Metronomic paclitaxel-loaded mPEG–PLA nanoparticles show enhanced anti-tumor efficacy compared to maximum tolerated dose administration

Low-dose metronomic (LDM) chemotherapy with cytotoxic agents, aimed at disrupting tumor endothelial cells, is an alternative method to maximum tolerated dose chemotherapy targeting proliferating tumor cells in clinical practice. However, even in the LDM schedule, cytotoxic agents still exhibit serious side effects due to non-distribution and high accumulated doses in the body. Nanocarriers can maximize the efficacy of the encapsulated drug by adjusting the pharmacokinetics and bio-distribution pattern, and minimize excessive toxic side effects. In the present study, we prepared polyethylene glycol (PEG)-coated stealth nanoparticles containing paclitaxel (PTX-NP) in order to evaluate their accumulation in tumor and their anti-tumor activity following LDM administration. PTX-NPs were prepared by a modified emulsification/solvent diffusion method with methoxy PEG–poly(lactide). The in vitro viability, migration, and tube formation of primary human umbilical vein endothelial cells, in addition to thrombospondin-1 positive expression and microvessel density in vivo, confirmed the anti-angiogenic activity of PTX-NP. The cellular uptake and retention study, in addition to pharmacokinetics in Sprague–Dawley rats demonstrated sustained circulation of PTX-NP. The in vivo tumor accumulation of PTX-NP was monitored using the Xenogen IVIS 200 non-invasive optical imaging system. The anti-tumor activity of LDM PTX-NP was studied in B16 melanoma cancer-bearing mice in vivo. In conclusion, PTX-NP improved tumor accumulation and anti-tumor efficacy following LDM administration.