Metformin (MET) is an anti-diabetic drug effective against breast cancer, targeting breast cancer stem cells (BCSCs). MET-encapsulating liposome (LP-MET) and Herceptin-conjugated LP-MET (Her-LP-MET) were evaluated for their anti-cancer effect in vitro and in vivo. Size and zeta potentials of LP-MET and Her-LP-MET were suitable for enhanced permeability and retention effects. Her-LP-MET yielded greater inhibition of BCSC proliferation in vitro than free MET or LP-MET, as well as a dose-dependent long-term anti-proliferation effect. Further, the anti-migration effect of Her-LP-MET on BCSCs was superior to that of MET or LP-MET, and was enhanced when used in concert with doxorubicin (DOX). In a mouse model, Her-LP-MET combined with free DOX was more effective than free MET, free DOX, or Her-LP-MET. Moreover, Her-LP-MET combined with free DOX yielded tumor remission, whereas free DOX alone resulted in metastasis or death. As such, Her-LP-MET formulation is expected to provide a new therapeutic modality targeting BCSCs.
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