Real-time fluorescent resonance energy transfer analysis to monitor drug resistance in chronic myelogenous leukemia

Shining Light on Protein Kinase Biomarkers with Fluorescent Peptide Biosensors

Protein kinases (PKs) are established gameplayers in biological signalling pathways, and a large body of evidence points to their dysregulation in diseases, in particular cancer, where rewiring of PK networks occurs frequently. Fluorescent biosensors constitute attractive tools for probing biomolecules and monitoring dynamic processes in complex samples. A wide variety of genetically encoded and synthetic biosensors have been tailored to report on PK activities over the last decade, enabling interrogation of their function and insight into their behaviour in physiopathological settings. These optical tools can further be used to highlight enzymatic alterations associated with the disease, thereby providing precious functional information which cannot be obtained through conventional genetic, transcriptomic or proteomic approaches. This review focuses on fluorescent peptide biosensors, recent developments and strategies that make them attractive tools to profile PK activities for biomedical and diagnostic purposes, as well as insights into the challenges and opportunities brought by this unique toolbox of chemical probes.

Genetically Encoded Fluorescent Biosensors for Biomedical Applications

One of the challenges of modern biology and medicine is to visualize biomolecules in their natural environment, in real-time and in a non-invasive fashion, so as to gain insight into their physiological behavior and highlight alterations in pathological settings, which will enable to devise appropriate therapeutic strategies. Genetically encoded fluorescent biosensors constitute a class of imaging agents that enable visualization of biological processes and events directly in situ, preserving the native biological context and providing detailed insight into their localization and dynamics in cells. Real-time monitoring of drug action in a specific cellular compartment, organ, or tissue type; the ability to screen at the single-cell resolution; and the elimination of false-positive results caused by low drug bioavailability that is not detected by in vitro testing methods are a few of the obvious benefits of using genetically encoded fluorescent biosensors in drug screening. This review summarizes results of the studies that have been conducted in the last years toward the fabrication of genetically encoded fluorescent biosensors for biomedical applications with a comprehensive discussion on the challenges, future trends, and potential inputs needed for improving them.

Drug Screening with Genetically Encoded Fluorescent Sensors: Today and Tomorrow

Genetically-encoded fluorescent sensors have been actively developed over the last few decades and used in live imaging and drug screening. Real-time monitoring of drug action in a specific cellular compartment, organ, or tissue type; the ability to screen at the single-cell resolution; and the elimination of false-positive results caused by low drug bioavailability that is not detected by in vitro testing methods are a few of the obvious benefits of using genetically-encoded fluorescent sensors in drug screening. In combination with high-throughput screening (HTS), some genetically-encoded fluorescent sensors may provide high reproducibility and robustness to assays. We provide a brief overview of successful, perspective, and hopeful attempts at using genetically encoded fluorescent sensors in HTS of modulators of ion channels, Ca2+ homeostasis, GPCR activity, and for screening cytotoxic, anticancer, and anti-parasitic compounds. We discuss the advantages of sensors in whole organism drug screening models and the perspectives of the combination of human disease modeling by CRISPR techniques with genetically encoded fluorescent sensors for drug screening.

Genetically encoded fluorescent biosensors illuminate kinase signaling in cancer

Protein kinase signaling networks stringently regulate cellular processes, such as proliferation, motility, and cell survival. These networks are also central to the evolution and progression of cancer. Accordingly, genetically encoded fluorescent biosensors capable of directly illuminating the spatiotemporal dynamics of kinase signaling in live cells are being increasingly used to investigate kinase signaling in cancer cells and tumor tissue sections. These biosensors enable visualization of biological processes and events directly in situ, preserving the native biological context and providing detailed insight into their localization and dynamics in cells. Herein, we first review common design strategies for kinase activity biosensors, including signaling targets, biosensor components, and fluorescent proteins involved. Subsequently, we discuss applications of biosensors to study the biology and management of cancer. These versatile molecular tools have been deployed to study oncogenic kinase signaling in living cells and image kinase activities in tumors or to decipher the mechanisms of anticancer drugs. We anticipate that the diversity and precision of genetically encoded biosensors will expand their use to further unravel the dysregulation of kinase signaling in cancer and the modes of actions of cancer-targeting drugs.

Biosensors and their applications - A review

The various types of biosensors such as enzyme-based, tissue-based, immunosensors, DNA biosensors, thermal and piezoelectric biosensors have been deliberated here to highlight their indispensable applications in multitudinous fields. Some of the popular fields implementing the use of biosensors are food industry to keep a check on its quality and safety, to help distinguish between the natural and artificial; in the fermentation industry and in the saccharification process to detect precise glucose concentrations; in metabolic engineering to enable in vivo monitoring of cellular metabolism. Biosensors and their role in medical science including early stage detection of human interleukin-10 causing heart diseases, rapid detection of human papilloma virus, etc. are important aspects. Fluorescent biosensors play a vital role in drug discovery and in cancer. Biosensor applications are prevalent in the plant biology sector to find out the missing links required in metabolic processes. Other applications are involved in defence, clinical sector, and for marine applications.

Fluorescent Reporters and Biosensors for Probing the Dynamic Behavior of Protein Kinases

Probing the dynamic activities of protein kinases in real-time in living cells constitutes a major challenge that requires specific and sensitive tools tailored to meet the particular demands associated with cellular imaging. The development of genetically-encoded and synthetic fluorescent biosensors has provided means of monitoring protein kinase activities in a non-invasive fashion in their native cellular environment with high spatial and temporal resolution. Here, we review existing technologies to probe different dynamic features of protein kinases and discuss limitations where new developments are required to implement more performant tools, in particular with respect to infrared and near-infrared fluorescent probes and strategies which enable improved signal-to-noise ratio and controlled activation of probes.

Crk at the quarter century mark: perspectives in signaling and cancer

The Crk adaptor protein, discovered 25 years ago as the transforming gene (v-crk) product encoded by the CT10 avian retrovirus, has made a great impact on the field of signal transduction. By encoding an oncoprotein that contained a viral gag protein fused to only SH2 and SH3 domains, v-Crk demonstrated the significance of SH2 and SH3 domains in oncogenic signaling by their virtue of binding in a sequence-specific context to organize and assemble protein networks. In more recent years, the cellular homologs of Crk (Crk II, Crk I, and CrkL) have been extensively studied, and shown to have critical functions in a wide spectrum of biological and pathological processes that include cell motility, invasion, survival, bacterial pathogenesis, and the efferocytosis of apoptotic cells. Clinically, Crk proteins are implicated in the aggressive behavior of human cancers, including adenocarcinomas of the lung, breast, and stomach, as well as in sarcomas and gliomas. Over-expression of Crk proteins in human cancers has led to a renewed interest in both their signal transduction pathways and mechanisms of up-regulation. This prospect summarizes recent developments in Crk biology, including new structural and biochemical roles for the atypical carboxyl-terminal SH3 (SH3C) domain, revelations regarding the molecular differences between Crk II and Crk L, and the significance of Crk expression in stratified human tumor samples.

Fluorescent biosensors for high throughput screening of protein kinase inhibitors

High throughput screening assays aim to identify small molecules that interfere with protein function, activity, or conformation, which can serve as effective tools for chemical biology studies of targets involved in physiological processes or pathways of interest or disease models, as well as templates for development of therapeutics in medicinal chemistry. Fluorescent biosensors constitute attractive and powerful tools for drug discovery programs, from high throughput screening assays, to postscreen characterization of hits, optimization of lead compounds, and preclinical evaluation of candidate drugs. They provide a means of screening for inhibitors that selectively target enzymatic activity, conformation, and/or function in vitro. Moreover, fluorescent biosensors constitute useful tools for cell- and image-based, multiplex and multiparametric, high-content screening. Application of fluorescence-based sensors to screen large and complex libraries of compounds in vitro, in cell-based formats or whole organisms requires several levels of optimization to establish robust and reproducible assays. In this review, we describe the different fluorescent biosensor technologies which have been applied to high throughput screens, and discuss the prerequisite criteria underlying their successful application. Special emphasis is placed on protein kinase biosensors, since these enzymes constitute one of the most important classes of therapeutic targets in drug discovery.

CRK SH3N Domain Diminishes Cell Invasiveness of Non-Small Cell Lung Cancer

CRK (c-Crk) as an adaptor protein is involved in several oncogenic signal transduction pathways, conveying oncogenic signals to its downstream effectors and thereby affecting multiple cellular processes including proliferation, differentiation, and migration. For example, we have observed that CRK expression and phosphorylation influence the invasiveness of non-small cell lung cancer (NSCLC) cells. To intervene in CRK signaling pathway, we examined whether CRK protein domains can be used as therapeutic tools to interrupt CRK signaling, thus influencing the biological behavior of NSCLC cells. For this purpose, Src Homology domains of CRK-I (i.e., SH2 and SH3N domains) were overexpressed in H157, Rh2, and A549 cells. CRK-SH3N domain expression induced epithelial morphology in H157 cells and enhanced epithelial morphology of A549 and Rh2 cells as compared to cells transfected with CRK-SH2 domain or empty vector. In addition, CRK-SH3N domain expression significantly decreased the motility and invasiveness of A549 and H157 cells. Furthermore, CRK-SH3N domain expression disrupted the interaction of CRK-II with DOCK180. In summary, these data provide evidence that the CRK-SH3N domain can be used to influence the malignant phenotype of NSCLC cells and also reduce the metastatic potential of these cells.

Application of FRET probes in the analysis of neuronal plasticity

Breakthroughs in imaging techniques and optical probes in recent years have revolutionized the field of life sciences in ways that traditional methods could never match. The spatial and temporal regulation of molecular events can now be studied with great precision. There have been several key discoveries that have made this possible. Since green fluorescent protein (GFP) was cloned in 1992, it has become the dominant tracer of proteins in living cells. Then the evolution of color variants of GFP opened the door to the application of Förster resonance energy transfer (FRET), which is now widely recognized as a powerful tool to study complicated signal transduction events and interactions between molecules. Employment of fluorescent lifetime imaging microscopy (FLIM) allows the precise detection of FRET in small subcellular structures such as dendritic spines. In this review, we provide an overview of the basic and practical aspects of FRET imaging and discuss how different FRET probes have revealed insights into the molecular mechanisms of synaptic plasticity and enabled visualization of neuronal network activity both in vitro and in vivo.

Fluorescent biosensors - probing protein kinase function in cancer and drug discovery

One of the challenges of modern biology and medicine is to visualize biomolecules in their natural environment, in real-time and in a non-invasive fashion, so as to gain insight into their physiological behavior and highlight alterations in pathological settings, which will enable to devise appropriate therapeutic strategies. Fluorescent biosensors constitute a class of imaging agents which have provided major insights into the function and regulation of enzymes in their cellular context. GFP-based reporters and genetically-encoded FRET biosensors, have been successfully applied to study protein kinases in living cells with high spatial and temporal resolution. In parallel, combined efforts in fluorescence chemistry and in chemical biology have enabled the design of non-genetic, polypeptide biosensors coupled to small synthetic fluorescent probes, which have been applied to monitor protein kinase activities in vitro and in more complex biological samples, with an equally successful outcome. From a biomedical perspective, fluorescent biosensor technology is well suited to development of diagnostic approaches, for monitoring disease progression and for evaluating response to therapeutics. Moreover it constitutes an attractive technology for drug discovery programs, for high content, high throughput screening assays, to assess the potency of new hits and optimize lead compounds, whilst also serving to characterize drugs developed through rational design. This review describes the utility and versatility of fluorescence biosensor technology to probe protein kinases with a specific focus on CDK/cyclin biosensors we have developed to probe abundance, activity and conformation. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

Emerging roles for crk in human cancer

Adaptor proteins are named for their function in assembling complexes of cellular proteins to execute and facilitate transmission of signals. The Crk family of adaptors consists of 2 members, Crk and CrkL. Crk, which was originally isolated as an oncogene, v-Crk, that transforms CEFs, has at least 2 splice variants, CrkI and CrkII, with differing biological activities. All Crk family proteins serve to act as molecular bridges between tyrosine kinases and their substrates and also modulate the specificity and stoichiometry of signaling processes. Signaling via CrkII and CrkL can be negatively regulated via tyrosine phosphorylation-mediated autoinhibition, while such a mechanism is not known to exist for CrkI. Although v-Crk clearly functions as a bona fide oncogene, in recent years, an emerging body of evidence suggests that cellular Crk proteins are overexpressed in human tumors and the expression levels correlate with aggressive and malignant behavior of cancer cells. These properties of Crk proteins make them potential cancer prognosis markers and therapeutic targets.