Role of positions 9 and 10 in the endothelin molecule for biological activity and discrimination of receptor subtypes

The importance of residues 9 and 10 in endothelin-1 was assessed by studying the responses of the guinea-pig ileum to [Ala9]endothelin-1 and [Ala10]endothelin-1. Both analogues induced relaxation followed by contraction. [Ala9]Endothelin-1 showed similar ED50 values and maximum response to those of endothelin-1, whereas [Ala10]endothelin-1 showed a larger ED50 value and was a partial agonist. Endothelin-1 and [Ala10]endothelin-1 induced similar degrees of tachyphylaxis, whereas [Ala9]endothelin-1 induced very little tachyphylaxis, indicating that Lys9 is important for inducing tachyphylaxis. Apamin inhibited the relaxation induced by endothelin-1 and [Ala9]endothelin-1 but not that induced by [Ala10]endothelin-1. BQ-123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu), a specific endothelin ETA receptor antagonist, inhibited [Ala9]endothelin-1-, but not [Ala10]endothelin-1-induced contraction. Cross-tachyphylaxis and additivity studies indicated that [Ala9]endothelin-1, like endothelin-1, acts at the endothelin ETA receptor, whereas [Ala10]endothelin-1 behaved as an endothelin ETB receptor agonist, like sarafotoxin S6c. Thus, the residue at position 10 plays a significant role in receptor activation and is a candidate for further exploration of receptor antagonism.

Side-reactions in peptide synthesis. 2. Formation of by-products in the large-scale synthesis of THF-gamma 2 by solution synthesis

The impurities which formed in the large-scale synthesis of THF-gamma 2, an immunomodulatory peptide of formula H-Leu-Glu-Asp-Gly-Pro-Lys-Phe-Leu-OH, were identified by a combination of analytical methods, and their structure confirmed by synthesis. Most impurities originated from side-reactions involving the aspartyl residue (cyclization, beta-aspartyl formation and cleavage). Based on this knowledge, modifications were introduced into the work up and the purification procedure which resulted in a very pure final product (> 99% by RP-HPLC).

Conformational studies on bombesin antagonists: CD and NMR characterization of [Thr6, Leu13 psi(CH2NH) Met14] bombesin (6-14)

The conformational flexibility of the [Thr6, Leu13 psi(CH2NH) Met14] bombesin (6-14) nonapeptide has been studied by CD and one- and two-dimensional (1D and 2D) nmr techniques. The CD and nmr parameters in different solvents and in a micellar environment (SDS) are compared with the data collected for the parent bombesin (BN) and [D-Phe12, Leu14]BN. A preliminary investigation on spantide is also reported. In particular, the results obtained from CD measurements indicate that there is a shift from random coil structures, in aqueous solutions, toward folded structures in apolar media (2,2,2-trifluoroethanol) and in a membrane-mimetic environment (40 mM SDS) for all three peptides, namely BN, [D-Phe12, Leu14]BN, and [Thr6, Leu13 psi(CH2NH) Met14]BN (6-14). Spantide, which also possesses some inhibitory activity against BN but very little sequence similarity, even in water, shows an ordered conformation. Nuclear magnetic resonance parameters such as backbone NH-alpha CH coupling constant values, amidic temperature coefficients, and the presence of only sequential nuclear Overhauser effects have not provided, so far, any clear evidence for a preferential ordered structure in the peptides studied, and this may be due to rapid exchange among different conformers in the nmr time scale.

Fluorescence, CD, and NMR studies on spantide, a bombesin and substance P antagonist

The conformational properties of spantide [(D-Arg, D-Trp, Leu) substance P] have been studied by fluorescence, CD, and nmr techniques. The fluorescence, CD, and nmr parameters in different solvents and in a micellar environment (SDS) are compared with the data collected for bombesin. A preliminary investigation on [D-Pro] spantide is also reported.

Bombesin receptor antagonists [corrected]. 1. Analogues with deleted, inverted or substituted amino acid residues

Bombesin is a 14-residue peptide hormone which serves a variety of biological functions, including cell growth control in Swiss 3T3 cultured fibroblasts. It has been also involved in an autocrine system regulating the growth of small cell lung carcinoma. A series of bombesin analogues were developed by amino acid deletion, inversion or substitution in the carboxy-terminal region, identified by the target cell receptor. Their properties were examined for: i) competitive binding assays; ii) mitogenic induction and inhibition assays; iii) effects on early cellular events (inositol phosphates production and protein tyrosine phosphorylation). Inversion of the Trp residue, or deletion of the C-terminal tripeptide amide, induced complete loss of receptor affinity and biological effects. Deletion of the His residue, or its derivatization as His (Dnp) in conjunction with Met deletion or modification, gave rise to compounds with reduced receptor affinity and weak antagonistic properties. Other modifications in the C-terminal tripeptide affected the potency but not the biological profile of the parent peptide. These results indicate the basis for the eventual design of improved, specific bombesin receptor antagonists and stimulate further studies on their possible application in the therapy of human small cell lung cancer.

Synthetic peptides reproducing the EGF-receptor segment homologous to the pp60v-src phosphoacceptor site. Phosphorylation by tyrosine protein kinases

The octapeptide E-E-K-E-Y-H-A-E, corresponding to the amino acid sequence 841-845 of EGF receptor, whose tyrosine-845 is homologous to the main phosphorylation site of pp60v-src, has been synthesized together with seven shorter peptides encompassing variable segments around the tyrosine residue. The peptides have been employed as model substrates for inspecting the local structural determinants of three tyrosine protein kinases (TPKs), namely; TPK-IIB and TPK-III, isolated from lymphoid cells (Eur. J. Biochem. 172, 451-457 (1988] and the TPK encoded by the oncogene of Abelson murine leukemia virus. The phosphorylation order with the different peptide substrates is variable depending on the TPK used: in particular, the lysine residue at position -2 relative to tyrosine proved especially harmful with TPK-IIB, the peptides K-E-Y-H and K-E-Y-H-A-E being very poor substrates compared with their shorter derivatives devoid of the N-terminal lysine (E-Y-H and E-Y-H-A-E, respectively). Conversely, such a basic residue is well tolerated by the other two TPKs. The negative effect of the N-terminal lysine on TPK-IIB-catalyzed phosphorylation is accounted for by an increase of Km and can be overcome by the presence of additional glutamic acid(s) on that side. On the other hand, the C-terminal acidic doublet Ala-Glu specifically impairs the phosphorylation efficiency of abl-TPK, by lowering the Vmax value, the heptapeptide E-K-E-Y-H-A-E being much less readily phosphorylated than E-K-E-Y-H. Collectively, these results would indicate that the site specificity of tyrosine protein kinases results from the balance of positive and negative determinants whose influence on the catalytic activity of the individual enzymes can differ greatly.

Syntheses of tetra- and pentapeptides from skin extracts of Phyllomedusa rhodei (tryptophyllins)

Syntheses by solution methods of tryptophyllins -4 and -5 (TPH-4 and TPH-5), tetra- and pentapeptides isolated from the skin extracts of the South American frog Phyllomedusa rhodei, are reported. The incorporation of the Pro2-Pro3 sequence into pentapeptides and the use of flash chromatography for purification of intermediates and target compounds are discussed. Preliminary biological results seem to indicate a growth-promoting activity for this peptide family.

Synthesis and preliminary biological investigations of O-sulphated dermorphin

Synthesis by a classical solution method of a sulphated analogue of dermorphin is reported. The product has proved to be devoid of any peripheral and central opiate- or CCK-like activity in the tests assayed.

Synthetic peptides related to the dermorphins. II. Synthesis and biological activities of new analogues

A new series of analogues of the potent opiate-like peptides dermorphins (mainly tetra- and pentapeptides) were synthesized in order to better evaluate the structure-activity relationships. Relative potencies were referred to dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2), the prototype of this class of frog skin peptides. Peripheral opioid activity (guinea-pig ileum and mouse vas deferens) was determined for all the dermorphin analogues. For a selected number of them also central analgesic (hot plate and tail-flick tests) and cataleptic activities were assayed in the rat by intracerebroventricular administration.

Tetracycline derivatives. Note III - 7- and 9-methyltetracyclines: synthesis and biological activity

The synthesis of some 7- and 9-methyltetracyclines is reported together with the biological activity of the new compounds.