ABSTRACT
Introduction of a 1-benzyl-1H-pyrazol-4-yl moiety at C7 of the imidazo[4,5-b]pyridine scaffold provided 7a which inhibited a range of kinases including Aurora-A. Modification of the benzyl group in 7a, and subsequent co-crystallisation of the resulting analogues with Aurora-A indicated distinct differences in binding mode dependent upon the pyrazole N-substituent. Compounds 7a and 14d interact with the P-loop whereas 14a and 14b engage with Thr217 in the post-hinge region. These crystallographic insights provide options for the design of compounds interacting with the DFG motif or with Thr217.
Subject(s)
Aurora Kinases/antagonists & inhibitors , Aurora Kinases/chemistry , Imidazoles/chemical synthesis , Imidazoles/pharmacology , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/pharmacology , Pyrazoles/chemical synthesis , Pyrazoles/pharmacology , Pyridines/chemical synthesis , Pyridines/pharmacology , Animals , Cell Line, Tumor , Cell Proliferation/drug effects , Crystallization , Dose-Response Relationship, Drug , Humans , Imidazoles/chemistry , Mice , Microsomes, Liver/chemistry , Microsomes, Liver/metabolism , Models, Molecular , Molecular Structure , Pyrazoles/chemistry , Pyridines/chemistry , Structure-Activity RelationshipABSTRACT
Aurora-A differs from Aurora-B/C at three positions in the ATP-binding pocket (L215, T217, and R220). Exploiting these differences, crystal structures of ligand-Aurora protein interactions formed the basis of a design principle for imidazo[4,5-b]pyridine-derived Aurora-A-selective inhibitors. Guided by a computational modeling approach, appropriate C7-imidazo[4,5-b]pyridine derivatization led to the discovery of highly selective inhibitors, such as compound 28c, of Aurora-A over Aurora-B. In HCT116 human colon carcinoma cells, 28c and 40f inhibited the Aurora-A L215R and R220K mutants with IC50 values similar to those seen for the Aurora-A wild type. However, the Aurora-A T217E mutant was significantly less sensitive to inhibition by 28c and 40f compared to the Aurora-A wild type, suggesting that the T217 residue plays a critical role in governing the observed isoform selectivity for Aurora-A inhibition. These compounds are useful small-molecule chemical tools to further explore the function of Aurora-A in cells.
Subject(s)
Aurora Kinase A/antagonists & inhibitors , Aurora Kinase B/antagonists & inhibitors , Drug Design , Imidazoles/chemistry , Imidazoles/pharmacology , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/pharmacology , Animals , Aurora Kinase A/chemistry , Aurora Kinase A/metabolism , Aurora Kinase B/chemistry , Aurora Kinase B/metabolism , Catalytic Domain , Drug Stability , HCT116 Cells , Humans , Imidazoles/metabolism , Indoles/chemistry , Indoles/metabolism , Indoles/pharmacology , Isoenzymes/antagonists & inhibitors , Isoenzymes/chemistry , Isoenzymes/metabolism , Male , Mice , Molecular Docking Simulation , Protein Kinase Inhibitors/metabolism , Substrate SpecificityABSTRACT
Optimization of the imidazo[4,5-b]pyridine-based series of Aurora kinase inhibitors led to the identification of 6-chloro-7-(4-(4-chlorobenzyl)piperazin-1-yl)-2-(1,3-dimethyl-1H-pyrazol-4-yl)-3H-imidazo[4,5-b]pyridine (27e), a potent inhibitor of Aurora kinases (Aurora-A K(d) = 7.5 nM, Aurora-B K(d) = 48 nM), FLT3 kinase (K(d) = 6.2 nM), and FLT3 mutants including FLT3-ITD (K(d) = 38 nM) and FLT3(D835Y) (K(d) = 14 nM). FLT3-ITD causes constitutive FLT3 kinase activation and is detected in 20-35% of adults and 15% of children with acute myeloid leukemia (AML), conferring a poor prognosis in both age groups. In an in vivo setting, 27e strongly inhibited the growth of a FLT3-ITD-positive AML human tumor xenograft (MV4-11) following oral administration, with in vivo biomarker modulation and plasma free drug exposures consistent with dual FLT3 and Aurora kinase inhibition. Compound 27e, an orally bioavailable dual FLT3 and Aurora kinase inhibitor, was selected as a preclinical development candidate for the treatment of human malignancies, in particular AML, in adults and children.
Subject(s)
Antineoplastic Agents/chemical synthesis , Imidazoles/chemical synthesis , Leukemia, Myeloid, Acute/drug therapy , Protein Serine-Threonine Kinases/antagonists & inhibitors , Purines/chemical synthesis , Pyrazoles/chemical synthesis , Pyridines/chemical synthesis , fms-Like Tyrosine Kinase 3/antagonists & inhibitors , Administration, Oral , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Aurora Kinase A , Aurora Kinase B , Aurora Kinases , Biological Availability , Cell Line, Tumor , Drug Screening Assays, Antitumor , ERG1 Potassium Channel , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Female , Humans , Imidazoles/chemistry , Imidazoles/pharmacology , Male , Mice , Mice, Inbred BALB C , Microsomes, Liver/metabolism , Models, Molecular , Mutation , Neoplasm Transplantation , Purines/chemistry , Purines/pharmacology , Pyrazoles/chemistry , Pyrazoles/pharmacology , Pyridines/chemistry , Pyridines/pharmacology , Rats , Rats, Sprague-Dawley , Transplantation, Heterologous , fms-Like Tyrosine Kinase 3/geneticsABSTRACT
Aurora kinases regulate key stages of mitosis including centrosome maturation, spindle assembly, chromosome segregation, and cytokinesis. Aurora A and B kinase overexpression has also been associated with various human cancers, and as such, they have been extensively studied as novel antimitotic drug targets. Here, we characterize the Aurora kinase inhibitor CCT137690, a highly selective, orally bioavailable imidazo[4,5-b]pyridine derivative that inhibits Aurora A and B kinases with low nanomolar IC(50) values in both biochemical and cellular assays and exhibits antiproliferative activity against a wide range of human solid tumor cell lines. CCT137690 efficiently inhibits histone H3 and transforming acidic coiled-coil 3 phosphorylation (Aurora B and Aurora A substrates, respectively) in HCT116 and HeLa cells. Continuous exposure of tumor cells to the inhibitor causes multipolar spindle formation, chromosome misalignment, polyploidy, and apoptosis. This is accompanied by p53/p21/BAX induction, thymidine kinase 1 downregulation, and PARP cleavage. Furthermore, CCT137690 treatment of MYCN-amplified neuroblastoma cell lines inhibits cell proliferation and decreases MYCN protein expression. Importantly, in a transgenic mouse model of neuroblastoma that overexpresses MYCN protein and is predisposed to spontaneous neuroblastoma formation, this compound significantly inhibits tumor growth. The potent preclinical activity of CCT137690 suggests that this inhibitor may benefit patients with MYCN-amplified neuroblastoma.
