Abstract LB367: CT1113, a dual USP25/28 inhibitor, promotes antitumor immunity by preventing YTHDF2-mediated complement activation and potentiates anti-PD-1 therapy

Abstract Immune checkpoint inhibitor (ICI) has reshaped the landscape of cancer therapy and improved the prognosis of a number of malignancies. However, a considerable proportion of cancer patients fail to benefit from ICI treatment. The main reason for the failure is the poor infiltration of lymphocytes due to the immunosuppressive milieu that dictates a “cold” tumor microenvironment. The ubiquitin-proteasome system plays crucial roles in many cellular processes including tumor progression and immune evasion. USP25 and USP28, two homologous deubiquitinases, maintain the stability of a wide range of oncoproteins by suppressing their proteasomal degradation. We previously found that CT1113, a novel dual USP25/28 inhibitor, could induce a potent and broad-spectrum anti-tumor effect. Here, we demonstrate that CT1113 triggers a robust cytotoxic CD8+ T cell-dependent anti-tumor immune response in several types of “cold” tumors. Dual inhibition of tumoral USP25/28 reverses the immunosuppressive microenvironment by increasing CD8+ T cell infiltration/activity and attenuates the priming of protumoral M2-like macrophages through flow cytometry and single-cell RNA-seq (scRNA-seq). Mechanistically, we identified YTH domain-containing family protein 2 (YTHDF2) as a substrate of USP25/28. The two deubiquitinases redundantly promote the stability of YTHDF2. Dual inhibition of the two increases the degradation of YTHDF2 and abolishes YTHDF2-mediated complement activation and immunosuppression. As a result, both pharmacologic and genetic inhibition of USP25/28 strongly enhance anti-PD-1 therapy against two murine “cold” tumor models without discernable systemic toxicity. Together, these results provide a rationale for future clinical trials evaluating the synergy between inhibiting USP25/28 and ICI to improve the efficacy of immunotherapy. Citation Format: Shujie Zhou, Jiarui Liu, Limin Chen, Jin Peng, Xinghua Zhen, Lingzhi Wu, Xupeng Bai, Pumin Zhang. CT1113, a dual USP25/28 inhibitor, promotes antitumor immunity by preventing YTHDF2-mediated complement activation and potentiates anti-PD-1 therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB367.