Effect of the concurrent LHRH antagonist administration with a LHRH superagonist in rats

Acute gonadotropin-releasing hormone agonist treatment enhances extinction memory in male rats

Leuprolide acetate (LEU), also known as Lupron, is commonly used to treat prostate cancer in men. As a gonadotropin-releasing hormone (GnRH) receptor agonist, it initially stimulates the release of gonadal hormones, testosterone (T) and estradiol. This surge eventually suppresses these hormones, preventing the further growth and spread of cancer cells. Individuals receiving this treatment often report anxiety and cognitive changes, but LEU's effects on the neural mechanisms that are involved in anxiety during the trajectory of treatment are not well known. In this study, we examined the acute effects of LEU on fear extinction, hypothesizing that increased T levels following a single administration of LEU will facilitate extinction recall by altering neuronal activity within the fear extinction circuitry. Two groups of naïve adult male rats underwent a 3-day fear conditioning, extinction, and recall experiment. The delayed group (n=15) received a single injection of vehicle or LEU (1.2mg/kg) 3weeks before behavioral testing. The acute group (n=25) received an injection one day after fear conditioning, 30min prior to extinction training. Following recall, the brains for all animals were collected for c-fos immunohistochemistry. Blood samples were also collected and assayed for T levels. Acute administration of LEU increased serum T levels during extinction training and enhanced extinction recall 24h later. This enhanced extinction memory was correlated with increased c-fos activity within the infralimbic cortex and amygdala, which was not observed in the delayed group. These results suggest that the elevation in T induced by acute administration of LEU can influence extinction memory consolidation, perhaps through modification of neuronal activity within the infralimbic cortex and amygdala. This may be an important consideration in clinical applications of LEU and its effects on anxiety and cognition.

Thymosin β4 sustained release from poly(lactide-co-glycolide) microspheres: synthesis and implications for treatment of myocardial ischemia

A sustained release formulation for the therapeutic peptide thymosin β4 (Tβ4) that can be localized to the heart and reduce the concentration and frequency of dose is being explored as a means to improve its delivery in humans. This review contains concepts involved in the delivery of peptides to the heart and the synthesis of polymer microspheres for the sustained release of peptides, including Tβ4. Initial results of poly(lactic-co-glycolic acid) microspheres synthesized with specific tolerances for intramyocardial injection that demonstrate the encapsulation and release of Tβ4 from double-emulsion microspheres are also presented.

Modification of the tri-phasic drug release pattern of leuprolide acetate-loaded poly(lactide-co-glycolide) microparticles

Leuprolide acetate-loaded poly(lactide-co-glycolide) (PLGA RG503H) microparticles prepared by the solvent evaporation method had a tri-phasic drug release pattern over a duration of up to 2 months. An initial release was followed by a slow drug release phase and a final rapid drug release. The objective of this study was to identify parameters, which shift the release profile from the tri-phasic to a more continuous release profile. Varying formulation and processing parameters (e.g., drug loading, volume of the external aqueous phase, using low molecular weight PLGA, different microparticle drying methods) affected the initial release (burst) but did not influence the drug release thereafter. The addition of the hydrophilic polymer polyvinylpyrrolidone (PVP) led to the formation of more porous microparticles. This influenced the initial release but did not change the tri-phasic drug release pattern. The inclusion of medium chain triglycerides (MCT) successfully shifted the tri-phasic pattern to a continuous release profile. MCT accelerated the leuprolide release in the second, slow release phase and reduced it in the final rapid release phase. MCT led to the formation of microparticles with an irregular surface and a highly porous inner structure. Differential scanning calorimetry (DSC) revealed a high encapsulation efficiency of MCT (88-105%) in the microparticles and an unchanged glass transition temperature (Tg) of PLGA.

Monitoring of peptide acylation inside degrading PLGA microspheres by capillary electrophoresis and MALDI-TOF mass spectrometry

The purpose of this research was to assess the acylation reactions of peptides, salmon calcitonin (sCT), human parathyroid hormone 1-34 (hPTH1-34) and leuprolide, in poly(lactic-co-glycolic acid) (PLGA) microspheres. Capillary electrophoresis (CE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were used for determining and monitoring peptide acylation and quantitating acylation products in the degrading PLGA microspheres. In the degrading PLGA microspheres of sCT and hPTH1-34, the acylation products were observed and determined to be adducts with glycolic acid units from degradable PLGA polymer by MALDI-TOF MS. In the microsphere of leuprolide, however, the acylation product was not observed even after 28 days of incubation at the release medium, which represents the different stabilities among peptides according to the primary structure. As the leuprolide contains tyrosine and serine having hydroxyl group of nucleophilic amino acids, the acylation reaction of peptide is shown to be mainly due to the primary amino groups of N-terminus or lysine residue. The complementary use of CE and MALDI-TOF MS will be useful for searching the counter measures as well as determining the peptide acylation in the manufactured formulations on the market.

Suppression and recovery of LH secretion by a potent and selective GnRH-receptor antagonist peptide in healthy early follicular-phase women are mediated via selective control of LH secretory burst mass

AIM

GnRH antagonists are competitive inhibitors of GnRH receptors. Their administration induces prompt suppression of the gonadal axis. In animals, GnRH antagonists upregulate the activity of GnRH-secreting neurones, which could cause gonadotrophin rebound following inhibition. The aim of this study was to evaluate the effects of a potent GnRH antagonist, Teverelix (TEV), on the gonadal axis in healthy young women.

SUBJECTS AND MEASUREMENTS

In nine women [20-35 years old, body mass index (BMI) 19-25 kg/m2] in the early follicular phase, serum LH and FSH levels were evaluated every 10 min from 08.00 to 12.00 h before, and 24 h and 96 h after TEV injection (2.5 mg in 1 ml subcutaneously on day 0). Serum gonadotrophin and oestradiol levels were also evaluated at baseline and at 6, 8, 12, 48, 72 h after TEV.

RESULTS

The antagonist reduced both serum LH and FSH concentrations; LH levels were significantly and promptly reduced at +6 h (nadir at +8 h) until +48 h and recovered at +72 h, while FSH levels were reduced (P<0.05) 24 h after the antagonist and normalized at +48 h. LH (but not FSH) concentrations at +96 h exceeded baseline (P<0.05). TEV suppressed oestradiol concentrations (P<0.05) with a nadir at +24 h, comparable reduction at +48 h and recovery to baseline at +72 h. Deconvolution analysis showed that the antagonist peptide suppressed (P<0.02) the pulsatile production rate, burst mass and amplitude of LH on day 1. Pulsatile FSH secretion also fell at this time (P<0.05). LH and FSH pulse frequency were not modified by TEV. At +96 h, LH pulsatility did not significantly differ from that at baseline. Suppression of mean LH or FSH concentrations did not affect the relative pattern regularity (approximate entropy) of LH and FSH secretion.

CONCLUSIONS

This study demonstrates that the acute administration of a potent GnRH antagonist induces prompt inhibition of the gonadal axis lasting for 2 days in women due to mechanistically specific suppression of LH secretory burst mass and the mean FSH secretion rate. The trend toward rebound release of LH following the end of the pharmacological effect of the antagonist could reflect a rise in endogenous GnRH activity.

Identification and determination of GnRH antagonist gelling at injection site

The purpose of this study was to first observe whether orntide, a GnRH antagonist, gels at the injection site and if so, to develop and validate an extraction method to quantitate the peptide amount as well as assess chemical stability in the gel. After subcutaneous injection of a large dose of orntide acetate solution, a white gel and local traumatized effect were observed at the injection site. Orntide remaining at the injection site was recovered by tissue excision, homogenization and tissue protein precipitation with perchloric acid and quantified by high performance liquid chromatography (HPLC) following separation on a C18 column. The standard curve was linear in the detection range and there was no interference from either blank tissue or excipients of the orntide formulation. The recovery from spiked tissue or that immediately following injection was in the range of 90-110%. MALDI-FT mass spectrometry (MS) of the peak fraction indicated that the orntide recovered from the injection site was in the intact form. The results showed that orntide solution, when injected at a large dose, formed a gel at the injection site. The gel delayed the release from the injection site and caused discernible tissue reaction.

Return to fertility after extended chemical castration with a GnRH antagonist

BACKGROUND

Antagonistic analogues of GnRH for the treatment of prostate cancer may be used clinically in persons for whom return to fertility after such treatment is important or desirable. The purpose of this study was, therefore, to evaluate the effects of a long term treatment with orntide, a GnRH antagonist, on testosterone levels and fertility in male rats.

METHODS

Two groups of male rats received either 120-day orntide microspheres (8.8 mg orntide/kg/120 days) or vehicle alone (control group). Serum orntide and testosterone levels in both groups were monitored at certain intervals for 9 months from the initiation of treatment. After recovery of normal serum testosterone levels in the treated animals, each rat was housed with two proven breeder, but drug-naive, females.

RESULTS

All mates of treated rats achieved pregnancy as rapidly as the mates of control rats although two of the control rats did not sire a litter with either female and one sired only one litter. The mean size of the litters of treated (12.3 offspring per litter) and control (10.6 offspring per litter) were similar. All offspring were grossly normal morphologically and behaviorally during the time to weaning.

CONCLUSIONS

These results suggest that lack of fertility due to testosterone suppression is reversible after cessation of treatment with this GnRH antagonist.

Preparation, characterization, and in vitro evaluation of 1- and 4-month controlled release orntide PLA and PLGA microspheres

PURPOSE

To prepare, characterize and evaluate in vitro sustained delivery formulations for a novel LHRH antagonist, Orntide acetate, using biodegradable microspheres (ms).

METHODS

Poly(d,l-lactide) (PLA) and poly(d,l-lactide-co-glycolide) (PLGA) were characterized for molecular weight (Mw, Mn) using gel permeation chromatography (GPC) and content of free end carboxyl groups (acid number, AN) by a titration method. 1- and 4-month Orntide ms were prepared by a dispersion/solvent extraction/evaporation process and characterized for drug content (HPLC), bulk density (tapping method), particle size (laser diffraction method), surface morphology (scanning electron microscopy, SEM), and structural integrity of encapsulated peptide by Fourier Transform Matrix Assisted Laser Desorption mass spectrometry (FT-MALDI). Peptide binding to PLA and PLGA and non-specific adsorption to blank ms was studied in 0.1 M phosphate buffer pH 7.4 (PB) and 0.1 M acetate buffer pH 4.0 (AB). In vitro release of peptide was assessed in PB and AB.

RESULTS

Mw for the PLGA copolymers varied from 10,777 to 31,281 Da and was 9,489 Da for PLA. AN was between 4.60 and 15.1 for the hydrophilic resomers and 0.72 for the hydrophobic 50:50 PLGA copolymer. Spherical ms (3.9 mu to 14 mu in diameter) with mostly nonporous surface and varying degree of internal porosity were prepared. FT-MALDI mass spectra of the extracted peptide showed that the encapsulation process did not alter its chemical structure. Peptide binding to PLGA and PLA and non-specific adsorption to blank PLGA ms were dependent upon pH and were markedly higher in PB than in AB. The initial in vitro release in PB varied from 0.5 to 26%/24 h but due to substantial binding of the peptide to the polymeric matrix the long-term release in PB could not be determined. Application of a dialysis method allowed for a more accurate determination of in vitro release and a good total drug recovery.

CONCLUSIONS

Orntide acetate was successfully incorporated into PLA and PLGA ms and the 1- and 4-month in vitro release profiles were achieved by polymer selection and optimization of the manufacturing parameters.

Evaluation of Orntide microspheres in a rat animal model and correlation to in vitro release profiles

Orntide acetate, a novel luteinizing hormone-releasing hormone (LHRH) antagonist, was prepared and evaluated in vivo in 30-day and 120-day sustained delivery formulations using a rat animal model. Orntide poly(d,l-lactide-co-glycolide) (PLGA) and poly(d,l- lactide) (PLA) microspheres were prepared by a dispersion method and administered subcutaneously in a liquid vehicle to rats at 2.2 mg Orntide/kg of body weight (30-day forms) or 8.8 mg Orntide/kg (120-day forms). Serum levels of Orntide and testosterone were monitored by radioimmunoassays, and a dose-response study at 4 doses (3, 2.25, 1.5, and 1.75 mg Orntide/kg) was conducted to determine the effective dose of Orntide. Microspheres with diameters between 3.9 and 14 micron were prepared. The onset and duration of testosterone suppression varied for different microsphere formulations and were influenced both by polymer properties and by microsphere characteristics. Microspheres prepared with 50:50 and 75:25 copolymers effectively sustained peptide release for 14 to 28 days, whereas an 85:15 copolymer and the PLA microspheres extended the pharmacological response for more than 120 days. Increase in drug load generally accelerated peptide release from the microspheres, resulting in higher initial serum levels of Orntide and shorter duration of the release. In general, apparent release was faster in vivo than under in vitro conditions. Orntide microspheres effectively suppressed testosterone in rats, providing rapid onset of release and extended periods of chemical castration. Testosterone suppression occurred immediately after microsphere administration without the initial elevation seen with LHRH superagonists.