Wolfgang Naumann

Fluorescence Spectroscopic Determination of the Critical Aggregation Concentration of the GnRH Antagonists Cetrorelix, Teverelix and Ozarelix

The fluorescence spectroscopic behavior of three 2-naphthylalanine containing Gonadotropin-releasing hormone (GnRH) antagonists Cetrorelix, Teverelix and Ozarelix has been investigated concerning their aggregation process in comparison to the non-aggregating peptide D-Phe6-GnRH. The aim of the present investigation consisted in developing a method to determine the critical aggregation concentration for these decapeptides. This was achieved by monitoring the incorporation of the fluorescent probe 1-anilino-8-naphthalene sulfonate (ANS) into aggregates and utilizing the modification of band shape and intensity of the intrinsic peptide fluorescence emission depending on the analyzed peptide concentrations. Finally an approach for the explanation of the observed band characteristics is presented analyzing the fluorescence of fragments Cetrorelix1–4 and Cetrorelix1–6.

Modification of the In Vitro Release Profile of Cetrorelix by Complexation with Biophilic Partners

Cetrorelix is a GnRH antagonist of the third generation. Its manifold therapeutic potential requires the adjustment of its resorption rates and effect profiles. The method of non-covalent complexation with suitable partner molecules enables the development of customized depot formulations. Investigating new partners and synthesis methods for Cetrorelix complexes we focused on maximal biocompatibility of the complexes. Compared to traditional depot forms the application of complexes aims at decreased aggregation of the peptide and increased biophily of the depots. The pharmacological properties of the new Cetrorelix complexes were analyzed by standardized dynamical in vitro liberation experiments. A new pharmacokinetic model has been developed and successfully applied for the quantitative analysis of the liberation profiles. With aromatic carboxylic acids and dipeptides we could synthesize stable complexes that have nearly linear release characteristics in aggregating environments close to in vivo conditions. The release rates were specific and very different for the complex partners. Thus several complexes have a great potential for a linear, characteristic release of the peptide in vivo and can be the basis for new depot forms for Cetrorelix.