Per Damkier

Adenocarcinoma of the Esophagus and Barrett's Esophagus: A Population-Based Study

Objective: We described incidence rates of esophageal adenocarcinoma in Denmark in a 20-yr period and determined the proportion of patients diagnosed with esophageal adenocarcinoma who had a previous diagnosis of Barretts esophagus, making them potential candidates for endoscopic surveillance. Methods: Rates of esophageal and gastric cancers were collected from the Danish Cancer registry for the period 1970–1991. The registry was used to identify all cases of esophageal adenocarcinoma in the period 1987–1992. Medical records were retrieved and details concerning previous diagnosis of reflux disease and Barretts esophagus were recorded. Results: The age- and gender-adjusted incidence of esophageal adenocarcinoma increased eightfold, from 0.3/105/yr in 1970 to 2.3/105/yr in 1990. This increase could not be explained by changes in classification or diagnostic routines. Medical data were retrieved for 524 of the 578 cases of esophageal adenocarcinoma reported during the period 1987–1992. A history of reflux symptoms or a diagnosis compatible with reflux was reported in 113 of 524 patients. A total of 119 patients (23%) had previously been investigated for dyspepsia or reflux symptoms, most often by endoscopy. A previous diagnosis of Barretts esophagus was found in only 1.3% of the cancer patients. Conclusions: The rate of esophageal adenocarcinoma in Denmark has increased eightfold over a 20-yr period, and this increase is not explained by changes in classification or diagnostic routines. More than 98% of esophageal adenocarcinomas were found in patients who could not have entered endoscopic surveillance, as Barretts esophagus had not been diagnosed before the cancer diagnosis. Endoscopic surveillance to detect dysplasia may be an option for the individual patient with Barretts esophagus, but these screening programs are not likely to reduce the death rate from esophageal adenocarcinomas in the general population.

The pharmacogenetics of metformin and its impact on plasma metformin steady-state levels and glycosylated hemoglobin A1c

OBJECTIVE The aim of this study was to evaluate the effect of genetic variations in OCT1, OCT2, MATE1, MATE 2, and PMAT on the trough steady-state plasma concentration of metformin and hemoglobin A1c (Hb1Ac). METHOD The South Danish Diabetes Study was a 2 x 2 x 2 factorial, prospective, randomized, double-blind, placebo-controlled, multicentre study. One hundred and fifty-nine patients received 1 g of metformin, twice daily continuously, and 415 repeated plasma metformin measurements were obtained after 3, 6, and 9 months of treatment. RESULTS The mean trough steady-state metformin plasma concentration was estimated to be 576 ng/ml (range, 54–4133 ng/ml, p = 0.55) and correlated to the number of reduced function alleles in OCT1 (none, one or two: 642, 542, 397 ng/ml; P = 0.001). The absolute decrease in Hb1Ac both initially and long term was also correlated to the number of reduced function alleles in OCT1 resulting in diminished pharmacodynamic effect of metformin after 6 and 24 months. CONCLUSION In a large cohort of type 2 diabetics, we either confirm or show for the first time: (a) an enormous (80-fold) variability in trough steady-state metformin plasma concentration, (b) OCT1 activity affects metformin steady-state pharmacokinetics, and (c) OCT1 genotype has a bearing on HbA1c during metformin treatment.

Optimizing clozapine treatment

Nielsen J, Damkier P, Lublin H, Taylor D. Optimizing clozapine treatment.

Impact of CYP2C8*3 on paclitaxel clearance: a population pharmacokinetic and pharmacogenomic study in 93 patients with ovarian cancer

The primary purpose of this study was to evaluate the effect of CYP2C8*3 and three genetic ABCB1 variants on the elimination of paclitaxel. We studied 93 Caucasian women with ovarian cancer treated with paclitaxel and carboplatin. Using sparse sampling and nonlinear mixed effects modeling, the individual clearance of unbound paclitaxel was estimated from total plasma paclitaxel and Cremophor EL. The geometric mean of clearance was 385 l h–1 (range 176–726 l h–1). Carriers of CYP2C8*3 had 11% lower clearance than non-carriers, P=0.03. This has not been shown before in similar studies; the explanation is probably the advantage of using both unbound paclitaxel clearance and a population of patients of same gender. No significant association was found for the ABCB1 variants C1236T, G2677T/A and C3435T. Secondarily, other candidate single-nucleotide polymorphisms were explored with possible associations found for CYP2C8*4 (P=0.04) and ABCC1 g.7356253C>G (P=0.04).

Statins and breast cancer prognosis: evidence and opportunities

Much preclinical and epidemiological evidence supports the anticancer effects of statins. Epidemiological evidence does not suggest an association between statin use and reduced incidence of breast cancer, but does support a protective effect of statins--especially simvastatin--on breast cancer recurrence. Here, we argue that the existing evidence base is sufficient to justify a clinical trial of breast cancer adjuvant therapy with statins and we advocate for such a trial to be initiated without delay. If a protective effect of statins on breast cancer recurrence is supported by trial evidence, then the indications for a safe, well tolerated, and inexpensive treatment can be expanded to improve outcomes for breast cancer survivors. We discuss several trial design opportunities--including candidate predictive biomarkers of statin safety and efficacy--and offer solutions to the key challenges involved in the enrolment, follow-up, and analysis of such a trial.

Tramadol as a New Probe for Cytochrome P450 2D6 Phenotyping: A Population Study

Polymorphic cytochrome P450 (CYP) 2D6 activity has been shown to be a determinant of the pharmacokinetics and pharmacodynamics of tramadol via hepatic phase I O‐demethylation of (+)‐tramadol to (+)‐O‐desmethyltramadol. Our objective was to investigate whether tramadol can be used as a probe for CYP2D6 phenotyping by determining the concordance between the 8‐hour tramadol and 12‐hour sparteine metabolic urinary ratios.

Polymorphism of CYP2D6, CYP2C19, CYP2C9 and CYP2C8 in the Faroese population

ObjectiveThe purpose of the study was to study the distribution of poor and extensive metabolizers of CYP2C19 and CYP2D6 and to genotype for CYP2C8 and CYP2C9 among 312 randomly selected Faroese.Methods and resultsThe participants were phenotyped for CYP2D6 with the use of sparteine. The distribution of the sparteine metabolic ratio (sparteine/didehydrosparteines) was bimodal, and 14.5% (n=44; 95% CI: 10.7–18.9%) of the subjects were phenotyped as poor metabolizers. The frequency of poor metabolizers was higher (P=0.0002; χ2 test) among the Faroese than in other European populations (7.4%). Genotype analyses for the CYP2D6*3, *4, *6 and *9 alleles were performed using real-time polymerase chain reaction (PCR) (TaqMan, Foster City, CA, USA), and we found 14.6% (n = 45) (95% CI: 10.8–19.0%) with deficient CYP2D6 genes (*3/*4, *4/*4, *4/*6, *6/*6) in the Faroese population. The subjects were phenotyped for CYP2C19 with the use of mephenytoin and 10 subjects, i.e., 3.2% (95% CI: 1.6–5.9%) were phenotyped as poor metabolizers. Genotype analysis for the CYP2C19*2 and *3 alleles was performed by means of PCR analysis, and 2.9% (n=9) (95% CI: 1.3–5.4%) of the Faroese were found to have a deficient CYP2C19 gene all explained by the CYP2C19*2/*2 genotype. The allele frequencies of the CYP2C9*2 and CYP2C9*3 alleles were 8.8% (95% CI: 6.7–11.4%) and 5.3% (95% CI: 3.7–7.4%), respectively, while the CYP2C8*3 allele frequency was 6.9% (95% CI: 5.0–9.2%). Real-time PCR (TaqMan) was used for both CYP2C9 and CYP2C8 genotype analyses.ConclusionThe frequency of CYP2D6 poor metabolizers is twofold higher among the Faroese population than other Caucasians, while the frequencies of Faroese subjects with decreased CYP2C19, CYP2C8 and CYP2C9 enzyme activity are the same as seen in other Caucasian populations. A possible consequence might be a higher incidence of side effects among Faroese patients taking pharmaceuticals that are CYP2D6 substrates.

Retrospective study of the impact of pharmacogenetic variants on paclitaxel toxicity and survival in patients with ovarian cancer

PurposePaclitaxel has a broad spectrum of anti-tumor activity and is useful in the treatment of ovarian, breast, and lung cancer. Paclitaxel is metabolized in the liver by CYP2C8 and CYP3A4 and transported by P-glycoprotein. The dose-limiting toxicities are neuropathy and neutropenia, but the interindividual variability in toxicity and also survival is large. The main purpose of this study was to investigate the impact of genetic variants in CYP2C8 and ABCB1 on toxicity and survival.MethodsThe 182 patients previously treated for ovarian cancer with carboplatin and paclitaxel in either the AGO-OVAR-9 or the NSGO-OC9804 trial in Denmark or Sweden were eligible for this study. Genotyping was carried out on formalin-fixed tissue. The patients’ toxicity profiles and survival data were derived from retrospective data. CYP2C8*3, ABCB1 C1236T, G2677T/A, and C3435T were chosen a priori for primary analysis; a host of other variants were entered into an exploratory analysis.ResultsClinical data and tissue were available from a total of 119 patients. Twenty-two single nucleotide polymorphisms (SNPs) in 10 genes were determined. Toxicity registration was available from 710 treatment cycles. In the primary analysis, no statistically significant correlation was found between CYP2C8*3, ABCB1 C1236T, G2677T/A, and C3435T and neutropenia, sensoric neuropathy, and overall survival.ConclusionCYP2C8*3 and the ABCB1 SNPs C1236T, G2677T/A, and C3435T were not statistically significantly correlated to overall survival, sensoric neuropathy, and neutropenia in 119 patients treated for ovarian cancer with paclitaxel/carboplatin.

A Comparative Pharmacokinetic Study in Healthy Volunteers of the Effect of Carbamazepine and Oxcarbazepine on Cyp3a4

Summary:  Purpose: Carbamazepine (CBZ) and oxcarbazepine (OXCZ) are well‐known inducers of drug metabolism via CYP3A4. Indirect interaction studies and clinical experience suggest that CBZ has a stronger potential in this regard than OXCZ. However this has never been subject to a direct comparative study. We performed a study in healthy volunteers to investigate the relative inductive effect of CBZ and OXCZ on CYP3A4 activity using the metabolism of quinidine as a biomarker reaction.

Metabolism and transport of tamoxifen in relation to its effectiveness: new perspectives on an ongoing controversy

Tamoxifen reduces the rate of breast cancer recurrence by approximately a half. Tamoxifen is metabolized to more active metabolites by enzymes encoded by polymorphic genes, including cytochrome P450 2D6 (CYP2D6). Tamoxifen is a substrate for ATP-binding cassette transporter proteins. We review tamoxifens clinical pharmacology and use meta-analyses to evaluate the clinical epidemiology studies conducted to date on the association between CYP2D6 inhibition and tamoxifen effectiveness. Our findings indicate that the effect of both drug-induced and/or gene-induced inhibition of CYP2D6 activity is likely to be null or small, or at most moderate in subjects carrying two reduced function alleles. Future research should examine the effect of polymorphisms in genes encoding enzymes in tamoxifens complete metabolic pathway, should comprehensively evaluate other biomarkers that affect tamoxifen effectiveness, such as the transport enzymes, and focus on subgroups of patients, such as premenopausal breast cancer patients, for whom tamoxifen is the only guideline endocrine therapy.