Abstract IA10: Developing rational combination therapy with checkpoint inhibitors

Targeting antibodies to programmed cell death protein-1 (PD-1) is an effective treatment across multiple cancer types. While a subset of patients receiving these therapies experience favorable responses, many still show disease progression, highlighting the importance of other mechanisms influencing immune responsiveness in these tumors. Therefore, combining therapies that enhance antitumor immunity has been an area of great interest to the entire cancer community. We have recently tackled this challenge in the rapidly evolving field of cancer immunotherapy by using in vivo functional genomics to identify genes whose inhibition potentiates the response to anti-PD-1 immunotherapy. Using an in vivo screening approach with a customized shRNA pooled library, we identified a number of candidates including DDR2 as promising targets for the enhancement of response to anti-PD-1 immunotherapy. In the case of DDR2, using isogenic in vivo murine models across five different tumor histologies—bladder, breast, colon, sarcoma, and melanoma—we show that DDR2 depletion increases sensitivity to anti-PD-1 treatment compared to monotherapy. Combination treatment of tumor-bearing mice with anti-PD-1 and dasatinib, a tyrosine kinase inhibitor of DDR2, also led to tumor load reduction and in some cases, complete clearance. RNAseq and CyTOF analysis revealed higher CD8+ T-cell populations in tumors with DDR2 depletion and those treated with dasatinib when either was combined with anti-PD-1 treatment. Our work provides strong scientific rationale for targeting DDR2 in combination with PD-1 inhibitors. In addition, a number of other potential druggable targets have been identified in our screen that we are currently pursuing. Citation Format: Megan M. Tu, Francis Y. F. Lee, Robert T. Jones, Abigail K. Kimball, Elizabeth Saravia, Robert F. Graziano, Brianne Coleman, Krista Menard, Jun Yan, Erin Michaud, Han Chang, Hany A. Abdel-Hafiz, Andrii I. Rozhok, Jason E. Duex, Neeraj Agarwal, Ana Chauca-Diaz, Linda K. Johnson, Terry L. Ng, John C. Cambier, Eric T. Clambey, James C. Costello, Alan J. Korman, Dan Theodorescu. Developing rational combination therapy with checkpoint inhibitors [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2019 May 18-21; Denver, CO. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(15_Suppl):Abstract nr IA10.