Tumor targeting of doxorubicin by anti-MT1-MMP antibody-modified PEG liposomes

Immunoliposomes are potent carriers for targeting of therapeutic drugs to specific cells. Membrane type-1 matrix metalloproteinase (MT1-MMP), which plays an important role in angiogenesis, is expressed on angiogenic endothelium cells as well as tumor cells. Then, the MT1-MMP might be useful as a target molecule for tumor and neovascularity. In the present study, we addressed a utility of antibodies against the MT1-MMP as a targeting ligand of liposomal anticancer drug. Fab′ fragments of antibody against the MT1-MMP were modified at distal end of polyethylene glycol (PEG) of doxorubicin (DXR)-encapsulating liposomes, DXR-sterically stabilized immunoliposomes (DXR-SIL[anti-MT1-MMP(Fab′)]). Modification with the antibody significantly enhanced cellular uptake of DXR-SIL[anti-MT1-MMP(Fab′)] into the HT1080 cells, which highly express MT1-MMP, compared with the non-targeted liposomes (DXR-stealthliposomes (DXR-SL)), suggesting that MT1-MMP antibody (Fab′) is a potent targeting ligand for the MT1-MMP expressed cells. In vivo systemic administration of DXR-SIL[anti-MT1-MMP(Fab′)] into the tumor-bearing mice showed significant suppression of tumor growth compared to DXR-SL. This is presumably due to the active targeting of immunoliposomes for tumor and neovascularity. However, tumor accumulation of DXR-SIL[anti-MT1-MMP(Fab′)] and DXR-SL were comparable, suggesting that both liposomal formulations accumulated in tumor via enhanced permeation and retention (EPR) effect, but not via targeting to the MT1-MMP expressed on both the endothelial and tumor cells. It appears that the enhanced antitumor activity of DXR-SIL[anti-MT1-MMP(Fab′)] resulted from acceleration of cellular uptake of lioposomes owing to the incorporated antibody after extravasation from capillaries in tumor.