Aminooxyacetic Acid Prodrugs for Colon Cancer Therapy

ABSTRACT Recent studies of the applicants support the role of the endogenous gaseous biological mediator hydrogen sulfide H S in colorectal cancer In specific the selective upregulation of cystathionine synthase CBS and the subsequent production of H S in colonic cancer cells serves as a pro survival factor by stimulating tumor cell bioenergetics growth proliferation migration and invasion This work identifies CBS as a novel antitumor target Currently the most potent inhibitor of CBS known is aminooxyacetic acid AOAA which exerts potent anticancer effects in vitro and in vivo However the concentrations of AOAA necessary to exert antiproliferative effects in cell based systems and preclinical animal models are rather high compared to its high in vitro potency on isolated CBS enzyme Based on the preliminary data the cell based potency of AOAA can be improved by synthesis of cell permeable prodrugs of AOAA For instance YD aminooxyacetic acid methyl ester markedly enhances the antiproliferative effect of its parent AOAA in HCT human colon cancer cells In order to advance the clinical translation of AOAA we will pursue the following two Aims Aim To synthesize diverse prodrug analogs of AOAA Various classes of ester prodrugs will be synthesized and tested both in a cell free CBS enzyme activity assay and a cell proliferation assay using HCT colon cancer cells Synthetic work and in vitro testing will be pursued in an iterative fashion in order to identify the most active prodrugs We will also evaluate prodrug selectivity in a proliferation assay comparing colonic cancer cells to non transformed colonic epithelial cells and characterize the release of the active metabolite from the prodrugs upon incubation with cells or plasma Aim To evaluate a selected subset of novel AOAA prodrugs in preclinical models of colon cancer First inhibition of tumor CBS activity will be established using an in vivo ex vivo approach Next in vivo pre and post treatment efficacy will be established in comparison to the parent compound AOAA in a stringent well established preclinical model of human cancer which utilizes tumor bearing mice subjected to orthotopic transplantation of patient derived colon cancer xenografts PDTX Successful completion of the current project will be evidenced by the identification of at least one AOAA prodrug which exerts antiproliferative effects with higher potency than AOAA in vitro and in vivo Selection of a development candidate will trigger a Phase II project aimed at IND enabling studies followed by clinical development The applicant team the PI at CBS Therapeutics the head of the subcontract at the University of Texas Galveston and all participating co investigators has all necessary theoretical and practical expertise know how and infrastructure to conduct the proposed work PROJECT RELEVANCE Recent data show that animal cells and human cells produce hydrogen sulfide H S and use it for various vital biological functions The applicants have discovered that tumor cells contain a specific protein CBS which produces large amounts of H S gas Subsequent work by the applicants showed that H S supports the growth and expansion of cancer cells within the cancer patientsandapos body via several mechanisms First tumor produced H S serves as a andquot hormoneandquot that stimulates the growth and expansion of the tumor Second tumor produced H S serves as a andquot fuelandquot to feed the metabolism of the tumor cells in order to keep them andquot energizedandquot Third H S stimulates the growth of new blood vessels around the tumor tissue so that the tumor can andquot suck awayandquot fresh blood and nutritients from the host Fourth the tumor andquot hijacksandquot the blood vessels and forces it to produce even more H S In summary the tumor produces a H S rich local environment in order to thrive The therapeutic implication of these processes is that by blocking the tumor from overproducing H S the tumor will lose its andquot fuel supplyandquot and will stop growing it will shrink and will be eliminated by the hostandapos s immunological defenses In the current project the applicants propose to synthesize test and optimize a diverse range of novel CBS inhibitor compound analogs that are all prodrug derivatives of the prototypical CBS inhibitor aminooxyacetic acid AOAA Based on preliminary data prodrugs of AOAA have improved cell uptake and anticancer effect compared to AOAA Appropriately selected AOAA prodrugs would be ideal candidates for future development for the experimental therapy of colorectal cancer The project plays a critical role in the practical translation of CBS inhibition a radically new concept for cancer therapy