Capping Silica Nanoparticles with Tryptophan-Mediated Cucurbit[8]uril Complex for Targeted Intracellular Drug Delivery Triggered by Tumor-Overexpressed IDO1 Enzyme.

Nanosystems responsive to tumor-specific enzymes are considered as a highly attractive approach to intracellular drug release for targeted cancer therapy. Mesoporous silica nanoparticles are capped with tryptophan-mediated cucurbit[8]uril complex with Fe₃ O₄ to minimize the premature drug leakage while being able to deliver the payload on demand at the target tissue. The supramolecular interaction between tryptophan and cucurbit[8]uril is disrupted in the presence of indoleamine 2,3-dioxygenase 1 (IDO1) enzyme (abundant in the tumor intracellular microenvironment), which catalyzes the metabolism of tryptophan into N-formylkynurenine, resulting in the disassembly of the "gate-keeper" of the nanocarriers and intracellular release of therapeutics exclusively in tumor cells. The drug release from the nanocarrier with high selectivity to overexpressed IDO1 enzyme induces significant cytotoxicity against HepG2 cells in vitro, as well as the superior antitumor effects in vivo. This robust supramolecular nanosystem with sophisticated structure and property provides a promising platform for intracellular drug release targeting the intrinsic microenvironmental enzyme inside the tumor cells.