Combination of metronomic administration and target delivery strategies to improve the anti-angiogenic and anti-tumor effects of triptolide.

The metronomic administration of a low-dose cytotoxic agent with no prolonged drug-free breaks is an anti-angiogenic cancer treatment method. The use of nano-formulations in this manner enhances anti-tumor efficacy and reduces toxicity by inhibiting angiogenic activity, reduces adverse effects, and changes the biodistribution of TP in the body, steering TP away from potentially endangering healthy tissues. The present study uses liposomes and Asn-Gly-Arg (NGR) peptide conjugated aminopeptidase N(APN)-targeted liposomes for triptolide (TP), as a model for the investigation of targeted metronomic administration and subsequent effects on the toxicity profile and efficacy of the chemotherapeutic agent. Metronomic NGR-PEG-TP-LPs have been found to have enhanced anti-tumor activity, a phenomenon that is attributed to an increase in angiogenic inhibition properties. In vitro experiments demonstrate that the viability, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) are obviously suppressed in comparison with that of other treatment groups. In vivo experiments also demonstrate that the anti-tumor efficacy of targeted metronomic administration is superior to that of liposome-administered treatments given at maximum tolerated dose (MTD) schemes, as is evidenced by markedly decreased tumor volume, vessel density, and the volume of circulating endothelial progenitor cells (CEPCs) in serum. Moreover, we observed that the metronomic administration of NGR-PEG-TP-LPs could elevate thrombospondin-1 (TSP-1) expression in tumors, a finding that is consistent with the promotion of TSP-1 secretion specifically from HUVECs. Additionally, metronomic NGR-PEG-TP-LPs have minimal drug-associated toxicity (weight loss, hepatotoxicity and nephrotoxicity in mice). Our research demonstrates the significance of targeted metronomic administration using liposomes for anti-angiogenic cancer therapy.