Abstract 5590: Combination of an oncokinase inhibitor merestinib with anti-PD-L1 results in enhanced immune mediated antitumor activity in CT26 murine tumor model

The combination of tumor targeted therapeutics with PD-L1 checkpoint blockade is being explored as a method to increase the clinical benefits of immunotherapy, and expand response to additional cancer types. Merestinib (Mer) is a kinase inhibitor targeting several oncokinases1 (including MET, MST1R, AXL, MERTK, and MKNK1/2) that can potentially modulate immune function, angiogenesis, as well as target the tumor 1-5. To determine the combinatorial potential with immunotherapy, the effects of Mer were evaluated in vitro on human T cells, PBMCs and murine tumor lines CT26 colon carcinoma (harbors KRASmt G12D expresses low Met/no p-Met/high Axl/p-Axl) and B16F10 melanoma (expressing high Met/pMet/peIF4E). Additionally, the anti-tumor effect of Mer was tested in vivo on established CT26 and B16F10 tumors compared to MET specific TKIs (savolitinib, PF4217903) alone or in combination with PD-L1 antibody (Ab) blockade. In vitro, Mer showed no significant effects on either T cells or PBMCs, but was able to inhibit downstream signaling in both CT26 and B16F10 showing activity on murine tumor cell lines. In vivo, daily Mer monotherapy (6, 12 or 24 mg/kg) showed significant anti-tumor effect at all doses in both CT26 and B16F10, that was not seen with either savolitinib or PF4217903. Concurrent combination of Mer (12 mg/kg) and anti-PD-L1 Ab (0.5 mg qw) in CT26 was found to have anti-tumor activity that was synergistic as compared to each single agent alone. While the effect of Mer monotherapy was lost when treatment ended, tumors continued to regress in the combination group even upon cessation of therapy. The combination was well tolerated and resulted in 90% complete responders compared to 30% with anti-PD-L1 Ab alone, 35 days after completing dosing. To test the ability to generate immunologic memory, complete responders were re-challenged with CT26 cells on the contralateral side. All mice in the combination group resisted re-challenge, showing that Mer/PD-L1 Ab combination was triggering immunologic memory. Although there was no significant change in intra-tumor immune cell populations between groups, combination therapy showed an enhanced and unique intra-tumor immune activation/inflammation gene expression signature compared to PD-L1 Ab monotherapy. The enhanced immune activation of the combination therapy, leading to synergistic anti-tumor efficacy, demonstrates that merestinib has the potential to augment immunotherapy while targeting the tumor directly. This preclinical data provides the rationale for the clinical investigation of merestinib in combination with checkpoint therapies targeting the PD-L1/PD1 axis (NCT02791334). 1 - Yan et al. Invest New Drugs 2013;31:833-44 2 - Balan et al. J Biol Chem 2015;290:8110-20 3 - Eyob et al. Cancer Discov 2013;3:751-60 4 - Lemke G. CSH Persp Biol 2013;5:a009076 5 - Piccirillo et al. Nat Immunol 2014;15:503-11 Citation Format: Sau-Chi Betty Yan, Victoria L. Peek, Jennifer R. Stephens, Um L. Um, Amaladas Nelusha, Colleen A. Burns, Kelly M. Credille, Thompson N. Doman, Scott W. Eastman, Beverly L. Falcon, Gerald E. Hall, Philip W. Iversen, Bruce W. Konicek, Jason R. Manro, Any T. Pappas, Julie A. Stewart, Michael B. Topper, Swee-Seong Wong, Michael Kalos, Ruslan D. Novosiadly, Richard A. Walgren, David Schaer. Combination of an oncokinase inhibitor merestinib with anti-PD-L1 results in enhanced immune mediated antitumor activity in CT26 murine tumor model [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 5590. doi:10.1158/1538-7445.AM2017-5590