Applying label-free dynamic mass redistribution assay for studying endogenous FPR1 receptor signalling in human neutrophils

The Neutrophil Dynamic Mass Redistribution Assay as a Medium throughput Primary Cell Screening Assay

In a typical G protein coupled receptor drug discovery campaign, an in vitro primary functional screening assay is often established in a recombinant system overexpressing the target of interest, which offers advantages with respect to overall throughput and robustness of compound testing. Subsequently, compounds are then progressed into more physiologically relevant but lower throughput ex vivo primary cell assays and finally in vivo studies. Here we describe a dynamic mass redistribution (DMR) assay that has been developed in a format suitable to support medium throughput drug screening in primary human neutrophils. Neutrophils are known to express both CXC chemokine receptor (CXCR) 1 and CXCR2 that are thought to play significant roles in various inflammatory disorders and cancer. Using multiple relevant chemokine ligands and a range of selective and nonselective small and large molecule antagonists that block CXCR1 and CXCR2 responses, we demonstrate distinct pharmacological profiles in neutrophil DMR from those observed in recombinant assays but predictive of activity in neutrophil chemotaxis and CD11b upregulation, a validated target engagement marker previously used in clinical studies of CXCR2 antagonists. The primary human neutrophil DMR cell system is highly reproducible, robust, and less prone to donor variability observed in CD11b and chemotaxis assays and thus provides a unique, more physiologically relevant, and higher throughput assay to support drug discovery and translation to early clinical trials. SIGNIFICANCE STATEMENT: Neutrophil dynamic mass redistribution assays provide a higher throughput screening assay to profile compounds in primary cells earlier in the screening cascade enabling a higher level of confidence in progressing the development of compounds toward the clinic. This is particularly important for chemokine receptors where redundancy contributes to a lack of correlation between recombinant screening assays and primary cells, with the coexpression of related receptors confounding results.

Future Directions for the Discovery of Natural Product-Derived Immunomodulating Drugs

Drug discovery from natural sources is going through a renaissance, having spent many decades in the shadow of synthetic molecule drug discovery, despite the fact that natural product-derived compounds occupy a much greater chemical space than those created through synthetic chemistry methods. With this new era comes new possibilities, not least the novel targets that have emerged in recent times and the development of state-of-the-art technologies that can be applied to drug discovery from natural sources. Although progress has been made with some immunomodulating drugs, there remains a pressing need for new agents that can be used to treat the wide variety of conditions that arise from disruption, or over-activation, of the immune system; natural products may therefore be key in filling this gap. Recognising that, at present, there is no authoritative article that details the current state-of-the-art of the immunomodulatory activity of natural products, this in-depth review has arisen from a joint effort between the International Union of Basic and Clinical Pharmacology (IUPHAR) Natural Products and Immunopharmacology, with contributions from a Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation number of world-leading researchers in the field of natural product drug discovery, to provide a "position statement" on what natural products has to offer in the search for new immunomodulatory argents. To this end, we provide a historical look at previous discoveries of naturally occurring immunomodulators, present a picture of the current status of the field and provide insight into the future opportunities and challenges for the discovery of new drugs to treat immune-related diseases.

Label-free real-time monitoring of the BCR-triggered activation of primary human B cells modulated by the simultaneous engagement of inhibitory receptors

Today, there is an intense demand for lab-on-a-chip and tissue-on-a-chip applications in basic cell biological research and medical diagnostics. A particular challenge is the implementation of advanced biosensor techniques in point-of-care testing utilizing human primary cells. In this study, a resonant waveguide grating (RWG)-based label-free optical biosensor technique has been applied for real-time monitoring of the integrated responses of primary human tonsillar B cells initiated by B cell receptor (BCR) and modified by FcγRIIb and CR1 engagement. The BCR-triggered biosensor responses of resting and activated B cells were revealed to be specific and dose-dependent, in some cases with strong donor dependency. Targeted inhibition of Syk attenuated the label-free biosensor response upon BCR stimulation. Indifferent protein human serum albumin (HSA) did not interfere with the recorded signal to BCR stimulation. Simultaneous engagement of BCR and FcγRIIb modulated the kinetic signal of the cells. Activated and resting B cells exhibited different response profiles upon simultaneous engagement of BCR and CR1. This advanced approach has the potential to decipher interfering signaling events in human B cells, manage differences between activated and resting B cell states, helping to understand the actual integrated response of these immune cells, and could be useful in the point-of-care diagnostic testing on human primary cells.

Delineation of molecular determinants for FR900359 inhibition of Gq/11 unlocks inhibition of Gαs

Heterotrimeric G proteins are essential mediators of intracellular signaling of G protein-coupled receptors. The G_q/11 subfamily consists of G_q, G₁₁, G₁₄, and G₁₆ proteins, of which all but G₁₆ are inhibited by the structurally related natural products YM-254890 and FR900359. These inhibitors act by preventing the GDP/GTP exchange, which is necessary for activation of all G proteins. A homologous putative binding site for YM-254890/FR900359 can also be found in members of the other three G protein families, G_s, G_i/o, and G_12/13, but none of the published analogs of YM-254890/FR900359 have shown any inhibitory activity for any of these. To explain why the YM-254890/FR900359 scaffold only inhibits G_q/11/14, the present study delineated the molecular selectivity determinants by exchanging amino acid residues in the YM-254890/FR900359-binding site in G_q and G_s We found that the activity of a G_s mutant with a G_q-like binding site for YM-254890/FR900359 can be inhibited by FR900359, and a minimum of three mutations are necessary to introduce inhibition in G_s In all, this suggests that although the YM-254890/FR900359 scaffold has proven unsuccessful to derive G_s, G_i/o, and G_12/13 inhibitors, the mechanism of inhibition between families of G proteins is conserved, opening up the possibility of targeting by other, novel inhibitor scaffolds. In lack of a selective Gα_s inhibitor, FR900359-sensitive Gα_s mutants may prove useful in studies where delicate control over Gα_s signaling would be of the essence.

Phenotypic assessment and ligand screening of ETA/ETB receptors with label-free dynamic mass redistribution assay

Endothelin receptors, consisting of two subtypes, ETA and ETB, are expressed in various tissues and widely regulate cardiovascular systems. The two receptors show distinct biological characteristics and are involved in different downstream pathways. Hence, to evaluate the ETA and ETB receptors on the same platform is helpful to display their pharmacological features. In this study, we developed a label-free dynamic mass redistribution (DMR) assay to investigate the phenotypic features of the ETA and ETB receptors in native cell lines. Meanwhile, specific agonists and antagonists were investigated for their pharmacological parameters. Results indicated that the DMR response of endothelin 1 (ET-1, an endogenous ETA/ETB agonist) was cell line dependent on ETA receptors and this ligand generated a biphasic dose-response curve in SH-SY5Y as well as PC3 cell lines. ET-1 and IRL 1620 (an ETB agonist) showed different DMR responses in U251 cells. IC₅₀ values of antagonists were consistent with the K_i values previously reported. Furthermore, a list of compounds was screened on the ETA and ETB receptor models established by the high-throughput DMR assays. This study demonstrated that the DMR assay had great potential in the phenotypic-based investigation and ligand screening of GPCRs.

Label-free dynamic mass redistribution analysis of endogenous adrenergic receptor signaling in primary preadipocytes and differentiated adipocytes

INTRODUCTION

Adipose tissues release adipokines, which regulate energy intake and expenditure. G protein-coupled receptors (GPCRs) and associated signaling pathways in adipocytes are potentially important drug targets for conditions with disturbed energy metabolism.

METHODS

The aim of the current study was to compare signaling of endogenously expressed GPCRs between primary preadipocytes and differentiated adipocytes using a novel state-of-the-art unbiased method that measures dynamic mass redistribution (DMR) in real-time. Adrenergic agonists were chosen since they control adipocyte functions such as lipolysis and glycogenolysis.

RESULTS

Isoprenaline (ISO) and phenylephrine (PE) elicited concentration-dependent responses in preadipocytes and differentiated adipocytes. The effect of ISO was cholera toxin (CTX)-sensitive, indicating it is G_s-dependent. The effect could also be blocked by propranolol proving the signal is mediated through β-adrenergic receptors. The signaling resulting from PE stimulation was completely abolished by the G_q/11-selective inhibitor FR900359 and CTX in preadipocytes but surprisingly became FR900359-insensitive but remained CTX-sensitive in differentiated adipocytes. The use of prazosin and propranolol revealed that the PE-response in differentiated adipocytes had a β-adrenergic receptor component to it. In addition, we tested the bone-derived peptide osteocalcin, which did not result in DMR changes in preadipocytes or differentiated adipocytes.

DISCUSSION

In conclusion, this study for the first time demonstrates that DMR assays can be used to assess signaling in differentiated adipocytes. This platform can serve as a tool for future drug screening in primary adipocytes. Furthermore, this study illustrates that PE-induced effects on adipocytes vary by developmental stage and are not as selective as originally thought.

Pharmacological profile of the neuropeptide S receptor: Dynamic mass redistribution studies

Neuropeptide S (NPS) is the endogenous ligand of the neuropeptide S receptor (NPSR). NPS modulates several biological functions including anxiety, wakefulness, pain, and drug abuse. The aim of this study was the investigation of the pharmacological profile of NPSR using the dynamic mass redistribution (DMR) assay. DMR is a label-free assay that offers a holistic view of cellular responses after receptor activation. HEK293 cells stably transfected with the murine NPSR (HEK293mNPSR) have been used. To investigate the nature of the NPS-evoked DMR signaling, FR900359 (Gq inhibitor), pertussis toxin (Gi inhibitor), and rolipram (phosphodiesterase inhibitor) were used. To determine the pharmacology of NPSR, several selective ligands (agonists, partial agonists, antagonists) have been tested. NPS, through selective NPSR activation, evoked a robust DMR signal with potency in the nanomolar range. This signal was predominantly, but not completely, blocked by FR900359, suggesting the involvement of the Gq-dependent signaling cascade. NPSR ligands (agonists and antagonists) displayed potency values in DMR experiments similar, but not identical, to those reported in the literature. Furthermore, partial agonists produced a higher efficacy in DMR than in calcium experiments. DMR can be successfully used to study the pharmacology and signaling properties of novel NPSR ligands. This innovative approach will likely increase the translational value of in vitro pharmacological studies.

Label-Free Whole Cell Biosensing for High-Throughput Discovery of Activators and Inhibitors Targeting G Protein-Activated Inwardly Rectifying Potassium Channels

Dynamic mass redistribution (DMR) and cellular dielectric spectroscopy (CDS) are label-free biosensor technologies that capture real-time integrated cellular responses upon exposure to extra- and intracellular stimuli. They register signaling routes that are accompanied by cell shape changes and/or molecular movement of cells proximal to the biosensor to which they are attached. Here, we report the unexpected observation that robust DMR and CDS signatures are also elicited upon direct stimulation of G protein-activated inwardly rectifying potassium (GIRK) channels, which are involved in the regulation of excitability in the heart and brain. Using ML297, a small-molecule GIRK activator, along with channel blockers and cytoskeletal network inhibitors, we found that GIRK activation exerts its effects on cell shape by a mechanism which depends on actin but not the microtubule network. Because label-free real-time biosensing (i) quantitatively determines concentration dependency of GIRK activators, (ii) accurately assesses the impact of GIRK channel blockers, (iii) is high throughput-compatible, and (iv) visualizes previously unknown cellular consequences downstream of direct GIRK activation, we do not only provide a novel experimental strategy for identification of GIRK ligands but also an entirely new angle to probe GIRK (ligand) biology. We envision that DMR and CDS may add to the repertoire of technologies for systematic exploitation of ion channel function and, in turn, to the identification of novel GIRK ligands in order to treat cardiovascular and neurological disorders.

Targeted delivery of antisense oligonucleotides to pancreatic β-cells

Antisense oligonucleotide (ASO) silencing of the expression of disease-associated genes is an attractive novel therapeutic approach, but treatments are limited by the ability to deliver ASOs to cells and tissues. Following systemic administration, ASOs preferentially accumulate in liver and kidney. Among the cell types refractory to ASO uptake is the pancreatic insulin-secreting β-cell. Here, we show that conjugation of ASOs to a ligand of the glucagon-like peptide-1 receptor (GLP1R) can productively deliver ASO cargo to pancreatic β-cells both in vitro and in vivo. Ligand-conjugated ASOs silenced target genes in pancreatic islets at doses that did not affect target gene expression in liver or other tissues, indicating enhanced tissue and cell type specificity. This finding has potential to broaden the use of ASO technology, opening up novel therapeutic opportunities, and presents an innovative approach for targeted delivery of ASOs to additional cell types.

NOP receptor pharmacological profile - A dynamic mass redistribution study

The Nociceptin/Orphanin FQ (N/OFQ) peptide NOP receptor is coupled to pertussis toxin (PTX)-sensitive G proteins (G_i/o) whose activation leads to the inhibition of both cAMP production and calcium channel activity, and to the stimulation of potassium currents. The label free dynamic mass redistribution (DMR) approach has been demonstrated useful for investigating the pharmacological profile of G protein-coupled receptors. Herein, we employ DMR technology to systematically characterize the pharmacology of a large panel of NOP receptor ligands. These are of peptide and non-peptide nature and display varying degrees of receptor efficacy, ranging from full agonism to pure antagonism. Using Chinese hamster ovary (CHO) cells expressing the human NOP receptor we provide rank orders of potency for full and partial agonists as well as apparent affinities for selective antagonists. We find the pharmacological profile of NOP receptor ligands to be similar but not identical to values reported in the literature using canonical assays for G_i/o-coupled receptors. Our data demonstrate that holistic label-free DMR detection can be successfully used to investigate the pharmacology of the NOP receptor and to characterize the cellular effects of novel NOP receptor ligands.