Abstract 5547: EGFR inhibition decreases immunosuppressive cytokines and reduces growth in STK11 mutant NSCLC

Abstract Mutations in the tumor suppressor gene STK11 have been associated with innate resistance to immune checkpoint inhibitors in NSCLC. Although this resistance mechanism is not fully defined, previous work has suggested a role for increased infiltration of suppressive immune cells in the tumor microenvironment. We investigated the ability of various treatments to alter immunosuppression associated with STK11 mutations to inform future treatment strategies in NSCLC. Comparison of STK11 mt and wt cell lines revealed 10-1,000-fold increased levels of the immunosuppressive cytokines IL-6 and IL-8 in STK11 mt lines. STK11 mt lines were treated with inhibitors of clinically actionable pathways (MEKi, ERKi, or EGFRi at 0.001-10 uM) and evaluated for changes in cell growth and cytokine production. Treatment with EGFRi significantly decreased IL-6 and IL-8 (≥25 fold) and inhibited cell growth (2-3 fold decreased IC50) in STK11 mt lines, which is particularly interesting since STK11 mt lines are EGFR wt. Both MEKi and ERKi also reduced cytokine production (≤7 fold for MEKi, ≤2 fold for ERKi), but neither recapitulated the magnitude of the changes observed with EGFRi. Genomic changes associated with increased sensitivity of STK11 mt lines to EGFRi included down-regulation (≥ 1.5-fold) of genes involved in EGFR signaling (BTC), as well as neutrophil and Treg recruitment (CXCL8, PPRB, CXCL1, CCL20). These alterations were associated with a substantial reduction of infiltrating neutrophils in a tumor spheroid model using STK11 mt NSCLC lines treated with EGFRi compared to control (0.8% vs. 13.6%). The in vitro effects of EGFRi were confirmed in vivo in STK11 mt NSCLC PDX models. Treatment with 100mg/kg of EGFRi led to 30% tumor growth inhibition compared to vehicle control and a decrease (≥1.7 fold) in cytokines (IL-6, IL-8, CXCL1, CXCL5) involved in recruitment of suppressive immune cells by day 13. The effect of this modification in cytokine secretion was an observed decrease (2.2 fold) in the absolute count of mMDSCs in tumors from EGFRi treated mice compared to vehicle control at day 7. A decrease in inflammatory cytokines and MDSCs was also observed with a lower dose of 6.25mg/kg of EGFRi. Our results suggest that EGFRi decreases cytokines/chemokines responsible for recruiting and maintaining neutrophils and other immunosuppressive cells in the TME of STK11 mt NSCLC. This, combined with the reduced growth of STK11 mt cells, indicate that EGFRi may promote important changes in the TME that could overcome innate resistance to checkpoint inhibition. Citation Format: Yelena Lazdun, Lydia Greenlees, Song Wu, Nicholas Holoweckyj, Fernanda Pilataxi, Susana Hayes, Brandon Higgs, Katie Streicher. EGFR inhibition decreases immunosuppressive cytokines and reduces growth in STK11 mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5547.