Pifithrin-μ is a cell-permeable sulfonamide inhibitor of p53 binding and an anti-apoptotic. Direct inhibition of p53 binding to mitochondria as well as to Bcl-xL and Bcl-2 proteins by Pifithrin-μ has been observed. Pifithrin-μ selectively inhibits p53 translocation to mitochondria without affecting the transactivation function of p53. Pifithrin-μ has been shown to reduce γ-radiation induced cell death in vitro. Unlike pifithrin-α (sc-45050), pifithrin-μ targets only the mitochondrial branch of the p53 pathway without affecting the important transcriptional functions of p53. Pifithrin-μ selectively inhibits HSP 70 (heat shock protein 70) activity.