Red-Light-Controlled Release of Drug-Ru Complex Conjugates from Metallopolymer Micelles for Phototherapy in Hypoxic Tumor Environments

Traditional photodynamic phototherapy is not efficient for anticancer treatment because solid tumors have a hypoxic microenvironment. The development of photoactivated chemotherapy based on photoresponsive polymers that can be activated by light in the therapeutic window would enable new approaches for basic research and allow for anticancer phototherapy in hypoxic conditions. This work synthesizes a novel Ru-containing block copolymer for photoactivated chemotherapy in hypoxic tumor environment. The polymer has a hydrophilic poly(ethylene glycol) block and a hydrophobic Ru-containing block, which contains red-light-cleavable (650-680 nm) drug-Ru complex conjugates. The block copolymer self-assembles into micelles, which can be efficiently taken up by cancer cells. Red light induces release of the drug-Ru complex conjugates from the micelles and this process is oxygen independent. The released conjugates inhibit tumor cell growth even in hypoxic tumor environment. Furthermore, the Ru-containing polymer for photoactivated chemotherapy in a tumor-bearing mouse model is applied. Photoactivated chemotherapy of the polymer micelles demonstrates efficient tumor growth inhibition. In addition, the polymer micelles do not cause any toxic side effects to mice during the treatment, demonstrating good biocompatibility of the system to the blood and healthy tissues. The novel red-light-responsive Ru-containing polymer provides a new platform for phototherapy against hypoxic tumors.