Tamoxifen pharmacokinetics and pharmacodynamics in older patients with non-metastatic breast cancer

BACKGROUND

We aimed to study the pharmacokinetics and -dynamics of tamoxifen in older women with non-metastatic breast cancer.

METHODS

Data for this analysis were derived from the CYPTAM study (NTR1509) database. Patients were stratified by age (age groups < 65 and 65 and older). Steady-state trough concentrations were measured of tamoxifen, N-desmethyltamoxifen, 4-hydroxy-tamoxifen, and endoxifen. CYP2D6 and CYP3A4 phenotypes were assessed for all patients by genotyping. Multiple linear regression models were used to analyze tamoxifen and endoxifen variability. Outcome data included recurrence-free survival at time of tamoxifen discontinuation (RFSt) and overall survival (OS).

RESULTS

668 patients were included, 141 (21%) were 65 and older. Demographics and treatment duration were similar across age groups. Older patients had significantly higher concentrations of tamoxifen 129.4 ng/ml (SD 53.7) versus 112.2 ng/ml (SD 42.0) and endoxifen 12.1 ng/ml (SD 6.6) versus 10.7 ng/ml (SD 5.7, p all < 0.05), independently of CYP2D6 and CYP3A4 gene polymorphisms. Age independently explained 5% of the variability of tamoxifen (b = 0.95, p < 0.001, R² = 0.051) and 0.1% of the variability in endoxifen concentrations (b = 0.45, p = 0.12, R² = 0.007). Older patients had worse RFSt (5.8 versus 7.3 years, p = 0.01) and worse OS (7.8 years versus 8.7 years, p = 0.01). This was not related to differences in endoxifen concentration (HR 1.0, 95% CI 0.96-1.04, p = 0.84) or CYP polymorphisms.

CONCLUSION

Serum concentrations of tamoxifen and its demethylated metabolites are higher in older patients, independent of CYP2D6 or CYP3A4 gene polymorphisms. A higher bioavailability of tamoxifen in older patients may explain the observed differences. However, clinical relevance of these findings is limited and should not lead to a different tamoxifen dose in older patients.

Real-World Metastatic Renal Cell Carcinoma Treatment Patterns and Clinical Outcomes in The Netherlands

The number of treatment options for patients with metastatic renal cell carcinoma (mRCC) has significantly grown in the last 15 years. Although randomized controlled trials are fundamental in investigating mRCC treatment efficacy, their external validity can be limited. Therefore, the efficacy of the different treatment options should also be evaluated in clinical practice. We performed a chart review of electronic health records using text mining software to study the current treatment patterns and outcomes. mRCC patients from two large hospitals in the Netherlands, starting treatment between January 2015 and May 2020, were included. Data were collected from electronic health records using a validated text mining tool. Primary endpoints were progression-free survival (PFS) and overall survival (OS). Statistical analyses were performed using the Kaplan-Meier method. Most frequent first-line treatments were pazopanib (n = 70), sunitinib (n = 34), and nivolumab with ipilimumab (n = 28). The overall median PFS values for first-line treatment were 15.7 months (95% confidence interval [95%CI], 8.8-20.7), 16.3 months (95%CI, 9.3-not estimable [NE]) for pazopanib, and 6.9 months (95% CI, 4.4-NE) for sunitinib. The overall median OS values were 33.4 months (95%CI, 28.1-50.9 months), 39.3 months (95%CI, 29.5-NE) for pazopanib, and 28.1 months (95%CI, 7.0-NE) for sunitinib. For nivolumab with ipilimumab, median PFS and median OS were not reached. Of the patients who finished first- and second-line treatments, 64 and 62% received follow-up treatments, respectively. With most patients starting on pazopanib and sunitinib, these real-world treatment outcomes were most likely better than in pivotal trials, which may be due to extensive follow-up treatments.

3D printed furosemide and sildenafil tablets: Innovative production and quality control

Three-dimensional (3D) printing of pharmaceuticals has the potential to revolutionise personalised medicine but is as yet largely unexplored. A proof-of-concept study of a novel heated, piston-driven semi-solid extrusion 3D printer was performed by producing furosemide and sildenafil tablets for paediatric patients. The average weight of the tablets was 141.1 mg (RSD 1.26%). The acceptance values of the content uniformity were 4.2-10.6 (concentration RSD 0.41-0.63%), 4.8-8.9 (concentration RSD 0.76-0.97%) and 6.6-9.2 (concentration RSD 0.94-1.44%) for furosemide 2 mg, 10 mg and sildenafil 4 mg, respectively. The dissolution rate limiting step was the dissolving and eroding of the tablet matrix and showed an immediate release. The tablets complied to the requirements of the European Pharmacopoeia (EP) for uniformity of mass (EP 2.9.5), content uniformity (EP 2.9.40) and conventional release (EP 2.9.3). While they complied, not all of these quality tests for tablets might be suitable for 3D printed tablets due to the layering of the tablets and the small batch production. To assess adequate layer adhesion adjusted friability (EP 2.9.7) and resistance to crushing (EP 2.9.8) tests are proposed.

Effect of CYP2C19 genotypes on tamoxifen metabolism and early-breast cancer relapse

CYP2C19*2 and CYP2C19*17 might influence tamoxifen metabolism and clinical outcome. Our aim was to investigate the effect of CYP2C19 genotypes on tamoxifen concentrations and metabolic ratios (MRs) and breast cancer recurrence in a large cohort of Caucasian women. Genetic variants (CYP2D6 and CYP2C19 genotypes), tamoxifen and metabolites concentrations, baseline characteristics, and breast cancer recurrence from the CYPTAM study (NTR1509) were used. CYP2C19*2 and CYP2C19*17 genotypes were evaluated as alleles and as groups based on CYP2D6 genotypes (high, intermediate and low activity). Log-rank test and Kaplan–Meier analysis were used to evaluate differences in recurrence defined as relapse-free survival (RFS). Classification tree analyses (CTAs) were conducted to assess the levels of interactions per polymorphism (CYP2D6 and CYP2C19 genotypes) on endoxifen concentrations. No differences in mean concentrations and MRs were observed when comparing CYP2C19 genotypes (CYP2C19*1/*1; CYP2C19*1/*2; CYP2C19*2/*2; CYP2C19*1/*17; CYP2C19*17/*17; CYP2C19*2/*17). Only significant differences (p value < 0.05) in mean concentrations and MRs were observed when comparing tamoxifen activity groups (high, intermediate and low activity). A log-rank test did not find an association across CYP2C19 genotypes (p value 0.898). CTAs showed a significant relationship between CYP2D6 and endoxifen (p value < 0.0001), but no association with CYP2C19 genotypes was found. CYP2C19 polymorphisms do not have a significant impact on tamoxifen metabolism or breast cancer relapse.

Identification of pharmacogenetic biomarkers for efficacy of cytoreductive surgery plus hyperthermic intraperitoneal mitomycin C in patients with colorectal peritoneal metastases

INTRODUCTION

Mitomycin C (MMC) is commonly used in patients with colorectal peritoneal metastases (CPM) treated with cytoreductive surgery plus hyperthermic intraperitoneal chemotherapy (CRS + HIPEC). MMC requires metabolic activation prior to exert its cytotoxic effect of which the main activating enzymes are NQO1 and POR. However, not all patients are able to activate MMC for example due to polymorphisms in the genes encoding these enzymes. The aim of this study was to investigate the association of NQO1∗2, NQO1∗3, and POR∗28 with the efficacy of CRS + HIPEC with MMC in patients with CPM.

METHOD

A retrospective follow-up design was used to study genetic association in patients with histologically proven CPM treated with CRS + HIPEC with MMC with respect to peritoneal recurrence rate after 3 months (primary endpoint), after 6 months, disease-free survival and overall survival. Genetic polymorphisms NQO1∗2, NQO1∗3, and POR∗28 were tested for association.

RESULTS

A total of 253 patients were included. In NQO1∗3 carriers the peritoneal recurrence rate 3 and 6 months after HIPEC was significantly higher than in wild type patients, respectively 30.0% vs 3.8% (p = 0.009) and 40.0% vs 12.1% (p = 0.031). In line with these results, NQO1∗3 was associated with a shorter disease-free survival (HR 2.04, 95% CI [1.03-4.03]). There was no significant association with overall survival (HR 1.42, 95% CI [0.66-3.07]).

CONCLUSION

Carriership of the NQO1∗3 allele is associated with worse peritoneal recurrence rate and disease-free survival. These results suggest that individualization of patients treated with CRS + HIPEC based upon pharmacogenetics may be beneficial.

Population pharmacokinetics of treosulfan in paediatric patients undergoing hematopoietic stem cell transplantation

Aims

Treosulfan is an alkylating agent increasingly used prior to haematopoietic stem cell transplantation. The aim of this study was to develop a population pharmacokinetic (PK) model of treosulfan in paediatric haematopoietic stem cell transplantation recipients and to explore the effect of potential covariates on treosulfan PK. Also, a limited sampling model (LSM) will be developed to accurately predict treosulfan exposure suitable for a therapeutic drug monitoring setting.

Methods

In this multicentre study, 91 patients, receiving a total dose of 30, 36 or 42 g/m² treosulfan, administered over 3 consecutive days, were enrolled. A population PK model was developed and demographic factors, as well as laboratory parameters, were included as potential covariates. In addition, a LSM was developed using data from 28 patients.

Results

A 2‐compartment model with first order elimination best described the data. Bodyweight with allometric scaling and maturation function were identified as significant predictors of treosulfan clearance. Treosulfan clearance reaches 90% of adult values at 4 postnatal years. A model‐based dosing table is presented to target an exposure of 1650 mg*h/L (population median) for different weight and age groups. Samples taken at 1.5, 4 and 7 hours after start of infusion resulted in the best limited sampling strategy.

Conclusions

This study provides a treosulfan population PK model in children and captures the developmental changes in clearance. A 3‐point LSM allows for accurate and precise estimation of treosulfan exposure.

Pharmacokinetics and safety of panitumumab in a patient with chronic kidney disease

Purpose

Data on panitumumab dosing in cancer patients with renal insufficiency are lacking. Here, we report a 63-year-old metastatic colorectal cancer patient with chronic kidney injury with a glomerular filtration rate of approximately 11 mL/min.

Methods

Pharmacokinetic parameters, including dose-normalized area under the curve, clearance and elimination half-life (T_1/2) after the 11th and 12th infusions were estimated using trapezoidal non-compartmental methods. Data were compared to previous reported pharmacokinetic data from studies in patients with normal renal function.

Results

The results show that the pharmacokinetic data in this patient with kidney failure are comparable to those in patients with adequate renal function. Moreover the treatment was well tolerated in this patient.

Conclusion

This study suggests that panitumumab can be safely used in cancer patients with renal impairment without dose adjustment.

Effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on tamoxifen metabolism

Background

Tamoxifen is one of the cornerstones of endocrine therapy for breast cancer. Recently, the decreased activity CYP3A4*22 allele and the loss of function CYP3A5*3 allele have been described as potential factors that could help to explain the inter-patient variability in tamoxifen metabolism. The aim of this study is to investigate the effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on tamoxifen metabolism.

Methods

DNA from 667 women enrolled in the CYPTAM study (NTR1509) was genotyped (CYP2D6, CYP3A4*22, and CYP3A5*3). Tamoxifen and metabolite concentrations were measured in serum, and metabolic ratios were calculated. The effect of the CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes in addition to the CYP2D6 genotypes was examined by multiple linear regression analysis.

Results

CYP3A4*22 carriers reached significant higher concentrations of tamoxifen, N-desmethyl-tamoxifen, and 4-hydroxy-tamoxifen compared to non-carriers, whereas a tendency toward increased endoxifen levels was observed (p = 0.088). The metabolic ratio tamoxifen/N-desmethyl-tamoxifen was significantly higher in CYP3A4*22 individuals (0.59 vs. 0.52, p < 0.001). At the same time, CYP3A4*22 genotype contributed to improving the inter-variability [R² of the (log-transformed) metabolic ratio tamoxifen/N-desmethyl-tamoxifen improved from 21.8 to 23.9%, p < 0.001]. CYP3A5*3 marginally improved the explained variability of the (log transformed) metabolic ratio 4-hydroxy-tamoxifen/endoxifen (from 44.9 to 46.2%, p < 0.038).

Conclusion

Our data demonstrate that CYP3A genotype has a minor effect to explaining the variability between patients in tamoxifen metabolism and has no added value in addition to CYP2D6 genotype.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2323-2) contains supplementary material, which is available to authorized users.

Population Modeling Integrating Pharmacokinetics, Pharmacodynamics, Pharmacogenetics, and Clinical Outcome in Patients With Sunitinib-Treated Cancer

The tyrosine kinase inhibitor sunitinib is used as first‐line therapy in patients with metastasized renal cell carcinoma (mRCC), given in fixed‐dose regimens despite its high variability in pharmacokinetics (PKs). Interindividual variability of drug exposure may be responsible for differences in response. Therefore, dosing strategies based on pharmacokinetic/pharmacodynamic (PK/PD) models may be useful to optimize treatment. Plasma concentrations of sunitinib, its active metabolite SU12662, and the soluble vascular endothelial growth factor receptors sVEGFR‐2 and sVEGFR‐3, were measured in 26 patients with mRCC within the EuroTARGET project and 21 patients with metastasized colorectal cancer (mCRC) from the C‐II‐005 study. Based on these observations, PK/PD models with potential influence of genetic predictors were developed and linked to time‐to‐event (TTE) models. Baseline sVEGFR‐2 levels were associated with clinical outcome in patients with mRCC, whereas active drug PKs seemed to be more predictive in patients with mCRC. The models provide the basis of PK/PD‐guided strategies for the individualization of anti‐angiogenic therapies.

Everolimus pharmacokinetics and its exposure-toxicity relationship in patients with thyroid cancer

Background

Everolimus is a mTOR inhibitor used for the treatment of different solid malignancies. Many patients treated with the registered fixed 10 mg dose once daily are in need of dose interruptions, reductions or treatment discontinuation due to severe adverse events. This study determined the correlation between systemic everolimus exposure and toxicity. Additionally, the effect of different covariates on everolimus pharmacokinetics (PK) was explored.

Methods

Forty-two patients with advanced thyroid carcinoma were treated with 10 mg everolimus once daily. Serial pharmacokinetic sampling was performed on days 1 and 15. Subsequently, a population PK model was developed using NONMEM to estimate individual PK values used for analysis of an exposure–toxicity relationship. Furthermore, this model was used to investigate the influence of patient characteristics and genetic polymorphisms in genes coding for enzymes relevant in everolimus PK.

Results

Patients who required a dose reduction (n = 18) due to toxicity at any time during treatment had significant higher everolimus exposures [mean AUC_0–24 (SD) 600 (274) vs. 395 (129) µg h/L, P = 0.008] than patients without a dose reduction (n = 22). A significant association between everolimus exposure and stomatitis was found in the four-level ordered logistic regression analysis (P = 0.047). The presence of at least one TTT haplotype in the ABCB1 gene was associated with a 21 % decrease in everolimus exposure.

Conclusion

The current study showed that dose reductions and everolimus-induced stomatitis were strongly associated with systemic everolimus drug exposure in patients with cancer. Our findings confirm observations from another study in patients with cancer and show us that everolimus is a good candidate for individualized dosing in patients with cancer.

ClinicalTrial.gov number

NCT01118065.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-016-3050-6) contains supplementary material, which is available to authorized users.

Abstract P3-07-54: Insulin-like growth factor 1 receptor expression and polymorphism are associated with response to neoadjuvant chemotherapy in breast cancer patients: Results from the NEOZOTAC trial (BOOG 2010-01)

Background

The insulin-like growth factor 1 (IGF-1) pathway is involved in cell growth, proliferation and cell cycle progression and associated with tumor genesis and therapy resistance. This study aims to elucidate whether variation in the IGF-1 pathway is predictive for pathologic response in early breast cancer (BC) patients taking part in the phase III NEOZOTAC trial, randomizing between 6 cycles of neoadjuvant TAC chemotherapy with or without zoledronic acid.

Method

Formalin-fixed paraffin-embedded (FFPE) tissue samples of pre-chemotherapy biopsies and operation specimens were collected for analysis of IGF-1 receptor (IGF-1R) expression using IHC (n=216) and for analysis of 8 candidate SNPs in genes of the IGF-1 pathway (n=184) using OpenArray® RealTime PCR. Optionally, blood samples were collected immediately before chemotherapy for determination of glucose, insulin, IGF-1, IGF-2 and IGF-BP3. Associations with patient and tumor characteristics and chemotherapy response according to Miller and Payne (MP) pathologic response were performed using chi square and logistic regression analyses.

Results

High IGF-1R expression was associated with estrogen receptor expression (P=0.001). During chemotherapy, a significant number of the tumors (47.2%) showed a decrease in IGF-1R expression, while in a small number of the tumors an upregulation was seen (15.1%). IGF-1R expression before treatment was not associated with pathological response, however absence of IGF-1R expression after treatment was associated with a better response in multivariate analyses (P=0.012) and patients with a decrease in expression during treatment showed a better response to chemotherapy as well (P=0.008). Moreover, the variant T allele of 3129G&gt;T in IGF-1R (rs2016347) was associated with a better pathological response in multivariate analyses (P=0.032). In addition, high glucose and insulin levels were associated with positive lymph node status before chemotherapy in multivariate analysis (P=0.019) and (P=0.031), respectively.

Conclusion

Neoadjuvant chemotherapy induced changes in the IGF-1R expression in most of the tumors. Absence or diminished expression of IGF-1R after treatment was associated with a better pathological response. Additionally, we found a SNP (rs2016347) in IGF-1R as a potential predictive marker for chemotherapy efficacy in BC patients treated with TAC. These findings may help to select patients who might benefit from (co-)treatment with an IGF-1 pathway inhibitor.

Citation Format: de Groot S, Charehbili A, van Laarhoven HWM, Mooyaart AL, Dekker-Ensink NG, van de Ven S, Janssen LGM, Swen JJ, Smit VTHBM, Heijns JB, Kessels LW, van der Straaten RJHM, Bhringer S, Gelderblom AJ, van der Hoeven JJM, Guchelaar HJ, Pijl H, Kroep JR. Insulin-like growth factor 1 receptor expression and polymorphism are associated with response to neoadjuvant chemotherapy in breast cancer patients: Results from the NEOZOTAC trial (BOOG 2010-01). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-54.

Exploratory analysis of candidate germline gene polymorphisms in breast cancer patients treated with neoadjuvant anthracycline-containing chemotherapy and associations with febrile neutropenia

AIM

SNPs may be associated with (side) effects of chemotherapy and may be useful as biomarkers to predict febrile neutropenia.

PATIENTS & METHODS

187 DNA samples extracted from formalin-fixed paraffin-embedded tissue from patients with stage II/III HER2-negative breast cancer were genotyped.

RESULTS

Candidate SNPs were selected and explored for association with febrile neutropenia and/or pathological complete response. TT genotype of 388 C>T in FGFR4 (rs351855) had a tendency toward higher incidence of febrile neutropenia during neoadjuvant chemotherapy, compared with the CT (p = 0.383) genotype and compared with the CC genotype (p = 0.068).

CONCLUSION

The TT genotype of 388 C>T FGFR4 may be related to incidence of febrile neutropenia during neoadjuvant TAC (docetaxel, doxorubicin, cyclophosphamide) chemotherapy and is possibly useful as a patient-related risk factor when assessing febrile neutropenia risk. Original submitted 23 January 2015; Revision submitted 26 May 2015.

Short-term variation in plasma mitotane levels confirms the importance of trough level monitoring

OBJECTIVE

Mitotane is the drug of choice in patients with adrenocortical carcinoma. The anti-neoplastic effect is correlated with mitotane plasma levels, which render it crucial to reach and maintain the concentration above 14 mg/l. However, mitotane pharmacokinetics is poorly understood. The aim of this study was to investigate the variation in plasma mitotane levels during the day and the influence of a single morning dose.

DESIGN

A prospective case-control study was conducted to investigate the variation in plasma mitotane levels.

METHODS

Patients who had been treated for at least 24 weeks and had reached the therapeutic plasma level (14 mg/l) at least once were eligible. In the first group, mitotane levels were determined hourly for the duration of 8 h after administration of a single morning dose. In the second group, mitotane levels were assessed similarly without administration of a morning dose.

RESULTS

Ten patients were included in this study, and three patients participated in both groups. Median plasma level at baseline was 16.2 mg/l (range 11.3-23.3 mg/l) in the first group (n=7) and 17.0 mg/l (13.7-23.8) in the second group (n=6). Plasma levels displayed a median increase compared with baseline of 24% (range 6-42%) at t=4 after morning dose and a change of 13% (range -14 to 33%) at t=4 without morning dose (P=0.02).

CONCLUSION

A substantial increase in mitotane plasma levels was observed in steady-state patients within a period of 8 h after morning dosing. Without morning dose, mitotane curves showed a variable profile throughout the day. This implies that random sampling could yield incidentally high levels. For this reason, we recommend early-morning trough sampling as standard management in monitoring mitotane treatment.

Relationship between specific adverse events and efficacy of exemestane therapy in early postmenopausal breast cancer patients

BACKGROUND

Many adverse events (AEs) associated with aromatase inhibitors (AIs) involve symptoms related to the depletion of circulating estrogens, and may be related to efficacy. We assessed the relationship between specific AEs [hot flashes (HF) and musculoskeletal AEs (MSAE)] and survival outcomes in Dutch and Belgian patients treated with exemestane (EXE) in the Tamoxifen Exemestane Adjuvant Multinational (TEAM) trial. Additionally, the relationship between hormone receptor expression and AEs was assessed.

METHODS

Efficacy end points were relapse-free survival (RFS), overall survival (OS) and breast cancer-specific mortality (BCSM), starting at 6 months after starting EXE treatment. AEs reported in the first 6 months of treatment were included. Specific AEs comprised HF and/or MSAE. Landmark analyses and Cox proportional hazards models assessed survival differences up to 5 years.

RESULTS

A total of 1485 EXE patients were included. Patients with HF had a better RFS than patients without HF [multivariate hazard ratio (HR) 0.393, 95% confidence interval (CI) 0.19-0.813; P = 0.012]. The occurrence of MSAE versus no MSAE did not relate to better RFS (multivariate HR 0.677, 95% CI 0.392-1.169; P = 0.162). Trends were maintained for OS and BCSM. Quantitative hormone receptor expression was not associated with specific AEs.

CONCLUSIONS

Some AEs associated with estrogen depletion are related to better outcomes and may be valuable biomarkers in AI treatment.

The tolerability and efficacy of low-dose simvastatin in statin-intolerant patients

BACKGROUND/AIM

Statin intolerance is increasingly recognized as a therapy limiting factor in the primary and secondary prevention of cardiovascular disease. Since vulnerability to dose related adverse events differ between subjects treated with statins we hypothesized low-dose simvastatin would be tolerated and effective in statin-intolerant patients.

METHOD

A single center open label prospective observational study was performed assessing tolerability and efficacy of low-dose simvastatin treatment in 35 statin-intolerant patients. Statin intolerance was defined as not being able to tolerate a registered dose statin due to myalgia-myopathy, myositis, or elevation of serum liver enzyme levels. These statin-intolerant patients were treated with simvastatin with an initial dose of 2.5mg every other day. The dose was titrated upwards if possible. Tolerability was defined as remaining on treatment. Efficacy was defined as change of LDL-cholesterol compared to baseline.

RESULTS

The reached simvastatin dose ranged from 0.825 to 8.75mg/day with a mean dose of 4mg/day. Fifty-seven percent of the patients tolerated low-dose therapy and remained on treatment. Of these patients, 30% noted recurrent myalgia. Low-dose simvastatin significantly decreased mean(SD) LDL-cholesterol levels with 25.9(12.1)% (p<0.001). Eleven percent of the patients reached LDL-cholesterol target levels (<2.6mmol/l) in an intention to treat analysis and in 20% of patients that tolerated low-dose simvastatin.

CONCLUSION

Low-dose simvastatin therapy is tolerated in a considerable proportion of statin-intolerant patients with significant lipid lowering efficacy. Low-dose statin therapy can be considered in multidrug regimens in statin-intolerant patients.

Pharmacogenetics in oncology: a promising field

Pharmacogenetics is a rapidly developing field, especially in oncology. In the most ideal situation pharmacogenetics will allow oncologists to individualize therapy based on patients' individual germline genetic test results. This can help to improve efficacy, reduce toxicity and predict non-responders in a way that alternative therapy can be chosen or individual dose adjustments can be made. Multiple pathways have been studied extensively of which a brief review is presented here. Increased 5FU toxicity is associated with variations in the DPYD gene, TYMS gene and MTHFR gene. Furthermore variations in the UGT1A gene and the ABCB1 gene influence irinotecan metabolism and disposition. Other genetic changes result in reduced DNA repair capacity related to platinum efficacy or reduced cytochrome P450 2D6 activity related to tamoxifen efficacy. Despite the extensive number of pharmacogenetic studies and promising results, it is still unclear when and how pretreatment genetic screening should be implemented in oncology. Future prospective studies should focus on the effect of pharmacogenetics on patient outcome and combine this with cost effectiveness evaluations. Thus supplying us with predictive models helping in deciding when pretreatment genetic screening is useful.

Pharmacogenetic pathway analysis for determination of sunitinib-induced toxicity

5006

Background: To identify genetic markers in the pharmacokinetic and pharmacodynamic pathways of sunitinib that predispose for development of toxicities; thrombocytopenia, leukopenia, mucosal inflammation, hand-foot syndrome and ‘any toxicity according to Common Terminology Criteria > grade 2.’ Methods: A multicenter pharmacogenetic association study was performed in 219 patients treated with single agent sunitinib. A total of 31 single nucleotide polymorphisms in 12 candidate genes, together with several non-genetic variants, were analyzed for a possible association with toxicity. In addition, genetic haplotypes were developed and related to toxicity. Results: The risk for leukopenia was increased when the G-allele in CYP1A1 2455A/G (OR = 6.24; p = 0.029) or the T-allele in FLT3 738T/C (OR = 2.8; p = 0.008) were present or CAG in the NR1I3 (5719C/T, 7738A/C, 7837T/G) haplotype (OR = 1.74; p = 0.041) was absent. ‘Any toxicity > grade 2’ prevalence was increased when the T-allele of VEGFR-2 1191C/T (OR = 2.39; p = 0.046) or a copy of TT in the ABCG2 (-15622C/T, 1143C/T) haplotype (OR = 2.63; p = 0.016) were present. The risk for mucosal inflammation was increased in the presence of the G-allele in CYP1A1 2455A/G (OR = 4.03; p = 0.021) and the prevalence of hand-foot syndrome was increased when a copy of TTT in the ABCB1 (3435C/T, 1236C/T, 2677G/T) haplotype (OR = 2.56; p = 0.035) was present. Conclusions: This exploratory study suggests that polymorphisms in specific genes encoding for metabolizing enzymes, efflux transporters and drug targets are associated with sunitinib related toxicities. A better understanding of genetic and non-genetic determinants of sunitinib toxicity should help to optimize drug treatment in individual patients.

[Table: see text]

Time to treatment as an important factor for the response to methotrexate in juvenile idiopathic arthritis

OBJECTIVE

Methotrexate (MTX) is the most commonly used disease-modifying antirheumatic drug in juvenile idiopathic arthritis (JIA). Currently, individual response to MTX cannot be reliably predicted. Identification of clinical and genetic factors that influence the response to MTX could be helpful in realizing the optimal treatment for individual patients.

METHODS

A cohort of 128 JIA patients treated with MTX were studied retrospectively. Eleven clinical parameters and genotypes of 6 single nucleotide polymorphisms in 5 genes related to the mechanism of action of MTX were compared between MTX responders and nonresponders using a multivariate regression analysis.

RESULTS

The time from diagnosis to start of MTX treatment, physician's global assessment at baseline, and the starting dose were significantly associated with the response to MTX at 6 months after initiation. Patients with a shorter time from diagnosis to start of MTX and a higher disease activity according to the physician but with a lower MTX dose showed an increased response. The effect of the starting dose on MTX response seemed to be mainly due to the influence of the systemic JIA subtype. The time from diagnosis to start of MTX treatment and physician's global assessment at baseline were highly correlated. Therefore, the precise effect size of each independent variable could not be determined.

CONCLUSION

In children with JIA, the time from diagnosis to start of MTX appears to be an important factor for MTX response. Our results suggest that an earlier start of MTX treatment will lead to an increased response.

Is statin use associated with a reduced incidence, a reduced Breslow thickness or delayed metastasis of melanoma of the skin?

BACKGROUND

Statins show anticancer activity in melanoma cells. We investigated the association between statins and incidence and Breslow thickness of cutaneous melanoma (CM).

METHODS

Data were used from PHARMO, a pharmacy database, and PALGA, a pathological database, in the Netherlands. Cases had a primary CM diagnosis between January 1st 1991 and December 14th 2004, were 18 years and had 3 years of follow up in PHARMO before CM diagnosis. Controls were matched for gender, date of birth and geographic region. Analyses were adjusted for age, gender, year of diagnosis, number of medical diagnoses and the use of NSAIDs and oestrogens.

FINDINGS

Finally, 1318 cases and 6786 controls were selected. CM risk was not associated with statin use (> or = 0.5 years) (adjusted odds ratio (OR)=0.98, 95% confidence interval (CI)=0.78-1.2). However, statin use was associated with a reduced Breslow thickness (-19%, 95% CI=-33, -2.3, p=0.03).

CONCLUSION

Our study suggests protective effects of statins on melanoma progression.

Cyclopentenyl cytosine (CPEC): an overview of its in vitro and in vivo activity

The experimental cytotoxic drug cyclopentenyl cytosine (CPEC) is an analogue of cytidine. Besides its antiviral effect, its potential use in the treatment of cancer has become an important area of research. CPEC is activated by intracellular phosphorylation ultimately forming its metabolite CPEC-TP. CPEC-TP is a non competitive inhibitor of cytidine-5'-triphosphate synthetase (CTP-synthetase), an important enzyme in the formation of CTP. Studies have shown that cancer cells have a high CTP synthetase activity, thus making them interesting targets for chemotherapy. CPEC has been preclinically studied in different malignancy models. In vitro results on leukemia show activity in the nanomolar range on several cell lines. However in vivo results are conflicting and the findings vary from increase in life span over 100% to only limited effectiveness. Interesting results have been obtained in colorectal and neuroblastoma cells. In several neuroblastoma cell lines incubation with CPEC in combination with cytarabine or gemcitabine has resulted in increased cell death compared to incubation with with only one of the agents. CPEC has been studied in a phase I trial in patients with solid tumors. In five of 26 patients unexplained cardiotoxicity (extreme hypotension) occurred. The cardiotoxic effects could not be reproduced in animal models. However, precautions should be taken when using this drug in future clinical trials. Low dosage of CPEC seems necessary and intensive cardiac monitoring is advisable. In this manuscript, it is demonstrated that CPEC has an anti-cancer effect in several tumor models: CPEC might be a potentially useful drug in anticancer treatment.

Insights into the role of heritable genetic variation in the pharmacokinetics and pharmacodynamics of anticancer drugs

Pharmacogenetics in oncology will ideally allow oncologists to individualise therapy based on a genetic test result. Severe toxicity and clinically significant underdosing may be avoided, whereas predicted non-responders can be offered alternative therapy. This manuscript gives an overview of heritable variants in the genes of nine enzymes or pathways that have been studied most extensively in anticancer chemotherapy. Even though many pharmacogenetic association studies have been published, there is a need for more research. In particular, there is a need for replication of data and development of predictive models. Prospective trials are required to establish clinical value and cost-effectiveness of pharmacogenetic testing in oncology.

Effect of smoking on imatinib pharmacokinetics

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Background: Smoking is a potent inducer of the cytochrome P450 1A2 isoenzyme (CYP1A2) and may therefore effect the pharmacokinetics (PK) of drugs metabolized by CYP1A2. Indeed, clinical studies with erlotinib (metabolized by CYP3A4 and also partly by CYP1A2) have shown a major increase in erlotinib clearance in smokers versus non-smokers. The effect of smoking on the PK of imatinib, which is also metabolized by CYP3A4 and partly by CYP1A2, is unknown. We aimed to study the effect of smoking on imatinib PK in order to explain a part of the interpatient variation. Methods: The effect of smoking on the PK parameters was analyzed in 34 patients with gastro-intestinal stromal tumors or soft tissue sarcoma included in the EORTC-STBSG phase I and phase II trials. This cohort included 9 smokers and 25 non-smokers. The daily smoking habits of the study patients were retrieved retrospectively from the patient’s record. PK parameters assessed with NONMEM, version V were clearance (Cl), distribution volume (V), elimination half life (T1/2) and the dose standardized area under the concentration curve (AUC). We considered a 40% reduction in imatinib exposure clinically relevant and this study is adequately powered to detect this difference. Results: The mean PK parameters in the smokers versus the non-smokers group ± SD were: Cl; 9.6 ± 5.5 L/h vs 9.2 ± 4.6 L/h, V; 216.5 ± 114.3 L vs 207.0 ± 116.9 L, T1/2; 16.1 ± 6.0 h vs 16.5 ± 6.0 h, AUC; 133.6 ± 71.0 ng.h/ml.mg vs 142.3 ± 84.0 ng.h/ml.mg. There was no significant difference in PK parameters observed between the smokers and the non- smokers. Conclusion: This retrospective study suggest that the PK of imatinib was not affected by smoking and therefore does not explain the large variation in imatinib PK.

No significant financial relationships to disclose.

Association between CYP1A2 activity and riluzole clearance in patients with amyotrophic lateral sclerosis

AIMS

Riluzole is used in a fixed dosing schedule of 50 mg twice daily to treat patients with amyotropic lateral sclerosis (ALS), one form of motor neurone disease. The large variability in the pharmacokinetics of riluzole may be a factor contributing to its limited therapeutic benefit. Riluzole is assumed to be mainly metabolized by the cytochrome P450 enzyme 1A2 (CYP1A2). The aim of the study was to investigate the relationship between CYP1A2 activity and riluzole clearance with a view to optimize drug treatment.

METHODS

A group of 30 ALS patients participated in the study. In each patient the CYP1A2 activity was determined using caffeine as a metabolic probe. Riluzole clearance was estimated from serum drug concentration measurements followed by Bayesian fitting.

RESULTS

Riluzole clearance and the serum paraxanthine : caffeine (P/C) ratio showed a positive correlation (r = 0.693; P = 0.0002). Linear regression analysis identified the P/C ratio (beta: 1.16) and height (beta: 0.027) as independent predictors of riluzole clearance (adjusted r2 = 0.369).

CONCLUSIONS

The P/C ratio, used as measure of CYP1A2 activity, significantly correlated with the riluzole clearance, although only 37% of the observed variability could be explained.

A validated HPLC assay to monitor riluzole plasma or serum concentrations in patients with amyotrophic lateral sclerosis

A specific, accurate and precise high-performance liquid chromatographic assay was developed for the determination of riluzole, a drug used to treat patients with amyotrophic lateral sclerosis. Samples were treated by extraction with dichloromethane followed by reversed-phase chromatography with ultraviolet detection at 260 nm. Preset validation criteria were met from 20 to 2000 ng/mL with a linear response curve. Extraction recovery of riluzole was 65-76%. The accuracy of the method was 102-103%. Intra- and inter-day coefficients of variation were in the ranges 2.8-4.9% and 1.8-9.7%. A detection limit of 5 ng/mL was found. Determination of concentrations in serum and plasma resulted in similar results below 500 ng/mL. At higher values a matrix effect cannot be excluded. This presented method can be used to monitor plasma or serum levels in ALS patients treated with riluzole.

Pharmacokinetic-pharmacodynamic modeling of the inhibitory effect of erythromycin on tumour necrosis factor-alpha and interleukin-6 production

Erythromycin inhibits the production of tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL6) induced by heat-killed Streptococcus pneumoniae in human whole blood ex-vivo. The objective of the present study was to determine and characterize the concentration-effect relationship of this phenomenon in order to predict its possible clinical relevance. Six healthy volunteers received a single intravenous dose of 1000 mg erythromycin. Blood samples were obtained up to 4 h after drug administration. Samples were assayed for erythromycin concentrations and (after heat-killed Streptococcus pneumoniae stimulation) for TNF-alpha and IL6 concentrations. Effect vs. time data from individual subjects were fitted to the indirect response model with an Emax concentration-effect relationship. Simulations of these effects were performed for therapeutic intravenous and oral erythromycin dosage regimens. The geometric means of the values of Kin, Kout and EC50 were 15.4 microg/h, 0.82/h, 9.4 mg/L for TNF-alpha and 321 microg/h, 2.02/h, 18.3 mg/L for IL6. Simulations revealed a maximal inhibition of TNF-alpha concentrations of 35%, 50%, 16% and 27% at erythromycin dosages of 500 mg i.v., 1000 mg i.v., 500 mg p.o and 1000 mg p.o. q 6 h, respectively, whereas a maximal inhibition of IL6 of 29%, 44%, 13% and 22% are predicted for the respective regimens. The inhibitory effect of erythromycin on TNF-alpha and IL6 production can be adequately described by the indirect response model with an Emax concentration-effect relationship. Simulations predicted a substantial decrease of production of these cytokines at intravenous and to a much lesser extent at oral erythromycin dosage regimens.

Inter- and intraindividual variability of riluzole serum concentrations in patients with ALS

All patients with amyotrophic lateral sclerosis (ALS) are treated with the same dose of riluzole: 50 mg twice daily. Reasonably large interindividual differences in clearance of the drug have been reported. The relatively small group of patients with high blood concentrations of riluzole has probably primarily influenced the efficacy and the incidence of side-effects in the previously conducted clinical trials with riluzole. Individual dosing of the drug may, in the case of large interindividual differences in serum concentrations of the drug, be necessary in the future. Exact data concerning the plasma and serum concentrations of riluzole in patients with ALS, after standardized intake of the drug, diet and blood sampling are unknown so far. In this study, inter- and intraindividual variability of serum and plasma levels of riluzole in 21 patients with "probable" or "definite" ALS were determined. The interindividual variability of peak serum levels (coefficient of variation=74%) was significantly larger than intraindividual variability (p<0.001). Serum levels were not correlated with age or smoking status. The determination of a correlation between riluzole serum concentrations and survival of patients with ALS will be the aim of further studies.

Simultaneous determination of clozapine, norclozapine and clozapine-N-oxide in human plasma by high-performance liquid chromatography with ultraviolet detection

A reversed-phase high-performance liquid chromatographic (HPLC) method for the simultaneous determination of clozapine and its two major metabolites, norclozapine and clozapine-N-oxide in human plasma has been developed and validated. The isocratic HPLC assay uses a mobile phase consisting of an acetonitril-buffered aqueous solution containing 146 microL of triethylamine and 200 microL of 85% phosphoric acid, adjusted to pH 3.3 with 10% potassiumhydroxide solution (400:600, v/v) at a flow-rate of 0.8 ml/min and a Lichrospher 100 RP-18 reversed-phase column and UV detection at 215 nm. Doxepine was used as the internal standard. Mean recoveries for clozapine, norclozapine, clozapine-N-oxide and doxepine were 95%, 98%, 96% and 94%, respectively, whereas the respective mean repeatability coefficients of variation were 3.4%, 2.7%, 4.3% and 0.9%. Reproducibility coefficients of variation were 1.3%, 1.8%, 3.6% and 0.5%, respectively. The mean correlation coefficient for the linear calibration curve (n = 2) for clozapine and norclozapine at a concentration range of 100-1600 ng/mL was 0.9998 and 0.9997, respectively; for clozapine-N-oxide (20-200 ng/mL) it was found to be 0.9986. The lower limits of quantitation were 12.5 ng/mL, 10 ng/mL and 12.5 ng/mL for clozapine, norclozapine and clozapine-N-oxide, respectively.

Simultaneous determination of flucytosine and fluorouracil in human plasma by high-performance liquid chromatography

A validated, sensitive and precise reversed-phase high-performance liquid chromatographic method for the simultaneous determination of 5-flucytosine (5-FC) and 5-fluorouracil (5-FU) in human plasma is described. Two compounds, 5-methylcytosine (5-MC) and 5-chlorouracil (5-CU), were used as internal standards for the determination of 5-FC and 5-FU, respectively. Plasma samples were deproteinized with trichloroacetic acid and chromatographed on an octylsilica column, maintained at 30 degrees C during elution, using a 0.04 M phosphate buffer, pH 7.0, as eleunt. Spectrophotometric diode array detection was used at 266 nm. 5-FC, 5-FU, 5-MC and 5-CU were found to have retention times of 4.8, 5.8, 7.7 and 11.0 min respectively. Recoveries of 91-120% with reproducibility and repeatability coefficients of variation of 0.8-6% were obtained. Mean correlation coefficients of 0.99989 and 0.9995 were found for the linear calibration curves (n = 2) of 5-FC (4.816-192.6 mg/l) and 5-FU (0.05368-5.368 mg/l), respectively. The limits of quantitation were 0.3 mg/l for 5-FC and 0.05 mg/l for 5-FU.

Population pharmacokinetics of flucytosine: comparison and validation of three models using STS, NPEM, and NONMEM

The objective of this study is to compare and validate three models of flucytosine (5-FC) population pharmacokinetics using three methods of analysis to elucidate which model describes 5-FC pharmacokinetics most accurately and which method is the most suitable for this purpose. Retrospectively, demographic and clinical data of two similar sets of a total of 88 intensive care unit (ICU) patients were gathered for calculation and validation of 5-FC pharmacokinetics respectively. Three pharmacokinetic models were analyzed: a one-compartment with renal elimination (renal model), a one-compartment with renal and metabolic elimination (mixed model), and a two-compartment with renal elimination (two-compartment model). Population pharmacokinetic parameters were calculated using the standard two-stage method (STS), NONMEM, and NPEM. Furthermore, a covariate model was built by NONMEM. Validation of the 10 calculated pharmacokinetic models showed that NONMEM is most suitable for predicting 5-FC population pharmacokinetics. Based upon AIC values, bias and precision, the best results are obtained using a two-compartment model with renal elimination (k(elr) = 0.000858 +/- 0.000143 l/h per mL per min, k12 = 0.0313 +/- 0.0168 h(-1), k21 = 0.0353 +/- 0.0145 h(-1), and Vd = 0.541 +/- 0.084 L/kg; bias = -13.16; 95% CI = -16.77; -9.55; precision = 30.50; 95% CI = 27.47; 33.26) or a two-compartment covariate model as built by NONMEM [Vd (L) = 0.572 x WT, Cl(5FC) (L/h) = 1.69 + 0.0273 x (Cl(cr) (mL/min) - 52.5), k12 = 0.0235 +/- 0.0107 h(-1), and k21 = 0.0375 +/- 0.0147 h(-1); bias = -8.29; 95% CI = -11.63; -4.95; precision = 26.77; 95% CI = 24.24; 29.07]. In conclusion, this study shows that a two-compartment model with renal elimination best describes 5-FC population pharmacokinetics and NONMEM is able to build a two-compartment covariate model that predicts 5-FC levels equally well in our population of ICU patients. Furthermore, NONMEM appeared to be the most suitable method of population pharmacokinetics in our population and for this purpose it offers more reliable and accurate results than NPEM or the STS method.

Hyperthermic isolated regional perfusion of the limb with carboplatin

AIMS

To investigate the feasibility of hyperthermic isolated regional perfusion (HIRP) with carboplatin in the management of locally recurrent and/or intransit metastases of melanoma or locally advanced soft tissue sarcoma.

METHODS

Three patients, two with locally advanced melanoma and one with a low-grade liposarcoma of the lower extremity, were treated with HIRP under mild hyperthermia (39-40 degrees C) with 125 mg carboplatin/l perfused limb volume.

RESULTS

No systemic toxicity was observed. Local toxicity consisted of post-perfusion oedema present in all three patients which resolved within 2 weeks. Clinically, a persistent local neuropathy was observed in all three patients, two of which were confirmed by electromyogram and nerve conduction study. Severe motor-sensory neuropathy was located mainly in the peroneal and sural nerves of the perfused limbs. Pharmacokinetic parameters of the carboplatin showed a higher concentration of carboplatin in the skin compared to the muscle. The two melanoma patients showed a complete response but developed local recurrences within 1.5 years after perfusion. The third patient underwent a delayed excision of the sarcoma 8 weeks after perfusion which revealed 50% viable tumour. One of the melanoma patients and the sarcoma patient died from lung metastases 56 and 31 months post-perfusion treatment, respectively. The other melanoma patient is alive 95+ months post-perfusion treatment.

CONCLUSIONS

The local neurotoxicity observed did not warrant further research of carboplatin in HIRP.

Prediction of flucytosine-induced thrombocytopenia using creatinine clearance

AIMS

To evaluate and investigate the efficacy and accuracy of an earlier derived relationship between thrombocyte nadir and mean creatinine clearance in order to make it possible to predict flucytosine (5-FC)-related thrombocytopenia.

METHODS

The earlier derived relationship between thrombocyte nadir and mean creatinine clearance is validated using a patient population of 35 intensive care unit (ICU) patients. Patients have to meet the inclusion criteria as defined in the initial study (i.e., developing thrombocytopenia during 5-FC treatment or remaining within the normal thrombocyte range; individual pharmacokinetic parameters within certain limits; a minimum of three measured 5-FC serum levels).

RESULTS

Of a total of 35 patients, 11 are eligible since they meet the inclusion criteria as defined in the initial study. A significant relationship between the observed and predicted thrombocyte nadir values can be derived: Y(pred) = 0.608.X(obs) + 24. 330 (r = 0.615; t(obs) = 2.337; t at p < 0.05 and 9 degrees of freedom = 2.262). The predicted value of the thrombocyte nadir corresponds with a mean prediction error (bias) of -18.3 (95% CI -45.9; 9.4) and a root mean squared prediction error (precision) of 48.3 (95% CI 23.9-63.9).

CONCLUSION

The earlier derived relationship between thrombocyte nadir and mean creatinine clearance is accurate and precise. However, due to the strict inclusion criteria used to derive and validate this relationship, it cannot be applied to all 5-FC-treated patients.