Present and future approaches to screening of G-protein-coupled receptors

Increased testosterone and proinflammatory cytokines in patients with polycystic ovary syndrome correlate with elevated GnRH receptor autoantibody activity assessed by a fluorescence resonance energy transfer-based bioassay

PURPOSE

The recently identified agonistic autoantibodies (AAb) to the gonadotropin-releasing hormone receptor (GnRHR) are a novel investigative and therapeutic target for polycystic ovary syndrome (PCOS). In this study, we used a new cell-based fluorescence resonance energy transfer (FRET) bioassay to analyze serum GnRHR-AAb activity and examine its relationship with testosterone and proinflammatory cytokines in patients with PCOS.

METHODS

Serum samples from 33 PCOS patients, 39 non-PCOS ovulatory infertile controls and 30 normal controls were tested for GnRHR-AAb activity and proinflammatory cytokines in a FRET-based bioassay and multiplex bead-based immunoassay, respectively. Correlation was analyzed using the Spearman's correlation test.

RESULTS

Serum GnRHR-AAb activity was significantly higher in the PCOS patients than for the ovulatory infertile (p < 0.05) and normal (p < 0.01) controls. GnRHR-AAb were positive in 39% of PCOS patients, 10% of ovulatory infertile controls, and 0% of normal controls. PCOS IgG-induced GnRHR activation was specifically blocked by the GnRHR antagonist cetrorelix. Serum levels of proinflammatory cytokines interleukin-2, interleukin-6, interferon-γ, and tumor necrosis factor-α were significantly increased in PCOS patients compared with ovulatory infertile and normal controls (p < 0.01). Correlation analysis demonstrated positive correlations of GnRHR-AAb activity with testosterone and proinflammatory cytokine levels in the PCOS group.

CONCLUSIONS

Elevated GnRHR-AAb activity, as assessed by a new FRET assay, is associated with increased testosterone and proinflammatory cytokines in PCOS, suggesting autoimmune activation of GnRHR may contribute to the pathogenesis of this common disorder.

Illuminating the Path to Target GPCR Structures and Functions

G-Protein-coupled receptors (GPCRs) are ubiquitous within eukaryotes, responsible for a wide array of physiological and pathological processes. Indeed, the fact that they are the most drugged target in the human genome is indicative of their importance. Despite the clear interest in GPCRs, most information regarding their activity has been so far obtained by analyzing the response from a "bulk medium". As such, this Perspective summarizes some of the common methods for this indirect observation. Nonetheless, by inspecting approaches applying super-resolution imaging, we argue that imaging is perfectly situated to obtain more detailed structural and spatial information, assisting in the development of new GPCR-targeted drugs and clinical strategies. The benefits of direct optical visualization of GPCRs are analyzed in the context of potential future directions in the field.

Cell-impedance-based label-free technology for the identification of new drugs

INTRODUCTION

Drug discovery has progressed from relatively simple binding or activity screening assays to high-throughput screening of sophisticated compound libraries with emphasis on miniaturization and automation. The development of functional assays has enhanced the success rate in discovering novel drug molecules. Many technologies, originally based on radioactive labeling, have sequentially been replaced by methods based on fluorescence labeling. Recently, the focus has switched to label-free technologies in cell-based screening assays. Areas covered: Label-free, cell-impedance-based methods comprise of different technologies including surface plasmon resonance, mass spectrometry and biosensors applied for screening of anticancer drugs, G protein-coupled receptors, receptor tyrosine kinase and virus inhibitors, drug and nanoparticle cytotoxicity. Many of the developed methods have been used for high-throughput screening in cell lines. Cell viability and morphological damage prediction have been monitored in three-dimensional spheroid human HT-29 carcinoma cells and whole Schistosomula larvae. Expert opinion: Progress in label-free, cell-impedance-based technologies has facilitated drug screening and may enhance the discovery of potential novel drug molecules through, and improve target molecule identification in, alternative signal pathways. The variety of technologies to measure cellular responses through label-free cell-impedance based approaches all support future drug development and should provide excellent assets for finding better medicines.

Semliki forest virus-based expression of recombinant GPCRs

Due to their importance as targets for drug development, rapid and consistent high-level production of G protein-coupled receptors (GPCRs) has become an essential part of drug discovery. Alphaviruses, particularly recombinant Semliki Forest virus (SFV) particles, have provided the means for expression of a number of GPCRs in a broad range of mammalian host cell lines for pharmacological characterization by determination of receptor binding activity and functional coupling to G proteins. The rapid high-titer virus particle production has made it possible to study a large number of GPCRs in parallel. Moreover, large-scale production in adherent and suspension cultures of mammalian cells has provided sufficient amounts of GPCRs for purification and subsequent structural studies. Furthermore, the high preference for neuronal delivery of SFV particles has allowed functional and localization studies of recombinant proteins in hippocampal slice cultures, in primary neurons, and in vivo.

RNA-based drugs and vaccines

RNA-based approaches have provided novel alternatives for modern drug discovery. The application of RNA as therapeutic agents has, until recently, been hampered by issues related to poor delivery and stability, but chemical modifications and new delivery approaches have increased progress. Moreover, the discovery of the importance of RNA in gene regulation and gene silencing has revealed new drug targets, especially related to treatment of cancer and other diseases. Recent engineering of small molecules designed from RNA sequences to target miRNAs opens up new possibilities in drug development. Furthermore, RNA-based vaccines have been engineered applying RNA virus vectors and non-viral delivery for vaccine development.