This study reports the antitumor effects of radioiodinated antisense oligonucleotides (ASON) mediated by anionic long-circulating liposomes (ALCL) on MCF-7 breast cancer cells in vitro and the pharmacokinetics and tissue distribution of ALCL in vivo. Our results found that ALCL improves the delivery of radioiodinated ASON, characterized by significant apoptosis, decreased cell survival, and suppressed bcl-2 protein expression in MCF-7 cells. ALCL exhibited bicompartmental clearance and demonstrated significantly favorable pharmacokinetic properties including long half-life, slow clearance, and a large concentrationtime curve. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 2028, 2012; View this article online at . DOI 10.1002/adv.20231