HDAC4-IN-1 (compound 1a), a class IIa HDACI inhibitor with an IC 50 of 0.077 μM, exhibits anticancer activity by enhancing Caspase-induced apoptosis. It is also utilized in cancer drug combination research [1].

HDAC4:0.012 μM, HDAC6:5.79 μM, HDAC2:6.13 μM, HDAC8:4.26 μM

HDAC4-IN-1 effectively inhibits class IIa HDACs with an IC50 of 0.077 μM. At a concentration of 100 μM over 72 hours, it shows low cytotoxicity in THP-1 cells (IC50 = 9.2 μM) but exhibits strong synergy with BTZ, enhancing the cytotoxic effects of BTZ. When combined at 5 μM with BTZ (7.9 nM) for 48 hours, HDAC4-IN-1 induces caspase-mediated apoptosis. Additionally, co-treatment at the same concentrations for 24 hours increases p21 protein expression in THP-1 cells. In the Cal27_HDAC4 cancer cell line, HDAC4-IN-1 at 5 μM over 72 hours inhibits cell proliferation. Cell viability assays in THP-1 cells with 100 μM concentration and 7.9 nM for BTZ reveal lower cytotoxicity compared to pan and class I inhibitors, while the combination enhances BTZ's cytotoxicity. Apoptosis analysis under similar conditions shows a significant increase in caspase 3/7 activation. Western blot analysis indicates elevated p21 protein levels with BTZ.