Abstract 372: Optimizing vertical MAPK pathway inhibition for RAS mutant non-small cell lung cancer
Authors: Köhler Jens , Paweletz Cloud P. , Kuang Yanan , Gokhale Prafulla , Wilkens Margaret K. , Tiv Hong , Ogino Atsuko , Choi Jihyun , Kirschmeier Paul T. , Jänne Pasi A. 
Published: July 2017

Abstract
Introduction: Non-small cell lung tumors (NSCLC) with mutations in genes encoding for Ras proteins (H-, N-, K-Ras) exhibit activation of the MAPK signaling pathway. Mek inhibitors, however, have limited efficacy in patients affected by this genotype-defined tumor subtype and major resistance derives from insufficient suppression or reactivation of the extracellular signal-regulated kinase (Erk) as a result of dynamic kinome reprogramming. Erk inhibitors may overcome limitations of Mek inhibition due to the bottleneck function of Erk proteins in submitting mitogenic and anti-apoptotic signals. Combinations of both drug classes (”vertical pathway inhibition“) may further increase treatment efficacy but inevitably potentiate toxicity hence requiring alternative dosing schedules.
Methods: We investigated the efficacy of vertical MAPK inhibition with selumetinib (Mek inhibitor) and SCH772984 (Erk inhibitor) in commercially available and patient-derived RAS mutant NSCLC models. A quantitative RT-PCR based 12-gene signature was used as a surrogate to assess Erk-dependent transcriptional output. Pulsatile drug regimens were investigated in xenograft models.
Results: In a genetically simple, patient-derived NRAS-mutant lung cancer cell line (DFCI168), we observed strongest in vitro suppression of Erk-dependent transcriptional output and delay of feedback reactivation by vertical MAPK pathway inhibition with a selumetinib/SCH772984 combination compared to either drug alone. Deeper MAPK pathway suppression in our model cell line was accompanied by higher anti-proliferative activity in a panel of RAS mutant cell lines in vitro (n=5 patient-derived, n=19 commercially available cell lines) and in vivo (n=2). The degree of transcriptional output suppression of cell lines (n=8) with different sensitivities towards Mek/Erk inhibition did not differ significantly at 24 hrs in vitro. Gastrointestinal toxicities (i.e. peritonitis-like symptoms) occurred when continuously administered SCH772984 was intermittently combined with selumetinib (4 days ON, 3 days OFF) but resolved when both drugs were given intermittently (4 days ON, 3 days OFF). None of the drug treatments, however, could cure the mice.
Conclusion: We have demonstrated that deeper and prolonged transcriptional output suppression by vertical MAPK pathway inhibition translates into superior efficacy in RAS mutant lung cancer models compared to single agent treatment. Other factors (e.g. signaling pathways) are likely to influence the overall outcome of vertical MAPK pathway inhibition. Toxicities observed in PDX models overlap with those reported from genetically engineered mouse models (GEMM) with loss of Mek1/2 or Erk1/2 and can be mitigated by pulsatile dosing schedules.
Citation Format: Jens Köhler, Cloud P. Paweletz, Yanan Kuang, Prafulla Gokhale, Margaret K. Wilkens, Hong Tiv, Atsuko Ogino, Jihyun Choi, Paul T. Kirschmeier, Pasi A. Jänne. Optimizing vertical MAPK pathway inhibition for RAS mutant non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 372. doi:10.1158/1538-7445.AM2017-372