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AIMS
To characterize the cytochrome P450 enzyme(s) responsible for the N-dealkylation of maraviroc in vitro, and predict the extent of clinical drug–drug interactions (DDIs).METHODS
Human liver and recombinant CYP microsomes were used to identify the CYP enzyme responsible for maraviroc N-dealkylation. Studies comprised enzyme kinetics and evaluation of the effects of specific CYP inhibitors. In vitro data were then used as inputs for simulation of DDIs with ketoconazole, ritonavir, saquinavir and atazanvir, using the Simcyp™ population-based absorption, distribution, metabolism and elimination (ADME) simulator. Study designs for simulations mirrored those actually used in the clinic.RESULTS
Maraviroc was metabolized to its N-dealkylated product via a single CYP enzyme characterized by a Km of 21 µM and Vmax of 0.45 pmol pmol−1 min−1 in human liver microsomes and was inhibited by ketoconazole (CYP3A4 inhibitor). In a panel of recombinant CYP enzymes, CYP3A4 was identified as the major CYP responsible for maraviroc metabolism. Using recombinant CYP3A4, N-dealkylation was characterized by a Km of 13 µM and a Vmax of 3 pmol pmol−1 CYP min−1. Simulations therefore focused on the effect of CYP3A4 inhibitors on maraviroc pharmacokinetics. The simulated median AUC ratios were in good agreement with observed clinical changes (within twofold in all cases), although, in general, there was a trend for overprediction in the magnitude of the DDI.CONCLUSION
Maraviroc is a substrate for CYP3A4, and exposure will therefore be modulated by CYP3A4 inhibitors. Simcyp™ has successfully simulated the extent of clinical interactions with CYP3A4 inhibitors, further validating this software as a good predictor of CYP-based DDIs.WHAT IS ALREADY KNOWN ABOUT THE SUBJECT
- Maraviroc is known to undergo oxidative metabolism in vivo and is a substrate for cytochrome P450 (CYP).
- Simcyp™ has recently become more widely used for the prediction of CYP-mediated drug–drug interactions (DDIs) using in vitro metabolism data.
WHAT THIS STUDY ADDS
- Maraviroc has been identified as a CYP3A4 substrate and the kinetic constants characterized.
- The predicted DDIs associated with maraviroc as a CYP3A4 substrate using Simcyp™ have been compared against the clinical data.
- This study demonstrates the value of a reliable Simcyp™ model for prediction of DDIs.
The aim of this study was to identify artificial single-nucleotide variants (SNVs) in degraded trace DNA samples. In a preliminary study, blood samples were stored for up to 120 days and whole-genome sequencing was performed using the Snakemake workflow dna-seq-gatk-variant-calling to identify positions that vary between the time point 0 sample and the aged samples. In a follow-up study on blood and saliva samples stored under humid and dry conditions, potential marker candidates for the estimation of the age of a blood stain (= time since deposition) were identified. Both studies show that a general decrease in the mean fragment size of the libraries over time was observed, presumably due to the formation of abasic sites during DNA degradation which are more susceptible to strand breaks by mechanical shearing of DNA. Unsurprisingly, an increase in the number of failed genotype calls (no coverage) was detected over time. Both studies indicated the presence of artificial SNVs with the majority of changes happening at guanine and cytosine positions. This confirms previous studies and can be explained by depurination through hydrolytic attacks which more likely deplete guanine while deamination leads to cytosine to thymine variants. Even complete genotype switches from homozygote 0/0 genotypes to the opposite 1/1 genotypes were observed. While positions with such drastic changes might provide suitable candidate markers for estimating short-term time since deposition (TsD), 11 markers were identified which show a slower gradual change of the relative abundance of the artificial variant in both blood and saliva samples, irrespective of storage conditions.
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