Simultaneous quantification of dextromethorphan and its metabolites dextrorphan, 3-methoxymorphinan and 3-hydroxymorphinan in human plasma by ultra performance liquid chromatography/tandem triple-quadrupole mass spectrometry

Altered cytochrome 2E1 and 3A P450-dependent drug metabolism in advanced ovarian cancer correlates to tumour-associated inflammation

BACKGROUND AND PURPOSE

Previous work has focussed on changes in drug metabolism caused by altered activity of CYP3A in the presence of inflammation and, in particular, inflammation associated with malignancy. However, drug metabolism involves a number of other P450s, and therefore, we assessed the effect of cancer-related inflammation on multiple CYP enzymes using a validated drug cocktail.

EXPERIMENTAL APPROACH

Patients with advanced stage ovarian cancer and healthy volunteers were recruited. Participants received caffeine, chlorzoxazone, dextromethorphan, and omeprazole as in vivo probes for CYP1A2, CYP2E1, CYP2D6, CYP3A, and CYP2C19. Blood was collected for serum C-reactive protein and cytokine analysis.

KEY RESULTS

CYP2E1 activity was markedly up-regulated in cancer (6-hydroxychlorzoxazone/chlorzoxazone ratio of 1.30 vs. 2.75), while CYP3A phenotypic activity was repressed in cancer (omeprazole sulfone/omeprazole ratio of 0.23 vs. 0.49). Increased activity of CYP2E1 was associated with raised serum levels of IL-6, IL-8, and TNF-α. Repression of CYP3A correlated with raised levels of serum C-reactive protein, IL-6, IL-8, and TNF-α.

CONCLUSIONS AND IMPLICATIONS

CYP enzyme activity is differentially affected by the presence of tumour-associated inflammation, affecting particularly CYP2E1- and CYP3A-mediated drug metabolism, and may have profound implications for drug development and prescribing in oncological settings.

Evaluation of Tetrahydropalmatine Enantiomers on the Activity of Five Cytochrome P450 Isozymes in Rats Using a Liquid Chromatography / Mass Spectrometric Method and a Cocktail Approach

The aim was to evaluate the effects of tetrahydropalmatine (THP) enantiomers on the activity of five cytochrome P450 (CYP450) isozymes in vivo. A liquid chromatography / mass spectrometric (LC-MS) method was developed for simultaneous determination of five specific probe substrates including metoprolol (2D6), caffeine (1A2), dapsone (3A4), chlorzoxazone (2E1), and tolbutamide (2C9) in rat plasma. Analytes were separated with the mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile in a gradient elution. The mass spectrometric detection via selected ion monitoring (SIM) was operated in both positive ion mode (for metoprolol m/z 268, caffeine m/z 195, and dapsone m/z 249) and negative ion mode (for chlorzoxazone m/z 168 and tolbutamide m/z 269) in the same run. Linear correlation was obtained (r(2)  > 0.99) over the concentration range of 0.050-25.0 µg/mL for caffeine and dapsone, 0.025-10.0 µg/mL for metoprolol, 0.050-50.0 µg/mL for chlorzoxazone, and 0.25-100.0 µg/mL for tolbutamide. Intra- and interday precision were less than 12.09%. The matrix effect ranged from 87.50% to 109.25% and the absolute recoveries were greater than 70%. The method was successfully applied to evaluate the effect of THP enantiomers on the activity of CYP450 isozymes by a cocktail approach. The pharmacokinetic results of five probe drugs indicated that there were stereoselective differences between the two THP enantiomers, i.e., d-THP had the potential to inhibit the activities of CYP2D6 and CYP1A2 isozymes, while l-THP inhibited CYP1A2 isozyme and induced CYP3A4 and CYP2C9 isozymes.

Population pharmacokinetic modelling to assess the impact of CYP2D6 and CYP3A metabolic phenotypes on the pharmacokinetics of tamoxifen and endoxifen

AIMS

Tamoxifen is considered a pro-drug of its active metabolite endoxifen. The major metabolic enzymes involved in endoxifen formation are CYP2D6 and CYP3A. There is considerable evidence that variability in activity of these enzymes influences endoxifen exposure and thereby may influence the clinical outcome of tamoxifen treatment. We aimed to quantify the impact of metabolic phenotype on the pharmacokinetics of tamoxifen and endoxifen.

METHODS

We assessed the CYP2D6 and CYP3A metabolic phenotypes in 40 breast cancer patients on tamoxifen treatment with a single dose of dextromethorphan as a dual phenotypic probe for CYP2D6 and CYP3A. The pharmacokinetics of dextromethorphan, tamoxifen and their relevant metabolites were analyzed using non-linear mixed effects modelling.

RESULTS

Population pharmacokinetic models were developed for dextromethorphan, tamoxifen and their metabolites. In the final model for tamoxifen, the dextromethorphan derived metabolic phenotypes for CYP2D6 as well as CYP3A significantly (P < 0.0001) explained 54% of the observed variability in endoxifen formation (inter-individual variability reduced from 55% to 25%).

CONCLUSIONS

We have shown that not only CYP2D6, but also CYP3A enzyme activity influences the tamoxifen to endoxifen conversion in breast cancer patients. Our developed model may be used to assess separately the impact of CYP2D6 and CYP3A mediated drug-drug interactions with tamoxifen without the necessity of administering this anti-oestrogenic drug and to support Bayesian guided therapeutic drug monitoring of tamoxifen in routine clinical practice.

Characterization of pancreatic NMDA receptors as possible drug targets for diabetes treatment

In the nervous system, NMDA receptors (NMDARs) participate in neurotransmission and modulate the viability of neurons. In contrast, little is known about the role of NMDARs in pancreatic islets and the insulin-secreting beta cells whose functional impairment contributes to diabetes mellitus. Here we found that inhibition of NMDARs in mouse and human islets enhanced their glucose-stimulated insulin secretion (GSIS) and survival of islet cells. Further, NMDAR inhibition prolonged the amount of time that glucose-stimulated beta cells spent in a depolarized state with high cytosolic Ca(2+) concentrations. We also noticed that, in vivo, the NMDAR antagonist dextromethorphan (DXM) enhanced glucose tolerance in mice, and that in vitro dextrorphan, the main metabolite of DXM, amplified the stimulatory effect of exendin-4 on GSIS. In a mouse model of type 2 diabetes mellitus (T2DM), long-term treatment with DXM improved islet insulin content, islet cell mass and blood glucose control. Further, in a small clinical trial we found that individuals with T2DM treated with DXM showed enhanced serum insulin concentrations and glucose tolerance. Our data highlight the possibility that antagonists of NMDARs may provide a useful adjunct treatment for diabetes.

CYP2D6 phenotype indicative for optimized antiestrogen efficacy associates with outcome in early breast cancer patients

BACKGROUND

Endoxifen serum concentrations seem to correlate with outcome in breast cancer (BC) patients. Concurrently, cytochrome P450 2D6 (CYP2D6) enzyme activity and dextromethorphan (DM) metabolism are deemed a surrogate marker for the formation of endoxifen. Here, we conducted a matched cohort study to determine the impact of an extensive CYP2D6 phenotype on relapse in patients with early-stage estrogen receptor (ER)-positive BC and adjuvant tamoxifen intake.

METHODS

CYP2D6 extensive metabolism was determined upon appropriate dextromethorphan/dextrorphan (DM/DX) urinary excretion ratios (≤0.30). Fifty-nine BC patients were identified as extensive phenotype metabolizers, while for 148 matched controls, CYP2D6 was not determined. Patients and controls did not differ with respect to age, stage, hormone receptor status, HER2, grade, menopausal status, chemotherapy and antihormonal therapy. Survival analysis was performed according to clinical follow-up.

RESULTS

Disease-free survival (DFS) of patients identified as extensive CYP2D6 metabolizers did not differ significantly from controls (p = 0.10). However, when patients with ER expression of ≤ 20 % were excluded from the analysis, DFS was associated with a more favorable outcome (p = 0.06).

CONCLUSIONS

This study suggests a positive association between extensive CYP2D6 metabolism and outcome in early-stage ER-positive BC patients using tamoxifen and in particular, when a sufficient number ERs are represented on the primary tumor.

Effects of CYP induction by rifampicin on tamoxifen exposure

Tamoxifen undergoes biotransformation into several metabolites, including endoxifen. Differences in metabolism contribute to the interindividual variability in endoxifen concentrations, potentially affecting treatment efficacy. We evaluated the effects of cytochrome P450 (CYP) induction by rifampicin on the exposure levels of tamoxifen and its metabolites and found that coadministration of rifampicin resulted in markedly reduced (up to 86%, P ≤ 0.040) concentrations of tamoxifen and its metabolites. Given the extensive metabolism undergone by tamoxifen, several factors may have contributed to this effect. Similar drug-drug interactions may exist between tamoxifen and other strong CYP inducers.

Simultaneous determination of chloropheniramine maleate and dextromethorphan hydrobromide in plasma sample by hollow fiber liquid phase microextraction and high performance liquid chromatography with the aid of chemometrics

A simple and high sensitive technique based on three phase hollow fiber liquid phase microextraction (HF-LPME), optimized by using a four-variable experimental design and response surface methodology was performed to evaluate dextromethorphan hydrobromide (DEX) and chloropheniramine maleate (CLP) simultaneously in human plasma. The influence of source phase pH, HCl concentration of acceptor phase, time and salt addition were investigated. Under the optimized conditions analytes were extracted in their neutral form, pH 12.5 and salt concentration 2% (w/v), through a supported liquid membrane (SLM) of hexadecane into the HCl 0.0005 mol L(-1) located inside the lumen of hollow fiber to be back extracted. The mass transfer of the analytes from the donor phase through the SLM into acceptor phase was driven by the pH gradient. Determination was accomplished by UV-high performance liquid chromatography with recoveries 92% and 84% for CLP and DEX, respectively. Linearity was obtained in the range of 0.01-1000 μg L(-1) (R(2)>0.994). The obtained enrichment factors (EFs) were 233-276 for DEX and CLP respectively and limits of detection were 0.003 μg L(-1) with RSDs below 6%. The method proposed acceptable values to determine CLP and DEX in plasma samples sensitively and accurately.

Dextromethorphan As a Phenotyping Test to Predict Endoxifen Exposure in Patients on Tamoxifen Treatment

Purpose

Tamoxifen, a widely used agent for the prevention and treatment of breast cancer, is mainly metabolized by CYP2D6 and CYP3A to form its most abundant active metabolite, endoxifen. Interpatient variability in toxicity and efficacy of tamoxifen is substantial. Contradictory results on the value of CYP2D6 genotyping to reduce the variable efficacy have been reported. In this pharmacokinetic study, we investigated the value of dextromethorphan, a known probe drug for both CYP2D6 and CYP3A enzymatic activity, as a potential phenotyping probe for tamoxifen pharmacokinetics.

Methods

In this prospective study, 40 women using tamoxifen for invasive breast cancer received a single dose of dextromethorphan 2 hours after tamoxifen intake. Dextromethorphan, tamoxifen, and their respective metabolites were quantified. Exposure parameters of all compounds were estimated, log transformed, and subsequently correlated.

Results

A strong and highly significant correlation (r = −0.72; P < .001) was found between the exposures of dextromethorphan (0 to 6 hours) and endoxifen (0 to 24 hours). Also, the area under the plasma concentration–time curve of dextromethorphan (0 to 6 hours) and daily trough endoxifen concentration was strongly correlated (r = −0.70; P < .001). In a single patient using the potent CYP2D6 inhibitor paroxetine, the low endoxifen concentration was accurately predicted by dextromethorphan exposure.

Conclusion

Dextromethorphan exposure after a single administration adequately predicted endoxifen exposure in individual patients with breast cancer taking tamoxifen. This test could contribute to the personalization and optimization of tamoxifen treatment, but it needs additional validation and simplification before being applicable in future dosing strategies.