Abstract 5329: Development of small molecule activators of protein phosphatase 2A for the treatment of lung cancer

KRAS is the most common recurrent oncogenomic mutations driving the growth of NSCLC and accounting for ∼25% of patients with advanced NSCLC. Patients with KRAS mutations respond poorly to current therapies. Thus, novel therapies, are critically needed, to improve the lives of patients suffering from KRAS driven lung cancers. While oncogenic kinases have proven to be successful targets for cancer treatment, the therapeutic targeting of phosphatases, the key negative regulators of these same pathways, has remained largely unexplored. Through reverse engineering of tricyclic neuroleptic drugs, we developed a first-in-class series of small molecule activators of PP2A activators (SMAPs) molecules, as represented by TRC-794 and TRC-1154, that have favorable pharmaceutical properties directly bind and activate the serine/threonine phosphatase 2A (PP2A). PP2A accounts for the majority of cellular serine/threonine phosphatase activity, and its dominant and best-defined targets are oncogenic protein kinases including ERK and AKT. In this study, we sought to determine both the association of PP2A inactivation in lung cancer with specific molecular genotypes and the biological and functional consequences of PP2A reactivation in lung cancer. We determined the PP2A activation status by immunohistochemistry for the Y307 PP2A residue, a well documented inactivating site on the phosphatase, in a large cohort of primary lung tumors and identified that KRAS G12C mutant tumors displayed coordinate overexpression of both pERK and PP2A Y307. Global phosphoproteomic analysis of TRC-794 treated KRAS lung cancer cell lines revealed ERK signaling as the only commonly perturbed pathway in drug treated cell lines which was confirmed by western blotting. Treatment of lung cancer cell lines with TRC resulted in decreased cell viability, decreased colony formation, and an increase in apoptosis. Given the marked dephosphorylation of ERK upon treatment of cell lines with TRC-1154, we overexpressed a constitutively active form of MEK (MEKDD) to blunt SMAP mediated ERK dephosphorylation to determine the relevance of ERK inactivation to the biological effects of SMAPs on cellular apoptosis. Overexpression of MEKDD resulted in blunting the apoptotic response to TRC-1154 treatment. Single agent TRC-794 or TRC-1154 treatment of KRAS GEMM and xenograft mouse models of lung cancer resulted in tumor stasis, induction of tumor cell apoptosis and cell cycle arrest to comparable levels seen with a combination of AKT and MEK inhibitors. Western blotting and immunohistochemical analysis of the tumors demonstrated that SMAP treatment resulted in of ERK, AKT, and PP2A-Y307 dephosphorylation in vivo. Additionally, these compounds demonstrate favorable pharmacokinetics and show no overt toxicity. Taken together, these findings point to therapeutic activation of PP2A as a novel strategy for the treatment of advanced KRAS-mutant NSCLC. Citation Format: Jaya Sangodkar, Sudeh Izadmehr, Sahar Mahzar, Divya Hoon, Shen Yao, David Kastrinsky, Daniela Schlatzer, Neelesh Sharma, Alain C. Borczuk, Michael Ohlmeyer, Yiannis Ioannou, Goutham Narla. Development of small molecule activators of protein phosphatase 2A for the treatment of lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5329. doi:10.1158/1538-7445.AM2015-5329