Abstract:
The receptor EP 4  is identified as the PGE 2  receptor that is most responsible enhancing the homing and engraftment of hematopoietic stem and progenitor cells. Treatment of graft sources and graft recipients with compounds that preferentially target the EP 4  receptor provide effective methods of increasing engraftment success while minimizing adverse side effects that may be associated with therapies that include the use of less selective molecules such as PGE 2  and dmPGE 2 . One effective molecule used in such therapies is 5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenyl-1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone or a pharmaceutically acceptable salt thereof (L-902, 688).

Description:
PRIORITY CLAIM 
       [0001]    This application claims the benefit of U.S. provisional patent application No. 61/261,349 filed on Nov. 15, 2009 and of U. S. provisional patent application No. 61/261,352 filed on Nov. 15, 2009, each of which is incorporated herein by reference in its entirety. 
     
    
     STATEMENT OF GOVERNMENTAL RIGHTS 
       [0002]    Part of the work during the development of this invention was made with government support from the National Institute of Health (NIH) under grant number HL069669. The U.S. government has certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    Methods of treating potential cell grafts comprising hematopoietic stem and progenitor cells with a selective receptor agonist of the EP 4  receptor to enhance their homing, survival, self-renewal and proliferation. 
       BACKGROUND 
       [0004]    Bone marrow transplantation, including the more popular procedures of mobilized peripheral blood stem cell transplantation and umbilical cord blood transplantation are routinely used as curative procedures for malignant and nonmalignant hematologic diseases and genetic disorders. These procedures require that hematopoietic grafts containing sufficient numbers of stems and progenitor cell populations be harvested from healthy normal donors or from patients at a time of low or absent disease and subsequently administered to patients whose hematopoietic system and presumably disease tissue has been eradicated. After transplantation, the appropriate stem cells travel to or “home” to the appropriate bone marrow micro-environmental niches. Once lodged within the appropriate niches, these cells proliferate and produce new stem cells, a process called self-renewal. The cells also differentiate into lineage restricted progenitor cells and mature cells, thereby restoring the blood forming hematopoietic system for the life of the recipient. Progenitor cells are required in said grafts to also produce mature cells; however since they are not stem cells and cannot self-renew, their participation is limited in lifespan. Successful transplantation procedures require that sufficient cells be collected from the donor and administered to the recipient. The need for large numbers of cells is aggravated by the fact that collection procedures and the process of homing and engraftment are stressful to the graft cells resulting in the loss of a portion of the cells in the graft. 
         [0005]    In particular, umbilical cord blood grafts contain limited numbers of stem cells and for this reason usually cannot be routinely used to transplant adults. Similarly, 10-25% of normal donors and up to 75% of specific patient populations, particularly those exposed to certain chemotherapeutic agents, e.g., fludarabine, fail to mobilize sufficient cells for use in transplant procedures. In general, the greater the number of viable cells that can be transplanted the greater the chances are for a successful treatment. Accordingly, there is a need for novel agents and/or methodologies that can increase the number of hematopoietic stem cells or progenitor cells in the transplant or alternatively to facilitate or enhance their homing to bone marrow. Some aspects of the current invention seek to address this need. 
       SUMMARY 
       [0006]    Some aspects of the present invention provided methods of treating a donor or donor cells or a recipient of hematopoietic stem or progenitor cells, comprising the steps of providing at least one compound that preferentially interacts with the PGE 2  EP 4  receptor, on hematopoietic stem or progenitor cells, or a pharmaceutically acceptable salt thereof and administering a therapeutically acceptable dose of said compound to a patient in need thereof. These compounds may be selected from the group consisting of: 2-[3-[(1R,2S,3R) -3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxocyclopentyl]sulfanylpropylsulfanyl]acetic acid; methyl 4-[2-[(1R,2R,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-4-[3-(methoxymethyl)phenyl]but-1-enyl]-5-oxocyclopentyl]ethylsulfanyl]butanoate; 16-(3-Methoxymethyl)phenyl-ω-tetranor-5-thiaPGE; 5-{3-[(2S)-2-{(3R)-3-hydroxy-4-[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl]thiophene-2-carboxylate; [4′-[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl)-1,5-dihydro-[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide]; and ((Z)-7-{(1R,4S ,5R)-5-[(E)-5-(3-chloro-benzo [b]thiophene-2-yl)-3-hydroxy-pent -1-enyl]-4-hydroxy-3,3 -dimethyl-2-oxo-cyclopentyl}-hept-5-enoic acid) 
         [0007]    In some embodiments the compound is 5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenyl -1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone (L-902,688). In some embodiments, the patient is recipient of a graft, wherein the graft includes at least one type of cell selected from the group consisting of hematopoietic stem cells and progenitor cells that have treated with an agonist that preferentially binds to the EP 4  receptor. 
         [0008]    Some embodiments include methods of treating a donor, donor cells or a recipient of hematopoietic stem or progenitor cells, comprising the steps of: providing at least one compound that preferentially interacts with the PGE 2  EP 4  receptor, on hematopoietic stem or progenitor cells, or a pharmaceutically acceptable salt thereof; and administering a therapeutically acceptable dose of said compound to a patient in which the patient is a donor or a recipient of hematopoietic stem or progenitor cells. In many of these methods the compound increases the homing and/or the engraftment of the hematopoietic stem or progenitor cells. 
         [0009]    Compounds that interact with the PGE 2  EP 4  receptor include, but are not limited to, compounds selected from the groups consisting of: 2-[3-[(1R,2S,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxocyclopentyl]sulfanylpropylsulfanyl]acetic acid; methyl 4-[2-[(1R,2R,3R)-3-hydroxy-2-[(E,3S) -3-hydroxy-4-[3-(methoxymethyl)phenyl]but-1-enyl]-5-oxocyclopentyl]ethylsulfanyl]butanoate; 16-(3-Methoxymethyl)phenyl-ω-tetranor-5-thiaPGE; 5-{3-[(2S)-2-{(3R)-3-hydroxy-4-[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl]thiophene-2-carboxylate; [4′-[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl)-1,5-dihydro -[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide]; and ((Z)-7-{(1R,4S ,5R)-5-[(E)-5-(3-chloro-benzo[b]thiophene-2-yl)-3-hydroxy-pent-1-enyl]-4-hydroxy-3,3-dimethyl-2-oxo-cyclopentyl}-hept-5-enoic acid) or a pharmaceutically acceptable salt thereof. Still another compound that interacts with PGE 2  EP 4  receptor and can be used in some embodiments of the invention is the compound 5-[(1E,3R)-4,4-difluoro-3-hydroxy -4-phenyl-1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone or a pharmaceutically acceptable salt thereof. 
         [0010]    In some embodiments recipient graft includes at least one type of cell selected from the group consisting of hematopoietic stem cells and progenitor cells that are treated with an EP 4  agonist. Either human or animal patients may be treated with these compounds or with cells that were first treated with these compounds either in vivo or in vitro. 
         [0011]    Still other embodiments of the invention include methods of treating a human or an animal patient, comprising the steps of: providing a therapeutically effective amount of a PGE 2  EP 4  agonist or a pharmaceutically acceptable salt thereof; harvesting a hematopoietic stem or progenitor cell from a donor; and contacting said PGE 2  EP 4  agonist to a hematopoietic stem or progenitor cell, wherein said hematopoietic stem or progenitor cell was harvested from the donor. 
         [0012]    Compounds that can be contacted with hematopoietic stem or progenitor cells in order to practice the invention include, but are not limited to, compounds selected from the group consisting of: 2-[3-[(1R,2S ,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxocyclopentyl]sulfanylpropylsulfanyl]acetic acid; methyl 4-[2-[(1R,2R,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-4-[3-(methoxymethyl)phenyl]but-1-enyl]-5-oxocyclopentyl]ethylsulfanyl]butanoate; 16-(3-Methoxymethyl)phenyl-ω-tetranor-5-thiaPGE; 5-{3-[(2S)-2-{(3R)-3-hydroxy-4-[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl]thiophene-2-carboxylate; [4′-[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl) -1,5-dihydro-[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide]; and ((Z)-7-{(1R,4S ,5R)-5-[(E)-5-(3-chloro-benzo[b]thiophene-2-yl)-3-hydroxy-pent-1-enyl]-4-hydroxy-3,3-dimethyl-2-oxo-cyclopentyl}-hept-5-enoic acid) or a pharmaceutically acceptable salt thereof. Still another compound that can be used to practice the invention is 5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenyl-1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone or a pharmaceutically acceptable salt thereof. In some embodiments, hematopoietic stem or progenitor cells treated with these compounds or other PGE 2  EP 4  agonist are then administered to a human or an animal patient. 
         [0013]    In some embodiments the therapeutically effective amount of the PGE 2  EP 4  agonist contacted with the hematopoietic stem or progenitor cells is on the order of between about 0.001 μM to about 10 μM per about 1.0×10 6  cell per ml to about 1.0×10 7  cells per ml of said hematopoietic stem or progenitor cells. In some embodiments the hematopoietic stem or progenitor cells treated and used to treat a human or animal recipient are harvested from marrow, umbilical cord or peripheral blood obtained from a human or an animal donor. In some embodiments the donor and the recipient of the hematopoietic stem or progenitor cells are the same human or animal patient. 
         [0014]    Some embodiments of the invention include a method for altering the activity of a cell, comprising the steps of: providing a hematopoietic stem or progenitor cell, wherein the cells express at least one PGE 2  EP 4  receptor; supplying at least one compound that preferentially interacts with the PGE 2  EP 4  receptor or a pharmaceutically acceptable salt thereof; and contacting the hematopoietic stem or progenitor cell with said compound. In some embodiments the hematopoietic stem or progenitor cell are isolated from marrow, umbilical cord or peripheral blood. In some embodiments contacting the cells with the compound(s) increases the homing of said cells and or the engrafting potential of the cells. In some embodiments the compounds contacted with the cells includes, but is not limited to, at least one compound selected from the group consisting of: 2-[3-[(1R,2S,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxocyclopentyl]sulfanylpropylsulfanyl]acetic acid; methyl 4-[2-[(1R,2R,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-4-[3-(methoxymethyl)phenyl]but-1-enyl]-5-oxocyclopentyl]ethylsulfanyl]butanoate; 16-(3-Methoxymethyl)phenyl-ω-tetranor-5-thiaPGE; 5-{3-[(2S)-2-{(3R)-3-hydroxy-4-[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl]thiophene-2-carboxylate; [4′-[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl) -1,5-dihydro-[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide]; and ((Z)-7-{(1R,4S,5R)-5-[(E)-5-(3-chloro-benzo[b]thiophene-2-yl)-3-hydroxy-pent-1-enyl]-4-hydroxy-3,3-dimethyl-2-oxo-cyclopentyl}-hept-5-enoic acid) or a pharmaceutically acceptable salt thereof. In some embodiments at least one of the compound is 5-[(1E,3R)-4,4-difluoro -3-hydroxy-4-phenyl-1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone or a pharmaceutically acceptable salt thereof. In some embodiments the amount of therapeutically effective compound contacting said cells is about 0.001-10 microMolar. In some embodiments the number of cells treated with the compound is on the order of between about 10 6  to about 10 7  cells per mL. 
         [0015]    Other aspects of the present invention provide methods of treating a donor, donor cells or a recipient of hematopoietic stem or progenitor cells comprising the step of administering to the donor, donor cells or recipient a therapeutically effective amount of an EP 4  agonist. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0016]      FIG. 1 . Graph illustrating that treatment of cells with EP 4  agonist ex vivo specifically up regulates CXCR 4  expression on CD34 +  cells. 
           [0017]      FIG. 2 . Graph illustrating that signaling via the EP 4  receptor is responsible for up regulation of CXCR4 expression. 
       
    
    
     DESCRIPTION 
       [0018]    For the purposes of promoting an understanding of the principles of the novel technology, reference will now be made to the preferred embodiments thereof, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, such alterations, modifications, and further applications of the principles of the novel technology being contemplated as would normally occur to one skilled in the art to which the novel technology relates. 
         [0019]    Unless stated otherwise the term, “therapeutically effective amount” refers to an amount of a pharmaceutically active compound that when administered to a human being or an animal patient or to a cell or collection of cells either alone or in combination with other pharmaceutically active ingredients or other components of medicaments that have a desirable effect on the physiological condition of a patient or the cell or collection of cells. 
         [0020]    Therapeutically effective, beneficial or efficacious doses of various compounds that preferentially bind to PGE 2  EP 4  receptors administered in vivo to either a human or an animal patient are in the range of between about 0.1 mg of the compound per Kg of body weight of the patient per day to about 100 mg of the compound per Kg of body weight of the patient per day. 
         [0021]    Compounds that preferentially bind to PGE 2  EP 4  receptors are compounds that have a higher affinity for the EP 4  receptor than for any of the other three EP receptors namely EP 1 , EP 1 and EP 3 . 
         [0022]    Compounds that can be used to practice some embodiments of the invention include, but are not limited to, the following: 5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenyl -1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone also referred to as L-902,688 (Young, et al., 2004); 2-[3-[(1R,2S,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxocyclopentyl]sulfanylpropylsulfanyl]acetic acid also referred to as ONO-AE1-329 (Suzawa et al., 2000); methyl 4-[2-[(1R,2R,3R)-3-hydroxy -2-[(E,3S)-3-hydroxy-4-[3-(methoxymethyl)phenyl]but-1-enyl]-5-oxocyclopentyl]ethylsulfanyl]butanoate also referred to as ONO-4819 (Maruyama et al., 2002; Ohta et al., 2009); 16-(3-Methoxymethyl)phenyl-ω-tetranor-5-thiaPGE 1  (Maruyama et al., 2002); 5-{3-[(2S)-2-{(3R)-3-hydroxy-4[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl]thiophene-2-carboxylate also referred to as PF-04475270 (Luu et al., 2009); APS-999 Na (El-Nefiawy et al., 2005); [4′-[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl)-1,5-dihydro -[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide](Machwate et al., 2001); and ((Z)-7-{(1R,4S,5R)-5-[(E)-5-(3-chloro-benzo[b]thiophene-2-yl) -3-hydroxy-pent-1-enyl]-4-hydroxy-3,3-dimethyl-2-oxo-cyclopentyl}-hept-5-enoic acid) U. S. Patent application number US2005/0164992A1, Jul. 28, 2005, to Donde Y, Nguyen J H, Kedzie K M, Gil D M, Donello J E and Im W B. 
         [0023]    Unless stated otherwise the term “about” as used herein refers to range of value of plus or minus 10%, e.g., ‘about 1.0’ includes values between 0.9 and 1.1. 
         [0024]    Treatment of bone marrow cells, umbilical cord blood cells, mobilized peripheral blood cells or any hematopoietic cell graft to be used for hematopoietic transplantation with Prostaglandin E 2  (PGE 2 ) or any active analogue or metabolite of PGE 2  or any E series prostaglandin with specificity for the PGE 2  EP 4  receptor, improves the homing, survival and proliferation of the transplanted hematopoietic stem cells. This treatment can be used to increase stem cell engraftment rates and thereby improve the efficiency of hematopoietic stem cell transplantation. 
         [0025]    By some estimates the success of peripheral blood stem cell transplantation requires administration of approximately 2 million CD34 +  cells per kilogram of recipient patient body weight. Any agent, combination of agents or manipulations that increases the number of stem cells that can be collected, enhances their survival rates, enhances their ability to home to the appropriate marrow environment and/or enhances their self-renewal and proliferation rates will likely have a positive impact on the efficacy of hematopoietic transplantation procedures. The success of these procedures may be measured in terms of reduced patient morbidity and mortality. Numerous studies have been undertaken to try and expand the number of human hematopoietic stem cells within isolated grafts in ex vivo settings, with limited success (Broxmeyer, 2006; Haylock and Nilsson, 2007). Recently, the CXCR4 antagonist AMD3100 has been shown to enhance mobilization of stem cells (Broxmeyer, et al., 2005; Liles, et al., 2003) and in clinical trials, (Plerixafor; Mozibil) has been shown to enhance collection of mobilized stem cells when used in combination with G-CSF (DiPersio et al., 2007b; DiPersio et al., 2007a). Truncation of chemokines has been used as a method to enhance the body&#39;s ability to mobilize stem cells. Some of these methods have been patented, e.g., U.S. Pat. Nos. 6,080,398; 6,447,766B 1; 639053B1; 6,713,052,  each of which is incorporated by reference in its entirety. Their ability to more efficiently mobilize stem cells has also been reported (King, et al., 2001; Pelus, et al., 2004). A role for blocking the activity of a surface peptidase (CD26) has been reported as a method for enhancing the homing of hematopoietic stem cells (Christopherson, et al., 2004). 
         [0026]    A number of agents when used in combination with G-CSF have been reported to increase the number of hematopoietic progenitor cells that can be recovered (Pelus and Fukuda, 2007; Herbert, et al., 2007), however, the ability of these agents to mobilize the long-term repopulating stem cells, i.e., the stem cells with self-renewal activity, has not been uniformly demonstrated. A recent study has shown that pulse exposure of mouse bone marrow cells to 16,16 dimethyl pGE 2  (dmpGE 2 ) enhances engraftment of hematopoietic stem cells, however this study provides no evidence of mechanism of action and specifically states that the effect of PGE 2  is not on cell homing (North, et al., 2007). It was unexpectedly demonstrated by Hoggatt, et al., 2009, that PGE 2  increases the CXCR4 receptor on hematopoietic stem and progenitor cells, and that this increase is responsible for increasing the homing to the bone marrow niche, resulting in a subsequent increase in engraftment. 
         [0027]    It is generally believed that PGE 2  interacts with  4  highly conserved G-protein coupled receptors (GPCR); EP 1 , EP 2 , EP 3 , and EP 4  that account for the multiple, sometimes opposing effects attributed to PGE 2  (Breyer, et al., 2001). EP receptor expression levels vary among different tissues, with EP 3  and EP 4  mRNA being most abundant (Sugimoto and Narumiya, 2007a) and EP 2  mRNA expressed at lower levels than EP 4  in most tissues (Katsuyama, et al., 1995). EP 1  activates phospholipase C (PLC) via an unidentified G protein (Tsuboi, et al., 2002), which increases intracellular Ca 2+  coupled to inositol phosphates resulting in activation of phosphokinase C (PKC) (Breyer, et al., 2001). EP 3  receptor ligation results in inhibition of adenylate cyclase and decreased cAMP that is Gα i  linked (Sugimoto, et al., 2007). Multiple EP 3  splice variants have been identified and depending on C-terminal splicing, they can couple to multiple G proteins (Namba, et al., 1993). EP 2  and EP 4  both couple to G α s leading to adenylate cyclase activation and increased cAMP, activating protein kinase A (PKA), as well as Rap1, Rac 1, and PKCζ (PKC zeta), a unique isoform implicated in HSC function (Goichberg, et al., 2006). EP 2  and EP 4  are thought to have partially redundant roles in some systems, while in others they play distinct roles (Sugimoto and Narumiya, 2007). EP 4  but not EP 2  can activate the PI3K/Akt pathway in addition to adenylate cyclase (Fujino, et al., 2003). EP 4  has a longer cytosolic domain allowing for more ligand dependent phosphorylation and more rapid desensitization (Nishigaki, et al., 1996) enabling a selective negative feedback loop (Sugimoto and Narumiya, 2007). Lastly, EP 4  is internalized when activated, while EP 2  is not (Desai, et al., 2000). As a consequence, EP 2  and EP 4  can have different roles based upon continuation or attenuation of signals generated by receptor activation (Breyer, et al., 2001). Treating with PGE 2  often exhibits a “bell-shaped” dose-response curve suggesting a different repertoire of EP receptors is activated dependent upon PGE 2  concentration (Hull, et al., 2004). 
         [0028]    Most current strategies to improve hematopoietic transplantation utilizing prostaglandin have used either native PGE 2  or a long acting derivative of PGE 2 , 16,16 dimethylprostaglandin E 2  (dmPGE 2 ). These prostaglandin compounds are thought to activate all 4 EP receptors leading to the numerous downstream signaling events briefly described above. As demonstrated herein, the enhancement in homing and engraftment of hematopoietic stem and progenitor cells is due to up regulation of the CXCR4 receptor by treatment with prostaglandin. Specifically focusing on the EP receptor that is responsible for the increase in CXCR4, (the EP 4  receptor) has the benefit of enhancing the grafting process without activating receptors that may be detrimental to the engraftment process and/or have other unknown possible deleterious consequences. 
         [0029]    Treating With An E4 Selective Agonist Affects Homing and Engraftment Efficiency 
         [0030]    Un-manipulated hematopoietic grafts or purified hematopoietic stem cell populations (e.g., SKL cells in mice or CD34 +  cells in humans) are incubated with an EP 4  specific agonist: 5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenyl-1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone (i.e. L-902,688), on ice or at room temperature at concentrations of 0.001-10 microMolar agonist per 1-10 million cells in 1 ml of culture medium, e.g. IMDM, for 15 minutes-6 hrs. After incubation, the cells are washed 3 times in sterile media or saline and administered to recipients, intravenously. L-902,688 was a generous gift from Merck Frosst (Kirkland, Canada) (Young, et al., 2004). 
         [0031]    Referring now to  FIG. 1 . This graph illustrates that treatment of cells with EP 4  agonist ex vivo specifically up regulates CXCR4 expression on CD34 +  cells. The insert shows cytometry histograms of CD34 +  cells from cord blood samples showing significant up regulation of CXCR4 on the surface of CD34 +  cells after pulse exposure to EP 4  agonist (light line) and dmPGE 2  (dark line) compared to isotype control (grey shaded area). The bar graph indicator data measured from such experiments graphed as a function of different compounds used dmPGE 2 , Butaprostone, sulprostone and EP 4 . 
         [0032]    Referring now to  FIG. 2 . This graph illustrates that signaling via the EP 4  receptor is responsible for up regulation of CXCR4 expression. The insert shows data for 3 cord blood samples. Treatment with EP 4  agonist ex vivo up regulates CXCR4 expression on CD34 +  cells. The bar chart shows combined data for 8 samples. The bar chart data demonstrates that ex vivo treatment with EP 4  agonist up regulates CXCR4 by about 3 fold. In the bar chart this effort is normalized to 100%. Pretreatment of cells with a specific antagonist of the EP 1, 2 and 3 receptor prior to exposure to EP 4  antagonist had no effect on up regulation of CXCR4 whereas pre-incubation with a selective EP 4  antagonist prior to exposure to EP 4  agonist significantly blocked up regulation of CXCR4. The fact that up regulation of CXCR4 by an EP 4  selective agonist is blocked by a selective EP 4  antagonist, but not by EP 1, 2, 3, antagonist, provides additional evidence that up regulation is mediated through the EP   4  receptor. 
         [0033]    Additional embodiments include administering EP 4  agonists (e.g., on the order of about 0.001-10 microMolar) to patients immediately prior to and daily afterwards after receiving a hematopoietic graft as a means of enhancing stem cell function. Therapeutic effective doses are amounts of the pharmaceutically active agent used either alone or in combination with another pharmaceutical agent or inert material that has a beneficial effect on a so treated human or animal patient. Such benefits may include, but are not limited to, increasing the effectiveness of other steps in a given treatment regimen. 
         [0034]    While the novel technology has been illustrated and described in detail in the figures and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the novel technology are desired to be protected. As well, while the novel technology was illustrated using specific examples, theoretical arguments, accounts, and illustrations, these illustrations and the accompanying discussion should by no means be interpreted as limiting the technology. All patents, patent applications, and references to texts, scientific treatises, publications, and the like referenced in this application are incorporated herein by reference in their entirety. 
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