Pifithrin-μ interferes with p53 binding to mitochondria and inhibits rapid p53-dependent apoptosis of primary cell cultures of mouse thymocytes in response to gamma radiation. Pifithrin-μ, as an inhibitor of inducible HSP70, significantly inhibited cell viability with IC50 values ranging from 2.5 to 12.7?μM in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) cell lines, as well as in primary AML blasts. Pifithrin-μ is also highly active in primary AML blasts with a median IC50 of 8.9?μ M(range 5.7-37.2 ?μ M) and induces apoptosis and cell cycle arrest in a dose-dependent fashion. In addition, Pifithrin-μ also increases the active form of caspase-3 and reduces AKT and ERK1/2 in NALM-6 cells. Pifithrin-μ increases Annexin V(+) cells in both caspase-dependent and -independent manners and promotes TRAIL-induced apoptosis and arrested cancer cell growth.