Fluorescence-quenching screening of protein kinase C ligands with an environmentally sensitive fluorophore

Discovery of Potent DAG-Lactone Derivatives as HIV Latency Reversing Agents

Toward human immunodeficiency virus type-1 (HIV-1) cure, cells latently infected with HIV-1 must be eliminated from people living with HIV-1. We previously developed a protein kinase C (PKC) activator, diacylglycerol (DAG)-lactone derivative 3, with high HIV-1 latency-reversing activity, based on YSE028 (2) as a lead compound and found that the activity was correlated with binding affinity for PKC and stability against esterase-mediated hydrolysis. Here, we synthesized new DAG-lactone derivatives not only containing a tertiary ester group or an isoxazole surrogate but also several symmetric alkylidene moieties to improve HIV-1 latency reversing activity. Compound 9a, with a dimethyl group at the α-position of the ester group, exerted twice higher HIV-1 latency reversing activity than compound 3, and compound 26, with the isoxazole moiety, was significantly active. In addition, DAG-lactone derivatives with moderate hydrophobicity and potent biostability showed high biological activity.

Synthesis and evaluation of DAG-lactone derivatives with HIV-1 latency reversing activity

Cells latently infected with human immunodeficiency virus type 1 (HIV-1) prevent people living with HIV-1 from obtaining a cure to the infectious disease. Latency reversing agents (LRAs) such as protein kinase C (PKC) activators and histone deacetylase (HDAC) inhibitors can reactivate cells latently infected with HIV-1. Several trials based on treatment with HDAC inhibitors alone, however, failed to reduce the number of latent HIV-1 reservoirs. Herein, we have focused on a diacylglycerol (DAG)-lactone derivative, YSE028 (1), which is a PKC activator with latency reversing activity and no significant cytotoxicity. Caspase-3 activation of YSE028 (1) led to cell apoptosis, specifically in HIV-1 latently infected cells. Structure-activity relationship studies of YSE028 (1) have produced several useful derivatives. Among these, compound 2 is approximately ten times more potent than YSE028 (1) in reactivation of cells latently infected with HIV-1. The activity of DAG-lactone derivatives was correlated with the binding affinity for PKC and the stability against esterase-mediated hydrolysis.

Fluorescence resonance energy transfer-based screening for protein kinase C ligands using 6-methoxynaphthalene-labeled 1,2-diacylglycerol-lactones

Protein kinase C (PKC) is associated with a central cellular signal transduction pathway and disorders such as cancer and Alzheimer-type dementia and is therefore a target for the treatment of these diseases. The development of simple methods suitable for high-throughput screening to find potent PKC ligands is desirable. We have developed an assay based on fluorescence-quenching screening with a solvatochromic fluorophore attached to a competitive probe and its alternative method based on Förster/fluorescence resonance energy transfer (FRET) phenomena. Here, an improved FRET-based PKC binding assay using a diacylglycerol (DAG) lactone labeled with a donor fluorescent dye, 6-methoxynaphthalene (6MN), was developed. The 6MN-labeled DAG-lactone has a higher binding affinity for the PKCδ C1b domain and the fluorescent PKCδ C1b domain labeled by fluorescein as an acceptor fluorescent dye (Fl-δC1b) than the diethylaminocoumarin (DEAC)-labeled DAG-lactone. The combination of the 6MN-labeled DAG-lactone and Fl-δC1b showed a change in fluorescence response larger than that of the DEAC-labeled DAG-lactone and Fl-δC1b. The IC₅₀ values of known PKC ligands calculated by the present FRET-based method using 6MN-labeled DAG-lactone agree well with the K_i values obtained by the conventional radioisotope-based assays. Some false positive compounds, identified by the previous solvatochromic fluorophore-based method, were found to be negative by this method. The present FRET-based PKC binding assay is more sensitive and could be more useful.

Synthesis of a Coumarin-Based PPARγ Fluorescence Probe for Competitive Binding Assay

Peroxisome proliferator-activated receptor γ (PPARγ) is a molecular target of metabolic syndrome and inflammatory disease. PPARγ is an important nuclear receptor and numerous PPARγ ligands were developed to date; thus, efficient assay methods are important. Here, we investigated the incorporation of 7-diethylamino coumarin into the PPARγ agonist rosiglitazone and used the compound in a binding assay for PPARγ. PPARγ-ligand-incorporated 7-methoxycoumarin, 1, showed weak fluorescence intensity in a previous report. We synthesized PPARγ-ligand-incorporating coumarin, 2, in this report, and it enhanced the fluorescence intensity. The PPARγ ligand 2 maintained the rosiglitazone activity. The obtained partial agonist 6 appeared to act through a novel mechanism. The fluorescence intensity of 2 and 6 increased by binding to the ligand binding domain (LBD) of PPARγ and the affinity of reported PPARγ ligands were evaluated using the probe.

Array-based "Chemical Nose" Sensing in Diagnostics and Drug Discovery

Array-based sensor "chemical nose/tongue" platforms are inspired by the mammalian olfactory system. Multiple sensor elements in these devices selectively interact with target analytes, producing a distinct pattern of response and enabling analyte identification. This approach offers unique opportunities relative to "traditional" highly specific sensor elements such as antibodies. Array-based sensors excel at distinguishing small changes in complex mixtures, and this capability is being leveraged for chemical biology studies and clinical pathology, enabled by a diverse toolkit of new molecular, bioconjugate and nanomaterial technologies. Innovation in the design and analysis of arrays provides a robust set of tools for advancing biomedical goals, including precision medicine.

Bioconjugation Methods for Coupling Targeting Ligands with Fluorescent Dyes

Targeted molecular imaging probes are essential tools for visualization of specific molecular processes in cells and living systems. Among these, targeted fluorescent probes are widely used due to the high sensitivity and resolution of fluorescence imaging. The conventional strategy for developing targeted fluorescent probes is to couple targeting ligands with fluorescent dyes by covalent bond via bioconjugation. Here, we describe several commonly used bioconjugation methods, from traditional amide and thiol coupling, to metal-catalyzed coupling reaction and catalyst free cycloaddition.

Screening technologies for small molecule discovery: the state of the art

Screening, high-throughput screening, and ultra-high-throughput screening are all really just points on a spectrum that represent differing applications of the same process: the creation of biologically relevant assays that are relevant, reproducible, reliable, and robust. Whether the discovery program is developing a pharmaceutical, an academic probe, cosmetics, pesticides, or a toxicity monitoring assay, the development of a screen focuses on generating a method that will reliably deliver reproducible results over a period of weeks, months, or years and that will generate consistent results for every test along the way. This review provides both historical perspective on how this unique scientific discipline evolved and commentary on the current state of the art technologies and techniques.

Screening for protein kinase C ligands using fluorescence resonance energy transfer

Protein kinase C (PKC) is correlated with cell signaling pathways and also receives attention as a therapeutic target for cancer and Alzheimer-type dementia. The application of Förster/fluorescence resonance energy transfer (FRET) phenomena to detect binding between proteins and small molecules, for example, PKC and its ligands, underlies a fluorescence-based assay method suitable for high-throughput screening. To accelerate studies on PKC functions in processing signals using small molecules and the development of drugs that target PKC, novel methods for the assessment of the PKC binding affinity of compounds are necessary. We previously developed solvatochromic fluorophore-based methods for that assessment. In this study, a novel method for a FRET-based PKC binding assay was developed and is expected to overcome the limitations of solvatochromic fluorophores.

Peptide-based ligand screening and functional analysis of protein kinase C

Protein kinase C (PKC) plays an important role in cell signaling pathways and is implicated in disorders ranging from cancer to Alzheimer's disease. Highly potent PKC ligands as therapeutic drugs have not been developed to date and useful methodologies for controlling PKC activation in defined areas are necessary to analyze precise PKC functions in cells. Studies focused on the development of PKC ligand screening systems and methods for regulation of PKC activation have been performed in our laboratory. In this review, our ligand screening methods involving synthetic peptides and solvatochromic fluorescent dye-labeled small compounds are summarized and the technique of spatio-temporal manipulation of PKC activation by caging strategies is introduced.