A Small-Molecule FRET Reporter for the Real-Time Visualization of Cell-Surface Proteolytic Enzyme Functions

Rapid Two-Photon Fluorescence Imaging of Monoamine Oxidase B for Diagnosis of Early-Stage Liver Fibrosis in Mice

Liver fibrosis could induce cirrhosis and liver cancer, causing serious damages to liver function and even death. Early diagnosis of fibrosis is extremely requisite for optimizing treatment schedule to improve cure rate. In early-stage fibrosis, overexpressed monoamine oxidase B (MAO-B) can serve as a biomarker, which greatly contributes to the diagnosis of early liver fibrosis. However, there is still a lack of desired strategy to precisely monitor MAO-B in situ. In this work, we established a two-photon fluorescence imaging method for in vivo detection of MAO-B activity counting on a simply prepared probe, BiPhAA. The BiPhAA could be activated by MAO-B within 10 min and fluoresced brightly. To our knowledge, this BiPhAA-based imaging platform for MAO-B is more rapid than other current detection methods. Furthermore, BiPhAA allowed the dynamic observation of endogenous MAO-B level changes in hepatic stellate cells (LX-2). Through two-photon fluorescence imaging, we observed six times higher fluorescence brightness in the liver tissue of fibrosis mice than that of normal mice, thus successfully distinguishing mice with liver fibrosis from normal mice. Our work offers a simple, fast, and highly sensitive approach for imaging MAO-B in situ and paves a way to the diagnosis of early liver fibrosis with accuracy.

A Cell Membrane-Targeting Self-Delivery Chimeric Peptide for Enhanced Photodynamic Therapy and In Situ Therapeutic Feedback

Nowadays, cell membrane-targeted therapy, which owns high antitumor efficacy by avoiding cell barriers, has received great attention. Here, a cell membrane-targeted self-delivery theranostic chimeric peptide CMP-PpIX is designed for simultaneously targeted photodynamic therapy (PDT) of tumor and real-time therapeutic feedback. Self-assembled CMP-PpIX nanoparticles can effectively accumulate in tumor by enhanced permeability and retention effect without additional vector. And this chimeric peptide CMP-PpIX has low background fluorescence, which is due to its relatively high intramolecular Förster resonance energy transfer (FRET) quenching efficiency between 5(6)-carboxyfluorescein (FAM) and 4-(dimethylaminoazo)-benzene-4-carboxylic acid (Dabcyl). More importantly, CMP-PpIX can be anchored on the tumor cell membrane for more than 8 h. Under irradiation, reactive oxygen species produced by CMP-PpIX directly damage cell membrane and rapidly induce apoptosis, which significantly improve the efficacy of PDT in vitro and in vivo. Then, peptide sequence Asp-Glu-Val-Asp (DEVD) is subsequently cleaved by activated caspase-3 and activated caspase-7, which separates the FAM and Dabcyl and terminates the FRET process. Therefore, fluorescence of FAM is recovered to monitor the expression of activated caspase-3 in vitro and in vivo to feedback real-time PDT therapeutic efficacy. In general, a novel cell membrane-targeted self-delivery theranostic chimeric peptide offers new promise for effective imaging-guided PDT.

Guiding Drugs to Target-Harboring Organelles: Stretching Drug-Delivery to a Higher Level of Resolution

The ratio between the dose of drug required for optimal efficacy and the dose that causes toxicity is referred to as the therapeutic window. This ratio can be increased by directing the drug to the diseased tissue or pathogenic cell. For drugs targeting fungi and malignant cells, the therapeutic window can be further improved by increasing the resolution of drug delivery to the specific organelle that harbors the drug's target. Organelle targeting is challenging and is, therefore, an under-exploited strategy. Here we provide an overview of recent advances in control of the subcellular distribution of small molecules with the focus on chemical modifications. Highlighted are recent examples of active and passive organelle-specific targeting by incorporation of organelle-directing molecular determinants or by chemical modifications of the pharmacophore. The outstanding potential that lies in the development of organelle-specific drugs is becoming increasingly apparent.

Self-Assembly of Amphiphilic Peptides for Recognizing High Furin-Expressing Cancer Cells

Self-assembled nanostructures of amphiphilic peptides have a wide range of applications in bioimaging and delivery systems. In this study, we design and synthesize a biocompatible amphiphilic peptide (C-3) consisting of an RVRRFFF sequence and a nitrobenzoxadiazole fluorophore that can self-assemble into stable micelles for specifically detecting furin, a kind of proprotein convertase with promoting tumor progression. The self-assembly of C-3 with a β-sheet nanostructure is capable of a rapid and specific response to furin in only 5 min in aqueous solution because of the existence of the RVRR motif in the C-3 molecule. The C-3 nanostructures thus can selectively distinguish high furin-expressing cancer cells, like MDA-MB-231 cells, a kind of human breast cancer cells, from normal cells. Furthermore, the C-3 self-assembly can stay in living cells for a long time and are capable of durable detection of intracellular furin, being good for tracer analysis. To our knowledge, this is the first example of self-assembly of a soluble amphiphilic peptide that can selectively detect furin in high furin-expressing live cells.

Recent progresses in small-molecule enzymatic fluorescent probes for cancer imaging

An overview of recent advances in small-molecule enzymatic fluorescent probes for cancer imaging, including design strategies and cancer imaging applications.

An optimized ratiometric fluorescent probe for sensing human UDP-glucuronosyltransferase 1A1 and its biological applications

This study aimed to develop a practical ratiometric fluorescent probe for highly selective and sensitive detection of human UDP-glucuronosyltransferase 1A1 (UGT1A1), one of the most important phase II enzymes. 4-Hydroxy-1,8-naphthalimide (HN) was selected as the fluorophore for this study because it possesses intramolecular charge transfer (ICT) feature and displays outstanding optical properties. A series of N-substituted derivatives with various hydrophobic, acidic and basic groups were designed and synthesized to evaluate the selectivity of HN derivatives toward UGT1A1. Our results demonstrated that the introduction of an acidic group to HN could significantly improve the selectivity of UGT1A1. Among the synthesized fluorescent probes, NCHN (N-3-carboxy propyl-4-hydroxy-1,8-naphthalimide) displayed the best combination of selectivity, sensitivity and ratiometric fluorescence response following UGT1A1-catalyzed glucuronidation. UGT1A1-catalyzed NCHN-4-O-glucuronidation generated a single fluorescent product with a high quantum yield (Φ=0.688) and brought remarkable changes in both color and fluorescence in comparison with the parental substrate. The newly developed probe has been successfully applied for sensitive measurements of UGT1A1 activities in human liver preparations, as well as for rapid screening of UGT1A1 modulators, using variable enzyme sources. Furthermore, its potential applications for live imaging of endogenous UGT1A1in cells have also been demonstrated.