Abstract 5591: Mek/erk inhibition enhances anti-pd-l1 effects on the susceptibility to NK cytotoxicity of cisplatin-resistant non-small cell lung cancer

Background: Immunotherapy is often used after chemotherapy failure or in combination with chemotherapy. Initial chemotherapy may yield clinical benefit, however; after continuous chemotherapy treatments, chemoresistance invariably develops. Immunotherapy has shown effects in a fraction of patients, but not all patients with chemoresistant non-small cell lung cancer (NSCLC) will respond. We investigated a new mechanism to enhance natural killer (NK) cell cytotoxicity against cisplatin-resistant NSCLC and propose to inhibit MEK/Erk pathway to enhance anti-PD-L1 effects on the susceptibility to NK cytotoxicity of cisplatin-resistant NSCLC. Methods: NK cell mediated cytotoxicity was conducted using two NK cell sources: NK92 cell line and primary NK cells. LDH release-based NK cytotoxicity test and the colony formation assay were applied to monitor NK cytotoxicity. NK cell cytotoxicities to parental vs. cisplatin-resistant A549 and H157 sublines (A549CisR and H157CisR) were compared. We investigated signaling molecules/pathways that are responsible for the constitutively up-regulated expression of PD-L1 and down-regulated NKG2D ligands in cisplatin-resistant cells using qPCR and Western blot analyses and inhibition studies using inhibitors of each signaling pathway were conducted in parallel. Results: We found cisplatin-resistant NSCLC cells were resistant to NK cell cytotoxicity, due to the up-regulation of PD-L1 and down-regulation of NKG2D ligands in A549CisR and H157CisR cells compared to parental cells. In addition, we found that the expression of PD-1 in NK cells was induced after co-culture with cisplatin-resistant cells, but not with parental cells. Susceptibility of cisplatin-resistant cells to NK cell cytotoxicity increased when the PD-L1/PD-1 interaction was inhibited by Abs of PD-1 or PD-L1. In inhibitor studies, we found that the inhibition of MEK/Erk signaling effectively reduced the PD-L1 level while recovered the NKG2D ligands levels in cisplatin-resistant cells. Subsequently, adding the MEK/Erk inhibitor enhanced the PD-L1 Ab effect in increasing the susceptibility of A549CisR and H157CisR cells to NK cell cytotoxic action. Conclusion and Impacts: Our data suggest that the inhibition of MEK/Erk pathway may enhance the anti PD-L1/PD-1 therapy efficacy in increasing the susceptibility of cisplatin-resistant cells to NK cell cytotoxicity via reducing the constitutively expressed PD-L1 levels, while simultaneously recovering NKG2D ligand levels in these cells. This strategy of dual effects has the therapeutic potential for molecular targeted drug development. The immune escape of cisplatin-resistant cells is an emerging task to overcome in lung cancer therapeutics, thus positive outcome of our studies may result in clinical significance. Citation Format: MingJing Shen, LiJun Xu, Ying Tsai, Peter C. Keng, Soo Ok Lee, Yuhchyau Chen. Mek/erk inhibition enhances anti-pd-l1 effects on the susceptibility to NK cytotoxicity of cisplatin-resistant 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 5591. doi:10.1158/1538-7445.AM2017-5591