Troels K. Bergmann

The predictive value of KRAS, NRAS, BRAF, PIK3CA and PTEN for anti-EGFR treatment in metastatic colorectal cancer: A systematic review and meta-analysis

Abstract Background. In metastatic colorectal cancer, mutation testing for KRAS exon 2 is widely implemented to select patients with wild-type tumors for treatment with the monocloncal anti-EGFR antibodies cetuximab and panitumumab. The added predictive value of additional biomarkers in the RAS-RAF-MAPK and PI3K-AKT-mTOR pathways in colorectal cancer is uncertain, which led us to systematically review the impact of alterations in KRAS (outside of exon 2), NRAS, BRAF, PIK3CA and PTEN in relation to the clinical benefit from anti-EGFR treatment. Methods. In total, 22 studies that include 2395 patients formed the basis for a meta-analysis on alterations in KRAS exons 3 and 4, NRAS, BRAF, and PIK3CA and PTEN and outcome of anti-EGFR treatment. Odds ratios for objective response rate (ORR) and hazard ratios (HR) for progression-free survival (PFS) and overall survival (OS) were calculated. Results. Mutations in KRAS exons 3 and 4, BRAF, PIK3CA and non-functional PTEN (mutations or loss of protein expression) significantly predicted poor ORR (OR = 0.26, OR = 0.29, OR = 0.39, and OR = 0.41, respectively). Significantly shorter PFS applied to mutations in KRAS exons 3 and 4 (HR = 2.19), NRAS (HR = 2.30) and BRAF (HR = 2.95) and non-functional PTEN (HR = 1.88). Significantly shorter OS applied to mutations in KRAS exons 3 and 4 (HR = 1.78), NRAS (HR = 1.85), BRAF (HR = 2.52), PIK3CA (HR = 1.43) and alterations in PTEN (HR = 2.09). Conclusions. Meta-analysis suggests that mutations in KRAS exons 3 and 4, NRAS, BRAF and PIK3CA and non-functional PTEN predict resistance to anti-EGFR therapies and demonstrates that biomarker analysis beyond KRAS exon 2 should be implemented for prediction of clinical benefit from anti-EGFR antibodies in metastatic colorectal cancer.

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).

Linkage disequilibrium between the CYP2C19*17 allele and wildtype CYP2C8 and CYP2C9 alleles: identification of CYP2C haplotypes in healthy Nordic populations

PurposeTo determine the distribution of clinically important CYP2C genotypes and allele frequencies in healthy Nordic populations with special focus on linkage disequilibrium.MethodsA total of 896 healthy subjects from three Nordic populations (Danish, Faroese, and Norwegian) were genotyped for five frequent and clinically important CYP2C allelic variants: the defective CYP2C8*3, CYP2C9*2, CYP2C9*3, and CYP2C19*2 alleles, and the CYP2C19*17 allele that causes rapid drug metabolism. Linkage disequilibrium was evaluated and CYP2C haplotypes were inferred in the entire population.ResultsTen CYP2C haplotypes were inferred, the most frequent of which (49%) was the CYP2C wildtype haplotype carrying CYP2C8*1, CYP2C9*1, and CYP2C19*1. The second most frequent haplotype (19%) is composed of CYP2C19*17, CYP2C8*1, and CYP2C9*1. This predicted haplotype accounts for 99.7% of the CYP2C19*17 alleles found in the 896 subjects.ConclusionCYP2C19*17 is a frequent genetic variant in Nordic populations that exists in strong linkage disequilibrium with wildtype CYP2C8*1 and CYP2C9*1 alleles, which effectively makes it a determinant for a haplotype exhibiting an efficient CYP2C substrate metabolism.

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.

Clinical Pharmacokinetics and Pharmacodynamics of Prednisolone and Prednisone in Solid Organ Transplantation

Prednisolone and prednisone are integral components of induction and maintenance immunosuppressive regimens in solid organ transplantation. The pharmacokinetics of these agents are extremely complex. Prednisolone is the active drug moiety while prednisone is both a pro-drug and inactive metabolite of prednisolone. Within the dosage range used in transplantation, prednisolone and prednisone exhibit concentration-dependent non-linear pharmacokinetics when parameters are measured with reference to total drug concentration. Dose dependency disappears when free (unbound) prednisolone is measured. Altered organ function, changing biochemistry and use of a number of concomitant medicines in transplantation appear to lead to pharmacokinetic differences in transplant recipients compared with other patient groups. Greater than threefold variability in dose-adjusted exposure to total prednisolone in transplant recipients is evident. Time post-transplant, hepatic and renal dysfunction, patient age, sex, bodyweight, serum albumin concentration, concomitant medication exposure, various disease states and genetic polymorphisms in metabolic enzymes and drug transporters have sometimes been associated with prednisolone pharmacokinetic variability. The clinical impact of corticosteroid therapy on the disposition of ciclosporin, tacrolimus and sirolimus and the impact of different immunosuppressant therapy combinations on prednisolone exposure needs to be further elucidated. Patient response patterns to prednisolone are consistent with delayed and indirect mechanisms of corticosteroid action involving modification of nuclear transcription and protein synthesis. Many adverse effects have been linked with prednisolone and prednisone therapy, but not all of these have been investigated thoroughly in transplant populations. Dyslipidaemia, growth restriction, diabetogenesis, hypertension and cataracts are well studied toxicities. Evidence is less clear for prednisolone-induced osteonecrosis, obesity and hypertriglyceridaemia. There have been some reports of a relationship between prednisolone pharmacokinetics and incidence of acute rejection, Cushing’s syndrome and adverse cardiovascular and metabolic events. Dosing of prednisolone and prednisone in transplantation is typically empirical and varies significantly across transplant centres. Currently, authoritative guidelines are conflicting in their opinions regarding corticosteroid avoidance and early discontinuation in adult kidney transplantation. Overall, data suggest the promise of corticosteroid-free immunosuppression in paediatric patients. Further investigation of the pharmacokinetics and pharmacodynamics of prednisolone and prednisone in transplant recipients based on new chromatography assay techniques and free drug measurement, population pharmacokinetic/pharmacodynamic modelling approaches, genetic testing and larger studies in patients on modern day immunosuppressant protocols may lead to better individualization of corticosteroid therapy in the future.

NR1I2 polymorphisms are related to tacrolimus dose-adjusted exposure and BK viremia in adult kidney transplantation

Background Pregnane X, encoded by the gene NR112, is a nuclear receptor whose primary role is to promote the detoxification and clearance of drugs and other foreign compounds from the body. Aim The aim of this study was to analyze associations between NR1I2 polymorphisms, immunosuppressant drug exposure, and clinical outcomes in adult kidney transplant recipients. Methods Exposures to tacrolimus, mycophenolic acid, and total and free prednisolone were estimated at month 1 posttransplant using validated multiple regression-derived limited sampling strategies. Results In the 158 subjects studied, median (interquartile range) dose-adjusted exposure to tacrolimus was significantly higher in individuals carrying the NR1I2 8055T variant allele, when compared with exposure in wild-type individuals [20 (14, 22) &mgr;g·h/L/mg versus 15 (9, 24) &mgr;g·h/L/mg; P =0.0007]. Using multivariable logistic regression, NR1I2 8055T carrier status was independently predictive of higher dose-adjusted tacrolimus exposure (P=0.0005). Moreover, BK viremia was seen significantly more frequently in NR1I2 8055T allele carriers compared with wild-type individuals (38% vs 18%, P=0.005) and possession of the NR1I2 8055T allele imposed significantly higher odds of BK viremia (adjusted odds ratio, 2.76 [95% confidence interval, 1.33–7.73]; P=0.006). No significant difference in geometric mean peak BK viral replication titer was observed between 8055T carriers and noncarriers. No NR1I2 SNP or haplotype was significantly, independently associated with total or free prednisolone or MPA exposure. Conclusions These data demonstrate an impact of pregnane X receptor polymorphisms on tacrolimus pharmacokinetics. Association of the 8055T allele with BK viremia suggests clinically significant “overimmunosuppression” in individuals with this genotype.

Improved prediction of tacrolimus concentrations early after kidney transplantation using theory-based pharmacokinetic modelling

Aims The aim was to develop a theory-based population pharmacokinetic model of tacrolimus in adult kidney transplant recipients and to externally evaluate this model and two previous empirical models. Methods Data were obtained from 242 patients with 3100 tacrolimus whole blood concentrations. External evaluation was performed by examining model predictive performance using Bayesian forecasting. Results Pharmacokinetic disposition parameters were estimated based on tacrolimus plasma concentrations, predicted from whole blood concentrations, haematocrit and literature values for tacrolimus binding to red blood cells. Disposition parameters were allometrically scaled to fat free mass. Tacrolimus whole blood clearance/bioavailability standardized to haematocrit of 45% and fat free mass of 60 kg was estimated to be 16.1 l h−1 [95% CI 12.6, 18.0 l h−1]. Tacrolimus clearance was 30% higher (95% CI 13, 46%) and bioavailability 18% lower (95% CI 2, 29%) in CYP3A5 expressers compared with non-expressers. An Emax model described decreasing tacrolimus bioavailability with increasing prednisolone dose. The theory-based model was superior to the empirical models during external evaluation displaying a median prediction error of −1.2% (95% CI −3.0, 0.1%). Based on simulation, Bayesian forecasting led to 65% (95% CI 62, 68%) of patients achieving a tacrolimus average steady-state concentration within a suggested acceptable range. Conclusion A theory-based population pharmacokinetic model was superior to two empirical models for prediction of tacrolimus concentrations and seemed suitable for Bayesian prediction of tacrolimus doses early after kidney transplantation.

Population Pharmacokinetics of Tacrolimus in Adult Kidney Transplant Patients: Impact of CYP3A5 Genotype on Starting Dose.

Objectives: The aims of this study were to develop a population pharmacokinetic model of tacrolimus in adult kidney transplant recipients, to use this model to compare cytochrome P450 3A5 (CYP3A5) genotype–based initial dosing of tacrolimus with standard per-kilogram–based dosing, and to predict the best starting dose of tacrolimus based on patient genotype to achieve a trough concentration between 6 and 10 µg/L by day 5 posttransplantation. Methods: Population analysis was performed using the software program NONMEM. Tacrolimus dosing regimens were compared by predicting tacrolimus trough concentrations in a simulated data set by running NONMEM with population parameters fixed at the final model estimates. Data from 173 patients with 1554 tacrolimus concentration–time measurements were modeled. Results: Tacrolimus disposition was well described by a 2-compartment model with first-order elimination and first-order absorption after a lag time. Patient CYP3A5 genotype (rs776746), weight, hematocrit, and postoperative day were identified as significant covariates effecting tacrolimus apparent oral clearance (CL/F), with higher CL/F in CYP3A5*1 allele carriers, heavier patients, patients with low hematocrit, and in the immediate posttransplantation period. Typical population estimates for tacrolimus CL/F in CYP3A5*1 allele carriers and noncarriers were 40.8 and 25.5 L/h, respectively. Conclusions: In patients carrying the CYP3A5*1 allele, a per-kilogram dose of 0.075 mg/kg twice daily seemed too much low with approximately 65% of simulated subjects predicted to achieve a trough below 6 µg/L at day 5 posttransplantation. To reduce the risk of under immunosuppression in the immediate posttransplantation period, carriers of a CYP3A5*1 allele are likely to benefit from a tacrolimus starting dose of either 10 mg or 0.115 mg/kg twice daily.

Impact of ABCB1 Variants on Neutrophil Depression: A Pharmacogenomic Study of Paclitaxel in 92 Women with Ovarian Cancer

The standard treatment for ovarian cancer in advanced stages is post-surgery treatment with taxane-platin chemotherapy. Despite an initial high response rate, most patients eventually relapse. The dose-limiting toxicities of paclitaxel are neutropenia and neuropathy, but the inter-individual variability is large. The aim of this prospective study was to investigate the impact of genetic variants in key drug metabolizing/transporter genes on toxicity and compliance. CYP2C8*3 and three ABCB1 polymorphisms were chosen for primary analysis, and a host of other candidate genes was explored in 92 prospectively recruited Scandinavian Caucasian women with primary ovarian cancer who were treated with paclitaxel and carboplatin. A single investigator assessed the clinical toxicity in 97% of the patients. Patients carrying variant alleles of ABCB1 C3435T experienced more pronounced neutrophil decrease (63%, 72% and 80% for 3435CC, CT and TT, respectively; p-value 0.03). A similar association was found for G2677T/A, p-value 0.02. For C1236T, there was a trend with p-value 0.06. No statistically significant correlations were found for paclitaxel compliance and sensory neuropathy in the primary analysis. Variants in the drug transporter ABCB1 gene are possibly associated with the neutrophil suppressing effect of paclitaxel in patients with ovarian cancer. This finding has implications for the understanding of bone marrow suppression and future tailored chemotherapy.

GWAS-based association between RWDD3 and TECTA variants and paclitaxel induced neuropathy could not be confirmed in Scandinavian ovarian cancer patients

GWAS-based association between RWDD3 and TECTA variants and paclitaxel induced neuropathy could not be confirmed in Scandinavian ovarian cancer patients