Synthesis and tyrosine kinase inhibitory activity of a series of 2-amino-8H-pyrido[2,3-d]pyrimidines: identification of potent, selective platelet-derived growth factor receptor tyrosine kinase inhibitors.

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.

2-Substituted aminopyrido[2,3-d]pyrimidin-7(8H)-ones. structure-activity relationships against selected tyrosine kinases and in vitro and in vivo anticancer activity.

While engaged in therapeutic intervention against a number of proliferative diseases, we have discovered the 2-aminopyrido[2, 3-d]pyrimidin-7(8H)-ones as a novel class of potent, broadly active tyrosine kinase (TK) inhibitors. An efficient route was developed that enabled the synthesis of a wide variety of analogues with substitution on several positions of the template. From the lead structure 2, a series of analogues bearing variable substituents at the C-2 position and methyl or ethyl at N-8 was made. Compounds of this series were competitive with ATP and displayed submicromolar to low nanomolar potency against a panel of TKs, including receptor (platelet-derived growth factor, PDGFr; fibroblast growth factor, FGFr; epidermal growth factor, EGFr) and nonreceptor (c-Src) classes. One of the more thoroughly evaluated members was 63 with IC50 values of 0.079 microM (PDGFr), 0.043 microM (bFGFr), 0.044 microM (EGFr), and 0.009 microM (c-Src). In cellular studies, 63 inhibited PDGF-mediated receptor autophosphorylation in a number of cell lines at IC50 values of 0.026-0.002 microM and proliferation of two PDGF-dependent lines at 0.3 microM. It also caused inhibition of soft agar colony formation in three cell lines that overexpress the c-Src TK, with IC50 values of 0.33-1.8 microM. In in vivo studies against a panel of seven xenograft tumor models with known and/or inferred dependence on the EGFr, PDGFr, and c-Src TKs, compound 63 produced a tumor growth delay of 10.6 days against the relatively refractory SK-OV-3 ovarian xenograft and also displayed activity against the HT-29 tumor. In rat oral bioavailability studies, compound 63 plasma concentrations declined in a biexponential manner, and systemic plasma clearance was high relative to liver blood flow. Finally, in rat metabolism studies, HPLC chromatography identified two metabolites of 63, which were proved by mass spectrometry and synthesis to be the primary amine (58) and N-oxide (66). Because of the excellent potency of 63 against selected TKs, in vitro and in vivo studies are underway for this compound in additional tumor models dependent upon PDGFr, FGFr, and c-Src to assess its potential for advancement to clinical trials.

In vitro pharmacological characterization of PD 166285, a new nanomolar potent and broadly active protein tyrosine kinase inhibitor.

PD 166285, a novel protein tyrosine kinase inhibitor of a new structural class, the 6-aryl-pyrido[2,3-d]pyrimidines, was synthesized as the most potent and soluble analog of a series of small molecules originally identified by screening a compound library with assays that measured protein tyrosine kinase activity. PD 166285 was found to inhibit Src nonreceptor tyrosine kinase, fibroblast growth factor receptor-1, epidermal growth factor receptor and platelet-derived growth factor receptor beta subunit (PDGFR-beta), tyrosine kinases with half-maximal inhibitory potencies (IC50 values) of 8.4 +/- 2.3 nM (n = 6), 39.3 +/- 2.8 nM (n = 16), 87.5 +/- 13.7 nM (n = 6) and 98.3 +/- 7.9 nM (n = 16), respectively. PD 166285 also demonstrated inhibitory activity against mitogen-activated protein kinase (IC50 = 5 microM) and protein kinase C (IC50 = 22.7 microM). PD 166285 was further characterized as an ATP competitive inhibitor of Src nonreceptor tyrosine kinase, PDGFR-beta, fibroblast growth factor receptor-1 and epidermal growth factor receptor tyrosine kinases. In addition, PD 166285 inhibited PDGF- and EGF-stimulated receptor autophosphorylation in vascular smooth muscle cells (VSMCs) and A431 cells, respectively, and basic fibroblast growth factor-mediated tyrosine phosphorylation in Sf9 cells, with IC50 values of 6.5 nM, 1.6 microM and 97.3 nM, respectively, further establishing a tyrosine kinase mechanism of inhibition. The inhibition of PDGF receptor autophosphorylation in VSMCs by PD 166285 was long lasting and persisted for 4 days after a single 1-hr exposure followed by extensive washing. The PDGF-induced tyrosine phosphorylation of the 44- and 42-kDa mitogen-activated protein kinase isoforms was also blocked as a result of the inhibition of PDGF-stimulated receptor autophosphorylation by PD 166285 in VSMCs. The effects of PD 166285 were also demonstrated in functional assays of cell attachment, migration and proliferation, in which vascular cell adhesion to vitronectin, PDGF-directed chemotaxis and serum-stimulated cell growth were all potently inhibited with IC50 values of 80 yo 120 nM. Finally, PD 166285 uniquely demonstrated potent inhibition of phorbol ester-induced production of 92-kDa gelatinase A (MMP-9) in VSMC without affecting 72-kDa gelatinase B (MMP-2) as measured by gelatin zymography. These results highlight the biological characteristics of PD 166285 as a broadly active protein tyrosine kinase capable of potently inhibiting a number of kinase mediated cellular functions, including cell attachment, movement and replication. The potential therapeutic utility of this broadly acting inhibitor as an antiproliferative and antimigratory agent could extend to such diseases as cancer, atherosclerosis and restenosis, in which redundancies in protein kinase signaling pathways are known to exist.

Structure-activity relationships of a series of 2-amino-4-thiazole-containing renin inhibitors.

A series of renin inhibitors was synthesized that contained a 2-amino-4-thiazolyl moiety at the P2 position. These derivatives are potent inhibitors of monkey renin in vitro and are selective in that they only weakly inhibit the closely related aspartic proteinase, bovine cathepsin D. Four compounds exhibited oral blood pressure lowering activity in high-renin normotensive monkeys. One of these compounds, 22 (PD 134672), was selected for further evaluation in renal hypertensive monkeys, on the basis of its superior efficacy and duration of action in the in vitro assays and the normotensive primate model.

Synthesis and structure-activity relationships of a novel series of non-peptide angiotensin II receptor binding inhibitors specific for the AT2 subtype.

Structure-activity relationships are reported for a novel class of 4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid derivatives that displace 125I-labeled angiotensin II from a specific subset of angiotensin II (Ang II) binding sites in rat adrenal preparations. This binding site is not the Ang II receptor mediating vascular contraction or aldosterone release, but, rather, is one whose function has not yet been fully elucidated. It has been identified in a number of tissues and has a similar affinity for Ang II and its peptide analogues as does the vascular receptor. The non-peptide compounds reported here are uniquely specific in displacing Ang II at this binding site and are inactive in antagonizing Ang II at the vascular receptor or in pharmacological assays measuring vascular effects. PD 123,319 (79), one of the most potent compounds, has an IC50 of 34 nM. Certain of these compounds may have utility in the definition and study of Ang II receptor subtypes.