title: Enhanced sensitization to taxol-induced apoptosis by herceptin pretreatment in ErbB2-overexpressing breast cancer cells.
abstract: The recombinant humanized anti-ErbB2/HER2 monoclonal antibody Herceptin (Trastuzumab) has been shown to significantly enhance the tumoricidaleffects of antitumor drugs such as paclitaxel (Taxol) in patients with ErbB2-overexpressing breast cancers. Here, we investigated the molecular mechanisms by which Herceptin enhances the antitumor effects of Taxol. Because activation of p34(Cdc2) is required for Taxol-induced apoptosis and because overexpression of ErbB2 blocks Taxol-induced apoptosis by inhibiting p34(Cdc2) activation, we studied the effect of Herceptin treatment on p34(Cdc2) kinase activation and apoptosis in Taxol-treated human breast carcinoma cell lines MDA-MB-435, SKBr3, MDA-MB-453, and 435.eB, which is an ErbB2 transfectant of MDA-MB-435. Herceptin treatment down-regulated ErbB2, reduced the inhibitory phosphorylation of Cdc2 on Tyr-15, and down-regulated the expression of p21(Cip1), a Cdc2 inhibitor. Herceptin plus Taxol treatment led to higher levels of p34(Cdc2) kinase activity and apoptosis in ErbB2-overexpressing breast cancer cells, which is likely attributable to inhibition of Cdc2-Tyr-15 phosphorylation and p21(Cip1) expression. Because significant dephosphorylation of Cdc2-Tyr-15 and down-regulation of p21(Cip1) occur at least 24 h after Herceptin treatment, we investigated whether 24 h Herceptin pretreatment will render ErbB2-overexpressing breast cancer cells more sensitive to Taxol-induced apoptosis compared with the simultaneous treatment of Herceptin plus Taxol. Indeed, Herceptin pretreatment increased Taxol-induced apoptosis and cytotoxicity in vitro and more effectively inhibited the growth of tumor xenografts with enhanced in vivo apoptosis. Thus, Herceptin treatment of ErbB2-overexpressing cells can inhibit ErbB2-mediated Cdc2-Tyr-15 phosphorylation and p21(Cip1) up-regulation, which allows effective p34(Cdc2) activation and induction of apoptosis upon Taxol treatment. Herceptin pretreatment renders ErbB2-overexpressing breast cancers more susceptible to Taxol-induced cell death, which may have important clinical therapeutic implications.
authors.affiliation: Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: Sangkyou
authors.initials: S
authors.lastname: Lee
authors.forename: Wentao
authors.initials: W
authors.lastname: Yang
authors.forename: Keng-Hsueh
authors.initials: KH
authors.lastname: Lan
authors.forename: Shankar
authors.initials: S
authors.lastname: Sellappan
authors.forename: Kristine
authors.initials: K
authors.lastname: Klos
authors.forename: Gabriel
authors.initials: G
authors.lastname: Hortobagyi
authors.forename: Mien-Chie
authors.initials: MC
authors.lastname: Hung
authors.forename: Dihua
authors.initials: D
authors.lastname: Yu
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D061067:Antibodies, Monoclonal, Humanized; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006801:Humans; D051379:Mice; D008813:Mice, Inbred ICR; D016513:Mice, SCID; D017239:Paclitaxel / Q000008:administration & dosage; D010766:Phosphorylation; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis*; D000068878:Trastuzumab; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D016203:CDC2 Protein Kinase; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D017239:Paclitaxel; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse