Active Motif's EX-527 is a selective Sirtuin (SIRT1) inhibitor (IC50 = 98 nM). It does not inhibit other HDACs or SIRT family members. EX-527 increases p53 acetylation following DNA damage and causes cell cycle arrest at G1. It inhibits differentiation and facilitates expansion of hematopoietic progenitor cells. EX-527 is an extremely useful tool for determining the involvement of SIRT1 in cellular physiology. It is cell permeable.