Iridium nanocrystals encapsulated liposomes as near-infrared light controllable nanozymes for enhanced cancer radiotherapy

Owing to the existence of severe tumor hypoxia and limited X-ray absorption of solid tumors, the therapeutic efficacy of radiotherapy is far from satisfactory. Herein, ultrasmall iridium nanocrystals (IrNCs) with homogeneous size distribution are successfully synthesized. The obtained IrNCs show catalase-like catalytic activity towards hydrogen peroxide (H2O2) with great temperatures/pH stability. As free IrNCs are prone to be toxified by thiol-containing biomolecules, we encapsulate as-prepared IrNCs within stealth liposomal carriers, obtaining Ir@liposome with well-protected catalytic activity in physiological conditions. By utilizing its efficient photothermal conversion ability, such Ir@liposome shows effective near-infrared-(NIR)-responsive catalytic activity towards H2O2 decomposition. As revealed by in vivo photoacoustic imaging, our Ir@liposome exhibits efficient passive tumor accumulation upon intravenous injection, and could efficiently decompose the tumor endogenous H2O2 into O2, particularly upon exposure to the NIR laser. As the results of relieved tumor hypoxia after such treatment and the radiosensitization capability of Ir as a high-Z element, greatly enhanced radio-therapeutic efficacy with Ir@liposome is then achieved. This work thus presents a unique type of NIR light controllable theranostic nanozyme based on noble metal nanocrystals as a nanoscale radiosensitizer with great performance in enhancing cancer radiotherapy.