Accumulation of protein-loaded long-circulating micelles and liposomes in subcutaneous Lewis lung carcinoma in mice

The purpose of our work was to compare the biodistribution and tumor accumulation of a liposome- or micelle-incorporated protein in mice bearing subcutaneously-established Lewis lung carcinoma. A model protein, soybean trypsin inhibitor (STI) was modified with a hydrophobic residue of N-glutaryl-phosphatidyl-ethanolamine (NGPE) and incorporated into both polyethyleneglycol(MW 5000)-distearoyl phosphatidyl ethanolamine (PEG-DSPE) micelles (< 20 nm) and PEG-DSPE-modified long-circulating liposomes (ca. 100 nm). The protein was labeled with 111In via protein-attached diethylene triamine pentaacetic acid (DTPA), and samples of STI-containing liposomes or micelles were injected via the tail vein into mice bearing subcutaneously-established Lewis lung carcinoma. At appropriate time points, mice were sacrificed and the radioactivity accumulated in the tumor and main organs was determined. STI incorporated into PEG-lipid micelles accumulates in subcutaneously established Lewis lung carcinoma in mice better than the same protein anchored in long-circulating PEG-liposomes. Small-sized long-circulating delivery systems, such as PEG-lipid micelles, are more efficient in the delivery of protein to Lewis lung carcinoma than larger long-circulating liposomes.