Abstract
The acidic microenvironment is one of the remarkable features of tumor and is also a reliable target for tumor theranostics. Ultrasmall gold nanoclusters (AuNCs) have good in vivo behaviors, such as non-retention in liver and spleen, renal clearance, and high tumor permeability, and held great potential for developing novel radiopharmaceuticals. Herein, we developed pH-sensitive ultrasmall gold nanoclusters by introducing quaternary ammonium group (TMA) or tertiary amine motifs (C6A) onto glutathione-coated AuNCs (TMA/GSH@AuNCs, C6A-GSH@AuNCs). Density functional theory simulation revealed that radiometal 89Sr, 223Ra, 44Sc, 90Y, 177Lu, 89Zr, 99mTc, 188Re, 106Rh, 64Cu, 68Ga, and 113Sn could stably dope into AuNCs. Both TMA/GSH@AuNCs and C6A-GSH@AuNCs could assemble into large clusters responding to mild acid condition, with C6A-GSH@AuNCs being more effective. To assess their performance for tumor detection and therapy, TMA/GSH@AuNCs and C6A-GSH@AuNCs were labeled with 68Ga, 64Cu, 89Zr and 89Sr, respectively. PET imaging of 4T1 tumor-bearing mice revealed TMA/GSH@AuNCs and C6A-GSH@AuNCs were mainly cleared through kidney, and C6A-GSH@AuNCs accumulated in tumors more efficiently. As a result, 89Sr-labeled C6A-GSH@AuNCs eradicated both the primary tumors and their lung metastases. Therefore, our study suggested that GSH-coated AuNCs held great promise for developing novel radiopharmaceuticals that specifically target the tumor acidic microenvironment for tumor diagnosis and treatments.