Purity >95%. Pifithrin-Alpha is an inactivator of p53 that blocks p53-dependent transcriptional activation and apoptosis. p -nitro-Pifithrin-Alpha is a cell-permeable analog of pifithrin-Alpha. It blocks p53-mediated expression of p21/WAF1 and apoptosis in cortical neurons ten-fold more potently than pifithrin-Alpha. p- nitro-Pifithrin-Alpha, at 10 μM, suppresses p53-mediated TGF-Beta1 expression in human proximal tubular cells and attenuates steatosis and liver injury in mice fed a high-fat diet. It is slowly converted into a more potent cyclized form, p- nitro cyclic pifithrin-Alpha, when incubated in biological media (t1/2 = 8 h).