HDAC6 inhibitors(RCSI)

Histone deacetylase 6 (HDAC6) has emerged as an attractive target for its unique cytoplasmic localization and structural features among HDAC enzymes. HDAC6 inhibitors are generally composed by three main moieties, namely a cap group, a zinc binding group (ZBG) and a linker moiety connecting them. The most frequently embedded ZBGs for HDAC inhibition are represented by hydroxamic acids which, despite their strong ability in coordinating Zn²⁺ ions, are often related to toxicity concerns and suboptimal drug-like properties. Compelling new evidence supported the use of difluoromethyl-1,3,4-oxadiazoles (DFMOs) and trifluoromethyl-1,2,4-oxadiazoles (TFMOs) as novel ZBGs able to selectively target HDAC6 isoform. Building on our background and interest in the identification of novel spirocyclic cap groups for selective HDAC6 inhibition, we have herein investigated the effect of fine-tuning the combination of newly conceived spirofused capping moieties with traditional (hydroxamic) or heterocyclic (DFMOs and TFMOs) ZBGs. Western Blot analysis and NanoBRET assays confirmed robust HDAC6 target engagement in cell. Furthermore, mechanistic investigation was performed on DFMO- and TFMO-based compounds, confirming a time dependent tight-binding interaction within HDAC6 active site. Finally, we have engaged the best performing compounds in the evaluation of their effect in the human urothelial carcinoma cell line T24. Our findings suggest that compound 21e inhibits T24 cell proliferation by sequentially activating autophagy and apoptosis, two interconnected cell death pathways that may cooperate in mediating its anticancer effects. These results foster further optimization of our compounds and pave the way to more selective and safer HDAC6 inhibitors.

Current treatments for pain often have moderate efficacy and cause unwanted effects, highlighting the urgent need to develop more effective therapeutic strategies. Accumulating evidence suggests that histone acetylation plays essential roles in acute and chronic pain. Pharmacological inhibition of HDAC6 has emerged as a promising therapeutic approach for pain management. Herein, we report the design, synthesis, and characterization of a series of diphenyl-1,2,4-oxadiazole analogues, which exhibit good selectivity and potent inhibitory activity against HDAC6. Among the new analogues, compounds 13 and 36 showed potent inhibitory activities against HDAC6 with IC₅₀ values of 12.5 and 8.5 nM, respectively, along with good selectivity over other HDAC isoforms. Both compounds significantly alleviate analgesic effects on sensory hypersensitivity behaviors in the carrageenan-induced inflammatory pain model (ED₅₀ = 31.62 and 37.89 mg/kg, respectively) and the paclitaxel-induced neuropathic pain model (ED₅₀ = 45.76 and 35.66 mg/kg, respectively). Furthermore, compound 36 suppressed the lipopolysaccharides (LPS)-induced microglia activation by inhibiting the levels of key pro-inflammatory cytokines (iNOS, COX-2, TNF-α and IL-6) in BV2 microglial cells. Compound 36 also demonstrated moderate oral bioavailability and favorable motor function safety. Together, these findings highlight compound 36 as a promising lead compound for further pharmacophore optimization, thereby paving the way for the development of selective HDAC6 inhibitors as a viable therapeutic strategy for the treatment of mechanical allodynia.