Metronomic chemotherapy aiming at inhibiting tumor angiogenesis with conventional chemotherapeutics is a promising strategy for antiangiogenic cancer therapy. However, current metronomic chemotherapy mainly focuses on free small-molecule drugs, without any effort to achieve tumor-specific biodistribution, which may lead to long-term toxicity concerns. Metronomic chemotherapy using nanoparticulate drug delivery system (DDS) offers significant upside to reduce off-target side effects, decrease accumulated dose, and enhance the efficacy of tumor vessel targeting without compromising antitumor efficacy; but there has been a lack of thorough experimental data describing the targeted metronomic chemotherapy. Here, we develop a new nanoparticulate DDS, SP5.2 peptide conjugated, Flt-1 (VEGFR-1) targeted nanoparticles for docetaxel (SP5.2-DTX-NP), as a model for the investigation of targeted metronomic chemotherapy with respect to both antitumor efficacy and toxicity. The results demonstrate that metronomic SP5.2-DTX-NP exerts antitumor activity mainly through the antiangiogenic effect of docetaxel, which is specifically delivered into the tumor vascular endothelial cells through the nanoparticle internalization mediated by the interaction of SP5.2 and over-expressed Flt-1 receptors on tumor vessels. Moreover, the antitumor efficacy of targeted metronomic chemotherapy is better than that of the treatment with the DDS given in the maximum tolerated dose (MTD) regimen, which is shown in significantly prolonged mice survival and minimal drug-associated toxicity (bone marrow suppression, hematological toxicity, and mucosal injury of small intestine). The present research reveals and highlights the significance of targeted metronomic therapy with nanoparticulate DDS in antiangiogenic cancer therapy.
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