title: Autophagy and ER stress play an essential role in the mechanism of action and drug resistance of the cyclin-dependent kinase inhibitor flavopiridol.
abstract: Chronic lymphocytic leukemia (CLL) is a mature B cell malignancy and is the most prevalent type of leukemia in adults. There is no curative therapy for this disease; however, several new agents have shown very promising results. Autophagy has not been studied in CLL and in this study we first sought to determine if autophagy was functional in CLL with classic inducers, and if this contributes to direct cytotoxicity or protection from cell death. While autophagy is activated with all classic stimuli of this process, only unfolded protein endoplasmic reticulum (ER) stress-mediated autophagy protects from cell death. Interestingly, select therapeutic agents (fludarabine, GS-1101, flavopiridol), which are active in CLL, also induce autophagy. Of interest, only the broad cyclin-dependent kinase inhibitor flavopiridol has improved efficacy when autophagy is antagonized biochemically (chloroquine) or by siRNA. This promoted an investigation which demonstrated unexpectedly that flavopiridol mediates ER stress and downstream activation of MAP3K5/ASK1, which ultimately is responsible for cell death. Similarly, autophagy activated in part via ER stress and also CDK5 inhibition is protective against cell death induced by this process. Collectively, our studies demonstrate that in CLL, autophagy is induced by multiple stimuli but only acts as a mechanism of resistance against ER stress-mediating agents. Similarly, flavopiridol mediates ER stress as a primary mechanism of action in CLL, and autophagy serves as a mechanism of resistance to this agent.
authors: Division of Hematology, Department of Internal Medicine, Ohio State University, Columbus, OH, USA.
authors: Emilia
authors: E
authors: Mahoney
authors: John C
authors: JC
authors: Byrd
authors: Amy J
authors: AJ
authors: Johnson
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001343:Autophagy; D053471:Caspases, Initiator / Q000378:metabolism; D045744:Cell Line, Tumor; D002738:Chloroquine / Q000494:pharmacology; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004351:Drug Resistance; D059865:Endoplasmic Reticulum Stress; D005419:Flavonoids / Q000494:pharmacology*; D015973:Gene Expression Regulation, Leukemic; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy*; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism; D010880:Piperidines / Q000494:pharmacology*; D017510:Protein Folding; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D005419:Flavonoids; D010880:Piperidines; D034741:RNA, Small Interfering; C077990:alvocidib; D002738:Chloroquine; D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; D018844:Cyclin-Dependent Kinases; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human; C093516:CASP4 protein, human; D053471:Caspases, Initiator
keywords: ER stress; autophagy; chloroquine; chronic lymphocytic leukemia; cyclin-dependent kinase inhibitors; drug resistance; flavopiridol