Kamel Besseghir

Cyclosporine A delivery to the eye: A pharmaceutical challenge

Systemic administration of cyclosporine A (CsA) is commonly used in the treatment of local ophthalmic conditions involving cytokines, such as corneal graft rejection, autoimmune uveitis and dry eye syndrome. Local administration is expected to avoid the various side effects associated with systemic delivery. However, the currently available systems using oils to deliver CsA topically are poorly tolerated and provide a low bioavailability. These difficulties may be overcome through formulations aimed at improving CsA water solubility (e.g. cyclodextrins), or those designed to facilitate tissue drug penetration using penetration enhancers. The use of colloidal carriers (micelles, emulsions, liposomes and nanoparticles) as well as the approach using hydrosoluble prodrugs of CsA have shown promising results. Solid devices such as shields and particles of collagen have been investigated to enhance retention time on the eye surface. Some of these topical formulations have shown efficacy in the treatment of extraocular diseases but were inefficient at reaching intraocular targets. Microspheres, implants and liposomes have been developed to be directly administered subconjunctivally or intravitreally in order to enhance CsA concentration in the vitreous. Although progress has been made, there is still room for improvement in CsA ocular application, as none of these formulations is ideal.

In vitro and in vivo evaluation of a somatostatin analogue released from PLGA microspheres.

The purpose of this study was to design poly(lactide-co-glycolide) (PLGA) microspheres for the continuous delivery of the somatostatin analogue, vapreotide, over 2-4 weeks. The microspheres were produced by spray-drying and the desired characteristics, i.e. high encapsulation efficiency and controlled release over 2-4 weeks, achieved through optimizing the type of polymer, processing solvent, and co-encapsulated additive. The in vitro release was tested in fetal bovine serum preserved with 0.02% of thiomersal. Furthermore, formulations were injected intramuscularly into rats to obtain pharmacokinetic profiles. Encapsulation efficiency was between 34 and 91%, depending on the particular formulation. The initial peptide release (within 6 h) was lowest, i.e. <20%, when acetic acid was used as processing solvent and highest, i.e. 57%, with dichloromethane. The various co-encapsulated additives generally lowered the encapsulation efficiency by 15-30%. The best formulation in terms of low burst and effective drug serum levels (>1 ng/ml) over 21-28 days in rats was the one made with end-group uncapped PLGA 50:50, the solvent acetic acid and the additive polyethyleneglycol. In conclusion, the optimization of formulation parameters allowed us to produce vapreotide-loaded PLGA microspheres of suitable characteristics for therapeutic use.

Injection-molding versus extrusion as manufacturing technique for the preparation of biodegradable implants

Polylactic acid (PLA) is a biocompatible and biodegradable material with wide utility for many applications, including the design of controlled-release systems for pharmaceutical agents. The factors determining the degradation kinetics of these systems include the composition and the molecular mass of the polymer, the morphology and the structure of the device, and the influence of thermal processes. The processing of the polymer determines the structure and design of the device, and influences to a high degree its morphology, namely its microporous structure, polymeric chain orientation and crystallinity.In this work, we aimed to compare the influence of two different implant manufacturing techniques, extrusion and injection-molding, on the in vitro degradation of the polymeric matrix. Both kinds of implants were loaded with a somatostatin analogue. Decrease in molecular weight, and polydispersity evolution during an accelerated in vitro degradation test were studied by size exclusion chromatography. Morphological changes in the polymeric matrix during degradation were followed after defined time intervals by means of scanning electron microscopy. Crystallinity studies were performed by differential scanning calorimetry and by X-ray analysis. Peptide stability in the polymeric matrix after both manufacturing methods was evaluated. Peptide release profiles, obtained in vitro during a week dissolution test, from both implant samples, were studied. It was shown that both molecular weight and polydispersity decreased after extrusion or injection-molding. This decrease was more pronounced with the latter technique. Crystallinity studies demonstrated that the crystalline network was not destroyed after both manufacturing methods. Peptide release profiles obtained in vitro were in good accordance with scanning electron microscopy. It was found that both manufacturing techniques had to be considered, although the extruded implants degraded more rapidly in vitro than the injection-molded ones.

Formation of peptide impurities in polyester matrices during implant manufacturing

Most peptides are susceptible, in vivo, to proteolytic degradation, and it is difficult to formulate and to deliver them without loss of biological activity. In addition, it is often desirable to release them continuously and at a controlled rate over a period of weeks or months. For these reasons, a controlled release system is suitable. Poly(lactic acid) (PLA) is a biocompatible and biodegradable material that can be used for many applications, including the design of injectable controlled release systems for pharmaceutical agents. Development of these delivery systems presents challenges in the assessment of stability, specially for peptide drugs. By means of an extrusion method, long-acting poly(lactic acid) implants containing vapreotide, a somatostatin analogue, were prepared. The nature of the main degradation product obtained after implant manufacturing was elucidated. It was found that the main peptide impurity was a lactoyl lactyl-vapreotide conjugate. Because lactide are found in small quantities in most commercially available PLA, the influence of residual lactide in the polymeric matrix, on the formation of peptide impurities during manufacturing, was specially investigated. This work demonstrates that the degree of purity of the carrier is of great importance with regard to the formation of peptide impurities.

Importance of the test medium for the release kinetics of a somatostatin analogue from poly(d,l-lactide-co-glycolide) microspheres

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20-40 microg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500-1000 microg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1-66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 microg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33+/-1% of the peptide were released within 4 days, whereas 53+/-2 and 61+/-0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by gamma-irradiation had only a minor effect on the in vivo pharmacokinetics.

Development and evaluation in vivo of a long-term delivery system for vapreotide, a somatostatin analogue

In recent years peptides and proteins have received much attention as candidate drugs. For many peptides, particularly hormones, it is desirable to release the drug continuously at a controlled rate over a period of weeks or even months. Polylactic acid and poly (lactic-co-glycolic) acid are well known biocompatible biodegradable materials with wide applications including the design of controlled-release systems for pharmaceutical agents. Polylactic acid implants containing vapreotide were prepared by an extrusion method and drug release was evaluated in vivo in rats using an RIA method The development of an injectable, biodegradable depot formulation of a somatostatin analogue (vapreotide) is described which ensures satisfactory peptide blood level in rats over approximately 250 days. A modification of this formulation by means of a wear coating allows minimisation of the initial burst a feature rarely discussed.

Analysis of the influence of polymer characteristics and core loading on the in vivo release of a somatostatin analogue

Abstract Peptides and proteins have received much attention in recent years as candidate drugs. Vapreotide (RC-160) is a somatostatin analogue used for the therapy of hormone-dependent tumors and endocrine disorders. Like other peptides, it cannot be administered by the oral route and its plasma half-life is relatively short after parenteral administration. For these reasons, its use would be greatly enhanced by a sustained delivery system capable of maintaining controlled plasma levels of the peptide over an extended period of time. Poly( d,l -lactide-co-glyco (PLGA) are biocompatible biodegradable materials useful for a variety of applications, including the design of controlled-release systems for pharmaceutical agents. RC-160 pamoate loaded implants are proposed in this work as a means for controlling the drug release. Various PLGA were studied as biodegradable drug carriers and their in vivo release profiles were examined. Poly( d,l -lactide-co-glycolide) implants containing RC-160 were prepared by an extrusion method and the drug release was evaluated in vivo in rats using a radioimmunoassay method. The effects on the release profile, obtained by varying molecular weight, lactide/glycolide ratio and core loading were studied. The effects of polymer end groups were also investigated. Gel permeation chromatography was employed to characterize the loss in molecular weight of the different polymers after extrusion and γ-sterilization. It was found that drug loading, polymer molecular weight, copolymer composition and end group modifications were critical factors affecting the in vivo release properties. However, even though complex problems still exist, controlled release of peptides from biodegradable PLGA matrices can be achieved.

Stability studies of a somatostatin analogue in biodegradable implants.

In recent years, peptides and proteins have received much attention as drug candidates. For many polypeptides, particularly hormones, it is desirable to release the drug continuously at a controlled rate over a period of weeks or even months, and thus a controlled release system is needed. Polylactic acid (PLA) is a biocompatible and biodegradable material with wide utility for many applications, including the design of controlled release systems for pharmaceutical agents. Pharmaceutical development of these delivery systems presents new problems in the area of stability assessment, especially for peptide drugs. In this study, we aimed to investigate the influence of different steps, during the manufacturing of an implant, on peptide stability in the polymeric matrix. Polylactic acid implants containing vapreotide, a somatostatin analogue, were prepared by extrusion. The effects of time, extrusion and temperature on the peptide stability were studied. The influence of various gamma sterilization doses, as well as the conditions under which the implants were irradiated, were also investigated. Peptide stability in the polymeric matrix was evaluated at various temperatures and at various time intervals up to 9 months.