A cell-permeable, reversible, potent, and selective inhibitor of Akt1/Akt2 activity (IC50=58nM, 210nM, and 2.12uM for Akt1, Akt2, and Akt3, respectively, in in vitro kinase assays). The inhibition is reported to be pleckstrin homology (PH) domain-dependent. It does not exhibit any inhibitory effect against PH domain-lacking Akts, or other closely related AGC family kinases, PKA, PKC, and SGK, even at concentrations as high as 50uM. Overcomes Akt1/Akt2-mediated resistance to chemotherapeutics in tumor cells and is shown to block basal and stimulated phosphorylation/activation of Akt1/Akt2 both in cultured cells in vitro and in mice in vivo.