Abstract 5467: Efficacy of the ERK inhibitor LY3214996 and the PI3K/mTOR inhibitor LY3023414 in patient-derived RAS-mutant NSCLC models
Authors: Köhler Jens , Gokhale Prafulla C. , Li Jiaqi , Wilkens Margaret K. , Tiv Hong , Bhagwat Shripad V. , Donoho Greg , Brueck Patrick , Tiu Ramon V. , Redig Amanda J. , Chambers Emily S. , Ogino Atsuko , Choi Jihyun , Xu Man , Kirschmeier Paul , Jänne Pasi A. 
Published: August 2018

Abstract
Introduction: RAS mutations are present in 30% of non-small cell lung cancer (NSCLC) and, despite activated MAPK signaling, MEK inhibitors have disappointed in clinical trials. MAPK pathway reactivation and activation of anti-apoptotic signaling via the PI3K/mTOR axis are major resistance mechanisms, among others. ERK inhibitors are believed to overcome some of the restrictions of MEK inhibitors, and combinations with PI3K/mTOR inhibitors could potentially increase therapeutic efficacy. Past trials of MEK and PI3K inhibitor combinations, however, showed that toxicities and side effects are likely to be expected also for the ERK-PI3K/mTOR inhibitor combination. Therefore, more specific and potent drugs as well as alternating dosing schedules may overcome toxicities and improve treatment outcome.
Methods: We so far established five patient-derived RAS-mutant NSCLC cell lines (1/5 NRASQ61K, 1/5 KRASQ61K, 2/5 KRASG12C, 1/5 KRASG12D) and xenograft models (PDX), characterized them by next-generation sequencing (DFCI Oncopanel) and tested the antiproliferative (CellTiter-Glo® assay) and apoptosis-inducing (Caspase3/7 activity, IncuCyte® technology) efficacy of LY3214996 (ERK inhibitor) and LY3023414 (PI3K/mTOR inhibitor) in vitro. Effects on signal transduction were investigated by Western blot analysis.
Results: The ERK inhibitor LY3214996 and the PI3K/mTOR inhibitor LY3023414 exhibit single-agent antiproliferative and apoptosis-inducing activity in patient-derived RAS-mutant NSCLC cell lines (for LY3214996: 1/5 sensitive (IC50&lt;1μM), 2/5 intermediate sensitive (IC50&lt;5μM), 2/5 resistant (IC50&gt;10μM); for LY3023414: all IC50 &lt;3μM, 3/5 &lt;1μM). Despite reactivation of MAPK signaling (pMEK) upstream of ERK during LY3214996 treatment, ERK downstream targets (cMyc, DUSP4, SPRY2) were strongly suppressed. In sensitive cell lines, LY3214996 induced PARP cleavage and Bim accumulation in a dose- and time-dependent manner. Sensitivities to ERK and PI3K/mTOR inhibition varied between cell lines, indicating different pathway dependencies for proliferation and cancer cell survival.
Conclusions and Outlook: Both LY3214996 and LY3023414 have single-agent in vitro efficacy in patient-derived NSCLC models with different RAS mutations and co-mutational landscapes. Single-agent in vivo studies and tolerability studies of drug combinations are ongoing, and treatment predictors and intrinsic/adaptive resistance mechanisms will be investigated via RNAseq/GSEA and phospho-receptor tyrosine kinase arrays.
Citation Format: Jens Köhler, Prafulla C. Gokhale, Jiaqi Li, Margaret K. Wilkens, Hong Tiv, Shripad V. Bhagwat, Greg Donoho, Patrick Brueck, Ramon V. Tiu, Amanda J. Redig, Emily S. Chambers, Atsuko Ogino, Jihyun Choi, Man Xu, Paul Kirschmeier, Pasi A. Jänne. Efficacy of the ERK inhibitor LY3214996 and the PI3K/mTOR inhibitor LY3023414 in patient-derived RAS-mutant NSCLC models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5467.