Polyamino acid microspheres: Preparation, characterization and distribution after intravenous injection in rats

A series of poly(hydroxypropyl l-glutamine) (PHPG) microspheres (mean diameter 2-3 μm) modified from poly(benzyl 1-glutamate) (PBLG) were prepared and characterized. The microspheres were radiolabeled with ¹³¹1 for in vivo evaluation. Two different labeling methods were used for these particles. For PHPG, microspheres were directly labeled with ¹³¹ I via Iodogen. For PBLG, microcapsuies loaded with a radiotracer ([¹³¹I]ethyliopanoate) were prepared. The tissue distribution of these particles was studied after intravenous injection in rats. The liver uptake of PHPG microspheres at 20 minutes postadministration was reduced from 74 to 19% of injected dose when hydrophilicity of PHPG microspheres increased. Such reduction was also noted by increasing blood activity and decreasing spleen activity. Moderate clearance of PHPG microspheres from the liver and the spleen was observed in the experimental period (2 days), suggesting that the polymer was degraded. The hydroxy functional groups present on the surface of poly (hydroxypropyl l-glutamine) microspheres allow attachment of targeting devices or drugs. Thus they may find potential applications as targetable drug carriers.