Abstract 2363: Targeting squamous lung tumor heterogeneity with EZH2 inhibition to improve immunotherapy responses

Immunotherapies, including those targeting the PD1/PD-L1 immune checkpoint, have become popular treatment options, but they are effective for only 20% of squamous lung cancer patients. Work in our laboratory has suggested that inhibition of the histone methyltransferase EZH2 drives a basal-like transcriptional state which includes expression of the immunotherapy target PD-L1, and work from others has demonstrated that EZH2 inhibition could influence the tumor microenvironment. Therefore, we hypothesize that combining EZH2 inhibition with anti-PD1 therapy could boost response in squamous lung cancers by targeting both the tumor and the microenvironmental heterogeneity. Our laboratory uses genetically engineered mouse models of lung cancer and patient-derived cell lines and organoids to dissect the mechanistic effects of EZH2 inhibition on tumor cells and immune cells. First, we treated a panel of squamous and adeno-squamous human NSCLC cell lines with EZH2 inhibition and observed increased expression of PD-L1 and another basal cell marker, NGFR, by flow cytometry. Similar results were obtained by treating two patient-derived organoids of squamous lung cancer with EZH2 inhibitor, suggesting that EZH2 inhibition drives squamous tumor cells into a more basal-like state which may be more susceptible to anti-PD1 immunotherapy. In our mouse models of squamous lung cancer, we noted abundant tumor-associated neutrophils, which we believe may be inhibiting efficacy of immunotherapy by suppressing CD8 T cell function. In support of the idea that inhibiting EZH2 will ameliorate this phenotype, lung neutrophils isolated from EZH2 conditional knock-out mice had significantly lower levels of the T cell suppressive protein Arginase 1 than WT lung neutrophils or Lkb1/Pten TANs. Lastly, we treated mice harboring autochthonous squamous lung tumors with EZH2 inhibitor, and observed a striking increase in the proportion of tumor cells expressing PD-L1 but now defect in tumor growth. In contrast, two squamous lung tumor bearing mice treated with EZH2 inhibitor and anti-PD-1 immunotherapy had tumor regression that was durable up to 4 weeks post-treatment initiation. We plan to expand the cohorts of mice and test this promising combination therapy in a variety of lung cancer mouse models. Completion of these studies will solidify the efficacy of a promising therapeutic combination and uncover mechanisms by which tumor hierarchies and microenvironments are changed by EZH2 inhibitors in squamous lung cancers. Given that one arm of a Phase 1/2 clinical trial combining EZH2 inhibition with anti-PDL1 just began recruiting late stage non-small cell lung cancer patients, learning the phenotypes and mechanisms of responders and non-responders will be extremely timely for any Phase 2/3 trials that ensue. Funded by V Foundation Scholar Award, K22 CA201036 and KY LCRP to CFB Citation Format: Tanner J. DuCote, Christine Fillmore Brainson. Targeting squamous lung tumor heterogeneity with EZH2 inhibition to improve immunotherapy responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2363.