A New γ-Glutamyltranspeptidase-Based Intracellular Self-Assembly of Fluorine-18 Labeled Probe for Enhancing PET Imaging in Tumors

Abstract

γ-Glutamyltranspeptidase (GGT) is a cell -membrane-associated enzyme which has been recognized as a promising biomarker for the diagnosis of many malignant tumors. Herein, we rationally designed a fluorine-18 labeled small-molecule probe, [ 18 F]γ-Glu-Cys(StBu)-PPG(CBT)-AmBF 3 ( 18 F-1G), by applying a biocompatible CBT-Cys condensation reaction and ingeniously decorating it with a GGT-recognizable substrate, γ-glutamate (γ-Glu), for enhancing PET imaging to detect GGT level of tumors in living nude mice. The probe had exceptional stability at physiological conditions, but could be efficiently cleaved by GGT, followed by a reduction-triggered self-assembly and formation of nanoparticles (NPs) progressively that could be directly observed by transmission electron microscopy (TEM). In in vitro cell experiments, 18 F-1G showed GGT-targeted uptake contrast of 2.7-fold to that of 18 F-1 for the detection of intracellular GGT level. Moreover, the higher uptake in GGT overexpressed HCT116 tumor cells (∼4-fold) compared to GGT-deficient L929 normal cells demonstrated that 18 F-1G was also capable of distinguishing some tumor cells from normal cells. In vivo PET imaging revealed enhanced and durable radioactive signal in tumor regions after 18 F-1G coinjecting with 1G, thus allowing real-time detection of endogenous GGT level with high sensitivity and noninvasive effect. We anticipated that our probe could serve as a new tool to investigate GGT-related diseases in the near future.

Responsive Fluorophore Aggregation Provides Spectral Contrast for Fluorescence Lifetime Imaging

“…Compound 1 as a 100 μM, 10 μM, or 1 μM solution in PBS (pH 7.4) was incubated with 10 mM GSH, and aggregation of the activated (reduced) compound was detected by nanoparticle tracking analysis (NTA). Nanoparticles of 150–200 nm average size were detected when 1 was incubated with GSH (Table S2), similar in size to other iterations of this scaffold …”

“…This reaction is rapid [24] (with a second-order rate constant of 9.19 M À 1 s À 1 ) and can be controlled by caging portions of the 1,2-aminothiol group to create a bioresponsive aggregation system. [23] This system has been used as a platform for a wide variety of imaging methods, [25][26][27][28][29][30][31][32][33][34] including steadystate fluorescence imaging, [20,[35][36][37][38] but it has not been examined as a platform for time-resolved fluorescence imaging.…”

Responsive fluorophore aggregation provides spectral contrast for fluorescence lifetime imaging

“…Compound 1 as a 100 μM,10 μM, or 1 μM solution in PBS (pH = 7.4) was incubated with 10 mM GSH, and aggregation of the activated (reduced) compound was detected by Nanoparticle Tracking Analysis (NTA). Nanoparticles of 150-200 nm average size were detected when 1 was incubated with GSH (Table S2), similar in size to other iterations of this scaffold 25, 33, 34, 37, 42 .…”

“…This reaction is rapid 24 (with a second-order rate constant of 9.19 M −1 s -1 ) and can be controlled by caging portions of the 1,2-aminothiol group to create a bio-responsive aggregation system 23 . This system has been used as a platform for a wide variety of imaging methods 25–34 , including steady-state fluorescence imaging 20, 35–38 , but it has not been examined as a platform for time-resolved fluorescence imaging.…”

Intra-mitochondrial reaction for cancer cell imaging and anti-cancer therapy by aggregation-induced emission

“…11,12 As such unique reactions do not exist in the living cell, they may be controllable in the intracellular environment, and may be utilized to develop an articial chemical system to control cellular fate. [13][14][15] Nevertheless, designing efficient bioorthogonal reactions that can respond to driving processes in a dynamic intracellular environment, is still a challenge. It is also important that these reactions occur at a particular subcellular location to control specic cellular functions, as various signaling pathways are controlled by spatial separation of proteins inside the cell.…”