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Introduction: Modulating tumor-infiltrating immune cells is the key mission for the development of cancer immunotherapy. However, current immunotherapies including immune-checkpoint inhibitors (ICI) have limited patient response rates and some with adverse effects, which drives us to seek novel targets to improve immunotherapeutic efficiency. Based on recent literature and our bioinformatic analysis, we believe that NR4A1 is an ideal target for cancer immunotherapy due to its important role in T cell exhaustion, Treg cell function as well as neoangiogenesis. Here we developed an immunotherapeutic strategy that targets nuclear receptor subfamily 4 group A member 1 (NR4A1) via proteolysis-targeting chimeric (PROTAC) technology, with an expectation that NR4A1 degradation leads to immune activation and cancer clearance via the inhibition of Treg cell function as well as the activation of effector T cells. Results: We designed, synthesized, and screened over 80 NR4A1 PROTACs based on several reported NR4A1 ligands, including celastrol, cytosporine B, and diindolylmethane analogs. We found that several celastrol-based PROTACs achieved effective degradation of target protein NR4A1. Our current focus is to understand the mechanism of action of the lead NR-V04, a celastrol- and von Hippel-Lindau (VHL)-based PROTAC. We confirmed that the NR-V04-induced NR4A1 degradation is through the proteasome- and VHL-dependent mechanisms as expected and further demonstrated the NR-V04-induced ternary complex formation between NR4A1, VHL, and NR-V04. The lead NR-V04 exhibits outstanding pharmacokinetics and effectively inhibits tumor growth at a very low dose, 1.8mg/kg twice a week, in several tumor models including B16F10, Yummer 1.7, and MC38. Interestingly, we found that NR-V04 significantly enhances anti-tumor immunity in previously mentioned mouse tumor models with seemingly distinct mechanisms of immune activation in a tumor-dependent manner. For example, NR-V04 induces the expansion of B cells and the reduction in myeloid-derived suppressor cells (MDSC) in B16F10; the reduction of Tregs, and the induction of CD8 effector population in Yummer 1.7 and MC38 tumors. we did not find obvious toxicity at these effective doses for up to 2 months. Conclusion: The lead NR-V04 is a very promising agent that induces specific degradation of NR4A1 in tumors, resulting in tumor type-dependent immune activation and tumor reduction. Targeting NR4A1 within the tumor microenvironment is effective and safe. Therefore, the lead NR-V04 or other better ones under test have the potential for translation as a novel immunotherapeutic strategy. Citation Format: Lei Wang, Yufeng Xiao, Rohan P. Master, Zeng Jin, Urvi M. Patel, Yuewan Luo, Daohong Zhou, Guangrong Zheng, Weizhou Zhang. Proteolysis-targeting chimera against NR4A1 for cancer immunotherapy [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 2326. |
