"Watson-Crick G[triple bond, length as m-dash]C"-inspired supramolecular nanodrug of methotrexate and 5-fluorouracil for tumor microenvironment-activatable self-recognizing synergistic chemotherapy.

Carrier-free nanodrugs, generated via the straightforward small-molecule self-assembly of anticancer drugs, provide a promising route for cancer chemotherapy. However, their low structural stability, lack of targeting specificity, and poor stimulus responsiveness are still limiting their therapeutic effect. Inspired by Watson-Crick G[triple bond, length as m-dash]C base pairing, the FDA-approved chemo-drug methotrexate (MTX, which can bind with folate receptors) and 5-fluorouracil (5-FU, a DNA/RNA synthetase inhibitor) were adopted for direct assembly into self-recognizing MTX-5-FU nanoparticles via "Watson-Crick-like base pairing"-driven precise supramolecular assembly. Sequentially, our synthesized weak acidity-responsive polyethylene glycol (PEG) was inserted onto the nanoparticle surface to temporarily shield the self-targeting function of MTX and prolong the blood circulation time. Once PEG-MTX-5-FU nanoparticles reached the weakly acidic tumor microenvironment, the PEG corona could be cleaved from their surface and then MTX could be re-exposed to recover its self-recognition ability and significantly elevate tumor cell uptake; furthermore, the de-PEGylated MTX-5-FU nanoparticles could respond to the stronger acidity of lysosome, triggering core disassembly and thus the burst release of both MTX and 5-FU. Further in vitro and in vivo studies consistently confirmed that the nanodrugs exhibited preferable accumulation at the tumor sites with highly synergistic chemotherapeutic effects. The supramolecular recognition-inspired, cascade-triggered self-targeting and controlled release of nanodrugs could be a promising strategy to improve synergistic chemotherapy.