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12 Publications visible to you, out of a total of 12
The formation of estrogen-like tamoxifen metabolites and their influence on enzyme activity and gene expression of ADME genes.

Abstract (Expand)

Tamoxifen, a standard therapy for breast cancer, is metabolized to compounds with anti-estrogenic as well as estrogen-like action at the estrogen receptor. Little is known about the formation of … estrogen-like metabolites and their biological impact. Thus, we characterized the estrogen-like metabolites tamoxifen bisphenol and metabolite E for their metabolic pathway and their influence on cytochrome P450 activity and ADME gene expression. The formation of tamoxifen bisphenol and metabolite E was studied in human liver microsomes and Supersomes. Cellular metabolism and impact on CYP enzymes was analyzed in upcyte(R) hepatocytes. The influence of 5 microM of tamoxifen, anti-estrogenic and estrogen-like metabolites on CYP activity was measured by HPLC MS/MS and on ADME gene expression using RT-PCR analyses. Metabolite E was formed from tamoxifen by CYP2C19, 3A and 1A2 and from desmethyltamoxifen by CYP2D6, 1A2 and 3A. Tamoxifen bisphenol was mainly formed from (E)- and (Z)-metabolite E by CYP2B6 and CYP2C19, respectively. Regarding phase II metabolism, UGT2B7, 1A8 and 1A3 showed highest activity in glucuronidation of tamoxifen bisphenol and metabolite E. Anti-estrogenic metabolites (Z)-4-hydroxytamoxifen, (Z)-endoxifen and (Z)-norendoxifen inhibited the activity of CYP2C enzymes while tamoxifen bisphenol consistently induced CYPs similar to rifampicin and phenobarbital. On the transcript level, highest induction up to 5.6-fold was observed for CYP3A4 by tamoxifen, (Z)-4-hydroxytamoxifen, tamoxifen bisphenol and (E)-metabolite E. Estrogen-like tamoxifen metabolites are formed in CYP-dependent reactions and are further metabolized by glucuronidation. The induction of CYP activity by tamoxifen bisphenol and the inhibition of CYP2C enzymes by anti-estrogenic metabolites may lead to drug-drug-interactions.

Authors: J. Johanning, P. Kroner, M. Thomas, U. M. Zanger, A. Norenberg, M. Eichelbaum, M. Schwab, H. Brauch, W. Schroth, T. E. Murdter

Date Published: 28th Dec 2017

Publication Type: Not specified

Physiologically-based modelling in mice suggests an aggravated loss of clearance capacity after toxic liver damage

Abstract (Expand)

Diseases and toxins may lead to death of active liver tissue, resulting in a loss of total clearance capacity at the whole-body level. However, it remains difficult to study, whether the loss of … metabolizing tissue is sufficient to explain loss of metabolic capacity of the liver or whether the surviving tissue undergoes an adaptive response to compensate the loss. To understand the cellular impact of toxic liver damage in an in vivo situation, we here used physiologically-based pharmacokinetic modelling to investigate pharmacokinetics of a specifically designed drug cocktail at three different sampling sites of the body in healthy mice and mice treated with carbon tetrachloride (CCl4). Liver zonation was explicitly quantified in the models through immunostaining of cytochrome P450s enzymes. Comparative analyses between the simulated decrease in clearance capacity and the experimentally measured loss in tissue volume indicated that CCl4-induced impairment of metabolic functions goes beyond the mere loss of metabolically active tissue. The here established integrative modelling strategy hence provides mechanistic insights into functional consequences of toxic liver damage in an in vivo situation, which would not have been accessible by conventional methods.

Authors: Arne Schenk, Ahmed Ghallab, Ute Hofmann, Reham Hassan, Michael Schwarz, Andreas Schuppert, Lars Ole Schwen, Albert Braeuning, Donato Teutonico, Jan G. Hengstler, Lars Kuepfer

Date Published: 1st Dec 2017

Publication Type: Not specified

Pharmacokinetics and pharmacodynamics of thiopurines in an in vitro model of human hepatocytes: Insights from an innovative mass spectrometry assay.

Abstract (Expand)

AIM: To apply an innovative LC-MS/MS method to quantify thiopurine metabolites in human hepatocytes and to associate them to cytotoxicity. METHODS: Immortalized human hepatocytes (IHH cells) were treated … for 48 and 96 h, with 1.4 x 10(-4) M azathioprine and 1.1 x 10(-3) M mercaptopurine, concentrations corresponding to the IC50 values calculated after 96 h exposure in previous cytotoxicity analysis. After treatments, cells were collected for LC-MS/MS analysis to quantify 11 thiopurine metabolites with different level of phosphorylation and viable cells were counted by trypan blue exclusion assay to determine thiopurines in vitro effect on cell growth and survival. Statistical significance was determined by analysis of variance (ANOVA). RESULTS: Azathioprine and mercaptopurine had a significant time-dependent cytotoxic effect (p-value ANOVA = 0.012), with a viable cell count compared to controls of 55.5% and 67.5% respectively after 48 h and 23.7% and 36.1% after 96 h; no significant difference could be observed between the two drugs. Quantification of thiopurine metabolites evidenced that the most abundant metabolite was TIMP, representing 57.1% and 40.3% of total metabolites after 48 and 96 h. Total thiopurine metabolites absolute concentrations decreased over time: total mean content decreased from 469.9 pmol/million cells to 83.6 pmol/million cells (p-value ANOVA = 0.0070). However, considering the relative amount of thiopurine metabolites, TGMP content significantly increased from 11.4% cells to 26.4% (p-value ANOVA = 0.017). A significant association between thiopurine effects and viable cell counts could be detected only for MeTIMP: lower MeTIMP concentrations were associated with lower cell survival (p-value ANOVA = 0.011). Moreover, the ratio between MeTIMP and TGMP metabolites directly correlated with cell survival (p-value ANOVA = 0.037). CONCLUSION: Detailed quantification of thiopurine metabolites in a human hepatocytes model provided useful insights on the association between thioguanine and methyl-thioinosine nucleotides with cell viability.

Authors: M. Pelin, E. Genova, L. Fusco, M. Marisat, U. Hofmann, D. Favretto, M. Lucafo, A. Taddio, S. Martelossi, A. Ventura, G. Stocco, M. Schwab, G. Decorti

Date Published: 12th Aug 2017

Publication Type: Not specified

Translational learning from clinical studies predicts drug pharmacokinetics across patient populations.

Abstract (Expand)

Early indication of late-stage failure of novel candidate drugs could be facilitated by continuous integration, assessment, and transfer of knowledge acquired along pharmaceutical development programs. … We here present a translational systems pharmacology workflow that combines drug cocktail probing in a specifically designed clinical study, physiologically based pharmacokinetic modeling, and Bayesian statistics to identify and transfer (patho-)physiological and drug-specific knowledge across distinct patient populations. Our work builds on two clinical investigations, one with 103 healthy volunteers and one with 79 diseased patients from which we systematically derived physiological information from pharmacokinetic data for a reference probe drug (midazolam) at the single-patient level. Taking into account the acquired knowledge describing (patho-)physiological alterations in the patient cohort allowed the successful prediction of the population pharmacokinetics of a second, candidate probe drug (torsemide) in the patient population. In addition, we identified significant relations of the acquired physiological processes to patient metadata from liver biopsies. The presented prototypical systems pharmacology approach is a proof of concept for model-based translation across different stages of pharmaceutical development programs. Applied consistently, it has the potential to systematically improve predictivity of pharmacokinetic simulations by incorporating the results of clinical trials and translating them to subsequent studies.

Authors: M. Krauss, U. Hofmann, C. Schafmayer, S. Igel, J. Schlender, C. Mueller, M. Brosch, W. von Schoenfels, W. Erhart, A. Schuppert, M. Block, E. Schaeffeler, G. Boehmer, L. Goerlitz, J. Hoecker, J. Lippert, R. Kerb, J. Hampe, L. Kuepfer, M. Schwab

Date Published: 27th Jun 2017

Publication Type: Not specified

Conditional loss of hepatocellular Hedgehog signaling in female mice leads to the persistence of hepatic steroidogenesis, androgenization and infertility

Abstract (Expand)

The Hedgehog signaling pathway is known to be involved in embryogenesis, tissue remodeling, and carcinogenesis. Because of its involvement in carcinogenesis, it seems an interesting target for cancer … therapy. Indeed, Sonidegib, an approved inhibitor of the Hedgehog receptor Smoothened (Smo), is highly active against diverse carcinomas, but its use is also reported to be associated with several systemic side effects. Our former work in adult mice demonstrated hepatic Hedgehog signaling to play a key role in the insulin-like growth factor axis and lipid metabolism. The current work using mice with an embryonic and hepatocyte-specific Smo deletion describes an adverse impact of the hepatic Hedgehog pathway on female fertility. In female SAC-KO mice, we detected androgenization characterized by a 3.3-fold increase in testosterone at 12 weeks of age based on an impressive induction of steroidogenic gene expression in hepatocytes, but not in the classic steroidogenic organs (ovary and adrenal gland). Along with the elevated level of testosterone, the female SAC-KO mice showed infertility characterized by juvenile reproductive organs and acyclicity. The endocrine and reproductive alterations resembled polycystic ovarian syndrome and could be confirmed in a second mouse model with conditional deletion of Smo at 8 weeks of age after an extended period of 8 months. We conclude that the down-regulation of hepatic Hedgehog signaling leads to an impaired hormonal balance by the induction of steroidogenesis in the liver. These effects of Hedgehog signaling inhibition should be considered when using Hedgehog inhibitors as anti-cancer drugs.

Authors: Christiane Rennert, Franziska Eplinius, Ute Hofmann, Janina Johänning, Franziska Rolfs, Wolfgang Schmidt-Heck, Reinhardt Guthke, Rolf Gebhardt, Albert M. Ricken, Madlen Matz-Soja

Date Published: 30th May 2017

Publication Type: Not specified

Ligand-dependent and -independent regulation of human hepatic sphingomyelin phosphodiesterase acid-like 3A expression by pregnane X receptor and crosstalk with liver X receptor.

Abstract (Expand)

Pregnane X receptor (PXR) mainly regulates xenobiotic metabolism and detoxification. Additionally, it exerts pleiotropic effects on liver physiology, which in large parts depend on transrepression of … other liver-enriched transcription factors. Based on the hypothesis that lower expression levels of PXR may reduce the extent of this inhibition, an exploratory genome-wide transcriptomic profiling was performed using HepG2 cell clones with different expression levels of PXR. This screen and confirmatory real-time RT-PCR identified sphingomyelin phosphodiesterase acid-like (SMPDL) 3A, a novel nucleotide phosphodiesterase and phosphoramidase, as being up-regulated by PXR-deficiency. Transient siRNA-mediated knock-down of PXR in HepG2 cells and primary human hepatocytes similarly induced mRNA up-regulation, which translated into increased intracellular and secreted extracellular protein levels. Interestingly, ligand-dependent PXR activation also induced SMPDL3A in HepG2 cells and primary human hepatocytes. Electrophoretic mobility shift assays and chromatin immunoprecipitation demonstrated binding of PXR to the previously identified liver X receptor (LXR)-binding DR4 motif as well as to an adjacent ER8 motif in intron 1 of SMPDL3A. Constitutive binding of the unliganded receptor to the intron 1 chromatin indicated ligand-independent repression of SMPDL3A by PXR. Transient transfection and reporter gene analysis confirmed the specific role of these motifs in PXR- and LXR-dependent activation of the SMPDL3A intronic enhancer. PXR inhibited LXR mainly by competition for binding sites. In conclusion, this study describes that a decrease in PXR expression levels and ligand-dependent activation of PXR and LXR increase hepatic SMPDL3A levels, which possibly connects these receptors to hepatic purinergic signaling and phospholipid metabolism and may result in drug-drug interactions with phosphoramidate pro-drugs.

Authors: J. Jeske, A. Bitter, W. E. Thasler, T. S. Weiss, M. Schwab, O. Burk

Date Published: 18th Apr 2017

Publication Type: Not specified

Towards knowledge-driven cross-species extrapolation

Abstract

Not specified

Authors: Christoph Thiel, Ute Hofmann, Ahmed Ghallab, Rolf Gebhardt, Jan G. Hengstler, Lars Kuepfer

Date Published: 1st Apr 2017

Publication Type: Not specified

The importance of drug transporter characterization to precision medicine.

Abstract

Not specified

Authors: P. Fisel, A. T. Nies, E. Schaeffeler, M. Schwab

Date Published: 1st Feb 2017

Publication Type: Not specified

Impact of Membrane Drug Transporters on Resistance to Small-Molecule Tyrosine Kinase Inhibitors.

Abstract (Expand)

Small-molecule inhibitors of tyrosine kinases (TKIs) are the mainstay of treatment for many malignancies and represent novel treatment options for other diseases such as idiopathic pulmonary fibrosis. … Twenty-five TKIs are currently FDA-approved and >130 are being evaluated in clinical trials. Increasing evidence suggests that drug exposure of TKIs may significantly contribute to drug resistance, independently from somatic variation of TKI target genes. Membrane transport proteins may limit the amount of TKI reaching the target cells. This review highlights current knowledge on the basic and clinical pharmacology of membrane transporters involved in TKI disposition and their contribution to drug efficacy and adverse drug effects. In addition to non-genetic and epigenetic factors, genetic variants, particularly rare ones, in transporter genes are promising novel factors to explain interindividual variability in the response to TKI therapy.

Authors: C. Neul, E. Schaeffeler, A. Sparreboom, S. Laufer, M. Schwab, A. T. Nies

Date Published: 25th Oct 2016

Publication Type: Not specified

Polymorphic variation in TPMT is the principal determinant of TPMT phenotype: A meta-analysis of three genome-wide association studies.

Abstract (Expand)

Thiopurine-related hematotoxicity in pediatric acute lymphoblastic leukemia (ALL) and inflammatory bowel diseases has been linked to genetically defined variability in thiopurine S-methyltransferase … (TPMT) activity. While gene testing of TPMT is being clinically implemented, it is unclear if additional genetic variation influences TPMT activity with consequences for thiopurine-related toxicity. To examine this possibility, we performed a genome-wide association study (GWAS) of red blood cell TPMT activity in 844 Estonian individuals and 245 pediatric ALL cases. Additionally, we correlated genome-wide genotypes to human hepatic TPMT activity in 123 samples. Only genetic variants mapping to chromosome 6, including the TPMT gene region, were significantly associated with TPMT activity (P < 5.0 x 10-8 ) in each of the three GWAS and a joint meta-analysis of 1,212 cases (top hit P = 1.2 x 10-72 ). This finding is consistent with TPMT genotype being the primary determinant of TPMT activity, reinforcing the rationale for genetic testing of TPMT alleles in routine clinical practice to individualize mercaptopurine dosage.

Authors: R. Tamm, R. Magi, R. Tremmel, S. Winter, E. Mihailov, A. Smid, A. Moricke, K. Klein, M. Schrappe, M. Stanulla, R. Houlston, R. Weinshilboum, I. Mlinaric Rascan, A. Metspalu, L. Milani, M. Schwab, E. Schaeffeler

Date Published: 23rd Oct 2016

Publication Type: Not specified

DNA Methylation of ADME Genes.

Abstract (Expand)

The epigenetic regulation of expression of genes involved in the absorption, distribution, metabolism, and excretion (ADME) of drugs contributes to interindividual variability in drug response. Epigenetic … mechanisms include DNA methylation, histone modifications, and miRNAs. This review systematically outlines the influence of DNA methylation on ADME gene expression and highlights the consequences for interindividual variability in drug response or drug-induced toxicity and the implications for personalized medicine.

Authors: P. Fisel, E. Schaeffeler, M. Schwab

Date Published: 12th Apr 2016

Publication Type: Not specified

Model-guided identification of a therapeutic strategy to reduce hyperammonemia in liver diseases

Abstract (Expand)

BACKGROUND & AIMS: Recently, spatial-temporal/metabolic mathematical models have been established that allow the simulation of metabolic processes in tissues. We applied these models to decipher …er ammonia detoxification mechanisms in the liver. METHODS: An integrated metabolic-spatial-temporal model was used to generate hypotheses of ammonia metabolism. Predicted mechanisms were validated using time-resolved analyses of nitrogen metabolism, activity analyses, immunostaining and gene expression after induction of liver damage in mice. Moreover, blood from the portal vein, liver vein and mixed venous blood was analyzed in a time dependent manner. RESULTS: Modeling revealed an underestimation of ammonia consumption after liver damage when only the currently established mechanisms of ammonia detoxification were simulated. By iterative cycles of modeling and experiments, the reductive amidation of alpha-ketoglutarate (α-KG) via glutamate dehydrogenase (GDH) was identified as the lacking component. GDH is released from damaged hepatocytes into the blood where it consumes ammonia to generate glutamate, thereby providing systemic protection against hyperammonemia. This mechanism was exploited therapeutically in a mouse model of hyperammonemia by injecting GDH together with optimized doses of cofactors. Intravenous injection of GDH (720 U/kg), α-KG (280 mg/kg) and NADPH (180 mg/kg) reduced the elevated blood ammonia concentrations (>200 μM) to levels close to normal within only 15 min. CONCLUSION: If successfully translated to patients the GDH-based therapy might provide a less aggressive therapeutic alternative for patients with severe hyperammonemia.

Authors: Ahmed Ghallab, Géraldine Cellière, Sebastian G. Henkel, Dominik Driesch, Stefan Hoehme, Ute Hofmann, Sebastian Zellmer, Patricio Godoy, Agapios Sachinidis, Meinolf Blaszkewicz, Raymond Reif, Rosemarie Marchan, Lars Kuepfer, Dieter Häussinger, Dirk Drasdo, Rolf Gebhardt, Jan G. Hengstler

Date Published: 1st Apr 2016

Publication Type: Not specified

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