Discovery of novel inhibitors of histone deacetylase 6: Structure-based virtual screening, molecular dynamics simulation, enzyme inhibition and cell viability assays

Histone deacetylase 6 (HDAC6) contributes to cancer metastasis in several cancers, including triple-negative breast cancer (TNBC)-the most lethal form that lacks effective therapy. Although several efforts have been invested to develop selective HDAC6 inhibitors, none have been approved by the FDA. Toward this goal, existing computational studies used smaller compound libraries and shorter MD simulations. Here, we conducted a structure-based virtual screening of ZINC "Druglike" library containing 17,900,742 compounds using a Glide virtual screening protocol comprising various filters with increasing accuracy. The top 20 hits were subjected to molecular dynamics simulation, MM-GBSA binding energy calculations, and further ADMET prediction. Furthermore, enzyme inhibition assay and cell viability assay were performed on six available compounds from the identified hits. C4 (ZINC000077541942) with a good profile of predicted drug properties was found to inhibit HDAC6 (IC50: 4.7 ± 11.6 μM) with comparative affinity to that of the known HDAC6 selective inhibitor Tubacin (TA) in our experiments. C4 also demonstrated cytotoxic effects against triple-negative breast cancer (TNBC) cell line MDA-MB-231 with EC50 of 40.6 ± 12.7 μM comparable to that of TA (2-20 μM). Therefore, this compound, with pharmacophore features comprising a non-hydroxamic acid zinc-binding group, heteroaromatic linker, and cap group, is proposed as a novel HDAC6 inhibitor.