Abstract 317: Combination of a novel ERK1/2 inhibitor (LY3214996) with CDK4 and CDK6 inhibitor (abemaciclib) enhances antitumor efficacy in KRAS mutant non-small cell lung cancer (NSCLC)
Authors: Wu Wenjuan , Bhagwat Shripad V. , King Constance , Pratt Susan , Gong Xueqian , Stewart Julie , Jones Bonita , Flack Robert , Beckman Richard , Falcon Beverly , Manro Jason , McMillen William T. , Tiu Ramon V. , Peng Sheng-Bin , Reinhard Christoph , Joseph Sajan , Buchanan Sean 
Published: July 2017

Abstract
ERK1/2, a key downstream effector of RAS mutations, is involved in the signaling network which drives cell proliferation, survival, metastasis and cancer resistance to drug treatment (including MEK and BRAF inhibitors). Lung cancer is a leading cause of cancer death worldwide. KRAS mutation present in up to 30% of NSCLC patients is associated with a poor prognosis and represents an unmet medical need. In KRAS mutant NSCLC, enhanced ERK activation cooperates with dysregulation of the cell cycle checkpoint (e.g., cyclin D, CDK4 and CDK6 complex), and contributes to tumor progression; thus, the simultaneous inhibition of ERK and the CDK4/6 pathway is hypothesized to augment tumor growth inhibition. LY3214996, a novel and highly selective small molecule inhibitor of ERK1 and ERK2, is currently in phase I clinical trial and has been shown to inhibit cell proliferation in RAS or BRAF mutant tumor cells in vitro and xenograft tumor growth in vivo. Abemaciclib, a CDK4 and CDK6-selective inhibitor is currently in phase III studies for ER positive breast cancer and KRAS mutant NSCLC. In this study we explore the potential efficacy of combined inhibition of ERK1/2 and CDK4 and CDK6 in KRAS mutant NSCLC. The combination of LY3214996 and abemaciclib synergistically inhibited cell proliferation in 85% of KRAS mutant cells in an unbiased NSCLC panel. Combination treatment with LY3214996 and abemaciclib significantly decreased levels of phospho- p90RSK, phospho-Rb, phospho-S6 and Ki67; and synergistically inhibited cell proliferation and survival in KRAS mutant NSCLC cell lines including NCI-H2122 (G-12C), A549 (G-12S) and NCI-H441 (G-12V). Subsequent in vivo studies showed that the combination treatment with LY3214996 and abemaciclib was well tolerated and led to more robust tumor growth inhibition or regression in all KRAS mutant NSCLC xenograft models (H2122, A549 and H441) compared with either single agent treatment (p≤0.002). Furthermore, in xenograft tumors the combination of LY3214996 and abemaciclib resulted in more significant reduction of phospho-p90RSK, phospho-Rb, phospho-S6 and Ki67 in H2122 tumors compared with either single agent. Overall, the combined inhibition of ERK1/2 and CDK4 and CDK6 was tolerated and enhanced antitumor efficacy in several KRAS mutant NSCLC preclinical models. These data support the feasibility of combining ERK inhibitor LY3214996 with CDK4 and CDK6 inhibitor abemaciclib as a promising strategy for the treatment of KRAS mutant NSCLC patients, and provides the rationale for the combination study in the on-going phase I LY3214996 clinic trial (NCT02857270).
Citation Format: Wenjuan Wu, Shripad V. Bhagwat, Constance King, Susan Pratt, Xueqian Gong, Julie Stewart, Bonita Jones, Robert Flack, Richard Beckman, Beverly Falcon, Jason Manro, William T. McMillen, Ramon V. Tiu, Sheng-Bin Peng, Christoph Reinhard, Sajan Joseph, Sean Buchanan. Combination of a novel ERK1/2 inhibitor (LY3214996) with CDK4 and CDK6 inhibitor (abemaciclib) enhances antitumor efficacy in KRAS mutant non-small cell lung cancer (NSCLC) [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 317. doi:10.1158/1538-7445.AM2017-317