Development and Testing of Recombinant Clostridia for Cancer Therapy

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DESCRIPTION (provided by applicant): This STTR application is to develop and test for eventual clinical use a new strategy for tumor specific anticancer drug delivery. The technology, Clostridia-directed enzyme prodrug therapy, or CDEPT, exploits the fact that certain non-pathogenic bacteria of the Clostridia genus, which only grow in the absence of oxygen (hypoxia), colonize the hypoxic and necrotic areas that are unique to solid tumors. Growth of these bacteria in these areas can be exploited by engineering the bacteria to produce an enzyme, not normally present in humans that will convert a non-toxic "prodrug" into a toxic drug. Following i.v. injection of spores of the recombinant clostridia, germination of the spores and production of the prodrug activating enzyme occurs solely in the tumors. Since the enzyme is only in the tumor, the prodrug is converted to the toxic drug only in the tumor, hence targeting the cytotoxic activity of the drug selectively to the tumor. We will use a Clostridial species, C. sporogenes, that has been shown (in its non-engineered state) to be well tolerated in human patients, and a new anticancer drug, PR-104, which has recently entered clinical testing and which is highly toxic to cells when it is metabolized by the E. coli nitroreductase (NTR) enzyme (the enzyme that we have engineered C. sporogenes to express). We have demonstrated the efficacy of the combination of our C. sporogenes expressing NTR with PR-104 in rodent tumor models. Our overall goal in this STTR is to combine the expertise of SGM Biotech, which has manufactured C. sporogenes spores under GMP conditions for the past 15 years, with the Brown laboratory at Stanford University, which has genetically engineered C. sporogenes for the CDEPT strategy, to develop the organism for eventual clinical testing. We have three specific aims to achieve this goal: 1) Integrate the Clostridial codon optimized E. coli NTR gene into the genome of C. sporogenes (Stanford University). 2) Produce the recombinant C. sporogenes with the integrated E. coli NTR gene in sufficient quantities to conduct the initial safety and efficacy studies at Stanford University (SGM Biotech), and 3) Test the expression and efficacy (with PR-104) of the GMP produced recombinant C. sporogenes with tumor bearing mice (Stanford University). This project, if successful, will enable clinical testing of the specific delivery of a cytotoxic chemotherapeutic agent to solid tumors in patients thereby enhancing antitumor activity and minimizing normal tissue toxicity. PUBLIC HEALTH RELEVANCE: This STTR proposal presents a unique strategy for targeting effective killing concentrations of a specific chemotherapeutic agent to solid tumors. The approach we are proposing prevents indirect toxic effects on the animal as a whole, but allows for killing concentrations of the drug to be achieved specifically in the tumor, as we are directly activating the drug only in the tumors.