Fluorogenic and Cell-Permeable Rhodamine Dyes for High-Contrast Live-Cell Protein Labeling in Bioimaging and Biosensing.

The advancement of fluorescence microscopy techniques has opened up new opportunities for visualizing proteins and unraveling their functions in living biological systems. Small-molecule organic dyes, which possess exceptional photophysical properties, small size, and high photostability, serve as powerful fluorescent reporters in protein imaging. However, achieving high-contrast live-cell labeling of target proteins with conventional organic dyes remains a considerable challenge in bioimaging and biosensing due to their inadequate cell permeability and high background signal. Over the past decade, a novel generation of fluorogenic and cell-permeable dyes has been developed, which have substantially improved live-cell protein labeling by fine-tuning the reversible equilibrium between a cell-permeable, nonfluorescent spirocyclic state (unbound) and a fluorescent zwitterion (protein-bound) of rhodamines. In this review, we present the mechanism and design strategies of these fluorogenic and cell-permeable rhodamines, as well as their applications in bioimaging and biosensing.

One-Pot Tandem Access to Phenothiazine Derivatives from Acetanilide and 2-Bromothiophenol via Rhodium-Catalyzed C-H Thiolation and Copper-Catalyzed C-N Amination.

A one-pot and step economic reaction involving Rh(III)-catalyzed C-H thiolation and relay Cu(II)-catalyzed C-N amination of acetanilide and 2-bromothiophenol is reported here, with several valuable phenothiazine products obtained. This synthesis protocol proceeds from easily starting materials, demonstrating high atom economy, broad substrate scope, and good yield. Furthermore, the directing group can be easily eliminated, and chlorpromazine is provided in a large scale; thus this synthesis protocol could be utilized to construct phenothiazine scaffolds.

Design, synthesis and biological evaluation of novel pyrrolidone-based derivatives as potent p53-MDM2 inhibitors.

Inhibition of the interactions of the tumor suppressor protein p53 with its negative regulators MDM2 in vitro and in vivo, representing a valuable therapeutic strategy for cancer treatment. The natural product chalcone exhibited moderate inhibitory activity against MDM2, thus based on the binding mode between chalcone and MDM2, a hit unsaturated pyrrolidone scaffold was obtained through virtual screening. Several unsaturated pyrrolidone derivatives were synthesized and biological evaluated. As a result, because the three critical hydrophobic pockets of MDM2 were occupied by the substituted-phenyl linked at the pyrrolidone fragment, compound 4 h demonstrated good binding affinity with the MDM2. Additionally, compound 4 h also showed excellent antitumor activity and selectivity, and no cytotoxicity against normal cells in vitro. The further antitumor mechanism studies were indicated that compound 4 h could successfully induce the activation of p53 and corresponding downstream p21 proteins, thus successfully causing HCT116 cell cycle arrest in the G1/M phase and apoptosis. Thus, the novel unsaturated pyrrolidone p53-MDM2 inhibitors could be developed as novel antitumor agents.

Structure-based discovery of novel α-aminoketone derivatives as dual p53-MDM2/MDMX inhibitors for the treatment of cancer.

The function of the p53 protein is impaired by the overexpression of its negative regulator murine double minute 2 protein (MDM2) and homologous protein MDMX. Disruption of the p53-MDM2/MDMX interaction to restore the transcriptional function of p53 is considered a promising strategy for cancer therapy. To design dual MDM2/MDMX inhibitors, the binding modes of MDM2 or MDMX with their inhibitors are elucidated. Several hot-spot residues of MDM2 or MDMX are identified by molecular dynamics simulations, alanine scanning and MM-GBSA calculations. Then, focusing on the interaction with hot-spot residues, two series of derivatives bearing 1,3-diketone and α-aminoketone scaffolds are designed and synthesized. Among these compounds, C16 is identified as the most potent compound with low micromolar binding affinities with MDM2 and MDMX. C16 also displays moderate antiproliferative activities against MDM2-overexpressing and MDMX-overexpressing cells, with IC50 values of 0.68 µM in HCT116 cells and 0.54 µM in SH-SY5Y cells. Furthermore, C16 inhibits cell migration and invasion, reactivates the function of p53, arrests the cell cycle and induces cellular apoptosis in HCT116 and SH-SY5Y cells. Collectively, C16 can be developed as a dual MDM2 and MDMX inhibitor for cancer therapy.

Discovery of 1,6-Naphthyridin-2(1H)-one Derivatives as Novel, Potent, and Selective FGFR4 Inhibitors for the Treatment of Hepatocellular Carcinoma.

Fibroblast growth factor receptor 4 (FGFR4) has been identified as a potential target due to its transmission of the FGF19 signaling pathway, which is critical to hepatocellular carcinoma (HCC). Therefore, focusing on the specific Cys552 of FGFR4 subtype, we designed and synthesized a novel family of 1,6-naphthyridin-2(1H)-one derivatives as potent and highly selective FGFR4 inhibitors. Through detailed structural optimizations, the representative compound A34 exhibited improved FGFR4 inhibitory capability and selectivity and excellent anti-proliferative activities against FGFR4-dependent HCC cell lines. Additionally, A34 demonstrated remarkable antitumor efficacy in a Hep-3B HCC xenograft model, with favorable pharmacokinetic properties, and low risk of hERG toxicity. A34 also showed moderate inhibitory activities against the FGFR4 V550L mutant in vitro, which indicates that it has the potential as a novel anticancer agent for HCC.

Discovery of novel serine/threonine protein phosphatase 1 inhibitors from traditional Chinese medicine through virtual screening and biological assays.

Protein phosphatase 1 (PP1) is a critical regulator of several processes, such as muscle contraction, neuronal signaling, glycogen synthesis, and cell proliferation. Dysregulation of PP1 has recently been found to be implicated in cardiac dysfunctions, which indicates that PP1 could be an attractive therapeutic target. However, discovery of PP1 inhibitors with satisfied safety and efficiency is still a challenge. Here, in order to discover potential PP1 inhibitors, compounds extracted from traditional Chinese medicine (TCM) were screened by a novel integrated virtual screening protocol including pharmacophore modeling and docking approaches. Combined with protein phosphatase inhibition assay, ZINC43060554 showed strongly inhibitory activity with IC50 values of 26.78 µM. Furthermore, molecular dynamics simulation and Molecular Mechanics/Generalized Born Surface Area binding free-energy analysis were performed to examine the stability of ligand binding modes. These novel scaffolds discovered in the present study can be used for rational design of PP1 inhibitors with high affinity.Communicated by Ramaswamy H. Sarma.

Rhodium(III)-Catalyzed Oxidative Annulation of 4-Aminoquinolines and Acrylate through Two Consecutive C(sp2)-H Activations.

The C-H annulation of the five-position of quinolines and acrylates to afford heterocycles is an active field of research in organic synthesis. Herein the annulation of 4-aminoquinolines with acrylates through two consecutive C-H activations catalyzed by Rh(III) is described. The reaction proceeds with high atom efficiency under mild reaction conditions, and this protocol will provide appealing strategies for the synthesis of fused quinoline heterocycles.