title: Enzastaurin, a protein kinase C beta inhibitor, suppresses signaling through the ribosomal S6 kinase and bad pathways and induces apoptosis in human gastric cancer cells.
abstract: Activation of protein kinase C (PKC) has been implicated in gastric carcinogenesis. Enzastaurin is an oral ATP-competitive inhibitor of the PKC beta isozyme. Although enzastaurin was initially advanced to the clinic based on its antiangiogenic activity, it is also known to have a direct effect on a variety of human cancer cells, inducing apoptosis by inhibiting the Akt signal pathway. However, data on enzastaurin for gastric cancer are limited. Therefore, this study was performed to assess the antitumor activity of enzastaurin on gastric cancer cells and to investigate the underlying antitumor mechanisms. Enzastaurin suppressed the proliferation of cultured gastric cancer cells and the growth of gastric carcinoma xenografts. Enzastaurin did not have an effect on gastric cancer cell cycle progression; however, it had a direct apoptosis-inducing effect through the caspase-mediated mitochondrial pathway. Glycogen synthase kinase 3beta phosphorylation, a reliable pharmacodynamic marker of enzastaurin activity, and Akt phosphorylation were both decreased after treatment with enzastaurin. Although the p90 ribosomal S6 kinase (Rsk) was also dephosphorylated, Erk phosphorylation was not affected in the enzastaurin-treated gastric cancer cells. Enzastaurin activated Bad, one of the Bcl-2 proapoptotic proteins, through dephosphorylation at Ser(112), and depletion of Bad activity resulted in resistance to enzastaurin-induced apoptosis and cytotoxicity in gastric cancer cells. These data suggest that enzastaurin induces apoptosis through Rsk-mediated and Bad-mediated pathways, besides inhibiting the Akt signal cascade. Furthermore, enzastaurin had synergistic or additive effects when combined with 5-fluorouracil, cisplatin, paclitaxel, or irinotecan. These results warrant further clinical investigation of enzastaurin for gastric cancer treatment.
authors.affiliation: Department of Internal Medicine, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Keun-Wook
authors.initials: KW
authors.lastname: Lee
authors.forename: Sang Gyun
authors.initials: SG
authors.lastname: Kim
authors.forename: Hwang-Phill
authors.initials: HP
authors.lastname: Kim
authors.forename: Euna
authors.initials: E
authors.lastname: Kwon
authors.forename: Jiran
authors.initials: J
authors.lastname: You
authors.forename: Hyung-Jun
authors.initials: HJ
authors.lastname: Choi
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Park
authors.forename: Byeong-Cheol
authors.initials: BC
authors.lastname: Kang
authors.forename: Seock-Ah
authors.initials: SA
authors.lastname: Im
authors.forename: Tae-You
authors.initials: TY
authors.lastname: Kim
authors.forename: Woo Ho
authors.initials: WH
authors.lastname: Kim
authors.forename: Yung-Jue
authors.initials: YJ
authors.lastname: Bang
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007211:Indoles / Q000008:administration & dosage / Q000494:pharmacology*; D051379:Mice; D008819:Mice, Nude; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D064546:Protein Kinase C beta; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013274:Stomach Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D023041:Xenograft Model Antitumor Assays; D051025:bcl-Associated Death Protein / Q000378:metabolism*
chemical_list: C494819:BAD protein, human; D007211:Indoles; D047428:Protein Kinase Inhibitors; D051025:bcl-Associated Death Protein; D051057:Proto-Oncogene Proteins c-akt; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D011493:Protein Kinase C; D064546:Protein Kinase C beta; C504878:enzastaurin