Development and in vitro/in vivo evaluation of controlled release delivery systems for a LHRH analogue, orntide acetate

The first objective was to evaluate the effectiveness of a novel luteinizing hormone—releasing hormone (LHRH) analogue, Orntide acetate, to suppress testosterone levels in a rat animal model and to diminish initial testosterone elevation caused by treatment with LHRH superagonists. Animals received injections of liquid Orntide, liquid Leuprolide, Orntide poly(d, l-lactide-co-glycolide) (PLGA) microspheres (ms) and Leuprolide PLGA ms. Injection of liquid Orntide resulted in immediate testosterone suppression but the suppression lasted less than a day. Simultaneous injection of Orntide and Leuprolide or pretreatment with Orntide before Leuprolide administration did not eliminate the initial elevation in testosterone. Administration of Orntide ms resulted in rapid and prolonged chemical castration in rats. This formulation showed potential for sustained delivery of the peptide over extended periods of time.; The second objective was to establish a reliable in vitro release method. A new method utilizing a dialysis technique and acetate buffer as the release medium was developed and evaluated. The method did not require frequent centrifugations, allowed sampling and release medium replacement without loss of microspheres, and the obtained release profiles correlated well with in vivo results.; The final objectives were to develop and evaluate 30-day and 120-day Orntide formulations. Polymers were characterized by molecular weight, polydispersity, acid number and glass transition temperature. Ten batches of PLGA and poly( d,l-lactide) (PLA) ms were prepared and characterized for drug content, bulk density, size, surface morphology and thermal properties. Peptide was analyzed by FT-MALDI mass spectrometry and quantitated with reverse phase HPLC. The particles were spherical with a relatively nonporous surface. The internal structure of fractioned ms varied markedly and particles with very porous, granular and solid interior were observed by scanning electron microscopy. Incorporation of the peptide into the polymeric matrix did not alter its structural integrity. In vitro release from Orntide ms was studied with the dialysis method and was influenced by pH of the release medium. Peptide adsorption to PLGA and PLA was dependent upon pH and acid number and was a major factor affecting release from the systems. Administration of Orntide ms to rats resulted in immediate castration and the suppressed levels of testosterone were maintained for 30 or 120 days. The apparent in vivo release rates were generally higher compared to the in vitro release profiles. Overall, controlled delivery of Orntide acetate over desired periods of time was achieved by polymer selection and optimization of manufacturing parameters.