A mass spectrometric approach for the study of the metabolism of clomiphene, tamoxifen and toremifene by liquid chromatography time-of-flight spectroscopy

Identification and synthesis of (Z)-3'-hydroxy clomiphene as a new potential doping-relevant metabolite of clomiphene

A recent study addressed the possibility of unintentional ingestion of clomiphene through residues in chicken eggs. The method developed here helped distinguish between microdose intake of (E/Z)-clomiphene citrate and consumption of clomiphene-containing eggs by the urinary pattern of four mono-hydroxylated clomiphene metabolites. However, reanalyses of doping-control samples, which showed an adverse analytical finding for clomiphene, revealed a hydroxy clomiphene (HC) isomer that was not found after microdose intake or after consumption of clomiphene-containing eggs and could not be assigned to any of the available reference compounds. The aim of the present follow-up study was to identify this HC isomer and to characterize this metabolite with respect to its potential properties as long-term metabolite in doping controls.

METHODS

(E/Z)-3'-HC and (E/Z)-4'-HC were synthesized involving the McMurry reaction. An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and optimized after a derivatization step with dansyl chloride to separate eight HC isomers. Using this method, urine samples from a controlled clomiphene administration study were analyzed, in which male study participants received therapeutic doses of clomiphene for 30 days and collected urine samples for up to 8 months. Thus, isomer-specific HC elimination profiles could be monitored.

RESULTS

The metabolite previously found in doping-control samples was identified as (Z)-3'-HC. The elimination profiles of the different HCs confirmed previous results, with (Z)-3-HC being the most abundant urinary hydroxy metabolite shortly after administration. A new finding was that the data suggest that (Z)-3'-HC is excreted at higher relative concentrations only several weeks after drug intake.

CONCLUSION

These findings might be of particular importance in sport drug testing as they can assist in the decision-making process to distinguish between intentional doping and inadvertent exposure to clomiphene via food contamination.

Synthesis and characterization of octopamine sulfate, norfenefrine sulfate and etilefrine sulfate reference materials for doping control

BACKGROUND

Doping is the use of prohibited substances by athletes to improve their performance. World Anti‐Doping Agency (WADA)‐accredited laboratories require various metabolite reference standards of the prohibited chemical substances or drugs for routine quality control. Therefore, it was proposed to develop efficient synthetic methodologies for highly pure reference materials of Phase II metabolites of octopamine, norfenefrine and etilefrine, which are prohibited in sports by WADA under the S6 stimulant category. The reference materials were characterized using various analytical techniques. New high‐performance liquid chromatography with diode‐array detection (HPLC‐DAD) methods were developed for purity assessment.

RESULTS

The synthesized Phase II metabolite reference standards, i.e. octopamine sulfate, norfenefrine sulfate and etilefrine sulfate, were confirmed by 1H NMR, 13C NMR, liquid chromatography–high‐resolution mass spectrometry (LC‐HRMS), attenuated total reflectance Fourier transform infrared and thermogravimetric analysis. In the LC‐HRMS study, the mass error value of synthesized compounds was less than 10 ppm (error) which confirms the identity of the reference materials. New HPLC‐DAD method were developed to ensure the purity of the reference materials. We used the HILIC column as metabolite reference standards are highly polar. The mobile phase was composed of water and acetonitrile in fixed composition. The HPLC‐DAD purity of the developed reference materials was observed as 100%.

CONCLUSION

We have developed reproducible synthetic routes for octopamine sulfate, norfenefrine sulfate and etilefrine sulfate, which are prohibited in sports by WADA. The synthesized metabolites were characterized using different advanced analytical techniques. These reference standards will be helpful to all WADA‐accredited laboratories in routine anti‐doping testing. © 2023 Society of Chemical Industry (SCI).

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 C_max and 80% of AUC_last 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.

Detection of bazedoxifene, a selective estrogen receptor modulator, in human urine by liquid chromatography-tandem mass spectrometry

Bazedoxifene, a selective estrogen receptor modulator, has been explicitly included in the prohibited list issued by the World Anti-Doping Agency (WADA) since January 2020. A high-resolution liquid chromatography-tandem mass spectrometric detection method was developed to identify bazedoxifene and its metabolites in human urine and to quantify bazedoxifene (free plus glucuronide) for doping control purposes. Bazedoxifene acetate (20 mg) was orally administered to seven male volunteers, and the urine samples collected were analyzed using the developed method. The linearity ranged from 0.5 to 200 ng/ml, and the limit of detection was <0.2 ng/ml. The interday precision (2.2% to 3.6%) and the interday accuracy (-10.0% to 1.9%) were adequate. Bazedoxifene, bazedoxifene-N-oxide, and bazedoxifene glucoconjugates were identified in the urine samples. The profiles of the urinary excretion indicated the presence of small amounts of free bazedoxifene and bazedoxifene-N-oxide, whereas bazedoxifene glucuronide was the predominant metabolite. The cumulative excretion amount of bazedoxifene (free form plus glucuronide conjugate) within 78 h after the administration was 0.7% to 1.3% of the total dose. In all subjects, bazedoxifene (free plus glucuronide) could be detected in urine up to 78 h after administration.

Insights for applying erythrosine B as a green fluorescence probe for estimation of anticancer tamoxifen and its analog; clomiphene in nanogram concentration

The growth of tumor tissue is extremely pervasive among post-menopausal women. Commonly, from the clinical application, adjuvant selective estrogen receptor modulators such as tamoxifen are prescribed for prohibiting metastatic breast cancer, while its analog, clomiphene, is used to treat infertility in women. Lately, the significance of green chemistry on our environment was through reducing the influence of hazardous chemicals. Consequently, efforts were screened to perform a fast and simple eco-friendly green method for the determination of two aromatase inhibitors. In this study, a sensitive green spectrofluorimetric approach was developed to detect and characterize tamoxifen citrate (TAM) and clomiphene citrate (CLO) via complex formation with erythrosine B. The reaction between erythrosine B dye (EB) and the two aromatase inhibitors results in quenching the fluorescence activity of the dye by the formation of ion-pair in Britton-Robinson buffer (BRB) solution (pH 4.3) at 554 nm (λ_ex = 527 nm). The approach outcome confirmed that the solvent's inherent nature has a critical impact on the approachs' sensitivity and reproducibility. An approved linear correlation was achieved between the reduction in the emission value of EB's fluorescence and the concentration in the ranges of 40.0-600.0 ng/mL for both TAM and CLO with mean % recoveries 100.20 ± 0.93 and 100.07 ± 1.09, respectively. The approach was validated regarding ICH protocols, and the outcomes were acceptable. The changes in Gibb's free energy (ΔG°) by the obtained ion-pair between EB and TAM or CLO were -36.65 or -37.03 kJ mol^-1, respectively, which indicates the reaction feasibility at ambient temperature. Commercial dosage forms for TAM and CLO were simply analyzed, and good recoveries were achieved within the range. The National Environmental Methods Index, Analytical Eco-Scale, and Green Analytical Procedure Index applications to our illustrated approach present additional eligibility to this study.

Physical Separation of Amphiprotic-Polar AproticS for Simultaneous Extraction and Clean-up of Clomiphene from Plasma before Liquid Chromatographic Analysis

An efficient and quantitative two phase freezing (TPF) method coupled with high performance liquid chromatography and UV-Vis detector was developed for the extraction, clean up, and determination of clomiphene citrate (CLC) in plasma samples. The separation of two miscible solvents by TPF method permits that the CLC was efficiently removed from proteins and transferred into the relative aprotic dipolar organic phase and in consequence, gave a higher recovery. The TPF method was compared to conventional liquid-liquid extraction and it gave more clean solution with better reproducibility. Linear range, limit of detection, and limit of quantification for CLC in plasma were obtained in the range of 0.06-18, 0.02, and 0.06 µg mL^-1, respectively. The intraday and interday reproducibility for concentration of 1.0 µg mL^-1 (%RSD) were 3.2% and 4.6%, respectively. In addition, the trueness, ruggedness, and reality of TPF were assessment. Finally, several real plasma samples were successfully analyzed using the developed method.

Nano-Targeted Delivery of Toremifene, an Estrogen Receptor-α Blocker in Prostate Cancer

PURPOSE

Estrogen Receptor-α (ERα) expression is increased in prostate cancer and acts as an oncogene. We propose that blocking of estrogen hormone binding to ERα using the ERα blocker toremifene will reduce the tumorigenicity of prostate cancer, and nano-targeted delivery of toremifene will improve anticancer efficacy. We report the synthesis and use in an orthotopic mouse model of PLGA-PEG nanoparticles encapsulating toremifene and nanoparticles encapsulating toremifene that are also conjugated to anti-PSMA for targeted prostate tumor delivery.

METHODS

Human prostate cancer cell line PC3M and a nude mouse model were used to test efficacy of nano-targeted and nano-encapsulated toremifene versus free toremifene on the growth and differentiation of tumor cells.

RESULTS

Treatment with free toremifene resulted in a significant reduction in growth of prostate tumor and proliferation, and its nano-targeting resulted in greater reduction of prostate tumor growth, greater toremifene tumor uptake, and enhanced tumor necrosis. Tumors from animals treated with nano-encapsulated toremifene conjugated with anti-PSMA showed about a 15-fold increase of toremifene compared to free toremifene.

CONCLUSIONS

Our data provide evidence that blocking ERα by toremifene and targeting prostate cancer tissues with anti-PSMA antibody on the nanoparticles' surface repressed the tumorigenicity of prostate cancer cells in this mouse model.

Rapid determination of anti-estrogens by gas chromatography/mass spectrometry in urine: Method validation and application to real samples

A fast screening protocol was developed for the simultaneous determination of nine anti-estrogenic agents (aminoglutethimide, anastrozole, clomiphene, drostanolone, formestane, letrozole, mesterolone, tamoxifen, testolactone) plus five of their metabolites in human urine. After an enzymatic hydrolysis, these compounds can be extracted simultaneously from urine with a simple liquid-liquid extraction at alkaline conditions. The analytes were subsequently analyzed by fast-gas chromatography/mass spectrometry (fast-GC/MS) after derivatization. The use of a short column, high-flow carrier gas velocity and fast temperature ramping produced an efficient separation of all analytes in about 4 min, allowing a processing rate of 10 samples/h. The present analytical method was validated according to UNI EN ISO/IEC 17025 guidelines for qualitative methods. The range of investigated parameters included the limit of detection, selectivity, linearity, repeatability, robustness and extraction efficiency. High MS-sampling rate, using a benchtop quadrupole mass analyzer, resulted in accurate peak shape definition under both scan and selected ion monitoring modes, and high sensitivity in the latter mode. Therefore, the performances of the method are comparable to the ones obtainable from traditional GC/MS analysis. The method was successfully tested on real samples arising from clinical treatments of hospitalized patients and could profitably be used for clinical studies on anti-estrogenic drug administration.

MS2/TOF and LC-MS/TOF studies on toremifene to characterize its forced degradation products

The present study was designed to characterize the possible degradation products of toremifene under varied conditions as prescribed by ICH guidelines Q1A(R2). The forced degradation studies were conducted on toremifene citrate under the conditions of hydrolysis (acidic, basic and neutral), photolysis, oxidation and dry heat. The drug was found unstable to photolysis and hydrolysis in water and acidic media but stable to alkaline hydrolysis, peroxide oxidation and thermal degradation. In total fifteen degradation products (I-XV) were formed, which were resolved from each other and the drug on a C-18 column employing an isocratic elution method. A complete mass fragmentation pattern of the drug was established with the help of LC/ESI-MS/TOF to assist characterization of the degradation products. Of the fifteen products, six products III, IV, VII, VIII, XIV and XV were detected in LC-MS. The molecular masses of III, IV, VII and VIII were found to be the same i.e., 387, while those of XIV and XV were 389 and 403, respectively. Structures of these products were elucidated through comparison of their mass fragmentation patterns with the drug, which were proposed on the basis of accurate masses of the parent and fragment ions. These were characterized as (Z)-2-(2-(dimethylamino)ethyl)-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol (III), (E)-2-(2-(dimethylamino)ethyl)-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol (IV), (E)-4-(4-(2-(dimethylamino)ethoxy)phenyl)-3,4-diphenylbut-3-en-1-ol (VII), (Z)-4-(4-(2-(dimethylamino)ethoxy)phenyl)-3,4-diphenylbut-3-en-1-ol (VIII), 2-(4-(10-(2-chloroethyl)phenanthren-9-yl)phenoxy)-N-methylethanamine (XIV), and 2-(4-(10-(2-chloroethyl)phenanthren-9-yl)phenoxy)-N,N-dimethylethanamine (XV). Finally, a most plausible mechanistic explanation for degradation of the drug in different chemical environments is also proposed. The results of the study disclose six new degradation related impurities of the drug.

Preventive doping control screening analysis of prohibited substances in human urine using rapid-resolution liquid chromatography/high-resolution time-of-flight mass spectrometry

Unification of the screening protocols for a wide range of doping agents has become an important issue for doping control laboratories. This study presents the development and validation of a generic liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) screening method of 241 small molecule analytes from various categories of prohibited substances (stimulants, narcotics, diuretics, beta(2)-agonists, beta-blockers, hormone antagonists and modulators, glucocorticosteroids and anabolic agents). It is based on a single-step liquid-liquid extraction of hydrolyzed urine and the use of a rapid-resolution liquid chromatography/high-resolution time-of-flight mass spectrometric system acquiring continuous full scan data. Electrospray ionization in the positive mode was used. Validation parameters consisted of identification capability, limit of detection, specificity, ion suppression, extraction recovery, repeatability and mass accuracy. Detection criteria were established on the basis of retention time reproducibility and mass accuracy. The suitability of the methodology for doping control was demonstrated with positive urine samples. The preventive role of the method was proved by the case where full scan acquisition with accurate mass measurement allowed the retrospective reprocessing of acquired data from past doping control samples for the detection of a designer drug, the stimulant 4-methyl-2-hexanamine, which resulted in re-reporting a number of stored samples as positives for this particular substance, when, initially, they had been reported as negatives.

Mass spectrometric characterization of tamoxifene metabolites in human urine utilizing different scan parameters on liquid chromatography/tandem mass spectrometry

Different liquid chromatographic/tandem mass spectrometric (LC/MS/MS) scanning techniques were considered for the characterization of tamoxifene metabolites in human urine for anti-doping purpose. Five different LC/MS/MS scanning methods based on precursor ion scan (precursor ion scan of m/z 166, 152 and 129) and neutral loss scan (neutral loss of 72 Da and 58 Da) in positive ion mode were assessed to recognize common ions or common losses of tamoxifene metabolites. The applicability of these methods was checked first by infusion and then by the injection of solution of a mixture of reference standards of four tamoxifene metabolites available in our laboratory. The data obtained by the analyses of the mixture of the reference standards showed that the five methods used exhibited satisfactory results for all tamoxifene metabolites considered at a concentration level of 100 ng/mL, whereas the analysis of blank urine samples spiked with the same tamoxifene metabolites at the same concentration showed that the neutral loss scan of 58 Da lacked sufficient specificity and sensitivity. The limit of detection in urine of the compounds studied was in the concentration range 10-100 ng/mL, depending on the compound structure and on the selected product ion. The suitability of these approaches was checked by the analysis of urine samples collected after the administration of a single dose of 20 mg of tamoxifene. Six metabolites were detected: 4-hydroxytamoxifene, 3,4-dihydroxytamoxifene, 3-hydroxy-4-methoxytamoxifene, N-demethyl-4-hydroxytamoxifene, tamoxifene-N-oxide and N-demethyl-3-hydroxy-4-methoxytamoxifene, which is in conformity to our previous work using a time-of-flight (TOF) mass spectrometer in full scan acquisition mode.