Exploration of non-hydroxamate based quinoline analogues as HDAC8 inhibitors

Histone deacetylase 8 (HDAC8) has emerged as a promising therapeutic target due to its role in epigenetic regulation. In this study, novel non-hydroxamate-based quinoline analogues were designed and explored as HDAC8-selective inhibitors that exhibit nanomolar HDAC8 enzymatic inhibition. Notably, compounds BHC-10 and BHC-13 showed 30 and 42 nM activity, respectively. Compounds exhibiting below 500 nM activity were evaluated for their in vitro cellular activity, and two compounds, BHC-2 and BHC-10, showed promising activity in neuroblastoma cell lines (IMR-32 and SH-SY5Y). Based on both enzymatic and cellular assays, compounds BHC-2, BHC-10, and BHC-13 were selected for further evaluation using clonogenic growth assays, apoptosis assays, and cell cycle analysis. Clonogenic assays revealed a significant, dose-dependent reduction in colony formation. Flow cytometry analysis indicated a dose-dependent increase in apoptotic cell populations and induction of cell cycle arrest at the S phase. Mechanistic studies confirmed target engagement through enhanced acetylation of SMC3, as demonstrated by western blot analysis. Additionally, molecular docking analysis provided insights into the binding interactions of these compounds with the HDAC8 protein. Two compounds from the current work, BHC-10 and BHC-13, emerged as more potent and selective than the reference compound B. Together, the current findings establish these compounds as promising HDAC8 modulators with potential for therapeutic development in neuroblastoma.