Preparation of a Multiple-Targeting NIR-Based Fluorogenic Probe and Its Application for Selective Cancer Cell Imaging

Engineering a Dual-Receptor Targeted Multivalent Probe for Enhanced Magnetic Resonance Imaging of Metastatic Cancer

Noninvasive monitoring of cancer metastasis is essential to improving clinical outcomes. Molecular MRI (mMRI) is a special implementation of noninvasive molecular imaging that promises to offer a powerful means for early detection and analysis of pathological states of cancer by tracking molecular markers. However, this is often hindered by the challenging issue of obtaining transformable mMRI contrast agents with high sensitivity, specificity, and broad applicability, given the high tumor heterogeneity and complex metastatic features. Herein, we present a dual-receptor targeted, multivalent recognition strategy and report a new class of mMRI probes for enhanced imaging of metastatic cancer. This probe is designed by covalently conjugating Gd-chelate with phenylboronic acid and an aptamer via an affordable polymerization chemistry to concurrently target two different cell-membrane receptors that are commonly overexpressed and highly implicated in both tumorigenesis and metastasis. Moreover, the polymerization chemistry allows the probe to contain a bunch of targeting ligands and signal reporters in a single chain, which not only leads to more than 2-fold enhancement in T1 relaxivity at 1.5 T compared to the commercial contrast agent but also enables it to actively target tumor cells in a multivalent recognition manner, contributing to a much higher imaging contrast than single-receptor targeted probes and the commercial agent in mouse models with lung metastases, yet without inducing systemic side effects. We expect this study to offer a useful molecular tool to promote transformable applications of mMRI and a better understanding of molecular mechanisms involved in cancer development.

Glycosidase-targeting small molecules for biological and therapeutic applications

Glycosidases are ubiquitous enzymes that catalyze the hydrolysis of glycosidic linkages in oligosaccharides and glycoconjugates. These enzymes play a vital role in a wide variety of biological events, such as digestion of nutritional carbohydrates, lysosomal catabolism of glycoconjugates, and posttranslational modifications of glycoproteins. Abnormal glycosidase activities are associated with a variety of diseases, particularly cancer and lysosomal storage disorders. Owing to the physiological and pathological significance of glycosidases, the development of small molecules that target these enzymes is an active area in glycoscience and medicinal chemistry. Research efforts carried out thus far have led to the discovery of numerous glycosidase-targeting small molecules that have been utilized to elucidate biological processes as well as to develop effective chemotherapeutic agents. In this review, we describe the results of research studies reported since 2018, giving particular emphasis to the use of fluorescent probes for detection and imaging of glycosidases, activity-based probes for covalent labelling of these enzymes, glycosidase inhibitors, and glycosidase-activatable prodrugs.

Activity-Based Sensing for Chemistry-Enabled Biology: Illuminating Principles, Probes, and Prospects for Boronate Reagents for Studying Hydrogen Peroxide

Activity-based sensing (ABS) offers a general approach that exploits chemical reactivity as a method for selective detection and manipulation of biological analytes. Here, we illustrate the value of this chemical platform to enable new biological discovery through a case study in the design and application of ABS reagents for studying hydrogen peroxide (H2O2), a major type of reactive oxygen species (ROS) that regulates a diverse array of vital cellular signaling processes to sustain life. Specifically, we summarize advances in the use of activity-based boronate probes for the detection of H2O2 featuring high molecular selectivity over other ROS, with an emphasis on tailoring designs in chemical structure to promote new biological principles of redox signaling.

Activity-based NIR fluorescent probes based on the versatile hemicyanine scaffold: design strategy, biomedical applications, and outlook

The discovery of a near-infrared (NIR, 650-900 nm) fluorescent chromophore hemicyanine dye with high structural tailorability is of great significance in the field of detection, bioimaging, and medical therapeutic applications. It exhibits many outstanding advantages including absorption and emission in the NIR region, tunable spectral properties, high photostability as well as a large Stokes shift. These properties are superior to those of conventional fluorogens, such as coumarin, fluorescein, naphthalimides, rhodamine, and cyanine. Researchers have made remarkable progress in developing activity-based multifunctional fluorescent probes based on hemicyanine skeletons for monitoring vital biomolecules in living systems through the output of fluorescence/photoacoustic signals, and integration of diagnosis and treatment of diseases using chemotherapy or photothermal/photodynamic therapy or combination therapy. These achievements prompted researchers to develop more smart fluorescent probes using a hemicyanine fluorogen as a template. In this review, we begin by describing the brief history of the discovery of hemicyanine dyes, synthetic approaches, and design strategies for activity-based functional fluorescent probes. Then, many selected hemicyanine-based probes that can detect ions, small biomolecules, overexpressed enzymes and diagnostic reagents for diseases are systematically highlighted. Finally, potential drawbacks and the outlook for future investigation and clinical medicine transformation of hemicyanine-based activatable functional probes are also discussed.

A fluorogenic probe targeting two spatially separated enzymes for selective imaging of cancer cells

We describe a fluorogenic probe BocLys(Ac)-AB-FC targeting both histone deacetylases (HDACs) and cathepsin L, which are overexpressed in spatially separated subcellular organelles of cancer cells. The results show that the...

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

Recent Advances in Hydrogen Peroxide Responsive Organoborons for Biological and Biomedical Applications

Hydrogen peroxide is the most stable reactive oxygen species generated endogenously, participating in numerous physiological processes and abnormal pathological conditions. Mounting evidence suggests that a higher level of H₂ O₂ exists in various disease conditions. Thus, H₂ O₂ functions as an ideal target for site-specific bioimaging and therapeutic targeting. The unique reactivity of organoborons with H₂ O₂ provides a method for developing chemoselective molecules for biological and biomedical applications. This review highlights the design and application of boron-derived molecules for H₂ O₂ detection, and the utility of boron moieties toward masking reactive compounds leading to the development of metal prochelators and prodrugs for selectively delivering an active species at the target sites with elevated H₂ O₂ levels. Additionally, the emergence of H₂ O₂ -responsive theranostic agents consisting of both therapeutic and diagnostic moieties in one integrated system are discussed. The purpose of this review is to provide a better understanding of the role of boron-derived molecules toward biological and pharmacological applications.

A triple-targeting delivery system carrying two anticancer agents

To improve tumor selectivity, a triple-targeting delivery system (Oct-FK(PBA-Az)-Dox) carrying two anticancer agents (apoptozole (Az) and doxorubicin (Dox)) was designed and synthesized. The results showed that both anticancer agents in Oct-FK(PBA-Az)-Dox are liberated in the presence of both H2O2 and cathepsin B, which are normally present at high levels in tumors.

Cancer cell death using metabolic glycan labelling techniques

Herein we describe a method for inducing cancer cell death, which relies on the use of a H2O2-responsive glycan metabolic precursor in conjunction with antibody-dependent cellular cytotoxicity (ADCC) or photodynamic therapy (PDT).

Reactive Oxygen Species (ROS)-Responsive Prodrugs, Probes, and Theranostic Prodrugs: Applications in the ROS-Related Diseases

Elevated levels of reactive oxygen species (ROS) have commonly been implicated in a variety of diseases, including cancer, inflammation, and neurodegenerative diseases. In light of significant differences in ROS levels between the nonpathogenic and pathological tissues, an increasing number of ROS-responsive prodrugs, probes, and theranostic prodrugs have been developed for the targeted treatment and precise diagnosis of ROS-related diseases. This review will summarize and provide insight into recent advances in ROS-responsive prodrugs, fluorescent probes, and theranostic prodrugs, with applications to different ROS-related diseases and various subcellular organelle-targetable and disease-targetable features. The ROS-responsive moieties, the self-immolative linkers, and the typical activation mechanism for the ROS-responsive release are also summarized and discussed.

Folate Receptor Targeting and Cathepsin B-Sensitive Drug Delivery System for Selective Cancer Cell Death and Imaging

In this work, a folate receptor (FR)-mediated dual-targeting drug delivery system was synthesized to improve the tumor-killing efficiency and inhibit the side effects of anticancer drugs. We designed and synthesized an FR-mediated fluorescence probe (FA-Rho) and FR-mediated cathepsin B-sensitive drug delivery system (FA-GFLG-SN38). FA-GFLG-SN38 is composed of the FR ligand (folic acid, FA), the tetrapeptide substrate for cathepsin B (GFLG), and an anticancer drug (SN38). The rhodamine B (Rho)-labeled probe FA-Rho is suitable for specific fluorescence imaging of SK-Hep-1 cells overexpressing FR and inactive in FR-negative A549 and 16-HBE cells. FA-GFLG-SN38 exhibited strong cytotoxicity against FR-overexpressing SK-Hep-1, HeLa, and Siha cells, with IC₅₀ values of 2-3 μM, but had no effect on FR-negative A549 and 16-HBE cells. The experimental results show that the FA-CFLG-SN38 drug delivery system proposed by us can effectively inhibit tumor proliferation in vitro, and it can be adopted for the diagnostics of tumor tissues and provide a basis for effective tumor therapy.