Abstract B25: PI3K targeted inhibition in NSCLC: An in vitro evaluation and correlation of mutation status to activated PI3K pathway signaling in NSCLC patients
Authors: Heavey Susan , Toomey Sinead , Carr Aoife , Cuffe Sinead , Finn Stephen , Hennessy Bryan , Crown John , Barr Martin , O'Byrne Kenneth , Gately Kathy 
Published: October 2015

Background: The success of PI3K targeted inhibition has been hampered by a high rate of drug resistance, which may be facilitated by MEK pathway signaling. As such, investigation of PI3K-MEK co-targeted inhibition is warranted. With high morbidity and mortality rates and a clear need for new therapeutic intervention strategies, non-small cell lung cancer (NSCLC) is an ideal setting to investigate the effectiveness of this co-targeted inhibition strategy. GDC-0941 is a pan-PI3K inhibitor which has been investigated in combination with GDC-0973, a MEK inhibitor, in early clinical studies. No data has been published to date on the combination of GDC-0980 (a dual PI3K/mTOR inhibitor) and GDC-0973, which we believe may induce improved responses. We aim to elucidate the role of mutation status in response to this co-targeted inhibition approach in vitro, as well as correlating the frequency/type of PI3K/ MEK pathway mutations to PI3K pathway signaling in a well characterized NSCLC patient cohort.

Methods: The effects of GDC-0941, GDC-0980 and GDC-0973 on proliferation, apoptosis and protein expression were examined in a panel of 4 NSCLC cell lines by BrdU Assay, HCA, PathScan protein array and Western blot. DNA was extracted from 120 NSCLC patient tissue samples, and screened for 547 clinically relevant mutations in 46 genes using the Sequenom platform. Total protein extracts, from freshly resected matched tumor/normal tissues from PIK3CA mutation positive versus wild-type patients, were subjected to phosphoproteomic analysis using Pathscan arrays (CST).

Results: GDC-0941 and GDC-0980 treatment induced dose-dependent anti-proliferative and pro-apoptotic responses across all 4 NSCLC cell lines, while GDC-0973 treatment induced only anti-proliferative responses. GDC-0980 & GDC-0973 combination treatment induced significantly greater phosphoprotein inhibition than treatment with either inhibitor alone, most notably in cell lines harboring PIK3CA mutations. This combined treatment approach also led to significant increases in apoptosis and synergistic reductions in proliferation across the panel of cell lines as calculated using the Chou Talalay method. NSCLC patient mutational profiling identified a PIK3CA mutation frequency of &gt;11%. Differences in PI3K pathway signaling were quantified in PIK3CA mutant versus wild-type patient matched tumor/normal tissues and results will be presented.

Conclusion: This research underpins the importance of mutation status and pathway activation in sensitivity to targeted therapies. Combined inhibition of the PI3K and MEK pathways is a promising strategy for treatment of NSCLC, although efficacy is dependent on molecular subtype. In the era of personalized medicine, patient genotyping is crucial to improve patient survival and reduce toxicities.

Citation Format: Susan Heavey, Sinead Toomey, Aoife Carr, Sinead Cuffe, Stephen Finn, Bryan Hennessy, John Crown, Martin Barr, Kenneth O'Byrne, Kathy Gately. PI3K targeted inhibition in NSCLC: An in vitro evaluation and correlation of mutation status to activated PI3K pathway signaling in NSCLC patients. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B25.