Doxorubicin (Dox) is one of the most commonly used and highly effective antineoplastic agents, but the clinical application of this broad spectrum drug is largely hampered by its poor stability and serious toxicity to normal tissues. Hence, it is essential to improve the therapeutic effect and decrease the systematic toxicity for the administration of doxorubicin. In our study, doxorubicin was incorporated into monomethoxy poly(ethylene glycol)-poly(ε-caprolactone) (MPEG-PCL) micelle by a self-assembly method. The cytotoxicity and cellular uptake efficiency of Dox-loaded MPEG-PCL (Dox/MPEG-PCL) micelle against B16-F10 murine melanoma cells was examined by the methylthiazoltetrazolium (MTT) test and flow cytometry. The antitumor activity of Dox/MPEG-PCL was evaluated in C57BL/6 mice injected subcutaneously with B16-F10 cells. Toxicity was evaluated in tumor-free mice. Meanwhile, tumor proliferation, intratumoal angiogenesis and apoptotic cells were evaluated by PCNA, CD31 staining and TUNEL assay, respectively. Encapsulation of doxorubicin in MPEG-PCL micelle improved the cytotoxicity of doxorubicin and enhanced its cellular uptake on B16-F10 cell in vitro. Administration of Dox/MPEG-PCL micelle resulted in significant inhibition (75% maximum inhibition relative to controls) in the growth of B16-F10 tumor xenografts and prolonged the survival of the treated mice (P<0.05). These anti-tumor responses were associated with marked increase of tumor apoptosis and notable reduction of cell proliferation and intratumoral microvessel density (P<0.05). The system toxicity also decreased in the Dox/MPEG-PCL group compared with free doxorubicin group. Our data indicate that the encapsulation of doxorubicin in MPEG-PCL micelle improved the anti-tumor activity in vivo without conspicuous systemic toxic effects.

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