Testing for the erythropoiesis-stimulating agent Sotatercept/ACE-011 (ActRIIA-Fc) in serum by means of Western blotting and LC-HRMS

Detection of the GH analog somatrogon in sports drug testing: Immunological approaches and LC-HRMS/MS

Due to the presumed lipolytic and anabolic properties, the misuse of human growth hormone (hGH) and its synthetic analogs in sports is prohibited both in- and out-of-competition. Within this research project, the detectability of somatrogon, a recombinant fusion glycoprotein of 22 kDa hGH and the C-terminal peptide (CTP) of the human chorionic gonadotropin (hCG) β-subunit, with current WADA-approved doping control assays for hGH and hCG was investigated. For that purpose, cross-reactivity tests and a somatrogon administration study were conducted, and only "Kit 2" of the GH isoform differential immunoassays proved applicable to the detection of somatrogon administration in serum. In urine, the immunoassay specific for total hCG yielded presumptively positive findings for several post-administration samples, which can probably be attributed to the presence of an immunoreactive fragment of the hCG β-subunit. As the detectability of somatrogon with these approaches was found to be limited, a highly specific detection assay (LOD: 10 ng/mL) for the drug in serum samples was developed by using affinity purification with GH receptor (GHR)-conjugated magnetic beads, proteolytic digestion, and liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). Following optimization, the approach was comprehensively characterized, and authentic post-administration serum samples were successfully analyzed as proof-of-concept, indicating a detection window of at least 96 h. Consequently, the presented method can be employed to confirm the presence of somatrogon in serum samples, where only "Kit 2" of the currently used immunoassay kits yielded an abnormally high Rec/Pit ratio.

Human Chorionic Gonadotropin Regulates the Smad Signaling Pathway by Antagonizing TGF-β in Giant Cell Tumor of Bone

BACKGROUND

Giant cell tumor of bone (GCTB) is a locally aggressive bone tumour aggravated by stromal cell proliferation and metastasis.

OBJECTIVE

We investigated the mechanism of action of human chorionic gonadotropin (HCG) in mediating GCTB proliferation and invasion.

METHODS

The expression of HCG was quantified using quantitative real-time PCR. After the primary stromal cells were isolated and identified, the function of HCG in GCTB was estimated using the cell counting kit-8, flow cytometry, scratch experiment, transwell assay, Western blot, and immunofluorescence. Moreover, the mechanism of HCG was assessed through western blotting.

RESULTS

HCG expression was decreased in clinical tissue samples from patients with GCTB. We validated that HCG repressed stromal cell proliferation, migration, invasion, autophagy, and epithelial- mesenchymal transition (EMT) and promoted cell apoptosis in GCTB. We also verified that HCG repressed the autophagy and EMT of stromal cells through the Smad signaling axis in GCTB. HCG inhibited the transduction of the Smad signaling pathway by restraining the binding of the TGF-β II receptor to ligand Activin A.

CONCLUSION

HCG restrained the Smad signaling pathway by antagonizing TGF-β signaling in GCTB. HCG may serve as a useful patent to treat GCTB.

Recent advances in mass spectrometry for the detection of doping

INTRODUCTION

The analysis of doping control samples is preferably performed by mass spectrometry, because obtained results meet the highest analytical standards and ensure an impressive degree of reliability. The advancement in mass spectrometry and all its associated technologies thus allow for continuous improvements in doping control analysis.

AREAS COVERED

Modern mass spectrometric systems have reached a status of increased sensitivity, robustness, and specificity within the last decade. The improved sensitivity in particular has, on the other hand, also led to the detection of drug residues that were attributable to scenarios where the prohibited substances were not administered consciously but rather by the unconscious ingestion of or exposure to contaminated products. These scenarios and their doubtless clarification represent a great challenge. Here, too, modern MS systems and their applications can provide good insights in the interpretation of dose-related metabolism of prohibited substances. In addition to the development of new instruments itself, software-assisted analysis of the sometimes highly complex data is playing an increasingly important role and facilitating the work of doping control laboratories.

EXPERT OPINION

The sensitive analysis and evaluation of a higher number of samples in a shorter time is made possible by the ongoing developments in mass spectrometry.

Detection of follistatin-based inhibitors of the TGF-β signaling pathways in serum/plasma by means of LC-HRMS/MS and Western blotting

Cytokines of the transforming growth factor beta (TGF-β) superfamily such as myostatin and activin A are considered as key regulators of skeletal muscle mass. In vivo, their activity is controlled by different binding proteins such as follistatin (FST), whose interaction with the circulating growth factors prevents activation of the activin type II receptors. FST-based protein therapeutics are therefore not only promising drug candidates for the treatment of muscular diseases but also potential performance-enhancing agents in sports. Within this study, two complementary detection assays for FST-based inhibitors of the TGF-β signaling pathways in doping control serum and plasma samples were developed by using both monomeric FST and dimeric FST-Fc fusion proteins as model compounds. The initial testing procedure is based on immunoaffinity purification, tryptic digestion, and LC-HRMS/MS, offering high specificity by targeting tryptic signature peptides of FST. As the glycoprotein is also produced endogenously, the confirmation method employs immunoaffinity purification, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and Western blotting in order to detect the intact proteins and differentiate synthetic FST-Fc constructs from naturally occurring FST isoforms. Both assays were found to be highly specific with an estimated detection limit of 10 ng/ml. Moreover, a commercial sandwich enzyme-linked immunosorbent assay was used to determine endogenous FST values. The detected FST serum levels of healthy volunteers were found below 5 ng/ml, which is in accordance with reference values from the literature and below the doping control detection methods' limit of detection (LOD). The presented assays expand the range of available tests for emerging doping agents, and the initial testing procedure can readily be modified to include further protein drugs.

Development of two complementary LC–HRMS methods for analyzing sotatercept in dried blood spots for doping controls

Aim: sotatercept is a therapeutic Fc-fusion protein with erythropoiesis-stimulating activity. Due to a potential abuse of the drug by athletes in professional sports, a sensitive detection method is required. In sports drug testing, alternative matrices such as dried blood spots (DBS) are gaining increasing attention as they can provide several advantages over conventional matrices. Materials & methods: Herein, two complementary LC–high-resolution mass spectrometry (HRMS) detection methods for sotatercept from DBS, an initial testing procedure (ITP) and a confirmation procedure (CP) were developed and validated for the first time. Both methods comprise an ultrasonication-assisted extraction, affinity enrichment, proteolytic digestion and HRMS detection. Results & conclusion: For the multianalyte ITP, artificial samples fortified with sotatercept, luspatercept and bimagrumab, and authentic specimens containing bimagrumab were successfully analyzed as proof-of-concept. The validated detection methods for sotatercept are fit for purpose and the ITP was shown to be suitable for the detection of novel IgG-based pharmaceuticals in doping control DBS samples.

Bone morphogenetic protein receptor signal transduction in human disease

Bone morphogenetic proteins (BMPs) are secreted cytokines that were initially discovered on the basis of their ability to induce bone. Several decades of research have now established that these proteins function in a large variety of physiopathological processes. There are about 15 BMP family members, which signal via three transmembrane type II receptors and four transmembrane type I receptors. Mechanistically, BMP binding leads to phosphorylation of the type I receptor by the type II receptor. This activated heteromeric complex triggers intracellular signaling that is initiated by phosphorylation of receptor‐regulated SMAD1, 5, and 8 (also termed R‐SMADs). Activated R‐SMADs form heteromeric complexes with SMAD4, which engage in specific transcriptional responses. There is convergence along the signaling pathway and, besides the canonical SMAD pathway, BMP‐receptor activation can also induce non‐SMAD signaling. Each step in the pathway is fine‐tuned by positive and negative regulation and crosstalk with other signaling pathways. For example, ligand bioavailability for the receptor can be regulated by ligand‐binding proteins that sequester the ligand from interacting with receptors. Accessory co‐receptors, also known as BMP type III receptors, lack intrinsic enzymatic activity but enhance BMP signaling by presenting ligands to receptors. In this review, we discuss the role of BMP receptor signaling and how corruption of this pathway contributes to cardiovascular and musculoskeletal diseases and cancer. We describe pharmacological tools to interrogate the function of BMP receptor signaling in specific biological processes and focus on how these agents can be used as drugs to inhibit or activate the function of the receptor, thereby normalizing dysregulated BMP signaling. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Combined detection of the ActRII-Fc fusion proteins Sotatercept (ActRIIA-Fc) and Luspatercept (modified ActRIIB-Fc) in serum by means of immunoaffinity purification, tryptic digestion, and LC-MS/MS

Therapeutic proteins are a continuously growing class of pharmaceuticals and comprise several drug candidates with potential performance-enhancing properties. In particular, activin receptor competitors, such as the ActRII-Fc fusion proteins Sotatercept (ActRIIA-Fc) and Luspatercept (modified ActRIIB-Fc), have the potential for being misused as doping agents in sports as they were found to inhibit negative regulators of late-stage erythropoiesis. Within this study, ammonium sulfate precipitation, immunoaffinity purification, tryptic digestion, and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were employed to develop an assay for the combined detection of Sotatercept and Luspatercept in doping control serum samples. The assay was optimized, comprehensively characterized, and found to be fit-for-purpose for application to sports drug testing. It complements existing tests for ActRII-Fc fusion proteins and expands the range of available detection methods for novel protein therapeutics.

A validated, sensitive electrophoretic method for the detection of activin receptor type II-Fc fusion proteins in human blood

New therapeutic proteins that trap circulating members of the transforming growth factor (TGF) beta superfamily (activins and growth differentiation factors) show promising effects on erythropoiesis and muscular growth. They are dimeric recombinant fusion proteins composed of the extracellular domain of a human activin receptor (ActRIIA or IIB) linked to the Fc part of human IgG1. Sotatercept (ActRIIA-Fc) and Luspatercept (a modified ActRIIB-Fc) in particular are now in phase 2/3 of clinical trials against anemia and included in the prohibited list established by the World Anti-Doping Agency. To prevent a potential misuse by athletes in the near future, a robust and sensitive method of detection is needed. We validated an approach adapted from an electrophoretic method used for the detection of recombinant erythropoietins that allowed detection of various ActRIIA-Fc and ActRIIB-Fc proteins, including variants produced in different cell types, after a single immuno-extraction step. After separation by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), an initial testing procedure performed by single-blotting can indicate the presence of an ActRII-Fc (indifferently type IIA or IIB). A confirmation performed by double-blotting using different antibodies for detection allows a more precise identification of the type of ActRII-Fc (IIA, IIB). Starting from a few hundred microliters of serum or plasma, this method is specific, sensitive, and easy to perform. It could easily be adopted by anti-doping laboratories.

Immunoaffinity techniques coupled to mass spectrometry for the analysis of human peptide hormones: advances and applications

INTRODUCTION

The accurate and comprehensive determination of peptide hormones from biological fluids has represented a considerable challenge to analytical chemists for decades. Besides long-established bioanalytical ligand binding assays (or ELISA, RIA, etc.), more and more mass spectrometry-based methods have been developed recently for purposes commonly referred to as targeted proteomics. Eventually the combination of both, analyte extraction by immunoaffinity and subsequent detection by mass spectrometry, has shown to synergistically enhance the test methods' performance characteristics. Areas covered: The review provides an overview about the actual state of existing methods and applications concerning the analysis of endogenous peptide hormones. Here, special focus is on recent developments considering the extraction procedures with immobilized antibodies, the subsequent separation of target analytes, and their detection by mass spectrometry. Expert commentary: Key aspects of procedures aiming at the detection and/or quantification of peptidic analytes in biological matrices have experienced considerable improvements in the last decade, particularly in terms of the assays' sensitivity, the option of multiplexing target compounds, automatization, and high throughput operation. Despite these advances and progress as expected to be seen in the near future, immunoaffinity purification coupled to mass spectrometry is not yet a standard procedure in routine analysis compared to ELISA/RIA.

Patent Highlights October-November 2016

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.