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 125I. The copolymer was [125I] iodinated in the organic medium by a chloramine T method. The labeling efficiency was about 5%, and the agent was freed from [125I] 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 125I-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 125I 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 along residence time in the blood stream and, therefore, it could be employed as a drug delivery system for inflammatory and cancer treatment.