Abstract 1836: Combining a novel retinoic acid receptor-γ agonist with immune checkpoint blockade represses lung cancer growth in vivo

All-trans-retinoic acid (ATRA), a pan-agonist for retinoic acid receptors (RARs), regulates diverse cellular functions including growth, differentiation and immune function. We report here that ATRA-treatment represses tumor growth in syngeneic, immunocompetent but not in immunodeficient mice. Tumor immune microenvironment was implicated since depletion of cytotoxic T lymphocytes antagonized these effects in syngeneic mice. Combining ATRA with immune checkpoint blockade did not inhibit lung cancer growth in mice. We sought to augment retinoid anti-tumor effects without affecting its pro-tumorigenicity. We previously reported that CD38 mediated resistance to checkpoint blockade in murine 344SQ lung cancer cells via RARα transcriptional activation of CD38 expression. Yet, combining the RARα antagonist (IRX6696) with anti-PD-L1 did not augment anti-tumorigenicity in transplanted 344SQ cells in syngeneic mice. Prior work implicated RARγ in regulating T cell response. Combining the novel RARγ agonist (IRX4647) with anti-PD-L1 statistically-significantly repressed 344SQ lung cancer cell growth in syngeneic mice. This line is relatively resistant to checkpoint blockade. Immunofluorescent analysis of these treated tumors revealed that combined IRX4647 and anti-PD-L1 treatments reduced CD38 expression in the tumor stroma relative to IRX4647 or anti-PD-L1 treatment alone. Statistically-significantly elevated helper (CD4+) T cells were detected in treated tumors along with increased IL-5 and IL-13 expression observed in plasma and tumors. These cytokines can activate helper T cells, altering lung cancer growth. These microenvironment effects were associated with in vivo anti-tumorigenicity. IRX4647-treatment did not appreciably alter in vitro growth of lung cancer cells although retinoid receptors expression profiles were affected. Pharmacokinetic study of IRX4647 found its plasma half-life was 6 hours. Combining an RARγ agonist with immune checkpoint blockade exerted superior anti-neoplastic efficacy against lung cancer versus an ATRA-based regimen. Given these findings we propose exploring activity of this RARγ agonist with an optimal checkpoint inhibitor in a lung cancer clinical trial. Citation Format: Cheng-Hsin Wei, Lu Huang, Blair Kreh, Xiuxia Liu, Liliya Tyutyunyk-Massey, Zibo Chen, Mi Shi, Vidyasagar Vuligonda, Martin Sanders, Serguei Kozlov, King Chan, Amir Horowitz, Mary Carrington, Patrick Hwu, Weiyi Peng, Ethan Dmitrovsky, Xi Liu. Combining a novel retinoic acid receptor-γ agonist with immune checkpoint blockade represses lung cancer growth in vivo [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 1836.