Abstract 3199: Targeting LHRH-R to improve immune response in ovarian cancer

Abstract

Abstract Background: While immune checkpoint inhibitors have revolutionized the treatment of multiple cancers, such therapies have had limited efficacy in ovarian cancer. We hypothesized that a lytic peptide could stimulate local immune response and enhance efficacy of checkpoint blockade. Here, we tested the effects of a synthetic lytic peptide targeting the luteinizing hormone receptor (LHRH-R), EP-100, on immune therapy in ovarian cancer models. Methods: We carried out series of in vitro (MTT assay, immunoblot analysis, cytokine array, and immune profiling assay) and in vivo (orthotopic mouse model) experiments to determine the biological effects of EP-100 monotherapy and its combination with checkpoint blockade, α-PD-L1. Results: We found that LHRH-R positive murine ovarian cancer cells (ID8, IG10, IF5, and 2C12) were sensitive to EP-100 and were specifically killed at low micromolar levels through LHRH-R. The in vivo syngeneic mouse models (ID8 and IG10) demonstrated that EP-100 reduced tumor volume, tumor weight, and ascites volume as a single agent. The greatest effects on tumor volume reduction and ascites volume were observed with the combination of EP-100 and α-PD-L1 antibody, indicating a potentially synergistic effect in vivo. Immune profiling of tumors showed that the population of CD8+ T cells, NK cells, dendritic cells, and macrophages were significantly increased in tumor and ascites treated with α-PD-L1, EP-100 and in the combination group. However, monocytic myeloid suppressor cells, B cells, and regulatory T cells were decreased in tumors treated with α-PD-L1, EP-100 and in the combination group. We found similar effects of EP-100 combination with α-PD-L1 antibody in ascites from each group. These data indicate that EP-100 promotes a tumor microenvironment that is favorable for immune response. In vitro cytokine arrays revealed that EP-100 induced IL-1α, IL-33, CCL20, VEGF, and LDLR secretion. Among them, we validated increasing Il-33 level following EP-100 treatment in vivo and in vitro and determined the specific biological role of CD8+ T cell activation with IL-33 gene silencing using siRNA and Cas9-CRISPR approaches. In addition, we found that CD8+ T cell expressed a low level of LHRH-R and had minimal direct effects from EP-100. Conclusion: These data demonstrate strong efficacy of EP-100 and checkpoint blockade therapy. Our results provide new directions to enhance the efficacy of immune therapies for ovarian cancer. Citation Format: Mark S. Kim, Shaolin Ma, Carola Leuschner, Sanghoon Lee, Robert L. Coleman, Anil K. Sood. Targeting LHRH-R to improve immune response in ovarian cancer [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 3199.