Design, synthesis, and anti-inflammatory activity characterization of novel brain-permeable HDAC6 inhibitors

Targeting histone deacetylase 6 (HDAC6) has emerged as a promising therapeutic approach for anti-inflammation and related biological pathways, including inflammatory events associated with the brain. In this study, in order to develop brain-permeable HDAC6 inhibitors for anti-neuroinflammation, we report here the design, synthesis, and characterization of a number of N-heterobicyclic analogues that can inhibit HDAC6 with high specificity and strong potency. Among our analogues, PB131 exhibits potent binding affinity and selectivity against HDAC6, with an IC₅₀ value of 1.8 nM and more than 116-fold selectivity over other HDAC isoforms. In addition, PB131 shows good brain penetration, binding specificity, and reasonable biodistribution through our positron emission tomography (PET) imaging studies of [¹⁸F]PB131 in mice. Furthermore, we characterized the efficacy of PB131 on regulating neuroinflammation using the mouse microglia model BV2 cells in vitro and the LPS-induced inflammation mouse model in vivo. These data not only indicate the anti-inflammatory activity of our novel HDAC6 inhibitor PB131, but also strengthen the biological functions of HDAC6 and further extend the therapeutic approach inhibiting HDAC6. Our findings show that PB131 displays good brain permeability, high specificity, and strong potency toward inhibiting HDAC6 and is a potential HDAC6 inhibitor for inflammation-related disease treatment, especially neuroinflammation.