Zoledronic acid in combination with serine/threonine phosphatase inhibitors induces enhanced cytotoxicity and apoptosis in hormone-refractory prostate cancer cell lines by decreasing the activities of PP1 and PP2A
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2012
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Abstract
OBJECTIVES • To investigate if the cytotoxic and apoptotic effect of zoledronic acid (ZA) can be enhanced by the addition of the serine/threonine protein phosphatase inhibitors calyculin A (CA) and okadaic acid (OA) in hormone and drug refractory prostate cancer cells, PC-3 and DU-145. • To discover the effect of these combination treatments on phosphatase 1 (PP1) and PP2A protein expression levels in prostate cancer cells. MATERIALS AND METHODS • An XTT cell viability assay was used to determine cytotoxicity. • Apoptosis was evaluated by enzymelinked immunosorbent assay (ELISA) using a Cell Death Detection ELISA Plus Kit and verifi ed by measuring caspase 3/7 enzyme activity. • The PP1 and PP2A enzyme activities were evaluated by serine/threonine phosphatase ELISA and expression levels of PP1 and PP2A proteins were then re-assessed by Western blot RESULTS • Combination of ZA with either CA or OA showed synergistic cytotoxicity and apoptosis compared with any agent alone in both PC-3 and DU-145 prostate cancer cells. • The combination of ZA with phosphatase inhibitors resulted in enhanced suppression of both PP1 and PP2A enzyme activity andprotein levels, which was more overt with the ZA/CA combination. CONCLUSION • Results from our study increase the translational potential of our in vitro fi ndings and offer the basic rationale for the design of new combinatory strategies with ZA and phosphatase inhibitors for the treatment of prostate cancer, which may become resistant to conventional therapy. © 2012 B J U I N T E R N A T I O N A L.
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Apoptosis , Blotting, Western , Bone Density Conservation Agents , Cell Line, Tumor , Cell Proliferation , Diphosphonates , Enzyme-Linked Immunosorbent Assay , Humans , Imidazoles , Male , Phosphoprotein Phosphatases , Prostatic Neoplasms , Protein Phosphatase 1 , Protein Phosphatase 2 , calyculin A , caspase 3 , caspase 7 , okadaic acid , phosphoprotein phosphatase 1 , phosphoprotein phosphatase 2A , zoledronic acid , bisphosphonic acid derivative , bone density conservation agent , imidazole derivative , phosphoprotein phosphatase , phosphoprotein phosphatase 1 , phosphoprotein phosphatase 2 , zoledronic acid , MLCS , MLOWN , antineoplastic activity , apoptosis , article , cancer cell culture , cancer combination chemotherapy , cell viability , concentration response , controlled study , drug cytotoxicity , drug potentiation , enzyme activity , enzyme inhibition , enzyme linked immunosorbent assay , human , human cell , IC 50 , in vitro study , male , monotherapy , priority journal , protein expression , Western blotting , apoptosis , biosynthesis , cell proliferation , comparative study , drug antagonism , drug effect , metabolism , pathology , prostate tumor , tumor cell line