There is a critical need for new approaches to cancer treatment if significant improvements in morbidity and long term survival are to be achieved. Using the K6/ODC transgenic mouse model which exhibits enhanced susceptibility to skin tumor development, we have previously shown that targeting the polyamine biosynthetic pathway via inhibition of ornithine decarboxylase (ODC) can both completely prevent benign tumor development and also cause established tumors to completely regress. Despite the presence of oncogenic Ki-ras and Ha-ras mutations in tumors in this model, expression of the neoplastic phenotype is highly dependent on elevated intracellular polyamine levels. With the recent refinement of the K6/ODC model leading to the rapid and efficient production of squamous cell carcinomas, it is now possible to test the efficacy of polyamine-based therapy against highly aggressive malignant SCCs. By using a combinatorial approach involving a specific inhibitor of ODC (2-difluoromethylornithine or DFMO) and a polyamine transport inhibitor, we have been able to significantly improve the effectiveness of this therapy. In order to justify further clinical development, additional preclinical work is needed to optimize the therapy in the K6/ODC model of SCC as well as investigate the mechanisms underlying this novel therapeutic approach. To accomplish these objectives, the following questions will be addressed: (1) Does polyamine-based therapy enhance the effectiveness of existing chemotherapeutic drugs? The ability of this therapy to improve the response of SCCs to several chemotherapeutics used to treat human SCCs will be evaluated. Drugs to be examined include 5-fluorouracil, cisplatin, and paclitaxel. (2) Is polyamine-based therapy effective against human SCC? The response of the human HaCat-ras cell line, which forms well-differentiated SCCs in vivo, to PBT will be determined, using both a xenograft and an orthotopic assay in nude mice. (3) Can genes that predispose to murine SCC development be mapped and eventually identified? Since both the C3H/HeJ and FVB/N strains of mice appear to harbor SCC-predisposing genes, we will map the chromosomal location of these modifier loci in a large segregating population of K6/ODC(C3xFVB)F2 mice. We will also attempt to validate a candidate gene identified in the previous grant period (Pthlh) as a bona fide SCC modifier gene, using a variety of transgenic and knockout mouse models. The rationale for polyamine-based therapy is to starve tumor cells of polyamines by both shutting off de novo synthesis from tumor cell ODC and by inhibiting the import of polyamines from the tumor microenvironment. A salient advantage of this therapy is that it is relatively nontoxic, so that it can be added to existing protocols to increase therapeutic response while adding little or no toxicity. With the additional developmental work proposed in this project, it will be possible to rationally design pilot and/or Phase I trials of this therapy in the appropriate patient populations. ? ?
