title: Mechanisms of drug sensitization to TRA-8, an agonistic death receptor 5 antibody, involve modulation of the intrinsic apoptotic pathway in human breast cancer cells.
abstract: TRA-8, a monoclonal antibody to death receptor 5 induces apoptosis in various cancer cells; however, the degree of sensitivity varies from highly sensitive to resistant. We have previously shown that resistance to TRA-8 can be reversed by using chemotherapeutic agents, but the mechanism underlying this sensitization was not fully understood. Here, we examined the combination of TRA-8 with doxorubicin or bortezomib in breast cancer cells. In TRA-8-resistant BT-474 and T47D cells, both chemotherapy agents synergistically sensitized cells to TRA-8 cytotoxicity with enhanced activation of apoptosis shown by cleavage of caspases and PARP, reduced Bid, increased proapoptotic Bcl-2 proteins, and increased mitochondrial membrane depolarization. Doxorubicin or bortezomib combined with TRA-8 also reduced Bcl-XL and X-linked inhibitors of apoptosis (XIAP) in treated cells. Furthermore, targeting these proteins with pharmacologic modulators, AT-101, BH3I-2' and AT-406, produced sensitization to TRA-8. TRA-8 combined with AT-101 or BH3I-2', inhibitors of antiapoptotic Bcl-2 proteins, produced synergistic cytotoxicity against ZR-75-1, BT-474, and T47D cells. The IAP-targeting compound, AT-406, was synergistic with TRA-8 in BT-474 cells, and to a lesser extent T47D cells. Activation of the intrinsic apoptotic pathway was a common mechanism associated with sensitization of TRA-8-resistant breast cancer cell lines. Collectively, these studies show that the Bcl-2 and IAP families of proteins are involved in TRA-8 and chemotherapy resistance via their modulation of the intrinsic apoptotic pathway. Targeting these proteins with novel agents sensitized TRA-8-resistant breast cancer cells, suggesting this approach may represent a potent therapeutic strategy in the treatment of breast cancer.
authors.affiliation: Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, Alabama 35294-2182, USA.
authors.forename: Hope M
authors.initials: HM
authors.lastname: Amm
authors.forename: Tong
authors.initials: T
authors.lastname: Zhou
authors.forename: Adam D
authors.initials: AD
authors.lastname: Steg
authors.forename: Huichien
authors.initials: H
authors.lastname: Kuo
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Li
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Buchsbaum
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols; D017209:Apoptosis / Q000235:genetics; D001392:Azocines / Q000008:administration & dosage; D001559:Benzhydryl Compounds / Q000008:administration & dosage; D001897:Boronic Acids / Q000008:administration & dosage*; D000069286:Bortezomib; D001943:Breast Neoplasms / Q000188:drug therapy*; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000008:administration & dosage*; D019008:Drug Resistance, Neoplasm; D005260:Female; D019254:Genes, bcl-2; D006072:Gossypol / Q000008:administration & dosage / Q000031:analogs & derivatives; D006801:Humans; D051379:Mice; D011719:Pyrazines / Q000008:administration & dosage*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000819:agonists*; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D001392:Azocines; D001559:Benzhydryl Compounds; D001897:Boronic Acids; C559144:N-benzhydryl-5-(2-(methylamino)propanamido)-3-(3-methylbutanoyl)-6-oxodecahydropyrrolo(1,2-a)(1,5)diazocine-8-carboxamide; D011719:Pyrazines; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D000069286:Bortezomib; D004317:Doxorubicin; D020169:Caspases; D006072:Gossypol; C028178:gossypol acetic acid