title: AZ703, an imidazo[1,2-a]pyridine inhibitor of cyclin-dependent kinases 1 and 2, induces E2F-1-dependent apoptosis enhanced by depletion of cyclin-dependent kinase 9.
abstract: Preclinical studies were performed of a novel selective imidazopyridine cyclin-dependent kinase (cdk) inhibitor, AZ703. In vitro kinase assays showed that IC50 values for AZ703 against purified cyclin E/cdk2 and cyclin B/cdk1 were 34 and 29 nmol/L, respectively. In contrast, the IC50 against cdk4 was 10 micromol/L. AZ703 also inhibited cdk7 and cdk9 with IC50 values of 2.1 micromol/L and 521 nmol/L, respectively. Treatment of U2OS, NCI-H1299, and A549 cells for 24 hours resulted in growth arrest involving multiple cell cycle phases. At low drug concentrations (< 2 micromol/L), G2 arrest predominated, whereas at higher concentrations (> or = 2 micromol/L), S-G2 arrest was observed. When cells were synchronized in G1 by starvation and released into AZ703, a block in G1 occurred that was not evident in exponentially growing cells. Cell cycle arrest was associated with reduced phosphorylation of the retinoblastoma protein and p27(Kip1) at cdk2 phospho-sites. Following longer exposures, apoptosis was evident. Cells were further sensitized to AZ703 following recruitment to S phase by synchronization. Consistent with the inhibition of cdks during S and G2 that modulate the activity and stability of E2F-1, AZ703 treatment induced E2F-1 expression. In U2OS and NCI-H1299 cells engineered to inducibly express the dominant-negative mutant E2F-1 (1-374), expression of the mutant decreased AZ703-mediated apoptosis, indicating dependence on E2F-1 transcriptional targets. AZ703-induced apoptosis in NCI-H1299 cells was enhanced by small interfering RNA-mediated depletion of cdk9, which caused reduced levels of Mcl-1 and XIAP, suggesting that cdk2, cdk1, and cdk9 represent a rational subset of family members for drug targeting.
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.
authors.forename: Dongpo
authors.initials: D
authors.lastname: Cai
authors.forename: Kate F
authors.initials: KF
authors.lastname: Byth
authors.forename: Geoffrey I
authors.initials: GI
authors.lastname: Shapiro
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001859:Bone Neoplasms / Q000188:drug therapy / Q000201:enzymology; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2 / Q000037:antagonists & inhibitors*; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors; D042863:Cyclin-Dependent Kinase 9 / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000235:genetics; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000096:biosynthesis / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology; D012516:Osteosarcoma / Q000188:drug therapy / Q000201:enzymology; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics; D016160:Retinoblastoma Protein / Q000378:metabolism
chemical_list: C507945:AZ703 compound; C436291:CDKN1B protein, human; D050687:E2F1 Transcription Factor; D004791:Enzyme Inhibitors; D007093:Imidazoles; D047908:Intracellular Signaling Peptides and Proteins; D011725:Pyridines; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016203:CDC2 Protein Kinase; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D042863:Cyclin-Dependent Kinase 9