New dual inhibitors of EGFR and HER2 protein tyrosine kinases.

A novel series of dual EGFR and HER2 inhibitors based on the pyrrolo[2,1-f][1,2,4]triazine nucleus is described. A general route toward their synthesis, which enables functionalization at multiple sites, has been developed. Biological evaluation in enzymatic and cell-based assays has identified a series of C-6 carbamates with potent biochemical and cellular activities.

Discovery of the pyrrolo[2,1-f][1,2,4]triazine nucleus as a new kinase inhibitor template.

The pyrrolo[2,1-f][1,2,4]triazine nucleus was identified as a novel kinase inhibitor template which effectively mimics the well-known quinazoline kinase inhibitor scaffold. Attachment of a 4-((3-chloro-4-fluorophenyl)amino) substituent to the template provided potent biochemical inhibitors of the tyrosine kinase activity of EGFR, as well as inhibition of cellular proliferation of the human colon tumor cell line DiFi. Attachment of a 4-((3-hydroxy-4-methylphenyl)amino) substituent provided potent inhibitors of VEGFR-2 which also showed effects on the VEGF-dependent proliferation of human umbilical vein endothelial cells. Biological activity was maintained with substitution at positions 5 or 6, but not 7, suggesting that the former positions are promising sites for introducing side chains which modulate physicochemical properties. Preliminary inhibition studies with varying ATP concentrations suggest that, like the quinazoline-based kinase inhibitors, the pyrrolotriazine-based inhibitors bind in the ATP pocket.

Novel guanidine-based inhibitors of inosine monophosphate dehydrogenase.

A series of novel guanidine-based small molecule inhibitors of inosine monophosphate dehydrogenase (IMPDH) was explored. IMPDH catalyzes the rate determining step in guanine nucleotide biosynthesis and is a target for anticancer, immunosuppressive and antiviral therapy. The synthesis and the structure-activity relationships (SARs), derived from in vitro studies, for this new series of inhibitors is given.

Discovery of aminothiazole inhibitors of cyclin-dependent kinase 2: synthesis, X-ray crystallographic analysis, and biological activities.

High throughput screening identified 2-acetamido-thiazolylthio acetic ester 1 as an inhibitor of cyclin-dependent kinase 2 (CDK2). Because this compound is inactive in cells and unstable in plasma, we have stabilized it to metabolic hydrolysis by replacing the ester moiety with a 5-ethyl-substituted oxazole as in compound 14. Combinatorial and parallel synthesis provided a rapid analysis of the structure-activity relationship (SAR) for these inhibitors of CDK2, and over 100 analogues with IC(50) values in the 1-10 nM range were rapidly prepared. The X-ray crystallographic data of the inhibitors bound to the active site of CDK2 protein provided insight into the binding modes of these inhibitors, and the SAR of this series of analogues was rationalized. Many of these analogues displayed potent and broad spectrum antiproliferative activity across a panel of tumor cell lines in vitro. In addition, A2780 ovarian carcinoma cells undergo rapid apoptosis following exposure to CDK2 inhibitors of this class. Mechanism of action studies have confirmed that the phosphorylation of CDK2 substrates such as RB, histone H1, and DNA polymerase alpha (p70 subunit) is reduced in the presence of compound 14. Further optimization led to compounds such as water soluble 45, which possesses a favorable pharmacokinetic profile in mice and demonstrates significant antitumor activity in vivo in several murine and human models, including an engineered murine mammary tumor that overexpresses cyclin E, the coactivator of CDK2.