Jos H Beijnen

Slotervaartziekenhuis, Amsterdamo, North Holland, Netherlands

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Publications (794)3051.71 Total impact

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    ABSTRACT: Recently, there has been a renewed interest in the development of new drugs for the treatment of leishmaniasis. This has spurred the need for pharmacodynamic markers to monitor and compare therapies specifically for visceral leishmaniasis, in which the primary recrudescence of parasites is a particularly long-term event that remains difficult to predict. We performed a systematic review of studies evaluating biomarkers in human patients with visceral, cutaneous, and post-kala-azar dermal leishmaniasis, which yielded a total of 170 studies in which 53 potential pharmacodynamic biomarkers were identified. In conclusion, the large majority of these biomarkers constituted universal indirect markers of activation and subsequent waning of cellular immunity and therefore lacked specificity. Macrophage-related markers demonstrate favorable sensitivity and times to normalcy, but more evidence is required to establish a link between these markers and clinical outcome. Most promising are the markers directly related to the parasite burden, but future effort should be focused on optimization of molecular or antigenic targets to increase the sensitivity of these markers. In general, future research should focus on the longitudinal evaluation of the pharmacodynamic biomarkers during treatment, with an emphasis on the correlation of studied biomarkers and clinical parameters.
    Antimicrobial Agents and Chemotherapy 12/2015; 59(1):1-14. DOI:10.1128/AAC.04298-14 · 4.48 Impact Factor
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    ABSTRACT: Purpose: Fluoropyrimidines are frequently prescribed anticancer drugs. A polymorphism in the fluoropyrimidine metabolizing enzyme dihydropyrimidine dehydrogenase (DPD; ie, DPYD*2A) is strongly associated with fluoropyrimidine-induced severe and life-threatening toxicity. This study determined the feasibility, safety, and cost of DPYD*2A genotype-guided dosing. Patients and methods: Patients intended to be treated with fluoropyrimidine-based chemotherapy were prospectively genotyped for DPYD*2A before start of therapy. Variant allele carriers received an initial dose reduction of ≥ 50% followed by dose titration based on tolerance. Toxicity was the primary end point and was compared with historical controls (ie, DPYD*2A variant allele carriers receiving standard dose described in literature) and with DPYD*2A wild-type patients treated with the standard dose in this study. Secondary end points included a model-based cost analysis, as well as pharmacokinetic and DPD enzyme activity analyses. Results: A total of 2,038 patients were prospectively screened for DPYD*2A, of whom 22 (1.1%) were heterozygous polymorphic. DPYD*2A variant allele carriers were treated with a median dose-intensity of 48% (range, 17% to 91%). The risk of grade ≥ 3 toxicity was thereby significantly reduced from 73% (95% CI, 58% to 85%) in historical controls (n = 48) to 28% (95% CI, 10% to 53%) by genotype-guided dosing (P < .001); drug-induced death was reduced from 10% to 0%. Adequate treatment of genotype-guided dosing was further demonstrated by a similar incidence of grade ≥ 3 toxicity compared with wild-type patients receiving the standard dose (23%; P = .64) and by similar systemic fluorouracil (active drug) exposure. Furthermore, average total treatment cost per patient was lower for screening (€2,772 [$3,767]) than for nonscreening (€2,817 [$3,828]), outweighing screening costs. Conclusion: DPYD*2A is strongly associated with fluoropyrimidine-induced severe and life-threatening toxicity. DPYD*2A genotype-guided dosing results in adequate systemic drug exposure and significantly improves safety of fluoropyrimidine therapy for the individual patient. On a population level, upfront genotyping seemed cost saving.
    Journal of Clinical Oncology 11/2015; DOI:10.1200/JCO.2015.63.1325 · 18.43 Impact Factor
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    ABSTRACT: Treatment with monoclonal antibodies is becoming increasingly important in clinical oncology. These antibodies specifically inhibit signaling pathways in tumor growth and/or induce immunological responses against tumor cells. By combining monoclonal antibodies several pathways may be targeted simultaneously, potentially leading to additive or synergistic effects. Theoretically, antibodies are very suitable for use in combination therapy, because of limited overlapping toxicity and lack of pharmacokinetic interactions. In this article an overview is given of preclinical and clinical data on twenty-five different combinations of antibodies in oncology. Some of these combinations have proven clinical benefit, for example the combination of trastuzumab and pertuzumab in HER2-positive breast cancer, which exemplifies an additive or synergistic effect on antitumor activity in clinical studies and the combination of nivolumab and ipilimumab, which results in significant increases in progression-free and overall survival in patients with advanced melanoma. However, other combinations may lead to unfavorable results, such as bevacizumab with cetuximab or panitumumab in advanced colorectal cancer. These combinations result in shorter progression-free survival and increased toxicity compared to therapy with a single antibody. In summary, the different published studies showed widely varying results, depending on the combination of antibodies, indication and patient population. More preclinical and clinical studies are necessary to unravel the mechanisms behind synergistic or antagonistic effects of combining monoclonal antibodies. Most research on combination therapies is still in an early stage, but it is expected that for several tumor types the use of combination therapy of antibodies will become standard of care in the near future.
    Cancer Treatment Reviews 11/2015; DOI:10.1016/j.ctrv.2015.10.008 · 7.59 Impact Factor
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    ABSTRACT: Purpose: The prognosis of gastroesophageal cancer is poor, and current regimens are associated with limited efficacy. The purpose of this study was to explore the safety and preliminary efficacy of docetaxel, oxaliplatin plus capecitabine for advanced cancer of the stomach or the gastroesophageal junction (GEJ). Secondary objectives included pharmacokinetic and pharmacogenetic analyses. Methods: Patients were treated in escalating dose levels with docetaxel and oxaliplatin (both on day 1), plus capecitabine b.i.d. on days 1-14 every 3 weeks, to determine the dose-limiting toxicity and maximum tolerated dose (MTD). An expansion cohort was treated at the MTD. A total of ten polymorphisms in pharmacokinetic and pharmacodynamic candidate genes were analyzed and tested for association with treatment outcome. Results: A total of 34 evaluable patients were enrolled. The MTD was docetaxel 50 mg/m(2), oxaliplatin 100 mg/m(2) plus capecitabine 850 mg/m(2) b.i.d. The median number of treatment cycles was 6 (range 2-8). Grade ≥ 3 toxicities included neutropenia (24 %), leukocytopenia (15 %), febrile neutropenia (12 %), fatigue (9 %) and diarrhea (6 %). The overall response rate was 45 %; two patients achieved a complete response. Median progression-free survival and overall survival were 6.5 months (95 % CI 5.4-7.6) and 11.0 months (95 % CI 7.9-14.1), respectively. The polymorphisms ERCC1 354C>T, TYMS 1053C>T and rs2612091 in ENOSF1 were associated with severe toxicity; ERCC1 354C>T and ERCC2 2251A>C were associated with poor progression-free survival. Conclusion: Docetaxel, oxaliplatin plus capecitabine are a well-tolerable, safe and effective treatment regimen for patients with advanced cancer of the stomach or GEJ. Pharmacogenetic markers in pharmacokinetic and pharmacodynamic candidate genes may be predictive for treatment outcome.
    Cancer Chemotherapy and Pharmacology 10/2015; DOI:10.1007/s00280-015-2872-y · 2.77 Impact Factor

  • The Lancet Oncology 10/2015; DOI:10.1016/S1470-2045(15)00286-7 · 24.69 Impact Factor
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    ABSTRACT: A validated simple, fast and sensitive bio-analytical assay for ibrutinib and its dihydrodiol metabolite in human and mouse plasma was set up. Sample preparation was performed by protein precipitation, and addition of the respective deuterated internal standards, followed by LC-MS/MS analysis. Separation was performed on a 3.5μm particle-size, bridged ethylene hybrid column with gradient elution by 0.1% v/v formic acid and acetonitrile. The full eluate was transferred to an electrospray interface in positive ionization mode, and subsequently analyzed by a triple quadrupole mass spectrometer by selected reaction monitoring. The assay was validated in a 5-5000 ng/ml calibration range. Both ibrutinib and dihydrodiol-ibrutinib were deemed stable under refrigerated or frozen storage conditions. At room temperature, ibrutinib showed a not earlier described instability, and revealed rapid degradation at 37°C. Finally, the assay was used for a pharmacokinetic study of plasma levels in treated FVB mice.
    Journal of pharmaceutical and biomedical analysis 10/2015; 118. DOI:10.1016/j.jpba.2015.10.033 · 2.98 Impact Factor
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    ABSTRACT: We aimed to clarify the roles of the multidrug transporters ABCB1 and ABCG2 in oral availability and brain accumulation of ceritinib, an oral anaplastic lymphoma kinase (ALK) inhibitor used to treat metastatic non-small cell lung cancer (NSCLC) after progression on crizotinib. Importantly, NSCLC is prone to form brain metastases. Transport of ceritinib by human (h) ABCB1 or hABCG2 or mouse (m) Abcg2 was assessed in vitro. To study the single and combined roles of Abcb1a/1b and Abcg2 in ceritinib disposition in vivo, we used appropriate knockout mouse strains. Ceritinib was very efficiently transported by hABCB1, and efficiently by hABCG2 and mAbcg2 in vitro, and transport was specifically inhibited by the ABCB1 inhibitor zosuquidar and ABCG2 inhibitor Ko143, respectively. Absorption and 24-h oral availability were not significantly affected by the absence of Abcb1 and/or Abcg2, but the brain concentrations were greatly increased (>38-fold) in Abcb1a/1b(-/-) mice at 3 and 24h after oral administration of 20mg/kg ceritinib. The brain concentrations increased another ∼3-fold (to >90-fold) in Abcb1a/1b;Abcg2(-/-) mice, indicating that there was a significant additional effect of Abcg2-mediated transport of ceritinib as well in vivo. Overall, brain accumulation, but not the 24-h oral availability of ceritinib were profoundly restricted by Abcb1a/1b and Abcg2, with Abcb1a/1b being the dominant efflux protein. Our data suggest that coadministration of ceritinib with a dual ABCB1 and ABCG2 inhibitor may improve treatment of brain (micro) metastases positioned behind a functionally intact blood-brain barrier, and possibly also of tumors resistant to ceritinib due to ABCB1 or ABCG2 overexpression.
    Pharmacological Research 09/2015; 102. DOI:10.1016/j.phrs.2015.09.003 · 4.41 Impact Factor
  • C. Lamoth · M. De Groot · J. Van Campen · H. van der Jagt · J.H. Beijnen ·

    European geriatric medicine 09/2015; 6:S68-S69. DOI:10.1016/S1878-7649(15)30238-2 · 0.73 Impact Factor
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    ABSTRACT: We aimed to clarify the roles of the multidrug-detoxifying proteins ABCB1, ABCG2, ABCC2, and CYP3A in oral availability and brain accumulation of cabazitaxel, a taxane developed for improved therapy of docetaxel-resistant prostate cancer. Cabazitaxel pharmacokinetics were studied in Abcb1a/1b, Abcg2, Abcc2, Cyp3a, and combination knockout mice. We found that human ABCB1, but not ABCG2, transported cabazitaxel in vitro. Upon oral cabazitaxel administration, total plasma levels were greatly increased due to binding to plasma carboxylesterase Ces1c, which is highly upregulated in several knockout strains. Ces1c inhibition and in vivo hepatic Ces1c knockdown reversed these effects. Correcting for Ces1c effects, Abcb1a/1b, Abcg2, and Abcc2 did not restrict cabazitaxel oral availability, whereas Abcb1a/1b, but not Abcg2, dramatically reduced cabazitaxel brain accumulation (>10-fold). Coadministration of the ABCB1 inhibitor elacridar completely reversed this brain accumulation effect. After correction for Ces1c effects, Cyp3a knockout mice demonstrated a strong (6-fold) increase in cabazitaxel oral availability, which was completely reversed by transgenic human CYP3A4 in intestine and liver. Cabazitaxel markedly inhibited mouse Ces1c, but human CES1 and CES2 only weakly. Ces1c upregulation can thus complicate preclinical cabazitaxel studies. In summary, ABCB1 limits cabazitaxel brain accumulation and therefore potentially therapeutic efficacy against (micro)metastases or primary tumors positioned wholly or partly behind a functional blood-brain barrier. This can be reversed with elacridar coadministration, and similar effects may apply to ABCB1-expressing tumors. CYP3A4 profoundly reduces the oral availability of cabazitaxel. This may potentially be greatly improved by coadministering ritonavir or other CYP3A inhibitors, suggesting the option of patient-friendly oral cabazitaxel therapy.
    Molecular Pharmaceutics 08/2015; DOI:10.1021/acs.molpharmaceut.5b00470 · 4.38 Impact Factor

  • Current Colorectal Cancer Reports 08/2015; DOI:10.1007/s11888-015-0288-z
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    ABSTRACT: Computerized Adaptive Testing (CAT) of cognitive function, selects for every individual patient, only items of appropriate difficulty to estimate his or her level of cognitive impairment. Therefore, CAT has the potential to combine brevity with precision. We retrospectively examined the evaluation of treatment effects of cholinesterase inhibitors by CAT using longitudinal data from 643 patients from a Dutch teaching hospital who were diagnosed with Alzheimer disease or Lewy Body disease. The Cambridge Cognitive Examination (CAMCOG) was administered before treatment initiation and after intervals of six months of treatment. A previously validated CAT was simulated using 47 CAMCOG items. Results demonstrated that the CAT required a median number of 17 items (inter-quartile range 16–20), or a corresponding 64% test reduction, to estimate patients’ global cognitive impairment levels. At the same time, intraclass correlations between global cognitive impairment levels as estimated by CAT or based on all 47 CAMCOG items, ranged from 0.93 at baseline to 0.91–0.94 at follow-up measurements. Slightly more people had substantial decline on the original CAMCOG (N = 31/285, 11%) than on the CAT (N = 17/285, 6%). We conclude that CAT saves time, does not lose much precision, and therefore deserves a role in the evaluation of treatment effects in dementia. Copyright © 2015 John Wiley & Sons, Ltd.
    08/2015; DOI:10.1002/mpr.1484
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    ABSTRACT: Docetaxel (Taxotere®) is currently used intravenously as an anticancer agent and is primarily metabolized by Cytochrome P450 3A (CYP3A). The HIV protease inhibitor ritonavir, a strong CYP3A4 inhibitor, decreased first-pass metabolism of orally administered docetaxel. Anticancer effects of ritonavir itself have also been described. We here aimed to test whether ritonavir co-administration could decrease intratumoral metabolism of intravenously administered docetaxel and thus increase the antitumor activity of docetaxel in an orthotopic, immunocompetent mouse model for breast cancer. Spontaneously arising K14cre;Brca1(-/-) ;p53(-/-) mouse mammary tumors were orthotopically implanted in syngeneic mice lacking Cyp3a (Cyp3a(-/-) ) to limit ritonavir effects on systemic docetaxel clearance. Over three weeks, docetaxel (20 mg/kg) was administered intravenously once weekly, with or without ritonavir (12.5 mg/kg) administered orally for 5 days per week. Untreated mice were used as control for tumor growth. Ritonavir treatment alone did not significantly affect the median time of survival (14 vs 10 days). Median time of survival in docetaxel-treated mice was 54 days. Ritonavir co-treatment significantly increased this to 66 days, and substantially reduced relative average tumor size, without altering tumor histology. Concentrations of the major docetaxel metabolite M2 in tumor tissue were reduced by ritonavir co-administration, whereas tumor RNA expression of Cyp3a was unaltered. In this breast cancer model, we observed no direct antitumor effect of ritonavir alone, but we found enhanced efficacy of docetaxel treatment when combined with ritonavir. Our data therefore suggest that decreased docetaxel metabolism inside the tumor as a result of Cyp3a inhibition contributes to increased antitumor activity. This article is protected by copyright. All rights reserved. © 2015 UICC.
    International Journal of Cancer 08/2015; DOI:10.1002/ijc.29812 · 5.09 Impact Factor
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    ABSTRACT: To determine the health-related quality of life (HRQOL) of overweight and obese multi-ethnic children compared with normal-weight children; and to investigate differences in HRQOL between self- and parent-proxy reports and ethnic groups. Prospective cross-sectional study. Out-patient clinic where children and their parents filled out a validated HRQOL questionnaire (KIDSCREEN-52) and height, weight, waist circumference and fat percentage were measured. Overweight and obese children, aged 8-18 years (mean BMI Z-score 3·2 (sd 0·6)), from the obesity out-patient clinic. Three hundred and eight self- and 213 parent-proxy reported questionnaires were completed. Global HRQOL and the Physical Wellbeing, Moods & Emotions and Self-Perception subscales were markedly reduced in our multi-ethnic obese cohort, relative to the Dutch reference values. Parent proxies reported significantly lower on the global HRQOL and the Physical Wellbeing, Moods & Emotions and Bullying subscales. In Caucasian children, multivariate analyses showed that BMI was associated with the quality-of-life subscales Moods & Emotions, Self-Perception and Bullying. HRQOL was markedly reduced in our multi-ethnic overweight and obese out-patient clinic cohort, with significantly lower parent-proxy scores compared with self-reported scores. We believe intervention programmes aiming to improve HRQOL should be directed to both parents and children, while ethnic-specific programmes to enhance HRQOL seem of less importance.
    Public Health Nutrition 07/2015; DOI:10.1017/S1368980015002074 · 2.68 Impact Factor
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    ABSTRACT: The fluoropyrimidines act by inhibiting thymidylate synthase (TS). Recent studies have shown that patients' risk of severe fluoropyrimidine-associated toxicity is affected by polymorphisms in the 5'-untranslated region of TYMS, the gene encoding TS. A G>C substitution in the promoter enhancer region of TYMS, rs183205964 (known as the 2RC allele), markedly reduces TS activity in vitro, but its clinical relevance is unknown. We determined rs183205964 in 1605 patients previously enrolled in a prospective multicenter study. Associations between putative low TS expression genotypes (3RC/2RC, 2RG/2RC, and 2RC/2RC) and severe toxicity were investigated using univariable and multivariable logistic regression. Activity of TS and TYMS gene expression were determined in peripheral blood mononuclear cells (PBMCs) of a patient carrying genotype 2RC/2RC and of a control group of healthy individuals. Among 1605 patients, 28 patients (1.7%) carried the 2RC allele. Twenty patients (1.2%) carried a risk-associated genotype (2RG/2RC, n=13; 3RC/2RC, n=6; and 2RC/2RC, n=1), the eight remaining patients had genotype 3RG/2RC. Early severe toxicity and toxicity-related hospitalization were significantly more frequent in risk-associated genotype carriers (OR 3.0, 95%CI 1.04-8.93, p=0.043 and OR 3.8, 95%CI 1.19-11.9, p=0.024, respectively, in multivariable analysis). The patient with genotype 2RC/2RC was hospitalized twice and had severe febrile neutropenia, diarrhea, and hand-foot syndrome. Baseline TS activity and gene expression in PBMCs of this patient, and a healthy individual with the 2RC allele, were found to be within the normal range. This study suggests that patients carrying rs183205964 are at strongly increased risk of severe, potentially life-threatening, toxicity when treated with fluoropyrimidines. This article is protected by copyright. All rights reserved. © 2015 UICC.
    International Journal of Cancer 07/2015; 138(1). DOI:10.1002/ijc.29694 · 5.09 Impact Factor
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    ABSTRACT: Olaparib (AZD2281), a PARP-1/2 inhibitor, has been extensively investigated in clinical trials. However, limited clinical data are available about its long-term safety and anti-tumour activity. Patients had first participated in a phase I study of olaparib combined with carboplatin and/or paclitaxel. They continued with olaparib monotherapy in their best interest if they failed to tolerate the combination due to the treatment-related adverse events (TRAEs). Safety data were collected by physical examination and regular laboratory evaluations. Disease evaluations were performed by CT scan. At data cutoff, 21 patients were included; 10 with breast, 9 with ovarian and 2 with fallopian tube cancer of whom 16 patients had a BRCA mutation (13 BRCA1; 3 BRCA2). TRAEs were mostly haematological and most prominent shortly after switching from combination to monotherapy, probably due to carry-over effects of chemotherapy. Over time, both severity and frequency of TRAEs decreased. Responses to olaparib were durable with a median treatment duration of 52 (range 7-183) weeks. In total, nine (43%) patients were still on study at data cutoff. Continued long-term daily olaparib was found to be safe and tolerable. Encouragingly, patients who showed a favourable response on earlier combination therapy maintained this response on olaparib monotherapy.British Journal of Cancer advance online publication, 16 July 2015; doi:10.1038/bjc.2015.256
    British Journal of Cancer 07/2015; 113(3). DOI:10.1038/bjc.2015.256 · 4.84 Impact Factor
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    ABSTRACT: Introduction Palbociclib is a cyclin dependent kinase (CDK) 4/6 inhibitor with nanomolar potency and was recently approved for treatment of breast cancer. The drug may also be useful in glioblastoma (GBM) and diffuse intrinsic pontine gliomas (DIPG), which often have an activated CDK4/6-retinoblastoma signaling pathway. However, GBM and DIPG spread widely into the surrounding brain, which calls for a CDK4/6 inhibitor with sufficient blood-brain barrier penetration. Methods We first performed in vitro transwell assays and demonstrate that palbociclib is a substrate of both P-gp and BCRP. Next, we conducted pharmacokinetic studies using wildtype, Abcg2(-/-), Abcb1a/b(-/-) and Abcg2; Abcb1a/b(-/-) mice. Results The plasma levels were about 3000 and 500 nM and similar in all genotypes at 1 and 4 h after i.v. administration of 10 mg/kg. At 4 h the brain-to-plasma ratios were 0.3 in WT and Abcg2(-/-) mice versus 5.5 and 15 in Abcb1a/b(-/-) and Abcg2; Abcb1a/b(-/-) mice, respectively. The oral bioavailability of palbociclib was high (63 %) in WT mice and increased only modestly and non-significantly in Abcg2; Abcb1a/b(-/-) mice. The plasma level after oral dosing of 150 mg/kg was already much higher than observed in patients (200-400 nM) and exceeded 2500 nM for up to 24 h. This latter dose is commonly used in preclinical studies, which calls into question their predictive value as they were conducted at dose levels causing a clinically non-relevant systemic drug exposure. Conclusion Thus, the brain penetration of palbociclib is restricted by P-gp and BCRP, which may restrict the efficacy against GBM and DIPG. Moreover, preclinical studies with this agent should be conducted at a more clinically relevant dose level.
    Investigational New Drugs 07/2015; 33(5). DOI:10.1007/s10637-015-0266-y · 2.92 Impact Factor

  • Therapeutic drug monitoring 05/2015; DOI:10.1097/FTD.0000000000000224 · 2.38 Impact Factor
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    ABSTRACT: The antiestrogenic drug tamoxifen is widely used in the treatment of estrogen receptor-α-positive breast cancer and substantially decreases recurrence and mortality rates. However, high interindividual variability in response is observed, calling for a personalized approach to tamoxifen treatment. Tamoxifen is bioactivated by cytochrome P450 (CYP) enzymes such as CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4/5, resulting in the formation of active metabolites, including 4-hydroxy-tamoxifen and endoxifen. Therefore, polymorphisms in the genes encoding these enzymes are proposed to influence tamoxifen and active tamoxifen metabolites in the serum and consequently affect patient response rates. To tailor tamoxifen treatment, multiple studies have been performed to clarify the influence of polymorphisms on its pharmacokinetics and pharmacodynamics. Nevertheless, personalized treatment of tamoxifen based on genotyping has not yet met consensus. This article critically reviews the published data on the effect of various genetic polymorphisms on the pharmacokinetics and pharmacodynamics of tamoxifen, and reviews the clinical implications of its findings. For each CYP enzyme, the influence of polymorphisms on pharmacokinetic and pharmacodynamic outcome measures is described throughout this review. No clear effects on pharmacokinetics and pharmacodynamics were seen for various polymorphisms in the CYP encoding genes CYP2B6, CYP2C9, CYP2C19 and CYP3A4/5. For CYP2D6, there was a clear gene-exposure effect that was able to partially explain the interindividual variability in plasma concentrations of the pharmacologically most active metabolite endoxifen; however, a clear exposure-response effect remained controversial. These controversial findings and the partial contribution of genotype in explaining interindividual variability in plasma concentrations of, in particular, endoxifen, imply that tailored tamoxifen treatment may not be fully realized through pharmacogenetics of metabolizing enzymes alone.
    Clinical Pharmacokinetics 05/2015; 54(8). DOI:10.1007/s40262-015-0273-3 · 5.05 Impact Factor
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    ABSTRACT: Enhancer of Zeste Homolog 2 (EZH2) has emerged as a promising therapeutic target for treatment of a broad spectrum of tumors including gliomas. We explored the interactions of five novel, structurally similar EZH2 inhibitors (EPZ005687, EPZ-6438, UNC1999, GSK343 and GSK126) with P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2). The compounds were screened by in vitro transwell assays and EPZ005687, EPZ-6438 and GSK126 were further tested in vivo using wild-type (WT), Abcb1 and/or Abcg2 knockout mice. All EZH2 inhibitors are transported by P-gp and BCRP, although in vitro the transporter affinity of GSK126 was obscured by very low membrane permeability. Both P-gp and Bcrp1 restrict the brain penetration of EPZ005687 and GSK126, whereas the brain accumulation of EPZ-6438 is limited by P-gp only and efflux of EPZ-6438 was completely abrogated by elacridar. Intriguingly, an unknown factor present in all knockout mouse strains causes EPZ005687 and EPZ-6438 retention in plasma relative to WT mice, a phenomenon not seen with GSK126. In WT mice, the GSK126 tissue-to-plasma ratio for all tissues is lower than for EPZ005687 or EPZ-6438. Moreover, the oral bioavailability of GSK126 is only 0.2% in WT mice, which increase to 14.4% in Abcb1;Abcg2 knockout mice. These results are likely due to poor membrane permeability and question the clinical usefulness of GSK126. Although all tested EZH2 inhibitors are substrates of P-gp and BCRP, restricting the brain penetration and potential utility for treatment of glioma, EPZ-6438 would be the most suitable candidate of this series. This article is protected by copyright. All rights reserved. © 2015 UICC.
    International Journal of Cancer 04/2015; 137(8). DOI:10.1002/ijc.29566 · 5.09 Impact Factor

Publication Stats

20k Citations
3,051.71 Total Impact Points


  • 1991-2015
    • Slotervaartziekenhuis
      Amsterdamo, North Holland, Netherlands
  • 1988-2015
    • Utrecht University
      • • Department of Pharmaceutical Sciences
      • • Faculty of Science
      • • Division of Toxicology
      • • Division of Biomedical Analysis
      Utrecht, Utrecht, Netherlands
  • 1991-2014
    • Netherlands Cancer Institute
      • • Department of Clinical Pharmacology
      • • Department of Medical Oncology
      • • Division of Experimental Therapy
      • • Division of Molecular Biology
      Amsterdamo, North Holland, Netherlands
  • 2013
    • B.P. Koirala Institute of Health Sciences
      • Department of Biochemistry
      Dharan, Eastern Region, Nepal
  • 2012
    • Nederlands Jeugd Instituut
      Utrecht, Utrecht, Netherlands
  • 2010-2012
    • Slotervaart Ziekenhuis Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 2011
    • VU University Medical Center
      • Department of Clinical Pharmacology and Pharmacy
      Amsterdamo, North Holland, Netherlands
  • 2007
    • VU University Amsterdam
      Amsterdamo, North Holland, Netherlands
    • University of Groningen
      Groningen, Groningen, Netherlands
    • University Medical Center Utrecht
      Utrecht, Utrecht, Netherlands
    • University of Florence
      Florens, Tuscany, Italy
  • 2005
    • University of Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 2002
    • Pfizer Inc.
      New York, New York, United States
  • 1998-2000
    • Leiden University
      Leyden, South Holland, Netherlands
    • Erasmus MC
      • Department of Internal Oncology
      Rotterdam, South Holland, Netherlands
  • 1996
    • Centro de Investigación del Cáncer
      Helmantica, Castille and León, Spain