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

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. We performed gene expression profile analysis of SMB cells, in vivo primary MB, as well as cerebellum of normal P6 and adult mice. We also compared gene expression profiles of SMB cells to those of growth factor treated and RAS transformed cells. Overall design: 24 mouse samples were collected for RNA extraction and hybridization on Affymetrix microarrays, including 3 normal cerebellar as control, 3 primary tumor samples and 18 cell samples with different treatment conditions. We first compared gene expression profiles of SMB cells to those of in vivo primary MB and normal cerebellum. We then compared gene expression profiles of SMB cells to those of growth factor treated and RAS transformed cells.