Abstract 4441: CS3003, an HDAC6-selective inhibitor, improves anti-PD-1 immune checkpoint blockade therapy efficacy

Abstract Background: Histone deacetylases (HDACs) are involved in diverse cellular regulatory function including histone modification and non-histone modification. Several publications have demonstrated that selective HDAC inhibitors (HDACi) can influence tumor growth and immunogenicity. In particular, the selective inhibition of HDAC6 has function of inhibiting tumor growth in several malignancies. However, the mechanism of this effect is still not clear. Methods: In this study, we evaluated CS3003, a selective HDAC6 inhibitor, inhibition profile using cell-based free assays. In vivo anti-tumor efficacy was evaluated in MM.1S xenograft mouse model. CS3003 and PD-1 blockade combination effect was evaluated in CT26 syngeneic mouse model. RNA-seq method was used to explore the transcription regulation by CS3003 compared to other pan-HDAC, Class I HDAC inhibitor and selective HDAC6 inhibitors. Results: CS3003 has distinct inhibition profile in HDAC family members. Combination of CS3003 and proteasome inhibitor synergistically enhanced anti-tumor function in human multiple myeloma mouse model (coefficient of drug interaction, CDI=0.69). In addition, CS3003 improves the anti-tumor activity of anti-PD-1 immune checkpoint blockade in solid tumor model (CDI=0.62 and 0.88 when the dosage of CS3003 was 30 and 70mg/kg, respectively). Transcriptome analysis demonstrated a unique gene expression pattern of CS3003 from other pan-HDAC and selective HDAC6 inhibitors. Conclusions: These data provide a comprehensive pre-clinical characterization of CS3003 that supports its unique HDAC inhibition profile and its capability of improving anti-PD-1 immune checkpoint blockade therapy efficacy. Citation Format: Zhenhu Li, Zhaoxiang Ren, Jingshu Ma, Liang Tang, Liang Lu, Ying Zhu, Yunfei Wu, Tiancheng Liu, Juan Zhang, Yuanwu Bao, Kangyu Zhang, Changqing Wei, Shuhui Chen, Xinzhong Jon Wang. CS3003, an HDAC6-selective inhibitor, improves anti-PD-1 immune checkpoint blockade therapy efficacy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4441.