Methionine-Decorated Near Infrared Fluorescent Probe for Prolonged Tumor Imaging.

Methionine (Met) is one of the essential amino acids of which the transport system L is overexpressed in various tumor cells. In this study, a near-infrared fluorescent dye (IR-780) and methionine were conjugated through a piperazin-polyamines linker to form Cy-Met. The successful synthesis of Cy-Met was validated by optical characterization, NMR, and MS spectra. The absorption peak of Cy-Met was at 680 nm, and the fluorescence peak was at 790 nm. The cytotoxicity assay and cell imaging studies indicated that Cy-Met had good biocompatibility and specific affinity to tumor cells. The dynamic distribution and clearance investigations showed that Cy-Met was eliminated by the liver-intestine pathway. Notably, Cy-Met displayed tumor-targeting ability in U87, H22, and EAC tumor-bearing mice with an evident long circulation time. The results implied that Cy-Met could act as a promising fluorescence probe specialized for long-term tumor monitoring.