Yvonne Hari

HLA-restricted, processing- and metabolism-independent pathway of drug recognition by human alpha beta T lymphocytes.

T cell recognition of drugs is explained by the hapten-carrier model, implying covalent binding of chemically reactive drugs to carrier proteins. However, most drugs are nonreactive and their recognition by T cells is unclear. We generated T cell clones from allergic individuals specific to sulfamethoxazole, lidocaine (nonreactive drugs), and cef-triaxone (per se reactive beta-lactam antibiotic) and compared the increase of intracellular free calcium concentration ([Ca2+]i) and the kinetics of T cell receptor (TCR) downregulation of these clones by drug-specific stimulations. All drugs tested induced an MHC-restricted, dose- and antigen-presenting cell (APC)-dependent TCR downregulation on specific CD4(+) and CD8(+) T cell clones. Chemically nonreactive drugs elicited an immediate and sustained [Ca2+]i increase and a rapid TCR downregulation, but only when these drugs were added in solution to APC and clone. In contrast, the chemically reactive hapten ceftriaxone added in solution needed > 6 h to induce TCR downregulation. When APC were preincubated with ceftriaxone, a rapid downregulation of the TCR and cytokine secretion was observed, suggesting a stable presentation of a covalently modified peptide. Our data demonstrate two distinct pathways of drug presentation to activated specific T cells. The per se reactive ceftriaxone is presented after covalent binding to carrier peptides. Nonreactive drugs can be recognized by specific alphabeta+ T cells via a nonconventional presentation pathway based on a labile binding of the drug to MHC-peptide complexes.

T cell involvement in cutaneous drug eruptions

Background The most frequent side‐effects of drug therapy are skin eruptions. Their pathomechanism is rather unclear.

Distinct serum cytokine levels in drug- and measles-induced exanthema.

Background: Macular or maculopapular skin reactions are frequent events in drug allergy as well as in viral infections. Clinically, the differentiation may be difficult in the absence of a clear relationship to drug intake or failure to detect virus–specific antibodies of the IgM class. Studies on drug–specific T cell lines and T cell clones isolated from drug–allergic patients have suggested that these cells may represent a significant source of IL–5. On the other hand, viral infections are frequently associated with elevated IFN–γ levels. Objective: Determination of serum–cytokine levels to differentiate between drug– and virally induced skin eruptions. Patients: 18 patients suffering from acute drug allergy and 19 patients with acute measles, rubella or parvovirus infection. Measurements: Cytokine–ELISA (IL–5, IL–4 and IFN–γ) of sera collected during acute drug allergy or during acute measles, rubella or parvovirus infection. Results: In 12/18 patients with drug allergy, IL–5 and/or IL–4 were elevated. A significant correlation (rSpearman = 0.84) between IL–5 serum levels and eosinophil counts in the blood was found. No correlation was detected between IL–4 and blood eosinophilia or between IL–4 and IL–5 levels. After remission, IL–5 and IL–4 decreased to undetectable levels. IFN–γ on the other hand was not measurable in patients with drug allergy while elevated IFN–γ serum levels were detected in 17/19 patients with measles, rubella or parvovirus infection; 2 patients with acute virus infection had elevated IL–5, and/or IL–4 and IFN–γ levels. Conclusion: These data underline the distinct pathogenesis of these morphologically similar exanthemas and suggest that the combined analysis of eosinophilia in the blood, IL–4 and IFN–γ might help in differentiating skin eruptions.

Pharmacokinetics of GHB and detection window in serum and urine after single uptake of a low dose of GBL – an experiment with two volunteers

During the last few years γ-hydroxybutyric acid (GHB) and γ-butyrolactone (GBL) have attracted much interest as recreational drugs and knock-out drops in drug-facilitated sexual assaults. This experiment aims at getting an insight into the pharmacokinetics of GHB after intake of GBL. Therefore Two volunteers took a single dose of 1.5 ml GBL, which had been spiked to a soft drink. Assuming that GBL was completely metabolized to GHB, the corresponding amount of GHB was 2.1 g. Blood and urine samples were collected 5 h and 24 h after ingestion, respectively. Additionally, hair samples (head hair and beard hair) were taken within four to five weeks after intake of GBL. Samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after protein precipitation with acetonitrile. The following observations were made: spiked to a soft drink, GBL, which tastes very bitter, formed a liquid layer at the bottom of the glass, only disappearing when stirring. Both volunteers reported weak central effects after approximately 15 min, which disappeared completely half an hour later. Maximum concentrations of GHB in serum were measured after 20 min (95 µg/ml and 106 µg/ml). Already after 4-5 h the GHB concentrations in serum decreased below 1 µg/ml. In urine maximum GHB concentrations (140 µg/ml and 120 µg/ml) were measured after 1-2 h, and decreased to less than 1 µg/ml within 8-10 h. The ratio of GHB in serum versus blood was 1.2 and 1.6.

T-cell reaction to local anaesthetics: relationship to angioedema and urticaria after subcutaneous application--patch testing and LTT in patients with adverse reaction to local anaesthetics.

Local anaesthetics are known to elicit T‐cell reactions after epicutaneous application, namely contact dermatitis. In addition, adverse reactions like urticaria and angioedema are rather common after submucosal or subcutaneous injection. The pathogenesis of these side‐effects, which appear frequently hours after application, is unknown, but thought to be not immunoglobulin E‐mediated, since immediate skin tests are mostly negative.

Elucidation of nucleic acid-drug interactions by tandem mass spectrometry.

In continuation of the long tradition of mass spectrometric research at the University of Bern, our group focuses on the characterization of nucleic acids as therapeutic agents and as drug targets. This article provides a short overview of our recent work on platinated single-stranded and higher-order nucleic acids. Nearly three decades ago the development of soft ionization techniques opened a whole new chapter in the mass spectrometric analysis of not only nucleic acids themselves, but also their interactions with potential drug candidates. In contrast to modern next generation sequencing approaches, though, the goal of the tandem mass spectrometric investigation of nucleic acids is by no means the complete sequencing of genetic DNA, but rather the characterization of short therapeutic and regulatory oligonucleotides and the elucidation of nucleic acid-drug interactions. The influence of cisplatin binding on the gas-phase dissociation of nucleic acids was studied by the means of electrospray ionization tandem mass spectrometry. Experiments on native and modified DNA and RNA oligomers confirmed guanine base pairs as the preferred platination site and laid the basis for the formulation of a gas-phase fragmentation mechanism of platinated oligonucleotides. The study was extended to double-stranded DNA and DNA quadruplexes. While duplexes are believed to be the main target of cisplatin in vivo, the recently discovered DNA quadruplexes constitute another promising target for anti-tumor drugs owing to their regulatory functions in the cell cycle.

Specific Interactions of Antitumor Metallocenes with Deoxydinucleoside Monophosphates

AbstractBent metallocenes Cp2MCl2 (M = Ti, V, Nb, Mo) are known to exhibit cytotoxic activity against a variety of cancer types. Though the mechanism of action is not fully understood yet, the accumulation of the metal ions in the nucleus points towards DNA as one of the primary targets. A set of eight deoxydinucleoside monophosphates was used to study the adduct yields with metallocenes and cisplatin. The binding affinities are reflected by the relative intensities of the adducts and were found to follow the order of Pt > V > Ti > Mo (no adducts were detected with Nb). High-resolution tandem mass spectrometry was applied to locate the binding patterns in the deoxydinucleoside monophosphates. Whereas cisplatin binds to the soft nitrogen atoms in the purine nucleobases, the metallocenes additionally interact with the hard phosphate oxygen, which is in good agreement with the hard and soft (Lewis) acids and bases (HSAB) concept. However, the binding specificities were found to be unique for each metallocene. The hard Lewis acids titanium and vanadium predominantly bind to the deprotonated phosphate oxygen, whereas molybdenum, an intermediate Lewis acid, preferentially interacts with the nucleobases. Nucleobases comprise alternative binding sites for titanium and vanadium, presumably oxygen atoms for the first and nitrogen atoms for the latter. In summary, the intrinsic binding behavior of the different metallodrugs is reflected by the gas-phase dissociation of the adducts. Consequently, MS/MS can provide insights into therapeutically relevant interactions between metallodrugs and their cellular targets. Graphical Abstractᅟ

Transition Metal-based Anticancer Drugs Targeting Nucleic Acids: A Tandem Mass Spectrometric Investigation

The search for effective drugs against cisplatin-resistant tumors resulted in a large number of organometallic compounds that are evaluated for their antiproliferative activity. Among the most promising candidates are bent metallocenes based on various transition metal ions and ligands. The elucidation of structural features and the characterization of the interaction of a drug candidate with its target require accurate and sensitive analytical tools. Tandem mass spectrometry is applied to the investigation of the adduct sites and binding patterns of metallodrugs bound to single-stranded oligonucleotides and higher-order nucleic acids. Results reveal the binding specificities of the different metallodrugs and demonstrate the influence they exert on the dissociation pathways of the adducts in the gas-phase.

What Hinders Electron Transfer Dissociation (ETD) of DNA Cations

AbstractRadical activation methods, such as electron transfer dissociation (ETD), produce structural information complementary to collision-induced dissociation. Herein, electron transfer dissociation of 3-fold protonated DNA hexamers was studied to gain insight into the fragmentation mechanism. The fragmentation patterns of a large set of DNA hexamers confirm cytosine as the primary target of electron transfer. The reported data reveal backbone cleavage by internal electron transfer from the nucleobase to the phosphate linker leading either to a•/w or d/z• ion pairs. This reaction pathway contrasts with previous findings on the dissociation processes after electron capture by DNA cations, suggesting multiple, parallel dissociation channels. However, all these channels merely result in partial fragmentation of the precursor ion because the charge-reduced DNA radical cations are quite stable. Two hypotheses are put forward to explain the low dissociation yield of DNA radical cations: it is either attributed to non-covalent interactions between complementary fragments or to the stabilization of the unpaired electron in stacked nucleobases. MS3 experiments suggest that the charge-reduced species is the intact oligonucleotide. Moreover, introducing abasic sites significantly increases the dissociation yield of DNA cations. Consequently, the stabilization of the unpaired electron by π–π-stacking provides an appropriate rationale for the high intensity of DNA radical cations after electron transfer. Graphical Abstract

Highlights in Analytical Chemistry in Switzerland: OMA & OPA - A Software Tool for Mass Spectrometric Sequencing of Nucleic Acids

Oligonucleotides comprising unnatural building blocks, which interfere with the translation machinery, have gained increased attention for the treatment of gene-related diseases (e.g. antisense, RNAi). Due to structural modifications, synthetic oligonucleotides exhibit increased biostability and bioavailability upon administration. Consequently, classical enzyme-based sequencing methods are not applicable to their sequence elucidation and verification. Tandem mass spectrometry is the method of choice for performing such tasks, since gas-phase dissociation is not restricted to natural nucleic acids. However, tandem mass spectrometric analysis can generate product ion spectra of tremendous complexity, as the number of possible fragments grows rapidly with increasing sequence length. The fact that structural modifications affect the dissociation pathways greatly increases the variety of analytically valuable fragment ions. The gas-phase dissociation of oligonucleotides is characterized by the cleavage of one of the four bonds along the phosphodiester chain, by the accompanying loss of nucleases, and by the generation of internal fragments due to secondary backbone cleavage. For example, an 18-mer oligonucleotide yields a total number of 272’920 theoretical fragment ions. In contrast to the processing of peptide product ion spectra, which nowadays is highly automated, there is a lack of tools assisting the interpretation of oligonucleotide data. The existing web-based and stand-alone software applications are primarily designed for the sequence analysis of natural nucleic acids, but do not account for chemical modifications and adducts. Consequently, we developed a software to support the interpretation of mass spectrometric data of natural and modified nucleic acids and their adducts with chemotherapeutic agents.