Solar ultraviolet B (UVB) radiation is the major risk factor for the induction and development of non-melanoma skin cancer (NMSC) including squamous cell carcinoma (SCCs) and basal cell carcinoma (BCCs) which account for more than one million newly diagnosed human cancers annually in the USA. UVB causes structural alterations in DNA leading to hot spot mutations in tumor suppressor genes such as p53 and ptch in BCCs and in the perilesional skin surrounding these lesions. The pathogenesis of these tumors is thought to be driven by mutational activation of sonic hedgehog (shh) signaling and inactivation of p53 resulting in blockade of apoptosis and augmentation of cell proliferation and clonal expansion of initiated cells prompting the growth of BCCs. In this proposal we will test the hypothesis that the combination of shh activation and p53 inhibition drives the neoplastic process in BCCs and that finding chemical agents targeted to blocking the effects of UVB on these signaling pathways will abrogate the development of these lesions. For this study we will employ genetically engineered cancer-susceptible murine models that mimic the phenotype of tumor-susceptible human skin. These include: ptc1+ hairless mice carrying p53+/+p53+/- or p53-/-;in prior studies we have shown that ptc1+/SKH1 hairless mice carrying p53+/+ spontaneously develop multiple human BCCs-like lesions in addition to rhabdomyosarcomas. Chronic UVB irradiation of the skin of these mice readily induces multiple tumors including papillomas, SCCs and BCCs, providing a uniquely relevant murine model of human skin cancer induction. In this murine model we will investigate effects of targeted anti-cancer agents including cyclopamine and CP-31398, which block shh activation and convert mutant p53 into a functionally active protein respectively. We will also assess the role of nuclear factor kappa B (NFkB), which is also induced by UVB irradiation of the skin, by using sulfasalazine that blocks NFkB activation by directly inhibiting IkB kinases. Employing LC-MS, we have shown that co-administration of cyclopamine and CP-31398 or sulfasalazine does not alter individual agent's bioavailability. It is our belief that these studies will form the basis for translational clinical trials whereby a suitable combination of these test agents could prove highly effective in abrogating BCCs and may provide a mechanism-based uniquely effective approach for the chemoprevention of NMSCs in susceptible human populations.
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