Riociguat in children with pulmonary arterial hypertension: The PATENT-CHILD study.

Riociguat, a soluble guanylate cyclase stimulator, is approved for treatment of adults with pulmonary arterial hypertension (PAH). The safety, tolerability, and pharmacokinetics (PK) of oral riociguat in a pediatric population with PAH was assessed in PATENT-CHILD (NCT02562235), a multicenter, single-arm, 24-week, open-label, Phase 3 study. Patients aged 6-17 years in World Health Organization functional class (WHO-FC) I-III treated with stable endothelin receptor antagonists and/or prostacyclin analogs received riociguat equivalent to 0.5-2.5 mg three times daily in adults, as either oral pediatric suspension or tablets, based on bodyweight. Primary outcomes were safety, tolerability, and PK of riociguat. Twenty-four patients (mean age 12.8 years), 18 of whom were in WHO-FC II, were enrolled. Adverse events (AEs), mostly mild or moderate, were reported in 20 patients (83%). Four patients (17%) experienced a serious AE; all resolved by study end and two (8%) were considered study-drug related. Hypotension was reported in three patients and hemoptysis in one (all mild/moderate intensity). Riociguat plasma concentrations in pediatric patients were consistent with those published in adult patients. From baseline to Week 24, mean ± standard deviation increase in 6-minute walking distance was 23 ± 69 m (n = 19), and mean decrease in NT-proBNP was -66 ± 585 pg/ml (n = 14). There was no change in WHO-FC. Two patients experienced clinical worsening events of hospitalization for right heart failure. PK results confirmed a suitable riociguat dosing strategy for pediatric patients with PAH. The data suggest an acceptable safety profile with potential efficacy signals.

To Anion-π or not to Anion-π: The Case of Anion-Binding to Divalent Fluorinated Pyridines in the Gas Phase.

A series of mono- and divalent fluorinated pyridine derivatives is investigated by electrospray ionization (tandem) mass spectrometry and quantum chemical calculations with respect to their capability to bind anions in the gas phase. The pyridine derivatives differ not only in valency, but also with regard to the degree of fluorination of the pyridine rings, the positions of the fluorine atoms, the rigidity of the spacers connecting the two pyridines in the divalent compounds, and the relative configuration. While the monovalent compounds did not form anion complexes, the divalent analogues exhibit anion binding even to weakly coordinating anions such as tetrafluoroborate. Three different tandem mass spectrometric experiments were applied to rank the gas-phase binding energies: (i) collision-induced dissociation (CID) experiments in a Fourier transform ion-cyclotron-resonance (FTICR) mass spectrometer on two different, simultaneously mass-selected complexes with different receptors, (ii) determination of the collision energy required to fragment 50 % of the mass-selected complexes in an ESI-QToF mass spectrometer, and (iii) CID of heterodimers formed from two different, competing pyridine receptors and indigo carmine, a dianion with two identical binding sites. All three experiments result in consistent binding energy ranking. This ranking reveals surprising features, which are not in agreement with binding through anion-π interactions. Density functional theory (DFT) calculations comparing different potential binding modes provide evidence that the ranking can instead nicely be explained, when C-H⋅⋅⋅anion interactions with the spacers are invoked. These results are supported by gas-phase IR spectroscopy and ion mobility-mass spectrometry (IM-MS) on a selected set of chloride pyridine complexes.

Critical Evaluation of Native Electrospray Ionization Mass Spectrometry for Fragment-Based Screening.

Fragment-based screening presents a promising alternative to high-throughput screening and has gained great attention in recent years. So far, only a few studies have discussed mass spectrometry as a screening technology for fragments. Herein, we report the application of native electrospray ionization mass spectrometry (MS) for screening defined sets of fragments against four different target proteins. Fragments were selected from a primary screening conducted with a thermal shift assay (TSA) and represented different binding categories. Our data indicated that, beside specific complex formation, many fragments show extensive multiple binding and also charge-state shifts. Both of these factors complicate automated data analysis and decrease the attractiveness of native MS as a primary screening tool for fragments. A comparison of the hits identified by native MS and TSA showed good agreement for two of the proteins. Furthermore, we discuss general challenges, including the determination of an optimal fragment concentration and the question of how to rank fragment hits according to their affinity. In conclusion, we consider native MS to be a highly valuable tool for the validation and deeper investigation of promising fragment hits rather than a method for primary screening.

Ion mobility-mass spectrometry as a tool to investigate protein-ligand interactions.

Ion mobility-mass spectrometry (IM-MS) is a powerful tool for the simultaneous analysis of mass, charge, size, and shape of ionic species. It allows the characterization of even low-abundant species in complex samples and is therefore particularly suitable for the analysis of proteins and their assemblies. In the last few years even complex and intractable species have been investigated successfully with IM-MS and the number of publications in this field is steadily growing. This trend article highlights recent advances in which IM-MS was used to study protein-ligand complexes and in particular focuses on the catch and release (CaR) strategy and collision-induced unfolding (CIU). Graphical Abstract Native mass spectrometry and ion mobility-mass spectrometry are versatile tools to follow the stoichiometry, energetics, and structural impact of protein-ligand binding.

Presynaptic Calmodulin targets: lessons from structural proteomics.

INTRODUCTION: Calmodulin (CaM) is a highly conserved Ca2+-binding protein that is exceptionally abundant in the brain. In the presynaptic compartment of neurons, CaM transduces changes in Ca2+ concentration into the regulation of synaptic transmission dynamics. Areas covered: We review selected literature including published CaM interactor screens and outline established and candidate presynaptic CaM targets. We present a workflow of biochemical and structural proteomic methods that were used to identify and characterize the interactions between CaM and Munc13 proteins. Finally, we outline the potential of ion mobility-mass spectrometry (IM-MS) for conformational screening and of protein-protein cross-linking for the structural characterization of CaM complexes. Expert commentary: Cross-linking/MS and native MS can be applied with considerable throughput to protein mixtures under near-physiological conditions, and thus effectively complement high-resolution structural biology techniques. Experimental distance constraints are applicable best when obtained by combining different cross-linking strategies, i.e. by using cross-linkers with different spacer length and reactivity, and by using the incorporation of unnatural photo-reactive amino acids. Insights from structural proteomics can be used to generate CaM-insensitive mutants of CaM targets for functional studies in vitro or ideally in vivo.

Gas-phase microsolvation of ubiquitin: investigation of crown ether complexation sites using ion mobility-mass spectrometry.

In this study the gas-phase structure of ubiquitin and its lysine-to-arginine mutants was investigated using ion mobility-mass spectrometry (IM-MS) and electron transfer dissociation-mass spectrometry (ETD-MS). Crown ether molecules were attached to positive charge sites of the proteins and the resulting non-covalent complexes were analysed. Collision induced dissociation (CID) experiments revealed relative energy differences between the wild type and the mutant crown-ether complexes. ETD-MS experiments were performed to identify the crown ether binding sites. Although not all of the binding sites could be revealed, the data confirm that the first crown ether is able to bind to the N-terminus. IM-MS experiments show a more compact structure for specific charge states of wild type ubiquitin when crown ethers are attached. However, data on ubiquitin mutants reveal that only specific lysine residues contribute to the effect of charge microsolvation. A compaction is only observed for one of the investigated mutants, in which the lysine has no proximate interaction partner. On the other hand when the lysine residues are involved in salt bridges, attachment of crown ethers has little effect on the structure.