Selisistat (EX-527) is an inhibitor of SIRT1 enzymatic activity (IC50, 98 nM), identified in a high-throughput screen using bacterially expressed human SIRT1. Selisistat (EX-527) inhibits SIRT1 in a concentration-dependent manner with an IC50 of 38 nM, in agreement with the activity on bacterially expressed SIRT1. Selisistat (EX-527) has much lower potency against SIRT2 (IC50, 19.6 μM) or SIRT3 (IC50, 48.7 μM) but does not inhibit class I/II HDAC activity at concentrations up to 100 μM. Selisistat (EX-527) exerts an inhibitory effect on SIRT1 activity without affecting SIRT1 expression on both mRNA and protein levels.