p70S6 kinase is a target of the novel proteasome inhibitor 3,3′-diamino-4′-methoxyflavone during apoptosis in human myeloid tumor cells

► 3,3′-diamino-4′-methoxyflavone (DD1) induces human myeloid tumor-selective apoptosis. ► DD1-mediated proteasome inhibition dictates apoptosis. ► The mechanism relies on Bax activation and caspase-dependent p70S6 kinase degradation. ► Crosstalk by flavone and bortezomib contributes to additive apoptotic effects. ► Proteasome inhibition by DD1 could help in overcoming multidrug resistance in tumors.