Protein tyrosine kinase inhibitors in cancer treatment

Structure-based design and synthesis of high affinity tripeptide ligands of the Grb2-SH2 domain

The X-ray structure of the Grb2-SH2 domain in complex with a specific phosphopeptide ligand has revealed the existence of an extended hydrophobic area adjacent to the primary binding site of the ligand on the SH2 domain. This has been exploited to design hydrophobic C-terminal groups that improve the binding affinity of the minimal sequence pTyr-Ile-Asn recognized by the Grb2-SH2 domain. The most significant increase in affinity (25-fold compared to that of the reference peptide having a nonsubstituted carboxamide C-terminus) was obtained with a 3-naphthalen-1-yl-propyl group which was predicted to have the largest contact area with the SH2 domain hydrophobic region. This modification combined with replacement of the minimal sequence isoleucine residue by 1-aminocyclohexane carboxylic acid to stabilize the beta-turn conformation required for recognition by the Grb2-SH2 domain resulted in the high affinity (47 nM in an ELISA assay) and selective phosphopeptide Ac-pTyr-Ac6c-Asn-NH(3-naphthalen-1-yl-propyl).

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.

Synthesis and biological evaluations of 3-substituted indolin-2-ones: a novel class of tyrosine kinase inhibitors that exhibit selectivity toward particular receptor tyrosine kinases

3-Substituted indolin-2-ones have been designed and synthesized as a novel class of tyrosine kinase inhibitors which exhibit selectivity toward different receptor tyrosine kinases (RTKs). These compounds have been evaluated for their relative inhibitory properties against a panel of RTKs in intact cells. By modifying the 3-substituted indolin-2-ones, we have identified compounds which showed selective inhibition of the ligand-dependent autophosphorylation of various RTKs at submicromolar levels in cells. Structure-activity analysis for these compounds and their relative potency and selectivity to inhibit particular RTKs has determined that (1) 3-[(five-membered heteroaryl ring)methylidenyl]indolin-2-ones are highly specific against the VEGF (Flk-1) RTK activity, (2) 3-(substituted benzylidenyl)indolin-2-ones containing bulky group(s) in the phenyl ring at the C-3 position of indolin-2-ones showed high selectivity toward the EGF and Her-2 RTKs, and (3) the compound containing an extended side chain at the C-3 position of the indolin-2-one (16) exhibited high potency and selectivity when tested against the PDGF and VEGF (Flk-1) RTKs. Recent published crystallographic data for two of these 3-substituted indolin-2-ones provides a rationale to suggest that these compounds may bind in the ATP binding pocket of RTKs. The structure-activity analysis supports the use of subsets of these compounds as specific chemical leads for the development of RTK-specific drugs with broad application for the treatment of human diseases.

Structures of staurosporine bound to CDK2 and cAPK--new tools for structure-based design of protein kinase inhibitors

Protein kinases are involved in a wide variety of signal transduction processes; their deregulation has been implicated in a number of human diseases, including cancer and disorders of the immune system. The recently determined structures of two protein kinases, cAPK and CDK2, in complex with an inhibitor, staurosporine, provide a detailed account of inhibitor-kinase interactions and inhibitor selectivity.

Tyrosine kinase inhibitors. 13. Structure-activity relationships for soluble 7-substituted 4-[(3-bromophenyl)amino]pyrido[4,3-d]pyrimidines designed as inhibitors of the tyrosine kinase activity of the epidermal growth factor receptor

The general class of 4-(phenylamino)quinazolines are potent (some members with IC50 values << 1 nM) and selective inhibitors of the tyrosine kinase activity of the epidermal growth factor receptor (EGFR), via competitive binding at the ATP site of the enzyme, but many of the early analogues had poor aqueous solubility (<< 1 mM). A series of 7-substituted 4-[(3-bromophenyl)-amino]pyrido[4,3-d]pyrimidines, together with selected (3-methylphenyl)amino analogues, were prepared by reaction of the analogous 7-fluoro derivatives with appropriate amine nucleophiles in 2-BuOH or aqueous 1-PrOH. All of the compounds were evaluated for their ability to inhibit the tyrosine-phosphorylating action of EGF-stimulated full-length EGFR enzyme. Selected analogues were also evaluated for their inhibition of autophosphorylation of the EGF receptor in A431 human epidermoid carcinoma cells in culture and against A431 tumor xenografts in mice. Analogues bearing a wide variety of polyol, cationic, and anionic solubilizing substituents retained activity, but the most effective in terms of both increased aqueous solubility (> 40 mM) and retention of overall inhibitory activity (IC50's of 0.5-10 nM against isolated enzyme and 8-40 nM for inhibition of EGFR autophosphorylation in A431 cells) were weakly basic amine derivatives. These results are broadly consistent with a proposed model for the binding of these compounds to EGFR, in which the 6- and 7-positions of the pyridopyrimidine ring are in a largely hydrophobic binding region of considerable steric freedom, at the entrance of the adenine binding cleft. The most active cationic analogues have a weakly basic side chain where the amine moiety is three or more carbon atoms away from the nucleus. Two of the compounds (bearing weakly basic morpholinopropyl and strongly basic (dimethylamino)butyl solubilizing groups) produced in vivo tumor growth delays of 13-21 days against advanced stage A431 epidermoid xenografts in nude mice, when administered i.p. twice per day on days 7-21 posttumor implant. Treated tumors did not increase in size during therapy and resumed growth at the termination of therapy, indicating an apparent cytostatic effect for these compounds under these treatment conditions. The data suggest that continuous long-term therapy with these compounds may result in substantial tumor growth inhibition.