Andrew K.L. Goey

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. Johns 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 mania-like exploratory profile in genetic dopamine transporter mouse models is diminished in a familiar environment and reinstated by subthreshold psychostimulant administration

Bipolar Disorder (BD) is a neuropsychiatric disorder characterized by symptoms ranging from a hyperactive manic state to depression, with periods of relative stability, known as euthymia, in between. Although prognosis for BD sufferers remains poor, treatment development has been restricted due to a paucity of validated animal models. Moreover, most models focus on the manic state of BD with little done to characterize the longitudinal behavior of these models. We recently presented two dopamine transporter (DAT) mouse models of BD mania: genetic (DAT knockdown; KD, mice) and pharmacological (the selective DAT inhibitor GBR 12909). These models exhibit an exploratory profile consistent with the quantified exploratory profile of manic BD patients observed in the cross-species translational test, the Behavioral Pattern Monitor (BPM). To further explore the suitability of these models, we examined the effects of reduced DAT function on the behavior of mice tested after familiarization to the BPM environment. Testing with 16mg/kg GBR 12909 in familiarized mice resulted in a consistent mania-like profile. In contrast, the mania-like profile of DAT KD mice disappears in a familiar environment, with partial reinstatement elicited by the introduction of novelty. In addition, we found that a subthreshold dose of GBR 12909 (9mg/kg) reinstated the mania-like profile in DAT KD mice without affecting wildtype behavior. Thus, the mania-like exploratory profile of DAT KD mice is reduced in a familiar environment, partially reinstated with novelty, but is fully restored when administered a stimulant that is ineffective in wildtype mice. These mice may provide a model of BD from mania to euthymia and back again with stimulant treatment. Acute blockade of the DAT by GBR 12909 however, may provide a consistent model for BD mania.

Pharmacogenetics of Membrane Transporters: A Review of Current Approaches

This chapter provides a review of the pharmacogenetics of membrane transporters, including ABC transporters and OATPs. Membrane transporters are heavily involved in drug disposition, by actively transporting substrate drugs between organs and tissues. As such, polymorphisms in the genes encoding these proteins may have a significant effect on the absorption, distribution, metabolism, excretion, and activity of compounds. Although few drug transporter polymorphisms have transitioned from the bench to the bedside, this chapter discusses clinical development of transporter pharmacogenetic markers. Finally, development of SLCO1B1 genotyping to avoid statin induced adverse drug reactions is discussed as a model case for transporter pharmacogenetics clinical development.

Structural Elucidation and Synthesis of Eudistidine A: An Unusual Polycyclic Marine Alkaloid that Blocks Interaction of the Protein Binding Domains of p300 and HIF-1α

Low oxygen environments are a hallmark of solid tumors, and transcription of many hypoxia-responsive genes needed for survival under these conditions is regulated by the transcription factor HIF-1 (hypoxia-inducible factor 1). Activation of HIF-1 requires binding of its α-subunit (HIF-1α) to the transcriptional coactivator protein p300. Inhibition of the p300/HIF-1α interaction can suppress HIF-1 activity. A screen for inhibitors of the protein binding domains of p300 (CH1) and HIF-1α (C-TAD) identified an extract of the marine ascidian Eudistoma sp. as active. Novel heterocyclic alkaloids eudistidines A (1) and B (2) were isolated from the extract, and their structures assigned by spectroscopic analyses. They contain an unprecedented tetracyclic core composed of two pyrimidine rings fused with an imidazole ring. Eudistidine A (1) was synthesized in a concise four-step sequence featuring a condensation/cyclization reaction cascade between 4-(2-aminophenyl)pyrimidin-2-amine (3) and 4-methoxy-phenylglyoxal (4), while eudistidine B (2) was synthesized in a similar fashion with glyoxylic acid (5) in place of 4. Naturally occurring eudistidine A (1) effectively inhibited CH1/C-TAD binding with an IC50 of 75 μM, and synthetic 1 had similar activity. The eudistidine A (1) scaffold, which can be synthesized in a concise, scalable manner, may provide potential therapeutic lead compounds or molecular probes to study p300/HIF-1α interactions and the role these proteins play in tumor response to low oxygen conditions. The unique structural scaffolds and functional group arrays often found in natural products make these secondary metabolites a rich source of new compounds that can disrupt critical protein-protein binding events.

Sequence-Specific Pharmacokinetic and Pharmacodynamic Phase I/Ib Study of Olaparib Tablets and Carboplatin in Women's Cancer.

Purpose: Our preclinical studies showed that the PARP inhibitor, olaparib, prior to carboplatin attenuated carboplatin cytotoxicity. We evaluated sequence-specific pharmacokinetic and pharmacodynamic effects, safety, and activity of the combination. Experimental Design: Eligible patients had metastatic or recurrent womens cancer. Olaparib tablets were introduced (100 or 200 mg twice daily, days 1–7) in a 3 + 3 dose escalation with carboplatin AUC4 or 5 every 21 days, up to eight cycles, followed by olaparib 300 mg twice daily maintenance. Patients were randomly assigned to starting schedule: cohort A (olaparib days 1–7, carboplatin on day 8) or B (carboplatin on day 1, olaparib days 2–8) during cycle 1. Patients received the reversed scheme in cycle 2. Blood was collected for olaparib pharmacokinetics, platinum–DNA adducts, comet assay, and PAR concentrations. The primary objectives were to examine schedule-dependent effects on olaparib pharmacokinetics and platinum–DNA adducts. Results: A total of 77 (60 ovarian, 14 breast, and 3 uterine cancer) patients were treated. Dose-limiting toxicity was thrombocytopenia and neutropenia, defining olaparib 200 mg twice daily + carboplatin AUC4 as the MTD. Olaparib clearance was increased approximately 50% when carboplatin was given 24 hours before olaparib. In vitro experiments demonstrated carboplatin preexposure increased olaparib clearance due to intracellular olaparib uptake. Quantities of platinum–DNA adducts were not different as a function of the order of drug administration. Responses included 2 CRs and 31 PRs (46%) with a higher RR in BRCA mutation carriers compared with nonmutation carriers (68% vs. 19%). Conclusions: Tablet olaparib with carboplatin is a safe and active combination. Carboplatin preexposure causes intracellular olaparib accumulation reducing bioavailable olaparib, suggesting carboplatin should be administered prior to olaparib. Clin Cancer Res; 23(6); 1397–406. ©2016 AACR.

Herb–Drug Interactions in Oncology

1Clinical Pharmacology Program, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA; 2Division of Pharmacoepidemiology and Clinical Pharmacology, Department of Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands; 3Department of Pharmacy and Pharmacology, Slotervaart Hospital/The Netherlands Cancer Institute, Amsterdam, The Netherlands; 4Department of Clinical Pharmacology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. Correspondence: JHM Schellens (j.schellens@nki.nl)

Screening and Biological Effects of Marine Pyrroloiminoquinone Alkaloids: Potential Inhibitors of the HIF-1α/p300 Interaction

Inhibition of the hypoxia-inducible factor 1α (HIF-1α) pathway by disrupting its association with the transcriptional coactivator p300 inhibits angiogenesis and tumor development. Development of HIF-1α/p300 inhibitors has been hampered by preclinical toxicity; therefore, we aimed to identify novel HIF-1α/p300 inhibitors. Using a cell-free assay designed to test compounds that block HIF-1α/p300 binding, 170 298 crude natural product extracts and prefractionated samples were screened, identifying 25 active extracts. One of these extracts, originating from the marine sponge Latrunculia sp., afforded six pyrroloiminoquinone alkaloids that were identified as positive hits (IC50 values: 1-35 μM). Luciferase assays confirmed inhibition of HIF-1α transcriptional activity by discorhabdin B (1) and its dimer (2), 3-dihydrodiscorhabdin C (3), makaluvamine F (5), discorhabdin H (8), discorhabdin L (9), and discorhabdin W (11) in HCT 116 colon cancer cells (0.1-10 μM, p < 0.05). Except for 11, all of these compounds also reduced HIF-1α transcriptional activity in LNCaP prostate cancer cells (0.1-10 μM, p < 0.05). These effects occurred at noncytotoxic concentrations (<50% cell death) under hypoxic conditions. At the downstream HIF-1α target level, compound 8 (0.5 μM) significantly decreased VEGF secretion in LNCaP cells (p < 0.05). In COLO 205 colon cancer cells no activity was shown in the luciferase or cytotoxicity assays. Pyrroloiminoquinone alkaloids are a novel class of HIF-1α inhibitors, which interrupt the protein-protein interaction between HIF-1α and p300 and consequently reduce HIF-related transcription.

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.

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.

Effects of UGT1A1 genotype on the pharmacokinetics, pharmacodynamics, and toxicities of belinostat administered by 48-hour continuous infusion in patients with cancer.

The histone deacetylase inhibitor belinostat is eliminated through glucuronidation by UGT1A1. Polymorphisms that reduce UGT1A1 function could result in increased belinostat exposure and toxicities. We wanted to determine which single‐nucleotide polymorphisms alter belinostat exposure and toxicity. In a phase 1 trial (belinostat over 48 hours in combination with cisplatin and etoposide), belinostat (400, 500, 600, or 800 mg/m2/24 h, 48‐hour continuous infusion) was administered to patients with cancer in combination with cisplatin and etoposide (n = 25). Patients were genotyped for UGT1A1 variants associated with reduced function: UGT1A1*6, UGT1A1*28, and UGT1A1*60. End points were associations between UGT1A1 genotype and belinostat pharmacokinetics (PK), toxicities, and global protein lysine acetylation (AcK). Belinostat AUC was increased (P = .003), and t1/2 increased (P = .0009) in UGT1A1*28 and UGT1A1*60 carriers who received more than 400 mg/m2/24 h. The incidence of grades 3–4 thrombocytopenia (P = .0081) was associated with UGT1A1 polymorphisms. The US Food and Drug Administration–approved package insert recommends dose adjustment of belinostat for UGT1A1*28. However, our data suggest dose adjustment is also necessary for UGT1A1*60. UGT1A1 polymorphisms were associated with increased systemic belinostat exposure, increased AcK, and increased incidence of toxicities, particularly at doses > 400 mg/m2/24 h.