title: Carfilzomib Triggers Cell Death in Chronic Lymphocytic Leukemia by Inducing Proapoptotic and Endoplasmic Reticulum Stress Responses.
abstract: OBJECTIVE
  Carfilzomib, while active in B-cell neoplasms, displayed heterogeneous response in chronic lymphocytic leukemia (CLL) samples from patients and showed interpatient variability to carfilzomib-induced cell death. To understand this variability and predict patients who would respond to carfilzomib, we investigated the mechanism by which carfilzomib induces CLL cell death.
  
  
  METHODS
  Using CLL patient samples and cell lines, complementary knockdown and knockout cells, and carfilzomib-resistant cell lines, we evaluated changes in intracellular networks to identify molecules responsible for carfilzomib's cytotoxic activity. Lysates from carfilzomib-treated cells were immunoblotted for molecules involved in ubiquitin, apoptotic, and endoplasmic reticulum (ER) stress response pathways and results correlated with carfilzomib cytotoxic activity. Coimmunoprecipitation and pull-down assays were performed to identify complex interactions among MCL-1, Noxa, and Bak.
  
  
  RESULTS
  Carfilzomib triggered ER stress and activation of both the intrinsic and extrinsic apoptotic pathways through alteration of the ubiquitin proteasome pathway. Consequently, the transcription factor CCAAT/enhancer-binding protein homology protein (CHOP) accumulated in response to carfilzomib, and CHOP depletion conferred protection against cytotoxicity. Carfilzomib also induced accumulation of MCL-1 and Noxa, whereby MCL-1 preferentially formed a complex with Noxa and consequently relieved MCL-1's protective effect on sequestering Bak. Accordingly, depletion of Noxa or both Bak and Bax conferred protection against carfilzomib-induced cell death.
  
  
  CONCLUSIONS
  Collectively, carfilzomib induced ER stress culminating in activation of intrinsic and extrinsic caspase pathways, and we identified the CHOP protein level as a biomarker that could predict sensitivity to carfilzomib in CLL. Clin Cancer Res; 22(18); 4712-26. ©2016 AACR.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Betty
authors.initials: B
authors.lastname: Lamothe
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: William G
authors.initials: WG
authors.lastname: Wierda
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Keating
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas. Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas. vgandhi@mdanderson.org.
authors.forename: Varsha
authors.initials: V
authors.lastname: Gandhi
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D015415:Biomarkers; D045744:Cell Line, Tumor; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000175:diagnosis / Q000378:metabolism* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009842:Oligopeptides / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D051742:Transcription Factor CHOP / Q000378:metabolism; D057149:Ubiquitinated Proteins / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D015415:Biomarkers; C497249:DDIT3 protein, human; D009842:Oligopeptides; D057149:Ubiquitinated Proteins; D051742:Transcription Factor CHOP; C524865:carfilzomib; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D046988:Proteasome Endopeptidase Complex