iRGD is a tumor tissue penetrating peptide due to its targeted binding of integrin and neuropilin-1 receptors. Whether iRGD carries the liposomes in a similar way as it penetrates the cancer drugs or conjugated drugs into tumor tissues and cells has not been fully defined. Here, iRGD-modified and doxorubicin-loaded sterically stabilized liposomes (iRGD-SSL-DOX) and passive liposomes (SSL-DOX) were prepared. A series of experiments were performed to evaluate the tissue penetration, cell penetration, tumor blood vessel damage and anti-tumor effect. The results of flow cytometry and confocal microscopy studies showed that iRGD-SSL-DOX with 5% DSPE-PEG2000-iRGD achieved higher cellular uptake level than that of SSL-DOX on B16 melanoma cells. iRGD-SSL-DOX also exhibited stronger cell growth inhibition in cytotoxicity experiments. The tumor penetrating effect of iRGD was further confirmed by imaging and cellular uptake studies in vivo, in which higher distribution of iRGD-modified liposomes in tumor tissue and tumor cells was observed. Moreover, iRGD-SSL-DOX displayed improved tumor growth inhibition and anti-angiogenesis with less systemic toxicity in an armpit B16 melanoma model. In conclusion, iRGD reserved its tumor-penetrating properties well when modified on the surface of liposomes at optimal density and iRGD-SSL-DOX would be a promising drug delivery system for active targeting tumor therapy.
Keywords: B16 melanoma cells; iRGD; integrin receptors; neuropilin-1 receptors; tumor penetrating.