Design, synthesis, and biological evaluation of quinazoline derivatives as dual <scp>HDAC</scp>1 and <scp>HDAC</scp>6 inhibitors for the treatment of cancer

Fifty-eight quinazoline-based compounds were designed and synthesized based on the structural optimizations from the lead compound 23bb in an attempt to search for more potent dual HDAC1 and HDAC6 inhibitors. Among them, 32c (HDAC1, IC₅₀ = 31.10 ± 0.37 nM; HDAC6, IC₅₀ = 16.15 ± 0.62 nM) and 32d (HDAC1, IC₅₀ = 37.00 ± 0.24 nM; HDAC6, IC₅₀ = 35.00 ± 0.71 nM) were not only identified as potent dual-acting HDAC1 and HDAC6 inhibitors with over 10-fold selectivity to the other HDACs, but also displayed activities in tubulin acetylation and histone H₃ acetylation induction. Importantly, both of them displayed strong antiproliferative activities against various tumor cell lines in vitro with IC₅₀ values less than 40 nM, especially for hematologic tumors cells (U266 and RPMI8226, IC₅₀ < 1 nM), which were even better than 23bb and SAHA. Furthermore, 32c showed a significant tumor growth inhibition (antitumor rate = 63.98%, p < 0.05) in the resistant MCF-7/ADR xenograft model without any obvious body weight changes and abnormal behaviors. Our findings validate that 32c is a potent dual inhibitor of HDAC1/6 that can be an efficacious treatment for breast cancer with Adriamycin resistance.