EGF/TGFß1 co-stimulation of oral squamous cell carcinoma cells causes an epithelial-mesenchymal transition cell phenotype expressing laminin 332.

Epithelial-mesenchymal transition (EMT) is suggested to be crucial for the development of an invasive and metastatic carcinoma cell phenotype. Therefore, the definition of this phenotype is of great clinical interest. We recently evidenced vimentin positive cells in oral squamous cell carcinoma (OSCC) invasive front expressing laminin γ2 chain mRNA implicating an EMT origin of these cells. To further elucidate the nature of these cells, we have investigated the relation between EMT criteria and laminin-332 expression in a cell culture model of transforming growth factor beta-1 (TGFß1)/epithelial growth factor (EGF) long time co-stimulation. We demonstrate that in contrast to TGFß1 or EGF alone, co-stimulation induces phenotype transition in OSCC cells which fulfils the criteria of EMT in terms of vimentin up-regulation and E-cadherin down-regulation on protein level as well as cell scattering. Furthermore, cells displayed a strongly enhanced invasiveness and adhesion to type I-IV collagens. Phenotype transition is accompanied by an enhanced expression of laminin-332, especially of its γ2 chain. We further analyse the expression of extracellular matrix related genes by RT-PCR profiling. With respect to strongly enhanced proteins, data confirm the EMT phenotype of co-stimulated OSCC cells and expression of laminin-332. Furthermore, alpha catenin, collagen type 16, the integrin α7 and ß1 chains, and MMP11 are suggested as candidates with potential role in EMT in OSCC. In summary we are able to show that EMT in OSCC is mediated by multiple growth factors and is accompanied by laminin γ2 chain up-regulation evidencing the existence of an intermediate Vim(+) /Ln332(+) EMT phenotype as seen in situ.

Chimeric tyrosine kinase-HDAC inhibitors as antiproliferative agents.

Combined treatment with tyrosine kinase inhibitors (TKi) and additional drugs is emerging as a promising strategy for cancer therapy. TKi and histone-deacetylase inhibitors (HDI) are two classes of anti-tumor agents with distant mechanisms of action. We have designed and synthesized chimeric compounds, which comprise structural elements of the TKi imatinib, and of prototypical HDI compounds. These compounds retain TKi activity similar to imatinib, exemplified by the inhibition of the platelet-derived growth factor receptor, and c-Kit kinase in intact cells. In addition, the chimeric compounds have in vitro and cellular HDI activity, and potently inhibit growth of cancer cell lines, including that of imatinib-resistant cell lines. Chimeric molecules with combined TKi and HDI activity may simplify combination treatment and be applicable to overcome clinical resistance to TKi single-agent therapy.

Stent-based release of a selective PDGF-receptor blocker from the bis-indolylmethanon class inhibits restenosis in the rabbit animal model.

Long-term success of modern therapies for myocardial ischemia is limited by restenosis, with proliferation and migration of vascular smooth muscle cells (VSMC) as key events. Since findings in recent years indicate, that the Platelet Derived Growth Factor (PDGF) is an important selective factor in mitogenic and motogenic pathways of VSMC, different concepts for reducing restenosis by inhibiting PDGF signaling have been investigated, with local delivery of small receptor kinase inhibitors looking most promising. We tested the stent-based delivery of the PDGF-receptor inhibitor D-65495, a bis(1H-2-indolyl)methanone, in the rabbit iliac artery model of restenosis. New Zealand white rabbits underwent balloon dilation of iliac arteries for implantation of D-65495-coated or non-coated (solvent, either DMSO or 90%THF / 10% DMSO) coronary stents. After 4 weeks stents were removed and neointima formation in medial and proximal/ distal stent sections was histomorphometrically and immunohistochemically analyzed. Arteries with D-65495 eluting stents showed an up to 50% reduced restenosis compared to control stents. Also, the neointimal area was reduced, but there were no significant differences in injury score. Importantly, endothelialization was similar for control stents as well as for D-65495-coated stents, suggesting absence of a general cytostatic effect of the inhibitor. The impact of D-65495 on PDGF-receptor signaling in the vessel wall was indirectly assessed by immunohistochemical staining for activated protein kinase Akt, and PCNA as a proliferation marker and revealed some reduction for the inhibitor-treated vessels. In conclusion, the application of D-65495 caused a significant decrease in neointima formation, further supporting the concept of using locally released PDGF-receptor kinase inhibitors as anti-restenotic agents.

A substrate peptide for the FLT3 receptor tyrosine kinase.

FLT3 (fms-like tyrosine kinase 3) is frequently activated by mutation in acute myeloid leukemia, and is therefore under study as a drug target. Testing and characterization of tyrosine kinase inhibitors is facilitated by the availability of efficient peptide substrates. Searching for FLT3 peptide substrates using phosphorylation experiments on peptide arrays and in solution revealed that the peptide F-T-D-R-L-Q-Q-Y(8)-I-S-T-R-G-L-G is efficiently phosphorylated (apparent Km 10 micromol/l), with Y8 as the phosphorylated site. This peptide presents a novel tool for identifying and characterizing FLT3 kinase inhibitors.

Imatinib mesylate attenuates fibrosis in coxsackievirus b3-induced chronic myocarditis.

AIMS: Coxsackievirus B3 (CVB3)-induced chronic myocarditis in mice is accompanied by severe fibrosis and by sustained elevation of platelet-derived growth factor (PDGF)-A, -B, and -C levels in the cardiac tissue. To test if PDGF stimulation of resident fibroblasts causally contributes to fibrosis, we employed inhibition of PDGF receptor signalling with the orally available kinase inhibitor Imatinib. METHODS AND RESULTS: Chronic myocarditis was induced by CVB3 infection of major histocompatibility complex (MHC) class II knockout (B6Aa(0)/Aa(0)) mice. The mice were treated with 100 mg/kg Imatinib or vehicle, respectively, twice daily for 34 days. Expression of PDGF-C and of inflammatory cytokines were analysed by semi-quantitative RT-PCR. PDGFalpha receptor phosphorylation was detected by immunoblotting of cardiac tissue extracts and in situ by immunohistochemistry. Fibrosis formation was analysed by Sirius-Red staining and hydroxyproline (HP) determination. Fibronectin, and tenascin expression was analysed by RT-PCR and immunohistochemistry. Matrix metalloproteinase (MMP) activity was assessed with collagen, synthetic peptides, and gelatine as substrates. Imatinib significantly inhibited the myocarditis-related PDGFalpha receptor activation in the heart tissue. The virus titres in the hearts, inflammatory infiltrations, and elevated PDGF levels were unaffected by the Imatinib treatment. A significant attenuation of fibrosis occurred in Imatinib-treated animals. The Sirius Red-stained fibrotic area was reduced from 5.30 +/- 0.50 to 3.21 +/- 0.35%, and the HP content was reduced from 362 +/- 43 to 238 +/- 32 microMol/10 mg dry weight vs. 190 +/- 27 in uninfected controls. The expression of fibronectin, EIIIA+ fibronectin, and tenascin C were likewise reduced. The diminished matrix protein deposition was not caused by elevated MMP activity, since MMP activity was not changed or even reduced under Imatinib. CONCLUSION: The data suggest a causal role for elevated PDGF expression and PDGF receptor activity in the pathogenesis of cardiac fibrosis.

Inhibition of PDGFR tyrosine kinase activity by a series of novel N-(3-(4-(pyridin-3-yl)-1H-imidazol-2-ylamino)phenyl)amides: a SAR study on the bioisosterism of pyrimidine and imidazole.

A series of N-(3-(4-(pyridin-3-yl)-1H-imidazol-2-ylamino)phenyl)amides were synthesized and tested for inhibition of PDGFR and FLT3 autophosphorylation. The novel N-(3-(4-(pyridin-3-yl)-1H-imidazol-2-ylamino)phenyl)amides, obtained by replacement of the pyrimidine system in Imatinib (1) with an imidazole ring, exhibit potent inhibitory activity on PDGFR, similar to the parent compound (IC(50) (9e)=0.2 microM; IC(50) Imatinib (1)=0.3 microM). Selectivity hereby seems to be conserved, as shown by the lack of activity on FLT3, a closely related class III receptor tyrosine kinase, which is not affected by the parent compound Imatinib.

Inhibition of FLT3 and PDGFR tyrosine kinase activity by bis(benzo[b]furan-2-yl)methanones.

A series of bis(benzo[b]furan-2-yl)methanones was synthesized and tested for inhibition of FLT3 and PDGFR autophosphorylation. Mostly, C-5 substitution leads to PDGFR selectivity, which was strongest in the case of the 5,5'-dimethoxy derivative. The 5,5'-diamino and the 6,6'-dihydroxy compounds are more active at FLT3. At both kinases, the potency of the best inhibitors approaches IC50 values of ca. 0.5 microM. Molecular modeling studies suggest that the bisbenzofuranylmethanones are able to fit into the same binding site as their indolyl analogues which have been suggested to form a bidentate hydrogen bridge with the backbone in the hinge regions. The loss of one H bond by the NH-O exchange might be partially compensated by, for example, the weak interaction of one furanyl oxygen with FLT3 Cys-828.

Novel bis(1H-indol-2-yl)methanones as potent inhibitors of FLT3 and platelet-derived growth factor receptor tyrosine kinase.

FLT3 receptor tyrosine kinase is aberrantly active in many cases of acute myeloid leukemia (AML). Recently, bis(1H-indol-2-yl)methanones were found to inhibit FLT3 and PDGFR kinases. To optimize FLT3 activity and selectivity, 35 novel derivatives were synthesized and tested for inhibition of FLT3 and PDGFR autophosphorylation. The most potent FLT3 inhibitors 98 and 102 show IC50 values of 0.06 and 0.04 microM, respectively, and 1 order of magnitude lower PDGFR inhibiting activity. The derivatives 76 and 82 are 20- to 40-fold PDGFR selective. Docking at the recent FLT3 structure suggests a bidentate binding mode with the backbone of Cys-694. Activity and selectivity can be related to interactions of one indole moiety with a hydrophobic pocket including Phe-691, the only different binding site residue (PDGFR Thr-681). Compound 102 inhibited the proliferation of 32D cells expressing wildtype FLT3 or FLT3-ITD similarly as FLT3 autophosphorylation, and induced apoptosis in primary AML patient blasts.

Tricyclic quinoxalines as potent kinase inhibitors of PDGFR kinase, Flt3 and Kit.

Here we report on novel quinoxalines as highly potent and selective inhibitors of the type III receptor tyrosine kinases PDGFR, FLT3, and KIT. These compounds, tricyclic quinoxalines, were generated in order to improve bioavailability over the highly hydrophobic bicyclic quinoxalines. Four of the highly active compounds were characterized in detail and are shown to inhibit PDGFR kinase activity of the isolated receptor as well as in intact cells in the sub-micromolar concentration range. We show that the most active inhibitor (compound 13, AGL 2043) is approximately 15-20 times more potent than its isomer (compound 14, AGL 2044). We therefore compared the three dimensional structures of the two compounds by X-ray crystallography. These compounds are also highly effective in blocking the kinase activity of FLT3, KIT, and the oncogenic protein Tel-PDGFR in intact cells. These compounds are potent inhibitors of the proliferation of pig heart smooth muscle cells. They fully arrest the growth of these cells and the effect is fully reversible. The chemical, biochemical and cellular properties of these compounds as well as the solubility properties make them suitable for development as anti-restenosis and anti-cancer agents.

A single amino acid exchange inverts susceptibility of related receptor tyrosine kinases for the ATP site inhibitor STI-571.

The tyrosine kinase inhibitor STI-571 potently blocks BCR-Abl, platelet-derived growth factor (PDGF) alpha- and beta-receptors, and c-Kit kinase activity. Flt3, a receptor tyrosine kinase closely related to PDGF receptors and c-Kit is, however, not inhibited by STI-571. Sequence alignments of different kinases and indications from the crystal structure of the STI-571 Abl kinase complex revealed amino acid residues that are probably crucial for this activity profile. It was predicted that Flt3 Phe-691 in the beta5 strand may sterically prevent interaction with STI-571. The point mutants Flt3 F691T and PDGFbeta-receptor T681F were constructed, and kinase assays showed that the Flt3 mutant but not the PDGFbeta-receptor mutant is inhibited by STI-571. Docking of STI-571 into computer models of the PDGFbeta-receptor and Flt3 kinase domains and comparison with the crystal structure of the STI-571 Abl kinase complex indicated very similar binding sites among the three nonphosphorylated kinases, suggesting corresponding courses of their Asp-Phe-Gly motifs and activation loops. Accordingly, we observed reduced sensitivity of preactivated compared with nonactivated PDGFR-beta for the inhibition by STI-571. Courses of the activation loop that collide with STI-571 binding explain its inactivity at other kinases as the insulin receptor. The binding site models of PDGFR-beta and Flt3 were applied to predict structural approaches for more selective PDGFbeta-receptor inhibitors.

Bis(1H-2-indolyl)methanones as a novel class of inhibitors of the platelet-derived growth factor receptor kinase.

The novel lead bis(1H-2-indolyl)methanone inhibits autophosphorylation of platelet-derived growth factor (PDGF) receptor tyrosine kinase in intact cells. Various substituents in the 5- or 6-position of one indole ring increase or preserve potency, whereas most modifications of the ring structures and of the methanone group as well as substitution at both indoles result in weak or no activity. An ATP binding site model, derived by homology from the FGFR-1 tyrosine kinase crystal structure suggesting hydrogen bonds of one indole NH and the methanone oxygen with the backbone carbonyl and amide, respectively, of Cys684, explains why only one indole moiety is open for substitution and locates groups in the 5- or 6-position outside the pocket. The hitherto most active derivatives, 39, 53 and 67, inhibit both isoforms of the PDGF receptor kinase in intact cells, with IC(50) of 0.1-0.3 microM, and purified PDGFbeta-receptor in vitro, with IC(50) of 0.09, 0.1, or 0.02 microM, respectively. PDGF-stimulated DNA synthesis is inhibited by these derivatives with IC(50) values of 1-3 microM. Kinetic analysis of 53 showed an ATP-competitive mode of inhibition. The compounds are inactive or weakly active toward a number of other tyrosine kinases, including the FGF receptor 1, EGF receptor, and c-Src kinase, as well as toward serine-threonine kinases, including different PKC isoforms and GRK2, and appear therefore selective for PDGF receptor inhibition.