Abstract 4447: Generation of an acquired resistance model to the novel AKT inhibitor CCT129254. (2013)

Abstract The PI3K/AKT pathway is a key driver of cell growth, proliferation and survival, and deregulation at many levels of the pathway is observed in numerous cancers. Given the importance of PI3K/AKT signaling in cancer, a number of compounds targeting this pathway are currently in clinical development. Several AKT-targeted compounds, such as the ATP-competitive inhibitor AZD5363 and the allosteric inhibitor MK2206, have entered clinical trial. Whilst resistance to AKT inhibition has not yet been well defined, the development of acquired resistance has been a major barrier to the success of a number of molecularly targeted therapies, such as those which target V600E mutant BRAF. Identifying resistance mechanisms to AKT inhibition prior to the development of resistance in the clinic may assist in selecting patient populations and generating combination treatments to overcome resistance, potentially increasing the clinical utility of these inhibitors. The aims of this study were therefore to generate and characterize cell lines resistant to AKT inhibition. CCT129254, a precursor of AZD5363, is a novel ATP-competitive AKT inhibitor identified in a drug discovery program at The Institute of Cancer Research, London UK, in collaboration with Astex Therapeutics and AstraZeneca. CCT129254 is a potent and selective inhibitor of the three AKT isoforms (IC50 values between 13 and 66 nM), and treatment of cells with CCT129254 reduced phosphorylation of PRAS40, GSK3β and rpS6, downstream biomarkers of AKT activity. By exposing PTEN-deficient A2780 ovarian carcinoma cells to escalating doses of inhibitor, we have successfully generated a cell line with acquired resistance to CCT129254 (A2780 254R). We obtained approximately 4.8-fold resistance to CCT129254 in A2780 254R cells compared to parental A2780 (GI50: A2780 = 2.9 μM; A2780 254R = 14 μM). Interestingly, testing against a panel of signal transduction inhibitors revealed a 10-fold resistance to MK2206 in A2780 254R cells (GI50: A2780 = 0.30 μM; A2780 254R = 3.1 μM). Minimal cross-resistance was observed to the PI3K inhibitor GDC-0941 (1.9-fold, GI50: A2780 = 99 nM; A2780 254R = 185 nM), the mTORC1 inhibitor RAD001 (1.9-fold, GI50: A2780 = 1.65 nM; A2780 254R = 3.18 nM), and the dual PI3K/mTOR inhibitor PI-103 (1.7-fold, GI50: A2780 = 112 nM; A2780 254R = 188 nM). In addition, we have observed changes in PI3K/AKT pathway signaling biomarkers using western blot analysis. We have also utilized gene expression microarray analysis and exome sequencing to identify candidate genes involved in the resistance phenotype. We are currently validating potential resistance mechanisms identified in our candidate and global based approaches, and are investigating inhibitor combinations to overcome resistance. Citation Format: Denis T. Akan, Michael I. Walton, Michelle D. Garrett. Generation of an acquired resistance model to the novel AKT inhibitor CCT129254. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4447. doi:10.1158/1538-7445.AM2013-4447