Basal cell carcinomas (BCCs) are the most common type of human malignancy in the United States; more than 1,000,000 Americans are diagnosed with BCCs each year. The management of these tumors is a major contributor to health care costs. BCC risk directly correlates with exposure to environmental solar ultraviolet (UV) radiation and these tumors manifest activated sonic hedgehog (Shh) signaling and Shh is among the most fundamental signal transduction pathways in embryonic development. Activated Shh signaling secondary to inactivating germline mutations in Ptch, the repressor of this pathway, characterizes both human and murine BCCs. This is associated with the rare, dominantly inherited disorder known as Gorlin syndrome. These patients develop large numbers of BCCs in addition to developing various extracutaneous tumors such as medulloblastomas. Knowledge of the importance of Shh signaling in driving BCC pathogenesis has led to the identification of small molecules that target different components of this pathway including Smo, Shh, and Gli-1. However, because the Shh signaling pathway is indispensable for development and tissue homeostasis, the potential toxicity of Shh inhibitors is an important consideration for human use. Moreover, both preclinical and our recently-completed clinical trials indicate that simply targetin the Shh pathway does not totally block the proliferation of BCC cells, suggesting that additional pathway(s) may contribute to BCC pathogenesis. We have generated preliminary data showing efficacious suppression of the growth of UVB-induced BCCs by simultaneously inhibiting the Shh and Akt1 and mTOR pathways thereby implicating Akt1-mTOR signaling in BCC development. Furthermore, we have shown that the Shh pathway directly regulates mTOR expression and that mTOR is a direct transcriptional target of SOX9, a transcription factor regulated by Gli-1. In this proposal we will test the hypothesis that there are cooperative interactions between Akt1 and Shh pathways that converge on mTOR, and that blocking both Shh and Akt1 pathways is necessary to successfully block BCC pathogenesis. Using both in vitro assays and BCC murine models generated in our laboratory to recapitulate Gorlin syndrome (Ptch1+/-/SKH-1 and Akt KO/Ptch1+/-/SKH-1, and Gli-luciferase/Ptch+/-/SKH-1), we will (1) define the importance of Akt1 in the pathogenesis of BCCs, (2) determine the mechanism of the cooperative interactions between Akt1 and Shh pathways in regulating mTOR, and (3) test the use of combinations of therapeutic agents capable of targeting both pathways simultaneously. The studies proposed here have substantial potential to provide important insights into the mechanisms underlying signaling events that drive the pathogenesis of BCCs. By utilizing non-toxic targeted agents in various combinations, it is likely that we can develop novel therapeutic approaches for preventing/treating human BCCs.
Basal cell carcinomas (BCCs) of the skin are the most common type of human cancer in the United States. BCCs are known to have abnormalities in the sonic hedgehog (Shh) signaling pathway, one of the key regulators of animal and human development. Our data show that a pathway crucial for survival of cells, the Akt1-mTOR pathway, cooperates with the Shh pathway, and these pathways together drive the growth of BCCs. The proposed study will investigate two aspects of BCC pathogenesis: 1) the cross-communication between the Shh and Akt1-mTOR pathways in driving BCC development, and 2) the efficacy and safety of simultaneously inhibiting the Shh and Akt1 pathways using a combination of drugs that long have been used to treat other human diseases. The studies to be conducted in this proposal are designed to help identify novel safe and effective drugs to treat BCCs.
