A pharmacokinetics study of radiolabeled micelles of a poly(ethylene glycol)-block-poly(caprolactone) copolymer in a colon carcinoma-bearing mouse model.

A copolymer of poly(ethylene glycol)-b-poly(caprolactone) (PEG-PCL) was modified with a benzyl moiety and labeled with I-131. A micelle system, (131)I-benzyl-micelles, formed from (131)I-benzyl-PEG-PCL and PEG-PCL-PC, was created and used for in vitro characterization and in vivo evaluation. Administration of (131)I-benzyl-micelles to a colon carcinoma-bearing mouse model gives a 4.9-fold higher tumor-to-muscle ratio at 48 h post-injection than treatment with the unimer (131)I-benzyl-PEG-PCL. Scintigraphic imaging, biodistribution results and pharmacokinetical evaluation all demonstrated that (131)I-benzyl-micelles are a plausible radioactive surrogate for PEG-PCL copolymer micelles. Modifying the amphiphilic copolymer with a benzyl moiety and labeled it with iodine-131 should make possible the real-time and noninvasive evaluation of the pharmacokinetics of copolymer micelles in vivo.