Asymmetrically PEGylated and amphipathic heptamethine indocyanine dyes potentiate radiotherapy of renal cell carcinoma via mitochondrial targeting

Enhancing the sensitivity of radiotherapy (RT) towards renal cell carcinoma (RCC) remains a challenge because RCC is a radioresistant tumor. In this work, we design and report asymmetrically Polyethylene Glycol (PEG)ylated and amphipathic heptamethine indocyanine dyes for efficient radiosensitization of RCC treatment. They were synthesized by modifying different lengths of PEG chains as hydrophilic moieties on one N-alkyl chain of a mitochondria-targeting heptamethine indocyanine dye (IR-808), and a radiosensitizer 2-nitroimidazole (NM) as a hydrophobic moiety on another N-alkyl chain. The PEG modification significantly improved water solubility, decreased the intermolecular π-π large aggregates, thereby enhanced renal excretion. The asymmetrical and amphipathic modification enhanced the preferential accumulation in renal tumors through self-assembly into small-size nanoparticles in aqueous environment. Radiosensitization was further improved by preferential accumulation in renal tumor cells and their mitochondria as mitochondria play a crucial role in rapid cancer cell growth, metastasis, and RT resistance. Additionally, the modification also increased the abilities of fluorescence emission and photostability, which is meaningful for imaging-guided precise RCC RT. Therefore, our findings may present a theranostic radiosensitizer for renal tumor-targeted imaging and radiosensitization.