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

Isoform-selective histone deacetylase (HDAC) inhibition is promoted as a rational strategy to develop safer anti-cancer drugs compared to non-selective HDAC inhibitors. Despite this presumed benefit, considerably more non-selective HDAC inhibitors have undergone clinical trials. In this report, we detail the design and discovery of potent HDAC inhibitors with 1-benzhydryl piperazine as a surface recognition group that differ in hydrocarbon linker. Surprisingly, in vitro HDAC screening identified two selective HDAC6 inhibitors (6b, IC50 = 186 nM and 9b, IC50 = 31 nM), as well as two non-selective nanomolar HDAC inhibitors (7b and 8b). The influence of linker chemistry of synthesized inhibitors on HDAC6 potency was studied using structure-based molecular modelling. The breast cancer cell-lines (MDA-MB-231 and MCF-7) were used to evaluate compound mediated in vitro anti-cancer, anti-migratory, and anti-invasive activities, leading to 8b as the most promising compound. In our study, 8b is identified as the HDAC inhibitor with very potent anti-angiogenic, anti-metastatic and anti-tumor effects in zebrafish MDA-MB-231 xenograft models at low micromolar concentrations.