Analytical challenges in quantifying abiraterone with LC-MS/MS in human plasma

Analytical Validation of a Volumetric Absorptive Microsampling Method for Therapeutic Drug Monitoring of the Oral Targeted Anticancer Agents, Abiraterone, Alectinib, Cabozantinib, Imatinib, Olaparib, and Sunitinib, and Metabolites

BACKGROUND

Volumetric Absorptive Microsampling (VAMS) is a useful tool for therapeutic drug monitoring (TDM) of oral targeted anticancer agents. VAMS aims to improve safety and efficacy by enabling at-home blood sample collection by patients. This study aimed to develop and validate an ultra-high performance liquid chromatography-tandem mass spectrometry method for the quantitative determination of abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and the metabolites, Δ(4)-abiraterone (D4A), alectinib-M4, imatinib-M1, and N -desethyl sunitinib, in dried whole blood samples using VAMS to support TDM.

METHODS

After the collection of 10 μL of whole blood sample using the VAMS device, the analytes were extracted from the tip using methanol with shaking, evaporated, and reconstituted in acetonitrile:0.1 mol/L ammonium hydroxide in water (1:1, vol/vol). The extracts were then analyzed using ultra-high performance liquid chromatography-tandem mass spectrometry. Validation experiments based on the ICH M10 guideline were carried out, and stability was evaluated under shipping and storage conditions. VAMS specimens were collected in the outpatient clinic to demonstrate the applicability of the assay.

RESULTS

The validated range of the method was considered accurate and precise for all analytes. Accordingly, the validation experiments met the relevant requirements, except for cross-analyte interference. Based on the stability data, shipment can be performed at room temperature within 14 days after sample collection and the VAMS specimen can be stored up to 9 months at -20 and -70°C. Samples from 59 patients were collected at the hospital.

CONCLUSIONS

The developed method could be used to successfully quantify the concentrations of abiraterone, D4A, alectinib, alectinib-M4, cabozantinib, imatinib, imatinib-M1, olaparib, sunitinib, and N -desethyl sunitinib within the validated range using VAMS. Therefore, the method can be used to estimate the dried whole blood-to-plasma ratios for TDM in the clinic.

Long-Term Pharmacokinetic Follow-Up of Abiraterone Acetate in Patients with Metastatic Castration-Resistant Prostate Cancer

This ABIGENE pharmacokinetic (PK) study sought mainly to characterize the unchanged drug PK during long-term abiraterone acetate (AA) administration in advanced prostate cancer patients (81 patients). It was observed that individual AA concentrations remained constant over treatment time, with no noticeable changes during repeated long-term drug administration for up to 120 days. There was no correlation between AA concentrations and survival outcomes. However, a significant association between higher AA concentrations and better clinical benefit was observed (p = 0.041). The safety data did not correlate with the AA PK data. A significant positive correlation (r = 0.40, p < 0.001) was observed between mean AA concentration and patient age: the older the patient, the higher the AA concentration. Patient age was found to impact steady-state AA concentration: the older the patient, the higher the mean AA concentration. Altogether, these data may help to guide future research and clinical trials in order to maximize the benefits of AA metastatic castration-resistant prostate cancer patients.

Results of the first international quality control programme for oral targeted oncolytics

AIMS

With the rising number of oral targeted oncolytics and growing awareness of the benefits of therapeutic drug monitoring (TDM) within the field of oncology, it is expected that the requests for quantifying concentrations of these drugs will increase. It is important to (cross-)validate available assays and ensure its quality, as results may lead to altered dosing recommendations. Therefore, we aimed to evaluate the performance of laboratories measuring concentrations of targeted oral oncolytics in a one-time international quality control (QC) programme.

METHODS

Participating laboratories received a set of plasma samples containing low, medium and high concentrations of imatinib, sunitinib, desethylsunitinib, pazopanib, cabozantinib, olaparib, enzalutamide, desmethylenzalutamide and abiraterone, with the request to report their results back within five weeks after shipment. Accuracy was defined acceptable if measurements where within 85%-115% from the weighed-in reference concentrations. Besides descriptive statistics, an exploratory ANOVA was performed.

RESULTS

Seventeen laboratories from six countries reported 243 results. Overall, 80.7% of all measurements were within the predefined range of acceptable accuracy. Laboratories performed best in quantifying imatinib and poorest in quantifying desethylsunitinib (median absolute inaccuracy respectively 4.0% (interquartile range (IQR) 1.8%-6.5%) and 15.5% (IQR 8.8%-34.9%)). The poorest performance of desethylsunitinib might be caused by using the stable-isotope-labelled sunitinib instead of desethylsunitinib as an internal standard, or due to the light-induced cis(Z)/trans(E) isomerization of (desethyl)sunitinib. Overall, drug substance and performing laboratory seemed to influence the absolute inaccuracy (F = 16.4; p < 0.001 and F = 35.5; p < 0.001, respectively).

CONCLUSION

Considering this is the first evaluation of an international QC programme for oral targeted oncolytics, an impressive high percentage of measurements were within the predefined range of accuracy. Cross-validation of assays that are used for dose optimization of oncolytics will secure the performance and will protect patients from incorrect advices.

Biotransformation of Abiraterone Into Five Characteristic Metabolites by the Rat Gut Microbiota and Liver Microsomes

It is well known that the role of gut microbiota in drug metabolism, especially in oral difficult absorbable drugs. Understanding the gut microbiota could enable us to understand drugs in new ways. The purpose of the study was to investigate explore the metabolites of the anti-prostate cancer drug Abiraterone by examining gut microbiota metabolism and hepatic metabolism in vitro. In this study, five metabolites (M1, M2, M3, M4 and M5) of Abiraterone were discovered using LC/MSⁿ-IT-TOF. Four isomeric metabolites M1-M4 were found in liver microsome. M5 was found in the intestinal contents of Sprague-Dawley rats with a molecular weight of 388.31. Among them, M4 was found to be Abiraterone N-Oxide by comparison with the standard sample. After further comparing the metabolic behavior of Abiraterone in rat gut microbiota and liver microsomes, we delineated the possible metabolic pathways of Abiraterone. In conclusion, Abiraterone is metabolized specifically in liver microsomes and gut microbiota. This study can provide a theoretical basis for elucidating the metabolic mechanism of Abiraterone and guide its rational application in clinic.

Determination of Abiraterone and Its Metabolites in Human Serum by LC-ESI-TOF/MS Using Solid-phase Extraction

We developed and validated a liquid chromatography-electrospray ionization-time of flight/mass spectrometry method for the determination of abiraterone (Abi) and its metabolites (Δ⁴-Abi, 3-keto-5α-Abi, 3α-OH-5α-Abi and 3β-OH-5α-Abi) in human serum using Abi-d₄ as the internal standard. As a pretreatment procedure of serum samples, solid-phase extraction based on a silica-gel cartridge was used. The relative recovery of Abi and its metabolites was over the ranges of 84.5 - 109.2% at a concentration of 6.0 ng mL^-1 for Abi and 0.6 ng mL^-1 for its metabolites. The method was free from matrix effects. The calibration curve of Abi was linear over the range of 2.0 - 400 ng mL^-1 and those of its metabolites over the ranges 0.2 - 40 ng mL^-1. The results of the intra- and inter-day accuracy and precision data were within the FDA acceptance criteria. The optimized method was applied for the determination of Abi and its metabolites in human serum after oral administration of Abi acetate.

The effect of chemotherapy on the exposure-response relation of abiraterone in metastatic castration-resistant prostate cancer

Aims

To assess whether the exposure–response relation for abiraterone is different in pre‐chemotherapy patients compared to post‐chemotherapy patients with metastatic castration‐resistant prostate cancer (mCRPC).

Methods

Data were collected from three clinical studies in mCRPC patients treated with abiraterone acetate. Cox regression analysis was used to determine the relation between abiraterone exposure and survival (progression‐free survival [PFS] and overall survival [OS]). An interaction term was used to test whether chemotherapy pretreatment was an effect modifier. To investigate the effect of the previously defined exposure threshold of 8.4 ng/mL on survival, Kaplan–Meier analysis was used.

Results

In total, 98 mCRPC patients were included, of which 78 were pre‐chemotherapy and 20 were post‐chemotherapy patients. Chemotherapy pretreatment in mCRPC setting appears to be an effect modifier. In pre‐chemotherapy patients, no significant association between abiraterone exposure and survival was observed (HR 0.68 [95% CI 0.42–1.10], P = .12 and HR 0.85 [95% CI 0.46–1.60], P = .61, PFS and OS, respectively) and no longer survival was seen for patients with an abiraterone exposure above the predefined threshold. In contrast, a significant association was seen in post‐chemotherapy patients (HR 0.30 [95% CI 0.12–0.74], P = .01 and HR 0.38 [95% CI 0.18–0.82] P = .01, PFS and OS, respectively), with an increased survival when exposed above this threshold.

Conclusion

Chemotherapy pretreatment in mCRPC setting modifies the abiraterone exposure–response relation. No relation between abiraterone exposure and survival was seen for pre‐chemotherapy patients. Therefore, potentially lower doses can be used in this setting to prevent overtreatment and reduce financial toxicity.

A Novel LC-MS Method for the Determination of Abiraterone in Rat Plasma and its Application to Pharmacokinetic Studies

Background:

High-Performance Liquid Chromatography (HPLC)-Ultraviolet (UV) and Liquid Chromatography (LC)-Mass Spectrometry (MS)/MS methods have been used to analyse abiraterone (ART); however, a single-quadrupole mass spectrometer with LC-MS systems has never been used to analyse ART.

Objective:

The study aimed to establish a novel, simple assay of quantitating ART in rat plasma through LC-MS.

Method:

The analytical procedure involved the extraction of ART and D4-ART (internal standard, IS) from rat plasma through simple protein precipitation. Chromatographic separation was achieved using an isocratic mobile phase (acetonitrile: 5 mM ammonium formate with 0.1% formic acid, 50:50 v/v) at a flow rate of 0.30 mL/min on a Waters XBridge® C18 column with a total run time of 5 min. LC-MS ion transitions monitored were 350.1 and 354.1 for ART and IS, respectively. The method was validated, and the results met acceptance criteria.

Results:

The lower limit of quantitation achieved was 1 ng/mL, and linearity was 1-8000 ng/mL. The intra- and inter-day precisions were 1.26%-14.20% and 5.49%-13.08%, respectively, in rat plasma.

Conclusion:

LC-MS offers a novel, specific, sensitive, and accurate method for quantifying ART and it was successfully applied to pharmacokinetic studies of ART in rats.

Liquid biopsy reveals KLK3 mRNA as a prognostic marker for progression free survival in patients with metastatic castration-resistant prostate cancer undergoing first-line abiraterone acetate and prednisone treatment

Circulating RNAs extracted from liquid biopsies represent a promising source of cancer‐ and therapy‐related biomarkers. We screened whole blood from patients with metastatic castration‐resistant prostate cancer (mCRPC) following their first‐line treatment with abiraterone acetate and prednisone (AA‐P) to identify circulating RNAs that may correlate with progression‐free survival (PFS). In a prospective multicenter observational study, 53 patients with mCRPC were included after they started first‐line AA‐P treatment. Blood was drawn at baseline, 1, 3, and 6 months after treatment initiation. The levels of predefined circulating RNAs earlier identified as being upregulated in patients with mCRPC (e.g., microRNAs, long noncoding RNAs, and mRNAs), were analyzed. Uni‐ and multivariable Cox regression and Kaplan–Meier analyses were used to analyze the prognostic value of the various circulating RNAs for PFS along treatment. Detectable levels of kallikrein‐related peptidase 3 (KLK3) mRNA at baseline were demonstrated to be an independent prognostic marker for PFS (201 vs 501 days, P = 0.00054). Three months after AA‐P treatment initiation, KLK3 could not be detected in the blood of responding patients, but was still detectable in 56% of the patients with early progression. Our study confirmed that KLK3 mRNA detection in whole blood is an independent prognostic marker in mCRPC patients receiving AA‐P treatment. Furthermore, the levels of circulating KLK3 mRNA in patients receiving AA‐P treatment might reflect treatment response or early signs of progression.

Systematic Development and Validation of a RP-HPLC Method for Estimation of Abiraterone Acetate and its Degradation Products

The present study described the development of a reversed-phase liquid chromatographic method for the estimation of abiraterone acetate by Quality by Design (QbD) approach. Using an isocratic solvent system for the mobile phase, the chromatographic estimation of analyte was performed on a Hypersil BDS C18 column using mobile phase mixture containing acetonitrile and water with pH adjusted with 0.1% v/v orthophosphoric acid (15:85%v/v ratio), flow rate 1.0 mL.min-1 and detection at 250 nm using photodiode array detector. Systematic development of the chromatographic method was carried out by factor screening using a half-factorial design which suggested organic modifier (%), flow rate (mL.min-1) and autosampler temperature (°C) as influential variables. Further, the method was optimized by Box-Behnken design and trials performed were evaluated for the area under peak, retention time, theoretical plate count and tailing factor as the responses. Validation of the developed method showed good linearity, accuracy, precision and sensitivity. Evaluation of the stability-indicating profile of the method using forced degradation studies revealed the formation of a possible degradation product under acidic and alkaline conditions, while no such degradation product peaks were observed under the oxidative environment. Overall, the study construed the successful development of HPLC assay method for pharmaceutical applications.

The impact of a 1-hour time interval between pazopanib and subsequent intake of gastric acid suppressants on pazopanib exposure

Co‐treatment with gastric acid suppressants (GAS) in patients taking anticancer drugs that exhibit pH‐dependant absorption may lead to decreased drug exposure and may hamper drug efficacy. In our study, we investigated whether a 1‐hour time interval between subsequent intake of pazopanib and GAS could mitigate this negative effect on drug exposure. We performed an observational study in which we collected the first steady‐state pazopanib trough concentration (C_min) levels from patients treated with pazopanib 800 mg once daily (OD) taken fasted or pazopanib 600 mg OD taken with food. All patients were advised to take GAS 1 hour after pazopanib. Patients were grouped based on the use of GAS and the geometric (GM) C_min levels were compared between groups for each dose regimen. Additionally, the percentage of patients with exposure below the target threshold of 20.5 mg/L and the effect of the type of PPI was explored. The GM C_min levels were lower in GAS users vs non‐GAS users for both the 800 and 600 mg cohorts (23.7 mg/L [95% confidence interval [CI]: 21.1‐26.7] vs 28.2 mg/L [95% CI: 25.9‐30.5], P = .015 and 26.0 mg/L [95% CI: 22.4‐30.3] vs 33.5 mg/L [95% CI: 30.3‐37.1], P = .006). Subtherapeutic exposure was more prevalent in GAS users vs non‐GAS users (33.3% vs 19.5% and 29.6% vs 14%). Sub‐analysis showed lower GM pazopanib C_min in patients who received omeprazole, while minimal difference was observed in those receiving pantoprazole compared to non‐users. Our research showed that a 1‐hour time interval between intake of pazopanib and GAS did not mitigate the negative effect of GAS on pazopanib exposure and may hamper pazopanib efficacy.

Evaluation of dried blood spots as an alternative matrix for therapeutic drug monitoring of abiraterone and delta(4)-abiraterone in prostate cancer patients

Therapeutic drug monitoring (TDM) approaches may benefit patients treated with abiraterone acetate (AA) as drug efficacy is imprecise and important pharmacokinetic variability is known. Current methods based on the analysis of plasma present the disadvantage of the fast degradation of the analytes in the liquid sample. Dried blood spots (DBS) consist of a minimally invasive and unexplored sampling strategy to monitor the levels of abiraterone (ABI) and delta(4)-abiraterone (D4A) in patients. This study presents the development and validation of a precise and accurate method to monitor ABI and D4A in DBS samples by UPLC-MS/MS. Bioanalytical method validation was carried out according to current guidelines, evaluating the impact of DBS-specific parameters such as hematocrit and spot volume on accuracy. Based on the analysis of quality control samples prepared at low, medium and high concentrations, the method was precise with CV ≤ 6.97 % and 10.26 % for ABI and D4A, respectively. The method was also highly accurate, between 93.6-106.8 % for ABI and 96.0-108.5 % for D4A. The DBS method is compatible with the analysis of samples of unknown volume and hematocrit range of the studied population. In addition, ABI and D4A were stable for 7 days in DBS at room temperature, which is feasible for sample transportation in postal service and analysis in the laboratory. Method application to 16 clinical samples revealed good correlation between measured plasma concentrations and estimated plasma concentrations for ABI (r = 0.884, P < 0.05) and D4A (r = 0.920, P < 0.05). Passing-Bablok regression analysis and Bland-Altmann plots indicated correlation between the results obtained from DBS and plasma, with a slight overestimation of the concentrations of ABI in DBS, which could be related to the small study cohort. Therefore, the results of this first work indicate that DBS consist of a promising alternative sampling strategy in TDM studies of AA.

A prospective phase I multicentre randomized cross-over pharmacokinetic study to determine the effect of food on abiraterone pharmacokinetics

Purpose

Abiraterone acetate is used at a fixed oral dose of 1000 mg once daily (OD) taken fasted. By administering abiraterone acetate with food, a reduced dose can potentially be given while maintaining equivalent abiraterone exposure. Moreover, administering abiraterone acetate with a breakfast is considered more patient friendly. The aim of this study was to establish the bio-equivalent lower dose of abiraterone when taken with a continental breakfast (CB) compared to the standard intake of 1000 mg OD fasted.

Methods

In this phase I, randomized cross-over, multi-center study, abiraterone pharmacokinetics (PK) were evaluated in patients with metastatic castration-resistant prostate cancer who were treated for 14 days with 1000 mg abiraterone acetate taken fasted, followed by 14 days of treatment with 500 mg taken with a CB.

Results

14 patients were enrolled into the study, of whom 12 were eligible for PK analysis. The geometric mean ratio (GMR) (fed/fasted) was 0.88 (90% CI 0.73–1.07) for area-under-the-curve (AUC_0–24h), 1.03 (90% CI 0.79–1.34) for C_max and 0.81 (90% CI 0.60–1.10) for C_trough, respectively. High inter-patient variability (> 50%) was found for all PK parameters under both intake conditions. Patients seemed to be slightly more satisfied about the intake of 500 mg abiraterone acetate when taken with a CB compared to 1000 mg fasted.

Conclusion

In conclusion, a bioequivalent lower dose of abiraterone taken with food could not be established in our study. Although based on the absence of a exposure–toxicity relationship, the strict bioequivalence margins as defined by the FDA guidelines could be applied more flexible for abiraterone. Information on the effect of food on abiraterone pharmacokinetics as presented in our study can be used for patients with difficulties taken their medication fasted.

Electronic supplementary material

The online version of this article (10.1007/s00280-019-03952-w) contains supplementary material, which is available to authorized users.

Development and validation of an UPLC-MS/MS method for the therapeutic drug monitoring of oral anti-hormonal drugs in oncology

A liquid chromatography-mass spectrometry assay was developed and validated for simultaneous quantification of anti-hormonal compounds abiraterone, anastrozole, bicalutamide, Δ(4)-abiraterone (D4A), N-desmethyl enzalutamide, enzalutamide, Z-endoxifen, exemestane and letrozole for the purpose of therapeutic drug monitoring (TDM). Plasma samples were prepared with protein precipitation. Analyses were performed with a triple quadrupole mass spectrometer operating in the positive and negative ion-mode. The validated assay ranges from 2 to 200 ng/mL for abiraterone, 0.2-20 ng/mL for D4A, 10-200 ng/mL for anastrozole and letrozole, 1-20 ng/mL for Z-endoxifen, 1.88-37.5 ng/mL for exemestane and 1500-30,000 ng/mL for enzalutamide, N-desmethyl enzalutamide and bicalutamide. Due to low sensitivity for exemestane, the final extract of exemestane patient samples should be concentrated prior to injection and a larger sample volume should be prepared for exemestane patient samples and QC samples to obtain adequate sensitivity. Furthermore, we observed a batch-dependent stability for abiraterone in plasma at room temperature and therefore samples should be shipped on ice. This newly validated method has been successfully applied for routine TDM of anti-hormonal drugs in cancer patients.

A clinically relevant decrease in abiraterone exposure associated with carbamazepine use in a patient with castration-resistant metastatic prostate cancer

ADVERSE EVENT

Decreased abiraterone exposure after introducing carbamazepine.

DRUGS IMPLICATED

Abiraterone acetate and carbamazepine.

THE PATIENT

A 65-year-old man with metastatic castration resistant prostate cancer, was treated with abiraterone acetate and prednisolone, and received concomitant carbamazepine for treatment of facial neuropathy.

EVIDENCE THAT LINKS THE DRUG TO THE EVENT

The interaction was confirmed by a decrease in abiraterone exposure >2-fold (area-under-the-curve and trough levels). After discontinuation of carbamazepine therapy, the abiraterone exposure normalized. No alternative causes were found that explain the decrease in abiraterone exposure.

MECHANISM

Induction of CYP3A and potentially phase I metabolism (SULT2A1) by carbamazepine.

IMPLICATIONS FOR THERAPY

Clinicians and pharmacists should be aware of this clinically relevant interaction. The national drug-drug interaction checker does not warn for this interaction, whereas both the Lexicomp® and Micromedex® advice to avoid if possible or to increase the abiraterone dose frequency to twice daily. Carbamazepine should not be combined with abiraterone to avoid underexposure and suboptimal therapy. Therapeutic drug monitoring of abiraterone is useful to guide therapy when drug-drug interactions cannot be avoided.