Development and validation of an LC-MS/MS method for the quantification of imatinib and imatinib-d8 in human plasma for the support of an absolute bioavailability microdose trial.

Here we describe the development and validation of an LC-MS/MS method for the quantification of imatinib and imatinib-d8 in plasma for the support of a clinical absolute bioavailability microdosing trial. The focus lies on the technical aspects to analyse high concentrations of imatinib and low concentrations of imatinib-d8 that are present simultaneously in study samples, using a single sample processing and analytical method. With the validated assay, imatinib and imatinib-d8 can be quantified simultaneously in ranges from 25.0 - 5,000 ng/mL and 0.01 - 2.0 ng/mL, respectively. The method was successfully applied in an imatinib-d8 absolute bioavailability microdosing trial, where a 100 µg imatinib-d8 microdose was intravenously administered to a patient on oral imatinib treatment 400 mg once daily.

Exposure-response analyses of abiraterone and its metabolites in real-world patients with metastatic castration-resistant prostate cancer.

BACKGROUND: Abiraterone acetate is an oral 17α-hydroxylase/C17,20-lyase (CYP17) inhibitor approved for the treatment of metastatic castration-resistant prostate cancer (mCPRC) patients. Previously, a prospective observational trial demonstrated a relationship between abiraterone trough concentrations (Cmin) in plasma and treatment efficacy. The aim of our study was to investigate the exposure-response relationship of abiraterone and its metabolites, and to study if the proposed target for abiraterone of 8.4 ng/mL is feasible in a "real-world" patient cohort. PATIENTS AND METHODS: mCRPC patients who had at least one abiraterone plasma concentration at steady-state were included in this study. Plasma abiraterone and its metabolites levels were analyzed using a validated liquid chromatography-mass spectrometry method. Using calculated Cmin values of abiraterone and its active metabolite Δ(4)-abiraterone (D4A), univariate, and multivariable Cox regression analyses were performed. RESULTS: Sixty-two patients were included in this retrospective analysis, of which 42% were underexposed (mean abiraterone Cmin ≤ 8.4 ng/mL). In multivariable analysis, Cmin ≥ 8.4 ng/mL was associated with longer prostate-specific antigen (PSA) independent progression-free survival (16.9 vs 6.1 months; p = 0.033), which resulted in a hazard ratio of 0.44 (95% confidence interval: 0.23-0.82, p = 0.01). D4A Cmin did not show a relationship with treatment efficacy. CONCLUSION: Our study shows that mCRPC patients with an abiraterone Cmin ≥ 8.4 ng/mL have a better prognosis compared with patients with low Cmin. Monitoring Cmin of abiraterone can help to identify those patients at risk of suboptimal treatment for whom treatment optimization may be appropriate.

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.