Pifithrin-β hydrobromide is an inhibitor of p53; reversibly blocks p53-dependent transcriptional activation and apoptosis. Protects against neuronal death in models of stroke and neurodegenerative disorders. Active in vivo; protects mice from the side-effects of Y therapy associated with p53 induction. Supresses self-renewal of embryonic stem cells. Also aryl hydrocarbon receptor (AHR) agonist, causes upregulation of AHR target gene CYP1A1 (EC50 = 1.1 μM).