Influence of new deltorphin analogues on reinstatement of cocaine-induced conditioned place preference in rats.

The aim of this study was to investigate whether the δ-opioid receptors are involved in the rewarding and reinstatement effect of cocaine in the conditioned place preference (CPP) test. Male Wistar rats were conditioned with cocaine (5 mg/kg) or saline in a biased CPP procedure. The intracerebroventricular (i.c.v.) administration of naltrindole (5 nmol), δ-opioid receptor antagonist but not ß-funaltrexamine (5 nmol), or nor-binaltorphimine (10 nmol), µ-opioid and κ-opioid receptor antagonists, respectively reversed the expression of the cocaine CPP. The i.c.v. administration of new analogues of deltorphins with potent agonist activity at δ-opioid receptors, such as cyclo(N, N-carbonyl-D-Orn, Orn)deltorphin (DEL-6) at the dose of 10 and 20 nmol and deltorphin II N-(ureidoethyl)amide (DK-4) at the dose of 10 and 20 nmol reinstated the rewarding effect of cocaine after extinction sessions in the CPP test. Naltrindole (5 nmol, i.c.v.) abolished the reinstated effect of DK-4 (10 nmol). In addition, DEL-6 and DK-4 induce anxiolytic-like effects in the elevated plus-maze test. However, neither peptide given alone either produced a rewarding effect in the CPP test, or influenced the locomotor activity and motor coordination, thus suggesting that these effects of peptides did not influence the results obtained in the reinstatement procedure of CPP. In conclusion, our results show that δ-opioid receptors play a dominant role in cocaine reward and reinstatement of cocaine seeking behavior in the CPP test.

A method for evaluation of activity of growth hormone-releasing hormone analogues.

OBJECTIVE: It has been found that hGH-RH analogues with increased resistance to enzymatic degradation have a much higher potency than the native hGH-RH (1-29)-NH2 and have an ability to partially reverse growth hormone deficiencies. THE AIM: The aim of these studies was to elaborate a method which can be used for preliminary evaluation of new GH-RH analogues both from the point of view of their potency to release GH and enzymatic stability. METHOD: Two highly active GH-RH analogues with increased resistance to trypsin-like enzymes, and hGH-RH(1-29)-NH2 used as a standard, in doses 1 nM, 10 nM, and 100 nM were added to pituitary rat cell culture, and medium was collected after 30, 60, 120 and 240 min. GH concentration was measured by RIA kit. RESULTS: It was observed that the potency of these two GH-RH analogues was several times higher than that of native compound. Moreover, the stimulation was much longer. This suggests that high activity of these analogues in vivo could be the result of increased enzymatic stability. CONCLUSION: This method can be used for selecting more potent and more stable releasing peptides before in vivo evaluation.

Synthesis and biological activity of homoarginine-containing opioid peptides.

Two tris-alkoxycarbonyl homoarginine derivatives, Boc-Har{omega,omega'-[Z(2Br)]2}-OH and Boc-Har{omega,omega'-[Z(2Cl)]2}-OH, were prepared by guanidinylation of Boc-Lys-OH, and used for the synthesis of neo-endorphins and dynorphins. The results were compared with that obtained in the synthesis in which Boc-Lys(Fmoc)-OH was incorporated into the peptide chain, and after removing Fmoc protection, the resulting peptide-resin was guanidinylated with N,N'-[Z(2Br)]2- or N,N'-[Z(2Cl)]2-S-methylisourea. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. The results indicated that replacement of Arg by Har may be a good avenue for the design of biologically active peptides with increased resistance to degradation by trypsin-like enzymes.

p-Nitrophenoxycarbonyl derivatives of Boc-protected diaminoalkanes in the synthesis of enkephalin peptidomimetics.

The synthesis of p-nitrophenoxycarbonyl derivatives of 1-Boc-1,2-diaminoethane, 1-Boc-1,3-diaminopropane and 1-Boc-1,4-diaminobutane is described. These derivatives were used to synthesize five peptidomimetics, analogues of enkephalin, containing alkylurea units inside the peptide chain and at the C-terminal. All syntheses were carried out in solid phase on MBHA resin. Peptidomimetics with alkylurea units inserted into the peptide chain were synthesized using the standard method employing the Boc-strategy, with TFA deprotection and HF cleavage. The analogue containing a C-terminal alkylurea unit was synthesized using the Boc-strategy, with HCl/dioxane deprotection and TFA cleavage. All of the analogues were examined for opioid activity in GPI and MVD assays. The activity of the analogue containing a C-terminal alkylurea unit was comparable to that of [Leu5]-enkephalin, while the other analogues were less active.

New tris-alkoxycarbonyl arginine derivatives for peptide synthesis.

alpha-Alkoxycarbonyl protected ornithines were treated with N,N'-[Z(2Cl)](2)-S-methylisothiourea and N,N'-[Z(2Br)](2)-S-methylisothiourea, N,N'-Z(2)-S-methylisothiourea and N,N'-Boc(2)-S-methylisothiourea to form N(alpha, omega, omega')-tris-alkoxycarbonyl arginines. Two of them, Boc-Arg-{omega,omega'-[Z(2Br)](2)}-OH and Boc-Arg-{omega,omega'-[Z(2Cl)](2)}-OH, were used for the synthesis of dermorphin fragments containing two or three arginine residues. Examination of the products by HPLC and ESI-MS revealed that the purity of the materials obtained with the use of the new derivatives was higher than that obtained in concurrent syntheses in which Boc-Arg(Tos) was used.

Potent trypsin-resistant hGH-RH analogues.

A series of analogues of hGH-RH-(1-29)-NH2 designed to have metabolic stability has been synthesized. Standard Boc-SPPS was employed, modified to permit the guanidinylation of amino side-chains after chain assembly but before release from the resin. [Dat1, Har(11, 12, 20, 21, 29), Ala15, Nle27, Asp28]-, [Dat1, Har(11, 20, 29), Orn12, Ala15, Nle27, Asp28]-, and [Dat1, Gap(11,12, 21, 29), Ala15, Har20, Nle27, Asp28]-hGH-RH-(1-29)-NH2 were completely resistant to trypsin and about 50 times as potent as hGH-RH-(1-29)-NH2 itself when injected subcutaneously in rats. These peptides are candidates for clinical application in the therapy of GH deficiency.

New potent hGH-RH analogues with increased resistance to enzymatic degradation.

Four hGH-RH analogues containing homoarginine (Har) and/or D-Arg were obtained by solid-phase methodology using Boc-chemistry. To introduce Har residues, a Lys(Fmoc) protected Lys derivative was incorporated in the appropriate positions (11, 12, 20, 21 or 29): after assembly of the peptide chain the Fmoc group was removed and the peptide-resin was guanidinylated by treatment with N,N'-bis(tert-butoxycarbonyl)-S-methylisothiourea. The peptides were cleaved from the resin by treatment with liquid HF, and the products were purified by RP-HPLC. The peptides were subjected to digestion by trypsin, and the course of the reaction was followed by HPLC and ESI-MS. It was found that peptide bonds formed by the carboxyl group of Har are completely stable to trypsin. The course of cleavage at Lys or Arg residues depends on the position of Har in the sequence. All the analogues investigated stimulate the release of GH in rats after subcutaneous administration, and were about 50-100 times as potent as rGH-RH itself. The analogues had no effect on PRL, LH and FSH levels.