3-Aminopyrazole inhibitors of CDK2/cyclin A as antitumor agents. 2. Lead optimization.

Inhibitors of cyclin-dependent kinases (CDK) such as CDK2/cyclin A-E are currently undergoing clinical trials to verify their potential as new anticancer agents. In a previous article we described the lead discovery process of a 3-aminopyrazole class of CDK2/cyclin A-E inhibitors. The endpoint of this process was PNU-292137, a compound endowed with in vivo antitumor activity in a mouse tumor xenograft model. We optimized this lead compound to improve some physicochemical properties, notably solubility and plasma protein binding. This lead optimization process brought us to the discovery of (2S)-N-(5-cyclopropyl-1H-pyrazol-3-yl)-2-[4-(2-oxo-1-pyrrolidinyl)phenyl]propanamide (PHA-533533, 13), a compound with a balanced activity vs druglike profile. Compound 13 inhibited CDK2/cyclin A with a K(i) of 31 nM, counteracting tumor cell proliferation of different cell lines with an IC(50) in the submicromolar range. Solubility was improved more than 10 times over the starting lead, while plasma protein binding was decreased from 99% to 74%. With exploitation of this globally enhanced in vitro profile, 13 was more active than PNU-292137 in vivo in the A2780 xenograft model showing a tumor growth inhibition of 70%. Proof of mechanism of action was obtained in vivo by immunohistochemical analysis of tumor slices of 13-treated vs untreated animals.

Cdc7 kinase inhibitors: 5-heteroaryl-3-carboxamido-2-aryl pyrroles as potential antitumor agents. 1. Lead finding.

Cdc7 serine/threonine kinase is a key regulator of DNA synthesis in eukaryotic organisms. Cdc7 inhibition through siRNA or prototype small molecules causes p53 independent apoptosis in tumor cells while reversibly arresting cell cycle progression in primary fibroblasts. This implies that Cdc7 kinase could be considered a potential target for anticancer therapy. We previously reported that pyrrolopyridinones (e.g., 1) are potent and selective inhibitors of Cdc7 kinase, with good cellular potency and in vitro ADME properties but with suboptimal pharmacokinetic profiles. Here we report on a new chemical class of 5-heteroaryl-3-carboxamido-2-substituted pyrroles (1A) that offers advantages of chemistry diversification and synthetic simplification. This work led to the identification of compound 18, with biochemical data and ADME profile similar to those of compound 1 but characterized by superior efficacy in an in vivo model. Derivative 18 represents a new lead compound worthy of further investigation toward the ultimate goal of identifying a clinical candidate.

First Cdc7 kinase inhibitors: pyrrolopyridinones as potent and orally active antitumor agents. 2. Lead discovery.

Cdc7 kinase is a key regulator of the S-phase of the cell cycle, known to promote the activation of DNA replication origins in eukaryotic organisms. Cdc7 inhibition can cause tumor-cell death in a p53-independent manner, supporting the rationale for developing Cdc7 inhibitors for the treatment of cancer. In this paper, we conclude the structure-activity relationships study of the 2-heteroaryl-pyrrolopyridinone class of compounds that display potent inhibitory activity against Cdc7 kinase. Furthermore, we also describe the discovery of 89S, [(S)-2-(2-aminopyrimidin-4-yl)-7-(2-fluoro-ethyl)-1,5,6,7-tetrahydropyrrolo[3,2-c]pyridin-4-one], as a potent ATP mimetic inhibitor of Cdc7. Compound 89S has a Ki value of 0.5 nM, inhibits cell proliferation of different tumor cell lines with an IC50 in the submicromolar range, and exhibits in vivo tumor growth inhibition of 68% in the A2780 xenograft model.

6-Substituted pyrrolo[3,4-c]pyrazoles: an improved class of CDK2 inhibitors.

We have recently reported a new class of CDK2/cyclin A inhibitors based on a bicyclic tetrahydropyrrolo[3,4-c]pyrazole scaffold. The introduction of small alkyl or cycloalkyl groups in position 6 of this scaffold allowed variation at the other two diversity points. Conventional and polymer-assisted solution phase chemistry provided a way of generating compounds with improved biochemical and cellular activity. Optimization of the physical properties and pharmacokinetic profile led to a compound which exhibited good efficacy in vivo on A2780 human ovarian carcinoma.