Phase I pharmacological study of continuous chronomodulated capecitabine treatment.

PURPOSE: Capecitabine is an oral pre-pro-drug of the anti-cancer drug 5-fluorouracil (5-FU). The biological activity of the 5-FU degrading enzyme, dihydropyrimidine dehydrogenase (DPD), and the target enzyme thymidylate synthase (TS), are subject to circadian rhythmicity in healthy volunteers. The aim of this study was to determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), safety, pharmacokinetics (PK) and pharmacodynamics (PD) of capecitabine therapy adapted to this circadian rhythm (chronomodulated therapy). METHODS: Patients aged ≥18 years with advanced solid tumours potentially benefitting from capecitabine therapy were enrolled. A classical dose escalation 3 + 3 design was applied. Capecitabine was administered daily without interruptions. The daily dose was divided in morning and evening doses that were administered at 9:00 h and 24:00 h, respectively. The ratio of the morning to the evening dose was 3:5 (morning: evening). PK and PD were examined on treatment days 7 and 8. RESULTS: A total of 25 patients were enrolled. The MTD of continuous chronomodulated capecitabine therapy was established at 750/1250 mg/m2/day, and was generally well tolerated. Circadian rhythmicity in the plasma PK of capecitabine, dFCR, dFUR and 5-FU was not demonstrated. TS activity was induced and DPD activity demonstrated circadian rhythmicity during capecitabine treatment. CONCLUSION: The MTD of continuous chronomodulated capecitabine treatment allows for a 20% higher dose intensity compared to the approved regimen (1250 mg/m2 bi-daily on day 1-14 of every 21-day cycle). Chronomodulated treatment with capecitabine is promising and could lead to improved tolerability and efficacy of capecitabine.

Patients homozygous for DPYD c.1129-5923C>G/haplotype B3 have partial DPD deficiency and require a dose reduction when treated with fluoropyrimidines.

PURPOSE: Dihydropyrimidine dehydrogenase (DPD) is a critical determinant of 5-fluorouracil pharmacology, and reduced activity of DPD as a result of deleterious polymorphisms in the gene encoding DPD (DPYD) can result in severe treatment-related toxicity. Dosing recommendations to individualize treatment have been provided for three DPYD variants (DPYD*2A, c.2846A>T, and c.1679T>G). A fourth variant, c.1129-5923C>G/HapB3, has been shown to increase the risk of fluoropyrimidine-associated toxicity, but little is known about the functional effects of this variant. METHODS: By performing a large retrospective screen for DPYD variants, we identified three patients who were homozygous for c.1129-5923C>G/HapB3. We describe their clinical course of treatment and analyzed DPD activity and DPYD gene expression, to provide insight into the phenotypic effects of c.1129-5923C>G/HapB3. RESULTS: DPD activity could be measured in two patients and was 4.1 and 5.4 nmol/mg/h (DPD activity 41 and 55 % compared to controls, respectively). The fluoropyrimidine dose had to be reduced during treatment in both patients. In line with partial DPD deficiency in both patients, sequence analysis of DPD cDNA demonstrated a normal-sized (wild type) cDNA fragment of 486 bp, as well as a larger-sized (mutant) 530-bp fragment containing an aberrant 44-bp insertion in intron 10. Patient three tolerated treatment well, but DPD activity measurement was not possible as the patient had deceased at the time of performing the study. CONCLUSIONS: The presented functional and clinical data indicate that the c.1129-5923C>G variant is both functionally and clinically relevant, and support an upfront dose reduction of the fluoropyrimidine starting dose in patients carrying c.1129-5923C>G homozygously.

Pronounced between-subject and circadian variability in thymidylate synthase and dihydropyrimidine dehydrogenase enzyme activity in human volunteers.

AIMS: The enzymatic activity of dihydropyrimidine dehydrogenase (DPD) and thymidylate synthase (TS) are important for the tolerability and efficacy of the fluoropyrimidine drugs. In the present study, we explored between-subject variability (BSV) and circadian rhythmicity in DPD and TS activity in human volunteers. METHODS: The BSVs in DPD activity (n = 20) in peripheral blood mononuclear cells (PBMCs) and in plasma, measured by means of the dihydrouracil (DHU) and uracil (U) plasma levels and DHU : U ratio (n = 40), and TS activity in PBMCs (n = 19), were examined. Samples were collected every 4 h throughout 1 day for assessment of circadian rhythmicity in DPD and TS activity in PBMCs (n = 12) and DHU : U plasma ratios (n = 23). In addition, the effects of genetic polymorphisms and gene expression on DPD and TS activity were explored. RESULTS: Population mean (± standard deviation) DPD activity in PBMCs and DHU : U plasma ratio were 9.2 (±2.1) nmol mg(-1) h(-1) and 10.6 (±2.4), respectively. Individual TS activity in PBMCs ranged from 0.024 nmol mg(-1) h(-1) to 0.596 nmol mg(-1) h(-1) . Circadian rhythmicity was demonstrated for all phenotype markers. Between 00:30 h and 02:00 h, DPD activity in PBMCs peaked, while the DHU : U plasma ratio and TS activity in PBMCs showed trough activity. Peak-to-trough ratios for DPD and TS activity in PBMCs were 1.69 and 1.62, respectively. For the DHU : U plasma ratio, the peak-to-trough ratio was 1.43. CONCLUSIONS: BSV and circadian variability in DPD and TS activity were demonstrated. Circadian rhythmicity in DPD might be tissue dependent. The results suggested an influence of circadian rhythms on phenotype-guided fluoropyrimidine dosing and supported implications for chronotherapy with high-dose fluoropyrimidine administration during the night.

The in-vitro effect of complementary and alternative medicines on cytochrome P450 2C9 activity.

OBJECTIVES: The aim of this study is to establish the inhibitory effects of 14 commonly used complementary and alternative medicines (CAM) on the metabolism of cytochrome P450 2C9 (CYP2C9) substrates 7-methoxy-4-trifluoromethyl coumarine (MFC) and tolbutamide. CYP2C9 is important for the metabolism of numerous drugs and inhibition of this enzyme by CAM could result in elevated plasma levels of drugs that are CYP2C9 substrates. Especially for anticancer drugs, which have a narrow therapeutic window, small changes in their plasma levels could easily result in clinically relevant toxicities. METHODS: The effects of CAM on CYP2C9-mediated metabolism of MFC were assessed in Supersomes, using the fluorometric CYP2C9 inhibition assay. In human liver microsomes (HLM) the inhibition of CYP2C9-mediated metabolism of tolbutamide was determined, using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). KEY FINDINGS: The results indicated milk thistle as the most potent CYP2C9 inhibitor. For milk thistle, silybin (main constituent of milk thistle) was mainly responsible for the inhibition of CY2C9. CONCLUSIONS: Milk thistle and green tea were confirmed as potent inhibitors of CYP2C9-mediated metabolism of multiple substrates in vitro. Clinical studies with milk thistle are recommended to establish the clinical relevance of the demonstrated CYP2C9 inhibition.

The effect of complementary and alternative medicines on CYP3A4-mediated metabolism of three different substrates: 7-benzyloxy-4-trifluoromethyl-coumarin, midazolam and docetaxel.

OBJECTIVE: Concomitant use of complementary and alternative medicine (CAM) and anticancer drugs can affect the pharmacokinetics of anticancer drugs by inhibiting the metabolizing enzyme cytochrome P450 3A4 (CYP3A4) (EC 1.14.13.157). Several in vitro studies determined whether CAM can inhibit CYP3A4, but these studies revealed contradictory results. A plausible explanation for these conflicting results is the use only of a single model CYP3A4 substrate in each study. Therefore, the objective was to determine the potential of selected CAM (ß-carotene, Echinacea, garlic, Ginkgo biloba, ginseng, grape seed extract, green tea extract, milk thistle, saw palmetto, valerian, vitamin B6, B12 and C) to inhibit CYP3A4-mediated metabolism of different substrates: 7-benzyloxy-4-trifluoromethyl-coumarin (BFC), midazolam and docetaxel. The effect of CAM on CYP3A4-mediated metabolism of an anticancer drug has never been determined before in vitro, which makes this study unique. The oncolytic CYP3A4 substrate docetaxel was used to establish the predictive value of the model substrates for pharmacokinetic interactions between CAM and anticancer drugs in vitro, and to more closely predict these interactions in vivo. METHODS: The inhibition of CYP3A4-mediated metabolism of 7-benzyloxy-4-trifluoromethyl-coumarin (BFC) by CAM was assessed in Supersomes, using the fluorometric CYP3A4 inhibition assay. In human liver microsomes (HLM) the inhibition of CYP3A4-mediated metabolism of midazolam and docetaxel was determined, using liquid-chromatography coupled to tandem mass spectrometry (LC-MS/MS). KEY FINDINGS: The results confirmed grape seed and green tea as potent inhibitors and milk thistle as moderate inhibitor of CYP3A4-mediated metabolism of BFC, midazolam and docetaxel. CONCLUSION: Clinical studies are required to determine the clinical relevance of the determined CYP3A4 inhibition by grape seed, green tea and milk thistle.

The effect of St John's wort on the pharmacokinetics of docetaxel.

BACKGROUND AND OBJECTIVE: St John's wort (SJW), a herbal antidepressant, is commonly used by cancer patients, and its component hyperforin is a known inducer of the cytochrome P450 (CYP) isoenzyme 3A4. Here, the potential pharmacokinetic interaction between SJW and the sensitive CYP3A4 substrate docetaxel was investigated. METHODS: In ten evaluable cancer patients, the pharmacokinetics of docetaxel (135 mg administered intravenously over 60 min) were compared before and after 14 days of supplementation with SJW (300 mg extract [Hyperiplant(®)] three times daily). RESULTS: SJW supplementation resulted in a statistically significant decrease in the mean area under the docetaxel plasma concentration-time curve extrapolated to infinity (AUC∞) from 3,035 ± 756 to 2,682 ± 717 ng · h/mL (P = 0.045). Furthermore, docetaxel clearance significantly increased from 47.2 to 53.7 L/h (P = 0.045) after SJW intake. The maximum plasma concentration and elimination half-life of docetaxel were (non-significantly) decreased after SJW supplementation. In addition, the incidence of docetaxel-related toxicities was lower after SJW supplementation. CONCLUSION: These results suggest that concomitant use of docetaxel and the applied SJW product should be avoided to prevent potential undertreatment of cancer patients.

The effect of grape seed extract on the pharmacokinetics of dextromethorphan in healthy volunteers.

PURPOSE: Grape seed extract (GSE) has been shown to inhibit the cytochrome P450 (CYP) 2D6 isoenzyme in vitro. To determine the clinical effect of GSE on CYP2D6, the pharmacokinetic interaction between GSE and the sensitive CYP2D6 probe dextromethorphan in healthy adult volunteers was examined. METHODS: In this open label, randomized, cross-over study, 30 subjects were assigned to cohort A or B. Both cohorts ingested 30 mg dextromethorphan hydrobromide on day 1 and day 10. Cohort A received 100 mg GSE capsules three times daily on days 8, 9 and 10, while cohort B started with GSE on day -1 until day 1. After urine collection (0-8 h) on day 1 and day 10, the urinary dextromethorphan to dextrorphan metabolic ratio was determined. RESULTS: Among 28 evaluable subjects, an increase of the urinary metabolic ratio was observed in 16 subjects (57 %). The mean metabolic ratio (± standard deviation) before and after GSE supplementation was 0.41 (± 0.56) and 0.48 (± 0.59), respectively. This result was neither statistically (P = 0.342) nor clinically [geometric mean ratio 1.10, 90 % CI (0.93-1.30)] significant. Further, the majority (73 %) of the included subjects did not experience any adverse events after intake of dextromethorphan or GSE. CONCLUSIONS: Supplementation of GSE did not significantly affect the urinary dextromethorphan to dextrorphan metabolic ratio in healthy volunteers. The results of this clinical study indicate that GSE appears to be safe to combine with drugs extensively metabolized by CYP2D6, such as dextromethorphan and tamoxifen.

The effect of Echinacea purpurea on the pharmacokinetics of docetaxel.

AIMS: The herbal medicine Echinacea purpurea (E. purpurea) has been shown to induce cytochrome P450 3A4 (CYP3A4) both in vitro and in humans. This study explored whether E. purpurea affects the pharmacokinetics of the CYP3A4 substrate docetaxel in cancer patients. METHODS: Ten evaluable cancer patients received docetaxel (135 mg, 60 min IV infusion) before intake of a commercially available E. purpurea extract (20 oral drops three times daily) and 3 weeks later after a 14 day supplementation period with E. purpurea. In both cycles, pharmacokinetic parameters of docetaxel were determined. RESULTS: Before and after supplementation with E. purpurea, the mean area under the plasma concentration-time curve of docetaxel was 3278 ± 1086 and 3480 ± 1285 ng ml(-1) h, respectively. This result was statistically not significant. Nonsignificant alterations were also observed for the elimination half-life (from 30.8 ± 19.7 to 25.6 ± 5.9 h, P = 0.56) and maximum plasma concentration of docetaxel (from 2224 ± 609 to 2097 ± 925 ng ml(-1) , P = 0.30). CONCLUSIONS: The multiple treatment of E. purpurea did not significantly alter the pharmacokinetics of docetaxel in this study. The applied E. purpurea product at the recommended dose may be combined safely with docetaxel in cancer patients.

Milk thistle's active components silybin and isosilybin: novel inhibitors of PXR-mediated CYP3A4 induction.

Because cancer is often treated with combination therapy, unexpected pharmacological effects can occur because of drug-drug interactions. Several drugs are able to cause upregulation or downregulation of drug transporters or cytochrome P450 enzymes, particularly CYP3A4. Induction of CYP3A4 may result in decreased plasma levels and therapeutic efficacy of anticancer drugs. Since the pregnane X receptor (PXR) is one of the major transcriptional regulators of CYP3A4, PXR antagonists can possibly prevent CYP3A4 induction. Currently, a limited number of PXR antagonists are available. Some of these antagonists, such as sulphoraphane and coumestrol, belong to the so-called complementary and alternative medicines (CAM). Therefore, the aim was to determine the potential of selected CAM (ß-carotene, Echinacea purpurea, garlic, Ginkgo biloba, ginseng, grape seed, green tea, milk thistle, saw palmetto, valerian, St. John's Wort, and vitamins B6, B12, and C) to inhibit PXR-mediated CYP3A4 induction at the transcriptional level, using a reporter gene assay and a real-time polymerase chain reaction assay in LS180 colon adenocarcinoma cells. Furthermore, computational molecular docking and a LanthaScreen time-resolved fluorescence resonance energy transfer (TR-FRET) PXR competitive binding assay were performed to explore whether the inhibiting CAM components interact with PXR. The results demonstrated that milk thistle is a strong inhibitor of PXR-mediated CYP3A4 induction. The components of milk thistle responsible for this effect were identified as silybin and isosilybin. Furthermore, computational molecular docking revealed a strong interaction between both silybin and isosilybin and PXR, which was confirmed in the TR-FRET PXR assay. In conclusion, silybin and isosilybin might be suitable candidates to design potent PXR antagonists to prevent drug-drug interactions via CYP3A4 in cancer patients.

Relevance of in vitro and clinical data for predicting CYP3A4-mediated herb-drug interactions in cancer patients.

The use of complementary and alternative medicines (CAM) by cancer patients is increasing. Concomitant use of CAM and anticancer drugs could lead to serious safety issues in patients. CAM have the potential to cause pharmacokinetic interactions with anticancer drugs, leading to either increased or decreased plasma levels of anticancer drugs. This could result in unexpected toxicities or a reduced efficacy. Significant pharmacokinetic interactions have already been shown between St. John's Wort (SJW) and the anticancer drugs imatinib and irinotecan. Most pharmacokinetic CAM-drug interactions, involve drug metabolizing cytochrome P450 (CYP) enzymes, in particular CYP3A4. The effect of CAM on CYP3A4 activity and expression can be assessed in vitro. However, no data have been reported yet regarding the relevance of these in vitro data for the prediction of CAM-anticancer drug interactions in clinical practice. To address this issue, a literature research was performed to evaluate the relevance of in vitro data to predict clinical effects of CAM frequently used by cancer patients: SJW, milk thistle, garlic and Panax ginseng (P. ginseng). Furthermore, in clinical studies the sensitive CYP3A4 substrate probe midazolam is often used to determine pharmacokinetic interactions. Results of these clinical studies with midazolam are used to predict pharmacokinetic interactions with other drugs metabolized by CYP3A4. Therefore, this review also explored whether clinical trials with midazolam are useful to predict clinical pharmacokinetic CAM-anticancer drug interactions. In vitro data of SJW have shown CYP3A4 inhibition after short-term exposure and induction after long-term exposure. In clinical studies using midazolam or anticancer drugs (irinotecan and imatinib) as known CYP3A4 substrates in combination with SJW, decreased plasma levels of these drugs were observed, which was expected as a consequence of CYP3A4 induction. For garlic, no effect on CYP3A4 has been shown in vitro and also in clinical studies garlic did not affect the pharmacokinetics of both midazolam and docetaxel. Milk thistle and P. ginseng predominantly showed CYP3A4 inhibition in vitro. However, in clinical studies these CAM did not cause significant pharmacokinetic interactions with midazolam, irinotecan, docetaxel and imatinib. Most likely, factors as poor pharmaceutical availability, solubility and bioavailability contribute to the lack of significant clinical interactions. In conclusion, in vitro data are useful as a first indication for potential pharmacokinetic drug interactions with CAM. However, the discrepancies between in vitro and clinical results for milk thistle and P. ginseng show that clinical studies are required for confirmation of potential interactions. At last, midazolam as a model substrate for CYP3A4, has convincingly shown to correctly predict clinical interactions between CAM and anticancer drugs.

The bioanalysis of the major Echinacea purpurea constituents dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamides in human plasma using LC-MS/MS.

Alkylamides are a group of active components of the widely used herb Echinacea purpurea (E. purpurea), which have immunostimulatory and anti-inflammatory effects. For the most abundant alkylamides, dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamides (DTAI), an LC-MS/MS assay has been developed and validated for quantification in human plasma. This assay will be used to support a clinical interaction study with E. purpurea. A 300 µL plasma aliquot underwent liquid-liquid extraction with diethylether-n-hexane (50:50, v/v). After evaporization and reconstitution in 100 µL of acetonitrile-water (50:50, v/v) 20 µL of sample were injected into the HPLC system. Chromatographic separation was achieved with a Polaris 3 C18-A column (50 mm × 2 mm ID, particle size 3 µm), a flow rate of 0.3 mL/min and isocratic elution with acetonitrile-water (50:50, v/v) containing 0.1% formic acid during the first 5 min. Hereafter, gradient elution was applied for 0.5 min, followed by restoration of the initial isocratic conditions. The total run time was 7.5 min. The assay was validated over a concentration range from 0.01 to 50 ng/mL for DTAI, with a lower limit of quantification of 0.01 ng/mL. Validation results show that DTAI can be accurately and precisely quantified in human plasma. DTAI also demonstrated to be chemically stable under relevant conditions. Finally, the applicability of this assay has been successfully demonstrated by measuring the plasma concentration of DTAI in patients after ingestion of a commercial extract of E. purpurea.

Pharmacodynamic biomarkers in model-based drug development in oncology.

INTRODUCTION: Model-based drug development (MBDD) is recognized as an initiative able to improve success rates in the development of new anti-cancer agents. The use of pharmacodynamic (PD) biomarkers may be valuable in this context. The implementation of biomarkers in MBDD in oncology is the subject of this review. METHODS: Literature was searched for articles and relevant conference abstract concerning application of biomarkers in MBDD in oncology. First, papers are discussed concerning the use of biomarkers in modeling and simulation analyses in preclinical and early clinical phases of drug development. Subsequently, articles concerning late-stage clinical drug development are discussed. RESULTS: Only a limited set of articles and conference presentations were identified. As expected, the majority of publications are concerned with targeted anti-cancer drugs. In the early development of novel anti-cancer agents, most publications are concerned to the evaluation of dosing regimens for further clinical evaluation, or the identification of the required levels of target modulation. In general, combined analysis of clinical and preclinical data provide the most informative analyses. The use of biomarkers in late-stage drug development has mainly been confined to the prediction of phase III outcome on the basis of tumor growth data obtained from phase II trials, with tumor growth as biomarker for outcome. CONCLUSION: The use of suitable biomarkers in MBDD, has shown its merits in oncology, especially in early clinical development. Considering the low number of reports in literature, we would propose a more active use of presented techniques during all developmental phases of new anticancer agents.

Liquid chromatography-tandem mass spectrometric assay for diclofenac and three primary metabolites in mouse plasma.

The first liquid chromatography-tandem mass spectrometric assay for the simultaneous determination of diclofenac, 4'-hydroxy-diclofenac, 5-hydroxy-diclofenac and diclofenac-acyl-glucuronide in mouse plasma, using a simple sample pre-treatment procedure, was developed and validated. Analytes in plasma were stabilized using acetic acid and ascorbic acid. After addition of the internal standard D(4)-diclofenac to a 10 microl sample volume and protein precipitation with acetonitrile, the supernatant was supplemented with an equal volume of water and injected into the chromatographic system. A polar embedded reversed-phase column with gradient elution using formic acid and ammonium acetate in water-methanol were used. The eluate was totally transferred into an electrospray interface with positive ionization and the analytes were quantified using triple quadrupole mass spectrometry. The assay was validated in the ranges 10-5000 ng/ml for 4'-hydroxy-diclofenac and 20-10,000 ng/ml for the other analytes, the lowest levels of these ranges (10 or 20 ng/ml) being the lower limits of quantification. Within day precisions were < or = 10%, between day precisions < or = 13% and accuracies were between 90 and 108%. The analytes were chemically stable under all relevant conditions. The assay was successfully applied in a pharmacokinetic study with diclofenac in mice.

Enhanced resolution triple-quadrupole mass spectrometry for ultra-sensitive and quantitative analysis of the investigational anticancer agent EO9 (apaziquone) and its metabolite EO5a in human and dog plasma to support (pre)-clinical studies of EOquin given intravesically.

A highly sensitive and selective liquid chromatography/tandem mass spectrometric (LC/MS/MS) method was developed to quantify the experimental anticancer agent EO9 and its metabolite EO5a in biological matrices. A 200-microL aliquot of human/dog plasma was spiked with a mixture of deuterated internal standards EO9-d3 and EO5a-d4 and extracted with 1.25 mL of ethyl acetate. Dried extracts were reconstituted in 0.1 M ammonium acetate/methanol (7:3, v/v) and 20-microL volumes were injected onto the LC system. Separation was achieved on a 150 x 2.1 mm C18 column using an alkaline eluent (1 mM ammonium hydroxide/methanol (gradient system)). The detection was performed by a Finnigan TSQ Quantum Ultra equipped with an electrospray ionization source operated in positive mode and enhanced mass resolution capability. It demonstrated improved sensitivity with a factor 10-20 for EO9 and EO5a over a 3-decades dynamic range, with acceptable accuracy and precision, when compared with the previously described assay for EO9 and EO5a, developed by our group, using an API 2000. The assay quantifies a range from 0.5 to 500 ng/mL for EO9 and EO5a using 200-microL human plasma and dog samples. The described mass resolution method was successfully applied for the evaluation of the pharmacokinetic profile of EO9 and its metabolite EO5a in human and dog plasma.

Concise review: Clinical relevance of drug drug and herb drug interactions mediated by the ABC transporter ABCB1 (MDR1, P-glycoprotein).

The importance of P-glycoprotein (P-gp) in drug-drug interactions is increasingly being identified. P-gp has been reported to affect the pharmacokinetics of numerous structurally and pharmacologically diverse substrate drugs. Furthermore, genetic variability in the multidrug resistance 1 gene influences absorption and tissue distribution of drugs transported. Inhibition or induction of P-gp by coadministered drugs or food as well as herbal constituents may result in pharmacokinetic interactions leading to unexpected toxicities or undertreatment. On the other hand, modulation of P-gp expression and/or activity may be a useful strategy to improve the pharmacological profile of anticancer P-gp substrate drugs. In recent years, the use of complementary and alternative medicine (CAM), like herbs, food, and vitamins, by cancer patients has increased significantly. CAM use substantially increases the risk for interactions with anticancer drugs, especially because of the narrow therapeutic window of these compounds. However, for most CAMs, it is unknown whether they affect metabolizing enzymes and/or drug transporter activity. Clinically relevant interactions are reported between St John's wort or grapefruit juice and anticancer as well as nonanticancer drugs. CAM-drug interactions could explain, at least in part, the large interindividual variation in efficacy and toxicity associated with drug therapy in both cancer and noncancer patients. The study of drug-drug, food-drug, and herb-drug interactions and of genetic factors affecting pharmacokinetics and pharmacodynamics is expected to improve drug safety and will enable individualized drug therapy. Disclosure of potential conflicts of interest is found at the end of this article.

Herb-drug interactions in oncology: focus on mechanisms of induction.

An increasing number of cancer patients are using complementary and alternative medicines (CAM) in combination with their conventional chemotherapeutic treatment. Considering the narrow therapeutic window of oncolytic drugs, this CAM use increases the risk of clinically relevant herb-anticancer drug interactions. Such a relevant interaction is that of St. John's wort with the anticancer drugs irinotecan and imatinib. It is, however, estimated that CAM-anticancer drug interactions are responsible for substantially more unexpected toxicities of chemotherapeutic drugs and possible undertreatment seen in cancer patients. Induction of drug-metabolizing enzymes and ATP-binding cassette drug transporters can be one of the mechanisms behind CAM-anticancer drug interactions. Induction will often lead to therapeutic failure because of lower plasma levels of the anticancer drugs, and will easily go unrecognized in cancer treatment, where therapeutic failure is common. Recently identified nuclear receptors, such as the pregnane X receptor, the constitutive androstane receptor, and the vitamin D-binding receptor, play an important role in the induction of metabolizing enzymes and drug transporters. This knowledge has already been an aid in the identification of some CAM probably capable of causing interactions with anticancer drugs: kava-kava, vitamin E, quercetin, ginseng, garlic, beta-carotene, and echinacea. Evidently, more research is necessary to prevent therapeutic failure and toxicity in cancer patients and to establish guidelines for CAM use.

Symptoms and treatment in cancer therapy-induced early menopause.

Young women with breast cancer often experience early menopause as a result of the therapy for their malignant disease. The sudden occurrence of menopause resulting from chemotherapy, oophorectomy, radiation, or gonadal dysgenesis frequently results in hot flashes that begin at a younger age and may occur at a greater frequency and intensity than hot flashes associated with natural menopause. Hormone therapy relieves symptoms effectively in 80%-90% of women who initiate treatment. This therapy, however, is generally contraindicated in estrogen-dependent cancers, such as breast cancer, because of the potentially increased risk for recurrence. Many agents have been investigated as potential means for alleviating hot flashes in survivors of breast cancer, such as progestagens, clonidine, gabapentin, and anti-depressants. Several complementary and alternative medicines frequently used by patients have also been studied. These include black cohosh, phytoestrogens, homeopathy, vitamin E, acupuncture, and behavior strategies. To support the use of one of more of these nonpharmacological or pharmacological options in the treatment of hot flashes in breast cancer patients, more evidence from well-controlled clinical trials is needed. In particular, soundly based scientific research with complementary and alternative medicine therapies is lacking. Pharmacological treatments appear to be more beneficial than nonpharmacological treatments. This article reviews the current literature to assess the epidemiology and diagnosis of hot flashes and the nonpharmacological and pharmacological options for the treatment of hot flashes, in breast cancer patients in particular. When specific treatment options have not been evaluated in breast cancer patients specifically, published data on the management of hot flashes with this modality in healthy postmenopausal women are described.

Mechanism of the pharmacokinetic interaction between methotrexate and benzimidazoles: potential role for breast cancer resistance protein in clinical drug-drug interactions.

The antifolate drug methotrexate (MTX) is transported by breast cancer resistance protein (BCRP; ABCG2) and multidrug resistance-associated protein1-4 (MRP1-4; ABCC1-4). In cancer patients, coadministration of benzimidazoles and MTX can result in profound MTX-induced toxicity coinciding with an increase in the serum concentrations of MTX and its main metabolite 7-hydroxymethotrexate. We hypothesized that benzimidazoles interfere with the clearance of MTX and/or 7-hydroxymethotrexate by inhibition of the ATP-binding cassette drug transporters BCRP and/or MRP2, two transporters known to transport MTX and located in apical membranes of epithelia involved in drug disposition. First, we investigated the mechanism of interaction between benzimidazoles (pantoprazole and omeprazole) and MTX in vitro in membrane vesicles from Sf9 cells infected with a baculovirus containing human BCRP or human MRP2 cDNA. In Sf9-BCRP vesicles, pantoprazole and omeprazole inhibited MTX transport (IC50 13 microm and 36 microm, respectively). In Sf9-MRP2 vesicles, pantoprazole did not inhibit MTX transport and at high concentrations (1 mm), it even stimulated MTX transport 1.6-fold. Secondly, we studied the transport of pantoprazole in MDCKII monolayers transfected with mouse Bcrp1 or human MRP2. Pantoprazole was actively transported by Bcrp1 but not by MRP2. Finally, the mechanism of the interaction was studied in vivo using Bcrp1-/- mice and wild-type mice. Both in wild-type mice pretreated with pantoprazole to inhibit Bcrp1 and in Bcrp1-/- mice that lack Bcrp1, the clearance of i.v. MTX was decreased significantly 1.8- to 1.9-fold compared with the clearance of i.v. MTX in wild-type mice. The conclusion is as follows: benzimidazoles differentially affect transport of MTX mediated by BCRP and MRP2. Competition for BCRP may explain the clinical interaction between MTX and benzimidazoles.