title: Lapatinib and obatoclax kill breast cancer cells through reactive oxygen species-dependent endoplasmic reticulum stress.
abstract: Previous studies showed that lapatinib and obatoclax interact in a greater-than-additive fashion to cause cell death and do so through a toxic form of autophagy. The present studies sought to extend our analyses. Lapatinib and obatoclax killed multiple tumor cell types, and cells lacking phosphatase and tensin homolog (PTEN) function were relatively resistant to drug combination lethality; expression of PTEN in PTEN-null breast cancer cells restored drug sensitivity. Coadministration of lapatinib with obatoclax elicited autophagic cell death that was attributable to the actions of mitochondrial reactive oxygen species. Wild-type cells but not mitochondria-deficient rho-zero cells were radiosensitized by lapatinib and obatoclax treatment. Activation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH(2)-terminal kinase 1/2 (JNK1/2) by the drug combination was enhanced by radiation, and signaling by p38 MAPK and JNK1/2 promoted cell killing. In immunohistochemical analyses, the autophagosome protein p62 was determined to be associated with protein kinase-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme 1, as well as with binding immunoglobulin protein/78-kDa glucose-regulated protein, in drug combination-treated cells. Knockdown of PERK suppressed drug-induced autophagy and protected tumor cells from the drug combination. Knockdown of PERK suppressed the reduction in Mcl-1 expression after drug combination exposure, and overexpression of Mcl-1 protected cells. Our data indicate that mitochondrial function plays an essential role in cell killing by lapatinib and obatoclax, as well as radiosensitization by this drug combination.
authors.affiliation: Department of Neurosurgery, School of Medicne, Virginia Commonwealth University, Richmond, VA 23298-0035, USA.
authors.forename: Nichola
authors.initials: N
authors.lastname: Cruickshanks
authors.forename: Yong
authors.initials: Y
authors.lastname: Tang
authors.forename: Laurence
authors.initials: L
authors.lastname: Booth
authors.forename: Hossein
authors.initials: H
authors.lastname: Hamed
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects / Q000235:genetics; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects* / Q000235:genetics; D005260:Female; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007211:Indoles; D000077341:Lapatinib; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000378:metabolism; D048056:Mitogen-Activated Protein Kinase 9 / Q000235:genetics / Q000378:metabolism; D011758:Pyrroles / Q000008:administration & dosage; D011799:Quinazolines / Q000008:administration & dosage; D017382:Reactive Oxygen Species / Q000378:metabolism*; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins; D007211:Indoles; D000077341:Lapatinib; D008565:Membrane Proteins; D048055:Mitogen-Activated Protein Kinase 8; D048056:Mitogen-Activated Protein Kinase 9; D011758:Pyrroles; D011799:Quinazolines; D017382:Reactive Oxygen Species; D019892:eIF-2 Kinase; D048051:p38 Mitogen-Activated Protein Kinases; C018551:glucose-regulated proteins; C520962:obatoclax