Abstract PR02: Recurrent oncogenic mutations in the small GTPase RIT1 activate PI3K and MEK

Recently, we identified somatic mutations in the RAS-family small GTPase gene RIT1 in 2.4% (10/413) of lung adenocarcinoma tumors. Mutation of RIT1 is mutually exclusive with other oncogenic mutations in the receptor tyrosine kinase/RAS pathway, suggesting that RIT1 mutations are rare driver mutations in lung adenocarcinoma. Oncogenic RIT1 mutations cluster in the switch II domain of the protein and are observed not only in lung adenocarcinoma but also in myeloid malignancies, breast carcinoma, cervical carcinoma, and in the germline of Noonan syndrome patients. Here we functionally characterize 26 RIT1 point mutations and in-frame insertions/deletions in murine fibroblasts and human immortalized lung epithelial cells and find that the majority of somatic RIT1 mutations are able to transform cells. Furthermore, we identified a human lung cancer cell line, NCI-H2110, with an endogenous RIT1 p.M90I mutation. Knockdown of RIT1 in NCI-H2110 cells revealed the role of RIT1 in regulation of PI3K and MEK signaling. Consistently, combination PI3K/MEK inhibition could inhibit cellular transformation induced by ectopic expression of mutated RIT1. Furthermore, PI3K inhibition suppressed in vivo growth of NCI-H2110 cells. These data identify RIT1 as an oncogene and nominate combined PI3K and MEK inhibition as a therapeutic strategy in RIT1-mutated cancers. This abstract is also presented as Poster A04. Citation Format: Alice H. Berger, Fujiko Duke, Marcin Imielinski, Nathan Kaplan, Jeremiah Wala, Geng-Xian Shi, Douglas A. Andres, Matthew Meyerson. Recurrent oncogenic mutations in the small GTPase RIT1 activate PI3K and MEK. [abstract]. In: Proceedings of the AACR-IASLC Joint Conference on Molecular Origins of Lung Cancer; 2014 Jan 6-9; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2014;20(2Suppl):Abstract nr PR02.