COL1A2 gene deletion polymorphism in an Italian and an Ivorian populations.

The COL1A2 gene is one of the two genes encoding for the polypeptides of type I collagen, that represent the major constituent of skin, bone, tendons, ligaments, blood vessels, dentin, and many interstitial tissues. The COL1A2 gene deletion polymorphism has been considered as an informative anthropological marker for describing geographically distinct human populations. Aim of the present study was to investigate the genetic variability at COL1A2 locus in two populations, one belonging to Ouangolodougou (N = 133), a village placed in Northern Ivory Coast, and one belonging to Lecco (N = 70), a village placed in a Northern Italy region called Lombardy. For each sampled population no data are available in literature. We reported, for the first time, the presence of the deleted allele among Ivorians (0.06), confirming the low deletion frequency of this polymorphism found in Sub Saharan Africa by other authors. For Italians, frequency analysis of this gene polymorphism (0.28 for the deleted allele) did not show any significant level of differentiation with respect to other Italian and European populations.

Erythrocyte polymorphisms in five ethnic groups of Northern Côte d'Ivoire.

Distribution of some erythrocyte polymorphisms was investigated in five Northern Côte d'Ivoire ethnic groups. For the ABO blood group system, the frequencies of alleles p, q and r were 0.119, 0.150 and 0.731, respectively, while the frequencies of alleles D and d of the Rh blood group system were 0.726 and 0.274, respectively. These values are consistent with published data, while the high incidence of HbAS genotype could result from microevolutionay trends acting on this relatively small population. No 27-bp Southeast Asian ovalocytosis gene deletion was found in the sample.

ACE and LRPAP1 insertion-deletion polymorphisms in a northern Ivory Coast population.

The ACE and the LRPAP1 gene insertion-deletion polymorphisms were determined in 133 healthy individuals sampled from Ouangolodougou, a village located in northern Ivory Coast. No sex differences were found in ACE and LRPAP1 gene frequencies. The ACE insertion and deletion alleles had frequencies of 0.346 and 0.654, respectively. The ACE gene was not in Hardy-Weinberg equilibrium because of an excess of heterozygote genotypes and a deficiency of I/I genotypes compared to the expected values. Statistical analysis showed a significantly lower frequency of I/I genotypes in the Ivory Coast population compared to Sudan, Kenya, African Americans, and African Brazilians (p < 0.05), whereas no differences were found with respect to Somalia. Conversely, the frequencies of the insertion and deletion alleles in the Ivorian population did not differ from those of other African populations. The LRPAP1 insertion and deletion allele frequencies found in our study (0.192 and 0.808, respectively) did not differ significantly from the Czech and Spanish populations, the only two populations previously characterized for this polymorphism. However, the frequency of the I/I genotype was significantly lower than the frequencies observed in the European samples. Because of the limited information on the LRPAP1 gene polymorphism distribution in worldwide populations, it was not possible to draw any conclusion.

Tyrosine kinase inhibitors: from rational design to clinical trials.

Protein kinases play a crucial role in signal transduction as well as in cellular proliferation, differentiation, and various regulatory mechanisms. The inhibition of growth related kinases, especially tyrosine kinases, might provide new therapies for diseases such as cancer. The progress made in the crystallization of protein kinases has confirmed that the ATP-binding domain of tyrosine kinases is an attractive target for drug design. Three successful examples of drug design at Novartis using a tyrosine kinase as a molecular target are described. PKI166, a pyrrolo[2,3,-d]pyrimidine derivative, is a dual inhibitor of both the EGFR and the ErbB2 kinases. The compound entered clinical trials in 1999, based on its favorable preclinical profile: potent inhibition of EGF-mediated signalling in cells, in vivo antitumor activity in several EGFR overexpressing xenograft tumor models in nude mice, long-lasting inhibition of EGF-stimulated EGFR autophosphorylation in tumor tissue, good oral bioavailability in animals, and no prohibitive in vitro and in vivo toxicity findings. The anilino-phthalazine derivative PTK787/ZK222584 (Phase I, co-developed by Schering AG, Berlin) is a potent and selective inhibitor of both the KDR and Flt-1 kinases with interesting anti-angiogenic and pharmacokinetic properties (orally bioavailable). STI571 (Glivec, Gleevec), a phenylamino-pyrimidine derivative, is a potent inhibitor of the Abl tyrosine kinase, which is present in 95% of patients with chronic myelogenous leukemia (CML). The compound specifically inhibits proliferation of v-Abl and Bcr-Abl expressing cells (including cells from CML patients) and shows anti-tumor activity as a single agent in animal models at well-tolerated doses. Pharmacologically relevant concentrations are achieved in the plasma of animals (oral administration). Promising data from phase I and II clinical trials in CML patients (98% haematological response rate in Phase I) support the fact that the STI571 represents a new treatment modality for CML. In addition, potent inhibition of the PDGFR and c-Kit tyrosine kinases also indicates its possible clinical use in solid tumors.

Convergent synthesis of potent peptide inhibitors of the Grb2-SH2 domain by palladium catalyzed coupling of a terminal alkyne.

A new strategy was developed to prepare in a very efficient and convergent manner C-terminal modified tripeptides with high affinities for the Grb2-SH2 domain. Using Pd(PPh3)2Cl2 as catalyst, selected naphthyl iodides and triflates were coupled to Ac-Pmp(t-Bu)2-Ac6c-Asn-NH(prop-2-ynyl). The resulting alkyne derivatives were hydrogenated and deprotected to afford potent Grb2-SH2 inhibitors.

Structure-based design and synthesis of phosphinate isosteres of phosphotyrosine for incorporation in Grb2-SH2 domain inhibitors. Part 1.

Based on X-ray crystal structure information, mono charged phosphinate isosteres of phosphotyrosine have been designed and incorporated in a short inhibitory peptide sequence of the Grb2-SH2 domain. The resulting compounds, by exploiting additional interactions, inhibit binding to the Grb2-SH2 domain as potently as the corresponding doubly charged (phosphonomethyl)phenylalanine analogue.

Structure-based design and synthesis of phosphinate isosteres of phosphotyrosine for incorporation in Grb2-SH2 domain inhibitors. Part 2.

A series of novel phosphinates, derived from 4-phosphonomethylphenylalanine, are described as isosteres of phosphotyrosine. Benzyl (or alkyl) phosphinomethylphenylalanine derivatives were prepared by alkylation of an amino acid P-H phosphinate.

Synthesis and biological evaluation of highly potent analogues of epothilones B and D.

A series of new epothilone B and D analogues incorporating fused hetero-aromatic side chains have been prepared. The synthetic strategy is based on olefin 3 as the common intermediate and allows variation of the side-chain structure in a highly convergent and stereoselective manner. Epothilone analogues 1a-d and 2a-d are more potent inhibitors of cancer cell proliferation than the corresponding parent epothilones B or D.

Selective GRB2 SH2 inhibitors as anti-Ras therapy.

Given the key role of Ras in the mitogenic signaling by receptor tyrosine kinases, several targets upstream of Ras may prove to be excellent targets for drugs in the treatment of cancer caused by oncogenic tyrosine kinases. CGP78850 is a potent competitor of Grb2 SH2-phosphopeptide interactions. This inhibitor has been obtained by rational drug design and is specific toward the Grb2 SH2 vs. other SH2 domains and the PTB domain of SHC in vitro. Accordingly, CGP78850 blocks epidermal growth factor receptor (EGFR)-Grb2 and Shc-Grb2 interactions in living cells. It also inhibits the growth of cells transformed by receptor tyrosine kinases, which transmit a proliferative signal through Grb2 to Ras, but not cells transformed by oncogenic Raf or cells that contain activating Ras mutations. Moreover, our results demonstrate that, in cells overexpressing receptor tyrosine kinases, such as the EGFR, Grb2 SH2 inhibitors induce expression of the cell cycle inhibitors p21(Waf1/Cip1/CAP1) and p27(Kip1) and reverse transformation.

Effect of potent and selective inhibitors of the Grb2 SH2 domain on cell motility.

Cell motility has been correlated both with oncogenic invasiveness and metastatic potential. The development of selective inhibitors of motility has thus great potential importance. Grb2 is a SH2/SH3 domain-containing adaptor protein that links growth factor receptor tyrosine kinases to the Ras signaling pathway. We have developed specific small molecule inhibitors of the Grb2 SH2 domain as potential leads for drug discovery. Synthesis of the inhibitors and their effects on growth factor-induced growth in cells have been reported previously. In the current study, we establish that these inhibitors inhibit hepatocyte growth factor/scatter factor-induced A431 and Madin-Darby canine kidney cell motility and various cell motility-related events, including epidermal growth factor-induced ruffling of A431 cells and epidermal growth factor-induced translocation of the small GTPase Rac in these cells. We demonstrate for the first time a direct role for Grb2 in cell motility and indicate a new avenue for cancer therapeutics.

Structure-based design of a non-peptidic antagonist of the SH2 domain of GRB2.

The structure-based design and synthesis of a completely non-peptidic, micromolar antagonist of the SH2 domain of Grb2 is presented. The compound mimics the two main pharmacophores of the natural ligand, the phenylphosphate of the phosphotyrosine residue and the beta-carboxamide of the X+2 asparagine, which are linked by a rigid aromatic spacer.

Highly potent inhibitors of the Grb2-SH2 domain.

Highly potent inhibitors of the Grb2-SH2 domain have been synthesized. They share the common sequence: Ac-Pmp-Ac6c-Asn-NH-(3-indolyl-propyl). Different substituents at the 3-indolyl-propylamine C-terminal group were explored to further improve the activity. This is the first example of inhibitors of SH2 domains with sub-nanomolar affinity reported to date.

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).

Structural basis for the high affinity of amino-aromatic SH2 phosphopeptide ligands.

An anthranyl moiety placed at the N terminus of a phosphotyrosine peptide potentiates the inhibitory effect of this small peptide on the binding of the Grb2 SH2 domain to the EGF receptor. Using molecular modeling procedures based on the Lck SH2 domain structure, this observation was rationalized in terms of a suitably favorable pi-pi stacking interaction between the anthranyl moiety and the arginine alphaA2 (ArgalphaA2) residue side-chain of Grb2 SH2. The crystal structure of the Grb2 SH2 domain in complex with the inhibitor 2-Abz-EpYINQ-NH2 (IC50 26 nM) has been solved in two different crystal forms at 2.1 and 1.8 A resolution. This structure confirms the modeling based on the Lck SH2 domain. The ArgalphaA2 residue is conserved in most SH2 domains. Thus, as expected, the anthranyl group also confers high affinity to small peptide ligands of other SH2 domains such as Lck-, PLC-gamma-amino-terminal and p85 amino-terminal SH2 domains as demonstrated by structure affinity relationships (SAR) data. These potent peptides with an amino-terminal surrogate group and the structure of Grb2 SH2 domain in complex with one such peptide represent good starting points for the design and optimization of new inhibitors of many SH2 domains.

Structure-based design of peptidomimetic ligands of the Grb2-SH2 domain.

We have designed and synthesized a (3-aminomethyl-phenyl)-urea scaffold to mimic the X+1-Asn part of the minimal phosphopeptide sequence, Ac-pTyr-X+1-Asn-NH2, recognized by the Grb2-SH2 domain. The resulting compounds show the same degree of affinity as their peptide counterparts for the Grb2-SH2 domain. This is the first example reported to date of ligands of the Grb2-SH2 domain with substantially reduced peptidic character.

Discovery of 3-aminobenzyloxycarbonyl as an N-terminal group conferring high affinity to the minimal phosphopeptide sequence recognized by the Grb2-SH2 domain.

The observation that anthranilic acid as N-terminal group produces a dramatic increase of the binding affinity of the phosphopeptide sequence Glu-pTyr-Ile-Asn for the Grb2-SH2 domain was rationalized by molecular modeling. The model, which invokes a stacking interaction between the N-terminal group and the SH2 domain residue Arg alpha A2, was subsequently used to design the 3-aminobenzyloxycarbonyl N-terminal group. The latter confers high affinity (IC50 = 65 nM in an ELISA assay) to the minimal sequence pTyr-Ile-Asn recognized by the Grb2-SH2 domain.

Dual specificity of Src homology 2 domains for phosphotyrosine peptide ligands.

SH2 domains mediate protein-protein interactions and are involved in a wide range of intracellular signaling events. SH2 domains are 100-amino acid stretches of protein that bind to other proteins containing phosphotyrosine residues. A current major research goal is formulation of the structural principles which govern peptide-binding specificity in SH2 domains. Several structures (both X-ray and NMR) of SH2 domains have now been determined. Short peptide fragments on the carboxyl-terminal side of the phosphotyrosine residue carry the sequence specific information for SH2 recognition. The bound peptides are held in an extended conformation. However, for the GRB2 SH2 domain, the peptide adopts a beta-turn as the motif for recognition [Rahuel, J., et al. (1996) Nat. Struct. Biol. 3, 586-589]. Our SAR data and molecular modeling studies suggest that many SH2 domains, such as the SH2 domains of Lck, Src, and p85, can interact with high affinity with short peptide sequences at least in two ways which are sequence-dependent. The peptide forms either an extended chain across the D-strand of SH2 domains with anchors at pY and pY+3 or, as in the case of GRB2 SH2, a beta-turn with anchors at pY and pY+2. Due to a bulky tryptophan in its EF1 loop, GRB2 SH2 cannot bind peptide conformations such as the extended chain and thus has a unique specificity.