Concentrating on RAS itself presents a nice-looking method of this presssing concern, as mutant tumors have already been shown to display oncogene addiction (6, 7). of induced NSCLC. PI3K pathway activity would depend on basal IGF1R activity in mutant, however, not wild-type, lung cancers cell lines. KRAS is needed for both MEK and GW6471 PI3K pathway activity in mutant, but not wild-type, lung cancer cells, while acute activation of KRAS causes stimulation of PI3K dependent upon IGF1R kinase activity. Coordinate direct input of both KRAS and IGF1R is thus required to activate PI3K in mutant lung cancer cells. INTRODUCTION Activating point mutations in the genes encoding the RAS subfamily of small GTP binding proteins contribute to the formation of a large proportion of human tumors. In lung cancer, one of the most prevalent cancer types worldwide (1), is mutationally activated in approximately 25% of adenocarcinomas (2, 3). This GW6471 poses a significant therapeutic challenge, as mutations are generally associated with resistance to existing therapies (4, 5). Targeting RAS itself presents an attractive approach to this issue, as mutant tumors have been shown to exhibit GW6471 oncogene Rabbit polyclonal to AADACL3 addiction (6, 7). However, in contrast to the efficacy of tyrosine kinase inhibitors in patients with mutant receptor tyrosine kinases (RTK), pharmacological targeting of activated RAS proteins has been unsuccessful to date. Thus, efforts have shifted towards targeting pathways acting downstream of RAS. Indeed, combined inhibition of ERK and PI3K signaling, two well-described RAS-controlled pathways, has shown some efficacy in mutant mutations can also show selective dependencies on activities that are not regulated directly by RAS. To identify factors or pathways necessary for survival and proliferation of cells harboring mutations, several groups have performed synthetic lethal RNA interference (RNAi) screens. The list of candidates obtained thus far includes the TANK-binding kinase GW6471 1 (TBK1) (9), the TAK1 kinase (10), the transcription factor GATA2 (11, 12), the G1/S GW6471 regulator CDK4 (13), mitotic regulators (14) and proteasome components (12, 14). Differences in cell type and in specific assay conditions may help explain some of the variability across these different datasets and deeper investigation is required in order to understand the broader significance of these factors in RAS-driven tumors. Crucially, most of these screens have identified candidate novel targets for drug development, meaning that a significant period must inevitably elapse until any such potential therapy reaches clinical trials. Thus, a complementary approach is to identify targets that are necessary for survival of mutant cells using compounds that are already available and/or in clinical use. The use of drugs in RAS synthetic lethal screening can permit the analysis of a larger panel of cells, help avoid some of the off-target effects associated with RNA interference and, more importantly, identify immediately applicable therapeutic strategies to treat mutant tumors. In this study we have assayed a collection of small molecule inhibitors on a panel of human lung cancer cell lines in order to identify drugs that show selectivity for the mutant genotype. Cells harboring mutations were found to be more sensitive than wild-type cells to inhibition of the RAF/MEK/ERK pathway, whereas no genotype selectivity was observed when the PI3K/AKT/mTOR pathway was inhibited. Interestingly, however, mutant cells exhibit increased dependence on the activity of the IGF1R. Mechanistically, we show that the ability of KRAS to directly activate the PI3K activity of the p110 catalytic subunit requires a coordinate input from a receptor tyrosine kinase – IGF1R in the case of lung cancer – acting via the p85 regulatory subunit. These findings suggest potential therapeutic strategies for lung tumors harboring mutations, while avoiding the potential toxicities of direct PI3K inhibition. RESULTS mutant NSCLC cell lines are selectively sensitive to MEK, RAF and IGF1R inhibitors Using a collection of small molecule inhibitors we aimed to identify pathways that are critical for the maintenance and survival of tumor cells carrying.