Abstract 5347: Selective targeting deacetylase 3 (HDAC3) and HDAC8 by PROTACs

Abstract Histone deacetylases (HDACs) are enzymes that play an essential role in multiple cellular processes such as DNA transcription, translation, replication, recombination, repair, and metabolism, and their dysregulation can be linked to many different diseases. Most commonly, the overexpression of HDACs is found in various cancer types including hematologic cancers, as well as solid malignancies. Of the many HDACs found in the body, class I HDACs, which consist of HDACs 1, 2, 3, and 8, play an essential role in activating oncogenes underlying tumorigenesis, disease progression, and treatment resistance. Several HDAC inhibitors (HDACis) have been approved for cancer treatment, however, they are pan-inhibitors. This lack of specificity poses many disadvantages for HDACis, including toxicity and other off-target effects. Isozyme-selective inhibitors may reduce these off-target effects and thus enhance their safety. Though favorable, selectivity is difficult to achieve from conventional inhibitors due to the highly homologous catalytic domain among HDAC isozymes. In addition, several HDAC isozymes have deacetylase-independent scaffolding functions that cannot be blocked by traditional inhibitors. Recently, there have been advances in Proteolysis Targeting Chimera (PROTAC), an emerging drug discovery technology designed to hijack cell’s existing protein degradation machinery, the ubiquitin-proteasome system (UPS) to selectively degrade target proteins. Selective degradation by PROTAC is a potential solution to many of the concerns associated with current HDACis. Previously, we reported an HDAC3-selective PROTAC, XZ9002, and following that we reported the discovery of PROTAC YX968, which can degrade both HDAC3 and HDAC8 isozymes with single-digit nanomolar DC50, this highly potent dual degrader exhibits distinct effects on modulating gene expression and is much more potent in inhibiting cancer cell proliferation compared to XZ9002. Based on this, we are further modifying the PROTACs to be selective for HDAC8. The HDAC3, HDAC8 selective degrader and HDAC3 and HDAC8 dual degrader we developed could be useful chemical probes to dissect the complex biological function of HDAC3 and HDAC8 and potential therapeutics for treating cancer. Citation Format: Yufeng Xiao, Seth Hale, Nikee Awasthee, Xuan Zhang, Yi Liu, Zhiguang Huo, Dongwen Lyu, Lei Wang, Weizhou Zhang, Megan Mosteiro, Daiqing Liao, Guangrong Zheng. Selective targeting deacetylase 3 (HDAC3) and HDAC8 by PROTACs. [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 5347.