Targeted Delivery of a γ-Glutamyl Transpeptidase Activatable Near-Infrared-Fluorescent Probe for Selective Cancer Imaging

Abstract

The noninvasive and specific detection of cancer cells in living subjects has been essential for the success of cancer diagnoses and treatments. Herein, we report a strategy of combining an αβ-integrin-receptor-targetable ligand, c-RGD, with the γ-glutamyl transpeptidase (GGT)-recognizable substrate, γ-glutamate (γ-Glu), to develop a tumor-targeting and GGT-activatable near-infrared (NIR)-fluorescent probe for the noninvasive imaging of tumors in living mice. We demonstrated that the probe's fluorescence was off initially, but when the γ-Glu in the probe was specifically cleaved by GGT, the fluorescent product was released and could be selectively taken up by U87MG-tumor cells via αβ-receptor-mediated endocytosis. Remarkably, enhanced intracellular NIR fluorescence distributed mainly in the lysosomes was observed in the tumor cells only, showing that the probe was capable of differentiating the tumor cells from the GGT-positive, αβ-deficient normal cells. Moreover, the probe also showed a high selectivity for the real-time and noninvasive detection of GGT activity in xenograft U87MG tumors following iv administration. This study reveals the advantage of using a combination of receptor-mediated cell uptake and molecular-target-triggered activation to design molecular probes for improved cancer imaging, which could facilitate effective cancer diagnoses.

Recent Advances in the Development of Optical Imaging Probes for γ‐Glutamyltranspeptidase

“…On the basis of 13 , we further incorporated a α v β 3 integrin receptor targeting ligand, c‐RGD, and developed a tumor‐targeting and GGT‐activatable NIR fluorescence probe ( 14 ) for tumor imaging (Figure A) . The introduction of c‐RGD into the probe could help to improve water solubility and trigger active delivery into tumor cells after intravenous administration into mice.…”

“…Figure 6A). [30] The introduction of c-RGD into the probe could help to improve water solubility and trigger active delivery into tumor cells after intravenous administration into mice. Moreover,u pon activation by GGT on the cell surface, the resultant fluorescentp roduct, mCy-RGD,c ould selectively enter into a v b 3 -postive tumor cells through a v b 3 -integrinmediated endocytosis,a llowing for the discrimination of tumor cells and normal tissue cells.…”

“…C) Real-timefluorescence imaging of U87MG-tumor-bearing mice receiving intravenous injections of 14, 14-ctrl, 14 with intratumoralinjections of GGsTop, or 14 with intratumorali njections of free c-RGD.Reprinted with permissionfrom ref. [30].Copyright: 2018,A merican Chemical Society. ChemBioChem 2019, 20,474 -487 www.chembiochem.org value of the TPAc ross-section of 15 in the presence of GGT was about 150 GM (1 GM = 10 À50 cm 4 s/photon) at l = 820 nm, which was suitable for two-photon fluorescence imaging.…”

Most recent advances on enzyme‐activatable optical probes for bioimaging

“…Reproduced with permission. [ 132 ] Copyright 2018, American Chemical Society. (D) Real‐time NIR FL and PA imaging of cisplatin‐induced acute kidney injury with 39 .…”

A protease‐responsive fluorescent probe for sensitive imaging of legumain activity in living tumor cells

“…In particular, fluorescent probes have attracted much attention due to their advantages of real‐time imaging and high spatial resolution. It also has extensive applications in molecular imaging (Qiu et al., ; Shi et al., ; Zheng et al., ), disease diagnosis (Chen et al., ; Luo et al., ), and drug development (Liu, Bajjuri, Liu, & Sinha, ; Qi et al., ). Among them, enzyme‐activated fluorescent probes have become the focus of recent research studies, because they can provide accurate information about the enzyme activity and show potential in disease diagnosis (Chen et al., ; Hai et al., ; Luo et al., ; Shaulov‐Rotem et al., ).…”