title: Mechanisms of action of a dual Cdc7/Cdk9 kinase inhibitor against quiescent and proliferating CLL cells.
abstract: In chronic lymphocytic leukemia (CLL) the proliferation rate and resistance to drug-induced apoptosis are recognized as important factors in the outcome of treatment. In this study, we assess the activity and the mechanism of action of the prototype cell division cycle kinase 7 (Cdc7) inhibitor, PHA-767491, which inhibits the initiation of DNA replication but also has cyclin-dependent kinase 9 (Cdk9) inhibitory activity. We have studied the effects of this dual Cdc7/Cdk9 inhibitor in both quiescent CLL cells and CLL cells that have been induced to proliferate using a cellular coculture system that mimics the lymph node microenvironment. We find that this compound, originally developed as a DNA replication inhibitor, is particularly active in promoting mitochondrial dependent apoptosis in quiescent CLL cells purified from peripheral blood of patients regardless of recognized risk factors. In this setting, apoptosis is preceded by a decrease in the levels of Mcl-1 protein and transcript possibly due to inhibition of Cdk9. Following stimulation by CD154 and interleukin-4, CLL cells become highly chemoresistant, reenter into the cell cycle, reexpress Cdc7 kinase, a key molecular switch for the initiation of DNA replication, replicate their DNA, and undergo cell division. In this context, treatment with PHA-767491 abolished DNA synthesis by inhibiting Cdc7 but is less effective in triggering cell death, although Mcl-1 protein is no longer detectable. Thus, dual Cdc7/Cdk9 inhibition has the potential to target both the quiescent and actively proliferating CLL populations through two distinct mechanisms and may be a new therapeutic strategy in CLL.
authors.affiliation: National Centre of Biomedical Engineering and Science and Centre for Chromosome Biology, National University of Ireland Galway, University Road, Galway, Ireland.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Natoni
authors.forename: Laura S
authors.initials: LS
authors.lastname: Murillo
authors.forename: Anna E
authors.initials: AE
authors.lastname: Kliszczak
authors.forename: Mark A
authors.initials: MA
authors.lastname: Catherwood
authors.forename: Alessia
authors.initials: A
authors.lastname: Montagnoli
authors.forename: Afshin
authors.initials: A
authors.lastname: Samali
authors.forename: Michael
authors.initials: M
authors.lastname: O'Dwyer
authors.forename: Corrado
authors.initials: C
authors.lastname: Santocanale
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D023201:CD40 Ligand / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002478:Cells, Cultured; D042863:Cyclin-Dependent Kinase 9 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D041681:NIH 3T3 Cells; D010766:Phosphorylation / Q000187:drug effects; D010881:Piperidones / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology; D012319:RNA Polymerase II / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C531237:PHA 767491; D010881:Piperidones; D047428:Protein Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011758:Pyrroles; D023201:CD40 Ligand; D015847:Interleukin-4; C068619:CDC7 protein, human; D017346:Protein Serine-Threonine Kinases; D042863:Cyclin-Dependent Kinase 9; D012319:RNA Polymerase II; D020169:Caspases