title: Flavopiridol targets c-KIT transcription and induces apoptosis in gastrointestinal stromal tumor cells.
abstract: Gastrointestinal stromal tumors (GIST) are characterized by activating mutations in the c-KIT gene which confers ligand-independent activation of the KIT receptor. Imatinib mesylate has been shown to effectively block constitutively active KIT and delay tumor growth. However, resistance to imatinib mesylate is emerging as a major clinical problem and novel therapies are needed. We report that treatment of GIST cells with the transcriptional inhibitor flavopiridol, initially down-regulates the antiapoptotic proteins bcl-2, mcl-1, and X-linked inhibitor of apoptosis protein which occurs as early as 4 hours after exposure. This is followed at 24 hours by the transcriptional suppression of KIT resulting in poly(ADP-ribose) polymerase cleavage and apoptosis. To separate the apoptotic effect of KIT suppression relative to the down-regulation of antiapoptotic proteins, we used small interfering RNA-directed knockdown of KIT. Results show that focused suppression of KIT alone is sufficient to induce apoptosis in GIST cells, but not to the same extent as flavopiridol. In contrast, imatinib mesylate, which inhibits KIT kinase activity but does not suppress total KIT expression, fails to cause apoptosis. We also show that flavopiridol suppresses KIT mRNA expression through positive transcriptional elongation factor inhibition and decreases KIT promoter activity. This causes a global decrease in the level of functionally mature KIT at the cell surface, resulting in a decrease in autophosphorylation at tyrosine residues 703 and 721, which characterizes activated KIT. Our results indicate that targeting KIT expression and these antiapoptotic proteins with flavopiridol represents a novel means to disrupt GIST cell dependence on KIT signaling and collectively renders these cells sensitive to apoptosis.
authors.affiliation: Sarcoma Biology Laboratory, Sarcoma Disease Management Program, Department of Surgery and Laboratory of New Drug Development, Department Memorial Sloan-Kettering Cancer Center, New York, New York, USA.
authors.forename: Elliot B
authors.initials: EB
authors.lastname: Sambol
authors.forename: Grazia
authors.initials: G
authors.lastname: Ambrosini
authors.forename: Rula C
authors.initials: RC
authors.lastname: Geha
authors.forename: Peter T
authors.initials: PT
authors.lastname: Kennealey
authors.forename: Penelope
authors.initials: P
authors.lastname: Decarolis
authors.forename: Rachael
authors.initials: R
authors.lastname: O'connor
authors.forename: Yuhsin V
authors.initials: YV
authors.lastname: Wu
authors.forename: Monica
authors.initials: M
authors.lastname: Motwani
authors.forename: Jin-Hong
authors.initials: JH
authors.lastname: Chen
authors.forename: Gary K
authors.initials: GK
authors.lastname: Schwartz
authors.forename: Samuel
authors.initials: S
authors.lastname: Singer
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology*; D046152:Gastrointestinal Stromal Tumors / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D000068877:Imatinib Mesylate; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D005419:Flavonoids; D010879:Piperazines; D010880:Piperidines; D011743:Pyrimidines; C077990:alvocidib; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D012319:RNA Polymerase II