Abstract B124: Drugging the undruggable: development of small molecule activators of protein phosphatase 2A for cancer treatment
Authors: Sangodkar Jaya , McQuaid Daniel , Kisselar Janna , Brautigan David , Chance Mark , Ohlmeyer Michael , Kastrinsky David , Ioannou Yiannis , Narla Goutham 
Published: May 2016

KRAS is the most common recurrent oncogenomic mutations driving the growth of 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 that have favorable pharmaceutic properties directly bind and activate the serine/threonine phosphatase 2A (PP2A). A critical role for PP2A as a tumor suppressor has previously been established, and PP2A inactivation is common feature in human lung cancers. Furthermore, protein phosphatase 2A (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. To understand the effects of SMAPs on cell viability and survival, we used MTT and colony formation assays in lung cancer cell lines. Apoptosis was evaluated through annexin V staining and cell cycle profile analysis. Additionally, global phosphoproteomic profiling was performed. Effects of SMAPs in vivo were assessed using A549, HH41 and H358 xenograft and Kras LA2 transgenic mouse models. Treatment of lung cancer cell lines with TRC resulted in decreased cell viability, decreased colony formation, and an increase in apoptosis. Global phosphoproteomic analysis of SMAP treated cell lines revealed ERK signaling as a commonly perturbed pathway which was confirmed by western blotting. Single agent SMAP 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. Furthermore, combination based therapy with kinase inhibitors and our novel phosphatase activators resulting in marked synergy and tumor regressions in vivo. Importantly, these compounds demonstrate favorable pharmacokinetics and show no overt toxicity both alone or in combination. Taken together, these findings point to therapeutic activation of PP2A as a novel strategy for the treatment of advanced KRAS-mutant NSCLC. While research and clinical effort has largely focused on development of inhibitors of oncogenic kinases, the identification of small molecule activators of tumor suppressor proteins has remained elusive. Activation of such proteins could offer the opportunity to identify novel synergistic strategies for the treatment of a number of cancer types. Nevertheless, translation of a PP2A activation strategy into clinical medicine has required pharmaceutically tractable agents for development. Our studies represent a first step into that new territory and highlight the potential for the development of small molecule activators of other protein phosphatases and tumor suppressor proteins

Citation Format: Jaya Sangodkar, Daniel McQuaid, Janna Kisselar, David Brautigan, Mark Chance, Michael Ohlmeyer, David Kastrinsky, Yiannis Ioannou, Goutham Narla. Drugging the undruggable: development of small molecule activators of protein phosphatase 2A for cancer treatment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B124.