Abstract 4709: Cell-specific gene program-based small-molecule immunomodulators targeting solid-tumor microenvironments

Cancer immunotherapy includes promising strategies based on immune checkpoint blockade (e.g., anti-PD-1/PD-L1, anti-CTLA-4). A limitation of such therapies for solid tumors stems from other immune-suppressive mechanisms mediated by myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages. We hypothesize that molecules that target specific suppressive immune cells in the tumor microenvironment can reprogram the pro-tumor microenvironment towards antitumor immunity. Using our proteome-scale target/antitarget network-based lead optimization method (CANDESIGN), we designed and synthesized cell-specific nontoxic chemical libraries with modular functions for anticancer potency and immunomodulation. We used machine learning iteratively on experimental data to identify cell-specific target/anti-target networks (gene programs) as well as designed and synthesized compound libraries targeting cell-specific programs for desired cancer and immune cell function ex vivo. Specifically, we altered suppressive function of MDSCs by targeting upregulated genes in activated monocytic MDSCs in the tumor microenvironment compared to cells in spleen. We synthesized a potent nontoxic compound that specifically modulates activated MDSC function and corresponding changes in CD4+ and CD8+ T-cell activity in a mouse bladder cancer model. We observed a significant reduction in tumor mass following treatment by oral gavage. Interestingly, the bladder cancer cells used in our mouse model (as well as human and dog bladder cancer cells) are insensitive to our lead compound in vitro, suggesting in vivo antitumor activity via immunomodulation. Our lead decreased frequency of monocytic and granulocytic MDSCs in the ascites and the tumor. Moreover, a decreased frequency of MDSC expressing suppressive functional markers (e.g., Arg1, iNOS, PD-L1) and increased IFNγ + CD8 + T cells were observed in the tumor microenvironment after compound treatment. Finally, we performed a small clinical trial on pet dogs with bladder tumors treated with our compound tablets for 4-5 weeks that resulted in ~50% reduction in tumor volume. We conclude that designing cell-specific compounds perturbing the tumor microenvironment to combat immune suppression gives a selective advantage to the immune system to combat solid tumors via single and combination drug/cell therapies. Citation Format: Erin Kischuk, Joydeb Majumder, Jonathan A. Fine, Travis C. Lantz, Deepika Dhawan, Deborah W. Knapp, Timothy L. Ratliff, Gaurav Chopra. Cell-specific gene program-based small-molecule immunomodulators targeting solid-tumor microenvironments [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4709.