Metal-ligand coordination nanomaterials for radiotherapy: emerging synergistic cancer therapy

Radiotherapy (RT) plays a central role in curing malignant tumors. However, the treatment outcome is often impeded by low radiation absorption coefficients and radiation resistance of tumors along with normal tissue radio-toxicity. With the development of nanotechnology, nanomaterials in combination with RT offer the possibility to improve the therapeutic efficacy yet reduce side-effects. Metal-ligand coordination nanomaterials, including nanoscale metal-organic frameworks (NMOFs) and nanoscale coordination polymers (NCPs), formed by coordination interactions between inorganic metal ions/clusters with organic bridging ligands, have shown great potential in the field of radiation oncology in recent years in view of their unique advantages including the porous structure, high surface area, periodic frameworks, and diverse selections of both metal ions/clusters and organic ligands. In this review, we summarize the recent advances in NMOF/NCP-mediated synergistic RT in combination with hypoxia relief, chemotherapy, photodynamic therapy, photothermal therapy, chemodynamic therapy or immunotherapy, which emerged in the last 3 years, and describe cooperative enhancement interactions among these synergistic combinations. Moreover, the potential challenges and future prospects of this rapidly growing direction were also addressed.