Christoph Welsch

Publications (30)162.36 Total impact

• Article: Will interferon-free regimens prevail?

  Christoph Welsch, Stefan Zeuzem
  Gastroenterology 05/2012; 142(6):1351-5. · 11.68 Impact Factor
• Article: New direct-acting antiviral agents for the treatment of hepatitis C virus infection and perspectives.

  Christoph Welsch, Arun Jesudian, Stefan Zeuzem, Ira Jacobson
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  ABSTRACT: Until recently, the standard of care (SOC) for patients with chronic hepatitis C virus (HCV) infection has consisted of a combination of pegylated interferon-α [corrected] plus ribavirin, administered for 24- to 48-weeks depending on the HCV genotype. The sustained virologic response rate for this SOC has been only about 50% in patients infected with genotype 1 HCV, the most prevalent genotype in Europe and North America. HCV therapy has been revolutionised recently by the approval of two direct-acting antiviral agents (DAA) against the NS3/4A serine protease for use in genotype 1 HCV, the ketoamide inhibitors boceprevir and telaprevir. The novel SOC marks the beginning of an extraordinary new era in HCV therapy. We review this new SOC with an emphasis on practical issues related to protease inhibitors, e.g. prescribing guidelines, futility rules and management of adverse events. We also give a perspective on what to expect in the coming years. Newer DAA with simplified dosing regimens and/or minimal toxicity which, when used in combination, will lead to viral eradication in most if not all CHC patients who undergo treatment. The novel agents in clinical development are paving the way for future interferon-sparing regimens.
  Gut 05/2012; 61 Suppl 1:i36-46. · 10.11 Impact Factor
• Article: Base pairing between hepatitis C virus RNA and microRNA 122 3' of its seed sequence is essential for genome stabilization and production of infectious virus.

  Tetsuro Shimakami, Daisuke Yamane, Christoph Welsch, Lucinda Hensley, Rohit K Jangra, Stanley M Lemon
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  ABSTRACT: MicroRNA 122 (miR-122) facilitates hepatitis C virus (HCV) replication by recruiting an RNA-induced silencing complex (RISC)-like complex containing argonaute 2 (Ago2) to the 5' end of the HCV genome, thereby stabilizing the viral RNA. This requires base pairing between the miR-122 "seed sequence" (nucleotides [nt] 2 to 8) and two sequences near the 5' end of the HCV RNA: S1 (nt 22 to 28) and S2 (nt 38 to 43). However, recent reports suggest that additional base pair interactions occur between HCV RNA and miR-122. We searched 606 sequences from a public database (genotypes 1 to 6) and identified two conserved, putatively single-stranded RNA segments, upstream of S1 (nt 2 and 3) and S2 (nt 30 to 34), with potential for base pairing to miR-122 (nt 15 and 16 and nt 13 to 16, respectively). Mutagenesis and genetic complementation experiments confirmed that HCV nt 2 and 3 pair with nt 15 and 16 of miR-122 bound to S1, while HCV nt 30 to 33 pair with nt 13 to 16 of miR-122 at S2. In genotype 1 and 6 HCV, nt 4 also base pairs with nt 14 of miR-122. These 3' supplementary base pair interactions of miR-122 are functionally important and are required for Ago2 recruitment to HCV RNA by miR-122, miR-122-mediated stabilization of HCV RNA, and production of infectious virus. However, while complementary mutations at HCV nt 30 and 31 efficiently rescued the activity of a 15C,16C miR-122 mutant targeting S2, similar mutations at nt 2 and 3 failed to rescue Ago2 recruitment at S1. These data add to the current understanding of miR-122 interactions with HCV RNA but indicate that base pairing between miR-122 and the 5' 43 nt of the HCV genome is more complex than suggested by existing models.
  Journal of Virology 04/2012; 86(13):7372-83. · 5.40 Impact Factor
• Article: Ketoamide resistance and hepatitis C virus fitness in val55 variants of the NS3 serine protease.

  Christoph Welsch, Sabine Schweizer, Tetsuro Shimakami, Francisco S Domingues, Seungtaek Kim, Stanley M Lemon, Iris Antes
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  ABSTRACT: Drug-resistant viral variants are a major issue in the use of direct-acting antiviral agents in chronic hepatitis C. Ketoamides are potent inhibitors of the NS3 protease, with V55A identified as mutation associated with resistance to boceprevir. Underlying molecular mechanisms are only partially understood. We applied a comprehensive sequence analysis to characterize the natural variability at Val55 within dominant worldwide patient strains. A residue-interaction network and molecular dynamics simulation were applied to identify mechanisms for ketoamide resistance and viral fitness in Val55 variants. An infectious H77S.3 cell culture system was used for variant phenotype characterization. We measured antiviral 50% effective concentration (EC₅₀) and fold changes, as well as RNA replication and infectious virus yields from viral RNAs containing variants. Val55 was found highly conserved throughout all hepatitis C virus (HCV) genotypes. The conservative V55A and V55I variants were identified from HCV genotype 1a strains with no variants in genotype 1b. Topology measures from a residue-interaction network of the protease structure suggest a potential Val55 key role for modulation of molecular changes in the protease ligand-binding site. Molecular dynamics showed variants with constricted binding pockets and a loss of H-bonded interactions upon boceprevir binding to the variant proteases. These effects might explain low-level boceprevir resistance in the V55A variant, as well as the Val55 variant, reduced RNA replication capacity. Higher structural flexibility was found in the wild-type protease, whereas variants showed lower flexibility. Reduced structural flexibility could impact the Val55 variant's ability to adapt for NS3 domain-domain interaction and might explain the virus yield drop observed in variant strains.
  Antimicrobial Agents and Chemotherapy 01/2012; 56(4):1907-15. · 4.84 Impact Factor
• Article: Peptidomimetic escape mechanisms arise via genetic diversity in the ligand-binding site of the hepatitis C virus NS3/4A serine protease.

  Christoph Welsch, Tetsuro Shimakami, Christoph Hartmann, Yan Yang, Francisco S Domingues, Thomas Lengauer, Stefan Zeuzem, Stanley M Lemon
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  ABSTRACT: It is a challenge to develop direct-acting antiviral agents that target the nonstructural protein 3/4A protease of hepatitis C virus because resistant variants develop. Ketoamide compounds, designed to mimic the natural protease substrate, have been developed as inhibitors. However, clinical trials have revealed rapid selection of resistant mutants, most of which are considered to be pre-existing variants. We identified residues near the ketoamide-binding site in x-ray structures of the genotype 1a protease, co-crystallized with boceprevir or a telaprevir-like ligand, and then identified variants at these positions in 219 genotype-1 sequences from a public database. We used side-chain modeling to assess the potential effects of these variants on the interaction between ketoamide and the protease, and compared these results with the phenotypic effects on ketoamide resistance, RNA replication capacity, and infectious virus yields in a cell culture model of infection. Thirteen natural binding-site variants with potential for ketoamide resistance were identified at 10 residues in the protease, near the ketoamide binding site. Rotamer analysis of amino acid side-chain conformations indicated that 2 variants (R155K and D168G) could affect binding of telaprevir more than boceprevir. Measurements of antiviral susceptibility in cell-culture studies were consistent with this observation. Four variants (ie, Q41H, I132V, R155K, and D168G) caused low-to-moderate levels of ketoamide resistance; 3 of these were highly fit (Q41H, I132V, and R155K). Using a comprehensive sequence and structure-based analysis, we showed how natural variation in the hepatitis C virus protease nonstructural protein 3/4A sequences might affect susceptibility to first-generation direct-acting antiviral agents. These findings increase our understanding of the molecular basis of ketoamide resistance among naturally existing viral variants.
  Gastroenterology 12/2011; 142(3):654-63. · 11.68 Impact Factor
• Article: Regulation of the production of infectious genotype 1a hepatitis C virus by NS5A domain III.

  Seungtaek Kim, Christoph Welsch, MinKyung Yi, Stanley M Lemon
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  ABSTRACT: Although hepatitis C virus (HCV) assembly remains incompletely understood, recent studies with the genotype 2a JFH-1 strain suggest that it is dependent upon the phosphorylation of Ser residues near the C terminus of NS5A, a multifunctional nonstructural protein. Since genotype 1 viruses account for most HCV disease yet differ substantially in sequence from that of JFH-1, we studied the role of NS5A in the production of the H77S virus. While less efficient than JFH-1, genotype 1a H77S RNA produces infectious virus when transfected into permissive Huh-7 cells. The exchange of complete NS5A sequences between these viruses was highly detrimental to replication, while exchanges of the C-terminal domain III sequence (46% amino acid sequence identity) were well tolerated, with little effect on RNA synthesis. Surprisingly, the placement of the H77S domain III sequence into JFH-1 resulted in increased virus yields; conversely, H77S yields were reduced by the introduction of domain III from JFH-1. These changes in infectious virus yield correlated well with changes in the abundance of NS5A in RNA-transfected cells but not with RNA replication or core protein expression levels. Alanine replacement mutagenesis of selected Ser and Thr residues in the C-terminal domain III sequence revealed no single residue to be essential for infectious H77S virus production. However, virus production was eliminated by Ala substitutions at multiple residues and could be restored by phosphomimetic Asp substitutions at these sites. Thus, despite low overall sequence homology, the production of infectious virus is regulated similarly in JFH-1 and H77S viruses by a conserved function associated with a C-terminal Ser/Thr cluster in domain III of NS5A.
  Journal of Virology 07/2011; 85(13):6645-56. · 5.40 Impact Factor
• Article: Impact of ribavirin on HCV replicon RNA decline during treatment with interferon-α and the protease inhibitors boceprevir or telaprevir.

  Wolf Peter Hofmann, Tje Lin Chung, Carola Osbahr, Simone Susser, Ursel Karey, Ulrike Mihm, Christoph Welsch, Jörn Lötsch, Christoph Sarrazin, Stefan Zeuzem, Eva Herrmann
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  ABSTRACT: Ribavirin increases early and sustained virological response rates in patients chronically infected with HCV who receive pegylated interferon-α and novel HCV protease inhibitors. To better characterize antiviral efficacies of these upcoming therapies, Huh7 cells harbouring a subgenomic HCV replicon system were cultivated with various doses and combinations of ribavirin, interferon-α, and the protease inhibitors boceprevir and telaprevir. Antiviral efficacy parameters were estimated from HCV RNA decay, and synergistic effects of combination therapies were analysed with the Bliss independency model. Single-drug antiviral activities showed dose-dependent HCV RNA reductions in replicon cells (50% inhibitory concentration of 386.16 μM, 81.67 IU, 0.44 μM and 0.81 μM after 48 h for ribavirin, interferon-α, boceprevir and telaprevir, respectively). For the dual combination of ribavirin with either boceprevir or telaprevir, no deviation from additivity was observed whereas the reduction of HCV RNA was synergistic for ribavirin with interferon-α (P<0.001). Triple combinations with ribavirin, interferon-α and protease inhibitors showed the most profound HCV RNA decay. The beneficial in vitro antiviral effect of ribavirin with interferon-α and novel HCV protease inhibitors demonstrates that ribavirin may be required as an antiviral backbone in the near future.
  Antiviral therapy 01/2011; 16(5):695-704. · 3.16 Impact Factor
• Article: Protease inhibitor-resistant hepatitis C virus mutants with reduced fitness from impaired production of infectious virus.

  Tetsuro Shimakami, Christoph Welsch, Daisuke Yamane, David R McGivern, Minkyung Yi, Stefan Zeuzem, Stanley M Lemon
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  ABSTRACT: Several small molecule inhibitors of the hepatitis C virus (HCV) nonstructural protein (NS) 3/4A protease have advanced successfully to clinical trials. However, the selection of drug-resistant mutants is a significant issue with protease inhibitors (PIs). A variety of amino acid substitutions in the protease domain of NS3 can lead to PI resistance. Many of these significantly impair the replication fitness of HCV RNA replicons. However, it is not known whether these mutations also adversely affect infectious virus assembly and release, processes in which NS3 also participates. We studied the impact of 25 previously identified PI-resistance mutations on the capacity of genotype 1a H77S RNA to replicate in cell culture and produce infectious virus. Most PI-resistance mutations resulted in moderate loss of replication competence, although several (V36A/L/M, R109K, and D168E) showed fitness comparable to wild type, whereas others (S138T and A156V) were severely impaired both in RNA replication and infectious virus production. Although reductions in RNA replication capacity correlated with decreased yields of infectious virus for most mutations, a subset of mutants (Q41R, F43S, R155T, A156S, and I170A/T) showed greater impairment in their ability to produce virus than predicted from reductions in RNA replication capacity. Detailed examination of the I170A mutant showed no defect in release of virus from cells and no significant difference in specific infectivity of extracellular virus particles. Replicon-based assays might underestimate the loss of fitness caused by PI-resistance mutations, because some mutations in the NS3 protease domain specifically impair late steps in the viral life cycle that involve intracellular assembly of infectious virus.
  Gastroenterology 11/2010; 140(2):667-75. · 11.68 Impact Factor
• Article: Dimerization of the hepatitis C virus nonstructural protein 4B depends on the integrity of an aminoterminal basic leucine zipper.

  Martin-Walter Welker, Christoph Welsch, Aline Meyer, Iris Antes, Mario Albrecht, Nicole Forestier, Bernd Kronenberger, Thomas Lengauer, Albrecht Piiper, Stefan Zeuzem, Christoph Sarrazin
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  ABSTRACT: The hepatitis C virus (HCV) nonstructural (NS) protein 4B is known for protein-protein interactions with virus and host cell factors. Only little is known about the corresponding protein binding sites and underlying molecular mechanisms. Recently, we have predicted a putative basic leucine zipper (bZIP) motif within the aminoterminal part of NS4B. The aim of this study was to investigate the importance of this NS4B bZIP motif for specific protein-protein interactions. We applied in silico approaches for 3D-structure modeling of NS4B-homodimerization via the bZIP motif and identified crucial amino acid positions by multiple sequence analysis. The selected sites were used for site-directed mutagenesis within the NS4B bZIP motif and subsequent co-immunoprecipitation of wild-type and mutant NS4B molecules. Respective interaction energies were calculated for wild-type and mutant structural models. NS4B-homodimerization with a gradual alleviation of dimer interaction from wild-type towards the mutant-dimers was observed. The putative bZIP motif was confirmed by a co-immunoprecipitation assay and western blot analysis. NS4B-NS4B interaction depends on the integrity of the bZIP hydrophobic core and can be abolished due to changes of crucial residues within NS4B. In conclusion, our data indicate NS4B-homodimerization and that this interaction is facilitated by the aminoterminal part containing a bZIP motif.
  Protein Science 07/2010; 19(7):1327-36. · 2.80 Impact Factor
• Article: Highly sensitive determination of HCV protease inhibitors boceprevir (SCH 503034) and telaprevir (VX 950) in human plasma by LC-MS/MS.

  Harald Farnik, Juliane El-Duweik, Christoph Welsch, Christoph Sarrazin, Jörn Lötsch, Stefan Zeuzem, Gerd Geisslinger, Helmut Schmidt
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  ABSTRACT: The purpose of this study was to develop a specific and highly sensitive method based on fast sample preparation and LC-MS/MS techniques for the determination of the HCV protease inhibitors boceprevir (SCH 503034) and telaprevir (VX 950) in human plasma. Boceprevir, telaprevir and the internal standard dimethylcelecoxib were separated on a Luna C18 column (150 mm x 2.0 mm I.D., 5 microm particle size) under gradient conditions with a mobile phase A consisting of water/ammonia solution (25%) (100:0.05, v/v) and mobile phase B consisting of methanol/ammonia solution (25%) (100:0.05, v/v) and a chromatographic run time of 11 min. The lower limit of quantification (LLOQ) of boceprevir and telaprevir is 0.25 pg on column (25 pg/mL at injection volume of 10 microL). The method possesses a reliable calibration range of 0.025-2.5 ng/mL. Due to the dilution of real life plasma samples by a factor of 10 during the precipitation process the method is suitable to quantify boceprevir and telaprevir at a concentration range of 0.25-25 ng/mL. Variations in accuracy and intraday and interday precision (n=6 for each concentration) were <15% over the whole range of calibration. For the first time, a rapid, specific, sensitive, accurate and reproducible LC-MS/MS method in human plasma has been developed and validated. It is suitable to quantify the concentrations of the hepatitis C virus protease inhibitors boceprevir and telaprevir in human plasma.
  Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 10/2009; 877(31):4001-6. · 2.78 Impact Factor
• Article: RNA-binding activity of hepatitis C virus NS4B: a novel target for small molecule inhibitors.

  Christoph Welsch, Stefan Zeuzem
  Gastroenterology 10/2009; 137(6):2170-2. · 11.68 Impact Factor
• Source

  Available from: Simone Susser

  Article: Characterization of resistance to the protease inhibitor boceprevir in hepatitis C virus-infected patients.

  Simone Susser, Christoph Welsch, Yalan Wang, Markus Zettler, Francisco S Domingues, Ursula Karey, Eric Hughes, Robert Ralston, Xiao Tong, Eva Herrmann, Stefan Zeuzem, Christoph Sarrazin
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  ABSTRACT: Boceprevir is a hepatitis C virus (HCV) nonstructural protein (NS) 3/4A protease inhibitor that is currently being evaluated in combination with peginterferon alfa-2b and ribavirin in phase 3 studies. The clinical resistance profile of boceprevir is not characterized in detail so far. The NS3 protease domain of viral RNA was cloned from HCV genotype 1-infected patients (n = 22). A mean number of 47 clones were sequenced before, at the end, and after treatment with 400 mg boceprevir twice or three times daily for 14 days for genotypic, phenotypic, and viral fitness analysis. At the end of treatment, a wild-type an NS3 protease sequence was observed with a mean frequency of 85.9%. In the remaining isolates, five previously observed resistance mutations (V36M/A, T54A/S, R155K/T, A156S, V170A) and one mutation (V55A) with unknown resistance to boceprevir were detected either alone or in combination. Phenotypic analysis in the HCV replicon assay showed low (V36G, T54S, R155L; 3.8- to 5.5-fold 50% inhibitory concentration [IC(50)]), medium (V55A, R155K, V170A, T54A, A156S; 6.8- to 17.7-fold IC(50)) and high level (A156T; >120-fold IC(50)) resistance to boceprevir. The overall frequency of resistant mutations and the level of resistance increased with greater declines in mean maximum HCV RNA levels. Two weeks after the end of treatment, the frequency of resistant variants declined and the number of wild-type isolates increased to 95.5%. With the exception of V36 and V170 variants all resistant mutations declined by more than 50%. Mathematical modeling revealed impaired replicative fitness for all single mutations, whereas for combined mutations a relative increase of replication efficiency was suggested. CONCLUSION: During boceprevir monotherapy, resistance mutations at six positions within the NS3 protease were detected by way of clonal sequence analysis. All mutations are associated with reduced replicative fitness estimated by mathematical modeling and show cross-resistance to telaprevir.
  Hepatology 08/2009; 50(6):1709-18. · 11.66 Impact Factor
• Article: Clinical relevance of the 2'-5'-oligoadenylate synthetase/RNase L system for treatment response in chronic hepatitis C.

  Ulrike Mihm, Oliver Ackermann, Christoph Welsch, Eva Herrmann, Wolf Peter Hofmann, Natalia Grigorian, Martin Walter Welker, Thomas Lengauer, Stefan Zeuzem, Christoph Sarrazin
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  ABSTRACT: Interferon-alpha induces 2'-5'-oligoadenylate synthetase which activates RNase L. Viral RNA is cleaved by RNase L at UU/UA dinucleotides. The clinical relevance of RNase L cleavage for response to an interferon-alpha-based therapy in chronic hepatitis C is unknown. RNase L cleavage sites within pre-treatment sequences coding for structural and non-structural hepatitis C virus proteins were compared between non-responders and responders to an interferon-alpha-based therapy. Furthermore, RNase L cleavage sites were analyzed in full length and partial genome isolates of hepatitis C virus genotype 1b infected non-responders before and during treatment and in different hepatitis C virus genotypes (1b, 2a/b, 3a/b). No differences in RNase L cleavage sites were observed between non-responders and responders within a given hepatitis C genotype. Non-responders with hepatitis C virus genotype 1b infection did not eliminate UA/UU dinucleotides during therapy. Hepatitis C virus genotype 1b isolates showed a lower number of UA/UU dinucleotides than hepatitis C virus genotypes 2/3 (p < 0.001). Response or non-response to an interferon-alpha-based therapy within a given hepatitis C virus genotype is not explained by differences for RNase L cleavage sites. General differences of interferon sensitivity between hepatitis C virus genotypes correlate significantly with frequencies of RNase L cleavage sites.
  Journal of Hepatology 12/2008; 50(1):49-58. · 9.26 Impact Factor
• Article: Validity of N-terminal propeptide of the brain natriuretic peptide in predicting left ventricular diastolic dysfunction diagnosed by tissue Doppler imaging in patients with chronic liver disease.

  Tanja M Raedle-Hurst, Christoph Welsch, Nicole Forestier, Bernd Kronenberger, Georg Hess, Eva Herrmann, Stefan Zeuzem, Jochen Raedle
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  ABSTRACT: Left ventricular diastolic dysfunction has been reported in patients with liver cirrhosis. Although conventional Doppler echocardiography has been used to assess diastolic filling dynamics, this technique is limited in diagnosing left ventricular diastolic dysfunction. The aim of the study was to validate the N-terminal propeptide of the brain natriuretic peptide (NT-proBNP) in predicting left ventricular diastolic dysfunction diagnosed by tissue Doppler imaging in patients with chronic liver disease. In 64 patients, left ventricular diastolic dysfunction was classified using tissue Doppler imaging and serum levels of NT-proBNP were measured. Left ventricular diastolic dysfunction was found in 25 of 31 (80.6%) patients with severe liver fibrosis/cirrhosis versus 2 of 8 (25.0%) patients with moderate and 6 of 25 (24.0%) patients with mild liver fibrosis (P<0.001). Mean NT-proBNP levels were 407.1+/-553.4 pg/ml in patients with severe fibrosis/cirrhosis as compared with 60.8+/-54.9 pg/ml and 55.4+/-41.4 pg/ml in patients with mild and moderate fibrosis (P=0.001). NT-proBNP was most accurate in predicting advanced left ventricular diastolic dysfunction with an area under the receiver-operating characteristic curve of 0.90 (95% confidence interval, 0.77-1.0; P<0.001). A cutoff value of greater than 290 pg/ml was highly predictive of advanced left ventricular diastolic dysfunction. NT-proBNP is a useful marker in detecting advanced left ventricular diastolic dysfunction in patients with chronic liver disease. Patients with severe liver fibrosis/cirrhosis and NT-proBNP levels exceeding 290 pg/ml should undergo further cardiac evaluation.
  European Journal of Gastroenterology & Hepatology 10/2008; 20(9):865-73. · 1.76 Impact Factor
• Article: Novel hepatitis C drugs in current trials.

  Bernd Kronenberger, Christoph Welsch, Nicole Forestier, Stefan Zeuzem
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  ABSTRACT: Almost half of the patients who have chronic hepatitis C cannot be cured with the current standard treatment. Recent progress in structure determination of HCV proteins and development of a subgenomic replicon system and a cell culture infectious HCV clone enabled the development of a specifically targeted antiviral therapy for hepatitis C (STAT-C). Many HCV-specific compounds are under investigation in preclinical and clinical trials. The development of agents in different classes may allow construction of antiviral combinations that enhance the effectiveness of antiviral treatment, reduce the duration of treatment, and, eventually, may even avoid the use of interferon-alfa.
  Clinics in Liver Disease 09/2008; 12(3):529-55, viii. · 3.18 Impact Factor
• Article: Evaluation of the MLH1 I219V alteration in DNA mismatch repair activity and ulcerative colitis.

  Guido Plotz, Jochen Raedle, Anna Spina, Christoph Welsch, Andreas Stallmach, Stefan Zeuzem, Carsten Schmidt
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  ABSTRACT: Inflammatory bowel diseases (IBDs; ulcerative colitis, UC, and Crohn's disease, CD) show familial clustering suggestive of a genetic background. A linkage susceptibility region for these diseases (IBD9) lies on chromosome 3p and includes the DNA mismatch repair gene MLH1. Loss of MLH1 confers the characteristic microsatellite instability (MSI) phenotype which is also frequently found in the mucosa of IBD patients. A common germline alteration of MLH1 (655A>G) results in the amino acid exchange MLH1 I219V. Conflicting data exist on its effect on the function of the protein and it has recently been reported to cosegregate with refractory UC, suggesting that this alteration may impair mismatch repair activity and thereby contribute to certain forms of UC. We analyzed the MLH1 I219V alteration using in silico and biochemical analyses and assessed its appearance in 67 well-classified UC patients in comparison to 40 healthy individuals. The analyses showed that I219 is a conserved, buried hydrophobic residue, and that I219V is unlikely to abolish MLH1 function but may modulate it. Quantitative biochemical evaluation showed identical stability and activity of the protein. Furthermore, the alteration occurred equally frequently in analyzed patients and healthy volunteers. The MLH1 I219V alteration does not directly contribute to the etiology of UC through an impairment of mismatch repair. A putative linkage disequilibrium of MLH1 I219V with the causative gene(s) of the IBD9 locus is rather distant.
  Inflammatory Bowel Diseases 05/2008; 14(5):605-11. · 4.86 Impact Factor
• Source

  Available from: Simone Susser

  Article: Molecular basis of telaprevir resistance due to V36 and T54 mutations in the NS3-4A protease of the hepatitis C virus.

  Christoph Welsch, Francisco S Domingues, Simone Susser, Iris Antes, Christoph Hartmann, Gabriele Mayr, Andreas Schlicker, Christoph Sarrazin, Mario Albrecht, Stefan Zeuzem, Thomas Lengauer
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  ABSTRACT: The inhibitor telaprevir (VX-950) of the hepatitis C virus (HCV) protease NS3-4A has been tested in a recent phase 1b clinical trial in patients infected with HCV genotype 1. This trial revealed residue mutations that confer varying degrees of drug resistance. In particular, two protease positions with the mutations V36A/G/L/M and T54A/S were associated with low to medium levels of drug resistance during viral breakthrough, together with only an intermediate reduction of viral replication fitness. These mutations are located in the protein interior and far away from the ligand binding pocket. Based on the available experimental structures of NS3-4A, we analyze the binding mode of different ligands. We also investigate the binding mode of VX-950 by protein-ligand docking. A network of non-covalent interactions between amino acids of the protease structure and the interacting ligands is analyzed to discover possible mechanisms of drug resistance. We describe the potential impact of V36 and T54 mutants on the side chain and backbone conformations and on the non-covalent residue interactions. We propose possible explanations for their effects on the antiviral efficacy of drugs and viral fitness. Molecular dynamics simulations of T54A/S mutants and rotamer analysis of V36A/G/L/M side chains support our interpretations. Experimental data using an HCV V36G replicon assay corroborate our findings. T54 mutants are expected to interfere with the catalytic triad and with the ligand binding site of the protease. Thus, the T54 mutants are assumed to affect the viral replication efficacy to a larger degree than V36 mutants. Mutations at V36 and/or T54 result in impaired interaction of the protease residues with the VX-950 cyclopropyl group, which explains the development of viral breakthrough variants.
  Genome biology 02/2008; 9(1):R16. · 6.63 Impact Factor
• Article: Identification and in silico characterization of a novel compound heterozygosity associated with hereditary aceruloplasminemia.

  Wolf Peter Hofmann, Christoph Welsch, Yoshitomo Takahashi, Hiroaki Miyajima, Ulrike Mihm, Christoph Krick, Stefan Zeuzem, Christoph Sarrazin
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  ABSTRACT: Hereditary aceruloplasminemia is an adult-onset autosomal recessive disease characterized by increased iron overload in the liver, pancreas, retina, and central nervous system. So far, 45 families with cases of aceruloplasminemia have been reported world-wide and mainly missense and nonsense mutations in the ceruloplasmin gene were detected. Here, we report the identification, clinical characterization, and in silico analysis of a novel compound heterozygosity in the ceruloplasmin gene of a 31-year-old man with iron overload. Increased serum ferritin levels, elevated iron saturation, as well as results of iron quantification in the liver and magnetic resonance imaging-based measurement of T2 relaxation times of the substantia nigra consistently suggested iron overload. By sequencing the ceruloplasmin gene, so far unknown nucleotide replacements G229C, and C2131A were detected in exons 2 and 12, respectively. In silico analyses showed that the resulting amino acid changes Asp58His and Gln692Lys are located at highly conserved positions. The Asp58His mutation is located on the surface of the protein, alters polarity, and may interfere with copper incorporation or ceruloplasmin trafficking. The Gln692Lys mutation is mapped to a beta-strand of domain 4 and may lead to conformational change of the cupredoxin fold. As causative for aceruloplasminemia, a formerly unknown compound heterozygosity in the ceruloplasmin gene was identified. In silico characterization suggests an impact on ceruloplasmin conformation and function.
  Scandinavian Journal of Gastroenterology 10/2007; 42(9):1088-94. · 2.02 Impact Factor
• Article: Structural and functional comparison of the non-structural protein 4B in flaviviridae.

  Christoph Welsch, Mario Albrecht, Jochen Maydt, Eva Herrmann, Martin Walter Welker, Christoph Sarrazin, Axel Scheidig, Thomas Lengauer, Stefan Zeuzem
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  ABSTRACT: Flaviviridae are evolutionarily related viruses, comprising the hepatitis C virus (HCV), with the non-structural protein 4B (NS4B) as one of the least characterized proteins. NS4B is located in the endoplasmic reticulum membrane and is assumed to be a multifunctional protein. However, detailed structure information is missing. The hydrophobic nature of NS4B is a major difficulty for many experimental techniques. We applied bioinformatics methods to analyse structural and functional properties of NS4B in different viruses. We distinguish a central non-globular membrane portion with four to five transmembrane regions from an N- and C-terminal part with non-transmembrane helical elements. We demonstrate high similarity in sequence and structure for the C-terminal part within the flaviviridae family. A palmitoylation site contained in the C-terminal part of HCV is equally conserved in GB virus B. Furthermore, we identify and characterize an N-terminal basic leucine zipper (bZIP) motif in HCV, which is suggestive of a functionally important interaction site. In addition, we model the interaction of the bZIP region with the recently identified interaction partner CREB-RP/ATF6beta, a human activating transcription factor involved in ER-stress. In conclusion, the versatile structure, together with functional sites and motifs, possibly enables NS4B to adopt a role as protein hub in the membranous web interaction network of virus and host proteins. Important structural and functional properties of NS4B are predicted with implications for ER-stress response, altered gene expression and replication efficacy.
  Journal of Molecular Graphics and Modelling 10/2007; 26(2):546-57. · 2.18 Impact Factor
• Source

  Available from: intmedpress.com

  Article: Amino acid variations in hepatitis C virus p7 and sensitivity to antiviral combination therapy with amantadine in chronic hepatitis C.

  Ulrike Mihm, Natalia Grigorian, Christoph Welsch, Eva Herrmann, Bernd Kronenberger, Gerlinde Teuber, Michael von Wagner, Wolf-Peter Hofmann, Mario Albrecht, Thomas Lengauer, Stefan Zeuzem, Christoph Sarrazin
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  ABSTRACT: Formation of transmembrane ion channels by hepatitis C virus (HCV) p7 and abrogation of channel function by amantadine was demonstrated in vitro. The relevance of HCV p7 amino acid (aa) variations for response to antiviral therapy with amantadine is unknown. HCV p7 was sequenced in 86 individuals who were infected with HCV genotype 1. Thirty-six of 86 patients received amantadine within an interferon-alpha (IFN-alpha)-based antiviral therapy. Helical wheel modelling for HCV p7 was performed. No significant correlation of overall aa variations within HCV p7 was observed with response to IFN-alpha-based therapy with amantadine in HCV genotype 1alpha/b infected patients. When analysis was restricted to non-conservative aa variations, a higher number of aa substitutions within complete HCV p7 and transmembrane helix 2 was associated with non-response in HCV-1b-infected patients receiving therapy with amantadine (P=0.015 and P=0.037, respectively), without amantadine (P=0.106 and P=0.118, respectively), and in the total cohort of HCV-1b-infected patients (P=0.00007 and P=0.011, respectively). Furthermore, substitution L20F was observed more often in non-responders than responders with HCV-1b infection and therapy with amantadine (P=0.099). By in silico modelling, aa 20 was located toward the p7 channel lumen. Substitution L20F may impair amantadine action by altering the shape of the ion channel pore. Substitution L20F within HCV p7 may be associated with non-response to combination therapy specifically with amantadine in HCV-1b-infected patients. Non-responders with HCV-1b infection showed higher numbers of non-conservative aa variations within HCV p7 than responders, irrespective of the application of amantadine.
  Antiviral therapy 02/2006; 11(4):507-19. · 3.16 Impact Factor