10th German Pharm-Tox Summit / 91. Jahrestagung der Deutschen Gesellschaft für Experimentelle und Klinische Pharmakologie und Toxikologie (DGPT)

Prof. Dr.

Chair

Dr. rer. nat.

Prof.

Feasibility and safety of supplementation of TAMoxifen with low-dose ENDOXifen in breast cancer patients with compromised CYP2D6-mediated tamoxifen bioactivation (TAMENDOX): a multi-center, placebo controlled, randomized trial

Pharmacogenomics and personalized medicine

AP06

BackgroundTamoxifen, used at a standard dose of 20 mg/day for the treatment of hormone receptor-positive breast cancer, undergoes cytochrome P450 2D6 (CYP2D6)-mediated bioactivation to its active metabolite (Z)-endoxifen, known to block estrogen-dependent tumor growth at about 100-times higher potency. We tested the feasibility and safety of supplementation of standard tamoxifen therapy with low-dose (Z)-endoxifen in breast cancer patients with compromised tamoxifen bioactivation.Patients and MethodsA prospective, multi-center, interventional, three group randomized trial included 235 hormone receptor-positive breast cancer patients receiving standard-of-care tamoxifen therapy (20mg/day) for at least 3 months. Patients with a compromised tamoxifen bioactivation stratified upfront either by CYP2D6 genetic testing (poor [PM], intermediate [IM] and normal metabolizers [NM]) or assessment of baseline (Z)-endoxifen plasma levels (≤15 nM, 15 to 25 nM and ≥25 nM) by UPLC-MS/MS were co-treated with (Z)-endoxifen (3 mg/day, 1.5 mg/day and placebo, respectively). Control patients received placebo irrespective of metabolizer phenotype. The primary endpoint was the number of patients with (Z)-endoxifen plasma levels >32 nM after 6 weeks treatment. Adverse events were monitored continuously.ResultsPatients" compliance was excellent in all groups (>96%). In both intervention groups significantly higher proportions of patients achieved the (Z)-endoxifen target concentrations >32 nM compared to controls (P < 0.0001). Specifically, 12 of 13 (92.3%) CYP2D6 PM patients and all patients with baseline (Z)-endoxifen ≤15 nM receiving 3 mg/day (Z)-endoxifen achieved the target concentration. Likewise, target endoxifen levels were reached in 22 of 25 (88%) CYP2D6 IM patients and 19 of 20 (95%) patients with baseline (Z)-endoxifen concentrations of 15 to 25 nM (1.5mg/day (Z)-endoxifen). Six out of 80 and eight out of 155 patients receiving (Z)-endoxifen and placebo, respectively, experienced Grade 3 adverse events. These adverse events were either disease related or well-known side effects of tamoxifen.ConclusionSupplementation of standard tamoxifen with low-dose (Z)-endoxifen up to 3 mg per day is feasible and safe, and offers a novel strategy for the individualization of tamoxifen treatment in patients with impaired tamoxifen bioactivation and insufficient endoxifen plasma concentrations.

Applied Pharmacology

Short talk

A pharmacokinetics, pharmacodynamics, and pharmacogenomics study of the diuretic drug hydrochlorothiazide in healthy volunteers

Diuretics are among the first-line drugs for the treatment of arterial hypertension and hydrochlorothiazide is one of the most frequently prescribed diuretics. However, large interindividual variation limits its safety and efficacy. A major contributing factor might be genetic polymorphism but the underlying mechanisms are still unclear. Here, a single-blinded, placebo-controlled study was conducted in which single doses of 25 mg and 100 mg hydrochlorothiazide were given to 103 healthy male volunteers. The AUC0-∞ varied 15-fold for the 25 mg and 7-fold for the 100 mg dose. Similarly large variation was observed for eight other pharmacokinetic and five pharmacodynamic parameters. Strong increases in the excretion of Na+, Cl- and, to a lesser extent, K+ were observed within the first 6 h, whereas urate excretion was modestly reduced during the 6-24 h interval. To identify single nucleotide polymorphisms as possible reasons for the interindividual differences, a series of genome-wide association studies were conducted on nine pharmacokinetic parameters, urine volume, and renal excretion of Na+, Cl-, K+, and urate. Altogether, 46 statistically significant (p < 5×10-8) associations were identified, among which an association between AUTS2 and the AUC0-∞ was observed. AUTS2 is linked to the netrin signalling pathway which has previously been suggested to influence the effects of hydrochlorothiazide. Other identified genes include, among others, MAML2/CNTN5, MAP2, and SLC19A1. Interestingly, associations with direct versus indirect effects of hydrochlorothiazide appeared differentially between the 25 mg and the 100 mg dose. No significant associations were found in or near the target gene SLC12A3 or other genes closely involved in the mechanisms of action of hydrochlorothiazide. Altogether, this study provides comprehensive pharmacokinetic and pharmacodynamic data that illustrates extensive interindividual variation, and newly identified several genes that might contribute to it.

Prof. Dr. med.

Tacrolimus Steady-State with Prolonged-Release or Immediate-Release Tacrolimus Preparations

Pharmacokinetics and PK/PD modelling

BR08

BackgroundTacrolimus, a commonly used immunosuppressant, is a narrow therapeutic index drug with a terminal half-life of 30-40 h. Individual dosing is guided by therapeutic drug monitoring (TDM) in clinical routine. In cases of newly started tacrolimus after solid organ transplantation (SOT) or significant deviations from the target range, concentrations are usually checked 2-3 days after a dose change, based on an effective half-life of 12-18 h [Schiff 2007]. Prolonged-release characteristics will not affect steady-state trough concentrations (unless associated with a change in systemic availability) but might affect the time course to steady-state, which has anecdotally been suspected by clinicians. Unpublished clinical observations report slower changes after tacrolimus dose adjustments when starting with the prolonged-release preparation Envarsus® (PR-Tac) shortly after SOT as compared to immediate-release preparations such as Prograf® (IR-Tac). It is unknown whether prolonged-release characteristics affect the time course to tacrolimus steady state.MethodsTacrolimus concentrations from 18 healthy volunteers were used (cross-over, single oral 5 mg doses, PR-Tac or IR-Tac, with or without St. John"s Wort (SJW) [Gümüs 2024]). Steady-state concentrations were predicted using the non-parametric superposition object in Phoenix WinNonlin 8.4, and the trough concentrations normalised as percentage of the individual steady-state. The effects of CYP3A4/P-gp induction and CYP3A5 genotype were analysed.ResultsOne, two, and three days after starting tacrolimus, approximately 50, 70, and 80 % of the steady-state were achieved, respectively (Figure 1). Tacrolimus preparation, SJW, and CYP3A5 genotype did not affect the time course to steady-state.ConclusionTacrolimus preparation, SJW, and CYP3A5 genotype had no effect on the time course to tacrolimus steady-state, which is consistent with minimal effects of these factors on the terminal half-life after single-dose tacrolimus. Thus, the timing of TDM can be similar for PR-Tac and IR-Tac. Slower changes after tacrolimus dose adjustments with PR-Tac after SOC, if present at all, would be explained by once-daily dosing (leading to a 24 h instead of a 12 h delay in administration of the first adjusted dose).Figure 1 Predicted relative steady-state trough concentrations with repeated tacrolimus administration using twice-daily IR-Tac or once-daily PR-Tac based on single-dose data in healthy volunteers.

Basic Research

Influence of sex and food intake on berberine (goldenseal) kinetics in healthy human volunteers

Berberine is an herbal nutritional supplement used OTC for the treatment of metabolic diseases. The kinetic properties are not well studied. We have recently excluded a significant role of hepatic OCT1 for human berberine kinetics (doi: 10.1002/cpt.3454). Based on preliminary data from this study, we now tested for possible effects of sex and food intake on berberine kinetics.To test the sex-dependency, 15 women received two single doses of 1000 mg berberine, one in the first and one in the second half of their menstrual cycle, and 15 men received a single dose of 1000 mg berberine. To test the food-dependency, 6 women and 6 men received a single dose of 1000 mg berberine, once in the fasting state, once after eating a light meal, and once after eating a high caloric meal ("FDA breakfast"). Blood and urine samples were collected and analyzed by LC-MS/MS to calculate standard kinetic parameters e.g., AUC0-24h, Cmax, Tmax, oral, and renal clearance.In the sex–effect study, the median AUC0-24h for women in their follicular phase was 333 min*ng/ml in correspondence to that of men with 332 min*ng/ml. In the luteal phase, the median was just slightly lower with 322 min*ng/ml. The only significant difference between the sexes was observed during the elimination phase, where the AUC10-24h was higher in women during the follicular phase compared to men. In the food-effect study, the median AUC0-24h in the fasting state was 112 min*ng/ml, 226 min*ng/ml after intake of the light meal, and 693 min*ng/ml after intake of the high caloric meal, the difference between that meal and the other conditions was statistically significant (p < 0.01, Friedman-Test with post-hoc Dunn correction). Whereas Cmax also differed considerably, Tmax was identical between the feeding conditions. When administered in the fasting condition, we typically observed two berberine plasma peaks, the second occurring in association with meal intake at noon. This phenomenon was not observed after eating the high caloric meal before berberine intake. Berberine administration was well tolerated in all volunteers.In conclusion, berberine kinetics is only slightly influenced by sex, but substantially by food intake. Berberine should be taken together with a high caloric, fat rich meal in order to achieve meaningful plasma concentrations, which is contradictory to its proposed use in metabolic diseases.

Papaverine induced ventricular fibrillation related to genetic variants of the cardiac sodium channel NaV1.5

Ion channels and membrane transporters

BR05

Background. Papaverine is a potent vasodilator inducing stable hyperemia and is used for fractional flow reserve (FFR) measurements requiring maximal hyperemia for the assessment of intermediate coronary artery stenosis. However, it can cause malignant ventricular tachyarrhythmia (VTA).Aim. To assess whether the occurrence of papaverine-induced VTA is associated with genetic variants in genes linked to cardiac arrhythmias.Methods and Results. In a cohort of 2,152 patients having FFR measurements with papaverine genetic testing was performed in 21/24 patients who exhibited papaverine induced ventricular arrythmias. In these patients whole-exome sequencing and bioinformatics analyses of pathogenic variants in genes linked to cardiac arrhythmias was performed followed by functional analyses of NaV1.5 sodium channel variants.We found four variants of uncertain significance (VUS) in the SCN5A gene encoding the cardiac sodium channel NaV1.5 in three patients. In the ClinVar database two of the variants were annotated as VUS for Brugada syndrome (BrS) and one as VUS for various cardiac conditions. For biophysical and pharmacological characterization functional studies using high-throughput patch-clamp electrophysiology of heterologously expressed NaV1.5 variants were performed. First results show that one variant exhibits (i) a significantly delayed recovery from inactivation in presence of papaverine and (ii) a depolarizing shift in activation, which was facilitated by papaverine. Therefore, in this single patient, the loss-of-function variant has contributed to the papaverine-induced VTA.Conclusion. In patients who exhibited papaverine induced ventricular arrythmias the frequency of rare genetic SCN5Avariants was higher than in the normal population. Our first data suggest that a subset of papaverine induced ventricular arrythmias are related to genetic variants of SCN5A encoding the cardiac sodium channel NaV1.5.Funding. Funded by a grant from the Interdisciplinary Center for Clinical Research of the Faculty of Medicine at the RWTH Aachen University (IZKF TN1-1/IA 532001, TN1-2/IA 532002 and TN1-5/IA 532005).

Hörsaal D

DGKlipha

Short talk 7

Short talks

Short talk 7
Pharmacogenomics and personalized medicine

Appointment

Chair

Programme

Short talk 7Pharmacogenomics and personalized medicine

Appointment

Chair

Programme

Short talk 7
Pharmacogenomics and personalized medicine