title: Inhibition of MCL-1 in breast cancer cells promotes cell death in vitro and in vivo.
abstract: The present studies have examined approaches to suppress MCL-1 function in breast cancer cells, as a means to promote tumor cell death. Treatment of breast cancer cells with CDK inhibitors (flavopiridol; roscovitine) enhanced the lethality of the ERBB1 inhibitor lapatinib in a synergistic fashion. CDK inhibitors interacted with lapatinib to reduce MCL-1 expression and over-expression of MCL-1 or knock down of BAX and BAK suppressed drug combination lethality. Lapatinib-mediated inhibition of ERK1/2 and to a lesser extent AKT facilitated CDK inhibitor -induced suppression of MCL-1 levels. Treatment of cells with the BH3 domain / MCL-1 inhibitor obatoclax enhanced the lethality of lapatinib in a synergistic fashion. Knock out of MCL-1 and BCL-XL enhanced lapatinib toxicity to a similar extent as obatoclax and suppressed the ability of obatoclax to promote lapatinib lethality. Pre-treatment of cells with lapatinib or with obatoclax enhanced basal levels of BAX and BAK activity and further enhanced drug combination toxicity. In vivo tumor growth data in xenograft and syngeneic model systems confirmed our in vitro findings. Treatment of cells with CDK inhibitors enhanced the lethality of obatoclax in a synergistic fashion. Over-expression of MCL-1 or knock down of BAX and BAK suppressed the toxic interaction between CDK inhibitors and obatoclax. Obatoclax and lapatinib treatment or obatoclax and CDK inhibitor treatment or lapatinib and CDK inhibitor treatment radiosensitized breast cancer cells. Lapatinib and obatoclax interacted to suppress mammary tumor growth in vivo. Collectively our data demonstrate that manipulation of MCL-1 protein expression by CDK inhibition or inhibition of sequestering function MCL-1 by Obatoclax renders breast cancer cells more susceptible to BAX/BAK-dependent mitochondrial dysfunction and tumor cell death.
authors.affiliation: Department of Neurosurgery, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Clint
authors.initials: C
authors.lastname: Mitchell
authors.forename: Adly
authors.initials: A
authors.lastname: Yacoub
authors.forename: Hamed
authors.initials: H
authors.lastname: Hossein
authors.forename: Aditi Pandya
authors.initials: AP
authors.lastname: Martin
authors.forename: M Danielle
authors.initials: MD
authors.lastname: Bareford
authors.forename: Patrick
authors.initials: P
authors.lastname: Eulitt
authors.forename: Chen
authors.initials: C
authors.lastname: Yang
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Nephew
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D016923:Cell Death; D045744:Cell Line, Tumor; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D004357:Drug Synergism; D004591:Electrophoresis, Polyacrylamide Gel; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D055786:Gene Knockout Techniques; D006801:Humans; D007211:Indoles; D000077341:Lapatinib; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors; D058990:Molecular Targeted Therapy; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010880:Piperidines / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology; D000077546:Roscovitine; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; C494772:BAK1 protein, human; C494826:BAX protein, human; D005419:Flavonoids; D007211:Indoles; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010880:Piperidines; D019253:Proto-Oncogene Proteins c-bcl-2; D011687:Purines; D011758:Pyrroles; D011799:Quinazolines; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D000077546:Roscovitine; D000077341:Lapatinib; C077990:alvocidib; D066246:ErbB Receptors; D018844:Cyclin-Dependent Kinases; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C520962:obatoclax