Light-Activated Hypoxia-Sensitive Covalent Organic Framework for Tandem-Responsive Drug Delivery

Covalent organic frameworks (COFs) have received much attention in the biomedical area. However, little has been reported about stimuli-responsive COF for drug delivery. Herein, we synthesized a hypoxia-responsive azo bond-containing COF with nanoscale size and immobilized both photosensitizers chlorin e6 (Ce6) and hypoxia-activated drug tirapazamine (TPZ) into the COFs. When such a COF entered the hypoxic environment and tumor, the COF structure was ruptured and loaded drugs were released from the COF. Together, upon near-infrared (NIR) light irradiation, Ce6 consumed oxygen to produce cytotoxic reactive oxygen species, leading to elevated hypoxia. Such two-step hypoxia stimuli successively induced the deintegration of COF, drug release and activation of TPZ. This promoted the TPZ to generate massive biotoxic oxyradical. In vitro and in vivo evaluation indicated that this two-step hypoxia-activated COF drug delivery system could kill cancer cells and inhibit the growth of tumors effectively.