Development and characterization of a novel drug delivery system with an affinity for fibronectin in vitro

Date of Completion

January 2000

Keywords

Chemistry, Pharmaceutical|Health Sciences, Pharmacy

Degree

Ph.D.

Abstract

The objective of this research was to develop gelatin based microspheres as targeted drug delivery systems with an affinity for fibronectin bearing surfaces which are associated with a number of disease states such as inflammatory disorders, cardiovascular disease, rheumatoid arthritis and cancer. Gelatin microspheres have been developed which have affinity for fibronectin-bearing surfaces exploiting the interaction between gelatin and fibronectin. Heparin was used to enhance this interaction. Poly (lactic-co-glycolic acid) copolymer (PLGA) microspheres were selected since they have reproducible and slow release characteristics in vivo. The PLGA microspheres were surface modified with gelatin to impart fibronectin recognition. The drug chosen for this project was dexamethasone since it is beneficial in chronic human diseases associated with extra fibronectin expression, including cardiovascular disease, inflammatory disorders and rheumatoid arthritis. ^ Both gelatin microspheres (gelatin-heparin complex coacervate and monolithic gelatin microspheres) and gelatin surface modified PLGA microspheres (adsorption, conjugation and spray-coating) were investigated and characterized in terms of: encapsulation efficiency, particle size, in vitro release and affinity for fibronectin. Dexamethasone was analyzed using a reversed-phase high performance liquid chromatography (HPLC) method. Any effect of microsphere cross-linking on heparin activity was evaluated using both metachromatic (azure A) and activated particle thromboplastin time (APTT) methods. Any effect of surface modification and cross-linking on gelatin-fibronectin interaction was evaluated using a direct binding method and analyzed using a bicinchoninic acid (BCA) protein assay. ^ Methods for microsphere preparation (gelatin-heparin complex coacervate, monolithic gelatin) and gelatin surface modification of PLGA microspheres (adsorption, conjugation and spray-coating) were developed. Non-aggregated microspheres with mean particle sizes within the range 1–10 μm. were prepared. Heparin incorporated gelatin microspheres had higher interaction with fibronectin compared to gelatin microspheres. Chemical cross-linking did not affect the interaction of gelatin with fibronectin and did not alter the bioactivity of heparin. Gelatin coated PLGA microspheres had higher interaction with fibronectin compared to other gelatin surface modified PLGA microspheres (adsorption and conjugation). The gelatin microspheres had fast release rates (within one day) whereas the gelatin surfaced modified PLGA microspheres had slow release rates (over 21 days). Blending these two populations of microspheres can provide initial rapid release and sustained release. ^

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