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Screening of a compound library led to the identification of 2-amino-6-(2,6-dichlorophenyl)-8-methylpyrido[2,3-d]pyrimidine (1) as a inhibitor of the platelet-derived growth factor receptor (PDGFr), fibroblast growth factor receptor (FGFr), and c-src tyrosine kinases (TKs). Replacement of the primary amino group at C-2 of 1 with a 4-(N,N-diethylaminoethoxy)phenylamino group yielded 2a, which had greatly increased activity against all three TKs. In the present work, variation of the aromatic group at C-6 and of the alkyl group at N-8 of the pyrido[2,3-d]pyrimidine core provided several analogues that retained potency, including derivatives that were biased toward inhibition of the TK activity of PDGFr. Analogues of 2a with a 3-thiophene or an unsubstituted phenyl group at C-6 were the most potent inhibitors. Compound 54, which had IC50 values of 31, 88, and 31 nM against PDGFr, FGFr, and c-src TK activity, respectively, was active in a variety of PDGF-dependent cellular assays and blocked the in vivo growth of three PDGF-dependent tumor lines.

Previously, our laboratories have reported on a new class of highly potent tyrosine kinase inhibitors based on the pyrido[2, 3-d]pyrimidine core template. To understand the structural basis for the potency and specificity, a model for the binding mode of this class of inhibitors to the tyrosine kinase domains of c-Src, PDGFr, FGFr, and EGFr tyrosine kinases was developed from structural information (principally utilizing the catalytic domain of c-AMP-dependent protein kinase as template) and structure-activity relationship (SAR) information. In the resulting docking mode, the pyrido[2,3-d]pyrimidine template shows a hydrogen-bonding pattern identical to that of olomoucine. The 6-aryl substituent of the heterocycle is located deep in the binding cleft in a pocket not used by ATP, which helps to confer high-affinity binding as well as specificity. The 2-anilino and 2-(dialkylamino)alkylamino substituents as well as the 7-urea substituent of inhibitors within this class are located at the entrance of the binding cleft and make contact with residues in the hinge region between the two kinase lobes. This allows considerable variability and bulk tolerance for C-2 and N-7 substituents. The models presented here are consistent with the SAR seen for the inhibition of a number of isolated enzymes and provide a structural basis to explain their specificity. They have been used successfully to design new highly potent protein kinase inhibitors.

Fibroblast growth factor receptor (FGFr) mediated signal transduction is implicated in vascular proliferative diseases and some cancers. We have identified methyl 1-oxo-3-phenyl-1H-indene-2-carboxylic ester as a small molecule inhibitor of the tyrosine kinase activity of FGFr-1, (IC50 = 5.1 μM). We report here the synthesis and structure-activity studies about this template core. Additionally, screening of this series against a panel of tyrosine kinases shows selective inhibition of FGFr.

The inhibition of tyrosine kinase-mediated signal transduction pathways represents a therapeutic approach to the intervention of proliferative diseases such as cancer, atherosclerosis, and restenosis. A novel series of pyrido[2,3-d]pyrimidine inhibitors of the PDGFr, bFGFr, and c-Src tyrosine kinases was developed from compound library screening and lead optimization.1 In addition, highly selective inhibitors of the FGFr tyrosine kinase were also discovered and developed from this novel series of pyrido[2,3-d]pyrimidines. The syntheses, biological evaluation, and structure-activity relationships of this series are reported.

A series of renin inhibitors were designed to examine the topography of the contiguous binding pocket of renin that is normally occupied by the P1 and P3 side chains. Molecular modeling suggested that extending the P1 hydrophobic side chain into the adjacent hydrophobic S3 enzyme pocket was feasible. Novel transition state isosteres with modified P1 → P3 side chains were synthesized and provided enhanced binding affinity when incorporated into renin inhibitors in which the P3 Phe was substituted by Gly. In a complementary approach, the binding affinities of a variety of P3-P4-modified peptidomimetic renin inhibitors that lacked substantial hydrophobic side chains at these sites were measured.

Syntheses and structure-activity relationships for a series of substituted tetrahydroisoquinoline-3-carboxylic acid derivatives with AT2-specific angiotensin II receptor binding inhibitory activity are reported.

A synthesis of 6-amino-7-cyclohexyl-3,5-heptanediol 1 (CDH) and related amino 1,3-diols involving a nucleophilic ring opening of N-acyl activated lactams is described. Stereochemical proof of the 1,3-diol moiety is also presented.

Fibroblast growth factor receptor (FGFr) mediated signal transduction is implicated in vascular proliferative diseases and some cancers. We have identified methyl 1-oxo-3-phenyl-1H-indene-2-carboxylic ester as a small molecule inhibitor of the tyrosine kinase activity of FGFr-1, (IC50 = 5.1 μM). We report here the synthesis and structure-activity studies about this template core. Additionally, screening of this series against a panel of tyrosine kinases shows selective inhibition of FGFr.

Angiogenesis is an exciting and promising new area of research. The concept that tumor cells are absolutely dependent upon neovascularization to grow and metastasize has opened the door to a multitude of new approaches and targets for developing anticancer therapies. These potential new antiangiogenic therapies offer the possibility for improved efficacy and reduced toxicity relative to conventional cancer treatments without the possibility of drug resistance. In particular, reports of small molecule inhibitors of tumor-promoted angiogenesis are appearing ever more frequently in the scientific literature. For this reason, the major focus of this review will be to cover small molecule inhibitors of tumor-promoted angiogenesis. The present review concentrates on selected literature, principally from mid-1996 to mid-1998, where there are sufficient biological data to support claims of antiangiogenic activities by small molecules. In addition, a historical background is presented and some of the important issues related to this field are discussed within.

Angiogenesis, the sprouting of new blood vessels from pre-existing ones, is an essential physiological process in development, yet also plays a major role in the progression of human diseases such as diabetic retinopathy, atherosclerosis and cancer. The effects of the most potent angiogenic factors, vascular endothelial growth factor (VEGF), angiopoietin and fibroblast growth factor (FGF) are mediated through cell surface receptors that possess intrinsic protein tyrosine kinase activity. In this report, we describe a synthetic compound of the pyrido[2,3-d]pyrimidine class, designated PD 173074, that selectively inhibits the tyrosine kinase activities of the FGF and VEGF receptors. We show that systemic administration of PD 173074 in mice can effectively block angiogenesis induced by either FGF or VEGF with no apparent toxicity. To elucidate the determinants of selectivity, we have determined the crystal structure of PD 173074 in complex with the tyrosine kinase domain of FGF receptor 1 at 2.5 A resolution. A high degree of surface complementarity between PD 173074 and the hydrophobic, ATP-binding pocket of FGF receptor 1 underlies the potency and selectivity of this inhibitor. PD 173074 is thus a promising candidate for a therapeutic angiogenesis inhibitor to be used in the treatment of cancer and other diseases whose progression is dependent upon new blood vessel formation.

Screening of a compound library for inhibitors of the fibroblast growth factor (FGFr) and platelet-derived growth factor (PDGFr) receptor tyrosine kinases led to the development of a novel series of ATP competitive pyrido[2,3-d]pyrimidine tyrosine kinase inhibitors. The initial lead, 1-[2-amino-6-(2,6-dichlorophenyl)pyrido[2,3-d]pyrimidin-7-yl]-3- tert-butylurea (4b, PD-089828), was found to be a broadly active tyrosine kinase inhibitor. Compound 4b inhibited the PDGFr, FGFr, EGFr, and c-src tyrosine kinases with IC50 values of 1.11, 0.13, 0.45, and 0.22 microM, respectively. Subsequent SAR studies led to the synthesis of new analogs with improved potency, solubility, and bioavailability relative to the initial lead. For example, the introduction of a [4-(diethylamino)butyl]amino side chain into the 2-position of 4b afforded compound 6c with enhanced potency and bioavailability. Compound 6c inhibited PDGF-stimulated vascular smooth muscle cell proliferation with an IC50 of 0.3 microM. Furthermore, replacement of the 6-(2,6-dichlorophenyl) moiety of 4b with a 6-(3',5'-dimethoxyphenyl) functionality produced a highly selective FGFr tyrosine kinase inhibitor 4e. Compound 4e inhibited the FGFr tyrosine kinase with an IC50 of 0.060 microM, whereas IC50s for the inhibition of the PDGFr, FGFr, EGFr, c-src, and InsR tyrosine kinases for this compound (4e) were all greater than 50 microM.

A series of renin inhibitors having alpha-heteroatom amino acids as P2 substitutions has been prepared. Examples where the heteroatom is oxygen, sulfur, or nitrogen are described. Many of the compounds exhibit subnanomolar potency when tested in vitro against monkey renin. When selected compounds were tested orally in conscious, salt-depleted, normotensive, Cynomolgus monkeys, low to moderate blood pressure lowering was observed. At an oral dose of 30 mg/kg, compound 53a lowered blood pressure by a maximum of 18 mmHg at 2.5 h post-dose.