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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.

The purpose of this study was to develop and evaluate a dialysis in vitro release technique for peptide-containing poly(d, l-lactide-co-glycolide) (PLGA) microspheres (ms) that would correlate with in vivo data. Using a luteinizing hormone- releasing hormone analogue (LHRH), Orntide acetate, solubility and stability were determined in 0.1 M phosphate buffer (PB), pH 7.4, and in 0.1 M acetate buffer (AB), pH 4.0, with high-performance liquid chromotography (HPLC), and peptide permeability through a dialysis membrane (molecular weight cut-off 300,000) was determined. Orntide ms were prepared by a dispersion/solvent extraction/evaporation method and characterized for drug content (HPLC), particle size distribution (laser diffraction method), and surface morphology (scanning electron microscopy). In vitro release was studied in PB using a conventional extraction method and with a new dialysis method in AB. Gravimetric analyses of polymer mass loss and matrix hydration, and peptide adsorption to blank PLGA ms (50:50, M(w) 28 022) were carried out in PB and AB upon incubation at 37 degrees C. Serum Orntide and testosterone levels in rats after administration of Orntide ms were determined by radioimmunoassay. Orntide acetate solubility was influenced by pH; approximately 2.3 mg/mL dissolved in PB and > 18 mg/mL in AB. Stability was pH- and temperature-dependent. The peptide was very stable at pH 4.0, 4 degrees C, but degraded rapidly at pH 7.4, 37 degrees C. Peptide permeability through the dialysis membrane was accelerated by agitation and >95% equilibrium was reached within 48 hours. The overall release rate was higher with the dialysis method. Mass loss of the Orntide ms was faster in AB (50% loss in 3 weeks; 95% in 35 days) than in PB (65% in 35 days). In contrast, hydration after 35 days was 4-fold higher in PB. The nonspecific adsorption to blank ms was greater in PB (128 microg Orntide/10 mg PLGA) compared with AB (< 5 microg Orntide/ 10 mg PLGA). Administration of 30-day Orntide PLGA ms to rats resulted in an initial serum Orntide level of 21 ng/mL after 6 hours and a Cmax of 87 ng/mL after 6 days. Testosterone levels were suppressed immediately after ms administration (3 mg Orntide /Kg) from 5.2 ng/mL to 0.3 ng/mL (after 24 hours) and remained suppressed for 38 days. Orntide acetate solubility and degradation kinetics were markedly influenced by pH of the buffer systems and mass loss; matrix hydration, as well as the nonspecific adsorption to blank ms, was pH-dependent. The in vitro release profile obtained with the dialysis method in AB correlated well with the in vivo data, thereby providing a more reliable prediction of in vivo performance.

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 µ 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.

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

Orntide acetate was found to be an effective LHRH antagonist with a rapid onset of pharmacological action and a short biological half-life. Administration of a single dose of liquid Orntide or Orntide microspheres, resulted in rapid testosterone suppression without an initial elevation, as seen with LHRH superagonists. However, combined administration of Orntide and Leuprolide did not have an effect on the initial testosterone elevation in rats.