Development of a luminescence-based method for measuring West Nile Virus MTase activity and its application to screen for antivirals.

West Nile virus (WNV) is a flavivirus responsible for causing febrile illness and severe neurological diseases, with an increasing impact on human health around the world. However, there is still no adequate therapeutic treatment available to struggle WNV infections. Therefore, there is an urgent need to develop new techniques to accelerate the discovery of drugs against this pathogen. The main protein implicated in the replication of WNV is the non-structural protein 5 (NS5). This multifunctional protein contains methyltransferase (MTase) activity involved in the capping formation at the 5'-end of RNA and the methylation of internal viral RNA residues, both functions being essential for viral processes, such as RNA translation and escape from the innate immune response. We have developed a straightforward luminescence-based assay to monitor the MTase activity of the WNV NS5 protein with potential for high-throughput screening. We have validated this method as a sensitive and suitable assay for the identification of WNV MTase inhibitors assessing the inhibitory effect of the broad MTase inhibitor sinefungin, a natural nucleoside analog of the universal methyl donor S-adenosyl methionine (SAM). The screening of a small series of purine derivatives identified an adenosine derivative as a dose-dependent inhibitor of the MTase activity. The antiviral efficacy of this compound was further confirmed in WNV infections, displaying a measurable antiviral effect. This result supports the utility of this novel method for the screening of inhibitors against WNV MTase activity, which can be of special relevance to the discovery and development of therapeutics against WNV.

Self-Esteem and Risk Behaviours in Adolescents: A Systematic Review.

Adolescence is recognised as a notoriously vulnerable period in the human life cycle. Influenced by a complex interplay of biological, psychological and social factors, adolescents show a marked propensity to engage in risk behaviours. A systematic review was conducted of studies published in the Web of Science, PsycInfo and MEDLINE databases over the last decade, with the aim of collecting studies on the relationship between self-esteem and risk behaviour in individuals aged 12-18 years. The aim was to confirm the role of high self-esteem as a consistent protective factor against risk behaviour. The results show that self-esteem is negatively related to risk behaviour. Our results also reflect the need for further research on how sociodemographic factors, among others, affect the relationship between self-esteem and risk behaviours. This review highlights the relevance of implementing specific educational interventions to strengthen self-esteem in adolescents, with the aim of preventing various risk behaviours that may emerge during adolescence and persist throughout life if not addressed early.

Protocol for in vitro establishment of heterogeneous stem-like cultures derived from whole human glioblastoma tumors.

Cultures enriched in glioblastoma stem-like cells (GSCs) are prominent in vitro models to investigate molecular determinants and therapeutic targets of glioblastoma; however, conventional GSC derivation protocols fail to preserve GSC heterogeneity. Here, we present a protocol for the propagation of heterogeneous GSC cultures starting from cell resuspensions containing the entire tumor mass. We describe steps for isolation of GSCs and their maintenance and expansion in culture. We then detail procedures for preliminary analysis to be performed on freshly isolated material. For complete details on the use and execution of this protocol, please refer to De Bacco et al.1.

Coexisting cancer stem cells with heterogeneous gene amplifications, transcriptional profiles, and malignancy are isolated from single glioblastomas.

Glioblastoma (GBM) is known as an intractable, highly heterogeneous tumor encompassing multiple subclones, each supported by a distinct glioblastoma stem cell (GSC). The contribution of GSC genetic and transcriptional heterogeneity to tumor subclonal properties is debated. In this study, we describe the systematic derivation, propagation, and characterization of multiple distinct GSCs from single, treatment-naive GBMs (GSC families). The tumorigenic potential of each GSC better correlates with its transcriptional profile than its genetic make-up, with classical GSCs being inherently more aggressive and mesenchymal more dependent on exogenous growth factors across multiple GBMs. These GSCs can segregate and recapitulate different histopathological aspects of the same GBM, as shown in a paradigmatic tumor with two histopathologically distinct components, including a conventional GBM and a more aggressive primitive neuronal component. This study provides a resource for investigating how GSCs with distinct genetic and/or phenotypic features contribute to individual GBM heterogeneity and malignant escalation.

Use of Impella Devices for Acute Cardiogenic Shock in the Perioperative Period of Cardiac Surgery

ABSTRACT Introduction: The Impella ventricular support system is a device that can be inserted percutaneously or directly across the aortic valve to unload the left ventricle. The purpose of this study is to determine the role of Impella devices in patients with acute cardiogenic shock in the perioperative period of cardiac surgery. Methods: A retrospective single-surgeon review of 11 consecutive patients who underwent placement of Impella devices in the perioperative period of cardiac surgery was performed. Patient records were evaluated for demographics, indications for placement, and postoperative outcomes. Results: Impella devices were placed for refractory cardiogenic shock preoperatively in 6 patients, intraoperatively in 4 patients, and postoperatively as a rescue in 1 patient. Seven patients received Impella CP, 1 Impella RP, 1 Impella CP and RP, and 2 Impella 5.0. Additionally, 3 patients required preoperative venovenous extracorporeal membrane oxygenation (VV-ECMO), and 1 patient required intraoperative venoarterial extracorporeal membrane oxygenation (VA-ECMO). All Impella devices were removed 1 to 28 days after implantation. Length of stay in the intensive care unit stay ranged from 2 to 53 days (average 23.9±14.6). The 30-day and 1-year mortality were 0%. Ten of 11 patients were alive at 2 years. Also, 1 patient died 18 months after surgery from complications of coronavirus disease (Covid-19). Device-related complications included varying degrees> of hemolysis in 8 patients (73%) and device malfunction in 1 patient (9%). Conclusions: The Impella ventricular support system can be combined with other mechanical support devices for additional hemodynamic support. All patients demonstrated myocardial recovery with no deaths in the perioperative period and in 1-year of follow-up. Larger studies are necessary to validate these findings.

Use of Impella Devices for Acute Cardiogenic Shock in the Perioperative Period of Cardiac Surgery.

INTRODUCTION: The Impella ventricular support system is a device that can be inserted percutaneously or directly across the aortic valve to unload the left ventricle. The purpose of this study is to determine the role of Impella devices in patients with acute cardiogenic shock in the perioperative period of cardiac surgery. METHODS: A retrospective single-surgeon review of 11 consecutive patients who underwent placement of Impella devices in the perioperative period of cardiac surgery was performed. Patient records were evaluated for demographics, indications for placement, and postoperative outcomes. RESULTS: Impella devices were placed for refractory cardiogenic shock preoperatively in 6 patients, intraoperatively in 4 patients, and postoperatively as a rescue in 1 patient. Seven patients received Impella CP, 1 Impella RP, 1 Impella CP and RP, and 2 Impella 5.0. Additionally, 3 patients required preoperative venovenous extracorporeal membrane oxygenation (VV-ECMO), and 1 patient required intraoperative venoarterial extracorporeal membrane oxygenation (VA-ECMO). All Impella devices were removed 1 to 28 days after implantation. Length of stay in the intensive care unit stay ranged from 2 to 53 days (average 23.9±14.6). The 30-day and 1-year mortality were 0%. Ten of 11 patients were alive at 2 years. Also, 1 patient died 18 months after surgery from complications of coronavirus disease (Covid-19). Device-related complications included varying degrees> of hemolysis in 8 patients (73%) and device malfunction in 1 patient (9%). CONCLUSIONS: The Impella ventricular support system can be combined with other mechanical support devices for additional hemodynamic support. All patients demonstrated myocardial recovery with no deaths in the perioperative period and in 1-year of follow-up. Larger studies are necessary to validate these findings.

Feasibility and outcomes with subclavian vein access for crescent jugular dual lumen catheter for venovenous extracorporeal membrane oxygenation in COVID-19 related acute respiratory distress syndrome.

INTRODUCTION: Femoral-femoral Veno-Venous ExtraCorporeal Life Support (V-V ECLS) has been associated with higher infections rates, vascular site bleeding complications, and restricted patient mobility. Jugular or bicaval dual lumen V-V ECLS conceptually overcomes some of these adverse factors, but experience has shown that jugular vein cannulation still limits mobility and has increased bleeding complications. Technique and outcomes of subclavian vein single-cannulation with Crescent jugular dual-lumen V-V ECLS is described. METHOD: five patients with COVID-19 related acute respiratory distress syndrome (ARDS) underwent right subclavian vein V-V ECLS placement with the Crescent 32 French jugular dual-lumen V-V ECLS catheter. A standardized percutaneous technique was developed that allowed efficient insertion without need for any specialized imaging (i.e. transesophageal echocardiogram) and outcomes assessed. RESULTS: Mean age of the five patients was 41.2 years, all obese with an average basal mass index of 45.2 kg/m2 and mean days to decannulation of 24.2 days. Outcomes discovered included; improved patient mobility allowing physical rehabilitation, no vascular access site related complications requiring surgery or endovascular intervention, and none had evidence of superior vena cava syndrome. One patient had subclavian/axillary vein thrombosis with resolution after 3 months of direct-acting oral anticoagulants, and one patient had blood cultures positive at day 37, nearing decannulation. CONCLUSION: Subclavian vein access for crescent jugular dual lumen V-V ECLS catheter appears to be safe and feasible with added benefits of decreased bleeding and increased mobility over jugular or femoral-femoral access site for long term V-V ECLS support in COVID-19 related ARDS patients.

The PSI Domain of the MET Oncogene Encodes a Functional Disulfide Isomerase Essential for the Maturation of the Receptor Precursor.

The tyrosine kinase receptor encoded by the MET oncogene has been extensively studied. Surprisingly, one extracellular domain, PSI, evolutionary conserved between plexins, semaphorins, and integrins, has no established function. The MET PSI sequence contains two CXXC motifs, usually found in protein disulfide isomerases (PDI). Using a scrambled oxidized RNAse enzymatic activity assay in vitro, we show, for the first time, that the MET extracellular domain displays disulfide isomerase activity, abolished by PSI domain antibodies. PSI domain deletion or mutations of CXXC sites to AXXA or SXXS result in a significant impairment of the cleavage of the MET 175 kDa precursor protein, abolishing the maturation of α and ß chains, of, respectively, 50 kDa and 145 kDa, disulfide-linked. The uncleaved precursor is stuck in the Golgi apparatus and, interestingly, is constitutively phosphorylated. However, no signal transduction is observed as measured by AKT and MAPK phosphorylation. Consequently, biological responses to the MET ligand-hepatocyte growth factor (HGF)-such as growth and epithelial to mesenchymal transition, are hampered. These data show that the MET PSI domain is functional and is required for the maturation, surface expression, and biological functions of the MET oncogenic protein.

Engineering, Characterization, and Biological Evaluation of an Antibody Targeting the HGF Receptor.

The Hepatocyte growth factor (HGF) and its receptor (MET) promote several physiological activities such as tissue regeneration and protection from cell injury of epithelial, endothelial, neuronal and muscle cells. The therapeutic potential of MET activation has been scrutinized in the treatment of acute tissue injury, chronic inflammation, such as renal fibrosis and multiple sclerosis (MS), cardiovascular and neurodegenerative diseases. On the other hand, the HGF-MET signaling pathway may be caught by cancer cells and turned to work for invasion, metastasis, and drug resistance in the tumor microenvironment. Here, we engineered a recombinant antibody (RDO24) and two derived fragments, binding the extracellular domain (ECD) of the MET protein. The antibody binds with high affinity (8 nM) to MET ECD and does not cross-react with the closely related receptors RON nor with Semaphorin 4D. Deletion mapping studies and computational modeling show that RDO24 binds to the structure bent on the Plexin-Semaphorin-Integrin (PSI) domain, implicating the PSI domain in its binding to MET. The intact RDO24 antibody and the bivalent Fab2, but not the monovalent Fab induce MET auto-phosphorylation, mimicking the mechanism of action of HGF that activates the receptor by dimerization. Accordingly, the bivalent recombinant molecules induce HGF biological responses, such as cell migration and wound healing, behaving as MET agonists of therapeutic interest in regenerative medicine. In vivo administration of RDO24 in the murine model of MS, represented by experimental autoimmune encephalomyelitis (EAE), delays the EAE onset, mitigates the early clinical symptoms, and reduces inflammatory infiltrates. Altogether, these results suggest that engineered RDO24 antibody may be beneficial in multiple sclerosis and possibly other types of inflammatory disorders.

ERBB3 overexpression due to miR-205 inactivation confers sensitivity to FGF, metabolic activation, and liability to ERBB3 targeting in glioblastoma.

In glioblastoma (GBM), the most frequent and lethal brain tumor, therapies suppressing recurrently altered signaling pathways failed to extend survival. However, in patient subsets, specific genetic lesions can confer sensitivity to targeted agents. By exploiting an integrated model based on patient-derived stem-like cells, faithfully recapitulating the original GBMs in vitro and in vivo, here, we identify a human GBM subset (∼9% of all GBMs) characterized by ERBB3 overexpression and nuclear accumulation. ERBB3 overexpression is driven by inheritable promoter methylation or post-transcriptional silencing of the oncosuppressor miR-205 and sustains the malignant phenotype. Overexpressed ERBB3 behaves as a specific signaling platform for fibroblast growth factor receptor (FGFR), driving PI3K/AKT/mTOR pathway hyperactivation, and overall metabolic upregulation. As a result, ERBB3 inhibition by specific antibodies is lethal for GBM stem-like cells and xenotransplants. These findings highlight a subset of patients eligible for ERBB3-targeted therapy.

The Long-Lasting Protective Effect of HGF in Cardiomyoblasts Exposed to Doxorubicin Requires a Positive Feed-Forward Loop Mediated by Erk1,2-Timp1-Stat3.

Previous studies showed that the hepatocyte growth factor (HGF)-Met receptor axis plays long-lasting cardioprotection against doxorubicin anti-cancer therapy. Here, we explored the mechanism(s) underlying the HGF protective effect. DNA damage was monitored by histone H2AX phosphorylation and apoptosis by proteolytic cleavage of caspase 3. In doxorubicin-treated H9c2 cardiomyoblasts, the long-lasting cardioprotection is mediated by activation of the Ras/Raf/Mek/Erk (extracellular signal-regulated kinase 1,2) signaling pathway and requires Stat3 (signal transducer and activator of transcription 3) activation. The HGF protection was abrogated by the Erk1,2 inhibitor, PD98059. This translated into reduced Y705 phosphorylation and impaired nuclear translocation of Stat3, showing crosstalk between Erk1,2 and Stat3 signaling. An array of 29 cytokines, known to activate Stat3, was interrogated to identify the molecule(s) linking the two pathways. The analysis showed a selective increase in expression of the tissue inhibitor of metalloproteinases-1 (Timp1). Consistently, inhibition in cardiomyoblasts of Timp1 translation by siRNAs blunted both Stat3 activation and the cardioprotective effect of HGF. Thus, Timp1 is responsible for the generation of a feed-forward loop of Stat3 activation and helps cardiomyocytes to survive during the genotoxic stress induced by anthracyclines.

Activation of the MET receptor attenuates doxorubicin-induced cardiotoxicity in vivo and in vitro.

BACKGROUND AND PURPOSE: Doxorubicin anti-cancer therapy is associated with cardiotoxicity, resulting from DNA damage response (DDR). Hepatocyte growth factor (HGF) protects cardiomyocytes from injury, but its effective use is compromised by low biodistribution. In this study, we have investigated whether the activation of the HGF receptor-encoded by the Met gene-by an agonist monoclonal antibody (mAb) could protect against doxorubicin-induced cardiotoxicity. EXPERIMENTAL APPROACH: The mAb (5 mg·kg-1 ) was injected in vivo into C57BL/6J mice, before doxorubicin (three doses of 7 mg·kg-1 ). Cardiac functions were evaluated through MRI after treatment termination. Heart histological staining and mRNA levels of genes associated with heart failure (Acta1 and Nppa), inflammation (IL-6), and fibrosis (Ctgf, Col1a2, Timp1, and Mmp9) were assessed. MAb (100 nM) was administered in vitro to H9c2 cardiomyoblasts before addition of doxorubicin (25 µM). DDR and apoptosis markers were evaluated by quantitative western blotting, flow cytometry, and immunofluorescence. Stattic was used for pharmacological inactivation of STAT3. KEY RESULTS: In vivo, administration of the mAb alleviated doxorubicin-induced cardiac dysfunction and fibrosis. In vitro, mAb mimicked the response to HGF by (a) inhibiting histone H2AX phosphorylation at S139, (b) quenching the expression of the DNA repair enzyme PARP1, and (c) reducing the proteolytic activation of caspase 3. The MET-driven cardioprotection involved, at least in vitro, the phosphorylation of STAT3. CONCLUSION AND IMPLICATIONS: The MET agonist mAb provides a new tool for cardioprotection against anthracycline cardiotoxicity.

MET inhibition overcomes radiation resistance of glioblastoma stem-like cells.

Glioblastoma (GBM) contains stem-like cells (GSCs) known to be resistant to ionizing radiation and thus responsible for therapeutic failure and rapidly lethal tumor recurrence. It is known that GSC radioresistance relies on efficient activation of the DNA damage response, but the mechanisms linking this response with the stem status are still unclear. Here, we show that the MET receptor kinase, a functional marker of GSCs, is specifically expressed in a subset of radioresistant GSCs and overexpressed in human GBM recurring after radiotherapy. We elucidate that MET promotes GSC radioresistance through a novel mechanism, relying on AKT activity and leading to (i) sustained activation of Aurora kinase A, ATM kinase, and the downstream effectors of DNA repair, and (ii) phosphorylation and cytoplasmic retention of p21, which is associated with anti-apoptotic functions. We show that MET pharmacological inhibition causes DNA damage accumulation in irradiated GSCs and their depletion in vitro and in GBMs generated by GSC xenotransplantation. Preclinical evidence is thus provided that MET inhibitors can radiosensitize tumors and convert GSC-positive selection, induced by radiotherapy, into GSC eradication.

Anti-HIV-1 activity of a tripodal receptor that recognizes mannose oligomers.

The glycoprotein gp120 of the HIV-1 viral envelope has a high content in mannose residues, particularly α-1,2-mannose oligomers. Compounds that interact with these high-mannose type glycans may disturb the interaction between gp120 and its (co)receptors and are considered potential anti-HIV agents. Previously, we demonstrated that a tripodal receptor (1), with a central scaffold of 1,3,5-triethylbenzene substituted with three 2,3,4-trihydroxybenzoyl groups, selectively recognizes α-1,2-mannose polysaccharides. Here we present additional studies to determine the anti-HIV-1 activity and the mechanism of antiviral activity of this compound. Our studies indicate that 1 shows anti-HIV-1 activity in the low micromolar range and has pronounced gp120 binding and HIV-1 integrase inhibitory capacity. However, gp120 binding rather than integrase inhibition seems to be the primary mechanism of antiviral activity of 1.

TNF-α promotes invasive growth through the MET signaling pathway.

The inflammatory cytokine Tumor Necrosis Factor Alpha (TNF-α) is known to trigger invasive growth, a physiological property for tissue healing, turning into a hallmark of progression in cancer. However, the invasive response to TNF-α relies on poorly understood molecular mechanisms. We thus investigated whether it involves the MET oncogene, which regulates the invasive growth program by encoding the tyrosine kinase receptor for Hepatocyte Growth Factor (HGF). Here we show that the TNF-α pro-invasive activity requires MET function, as it is fully inhibited by MET-specific inhibitors (small-molecules, antibodies, and siRNAs). Mechanistically, we show that TNF-α induces MET transcription via NF-κB, and exploits MET to sustain MEK/ERK activation and Snail accumulation, leading to E-cadherin downregulation. We then show that TNF-α not only induces MET expression in cancer cells, but also HGF secretion by fibroblasts. Consistently, we found that, in human colorectal cancer tissues, high levels of TNF-α correlates with increased expression of both MET and HGF. These findings suggest that TNF-α fosters a HGF/MET pro-invasive paracrine loop in tumors. Targeting this ligand/receptor pair would contribute to prevent cancer progression associated with inflammation.

Leishmania infantum EndoG is an endo/exo-nuclease essential for parasite survival.

EndoG, a member of the DNA/RNA non-specific ßßα-metal family of nucleases, has been demonstrated to be present in many organisms, including Trypanosomatids. This nuclease participates in the apoptotic program in these parasites by migrating from the mitochondrion to the nucleus, where it takes part in the degradation of genomic DNA that characterizes this process. We now demonstrate that Leishmania infantum EndoG (LiEndoG) is an endo-exonuclease that has a preferential 5' exonuclease activity on linear DNA. Regardless of its role during apoptotic cell death, this enzyme seems to be necessary during normal development of the parasites as indicated by the reduced growth rates observed in LiEndoG hemi-knockouts and their poor infectivity in differentiated THP-1 cells. The pro-life role of this protein is also corroborated by the higher survival rates of parasites that over-express this protein after treatment with the LiEndoG inhibitor Lei49. Taken together, our results demonstrate that this enzyme plays essential roles in both survival and death of Leishmania parasites.

5'-Trityl-substituted thymidine derivatives as a novel class of antileishmanial agents: Leishmania infantum EndoG as a potential target.

Two series of 5'-triphenylmethyl (trityl)-substituted thymidine derivatives were synthesized and tested against Leishmania infantum axenic promastigotes and amastigotes. Several of these compounds show significant antileishmanial activity, with IC50 values in the low micromolar range. Among these, 3'-O-(isoleucylisoleucyl)-5'-O-(3,3,3-triphenylpropanoyl)thymidine displays particularly good activity against intracellular amastigotes. Assays performed to characterize the nature of parasite cell death in the presence of the tritylthymidines indicated significant alterations in mitochondrial transmembrane potential, an increase in superoxide concentrations, and also significant decreases in DNA degradation during the cell death process. Results point to the mitochondrial nuclease LiEndoG as a target for the action of this family of compounds.

The MET oncogene is a functional marker of a glioblastoma stem cell subtype.

The existence of treatment-resistant cancer stem cells contributes to the aggressive phenotype of glioblastoma. However, the molecular alterations that drive stem cell proliferation in these tumors remain unknown. In this study, we found that expression of the MET oncogene was associated with neurospheres expressing the gene signature of mesenchymal and proneural subtypes of glioblastoma. Met expression was almost absent from neurospheres expressing the signature of the classical subtype and was mutually exclusive with amplification and expression of the EGF receptor (EGFR) gene. Met-positive and Met-negative neurospheres displayed distinct growth factor requirements, differentiated along divergent pathways, and generated tumors with distinctive features. The Met(high) subpopulation within Met-pos neurospheres displayed clonogenic potential and long-term self-renewal ability in vitro and enhanced growth kinetics in vivo. In Met(high) cells, the Met ligand HGF further sustained proliferation, clonogenicity, expression of self-renewal markers, migration, and invasion in vitro. Together, our findings suggest that Met is a functional marker of glioblastoma stem cells and a candidate target for identification and therapy of a subset of glioblastomas.

The thymidine phosphorylase inhibitor 5'-O-tritylinosine (KIN59) is an antiangiogenic multitarget fibroblast growth factor-2 antagonist.

5'-O-Tritylinosine (KIN59) is an allosteric inhibitor of the angiogenic enzyme thymidine phosphorylase. Previous observations showed the capacity of KIN59 to abrogate thymidine phosphorylase-induced as well as developmental angiogenesis in the chicken chorioallantoic membrane (CAM) assay. Here, we show that KIN59 also inhibits the angiogenic response triggered by fibroblast growth factor-2 (FGF2) but not by VEGF in the CAM assay. Immunohistochemical and reverse transcriptase PCR analyses revealed that the expression of laminin, the major proteoglycan of the basement membrane of blood vessels, is downregulated by KIN59 administration in control as well as in thymidine phosphorylase- or FGF2-treated CAMs, but not in CAMs treated with VEGF. Also, KIN59 abrogated FGF2-induced endothelial cell proliferation, FGF receptor activation, and Akt signaling in vitro with no effect on VEGF-stimulated biologic responses. Accordingly, KIN59 inhibited the binding of FGF2 to FGF receptor-1 (FGFR1), thus preventing the formation of productive heparan sulphate proteoglycan/FGF2/FGFR1 ternary complexes, without affecting heparin interaction. In keeping with these observations, systemic administration of KIN59 inhibited the growth and neovascularization of subcutaneous tumors induced by FGF2-transformed endothelial cells injected in immunodeficient nude mice. Taken together, the data indicate that the thymidine phosphorylase inhibitor KIN59 is endowed with a significant FGF2 antagonist activity, thus representing a promising lead compound for the design of multitargeted antiangiogenic cancer drugs.

Intramolecular cation-pi interactions as the driving force to restrict the conformation of certain nucleosides.

Despite the well-established importance of intermolecular cation-pi interactions in molecular recognition, intramolecular cation-pi interactions have been less studied. Here we describe how the simultaneous presence of an aromatic ring at the 5'-position of an inosine derivative and a positively charged imidazolium ring in the purine base drive the conformation of the nucleoside toward a very major conformer in solution that is stabilized by an intramolecular cation-pi interaction. Therefore, the cation-pi interaction between imidazolium ions and aromatic rings can also be proposed in the design of small molecules where this type of interaction is desirable. The imidazolium ion can be obtained by a simple acidification of the pH of the media. So a simple change in pH can shift the conformational equilibrium from a random to a restricted conformation stabilized by an intramolecular cation-pi interaction. Thus the here described nucleosides can be considered as a new class of pH-dependent conformationally switchable molecules.