RAS/MAPK activation drives resistance to Smo inhibition, metastasis and tumor evolution in Shh pathway-dependent tumors

Aberrant Shh signaling promotes tumor growth in diverse human cancers. The importance of Shh signaling is particularly evident in medulloblastoma and basal cell carcinoma (BCC), where inhibitors targeting the Shh pathway component Smoothened (Smo) show great therapeutic promise. However, the emergence of drug resistance limits long-term efficacy and the mechanisms of resistance remain poorly understood. Using new culturing techniques, we established a cohort of Shh pathway-driven medulloblastoma cell lines derived from Ptch+/- mice. Using this new model, we identify activation of the RAS/MAPK pathway circumvents Shh pathway-dependency, drives tumor growth and enhances metastatic behavior.Together these findings reveal a critical role of RAS/MAPK pathway in drug resistance and tumor evolution of Shh pathway-dependent tumors.

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Zhao X, Ponomaryov T, Ornell KJ, Zhou P, Dabral SK, Pak E, Li W, Atwood SX, Whitson RJ, Chang AL, Li J, Oro AE, Chan JA, Kelleher JF, Segal RA