Multidrug resistance inhibitors

There is disclosed a multidrug resistance inhibitor for overcoming a multidrug resistance of cancer, or an agent for enhancing the activity of anti-cancer agents, which comprises as an active ingredient a compound of formula (I) or a pharmaceutically acceptable salt thereof: ##STR1## wherein n is an integer of 5 to 12, PA1 R.sub.1 and R.sub.2 are each independently benzyl, of which a phenyl ring may be substituted by 1 to 5 substituents selected from hydroxy, (C.sub.1 -C.sub.4)alkyl, (C.sub.1 -C.sub.4)alkoxy and halogen, and/or by methylenedioxy, with the proviso that R.sub.1 and R.sub.2 are simultaneously not a compound of formula (II) ##STR2##

FIELD OF THE INVENTION 
This invention relates to multidrug resistance inhibitors for overcoming 
multidrug resistance of cancer which is found in cancer chemotherapy, and 
also agents for enhancing the activity of anti-cancer agents. 
BACKGROUND OF THE INVENTION 
It is a common problem for human beings to overcome cancer. For the 
purpose, many anti-cancer agents have been developed until now, but the 
expression of multidrug resistance of cancer has become a clinical 
problem. Multidrug resistance is a phenomenon (cross-resistance) in which 
cancer cells resist to not only the particular anti-cancer agent 
administered, but also the other anti-cancer agents, due to an 
administration of an anti-cancer agent or a resistance of cancer cells by 
nature to anti-cancer agents. Reportedly, about 50% of patients newly 
diagnosed as cancer showed a drug resistance in the treatment of cancer, 
and more than 90% of the deaths showed some behaviors associated with the 
resistance of cancer cells to anti-cancer agents during the treatment with 
anti-cancer agents. Therefore, it has become extremely important in cancer 
chemotherapy to overcome multidrug resistance to anti-cancer agents of 
cancer cells. 
Although a mechanism of cancer cells causing multidrug resistance has not 
been clearly elucidated, it is considered to result from a reduced 
concentration of anti-cancer agents in the cells when said cells have 
acquired multidrug resistance. On the other hand, many cancer cells having 
multidrug resistance produce P-glycoprotein excessively and this 
P-glycoprotein may play a role in transporting anti-cancer agents out of 
the cells. P-glycoprotein is coded by a gene called MDR1 on human being. 
Thus the over-expression of MDRI gene in human cancer cells is considered 
to be a cause of acquiring resistance (MDR1 resistance). P-glycoprotein 
has low substrate specificity and can bind with various kinds of compounds 
to transport drugs out of the cells. It follows that once P-glycoprotein 
expresses in cancer cells, the cells will acquire resistance to many other 
anti-cancer agents. In fact, it is known that many structurally different 
anti-cancer agents such as adriamycin, vinblastine, vincristine, 
actinomycin D, colchicine become a substrate for transporting outside 
cells by P-glycoprotein. Therefore, it is considered that inhibiting the 
function of P-glycoprotein will lead to overcoming multidrug resistance. 
It is reported that about 30% of multidrug resistances is caused by 
P-glycoprotein. 
It is known that messenger RNA of MDR1 gene encoding P-glycoprotein 
expresses in normal tissue, for example, kidney, adrenal, large intestine, 
small intestine, intestinum colon, lung, liver, pancreas, or lymphocyte. 
In kidney P-glycoprotein plays a part to transport drugs out of the body. 
The reason why anti-cancer agents have low activity in kidney cancer where 
kidney cells were cancerous is that P-glycoprotein produced therein will 
transport anti-cancer agents outside the cells. Recently, it is found that 
the main substance of blood brain barrier which controls transport of 
drugs into the brain is P-glycoprotein. This means that the concentration 
of anti-cancer agents delivered into brain, kidney, adrenal, large 
intestine, small intestine, intestinum colon, lung, liver, pancreas, 
lymphocyte of leukemia, etc., can be increased by inhibiting 
P-glycoprotein. Thus, P-glycoprotein inhibitors are expected to enhance 
effect of anti-cancer agents on brain tumor, kidney cancer, adrenal 
cancer, large intestine cancer, small intestine cancer, intestinum colon 
cancer, lung cancer, liver cancer, pancreas cancer, or leukemia, etc. 
In the field of cancer chemotherapy, many anti-cancer agents have been used 
such as mitomycin, cyclophosphamide, melphalan, nimustine, carboquone, 
vincristine, vinblastine, vindesine, bleomycin, 5-fluorouracil, 
adriamycin, cisplatin, actinomycin D, methotrexate, aclarubicin, 
toyomycin, neocarzinostatin, ifosfamide, etoposide, camptothecin, 
doxorubicin, irinotecan. Those drugs have characteristic anti-cancer 
spectra. Some of those anti-cancer agents are known to bring about a 
resistance of cancer cells to the agents by continuous or a long term 
administration. Further, the problem of cross-resistance has arisen. 
Therefore it has been required to activate or enhance the sensitivity of 
cancer cells having resistance to anti-cancer agents in the field of 
cancer chemotherapy. 
Taxol and its derivative taxotere were approved in U.S.A. in recent years, 
and will be done in Japan. They are expected to be one of the leading 
drugs of solid carcinoma chemotherapy in the future, because of having a 
potent and strong anti-cancer activity, particularly in the field of solid 
carcinoma. However, taxol is known to be a substrate for transporting 
outside cells by P-glycoprotein, and its activity may be weakened by MDRl 
resistance. Recently, it is reported that P-glycoprotein inhibitors can 
overcome taxol resistance in MDR1 resistance cells (Cancer Res. vol. 55, 
1086-1091, 1995). This shows that P-glycoprotein inhibitors are also 
effective for taxol resistance. 
Some of the instant compounds are included in a series of isoprenylamine 
derivatives having anti-viral and anti-tumor activities disclosed in 
Japanese Patent Kokoku 1-36457 in which there is no reference that the 
isoprenylamine derivatives have the function as multidrug resistance 
inhibitors for overcoming multidrug resistance of cancer. 
Tsuruo et al. report that verapamil represented by the following formula 
(III) 
##STR3## 
inhibits P-glycoprotein and overcomes MDR1 resistance (Cancer Res., vol. 
41, 1967-1972, 1981). 
Nakagawa et al., Japanese Patent Kokoku 5-16411 discloses a compound of 
formula (IV) 
##STR4## 
and the pharmaceutically acceptable salts thereof, which have an activity 
of overcoming adriamycin (ADM) resistance to ADM, one of anti-cancer 
drugs. Ogawa et al, Japanese Patent Kokai 2-138211, discloses that the 
malate of formula (IV) has an activity of enhancing the anti-cancer 
activity. 
There is no report that the compound of formula (IV) enhances an 
anti-cancer activity of taxol in MDR1 resistance cells. 
DETAILED DESCRIPTION OF THE INVENTION 
We have studied many compounds for enhancing the activity of anti-cancer 
agents in an effort to overcome the above-mentioned problems of multidrug 
resistance of cancer cells. As a result, we have found that the compounds 
of formula (I) have an activity of overcoming multidrug resistance in MDR1 
resistance cells, without Ca.sup.2+ antagonist activity and with a low 
cytotoxicity, and also an activity of enhancing the activity of 
anti-cancer agents, in particular taxol and its derivatives. 
Accordingly, the present invention provides a pharmaceutical composition 
which comprises as an active ingredient a compound of formula (I), or a 
pharmaceutically acceptable salt thereof: 
##STR5## 
wherein n is an integer of 5 to 12, 
R.sub.1 and R.sub.2 are each independently benzyl, of which a phenyl ring 
may be substituted by 1 to 5 substituents selected from hydroxy, (C.sub.1 
-C.sub.4)alkyl, (C1-C.sub.4)alkoxy, and halogen, and/or by methylenedioxy, 
with the proviso that R.sub.1 and R.sub.2 are simultaneously not a 
compound of formula (II) 
##STR6## 
The present invention also provides a multidrug resistance inhibitor 
comprising as an active ingredient a compound of formula (I) or a 
pharmaceutically acceptable salt thereof. Further, the invention provides 
an agent for enhancing the activity of anti-cancer agents in the treatment 
of cancers which include brain tumor, kidney cancer, adrenal cancer, large 
intestine cancer, small intestine cancer, intestinum colon cancer, lung 
cancer, liver cancer, pancreas cancer and leukemia. The present invention 
further provides an agent for enhancing the activity of taxol or its 
derivatives, which comprises a compound of formula (I) or a 
pharmaceutically acceptable salt thereof in combination with taxol and its 
derivatives. The taxol derivatives include, for example, taxotere. 
In the compounds of formula (I), the C.sub.1 -C.sub.4 alkyl group can be 
straight-chain or branched, which can include methyl, ethyl, n-propyl, 
isopropyl, n-butyl, sec-butyl, and tert-butyl. The C.sub.1 -C.sub.4 alkoxy 
group, the alkyl moiety of which can be straight-chain or branched, can 
include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, 
tert-butoxy. Halogen can include fluorine, chlorine, bromine and iodine. 
Examples of the groups represented by the following formula 
##STR7## 
wherein n is an integer of 5 to 12, can include geranylfarnesyl, 
farnesylfarnesyl, farnesylgeranylgeranyl, farnesylfarnesylgeranyl, 
solanesyl, decaprenyl, undecaprenyl and dodecaprenyl. 
The compounds of formula (I) may be converted, if desired, to the 
corresponding acid addition salts with pharmaceutically acceptable acids. 
The acid addition salts are included within the scope of this invention, 
which can include the salts with inorganic acids such as hydrochloric 
acid, hydrobromic acid, sulfuric acid, nitric acid and the like, and the 
salts with organic acids such as fumaric acid, citric acid, maleic acid, 
phthalic acid, malic acid, tartaric acid or the like. 
The compounds of formula (I) can be present in various geometrical isomeric 
forms, for example, cis/trans isomers. In addition to those compounds of 
formula (I), possible metabolites induced from the compounds of formula 
(I) and the metabolic precursors, i.e., "prodrug" which is metabolized in 
vivo to form the compounds of formula (I), are included within the scope 
of the present invention. 
The compounds of formula (I) may be prepared by various conventional 
methods, for example, as shown by the following Route 1 or 2. 
##STR8## 
Route 1 illustrates a process for the preparation of the compounds of 
formula (I) wherein R.sub.1 and R.sub.2 are identical, in accordance with 
the process described in Japanese Patent Kokai 3-2150. 
Step A in Route 1 is the step of reacting a compound of formula (V) 
##STR9## 
wherein R.sub.1 and R.sub.2 are as defined above and both are identical, 
with a compound of formula (VI) 
##STR10## 
wherein n is as defined above, and X is a leaving group such as halogen 
and sulfonate to prepare the compounds of formula (I) wherein R.sub.1 and 
R.sub.2 are identical. 
In the above Step A, the reaction is carried out in the presence or absence 
of solvents using 0.1-10 moles of a compound of formula (VI) per mole of a 
compound of formula (V). In this reaction, various bases may be added, if 
necessary, which include carbonates such as potassium carbonate, sodium 
carbonate, sodium hydrogencarbonate; hydroxides such as sodium hydroxide, 
potassium hydroxide, lithium hydroxide; amines such as triethylamine, 
diethylamine, diisopropylethylamine, tributylamine, diisopropylamine, 
trimethylamine; pyridines such as pyridine, 4-dimethylaminopyridine. 
Diisopropylamine is preferably used. 
The solvents employed in Step A are not specifically limited, unless giving 
an influence on the reaction, which can include hydrocarbons such as 
benzene, toluene, xylene, hexane, and heptane; halogenated hydrocarbons 
such as chloroform, methylene chloride, carbon tetrachloride, and 
1,2-dichloroethylene; ethers such as diethyl ether, diisopropyl ether, 
tetrahydrofuran, and dioxane; amides such as dimethylformamide, 
dimethylacetamide, and hexamethylphosphoric triamide; alcohols such as 
methanol, ethanol, and isopropanol; sulfoxides such as dimethylsulfoxide; 
sulforan; water; and these mixed solvents. 
Examples of compounds represented by formula (VI) can include 
geranylfarnesyl chloride, farnesylfarnesyl chloride, 
farnesylgeranylgeranyl chloride, farnesylfarnesylgeranyl chloride, 
solanesyl chloride, decaprenyl chloride, undecaprenyl chloride, 
dodecaprenyl chloride, geranylfarnesyl bromide, farnesylfarnesyl bromide, 
farnesylgeranylgeranyl bromide, farnesylfarnesylgeranyl bromide, solanesyl 
bromide, decaprenyl bromide, undecaprenyl bromide, dodecaprenyl bromide, 
geranylfarnesyl iodide, farnesylfarnesyl iodide, farnesylgeranylgeranyl 
iodide, farnesylfarnesylgeranyl iodide, solanesyl iodide, decaprenyl 
iodide, undecaprenyl iodide, dodecaprenyl iodide, methanesulfonyl 
geranylfarnesol, methanesulfonyl farnesylfarnesol, methanesulfonyl 
farnesylgeranylgeraniol, methanesulfonyl farnesylfarnesylgeraniol, 
methanesulfonyl solanesol, methanesulfonyl decaprenol, methanesulfonyl 
undecaprenol, methanesulfonyl dodecaprenol, ethanesulfonyl 
geranylfarnesol, ethanesulfonyl farnesylfarnesol, ethanesulfonyl 
farnesylgeranylgeraniol, ethanesulfonyl farnesylfarnesylgeraniol, 
ethanesulfonyl solanesol, ethanesulfonyl decaprenol, ethanesulfonyl 
undecaprenol, ethanesulfonyl dodecaprenol, propanesulfonyl 
geranylfarnesol, propanesulfonyl farnesylfarnesol, propanesulfonyl 
farnesylgeranylgeraniol, propanesulfonyl farnesylfarnesylgeraniol, 
propanesulfonyl solanesol, propanesulfonyl decaprenol, propanesulfonyl 
undecaprenol, propanesulfonyl dodecaprenol, butanesulfonyl 
geranylfarnesol, butanesulfonyl farnesylfarnesol, butanesulfonyl 
farnesylgeranylgeraniol, butanesulfonyl farnesylfarnesylgeraniol, 
butanesulfonyl solanesol, butanesulfonyl decaprenol, butanesulfonyl 
undecaprenol, butanesulfonyl dodecaprenol, isopropylsulfonyl 
geranylfarnesol, isopropylsulfonyl farnesylfarnesol, isopropylsulfonyl 
farnesylgeranylgeraniol, isopropylsulfonyl farnesylfarnesylgeraniol, 
isopropylsulfonyl solanesol, isopropylsulfonyl decaprenol, 
isopropylsulfonyl undecaprenol, isopropylsulfonyl dodecaprenol, 
p-toluenesulfonyl geranylfarnesol, p-toluenesulfonyl farnesylfarnesol, 
p-toluenesulfonyl farnesylgeranylgeraniol, p-toluenesulfonyl 
farnesylfarnesylgeraniol, p-toluenesulfonyl solanesol, p-toluenesulfonyl 
decaprenol, p-toluenesulfonyl undecaprenol, and p-toluenesulfonyl 
dodecaprenol. 
The reaction may be carried out at a temperature broadly ranging from 
ice-cooling to reflux-heating. The reaction time can be varied, depending 
on a reagent and a reaction temperature, etc., but is usually 0.5 to 36 
hours. This reaction is preferably carried out at a temperature of 10 to 
30.degree. C. for 1 to 24 hours in the solvent such as ethers. More 
preferably, this reaction is carried out at a temperature of 10 to 
25.degree. C. for 1 to 12 hours in tetrahydrofuran in the presence of 
diisopropylamine. 
Route 2 illustrates a process for the preparation of the compounds of 
formula (I) wherein R.sub.1 and R.sub.2 are the same or different. 
Step B in Route 2 is the step of reacting a compound of formula (VII) 
##STR11## 
wherein n and R.sub.1 are as defined above, with a compound of formula (IX 
) 
EQU R.sub.3 CHO (IX) 
wherein R.sub.3 is a phenyl group which may be substituted by 1 to 5 
substituents selected from hydroxy, (C.sub.1 -C.sub.4)alkyl, (C.sub.1 
-C.sub.4)alkoxy, and halogen, and/or by methylenedioxy, in the presence or 
absence of solvents to prepare a compound of formula (VIII) wherein n, 
R.sub.1 and R.sub.3 are as defined above. 
This reaction may be carried out while removing a producing water with 
Dean-Stark apparatus, etc., or in the presence of dehydrating agents such 
as anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous 
sodium sulfate, anhydrous potassium chloride, anhydrous magnesium sulfate 
and molecular sieve. In general, the reaction is preferably carried out in 
the presence of a solvent. The solvents employed in this reaction are not 
specifically limited, unless giving an influence on the reaction, which 
can include hydrocarbons such as benzene, toluene, xylene, hexane, and 
heptane; halogenated hydrocarbons such as chloroform, methylene chloride, 
carbon tetrachloride and 1,2-dichloroethylene; ethers such as diethyl 
ether, diisopropyl ether, tetrahydrofuran and dioxane; amides such as 
dimethylformamide, dimethylacetamide and hexamethylphosphoric triamide; 
alcohols such as methanol, ethanol and isopropanol; sulfoxides such as 
dimethylsulfoxide; sulforan; and these mixed solvent. 
The reaction may be carried out at a temperature broadly ranging from 
ice-cooling to reflux-heating. The reaction time can be varied, depending 
on a reagent and a reaction temperature, etc., but is usually 0.5 to 12 
hours. This reaction is preferably carried out at a temperature from 
ice-cooling to reflux-heating for 1 to 5 hours in the presence of the 
solvents such as hydrocarbons and alcohols or the mixed solvents of 
alcohols and halogenated hydrocarbons. More preferably, this reaction is 
carried out at a temperature ranging from 0.degree. C. to reflux-heating 
for 0.5 to 3 hours in the presence of methanol or ethanol, or the mixed 
solvent of methanol and chloroform. 
Step C in Route 2 is the step of reducing a compound of formula (VIII) to 
prepare the compounds of formula (I). This reaction is usually carried out 
in the presence of a reducing agent. The reducing agents which can be used 
include metal hydrides such as lithium borohydride, sodium borohydride, 
sodium cyanoborohydride, lithium aluminium hydride and diisobutyl 
aluminium hydride. This reaction is usually carried out in the presence of 
a solvent. The solvents used are not specifically limited, unless giving 
an influence on the reaction, which can include hydrocarbons such as 
benzene, toluene, xylene, hexane and heptane; halogenated hydrocarbons 
such as chloroform, methylene chloride, carbon tetrachloride and 
1,2-dichloroethylene; ethers such as diethyl ether, diisopropyl ether, 
tetrahydrofuran and dioxane; amides such as dimethylformamide, 
dimethylacetamide and triamide hexamethylphosphate; alcohols such as 
methanol, ethanol and isopropanol; sulfoxides such as dimethylsulfoxide; 
water; and these mixed solvents. 
The reaction may be carried out at a temperature broadly ranging from 
ice-cooling to reflux-heating. The reaction time can be varied, depending 
on a reagent and a reaction temperature, etc., but is usually 0.5 to 24 
hours. Preferably, this reaction is carried out at a temperature ranging 
from ice-cooling to 50.degree. C. for 0.5 to 5 hours in the presence of 
sodium borohydride or sodium cyanoborohydride in the solvent such as 
alcohols or the mixed solvents of alcohols and halogenated hydrocarbons. 
The reactions in the above Steps B and C may be optionally carried out in 
the same vessel. More specifically, a compound of formula (VII) and a 
compound of formula (IX) are reacted in a solvent to give a compound of 
formula (VIII), followed by reducing the compound of formula (VIII) with a 
reducing agent in the same vessel to give a compound of formula (I). 
Preferably, this reaction is carried out by reacting the compounds of 
formulas (VII) and (IX) at a temperature ranging from 0.degree. C. to 
reflux-heating in alcohols, in particular methanol or ethanol, or the 
mixed solvents of alcohols and halogenated hydrocarbons, in particular, 
those of methanol and chloroform, to afford the compound of formula 
(VIII), followed by reducing the compound of formula (VIII) in the same 
vessel with a reducing agent of sodium borohydride or sodium 
cyanoborohydride at a temperature of 0 to 30.degree. C. for 0.5 to 3 
hours. 
The invention provides a pharmaceutical composition comprising as an active 
ingredient a compound of formula (I) or a pharmaceutically acceptable salt 
thereof, and optionally a pharmaceutically acceptable carrier. 
The present compounds of formula (I) can usually be administered in various 
dosage forms which include the preparations adapted for oral or parenteral 
administration. The oral preparations include tablets, hard and soft 
capsules, granules, powders, syrups and elixirs. The parenteral 
preparations include injections (intravenous, intramuscular, subcutaneous, 
intraperitoneal), drops and suppositories. These preparations can be 
prepared by conventional methods employing conventional additives such as 
excipients, binders, disintegrants, lubricants, flavorings, solubilizing 
aids, suspending agents, coating agents or the like. Route and dosage of 
administration for the compounds of the invention are not specifically 
limited and are appropriately chosen depending upon form of the 
preparations, age, sex and weight of the patient, severity of the disease 
and other factors. Daily dosage of the active ingredient for adult is 0.1 
to 600 mg. No adverse toxicological effects are indicated at any of the 
above dosage range.