Tumor Microenvironment-Responsive Ultrasmall Nanodrug Generators with Enhanced Tumor Delivery and Penetration

Tumor microenvironment-induced ultrasmall nanodrug generation (TMIUSNG) is an unprecedented approach to overcome the drug penetration barriers across complex biological systems, poor circulation stability and limited drug loading efficiency (DLE). Herein, a novel strategy was designed to synthesize metal–organic nanodrug complexes (MONCs) through supramolecular coassembly of photosensitizer sinoporphyrin sodium, chemotherapeutic drug doxorubicin and ferric ions. Compared with the free photosensitizer, MONCs produced 3-fold more reactive oxygen species (ROS) through the energy transfer-mediated fluorescence quenching. Remarkably, the self-delivering supramolecular MONCs with high DLE acted as a potent ultrasmall-nanodrug generator in response to the mild acidic tumor microenvironment to release ultrasmall nanodrugs (5–10 nm in diameter) from larger parental nanoparticles (140 nm in diameter), which in turn enhanced the intratumor permeability and therapeutic efficacy. The key mechanism of MONC synthesis wa...