In vitro activity: WT161 selectively inhibits HDAC6 and dramatically increases levels of acetylated α-tubulin (Ac-α-tubulin) with little effect on global lysine acetylation. WT161 induces significant toxicity in all multiple myeloma cell lines tested, with IC50s between 1.5 and 4.7 μM . WT161 in combination with bortezomib triggers significant accumulation of polyubiquitinated proteins and cell stress, followed by caspase activation and apoptosis. More importantly, this combination treatment is effective in bortezomib-resistant cells and in the presence of bone marrow stromal cells, which have been shown to mediate multiple myeloma cell drug resistance

Kinase Assay: WT161 is a potent, selective, and orally bioavailable HDAC6 inhibitor with IC50 values of 0.4 nM, 8.35 nM and 15.4 nM for HDAC6, HDAC1 and HDAC2, respectively; shown to have>100-fold selectivity over other HDACs.

Cell Assay: MM1S cells are treated with increasing concentrations of WT161 (0-10 μM) for 48 hours. Cell viability is determined using the MTT assay.