DEVELOPMENT OF A REPRODUCIBLE IN-VITRO METHOD FOR ASSESSING THE BIODEGRADATION OF PROTEIN MICROSPHERES

Protein microspheres have been used for passive targeting of therapeut ic agents by chemoembolisation. The overall efficacy of such systems i s influenced by the in vivo degradation of the carrier matrix. In this paper we demonstrate a reproduceable method for assessing the degrada tion behaviour of protein microspheres using laser light scattering ap paratus and a model protease trypsin. Degradation has been quantified in terms of the characteristic time dependent effect of the enzyme on the measured volume concentration of the particles. The latent time (T 1) before the particles start to swell and the time taken to reduce th em to fifty percent of their original volume (T50) have been measured. Increasing trypsin concentrations up to 0.4% w/v reduce these values for example, the T50 of bovine serum albumin microspheres reduces from 150 min in 0.1% w/v trypsin to 50 min in 0.4% w/v. Degradation rate i s also dependent on the protein matrix used for example casein microsp heres provide a T50 of 150 min whilst transferrin samples provide valu es of 400 min. This in vitro method will allow comparison of different matrix proteins and investigation of the effects of changes in the me thodology of microsphere preparation.