Co-targeting S6 and TAM kinases in PTEN-deficient glioblastoma Project Summary The ribosomal S6 protein kinases (S6Ks) are activated in response to loss of the tumor suppressor PTEN in glioblastoma and other cancers of solid and hematopoietic tissues. We previously reported that genetic inactivation of S6K1 counteracts the metabolic and anti-apoptotic effects of PTEN loss in cancer, in agreement with several observations in comparable settings. Recently we investigated pharmacological inhibitors that target S6K1, which led to the identification of a PTEN-specific vulnerability to combination inhibition of S6K1 together with the TAM family of tyrosine kinases. The TAM family of tyrosine is named for its members, which are TYRO3, AXL, and MERTK. TAM tyrosine kinases are highly targetable in oncology, as there are several late-stage clinical trial and FDA-approved tyrosine kinase inhibitors that have activity against all three members. In a validation phase using genetic approaches to investigate the requirements for PTEN-selective cytotoxicity, results revealed that inactivation of TAM kinases is sufficient to sensitize PTEN-deficient cells to inhibition of S6K1. In the present research application, we propose to extend the genetic analysis of S6 and TAM kinases to elucidate the mechanisms that relate the kinases in the setting of PTEN-deficient glioblastoma. Experiments will make use of CRISPR Cas9 genome editing technologies to inactivate the S6K and TAM kinase family members, alone or in combination, while determining signaling and metabolic effects. Model systems will employ patient-derived tumor samples to assess the generality and applicability of genetic results to physiologic functions of glioblastoma tumors/cells. We anticipate that the results will provide the mechanistic framework that will inform the development of targeted therapeutic strategies affecting the S6Ks and TAMs themselves, or signaling components that are part of their pathways.