Patients with androgen withdrawal therapy develop androgen-independent prostate cancer associated with Bcl-2 up-regulation and resulting in disease progression and death.With the discovery of promising therapeutic agents,like BH3-only mimetic ABT-263 and proteasome inhibitor,alone or in combination with other chemotherapeutic agents have been developed and widely evaluated to against a broad spectrum cancer types including prostate cancer.Antitumor efficacy of ABT-263 and MLN2238 were evaluated as single agents or in combination in androgen-independent prostate cancer PC3 cells.Cell viability and hall marker of apoptosis were determined.Lentivirus-mediated short hairpin RNA was used to knockdown Bax and NOXA expression.Protein interactions were analyzed by co-immunoprecipitation in drug-treated cells.ABT-263 and MLN2238 alone exhibited little cytotoxicity,yet combination treatment displayed synergistic cytotoxic effect in PC3 cells in a time-and dose-dependent manner.Apoptotic cell death induction by drug co-treatment was shown as enhanced caspase 3 and PARP cleavage and annexin V positive staining.Bax downregulation by short hairpin RNA markedly protected cells from combination-triggered apoptosis,indicating the combination treatment induced mitochondrial-dependent pathway.MLN2238 treatment up-regulated NOXA expression and knockdown of NOXA using shRNA significantly attenuated cytotoxicity of co-administration of ABT-263 and MLN2238.ABT-263 induced the interaction of Bim with Mcl-1,while MLN2238 enhanced NOXA/Mcl-1 complexes and disassociated Bim from its complexes with Mcl-1 to trigger Bax activation.MLN2238 and ABT-263 synergistically triggered apoptosis in PC3 cells via up-regulation of NOXA,indicating a promising therapeutic strategy for treatment of androgen-independent prostate cancer.