Fluorescent vinblastine probes for live cell imaging

Investigating Tubulin-Drug Interaction Using Fluorescence Spectroscopy

Fluorescence spectroscopy is routinely used for the determination of the interaction of a ligand with a protein. The quick detection of the interaction between the ligand and the protein is one of the most significant advantages of fluorescence spectroscopic methods. In this chapter, we have described assays to monitor drug -tubulin interactions using several fluorescence spectroscopic techniques. We have provided detailed protocols for different assays for investigating tubulin-drug interactions with key practical considerations for performing the experiments. We have also discussed how to deduce the binding parameters by fitting the fluorescence change data in different binding isotherms. Further, we have described detailed protocols to monitor the binding site of a ligand on tubulin by competitive inhibition. Though the methods are described for tubulin, these methods can also be used to monitor any drug -protein interactions.

SMALL MOLECULE IMAGING AGENT FOR MUTANT KRAS G12C

Multiple potent covalent inhibitors for mutant KRAS G12C have been described and some are in clinical trials. These small molecule inhibitors potentially allow for companion imaging probe development, thereby expanding the chemical biology toolkit to investigate mutant KRAS biology. Herein, we synthesized and tested a series of fluorescent companion imaging drugs (CID) for KRAS G12C, using two scaffolds, ARS-1323 and AMG-510. We created four fluorescent derivatives of each by attaching BODIPY dyes. We found that two fluorescent derivatives (BODIPY FL and BODIPY TMR) of ARS-1323 bind mutant KRAS and can be used for biochemical binding screens. Unfortunately, these drugs could not be used as direct imaging agents in cells, likely because of non-specific membrane labeling. To circumvent this challenge, we then used a two step procedure in cancer cells where an ARS-1323 alkyne is used for target binding followed by fluorescence imaging after in situ click chemsitry with picolyl azide Alexa Fluor 647. We show that this approach can be used to image mutant KRAS G12C directly in cells. Given the current lack of mutant KRAS G12C specific antibodies, these reagents could be useful for specific fluorescence imaging.

RIP1/RIP3/MLKL-mediated necroptosis contributes to vinblastine-induced myocardial damage

Vinblastine (VBL) has been considered as a first-line anti-tumor drug for many years. However, vinblastine-caused myocardial damage has been continually reported. The underlying molecular mechanism of the myocardial damage remains unknown. Here, we show that vinblastine induces myocardial damage and necroptosis is involved in the vinblastine-induced myocardial damage both in vitro and in vivo. The results of WST-8 and flow cytometry analysis show that vinblastine causes damage to H9c2 cells, and the results of animal experiments show that vinblastine causes myocardial cell damage. The necrosome components, receptor-interacting protein 1 (RIP1) receptor-interacting protein 3 (RIP3), are significantly increased in vinblastine-treated H9c2 cells, primary neonatal rat ventricular myocytes and rat heart tissues. And the downstream substrate of RIP3, mixed lineage kinase domain like protein (MLKL) was also increased. Pre-treatment with necroptosis inhibitors partially inhibits the necrosome components and MLKL levels and alleviates vinblastine-induced myocardial injury both in vitro and in vivo. This study indicates that necroptosis participated in vinblastine-evoked myocardial cell death partially, which would be a potential target for relieving the chemotherapy-related myocardial damage.

Fluorescence-labeled neopeltolide derivatives for subcellular localization imaging

Design, synthesis and functional analysis of fluorescent derivatives of neopeltolide, an antiproliferative marine macrolide, are reported herein. Live cell imaging using the fluorescent derivatives showed rapid cellular uptake and localization within the endoplasmic reticulum as well as the mitochondria.

Imaging of Tie2 with a Fluorescently Labeled Small Molecule Affinity Ligand

The receptor tyrosine kinase inhibitor, Tie2, has significant roles in endothelial signaling and angiogenesis and is relevant in the pathophysiology of several diseases. However, there are relatively few small molecule probes available to study Tie2, making the evaluation of its activity in vivo difficult. Recently, it was discovered that the small molecule rebastinib (DCC-2036) is a potent Tie2 inhibitor. We hypothesized that fluorescent derivatives of rebastinib could be used as imaging agents for Tie2. On the basis of crystallography structures, we synthesized three fluorescent derivatives, which we then evaluated in both in vitro and in vivo assays. We found that the Rebastinib-BODIPY TMR (Reb-TMR) derivative has superior imaging characteristics in vitro, and we successfully labeled endothelial cells in vivo. We propose that this probe could be further used in in vivo applications for studying the role of Tie2 in disease.

Measurement of drug-target engagement in live cells by two-photon fluorescence anisotropy imaging

The ability to directly image and quantify drug-target engagement and drug distribution with subcellular resolution in live cells and whole organisms is a prerequisite to establishing accurate models of the kinetics and dynamics of drug action. Such methods would thus have far-reaching applications in drug development and molecular pharmacology. We recently presented one such technique based on fluorescence anisotropy, a spectroscopic method based on polarization light analysis and capable of measuring the binding interaction between molecules. Our technique allows the direct characterization of target engagement of fluorescently labeled drugs, using fluorophores with a fluorescence lifetime larger than the rotational correlation of the bound complex. Here we describe an optimized protocol for simultaneous dual-channel two-photon fluorescence anisotropy microscopy acquisition to perform drug-target measurements. We also provide the necessary software to implement stream processing to visualize images and to calculate quantitative parameters. The assembly and characterization part of the protocol can be implemented in 1 d. Sample preparation, characterization and imaging of drug binding can be completed in 2 d. Although currently adapted to an Olympus FV1000MPE microscope, the protocol can be extended to other commercial or custom-built microscopes.

Synthesis and cell imaging applications of fluorescent mono/di/tri-heterocyclyl-2,6-dicyanoanilines

Synthesis of 3,4,5-triheterocyclyl-2,6-dicyanoanilines, starting from heterocyclic aldehydes and 1,2-diheterocycle-substituted ethanones, is described. 2,6-Dicyanoanilines with one or two heterocyclic substituents have also been synthesized. It was found that some of these molecules have selective cell-staining properties useful for cell imaging applications. The compounds 1g, 10f and 11 were found to stain cytoplasm of the cells in contact but not the nucleus while the compound 12 showed affinity to apoptotic cells resulting in blue fluorescence. The cell imaging results with compound 12 were similar to Annexin V-FITC, a known reagent containing recombinant Annexin V conjugated to green-fluorescent FITC dye, used for detection of apoptotic cells. These compounds were found to be non-cytotoxic and have potential application as cell imaging agents.

Quantitating drug-target engagement in single cells in vitro and in vivo

Quantitation of drug target engagement in single cells has proven to be difficult, often leaving unanswered questions in the drug development process. We found that intracellular target engagement of unlabeled new therapeutics can be quantitated using polarized microscopy combined with competitive binding of matched fluorescent companion imaging probes. We quantitated the dynamics of target engagement of covalent BTK inhibitors, as well as reversible PARP inhibitors, in populations of single cells using a single companion imaging probe for each target. We then determined average in vivo tumor concentrations and found marked population heterogeneity following systemic delivery, revealing single cells with low target occupancy at high average target engagement in vivo.