No detrimental association between antibiotic use and immune checkpoint inhibitor therapy: an observational cohort study comparing patients with ICI-treated and TKI-treated melanoma and NSCLC.

BACKGROUND: The role of antibiotics in malignancies treated with immune checkpoint inhibitors (ICI) remains unclear. Several studies suggested a detrimental impact of antibiotic use on the response to ICI, but were susceptible to confounding by indication. Our objective was therefore to assess whether the relationship between antibiotic use and ICI response is causative or merely associative. METHODS: A large, single-center observational cohort study was performed with individuals treated for either non-small cell lung carcinoma (NSCLC) or metastatic melanoma. An effect modification approach was used, aiming to estimate the association between antibiotic use and overall survival (OS) and compare these estimates between individuals receiving first-line ICI treatment versus those receiving first-line tyrosine kinase inhibitors (TKIs). Exposure of interest was antibiotic use within 30 days before the start of anticancer treatment. HRs for OS were estimated for antibiotics versus no antibiotics in each cohort using multivariable propensity adjusted analysis. The "true antibiotic effect" within the ICI versus TKI cohort was modeled using an interaction term. RESULTS: A total of 4534 patients were included, of which 1908 in the ICI cohort and 817 in the TKI cohort. Approximately 10% of patients in each cohort used antibiotics within 30 days before the start of anticancer treatment. Our results demonstrate a lack of synergistic interaction between current antibiotic use and ICI therapy in relation to OS: although antibiotic use was significantly associated with OS decline in the ICI cohort (HR=1.26 (95% CI 1.04 to 1.51)), a similar magnitude in OS decline was found within the TKI cohort (HR=1.24 (95% CI 0.95 to 1.62)). This was reflected by the synergy index (HR=0.96 (95% CI 0.70 to 1.31)), which implied no synergistic interaction between current antibiotic use and ICI. CONCLUSION: This study strongly suggests that there is no causal detrimental association between antibiotic use and ICI therapy outcome when looking at OS in individuals with malignant melanoma or NSCLC. The frequently observed inverse association between antibiotics and ICI response in previous studies is most likely driven by confounding by indication, which was confirmed by the findings in our reference TKI cohort.

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 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.

Combined action and regulation of phase II enzymes and multidrug resistance proteins in multidrug resistance in cancer.

A major limitation in the treatment of cancer patients is the ability of cancer cells to become resistant to chemotherapeutic drugs, a phenomenon known as multidrug resistance (MDR). Two important mechanisms involved in multidrug resistance are the increased activity of efflux pumps, such as those of the multidrug resistance proteins (MRPs) and the detoxification by phase II conjugating enzymes, like glutathione S-transferases and UDP-glucuronosyltransferases. A synergistic interaction between these two mechanisms, MRPs and phase II enzymes, in conferring MDR has been shown for multiple anticancer drugs. In addition, there is substantial evidence of a coordinate regulation of the expression of phase II enzymes and MRPs, most likely mediated by the nuclear factor-erythroid 2 p45-related factor (Nrf2) and antioxidant response elements. Further elucidation of the combined action and regulation of phase II enzymes and MRPs in MDR will be an aid in the improvement of the chemotherapeutic treatment of cancer patients.

In vitro characterization of the human biotransformation pathways of aplidine, a novel marine anti-cancer drug.

Aplidine is a potent marine anti-cancer drug and is currently being investigated in phase II clinical trials. However, the enzymes involved in the biotransformation of aplidine and thus its pharmacokinetics are not known yet. To assess the biotransformation pathways of aplidine and their potential implications for human pharmacology and toxicology, the in vitro metabolism of aplidine was characterized using incubations with human plasma, liver preparations, cytochrome P450 (CYP) and uridine diphosphoglucuronosyl transferase (UGT) supersomes in combination with HPLC analysis and cytotoxicity assays with cell lines. Aplidine was metabolised by carboxyl esterases in human plasma. Using CYP supersomes and liver microsomes, it was shown that aplidine was metabolised mainly by CYP3A4 and also by CYP2A6, 2E1 and 4A11. Four metabolites were observed after incubation with human liver microsomes, one formed by CYP2A6 (C-demethylation) and three by CYP3A4 (hydroxylation and/or C-dealkylation). No conjugation was observed in human liver S9 fraction. However, the aplidine metabolites formed by CYP were further conjugated by the phase II enzymes UGT, GST and SULT. In accordance with the findings in microsomes and CYP supersomes, a significant effect of specific CYP2A6, 2E1, 3A4 and 4A11 inhibitors on the cytotoxicity of aplidine in Hep G2 and IGROV-1 cells could be observed. These results provide evidence that CYP3A4 has a major role in metabolising aplidine in vitro with additional involvement of CYP2A6, 2E1, and 4A11. Further, the metabolites formed by CYPs can be conjugated by UGT, SULT and GST. These findings could help interpret the in vivo pharmacokinetics of aplidine.

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.

Genetic polymorphisms of drug-metabolising enzymes and drug transporters in the chemotherapeutic treatment of cancer.

There is wide variability in the response of individuals to standard doses of drug therapy. This is an important problem in clinical practice, where it can lead to therapeutic failures or adverse drug reactions. Polymorphisms in genes coding for metabolising enzymes and drug transporters can affect drug efficacy and toxicity. Pharmacogenetics aims to identify individuals predisposed to a high risk of toxicity and low response from standard doses of anti-cancer drugs. This review focuses on the clinical significance of polymorphisms in drug-metabolising enzymes (cytochrome P450 [CYP] 2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, dihydropyrimidine dehydrogenase, uridine diphosphate glucuronosyltransferase [UGT] 1A1, glutathione S-transferase, sulfotransferase [SULT] 1A1, N-acetyltransferase [NAT], thiopurine methyltransferase [TPMT]) and drug transporters (P-glycoprotein [multidrug resistance 1], multidrug resistance protein 2 [MRP2], breast cancer resistance protein [BCRP]) in influencing efficacy and toxicity of chemotherapy. The most important example to demonstrate the influence of pharmacogenetics on anti-cancer therapy is TPMT. A decreased activity of TPMT, caused by genetic polymorphisms in the TPMT gene, causes severe toxicity with mercaptopurine. Dosage reduction is necessary for patients with heterozygous or homozygous mutation in this gene. Other polymorphisms showing the influence of pharmacogenetics in the chemotherapeutic treatment of cancer are discussed, such as UGT1A1*28. This polymorphism is associated with an increase in toxicity with irinotecan. Also, polymorphisms in the DPYD gene show a relation with fluorouracil-related toxicity; however, in most cases no clear association has been found for polymorphisms in drug-metabolising enzymes and drug transporters, and pharmacokinetics or pharmacodynamics of anti-cancer drugs. The studies discussed evaluate different regimens and tumour types and show that polymorphisms can have different, sometimes even contradictory, pharmacokinetic and pharmacodynamic effects in different tumours in response to different drugs. The clinical application of pharmacogenetics in cancer treatment will therefore require more detailed information of the different polymorphisms in drug-metabolising enzymes and drug transporters. Larger studies, in different ethnic populations, and extended with haplotype and linkage disequilibrium analysis, will be necessary for each anti-cancer drug separately.

Validation of in vitro cell models used in drug metabolism and transport studies; genotyping of cytochrome P450, phase II enzymes and drug transporter polymorphisms in the human hepatoma (HepG2), ovarian carcinoma (IGROV-1) and colon carcinoma (CaCo-2, LS180) cell lines.

Human cell lines are often used for in vitro biotransformation and transport studies of drugs. In vivo, genetic polymorphisms have been identified in drug-metabolizing enzymes and ABC-drug transporters leading to altered enzyme activity, or a change in the inducibility of these enzymes. These genetic polymorphisms could also influence the outcome of studies using human cell lines. Therefore, the aim of our study was to pharmacogenotype four cell lines frequently used in drug metabolism and transport studies, HepG2, IGROV-1, CaCo-2 and LS180, for genetic polymorphisms in biotransformation enzymes and drug transporters. The results indicate that, despite the presence of some genetic polymorphisms, no real effects influencing the activity of metabolizing enzymes or drug transporters in the investigated cell lines are expected. However, this characterization will be an aid in the interpretation of the results of biotransformation and transport studies using these in vitro cell models.

In vitro characterization of the human biotransformation and CYP reaction phenotype of ET-743 (Yondelis, Trabectidin), a novel marine anti-cancer drug.

ET-743 is a potent marine anti-cancer drug and is currently being investigated in phase I and II clinical trials, e.g. in combination with other anti-cancer agents. To assess the biotransformation and CYP reaction phenotype and their potential implications for human pharmacology and toxicology, the in vitro metabolism of ET-743 was characterized using incubations with human liver preparations, cytochrome P450 (CYP) and uridine diphosphoglucuronosyl transferase (UGT) supersomes.CYP supersomes and liver microsomes showed that ET-743 was metabolized mainly by CYP3A4, but also by CYP2C9, 2C19, 2D6, and 2E1. ET-743 showed the highest affinity for CYP3A4 and the highest maximal metabolic rate for CYP2D6 among the CYPs shown to metabolize ET-743. In addition, the Km value of ET-743 in female microsomes was significantly lower compared to male microsomes, while the Vmax values did not differ. ET-743 glucuronidation, catalyzed by UGT2B15, was observed in microsomes and S9 fraction. In addition, conjugation by glutathione-S-transferase and no sulphation was observed for ET-743 in cytosol and S9 fraction. ET-743 was more extensively metabolized when CYP activity was combined with phase II enzymes UGT and glutathione-S-transferase (GST), indicating that CYP, UGT, and GST simultaneously metabolize ET-743 in the S9 fraction. These results provide evidence that CYP3A4 has a major role in the metabolism of ET-743 in vitro with additional involvement of CYP2C9, 2C19, 2D6, and 2E1. Furthermore, ET-743 is conjugated by UGT and GST. This information could be important for interpretation of the pharmacokinetic data of clinical trials and prediction of drug-drug interactions.

In-vitro cytotoxicity of ET-743 (Trabectedin, Yondelis), a marine anti-cancer drug, in the Hep G2 cell line: influence of cytochrome P450 and phase II inhibition, and cytochrome P450 induction.

ET-743 is a marine anti-cancer drug and is currently in phase I trials in which the effect of combination therapies will be investigated. Its dose-limiting toxicity in patients is hepatotoxicity. In-vitro studies have shown that ET-743 is mainly metabolized by cytochrome P450 (CYP) 3A4, but also by 2C9, 2C19, 2D6 and 2E1, and the phase II enzymes uridine diphosphoglucuronosyl transferase and glutathione-S-transferase. Based on this metabolic profile, there is a risk of drug-drug interactions possibly influencing the hepatotoxicity of ET-743. Therefore, the effect of CYP and phase II activity on the cytotoxicity of ET-743 was investigated in vitro in a human cell line model system. The effect of different CYP and phase II inhibitors and CYP inducers on ET-743 cytotoxicity was studied after 48 and 120 h of treatment in Hep G2 cells using different assays. Furthermore, the toxicity of ET-743 metabolites was investigated. Potent cytotoxic activity of ET-743 after 120 h treatment was observed, which could be increased in combination with the CYP inhibitors metyrapone (3A4), phenanthrene (substrate for 2E1, 3A4), piperonyl butoxide (3A), proadifen (2C9, 2E1, 3A4), ritonavir (3A4), and warfarin (2C9, 2C19). No effect on the cytotoxicity of ET-743 was observed in combination with phase II enzyme inhibition and CYP induction. CYP metabolites of ET-743 were less toxic compared with ET-743. These findings indicate that combination therapy of ET-743 with CYP inhibitors, e.g. other anti-cancer drugs, could lead to changes in the hepatotoxicity of ET-743 and are therefore of clinical importance.

Detection of single nucleotide polymorphisms in the ABCG2 gene in a Dutch population.

BACKGROUND: ABCG2 is a drug transporter involved in the protection of tissues by actively transporting toxic substances and xenobiotics out of cells. Cancer cells overexpressing the ABCG2 gene show multidrug resistance to mitoxantrone-, methotrexate-, doxorubicin-, and camptothecin-based anticancer drugs, such as topotecan and SN-38. Large interindividual differences have been shown in oral availability and clearance of drugs that are substrates for ABCG2. Variation in the ABCG2 gene, such as single nucleotide polymorphisms (SNPs), can possibly explain the variability in pharmacokinetics of ABCG2 substrates. AIM: This study was performed to screen for SNPs in the ABCG2 gene to determine the frequencies of currently known and previously unknown SNPs in a Dutch population. METHODS: Blood samples were obtained from 100 healthy volunteers to isolate genomic DNA. PCR amplification was performed, followed by DNA sequencing. The population, of which the ethnicity was 93% Caucasian, consisted of 79 female individuals and 21 males. RESULTS: In total, 19 SNPs were found in the ABCG2 gene, of which 7 were previously unknown. The SNPs G8883A in exon 5 and C44168T in exon 14 cause an amino acid change of R160Q and R575X, respectively. Most of the previously unknown SNPs were found in introns. CONCLUSIONS: The results will be used in future studies to explore the influence of the different SNPs on ABCG2 protein expression, activity, and substrate specificity. In addition, the results can be used to study the effects of genetic polymorphisms in the ABCG2 gene on the pharmacokinetic profile of anticancer drugs.

In vitro characterization of the biotransformation of thiocoraline, a novel marine anti-cancer drug.

Thiocoraline is a potent new marine anti-cancer drug in vitro, which will be tested in phase I clinical studies shortly. To assess the biotransformation and the potential implications for human pharmacology and toxicology, the in vitro metabolism of thiocoraline was characterized using human plasma, human liver preparations, cytochrome P450 (CYP) and uridine diphosphoglucuronosyl transferase (UGT) supersomes and human cell lines. Thiocoraline is significantly metabolized by enzymes present in human plasma; t (1/2) shifted from 25.2 h in phosphate buffered saline to 4.3 h in human plasma. Using CYP supersomes it was shown that thiocoraline is mainly metabolized by CYP3A4, with CYP1A1, CYP2C8 and CYP2C9 playing a minor role in the biotransformation (<3%). Only minor glucuronidation was observed for thiocoraline by UGT1A1 and UGT1A9 and no glucuronidation was observed in human liver S9 fraction. In addition, no glucosidation and sulfation were observed for thiocoraline in human liver cytosol and S9 fraction. However, the metabolites formed by cytochrome P450 were further conjugated by UGT, glutathione-S-transferase (GST) and sulfotransferase (ST). In contrast to the CYP metabolism observed in supersomes, no effect could be observed from the CYP3A4 inhibitors on the cytotoxicity of thiocoraline in Hep G2 cells. However, this could be due to low CYP expression levels in the Hep G2 and IGROV-1 cell line. These results provide evidence that human CYP3A4 plays a major role in the metabolism of thiocoraline in vitro and that the metabolites formed by CYP are conjugated by the phase II enzymes UGT, ST and GST.