Dual-self-recognizing, stimulus-responsive and carrier-free methotrexate–mannose conjugate nanoparticles with highly synergistic chemotherapeutic effects†
Carrier-free nanoparticles (NPs) via chemotherapeutic drug–drug conjugate assembly are a promising alternative for tumor chemotherapy. However, these NPs are still hindered via their nonspecific internalization into certain healthy cells and tissues. Herein, dual-acting methotrexate (MTX) and mannose (MAN) were conjugated via a hydrolyzable ester bond to synthesize a MTX–MAN conjugate as one molecule, which could be directly self-assembled into stimulus-responsive carrier-free NPs (MTX–MAN NPs) in aqueous solution. Such carrier-free MTX–MAN NPs with an accurate drug to sugar ratio could achieve on-demand drug release by dual stimuli of lysosomal acidity and esterase. Besides, MTX–MAN NPs could be dual-recognized by tumor cells in vitro and specifically by tumors in vivo. Moreover, the large proportion of MAN located on the NPs’ surface could exert a shielding effect to avoid phagocytosis of macrophages, leading to long blood circulation. Therefore, the MTX–MAN NPs sharply reduced the drug dosage and decreased the toxicity to normal cells and tissues. Further in vitro and in vivo studies consistently confirmed that the MTX–MAN NPs exhibited superior tumor accumulation and highly synergistic chemotherapeutic effects. Furthermore, we found for the first time that MAN could enhance the antitumor activity of MTX. Considering that bi-functional MTX and MAN are approved via the FDA, and MAN is highly biosafe, the dual-self-recognizing, stimulus-responsive, and carrier-free MTX–MAN NPs might be a simple, selective, and safe chemotherapeutic strategy.