Effect of PK-guided tamoxifen dose escalation on endoxifen serum concentrations in CYP2D6 intermediate and poor metabolizers

595

Background: Breast cancer patients with absent or reduced CYP2D6 activity may benefit less from tamoxifen treatment because of impaired biotransformation to the active metabolite endoxifen. We investigated whether a temporary one-step dose escalation of tamoxifen in CYP2D6 poor (PM) and intermediate metabolizers (IM) could increase endoxifen serum concentration to a similar level observed in CYP2D6 extensive metabolizers (EM) without increasing toxicity. Methods: From a prospective study population of early breast cancer patients using tamoxifen, 12 CYP2D6 poor and 12 intermediate metabolizers were selected and included in a one-step tamoxifen dose escalation study during two months. The escalation dose (120 mg maximum) was calculated by multiplying the individual’s endoxifen level divided by the median endoxifen concentration (33.7 nM) observed in CYP2D6 extensive metabolizers by 20 mg. Toxicity was assessed and all patients returned to the standard dose of 20 mg after two months. Results: Tamoxifen dose escalation in CYP2D6 poor and intermediate metabolizers significantly increased endoxifen concentrations (PMs: from 8.0 nM to 27.3 nM, p<0.001; IMs: from 17.8 nM to 30.3 nM, p=0.002) without increasing side effects. In intermediate but not in poor metabolizers dose escalation increased endoxifen to levels comparable with those observed in extensive metabolizers using tamoxifen 20 mg once daily (33.7 nM). Conclusions: CYP2D6 genotype and endoxifen guided tamoxifen dose escalation increased endoxifen concentrations without increasing short term side effects. Whether such tamoxifen dose escalation is effective and safe in view of long term toxic effects is uncertain and needs to be explored. Clinical trial information: NTR1509.

Safety and efficacy of the addition of simvastatin to cetuximab in KRAS mutant metastatic colorectal cancer patients

e14586

Background: Epithelial growth factor receptor (EGFR) inhibitors are not effective in KRAS mutant colorectal tumors. In these tumors the k-ras protein is activated by post-translational modification by binding farnesyl (C15) and geranylgeranyl (C17) moieties. Both are products of the mevalonate pathway, as is cholesterol. Statins (HMG-CoA-reductase inhibitors) not only inhibit synthesis of cholesterol, but also of C15 and C17 and thus may reduce post-translational activation of ras proteins. Therefore, statins may inhibit the expression of the mutant KRAS phenotype and normalize the phenotype into KRAS wild type. In a phase II study we investigated whether simvastatin treatment renders KRAS mutant colorectal tumors sensitive to cetuximab. Methods: Major eligibility criteria were metastatic colorectal cancer failing 5-FU, oxaliplatin and irinotecan containing regimens, with a mutation in codon 12, 13 or 61 of KRAS gene in a tumor sample. Patients were treated with simvastatin 80mg once daily and cetuximab 250mg/m2 weekly (after a starting dose of 400mg/m2). Primary objective was to investigate the percentage of patients free from progression and alive 12.5 weeks after the first administration of cetuximab, similar to the results of the KRAS wild type population of the phase III study. This phase II study was performed in a Simon two stage design, performing an interim analysis after enrolment of 15 patients. If at least 6 of these patients (i.e. 40%) were to be alive and free from progression at 12.5 weeks after the start of cetuximab, another 31 patients would be included during stage II. Results: Fifteen evaluable patients were enrolled at 3 study sites. Four patients (i.e. 27%) were free from progression at time of the primary endpoint. Three patients experienced serious adverse events; an allergic reaction during cetuximab infusion, rhabdomyolysis and intracranial haemorrhage due to cerebral metastases. Conclusions: Though 4 patients experienced stable disease at 12.5 weeks, the predefined efficacy boundary was not met in order to continue enrolment to stage II. Simvastatin 80mg once daily does not induce sensitivity to cetuximab in colorectal cancer patients with a mutation in the KRAS gene. Clinical trial information: NCT01190462.

Safety and efficacy of the addition of simvastatin to panitumumab in KRAS mutant metastatic colorectal cancer patients

e14558

Background: Epithelial growth factor receptor (EGFR) inhibitors are not effective in KRAS mutant colorectal tumors. In these tumors the k-ras protein is activated by post-translational modification by binding farnesyl (C15) and geranylgeranyl (C17) moieties. Both are products of the mevalonate pathway, as is cholesterol. Statins (HMG-CoA-reductase inhibitors) not only inhibit synthesis of cholesterol, but also of C15 and C17 and thus may relevantly inhibit post-translational activation of ras proteins. Therefore, statins may inhibit the expression of the mutant KRAS phenotype and normalize the phenotype into KRAS wild type. In a phase II study we investigated whether simvastatin treatment renders KRAS mutant colorectal tumors sensitive to panitumumab. Methods: Major eligibility criteria were advanced or metastatic colorectal cancer failing prior 5FU, oxaliplatin and irinotecan containing regimens, with a mutation in codon 12, 13 or 61 of KRAS gene on tumor sample. Patients were treated with simvastatin 80mg once daily and panitumumab 6mg/kg every 2 weeks. Primary objective was to investigate the percentage of patients free from progression and alive 11 weeks after the first administration of panitumumab. This phase II study was performed in a Simon two stage design, performing an interim analysis after the enrolment of 15 patients. When at least 6 of these patients (i.e. 40%) were to be alive and free from progression free at 11 weeks after the first administration of panitumumab (similar to the results of the KRAS wild type population of the phase III study), another 31 patients would be included during stage 2. Results: Fifteen evaluable patients were enrolled by 4 study sites. Only one patient was free from progression 11 weeks after start of panitumumab treatment (6.7%). Mean progression free survival was 9.1 weeks (range 5-17 weeks). Most frequent reported side effect was skin toxicity (40%), one patient experienced myositis grade 3. Conclusions: Simvastatin 80mg once daily was not able to inhibit the KRAS mutant phenotype sufficiently to reach sensitivity to panitumumab in colorectal cancer patients with a mutation in the KRAS gene. Clinical trial information: NCT01110785.

CYP3A4 phenotyping with midazolam to predict sunitinib exposure

2592

Background: Patients treated with sunitinib show high inter-patient variability in drug exposure (40-60%), which is largely unexplained. Since sunitinib is metabolized by CYP3A4, variability in the activity of this enzyme may explain a considerable proportion of the observed variability. We therefore prospectively studied the relationship between CYP3A4 activity and systemic exposure to sunitinib. Methods: In fifteen patients treated with sunitinib in a four weeks “on” – two weeks “off” regimen the pharmacokinetics of sunitinib and its active metabolite SU12662 were assessed. To determine sunitinib+SU12662 steady-state exposure, samples were collected over 24hrs after at least 14 days of sunitinib therapy. To assess CYP3A4 activity, midazolam 7.5mg orally was administered on the final day of the two weeks “off”. Plasma concentrations were measured over a period of 7hrs to determine midazolam exposure. Exposures (AUC) were calculated using a trapezoidal approach (Phoenix WinNonlin v6.3). The relationship between CYP3A4 activity (midazolam exposure) and sunitinib+SU12662 exposure was determined by linear regression analysis. The percentage of variability in sunitinib+SU12662 exposure that could be explained by CYP3A4 activity was calculated by Pearson’s correlation. In addition, the correlation between sunitinib+SU12662 Ctrough levels and sunitinib+SU12662 exposure was assessed. Results: A strong correlation between midazolam exposure (AUC0-7hr) and steady-state sunitinib+SU12662 exposure (AUC0-24hr) was found (p= 0.002); CYP3A4 activity explained 55% of the observed inter-patient PK variability of sunitinib+SU12662. Furthermore sunitinib+SU12662 Ctrough levels were highly predictive (96%) for overall sunitinib+SU12662 exposure (AUC0-24hr). Conclusions: Midazolam as a phenotyping probe could be useful before start of sunitinib therapy to identify patients at risk for under- respectively overtreatment at a standard dosage regimen. Therefore, CYP3A4 phenotyping could be useful to individualize sunitinib therapy. Additionally, sunitinib+SU12662 trough levels are highly predictive for sunitinib+SU12662 exposure and thus can be used for monitoring and guiding sunitinib therapy in clinical practice. Clinical trial information: NCT01743300.

Genetic variation in CYP19A1 and occurrence of adverse events in exemestane treatment with early breast cancer patients in the Dutch TEAM trial

e22152

Background: Aromatase inhibitors (AI) are an important part of treatment of endocrine sensitive breast cancer. Adverse events in patients treated with AI’s often cause treatment discontinuation. The most common adverse events, such as arthralgia, myalgia and hot flushes are probably caused by estrogen deprivation and predict treatment efficacy. It is unclear which patients are at risk to develop these adverse events. The aim of this study was to examine if SNP’s in the CYP19A1 gene can predict the occurrence of adverse events in breast cancer patients treated with adjuvant exemestane. Methods: Patients of whom tissue was available and were selected from the Tamoxifen Exemestane Adjuvant Multinational (TEAM) trial. DNA was isolated from tumor samples and 30 SNPs were identified using a tagging SNP approach, aiming for 80% coverage of CYP19A1. Genotypes were determined with taqman assays. Primary endpoint of the study was the occurrence of adverse events. Secondary endpoints were the occurrence of hot flushes, arthralgia, and myalgia. Results: 807 patients were included in the analyses and genotypes were obtained in 722 cases. One SNP, rs8031311, was associated with a higher incidence of adverse events with an odds ratio of 2.8. Four SNP's were associated with an increased incidence of hot flushes: rs934635, rs4775928, rs16964189, rs6493496 with odds ratio’s of 2.9, 1.8, 1.8 and 2.6 respectively. No association was found between variation in CYP19A1 and the occurrence of arthralgia or myalgia. Conclusions: Germline variation in the CYP19A1 gene is related to the occurrence of adverse events, specifically hot flushes, in early breast cancer patients treated with exemestane. These findings may contribute to the individualization of hormonal therapy in breast cancer. [Table: see text]

The influence of gastrointestinal resection on sunitinib exposure in GIST patients

10547

Background: GIST patients often have an altered anatomy of the GI tract due to either primary resection of the tumor or palliative surgery. It is unknown whether such GI resections affect the exposure to sunitinib and its active metabolite SU12662. Previous studies showed that the exposure to imatinib and nilotinib was decreased in GIST patients with prior major gastrectomy. Therefore, we postulated that GI resections might similarly affect sunitinib exposure. Methods: A retrospective analysis was performed to assess the effect of GI resections on sunitinib exposure. Pharmacokinetic data from 305 GIST patients included in 4 phase I-II trials were analyzed. Patients were subdivided into 6 groups according to prior GI surgery: 1)Major gastrectomy: 2)Partial gastrectomy: 3)Small bowel resection: 4)Combination of gastrectomy and small bowel resection: 5)Colon resection and 6)Controls with no prior GI surgery. Patients with uncertain GI resections were excluded. Dose normalized exposure (AUC0-24hr) of sunitinib and SU12662 was estimated with a population PK approach using NONMEM. Analysis of covariance was performed to test for significant differences in AUC between each of the subgroups and controls. Results: The geometric mean of total exposure to sunitinib and SU12662 was decreased by 21% and 28% in subgroup 4, (n=8; sunitinib: 931 ng*hr/mL (95%CI;676-1283) and SU12662: 354 ng*hr/mL (95%CI;174-720)) compared to controls (n=63; sunitinib: 1177 ng*hr/mL (95%CI;1097-1263) and SU12662: 491 ng*hr/mL (95%CI;435-555)), with the differences being significant (p<0.05) on the log scale. However, no significant differences in total exposures were observed between each of the other subgroups and control. Conclusions: In patients with a combined gastrectomy and small bowel resection, sunitinib and SU12662 exposure is significantly decreased as compared to subjects with no prior GI surgery. Contrary to previous results for imatinib, gastrectomy alone does not appear to influence sunitinib exposure. This should be taken into consideration for the treatment of GIST patients who had a gastrectomy. In theory, such patients might have better outcomes if treated with sunitinib, given the risk of subtherapeutic exposure to imatininb.

CYP2D6 genotype related to tamoxifen efficacy: An analysis with exclusion of potential false CYP2D6 genotype assignment caused by loss of heterozygosity in tumor tissue

597

Background: The clinical importance of CYP2D6 genotype as predictor of tamoxifen efficacy is still unclear. Recent genotyping studies on CYP2D6 using DNA derived from tumor blocks have been criticized because loss of heterozygosity (LOH) in tumors may lead to false genotype assignment. Methods: Postmenopausal early breast cancer patients who were randomized to receive tamoxifen, followed by exemestane in the Tamoxifen Exemestane Adjuvant Multinational trial (TEAM) were genotyped for 5 CYP2D6 variant alleles. CYP2D6 genotypes and phenotypes were related to disease free survival during tamoxifen use (DFS-t) in 731 patients. By analyzing three microsatellites flanking the CYP2D6 gene, patients whose genotyping results were potentially affected by LOH were excluded. Results: Analysis of the CYP2D6 alleles and the microsatellite markers demonstrated heterozygosity for at least one of the CYP2D6 alleles or microsatellite markers in 97.7% of patients with a specified CYP2D6 phenotype. The 14 patients (2.3%) with a homozygous CYP2D6 genotype in which no heterozygosity could be demonstrated for the microsatellite markers were excluded from the analysis. No association was found between the CYP2D6 genotype or predicted phenotype and DFS-t. Conclusions: In postmenopausal early breast cancer patients treated with adjuvant tamoxifen followed by exemestane neither CYP2D6 genotype nor phenotype was associated with DFS-t. This is in accordance with two recent studies in the BIG1-98 and ATAC trials. Our study is the first CYP2D6 association study using DNA from paraffin embedded tumor tissue in which potentially false interpretation of genotyping results because of LOH was excluded.

Pharmacokinetics (PK) of panitumumab in a single patient with metastatic colorectal cancer (mCRC) and liver dysfunction

594

Background: Panitumumab is used for the treatment of metastatic KRAS wild type (WT) colorectal cancer (mCRC). It is likely that many of these patients will present with liver metastases and some with liver dysfunction. The pharmacokinetics in patients with hepatic impairment are unknown and dosage adjustments are undetermined. Here, we present a case of a patient with progressive mCRC and liver dysfunction. Methods: A heavily pre-treated KRAS WT mCRC patient with liver disease Child-Pugh class B was treated with two-weekly 6 mg/kg panitumumab. The patient received 2 doses of 490 mg iv panitumumab after which progressive disease was documented. Toxicities were graded using CTCAEv4.0. Serum samples were collected and panitumumab concentrations were determined using a validated immunoassay. PK parameters after the first dose, including dose-normalized AUC from time zero–day 14, clearance (CL), and elimination half-life (T1/2), were estimated via trapezoidal non compartmental methods. Data was compared to historical data from a normal population as reported by Stephenson (Clin Colorectal Cancer 2009). Values within the range of the mean ± 1 standard deviation (SD) were considered not deviant. Results: Calculated AUC after the first dose of 6 mg/kg panitumumab in this patient with hepatic dysfunction was 877 μg*day/mL (Stephenson’s cohort 1: 744 ± 195 μg*day/mL). Estimated T1/2was 3.58 days (5.28 ± 1.90 days) and CL was 6.9 mL/day/kg (8.21 ± 3.79 mL/day/kg). Estimated PK parameters during the first cycle were inside reported mean ± 1 SD of historical controls without liver dysfunction. No toxicity was reported during treatment, particularly, no diarrhea and skin toxicity. Conclusions: The pharmacokinetics of panitumumab in this patient suffering from colorectal cancer with liver dysfunction Child-Pugh class B was similar when compared to patients with adequate liver functions. Moreover, no substantial toxicity was detected. The here presented data may help clinical decision making in real life practice. Two-weekly panitumumab monotherapy seems to be safely applicable in patients with KRAS WT mCRC and hepatic dysfunction without the need for dose adjustments.

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.

Association of the genetic variants in the nucleotide excision repair genes XPA and XPC with cisplatin-induced hearing loss in patients with osteosarcoma

10077

Background: Cisplatin is a widely used and effective chemotherapeutic agent in the treatment of osteosarcoma. However, cisplatin-induced ototoxicity is a serious problem, affecting more than 60% of patients and compromising language and cognitive development. Unfortunately, individuals at risk to develop ototoxicity cannot be identified upfront. Genetic variants in genes involved in the metabolism of cisplatin may predispose to cisplatin-induced hearing loss and help to identify patients at risk. Methods: In a candidate gene pathway approach, we selected 224 SNPs in 30 candidate genes related to Platinum-DNA repair pathways and genotyped for a discovery group of 105 patients with osteosarcoma for these variants. Cisplatin-induced ototoxicity (n = 47), defined as the development of grade 2–4 hearing impairment using Common Terminology Criteria for Adverse Events (CTCAE version 3), showing a hearing loss of >25 dB at frequencies of 4–8 kHz, was associated with genetic variation. A replication study was performed in a independent cohort of 51 patients with osteosarcoma. Genotyping was performed using the Illumina GoldenGate assay. Association analysis and meta-analysis were performed using the whole genome association analysis toolset PLINK. Results: In the discovery cohort a total of 13 SNPs were significantly (p value < 0.05) associated with ototoxicity. Upon meta-analysis, addition of the replication set resulted in lower p-values for 2 SNPs. The two SNPs showing a strong association with hearing loss in patients with osteosarcoma were rs2805835 in the gene XPA (p-value 0.01, OR=2.7 (95%CI: 1.20-6.15) and rs2227999 in XPC (p-value 0.02; OR=3.2 (95% CI:1.19-8.80). Conclusions: The Nucleotide Excision Repair (NER) genes XPA and XPC form an important molecular mechanism by which cisplatin DNA adducts can be repaired and it has recently been shown that these genes have a high expression in the cochlea. Our data suggest that genetic variants in these genes, may contribute to cisplatin ototoxicity. This study should be viewed as the first step in the development of genetic markers to predict cisplatin-induced ototoxicity in individual patients.

Genetic variation in CYP19A1 and response to exemestane: Survival in early breast cancer in the Dutch TEAM trial

10518

Background: In patients with endocrine-sensitive breast cancer treated with adjuvant aromatase inhibitors (AI) it is unclear which patients will develop a recurrence and who will benefit from AI’s. Variations in the aromatase gene (CYP19A1) are associated with altered estrogen levels and altered aromatase activity. The aim of this study was to examine the effect of SNPs in the CYP19A1 gene on survival in a prospective cohort of breast cancer patients treated with adjuvant exemestane. Methods: Patients of whom tissue was available and who were treated with five years of exemestane were selected from the Tamoxifen Exemestane Adjuvant Multinational (TEAM) trial. DNA was isolated from tumor samples and 30 SNPs were identified using a tagging SNP approach, aiming for 80% coverage of CYP19A1. Genotypes were determined with taqman assays. Primary endpoint of the study was relapse-free survival (RFS) and secondary endpoint was overall survival (OS). A Kaplan-Meier analysis was performed and Cox proportional hazards models assessed survival differences. Analyses were adjusted for age at diagnosis, tumor size, nodal status, histological grade, surgery, adjuvant radiotherapy and chemotherapy. Results: 807 patients were included in the analyses and genotypes were obtained in 722 cases. A significant association with worse RFS was found with two SNPs: rs7176005 and rs16964211, showing hazard ratios (HR) of 3.48 and 5.42 for the homozygeous variant types respectively. These SNPs, as well as a third SNP, rs6493497, were also significantly associated with OS (HR 5.87, 5.3 and 3.36 respectively). Conclusions: Germline variations in the CYP19A1 gene are related to a worse outcome in early breast cancer patients treated with exemestane. These findings may contribute to the individualization of hormonal therapy in breast cancer. The relation between RFS and SNP’s in CYP19A1. [Table: see text]

Common polymorphisms in the estrogen receptor-1 may determine risk of hot flashes in early breast cancer patients using tamoxifen

526

Background: In breast cancer patients the occurrence of hot flashes as common side effect of tamoxifen therapy may be associated with effective estrogen receptor antagonism dependent on genetic variations of metabolic enzymes and the estrogen receptor. Methods: 742 early breast cancer patients who were randomized to receive tamoxifen, followed by exemestane after 2.5 to 3 years within the Tamoxifen Exemestane Adjuvant Multinational (TEAM) Trial were genotyped for 30 germ line genetic variants of 11 enzymes that are involved in the tamoxifen metabolism and the estrogen receptor 1 (ESR1). These genetic variants were related to the occurrence of hot flashes during the first year of tamoxifen use (primary aim) and during the complete tamoxifen treatment period (secondary aim). A multivariable logistic regression was used to adjust for age and adjuvant chemotherapy. Results: No genetic variant was associated with the occurrence of hot flashes during the first year. Higher age was related to a lower incidence of hot flashes in the first year (adjusted odds ratio 0.94, 95% CI 0.92-0.96; p<0.001). The ESR1 PvuII XbaI CG haplotype (CG/CG vs CG/other + other/other: adjusted odds ratio 0.44, 95% CI 0.21-0.92; p=0.03), ESR1 PvuII XbaI TA haplotype (TA/TA + TA/other vs other/other: adjusted odds ratio 1.86, 95% CI 1.09-3.14; p=0.02) and age (adjusted odds ratio 0.94, 95% CI 0.92-0.97; p<0.001) were associated with the occurrence of hot flashes during the total tamoxifen treatment period. No association was found between the CYP2D6 predicted phenotype and hot flashes. Conclusions: Common polymorphisms in the estrogen receptor-1 might help to predict the occurrence of hot flashes in breast cancer patients treated with adjuvant tamoxifen. If replicated, this may provide clinicians with a tool to offer more personalized hormonal therapy.

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.

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.

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.