated with DOX only and with a combination of DOX and fluoxetine as a chemosensitizer. The results, presented in FIG. 20, clearly indicate that fluoxetine does not alter doxorubicin pharmacokinetics, as the blood clearance of doxorubicin was found to be the same in both tested groups. These findings further demonstrate the efficacy of fluoxetine as a chemosensitizer which acts only within the tumor site and does not affect the pharmacokinetics of the chemotherapeutic agent.  
     [0277] The effect of fluoxetine on the biodistribution of doxorubicin was measured by determining the DOX concentration in selected organs, one hour post injection, in mice treated with DOX only and in mice treated with a combination of DOX and fluoxetine. The results, presented in FIG. 21, clearly show that while fluoxetine had no effect on the drug concentration in the tumor-free organs (spleen, kidneys and liver), a major increase (about 12 fold) in the DOX level was induced by fluoxetine at the tumor-bearing lungs. Again, these findings provide further support for the in vivo efficacy of fluoxetine as a chemosensitizer that acts solely at the tumor site and provides for elevated levels of the chemotherapeutic drugs thereat.  
     [0278] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.  
     [0279] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.