Pifithrin-μ is an inhibitor of p53 binding and anti-apoptotic, which directly inhibits p53 binding to mitochondria as well as to Bcl-xL and Bcl-2 proteins. PFTμ rescues cells from lethal γ-irradiation-induced cell death. Because pifithrin-μ shuts down only the p53-mitochondrial pathway without affecting the transcriptional functions of p53, it is superior to pifithrin-α.