A novel HDAC6 inhibitor interferes microtubule dynamics and spindle assembly checkpoint and sensitizes cisplatin‐induced apoptosis in castration‐resistant prostate cancer

Background Metastatic castration‐resistant prostate cancer (CRPC), the most refractory prostate cancer, inevitably progresses and becomes unresponsive to hormone therapy, revealing a pressing unmet need for this disease. Novel agents targeting HDAC6 and microtubule dynamics can be a potential anti‐CRPC strategy. Methods Cell proliferation was examined in CRPC PC‐3 and DU‐145 cells using sulforhodamine B assay and anchorage‐dependent colony formation assay. Flow cytometric analysis of propidium iodide staining was used to determine cell‐cycle progression. Cell‐based tubulin polymerization assay and confocal immunofluorescence microscopic examination determine microtubule assembly/disassembly status. Protein expressions were determined using Western blot analysis. Results A total of 82 novel derivatives targeting HDAC6 were designed and synthesized, and Compound 25202 stood out, showing the highest efficacy in blocking HDAC6 (IC50, 3.5 nM in enzyme assay; IC50, 1.0 μM in antiproliferative assay in CRPC cells), superior to tubastatin A (IC50, 5.4 μM in antiproliferative assay). The selectivity and superiority of 25202 were validated by examining the acetylation of both α‐tubulin and histone H3, detecting cell apoptosis and HDACs enzyme activity assessment. Notably, 25202 but not tubastatin A significantly decreased HDAC6 protein expression. 25202 prolonged mitotic arrest through the detection of cyclin B1 upregulation, Cdk1 activation, mitotic phosphoprotein levels, and Bcl‐2 phosphorylation. Compound 25202 did not mimic docetaxel in inducing tubulin polymerization but disrupted microtubule organization. Compound 25202 also increased the phosphorylation of CDC20, BUB1, and BUBR1, indicating the activation of the spindle assembly checkpoint (SAC). Moreover, 25202 profoundly sensitized cisplatin‐induced cell death through impairment of cisplatin‐evoked DNA damage response and DNA repair in both ATR–Chk1 and ATM–Chk2 pathways. Conclusion The data suggest that 25202 is a novel selective and potent HDAC6 inhibitor. Compound 25202 blocks HDAC6 activity and interferes microtubule dynamics, leading to SAC activation and mitotic arrest prolongation that eventually cause apoptosis of CRPC cells. Furthermore, 25202 sensitizes cisplatin‐induced cell apoptosis through impeding DNA damage repair pathways.