125I-labeled PLA/PEO block copolymer:: Biodistribution studies in rats

Block copolymers have a potential utility as drug carriers. In order to study their in vivo fate, the biodegradable block copolymer poly(D,L-lactide ethylene oxide) (PLA/PEO) (Mw 5000/5000) with a p-methoxyphenyl moiety was radio labeled with I-125. The copolymer was [I-125] iodinated in the organic medium by a chloramine T method. The labeling efficiency was about 5%, and the agent was freed from [I-125] iodide by dialysis. The tissue distribution of radioactivity was determined at 5 min, 1, 2 and 24 hrs after intravenous injection of male rats with I-125-labeled copolymer in the dose 4.5-5.5 mg/kg. After administration of the labeled copolymer, a high concentration of radioactivity in the liver during the. initial time intervals was found. At the subsequent intervals after dosing, an increase in I-125 activity in the bowels was determined. The distribution of radioactivity into inflamed areas was evaluated as well. The inflammatory-to-non-inflammatory muscle tissue ratios increased with time from 2.18 (5 min), 3.63 (1 h) to 3.68 (2 hrs); after 24 hrs, this ratio was significantly lower (1.70). The PLA/PEO copolymer exhibits a long residence time in the blood stream and, therefore, it could be employed as a drug delivery system for inflammatory and cancer treatment.