G-Quadruplex-Based Nanoscale Coordination Polymers to Modulate Tumor Hypoxia and Achieve Nuclear-Targeted Drug Delivery for Enhanced Photodynamic Therapy

Photodynamic therapy (PDT) is a light-triggered therapy used to kill cancer cells by producing reactive oxygen species (ROS). Herein, a new kind of DNA nanostructure based on the coordination between calcium ions (Ca2+) and AS1411 DNA G quadruplexes to form nanoscale coordination polymers (NCPs) is developed via a simple method. Both chlorine e6 (Ce6), a photosensitizer, and hemin, an iron-containing porphyrin, can be inserted into the G-quadruplex structure in the obtained NCPs. With further polyethylene glycol (PEG) modification, we obtain Ca-AS1411/Ce6/hemin@pHis-PEG (CACH-PEG) NCP nanostructure that enables the intranuclear transport of photosensitizer Ce6 to generate ROS inside cell nuclei that are the most vulnerable to ROS. Meanwhile, the inhibition of antiapoptotic protein B-cell lymphoma 2 (Bcl-2) expression by AS1411 allows for greatly improved PDT-induced cell apoptosis. Furthermore, the catalase-mimicking DNAzyme function of G-quadruplexes and hemin in those NCPs could decompose tumor endogenous H2O2 to in situ generate oxygen so as to further enhance PDT by overcoming the hypoxia-associated resistance. This work develops a simple yet general method with which to fabricate DNA-based NCPs and presents an interesting concept of a nanoscale drug-delivery system that could achieve the intranuclear delivery of photosensitizers, the down-regulation of anti-apoptotic proteins, and the modulation of the unfavorable tumor microenvironment simultaneously for improved cancer therapy.