The formation of estrogen-like tamoxifen metabolites and their influence on enzyme activity and gene expression of ADME genes.

Tamoxifen, a standard therapy for breast cancer, is metabolized to compounds with anti-estrogenic as well as estrogen-like action at the estrogen receptor. Little is known about the formation of estrogen-like metabolites and their biological impact. Thus, we characterized the estrogen-like metabolites tamoxifen bisphenol and metabolite E for their metabolic pathway and their influence on cytochrome P450 activity and ADME gene expression. The formation of tamoxifen bisphenol and metabolite E was studied in human liver microsomes and Supersomes™. Cellular metabolism and impact on CYP enzymes was analyzed in upcyte® hepatocytes. The influence of 5 µM of tamoxifen, anti-estrogenic and estrogen-like metabolites on CYP activity was measured by HPLC MS/MS and on ADME gene expression using RT-PCR analyses. Metabolite E was formed from tamoxifen by CYP2C19, 3A and 1A2 and from desmethyltamoxifen by CYP2D6, 1A2 and 3A. Tamoxifen bisphenol was mainly formed from (E)- and (Z)-metabolite E by CYP2B6 and CYP2C19, respectively. Regarding phase II metabolism, UGT2B7, 1A8 and 1A3 showed highest activity in glucuronidation of tamoxifen bisphenol and metabolite E. Anti-estrogenic metabolites (Z)-4-hydroxytamoxifen, (Z)-endoxifen and (Z)-norendoxifen inhibited the activity of CYP2C enzymes while tamoxifen bisphenol consistently induced CYPs similar to rifampicin and phenobarbital. On the transcript level, highest induction up to 5.6-fold was observed for CYP3A4 by tamoxifen, (Z)-4-hydroxytamoxifen, tamoxifen bisphenol and (E)-metabolite E. Estrogen-like tamoxifen metabolites are formed in CYP-dependent reactions and are further metabolized by glucuronidation. The induction of CYP activity by tamoxifen bisphenol and the inhibition of CYP2C enzymes by anti-estrogenic metabolites may lead to drug-drug-interactions.

Comprehensive Metabolomic and Lipidomic Profiling of Human Kidney Tissue: A Platform Comparison.

Metabolite profiling of tissue samples is a promising approach for the characterization of cancer pathways and tumor classification based on metabolic features. Here, we present an analytical method for nontargeted metabolomics of kidney tissue. Capitalizing on different chemical properties of metabolites allowed us to extract a broad range of molecules covering small polar molecules and less polar lipid classes that were analyzed by LC-QTOF-MS after HILIC and RP chromatographic separation, respectively. More than 1000 features could be reproducibly extracted and analyzed (CV < 30%) in porcine and human kidney tissue, which were used as surrogate matrices for method development. To further assess assay performance, cross-validation of the nontargeted metabolomics platform to a targeted metabolomics approach was carried out. Strikingly, from 102 metabolites that could be detected on both platforms, the majority (>90%) revealed Spearman's correlation coefficients ≥0.3, indicating that quantitative results from the nontargeted assay are largely comparable to data derived from classical targeted assays. Finally, as proof of concept, the method was applied to human kidney tissue where a clear differentiation between kidney cancer and nontumorous material could be demonstrated on the basis of unsupervised statistical analysis.

A Temperature of 40 °C Appears to be a Critical Threshold for Potentiating Cytotoxic Chemotherapy In Vitro and in Peritoneal Carcinomatosis Patients Undergoing HIPEC.

BACKGROUND: Hyperthermic intraperitoneal chemotherapy (HIPEC) following cytoreductive surgery is a radical but effective treatment option for patients with peritoneal carcinomatosis (PC). Unfortunately, a standardized HIPEC protocol is missing impeding systematic comparisons with regard to minimal effective temperatures. OBJECTIVE: The purpose of the present study was to systematically analyse the precise minimal temperature needed for potentiation of chemotherapy effects in vitro and for patient survival. METHODS: We established a cell line-based model to mimic HIPEC conditions used in clinical practice, and evaluated intracellular drug concentrations and long-term survival using different temperatures ranging from 38 to 42 °C combined with cisplatin or doxorubicin. In parallel, we evaluated the temperature reached in the clinical setting by measuring inflow and outflow, as well as in two locations in the peritoneal cavity in 34 patients. Finally, we determined the influence of different HIPEC temperatures on survival. RESULTS: Long-term survival of cells treated with either cisplatin or doxorubicin was further improved only at temperatures above 40 °C. In patients, during HIPEC, constant temperatures were reached after 10 min in the peritoneal cavity. A temperature above 40 °C for at least 40 min was achieved in 68 % of patients over the 60 min duration of HIPEC. Importantly, we observed a significantly enhanced overall survival (OS) and progression-free survival (PFS) in those patients reaching temperatures above 40 °C. CONCLUSIONS: Hyperthermia significantly potentiated the chemotherapy effects only at temperatures above 40 °C in vitro. Importantly, this temperature threshold was also critical for OS and PFS of PC patients.

Highly sensitive simultaneous quantification of estrogenic tamoxifen metabolites and steroid hormones by LC-MS/MS.

Tamoxifen is a mainstay in the treatment of estrogen receptor-positive breast cancer and is metabolized to more than 30 different compounds. Little is known about in vivo concentrations of estrogenic metabolites E-metabolite E, Z-metabolite E, and bisphenol and their relevance for tamoxifen efficacy. Therefore, we developed a highly sensitive HPLC-ESI-MS/MS quantification method for tamoxifen metabolites bisphenol, E-metabolite E, and Z-metabolite E as well as for the sex steroid hormones estradiol, estrone, testosterone, androstenedione, and progesterone. Plasma samples were subjected to protein precipitation followed by solid phase extraction. Upon derivatization with 3-[(N-succinimide-1-yl)oxycarbonyl]-1-methylpyridinium iodide, all analytes were separated on a sub-2-µm column with a gradient of acetonitrile in water with 0.1 % of formic acid. Analytes were detected on a triple-quadrupole mass spectrometer with positive electrospray ionization in the multiple reaction monitoring mode. Our method demonstrated high sensitivity, accuracy, and precision. The lower limits of quantification were 12, 8, and 25 pM for bisphenol, E-metabolite E, and Z-metabolite E, respectively, and 4 pM for estradiol and estrogen, 50 pM for testosterone and androstenedione, and 25 pM for progesterone. The method was applied to plasma samples of postmenopausal patients taken at baseline and under tamoxifen therapy. Graphical Abstract Sample preparation and derivatization for highly sensitive quantification of estrogenic tamoxifen metabolites and steroid hormones by HPLC-MS/MS.

Quantitative bile acid profiling by liquid chromatography quadrupole time-of-flight mass spectrometry: monitoring hepatitis B therapy by a novel Na(+)-taurocholate cotransporting polypeptide inhibitor.

A novel analytical approach for the targeted profiling of bile acids (BAs) in human serum/plasma based on liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) is presented. Reversed-phase chromatography enabled the baseline separation of 15 human BA species which could be readily detected by accurate mass analysis in negative ion mode. Blood proteins were removed by methanol precipitation in the presence of deuterium-labeled internal standards which allowed BA quantification in 50 µl plasma/serum. The assay was validated according to FDA guidance achieving quantification limits from 7.8 to 156 nM. Calibration curves prepared in charcoal-stripped serum/plasma showed excellent regression coefficients (R (2) > 0.997) and covered quantities from 7.8 to 10,000 nM depending on the analyzed species. Intra- and inter-day accuracy and precision were below 15 % for all analytes. Apparent extraction recoveries were above 97 %, and ion suppression rates were between 4 and 53 %. Mean BA level in serum/plasma from healthy volunteers ranged from 11 ± 4 nM (tauroursodeoxycholic acid) to 1321 ± 1442 nM (glycochenodeoxycholic acid). As a proof of concept, the assay was applied to plasma samples derived from a clinical phase I study of myrcludex B, a novel first-in-class virus entry inhibitor for the treatment of chronic hepatitis B and D. The results demonstrate that myrcludex-induced inhibition of the hepatic BA transporter Na(+)-taurocholate cotransporting polypeptide (NTCP) significantly affects plasma BA level. These observations provide novel insights into drug-induced metabolic responses and will be indispensable for the assessment of side effects and dose-finding processes during future clinical trials.

Genetic polymorphism of cytochrome P450 2D6 determines oestrogen receptor activity of the major infertility drug clomiphene via its active metabolites.

Clomiphene citrate is the most used drug for the treatment of female infertility, a common condition in western societies and developing countries. Despite dose escalation, up to 30% of women do not respond. Since clomiphene shares structural similarities with tamoxifen, which is predominantly bioactivated by the polymorphic cytochrome P450 (CYP) 2D6, we systematically explored clomiphene metabolism and action in vitro and in vivo by pharmacogenetic, -kinetic and -dynamic investigations. Human liver microsomes were incubated with clomiphene citrate and nine metabolites were identified by mass spectrometry and tested at the oestrogen receptor for their antagonistic capacity. (E)-4-hydroxyclomiphene and (E)-4-hydroxy-N-desethylclomiphene showed strongest inhibition of the oestrogen receptor activity with 50% inhibitory concentrations of 2.5 and 1.4 nm, respectively. CYP2D6 has been identified as the major enzyme involved in their formation using recombinant CYP450 isozymes as confirmed by inhibition experiments with CYP monoclonal antibodies. We correlated the CYP2D6 genotype of 30 human liver donors with the microsomal formation rate of active metabolites and observed a strong gene-dose effect. A healthy female volunteer study confirmed our in vitro data that the CYP2D6 polymorphism substantially determines the formation of the active clomiphene metabolites. Comparison of the C(max) of (E)-4-hydroxyclomiphene and (E)-4-hydroxy-N-desethylclomiphene showed 8 and 12 times lower concentrations in subjects with non-functional CYP2D6 alleles. Our results highlight (E)-4-hydroxyclomiphene and (E)-4-hydroxy-N-desethylclomiphene as the active clomiphene metabolites, the formation of which strongly depends on the polymorphic CYP2D6 enzyme. Our data provide first evidence of a biological rationale for the variability in the response to clomiphene treatment.

A new [2H]-labelled α-trichloroimidate glucuronic ester for the synthesis of deuterated drug conjugates.

A new reaction pathway for the synthesis of a [(2)H]-labelled trichloroacetimidate precursor for the preparation of glucuronides is described. Therewith, stable isotope-labelled drug glucuronides become accessible on a preparative scale, which can further be used as internal standards for quantitative analysis.

The letrozole phase 1 metabolite carbinol as a novel probe drug for UGT2B7.

Carbinol [4,4'-(hydroxymethylene)dibenzonitrile] is the main phase 1 metabolite of letrozole, a nonsteroidal aromatase inhibitor used for endocrine therapy in postmenopausal breast cancer. We elucidated the contribution of UDP-glucuronosyltransferase (UGT) isoforms on the glucuronidation of carbinol. Identification of UGT isoforms was performed using a panel of recombinant human UGT enzymes. Kinetic studies were done in recombinant human UGT2B7 and pooled human liver microsomes (HLMs). A liquid chromatography-tandem mass spectrometry method was used for detection of metabolites. To assess the impact of UGT2B7*2, we determined the carbinol glucuronidation activity using HLM as well as UGT2B7 protein expression in 148 human livers. Moreover, we analyzed the plasma concentrations of 60 letrozole-treated breast cancer patients. We identified UGT2B7 as the predominant UGT isoform involved in carbinol glucuronidation. In HLMs and recombinant UGT2B7, we determined K(m) values (9.99 and 9.56 µM) and V(max) values (3430 and 2399 pmol/min per milligram of protein), respectively. In the set of 148 human livers, carbinol glucuronidation activity significantly correlated with UGT2B7 protein as determined by Western blotting (r(s) = 0.5088, P < 0.0001). Neither carbinol glucuronidation activity (*1/*1: n = 25, 2434 ± 1018; *1/*2: n = 80, 2356 ± 1372; *2/*2: n = 43, 2251 ± 1421 pmol/min per milligram of protein) nor UGT2B7 protein expression was altered by the UGT2B7*2 genotype. No impact of UGT2B7*2 on plasma levels of carbinol and carbinol-gluc [bis(4-cyanophenyl)methyl hexopyranosiduronic acid] in 60 letrozole-treated patients was found. Taken together, these findings suggest carbinol as a novel in vitro probe substrate for UGT2B7. In vitro and in vivo data suggest a lack of influence of the UGT2B7*2 polymorphism on carbinol glucuronidation.

Performance comparison of narrow-bore and capillary liquid-chromatography for non-targeted metabolomics profiling by HILIC-QTOF-MS.

Clinical metabolomics studies often have to cope with limited sample amounts, thus miniaturized liquid chromatography (LC) systems are a promising alternative. Their applicability has already been demonstrated in various fields, including a few metabolomics studies that mainly used reversed-phase chromatography. However, hydrophilic interaction chromatography (HILIC), which is widely used in metabolomics due to its particular suitability for the analysis of polar molecules, has rarely been tested for miniaturized LC-MS analysis of small molecules. In the present work, the suitability of a capillary HILIC (CapHILIC)-QTOF-MS system for non-targeted metabolomics was evaluated based on extracts of porcine formalin-fixed, paraffin-embedded (FFPE) tissue samples. The performance was assessed with respect to the number and retention time span of metabolic features as well as the analytical repeatability, the signal-to-noise ratio and the signal intensity of 16 annotated metabolites from different compound classes. The results were compared with a well established narrow-bore HILIC-QTOF-MS system. Both platforms have detected a similar number of features and performed excellent with respect to retention time stability (median RT span <0.05 min) and analytical repeatability (>75% of features with CV < 20%). The signal areas of all metabolites assessed were increased up to 18-fold by the use of CapHILIC, although the signal-to-noise ratio was only improved for 50% of the metabolites. An even better reproducibility (median CV = 5.2%) and up to 80-fold increase in signal intensity were observed after optimization of CapHILIC conditions for analysis of bile acid standard solutions. Even though the observed improvement for specific bile acids (e.g. taurocholic acid) in biological matrix needs to be evaluated, the platform comparison indicates, that the tested CapHILIC system is particularly suitable for analyses of a less broad metabolite spectrum, and specifically optimized chromatography.

Toward model-informed precision dosing for tamoxifen: A population-pharmacokinetic model with a continuous CYP2D6 activity scale.

BACKGROUND: Tamoxifen is important in the adjuvant treatment of breast cancer. A plasma concentration of the active metabolite endoxifen of > 16 nM is associated with a lower risk of breast cancer-recurrence. Since inter-individual variability is high and > 20 % of patients do not reach endoxifen levels > 16 nM with the standard dose tamoxifen, therapeutic drug monitoring is advised. However, ideally, the correct tamoxifen dose should be known prior to start of therapy. Our aim is to develop a population pharmacokinetic (POP-PK) model incorporating a continuous CYP2D6 activity scale to support model informed precision dosing (MIPD) of tamoxifen to determine the optimal tamoxifen starting dose. METHODS: Data from eight different clinical studies were pooled (539 patients, 3661 samples) and used to develop a POP-PK model. In this model, CYP2D6 activity per allele was estimated on a continuous scale. After inclusion of covariates, the model was subsequently validated using an independent external dataset (378 patients). Thereafter, dosing cut-off values for MIPD were determined. RESULTS: A joint tamoxifen/endoxifen POP-PK model was developed describing the endoxifen formation rate. Using a continuous CYP2D6 activity scale, variability in predicting endoxifen levels was decreased by 37 % compared to using standard CYP2D6 genotype predicted phenotyping. After external validation and determination of dosing cut-off points, MIPD could reduce the proportion of patients with subtherapeutic endoxifen levels at from 22.1 % toward 4.8 %. CONCLUSION: Implementing MIPD from the start of tamoxifen treatment with this POP-PK model can reduce the proportion of patients with subtherapeutic endoxifen levels at steady-state to less than 5 %.

Perfusion Air Culture of Precision-Cut Tumor Slices: An Ex Vivo System to Evaluate Individual Drug Response under Controlled Culture Conditions.

Precision-cut tumor slices (PCTS) maintain tissue heterogeneity concerning different cell types and preserve the tumor microenvironment (TME). Typically, PCTS are cultured statically on a filter support at an air-liquid interface, which gives rise to intra-slice gradients during culture. To overcome this problem, we developed a perfusion air culture (PAC) system that can provide a continuous and controlled oxygen medium, and drug supply. This makes it an adaptable ex vivo system for evaluating drug responses in a tissue-specific microenvironment. PCTS from mouse xenografts (MCF-7, H1437) and primary human ovarian tumors (primary OV) cultured in the PAC system maintained the morphology, proliferation, and TME for more than 7 days, and no intra-slice gradients were observed. Cultured PCTS were analyzed for DNA damage, apoptosis, and transcriptional biomarkers for the cellular stress response. For the primary OV slices, cisplatin treatment induced a diverse increase in the cleavage of caspase-3 and PD-L1 expression, indicating a heterogeneous response to drug treatment between patients. Immune cells were preserved throughout the culturing period, indicating that immune therapy can be analyzed. The novel PAC system is suitable for assessing individual drug responses and can thus be used as a preclinical model to predict in vivo therapy responses.

Cross-Ancestry Genome-Wide Association Study Defines the Extended CYP2D6 Locus as the Principal Genetic Determinant of Endoxifen Plasma Concentrations.

The therapeutic efficacy of tamoxifen is predominantly mediated by its active metabolites 4-hydroxy-tamoxifen and endoxifen, whose formation is catalyzed by the polymorphic cytochrome P450 2D6 (CYP2D6). Yet, known CYP2D6 polymorphisms only partially determine metabolite concentrations in vivo. We performed the first cross-ancestry genome-wide association study with well-characterized patients of European, Middle-Eastern, and Asian descent (n = 497) to identify genetic factors impacting active and parent metabolite formation. Genome-wide significant variants were functionally evaluated in an independent liver cohort (n = 149) and in silico. Metabolite prediction models were validated in two independent European breast cancer cohorts (n = 287, n = 189). Within a single 1-megabase (Mb) region of chromosome 22q13 encompassing the CYP2D6 gene, 589 variants were significantly associated with tamoxifen metabolite concentrations, particularly endoxifen and metabolic ratio (MR) endoxifen/N-desmethyltamoxifen (minimal P = 5.4E-35 and 2.5E-65, respectively). Previously suggested other loci were not confirmed. Functional analyses revealed 66% of associated, mostly intergenic variants to be significantly correlated with hepatic CYP2D6 activity or expression (ρ = 0.35 to -0.52), and six hotspot regions in the extended 22q13 locus impacting gene regulatory function. Machine learning models based on hotspot variants (n = 12) plus CYP2D6 activity score (AS) increased the explained variability (~ 9%) compared with AS alone, explaining up to 49% (median R2 ) and 72% of the variability in endoxifen and MR endoxifen/N-desmethyltamoxifen, respectively. Our findings suggest that the extended CYP2D6 locus at 22q13 is the principal genetic determinant of endoxifen plasma concentration. Long-distance haplotypes connecting CYP2D6 with adjacent regulatory sites and nongenetic factors may account for the unexplained portion of variability.

Simultaneous quantitative analysis of letrozole, its carbinol metabolite, and carbinol glucuronide in human plasma by LC-MS/MS.

Letrozole is an efficient endocrine treatment of postmenopausal breast cancer, however, not all patients benefit from this treatment, and moreover, severe side-effects like arthralgia frequently lead to discontinuation. To better understand inter-individual variability in drug response and side-effects, plasma analysis of steady-state concentrations of letrozole and its major metabolites is crucial. We developed a rapid, sensitive, and specific method for the simultaneous quantification of letrozole and its metabolites 4,4'-(hydroxymethylene)dibenzonitrile (carbinol) and bis(4-cyanophenyl)methyl hexopyranosiduronic acid (carbinol-gluc) by UHPLC-ESI-MS/MS using in-house synthesized, stable isotope-labeled internal standards. Following solid-phase extraction in BondElut C18 96-well plates, the analytes were separated on a ZORBAX Eclipse XDB-C18 column (1.8 µm, 4.6 × 50 mm) with a gradient of acetonitrile in 0.1% acetic acid in water and detected on a triple quadrupole mass spectrometer with electrospray ionization in the multiple reaction monitoring mode. Lower limits of quantification were 20, 0.2, and 2 nM for letrozole, carbinol, and carbinol-gluc, respectively. The assay has been validated according to FDA guidance and applied to the analysis of 20 plasma samples of postmenopausal breast cancer patients treated with 2.5 mg of letrozole per day. Mean plasma levels (±SD) were 366 ± 173, 0.38 ± 0.09, and 34 ± 12 nM for letrozole, carbinol, and carbinol-gluc, respectively. Our rapid and sensitive mass spectrometry based method enables future pharmacokinetic investigations of letrozole outcome.

Triple Targeting of HER Receptors Overcomes Heregulin-mediated Resistance to EGFR Blockade in Colorectal Cancer.

Current treatment options for patients with advanced colorectal cancers include anti-EGFR/HER1 therapy with the blocking antibody cetuximab. Although a subset of patients with KRAS WT disease initially respond to the treatment, resistance develops in almost all cases. Relapse has been associated with the production of the ligand heregulin (HRG) and/or compensatory signaling involving the receptor tyrosine kinases HER2 and HER3. Here, we provide evidence that triple-HER receptor blockade based on a newly developed bispecific EGFR×HER3-targeting antibody (scDb-Fc) together with the HER2-blocking antibody trastuzumab effectively inhibited HRG-induced HER receptor phosphorylation, downstream signaling, proliferation, and stem cell expansion of DiFi and LIM1215 colorectal cancer cells. Comparative analyses revealed that the biological activity of scDb-Fc plus trastuzumab was sometimes even superior to that of the combination of the parental antibodies, with PI3K/Akt pathway inhibition correlating with improved therapeutic response and apoptosis induction as seen by single-cell analysis. Importantly, growth suppression by triple-HER targeting was recapitulated in primary KRAS WT patient-derived organoid cultures exposed to HRG. Collectively, our results provide strong support for a pan-HER receptor blocking approach to combat anti-EGFR therapy resistance of KRAS WT colorectal cancer tumors mediated by the upregulation of HRG and/or HER2/HER3 signaling.

(Z)-Endoxifen and Early Recurrence of Breast Cancer: An Explorative Analysis in a Prospective Brazilian Study.

Adherence to treatment and use of co-medication, but also molecular factors such as CYP2D6 genotype, affect tamoxifen metabolism, with consequences for early breast cancer prognosis. In a prospective study of 149 tamoxifen-treated early-stage breast cancer patients from Brazil followed up for 5 years, we investigated the association between the active tamoxifen metabolite (Z)-endoxifen at 3 months and event-free survival (EFS) adjusted for clinico-pathological factors. Twenty-five patients (16.8%) had recurred or died at a median follow-up of 52.3 months. When we applied a putative 15 nM threshold used in previous independent studies, (Z)-endoxifen levels below the threshold showed an association with shorter EFS in univariate analysis (p = 0.045) and after adjustment for stage (HR 2.52; 95% CI 1.13-5.65; p = 0.024). However, modeling of plasma concentrations with splines instead of dichotomization did not verify a significant association with EFS (univariate analysis: p = 0.158; adjusted for stage: p = 0.117). Hence, in our small exploratory study, the link between impaired tamoxifen metabolism and early breast cancer recurrence could not be unanimously demonstrated. This inconsistency justifies larger modeling studies backed up by mechanistic pharmacodynamic analyses to shed new light on this suspected association and the stipulation of an appropriate predictive (Z)-endoxifen threshold.

Subunits of BK channels promote breast cancer development and modulate responses to endocrine treatment in preclinical models.

BACKGROUND AND PURPOSE: Pore-forming α subunits of the voltage- and Ca2+ -activated K+ channel with large conductance (BKα) promote malignant phenotypes of breast tumour cells. Auxiliary subunits such as the leucine-rich repeat containing 26 (LRRC26) protein, also termed BKγ1, may be required to permit activation of BK currents at a depolarized resting membrane potential that frequently occur in non-excitable tumour cells. EXPERIMENTAL APPROACH: Anti-tumour effects of BKα loss were investigated in breast tumour-bearing MMTV-PyMT transgenic BKα knockout (KO) mice, primary MMTV-PyMT cell cultures, and in a syngeneic transplantation model of breast cancer derived from these cells. The therapeutic relevance of BK channels in the context of endocrine treatment was assessed in human breast cancer cell lines expressing either low (MCF-7) or high (MDA-MB-453) levels of BKα and BKγ1, as well as in BKα-negative MDA-MB-157. KEY RESULTS: BKα promoted breast cancer onset and overall survival in preclinical models. Conversely, lack of BKα and/or knockdown of BKγ1 attenuated proliferation of murine and human breast cancer cells in vitro. At low concentrations, tamoxifen and its major active metabolites stimulated proliferation of BKα/γ1-positive breast cancer cells, independent of the genomic signalling controlled by the oestrogen receptor. Finally, tamoxifen increased the relative survival time of BKα KO but not of wild-type tumour cell recipient mice. CONCLUSION AND IMPLICATIONS: Breast cancer initiation, progression, and tamoxifen sensitivity depend on functional BK channels thereby providing a rationale for the future exploration of the oncogenic actions of BK channels in clinical outcomes with anti-oestrogen therapy. LINKED ARTICLES: This article is part of a themed issue on New avenues in cancer prevention and treatment (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.12/issuetoc.

Prediction of Drug-Drug-Gene Interaction Scenarios of (E)-Clomiphene and Its Metabolites Using Physiologically Based Pharmacokinetic Modeling.

Clomiphene, a selective estrogen receptor modulator (SERM), has been used for the treatment of anovulation for more than 50 years. However, since (E)-clomiphene ((E)-Clom) and its metabolites are eliminated primarily via Cytochrome P450 (CYP) 2D6 and CYP3A4, exposure can be affected by CYP2D6 polymorphisms and concomitant use with CYP inhibitors. Thus, clomiphene therapy may be susceptible to drug-gene interactions (DGIs), drug-drug interactions (DDIs) and drug-drug-gene interactions (DDGIs). Physiologically based pharmacokinetic (PBPK) modeling is a tool to quantify such DGI and DD(G)I scenarios. This study aimed to develop a whole-body PBPK model of (E)-Clom including three important metabolites to describe and predict DGI and DD(G)I effects. Model performance was evaluated both graphically and by calculating quantitative measures. Here, 90% of predicted Cmax and 80% of AUClast values were within two-fold of the corresponding observed value for DGIs and DD(G)Is with clarithromycin and paroxetine. The model also revealed quantitative contributions of different CYP enzymes to the involved metabolic pathways of (E)-Clom and its metabolites. The developed PBPK model can be employed to assess the exposure of (E)-Clom and its active metabolites in as-yet unexplored DD(G)I scenarios in future studies.

Quantification of clomiphene metabolite isomers in human plasma by rapid-resolution liquid chromatography-electrospray ionization-tandem mass spectrometry.

Since the 1960s, clomiphene citrate is used for ovulation induction. Since nonresponse to clomiphene therapy is still not well understood, interindividual variability of clomiphene metabolism has been considered to be a plausible explanation. Therefore, a comprehensive, rapid, sensitive, and specific analytical method for the quantification of (E)- and (Z)-isomers of clomiphene and their putative N-desethyl, N,N-didesethyl, 4-hydroxy, and 4-hydroxy-N-desethyl metabolites, and the N-oxides in human plasma has been newly developed, using HPLC-tandem mass spectrometry and stable isotope-labeled internal standards. All standards other than the parent drug were synthesized in our laboratory. Following protein precipitation analytes were separated on a ZORBAX Eclipse plus C18 1.8 µm column with a gradient of 0.1% formic acid in water and 0.1% formic acid in acetonitrile and detected on a triple quadrupole mass spectrometer with positive electrospray ionization in the multiple reaction monitoring mode. Lower limit of quantification for metabolites ranged from 0.06 ng/mL for clomiphene-N-oxides to 0.3 ng/mL for (E)-N-desethylclomiphene. The assay was validated according to FDA guidelines. Plasma levels of clomiphene and its metabolites were measured in two women after single-dose treatment with clomiphene.

Stereoselective quantification of phase 1 and 2 metabolites of clomiphene in human plasma and urine.

Clomiphene citrate is first line therapy of female infertility but is also frequently abused by athletes. Human biotransformation of clomiphene results in numerous phase 1 and phase 2 metabolites. The involvement of the polymorphic cytochrome P450 2D6 leads to a high inter-individual variability. To comprehensively investigate clomiphene metabolism in vivo we established a highly sensitive and specific UPLC-MS/MS method for the stereoselective quantification of clomiphene and its phase 1 and phase 2 metabolites in plasma and urine. Reference compounds and stable isotope labelled internal standards were synthesized in-house. High-throughput sample preparation was done by protein precipitation. Analytes were separated by UPLC on a C18 column (1.8 µm, 2.1 * 100 mm) using a gradient of 0.1% formic acid in acetonitrile in 0.1% aqueous formic acid and detected by positive ESI-MS/MS in MRM mode. The lower limit of quantification was below 1 nM for all analytes. The method was validated according to recent guidelines. However, due to absorption effects during sampling the quantification of metabolites in urine was limited to phase 2 metabolites. The method was successfully applied to determine the pharmacokinetic of (E)- and (Z)-clomiphene and 14 metabolites following a single dose of 100 mg clomiphene citrate in 3 healthy subjects and proofed to be an essential tool to comprehensively investigate the human biotransformation of clomiphene.

Raman Imaging and Fluorescence Lifetime Imaging Microscopy for Diagnosis of Cancer State and Metabolic Monitoring.

Hurdles for effective tumor therapy are delayed detection and limited effectiveness of systemic drug therapies by patient-specific multidrug resistance. Non-invasive bioimaging tools such as fluorescence lifetime imaging microscopy (FLIM) and Raman-microspectroscopy have evolved over the last decade, providing the potential to be translated into clinics for early-stage disease detection, in vitro drug screening, and drug efficacy studies in personalized medicine. Accessing tissue- and cell-specific spectral signatures, Raman microspectroscopy has emerged as a diagnostic tool to identify precancerous lesions, cancer stages, or cell malignancy. In vivo Raman measurements have been enabled by recent technological advances in Raman endoscopy and signal-enhancing setups such as coherent anti-stokes Raman spectroscopy or surface-enhanced Raman spectroscopy. FLIM enables in situ investigations of metabolic processes such as glycolysis, oxidative stress, or mitochondrial activity by using the autofluorescence of co-enzymes NADH and FAD, which are associated with intrinsic proteins as a direct measure of tumor metabolism, cell death stages and drug efficacy. The combination of non-invasive and molecular-sensitive in situ techniques and advanced 3D tumor models such as patient-derived organoids or microtumors allows the recapitulation of tumor physiology and metabolism in vitro and facilitates the screening for patient-individualized drug treatment options.