Aminopeptidase‐N‐activated Theranostic Prodrug for NIR Tracking of Local Tumor Chemotherapy

Abstract The development of molecular theranostic prodrugs for in vivo cancer diagnosis and targeted chemotherapy is urgently required. Enzyme‐activated prodrugs display superior selectivity as a result of cancer‐specific enzymes which serve as cancer biomarkers. Herein, an aminopeptidase N (APN)‐activated theranostic prodrug Nile blue‐C₆‐amide‐p‐fluorophenylalanyl‐l‐melphalanyl (NBFMel) is reported for fluorescence cancer diagnosis and local tumor treatment. NBFMel demonstrates negligible cytotoxicity and very weak fluorescence due to the photoinduced electron transfer (PET) between melphalan and Nile blue fluorophore. After activation caused by APN, the prodrug releases free melphalan that inhibits tumor cell growth. Simultaneously, the reaction blocks the PET process and switches on the fluorescence, which can be used for cancer diagnosis. NBFMel is successfully utilized to report the presence of tumor and for in situ tracking of drug release in tumor‐bearing mouse models. Moreover, NBFMel demonstrates efficient tumor inhibition when intravenously injected into mice. Therefore, the APN‐activated theranostic prodrug provides a new platform for in vivo cancer diagnosis and targeted anticancer chemotherapy.