Zsolt Vadasz

A specifically radiolabeled somatostatin analog with strong antitumor activity induces apoptosis and accumulates in the cytosol and the nucleus of HT29 human colon carcinoma cells

The new heptapeptide somatostatin analog TT-232 decreases proliferation of HT-29 human colon carcinoma cells in vitro by reducing mitotic and increasing apoptotic activity. We have synthesized and characterized a specifically tritium labeled 3H-Tyr3-TT-232 (30 Ci/mmol) to investigate the effect and the fate of this antitumor peptide on human colon tumor cells. 3H-labeled TT-232 could be detected on the cell surface, on cytoplasmic membranes and also in the nucleus of HT-29 cells, 1–6 h after the administration of 0.5 and 50 μg/mL [3H]TT-232. Binding and internalization of TT-232 to human colon tumor cells at a relatively high dose provide further evidence for the existence of low-affinity somatostatin receptors in such cells, which might mediate the apoptosis-inducing effect. Our data suggest the possible use of TT-232 in the treatment of human colon tumors.

Potent GnRH agonists containing L-amino acid derivatives in the six position

New agonists related to gonadotropin-releasing hormone (GnRH) have been synthesized that are comparable in potency to the GnRH and its superagonists for release of LH and estrus suppression without substitutions with D- or unnatural amino acids in position 6. We now report a series of L-beta-aspartyl-6 GnRH analogs containing only naturally occurring L-amino acids in the whole sequence, exhibiting considerable in vivo biological activity. Dose and time dependent LH release capability of the different analogs in adult male mice, estrus suppression comparisons and blockade of ovulation in female rats are given. The incorporation of L-Asp-OMe and L-Asp-OBzl in position 6 of GnRH resulted in the most potent GnRH agonists (to 12-20xGnRH potency) in this series inducing a biphasic biological response similar to the D-amino acid-6 substituted superactive GnRH analogs. A correlation between the LH releasing potencies of the analogs and their HPLC retention times was also investigated. Peptide synthesis were achieved using either solid phase or solution phase methodology.

Aspartate racemization in synthetic peptides. Part 2. Tendency to racemization of aminosuccinyl residue

Aminosuccinyl (Asu) peptides, containing a strained ring system, are very vulnerable to epimerization and, during their formation, even as transients, in the presence of nucleophilic and nonnucleophilic bases, partial epimerization occurs. In the presence of nucleophilic bases, Asu-peptides transform to a partially epimerized mixture of α- and β-aspartyl peptides, with the preponderance of the β- over the α-peptides. In the absence of any internal basic functionality such as the protonated guanidino group, chirally pure Asu-peptides could be synthesized by heating of β-benzyl-aspartyl [Asp(OBzl)] peptides in dimethylformamide to elevated temperatures or, from aspartyl (Asp) peptides having a free carboxy group, by the usual treatment with pentafluorophenol or 1-hydroxybenzotriazole-dicyclohexylcarbodiimide. However, in the presence of the strongly basic acetate ion and/or a guanidinium group the probability of aspartate racemization is increased.

High-performance liquid chromatographic monitoring of transpeptidation reactions in analogues of gonadotropin releasing hormone containing aspartic acid derivatives in position six

High-performance liquid chromatographic systems were used for monitoring the hydrolysis of five potent agonistic gonadotropin releasing hormone analogues containing aspartic acid derivatives in position six. To separate the closely related nonapeptides formed during the hydrolysis, columns with reversed-phase packings were used under isocratic conditions. The mobile phases were methanol containing ammonium acetate or triethylammonium phosphate buffers. Good separations of the hydrolysis products from the investigated peptides allowed the reaction rate constants for the transformations examined to be calculated.

Studies on epimerization-free methods for the preparation of aminosuccinyl peptides

We have found that guanidine acetate catalyses the transformation of a β-benzyl-aspartyl peptide (Boc-Asp-(OBzl)-Leu-Trp-OMe) to an aminosuccinyl peptide (Boc-Asu-Leu-Trp-OMe). The reaction was accompanied by partial epimerization. However, not even a small amount of epimerization could be detected when the aminosuccinyl peptide was synthesised from Boc-Asp-Leu-Trp-OMe with the addition of DIC, HOPfp and guanidine acetate (as a catalyst). This reaction seems to be suitable for the epimerization-free solid phase synthesis of aminosuccinyl peptides, e.g. Asu6-Lamprey-III-GnRH (Glp-His-Trp-Ser-His-Asu-Trp-Lys-Pro-Gly-NH2).