Abstract 1798: ALDH inhibition as modulator of ovarian tumor associated immune cells

Abstract Rationale: Ovarian cancer (OC) is an aggressive disease with the 3rd highest mortality to incidence ratio of all cancers. Aldehyde dehydrogenase-1A enzymes play a key role in retinoic acid (RA) synthesis. RA regulates cell proliferation, differentiation, and survival by activating nuclear receptor transcription factors (RAR, RXR). In cancer cells, increased ALDH expression correlates with chemoresistance and poor prognosis. Our goal is to effectively utilize ALDH inhibitors (ALDHi) as novel therapeutics and identify their mechanism in cancer and immune cells. Based on RNAseq data, NR4A1 has emerged as a possible ALDHi target. After binding RXRγ, NR4A1 serves as a ‘molecular switch’ for cancer cell survival. Here, we explore the potential use of ALDHi as immune modulators in OC. Methods: T cells: The effect of several ALDHi on T cells following anti-CD3/CD28 polyclonal stimulation was tested via flow cytometry. Macrophages: Human OC ascites samples were cultured and treated for 72h with ALDHi or DMSO control. Flow cytometry was performed to identify ascites resident cell populations. Western blot to detect NR4A1 was conducted. Dendritic cells (DCs): Murine bone-marrow derived DCs were exposed to ALDHi or DMSO and expanded in culture; cells were counted via hematocytometer to assess myeloid cell expansion and DC differentiation. DC vaccine: ALDHi and DMSO were used with a DC vaccine and sonic hedgehog inhibitor in a study of ID8 tumor-bearing mice to assess effects on tumor progression and survival. Results: We identified several novel ALDHi that promote T cell proliferation and CD8 expansion in vitro. Exposure of 5 patient ascites samples to ALDHi showed a significant decrease in CD14+ and CD163+ cells, indicating a loss of M2 immune-suppressive macrophages vs DMSO. NR4A1 expression was decreased in ALDHi treated cells vs DMSO. In contrast, no deleterious effect was observed on ascites T cells. DC expansion: There was a 10-fold increase in DC proliferation when cells were exposed to ALDHi vs DMSO in culture. DC vaccine: In vivo, addition of ALDHi to a DC vaccine did not provide a survival significance. Discussion: In vitro, ALDHi have differential, complementary effects on tumor and immune cells in OC. In tumor cells, ALDHi lower chemoresistance and trigger necroptosis. ALDHi support the expansion of polyclonal CD8 T cells and type-1 DCs and inhibit T-regulatory cells. In contrast, ALDHi reduce M2 macrophages. Despite beneficial effects in vitro, suggesting anti-tumor competence, there was a modest effect on survival in tumor bearing mice. This may be explained by poor bioavailability of current ALDHi. Further analyses of cryopreserved murine tissues (tumor, lymph nodes, spleen) using flow and CHIP cytometry to assess surface markers, Western blot to test levels of NR4A1, and IHC to assess intratumoral immune cell invasion will continue to test target engagement. Alternative in vivo treatment regimens with other compounds are ongoing. Citation Format: Julia Knight, Bingsi Gao, Mainpal Rana, Ibrahim Uygun, Ronald Buckanovich, Anda Vlad. ALDH inhibition as modulator of ovarian tumor associated immune cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1798.