EX-527 is a cell-permeable, selective inhibitor of SIRT1 (IC50 = 98 nM in vivo, 38nM in vitro) that does not inhibit histone deacetylase (HDAC) or other sirtuin deacetylase family members (IC50 values are 20 uM, 49 uM, > 100 uM and > 100 uM for SIRT2, SIRT3, HDAC and NADase respectively). EX-527 has been used to investigate the relationship between SIRT1-mediated deacetylation of p53, p53 activity, and cell survival following DNA damage.