Discovery of 1-benzhydryl piperazine-based HDAC inhibitors with anticancer and antimetastatic properties against human breast cancer: synthesis, molecular modeling, in vitro and in vivo biological evaluation

Selective histone deacetylase 6 (HDAC6) inhibition is promoted as a rational strategy to develop safer anticancer drugs compared to nonselective HDAC inhibitors. Nevertheless, considerably more nonselective HDAC inhibitors have been undergoing clinical trials. Initially, we focused on synthesizing a selective HDAC6 inhibitor, with 1-benzhydryl piperazine as surface recognition CAP group, and its nonselective analogues with small structural perturbations in the hydrocarbon linker. Surprisingly, the in vitro HDAC screening identified two selective HDAC6 inhibitors (BDR-6, IC50=186 nM and BDR-9, IC50=31 nM), along with two nonselective nanomolar HDAC inhibitors (BDR-7 and BDR-8). Insight into the structural determinants for selective HDAC6 inhibition was studied by molecular dynamics. The breast cancer cell lines (MDA-MB-231 and MCF-7) were used to evaluate their in vitro anticancer, antiimigratory and anti-invasive activities, highlighting BDR-8 as the most promising lead compound. Toxicity assessment using zebrafish embryos indicated BDR-9 as a teratogenic, cardiotoxic and hepatotoxic compound, whereas the BDR-8 inhibitor at the same concentration (50 μM) was proven to be nontoxic. Finally, BDR-8 represents a promising and safe HDAC inhibitor with very potent antiangiogenic, antimetastatic and antitumor effects in the zebrafish MDA-MB-231 xenograft model in low micromolar concentrations.