Michael Ankersen

Investigation of bioisosters of the growth hormone secretagogue L-692,429

Abstract The synthesis and structure-activity relationships of several analogs of L-692,429 with modifications in the biaryl and tetrazole moieties are described and several derivatives were found to be equipotent or slightly more potent than L-692,429.

Growth hormone secretagogues derived from NN703 with hydrazidesas c-terminal

A series of GH secretagogues based on modifications in the C-terminal of NN703 is reported. The C-terminal N-methyl amide of NN703 has been replaced with alkylated hydrazides in order to decrease the volume of distribution and identify GH secretagogues with shorter duration of action. Most of the prepared compounds show high potency in a rat pituitary assay. Subsequent to an initial in vivo screening in dogs, four compounds were selected for further pharmacological and pharmacokinetic evaluation. The four compounds showed oral bioavailability around 35% and equipotency in vitro compared to NN703. The relationship between lipophilicity and volume of distribution is discussed and it is speculated whether the lower volume of distribution is attributed to the observed higher in vivo potency and shorter plasma elimination half-life.

Growth hormone secretagogues: recent advances and applications.

The discovery of a new class of compounds that stimulate the release of growth hormone (GH) in a manner distinctly different from growth hormone-releasing hormone (GHRH) is advancing the understanding of the mechanisms that control GH secretion. These compounds, the GH secretagogues, act at both pituitary and hypothalamic levels, and might even elicit effects in the CNS and peripheral systems. A receptor with high affinity for the GH secretagogues has been identified and several observations suggest the presence of additional receptors. The existence of these specific endogenous receptors could indicate that the mechanism of GH release is not yet fully understood. Several potential indications have been explored clinically and, as some of these compounds are orally active, they could offer attractive alternatives to recombinant human growth hormone (hGH) in treating GH disorders such as growth hormone deficiency (GHD), age-related conditions, obesity and catabolic conditions.

Kinetics of degradation of 4-imidazolidinone prodrug types obtained from reacting prilocaine with formaldehyde and acetaldehyde

The kinetics of decomposition of 4-imidazolidinone prodrug types obtained by reacting prilocaine (I) with formaldehyde and acetaldehyde has been studied in aqueous solution in the pH range 1-7.4 at 60 and 37 degrees C, respectively. At pH<5 the hydrolysis of the derivative derived from formaldehyde (II) to yield I obeyed apparent first-order kinetics. At higher pH, the decomposition reactions proceeded to an equilibrium and the reactions could be described by first- and second-order reversible kinetics. A plot of the logarithm of the apparent first-order rate constants for hydrolysis of II against pH resulted in a sigmoidal-shaped pH-rate profile characteristic for the hydrolysis of many N-Mannich bases. A half-life at pH 7.4 (60 degrees C) of 6.9h for compound II was calculated. Compared to II the 4-imidazolidinone derived from acetaldehyde (III) exhibited enhanced instability in aqueous buffer solutions. The decomposition was followed at 37 degrees C monitoring the decrease in concentration of intact (III). At acidic pH the reactions displayed strict first-order kinetics and the disappearance of III was accompanied by a concomitant formation of I. At pH 7.4, the rate data also applied reasonably well to first-order kinetics despite the observation that small amounts of III was formed at pH 7.4 from a solution containing equimolar concentrations of acetaldehyde and prilocaine (10(-4)M). In case of III, a bell-shaped pH-rate profile was obtained by plotting the logarithm of the pseudo-first-order rate constants against pH indicating the involvement of a kinetically significant intermediate in the reaction pathway and a change of the rate-limiting step in the overall reaction with pH. For the stability studies performed at pH 6.9 and 7.4 product analysis revealed that parallel to formation of (I) an unknown compound (X) emerged. Compared to III, compound X is hydrolysed to give I at a slower rate (t(50%)=30 h at 37 degrees C). Based on LC-MS data it is suggested that (X) is an isomeric form of III, which may exist in four diastereomeric forms. Thus, at physiological pH an initial relatively fast regeneration of I from III is to be expected followed by a slower drug activation resulting from hydrolysis of the isomeric form of III.

New highly potent dipeptidic growth hormone secretagogues with low molecular weight

Based on NN703, low molecular weight growth hormone secretagouges (GHSs) with a reduced number of hydrogen binding sites were designed by removal of the C-terminal amide group. The compounds were highly potent in combination with high efficacy in a rat pituitary cell assay, being characterized with EC(50) values down to 0.8 nM. Selected compounds were tested in in vivo animal models. The oral bioavailability in dogs was 16-44%. Also, the ED(50) values of the compounds were determined both in dog and swine.

Somatostatin Receptor Subtype 4 (sst4) Ligands: Synthesis and Evaluation of Indol-3-yl- and 2-Pyridyl-Thioureas

Thiourea analogues of NNC 26-9100 (2) were prepared as somatostatin receptor subtype 4 (sst4) ligands. The indole 9 exhibited high affinity (Ki = 23 nM) and about a 100-fold selectivity at sst4 compared to sst2 receptors. The (imidazol-4-yl) propyl group appears to play a major role in the affinity and selectivity of these thioureas at sst4.

Demonstration of the strength of focused combinatorial libraries in SAR optimisation of growth hormone secretagogues

Abstract Aseries of 96 growth hormone secretagogues, derived from ipamorelin are described. The compounds are prepared as a 6 × 4 × 4 member library on solid support using a PAL resin. The compounds are all acylated dipeptides, based on two aromatic amino acids and a free amino N-terminal. All compounds are characterised by HPLC, LC-MS and their ability to release GH in a pituitary cell based assay. The most potent compounds show EC50 values at 1 nM and are full agonists. We demonstrate the strength of focused combinatorial libraries and confirm the pitfall in broad SAR exploration by giving examples where selected fragments obviously show poor receptor interaction except in very defined structural arrangements.

Growth hormone secretagogues: discovery of small orally active molecules by peptidomimetic strategies.

Publisher Summary This chapter reviews that peptides are essential to many pharmacological processes as they are often of great interest in the drug-discovery process. It is the most challenging goals of modern medicinal chemistry to find rational principles for transforming the information provided by peptide ligands into lowmolecular-weight non-peptide molecules that bind to a target receptor. Such compounds are called peptidomimetics. The chapter discusses that low molecular weight peptidomimetics elicit similar pharmacodynamic effects as the native peptide and are expected to possess desirable pharmacokinetic properties superior to natural peptides, including good oral activity and long duration of action. Such compounds are; therefore, considered more useful targets for the drug discovery process. In principle, two types of peptidomimetics can be depicted. In the first one, the proposed pharmacophoric groups of the native peptide are kept in the correct spatial arrangement, but the peptide backbone is replaced with a non-peptidic scaffold. Such a scaffold may be reduced amides, N-methylated amides, D-aminoacids or any other organic scaffold, not related to a regular peptide bond. The second type does not necessarily hold any of the proposed pharmacophoric elements and may be structurally very distinct from the native peptide. The binding mode of such peptidomimetics is often quite different from the binding mode of the native peptide, but the pharmacological consequence is the same. Today, an extensive pool of peptidomimetic antagonists of G-protein coupled peptide receptors are known, while the number of nonpeptidic agonists is limited to agonists for angiotensin, cholecystokinin, bradykinin, opioid, arginine vasopressin, and somatostatin receptors.

Daily low-dose administration of growth hormone secretagogue stimulates pulsatile growth hormone secretion and elevates plasma insulin-like growth factor-1 levels in pigs.

Repeated administration of growth hormone secretagogues (GHSs) has proven to be a delicate matter owing to development of tolerance. The aim of the present study was to define conditions during which the responsiveness to the orally active NN703 was maintained over several days. Growing pigs were fitted with stomach and vascular catheters, permitting unstressed intragastric administrations and blood sampling. NN703 or vehicle was administered once daily. When NN703 was given at a dose of 18 mg/kg, there was a massive acute increase in plasma growth hormone (GH) levels, but this was only seen on the first day of administration. A dose of 1.8 mg/kg did not cause a significant acute increase in plasma GH concentrations, whereas stimulation of pulsatile GH release was sustained over a 4-d period. During the first 7 h following injection of vehicle, the area under the curve of plasma GH was 1211 ± 144 (µg/[L·7 h]), but increased to 1770 ± 269 and 1824 ± 198 (µg/[L·7 h]) on the first and fourth day of NN703 administration, respectively. Deconvolution analysis of the 7-h profiles revealed that the GH mass per burst as well as the GH burst amplitude were significantly (p < 0.001) increased during treatment with NN703, which led to an increase in pulsatile GH secretion rate (p < 0.001). Insulin-like growth factor-1 plasma concentrations increased steadily during NN703 administration (p < 0.01) and decreased after termination of treatment. The sustained increase in GH pulsatility observed with low-dose NN703 treatment suggests that development of tolerance to this GHS may be obviated by minimization of dose.

Highly potent growth hormone secretagogues: hybrids of NN703 and ipamorelin.

A series of NN703 analogues with lysine mimetics combined with naphthyl- or biphenylalanine in the core has been prepared and tested in vitro in a rat pituitary cell based assay and subsequently in vivo in pigs in a single dose at 50 nmol/kg. Re-introduction of certain pharmacophores in the C-terminal of NN703, which were originally removed during optimisation for oral bioavailability, led to unexpectedly potent compounds in vitro as well as in vivo.