Hemicyanine-Based Near-Infrared Fluorescence Off-On Probes for Imaging Intracellular and In Vivo Nitroreductase Activity

A mitochondrial targeted fluorescent probe for imaging nitroreductase activity and photodynamic therapy in tumor cells

The hypoxic environment in tumors is closely linked to tumor structure, function, dissemination, invasion, metastasis, and drug resistance. Nitroreductase (NTR) is often recognized as a biomarker to evaluate the hypoxia degree for tumor cells. Traditional detection methods such as PET, MRI and multispectral photoacoustic tomography have limitations. Fluorescent probes have garnered attention due to their high sensitivity, rapid response, specificity, and non-invasive nature. In this study, we introduced a novel small molecule fluorescent probe, T-TPE-NO2, designed with an AIE molecular framework TPE and successfully targeted to the mitochondria of tumor cells. The probe had high selectivity and could detect NTR activity in a broad pH range. Additionally, the probe exhibits high sensitivity with a LOD of 46.3 ng/mL. Under tumor NTR, the probe emitted strong fluorescence signals and generated a substantial amount of reactive oxygen species upon laser irradiation, thereby inducing tumor cell death and enabling photodynamic therapy. The synthesis, structural and morphological characterization of the probe were rigorously validated. Experimental results demonstrate that T-TPE-NO2 exhibited high sensitivity and selectivity for tumor cells, highlighting its potential application in photodynamic therapy. This research offers a new approach for the detection and treatment of tumor hypoxia.

Design strategies and applications of cyanine dyes in phototherapy

Cyanine dyes have been widely used in phototherapy in recent years due to their excellent optical properties and diverse modifiable structures. This review provides detailed descriptions of the basic structures of various cyanines and their derivatives as well as their optical properties. It summarizes the strategies for constructing cyanine dyes for phototherapy and discusses their structure-effect relationship. Furthermore, a comprehensive classification and summary of the applications of cyanine dyes in phototherapy are presented. Importantly, this review also addresses both the advances made in this field as well as the challenges that need to be overcome. We hope that these profound insights into phototherapy using cyanine dyes will facilitate the design of future systems for clinical applications based on these compounds.

Special Issue "Research Progress of Bioimaging Materials"

In the context of increasingly diverse diseases, early diagnosis and prevention, particularly in cancer control, have become more important than ever [...].

Hemicyanine-Based Highly Water-Soluble Probe for Extracellular Nitroreductase

Nitroreductase (NTR) has long been a target of interest for its important role involved in the nitro compounds metabolism. Various probes have been reported for NTR analysis, but rarely able to distinguish the extracellular NTR from intracellular ones. Herein we reported a new NTR sensor, HCyS-NO2, which was a hemicyanine molecule with one nitro and two sulfo groups attached. The nitro group acted as the reporting group to respond NTR reduction. Direct linkage of nitro group into the hemicyanine π conjugate system facilitated the intramolecular electron transfer (IET) process and thus quenched the fluorescence of hemicyanine core. Upon reduction with NTR, the nitro group was rapidly converted into the hydroxylamino and then the amino group, eliminating IET process and thus restoring the fluorescence. The sulfo groups installed significantly increased the hydrophilicity of the molecule, and introduced negative charges at physiological pH, preventing the diffusion into bacteria. Both gram-negative and gram-positive bacteria were able to turn on the fluorescence of HCyS-NO2, without detectable diffusion into cells, providing a useful tool to probe the extracellular reduction process.

A near-infrared fluorescence probe with large Stokes shift for selectively monitoring nitroreductase in living cells and mouse tumor models

Hypoxia is commonly regarded as a typical feature of solid tumors, which originates from the insufficient supply of oxygen. Herein, the development of an efficient method for assessing hypoxia levels in tumors is strongly desirable. Nitroreductase (NTR) is an overexpressed reductase in the solid tumors, has been served as a potential biomarker to evaluate the degrees of hypoxia. In this work, we elaborately synthesized a new near-infrared (NIR) fluorescence probe (MR) to monitor NTR activity for assessment of hypoxia levels in living cells and in tumors. Upon exposure of NTR, the nitro-unit of MR could be selectively reduced to amino-moiety with the help of nicotinamide adenine dinucleotide. Moreover, the obtained fluorophore emitted a prominent NIR fluorescence, because it possessed a classical "push-pull" structure. The MR displayed several distinguished characters toward NTR, including intense NIR fluorescent signals, large Stokes shift, high selectivity and low limit of detection (46 ng/mL). Furthermore, cellular confocal fluorescence imaging results validated that the MR had potential of detecting NTR levels in hypoxic cells. Significantly, using the MR, the elevated of NTR levels were successfully visualized in the tumor-bearing mouse models. Therefore, this detecting platform based on this probe may be tactfully constructed for monitoring the variations of NTR and estimating the degrees of hypoxia in tumors.