Hypoxia is lethal to all cells; therefore, tumors develop a set of responses to outstrip their blood supply to adapt to the stressful hypoxic environment.101 The master mediator of this response is the hypoxia‐inducible factor 1α (HIF‐1α).102 Therefore, the authors synthesized a CT‐based system consisting of the ROS‐level increasing [Gd(W5O18)2]9− and HIF‐1α siRNA, which interferes with the expression of HIF‐1α, to reduce the radioresistance of cancer cells. The gene discussed is HIF1A; the disease is cancer.