Fadraciclib (CYC065), a novel CDK inhibitor, targets key pro-survival and oncogenic pathways in cancer.

Cyclin-dependent kinases (CDKs) contribute to the cancer hallmarks of uncontrolled proliferation and increased survival. As a result, over the last two decades substantial efforts have been directed towards identification and development of pharmaceutical CDK inhibitors. Insights into the biological consequences of CDK inhibition in specific tumor types have led to the successful development of CDK4/6 inhibitors as treatments for certain types of breast cancer.

Dynamic Equilibrium of the Aurora A Kinase Activation Loop Revealed by Single-Molecule Spectroscopy.

The conformation of the activation loop (T-loop) of protein kinases underlies enzymatic activity and influences the binding of small-molecule inhibitors. By using single-molecule fluorescence spectroscopy, we have determined that phosphorylated Aurora A kinase is in dynamic equilibrium between a DFG-in-like active T-loop conformation and a DFG-out-like inactive conformation, and have measured the rate constants of interconversion. Addition of the Aurora A activating protein TPX2 shifts the equilibrium towards an active T-loop conformation whereas addition of the inhibitors MLN8054 and CD532 favors an inactive T-loop.

Structure-based design of orally bioavailable 1H-pyrrolo[3,2-c]pyridine inhibitors of mitotic kinase monopolar spindle 1 (MPS1).

The protein kinase MPS1 is a crucial component of the spindle assembly checkpoint signal and is aberrantly overexpressed in many human cancers. MPS1 is one of the top 25 genes overexpressed in tumors with chromosomal instability and aneuploidy. PTEN-deficient breast tumor cells are particularly dependent upon MPS1 for their survival, making it a target of significant interest in oncology.

Benzimidazole inhibitors of the protein kinase CHK2: clarification of the binding mode by flexible side chain docking and protein-ligand crystallography.

Two closely related binding modes have previously been proposed for the ATP-competitive benzimidazole class of checkpoint kinase 2 (CHK2) inhibitors; however, neither binding mode is entirely consistent with the reported SAR. Unconstrained rigid docking of benzimidazole ligands into representative CHK2 protein crystal structures reveals an alternative binding mode involving a water-mediated interaction with the hinge region; docking which incorporates protein side chain flexibility for selected residues in the ATP binding site resulted in a refinement of the water-mediated hinge binding mode that is consistent with observed SAR. The flexible docking results are in good agreement with the crystal structures of four exemplar benzimidazole ligands bound to CHK2 which unambiguously confirmed the binding mode of these inhibitors, including the water-mediated interaction with the hinge region, and which is significantly different from binding modes previously postulated in the literature.

Optimization of imidazo[4,5-b]pyridine-based kinase inhibitors: identification of a dual FLT3/Aurora kinase inhibitor as an orally bioavailable preclinical development candidate for the treatment of acute myeloid leukemia.

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).

Mechanism-based screen for G1/S checkpoint activators identifies a selective activator of EIF2AK3/PERK signalling.

Human cancers often contain genetic alterations that disable G1/S checkpoint control and loss of this checkpoint is thought to critically contribute to cancer generation by permitting inappropriate proliferation and distorting fate-driven cell cycle exit. The identification of cell permeable small molecules that activate the G1/S checkpoint may therefore represent a broadly applicable and clinically effective strategy for the treatment of cancer. Here we describe the identification of several novel small molecules that trigger G1/S checkpoint activation and characterise the mechanism of action for one, CCT020312, in detail.

Design, synthesis and biological evaluation of 6-pyridylmethylaminopurines as CDK inhibitors.

The cyclin-dependent kinase (CDK) inhibitor seliciclib (1, CYC202) is in phase II clinical development for the treatment of cancer. Here we describe the synthesis of novel purines with greater solubility, lower metabolic clearance, and enhanced potency versus CDKs. These compounds exhibit novel selectivity profiles versus CDK isoforms.

Preparation and evaluation of trisubstituted pyrimidines as phosphatidylinositol 3-kinase inhibitors. 3-Hydroxyphenol analogues and bioisosteric replacements.

Two classes of trisubstituted pyrimidines related to PI-103 1 have been prepared and their inhibitory activities against phosphatidylinositol 3-kinase (PI3K) p110α were determined. From those with direct 6-aryl substitution compound 11a was the most potent inhibitor with an IC₅₀ value of 62 nM, and showed similar activity against other class 1a PI3K isoforms tested, p110β and p110γ. When a linking chain was introduced, as in the second exemplified class, compound 15f inhibited p110α with IC₅₀ 142 nM, and showed greater selectivity towards p110α.

Biological properties of potent inhibitors of class I phosphatidylinositide 3-kinases: from PI-103 through PI-540, PI-620 to the oral agent GDC-0941.

The phosphatidylinositide 3-kinase pathway is frequently deregulated in human cancers and inhibitors offer considerable therapeutic potential. We previously described the promising tricyclic pyridofuropyrimidine lead and chemical tool compound PI-103. We now report the properties of the pharmaceutically optimized bicyclic thienopyrimidine derivatives PI-540 and PI-620 and the resulting clinical development candidate GDC-0941.

The phosphoinositide-specific phospholipase C inhibitor U73122 (1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione) spontaneously forms conjugates with common components of cell culture medium.

Phosphoinositide-specific phospholipase C (PLC) is a key enzyme in the regulation of Ca(2+) release from inositol 1,4,5-triphosphate-sensitive stores. U73122 (1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione) has been extensively used as a pharmacological inhibitor of PLC to elucidate the importance of this enzyme family in signal transduction pathways. U73122 has an electrophilic maleimide group, which readily reacts with nucleophiles such as thiols and amines.

Conformation analyses, dynamic behavior, and amide bond distortions of medium-sized heterocycles. 2. Partially and fully reduced 1-benzazocines, benzazonines, and benzazecines.

Partially and fully reduced forms of benzo-fused eight- to ten-membered nitrogen heterocycles (1-benzazecines, 1-benzazonines and 1-benzazecines) have been prepared. Conformational features, transannular distances and dynamic behavior were studied using X-ray crystallography and VT NMR spectroscopy. The amide moiety in the nine-membered benzazonine ring 5b favors N-pyramidization, whereas the ten-membered benzazecine 5c adopts an amide twist.

Conformation analyses, dynamic behavior and amide bond distortions of medium-sized heterocycles. 1. Partially and fully reduced 1-benzazepines.

Five 1-benzazepine heterocycles were synthesized by utilizing transition-metal-catalyzed processes in key bond-forming steps. exo-Methylene and methyl substituents were introduced at position 5, as well as a unit of unsaturation between positions 3 and 4, with benzoyl or benzyl N-substituents. Solution- and solid-state structures were examined, using dynamic NMR spectroscopy and X-ray crystallography, corroborated by molecular mechanics calculations.