Establishment of an analytical method for simultaneous quantitation of CDK4/6 inhibitors, aromatase inhibitors, and an estrogen receptor antagonist in human plasma using LC-ESI-MS/MS.

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors (palbociclib, abemaciclib, and ribociclib) are used to treat human epithelial growth factor receptor (HER)-2 negative and hormone receptor (HR) positive advanced breast cancer in combination with aromatase inhibitors (letrozole, anastrozole) or an estrogen receptor antagonist (fulvestrant). Administration of these drugs frequently causes severe side effects, such as neutropenia and diarrhea. Therefore, therapeutic drug monitoring (TDM) of CDK4/6 inhibitors, aromatase inhibitors, and the estrogen receptor antagonist is considered important for ensuring the efficacy and safety of these drugs. In this study, we describe a simple, highly sensitive, and specific liquid chromatography/electrospray ionization tandem mass spectrometry method for simultaneous quantitation of the concentrations of palbociclib, abemaciclib, ribociclib, letrozole, anastrozole, and fulvestrant. In addition, we analyzed plasma samples from patients with HER2-negative and HR-positive advanced breast cancer treated with these compounds using this novel method. In our method, the intra-assay relative error (RE) values ranged from -12.8% to 12.9%, the inter-assay RE values ranged from -4.8% to 6.2%, and the coefficient of variation (CV) values for intra- and inter-assay were ≤8.6% and ≤13.3%, respectively. The analytes showed good stability with RE values ranging from -13.5% to 13.6% and CV values <10.4%. Moreover, all the samples from patients were successfully quantified, and were within the range of measurement. This method can be used for TDM of routine anticancer drugs in clinical practice and for pharmacokinetics/pharmacodynamics research in future studies.

High-throughput liquid chromatography/electrospray ionization-tandem mass spectrometry method using in-source collision-induced dissociation for simultaneous quantification of imatinib, dasatinib, bosutinib, nilotinib, and ibrutinib in human plasma.

Recent studies have shown that therapeutic drug monitoring of tyrosine kinase inhibitors (TKIs) could improve treatment efficacy and safety. A simple analytical method using high-performance LC/electrospray ionization-tandem mass spectrometry has been developed and validated for simultaneous quantification of BCR-ABL and Bruton's TKIs used for chronic leukemia (imatinib, dasatinib, bosutinib, nilotinib, and ibrutinib) in human plasma. Although these structures and physical properties are similar, owing to their different linear ranges, simultaneously determining the plasma levels of these five TKIs by applying optimal MS parameters remains difficult. A quantitative range exceeding 60,000-fold was required, and the linear dynamic ranges of imatinib, bosutinib, and nilotinib were limited because of the presence of a saturated detection signal. In this study, we applied the in-source collision-induced dissociation technique to control the ion amounts in mass spectrometry. This new method allowed rapid determination within 5 min with simple pretreatment. The method was validated according to the US Food and Drug Administration guidelines. Moreover, all samples of patients with chronic leukemia were successfully measured and their values were within the linear range of measurement. Therefore, our high-throughput analytical system is useful to measure the plasma concentrations of imatinib, dasatinib, bosutinib, nilotinib, and ibrutinib in clinical practice.

Development of a precise quantitative method for monitoring sirolimus in whole blood using LC/ESI-MS/MS.

Sirolimus is used on patients after solid organ transplantation and on lymphangioleiomyomatosis (LAM) patients, and therapeutic drug monitoring is required in clinical practice. We have previously reported an accurate method for quantitative determination of sirolimus, but its sample preparation step was complicated. In this study, we developed a modified liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for sirolimus quantification. A supported liquid extraction cartridge was used to purify sirolimus from whole blood and ion suppression was mostly prevented. The validation results met the acceptance criteria. This method was compared with the antigen conjugated magnetic immunoassay (ACMIA) and our previously reported method, using whole blood samples from LAM patients. Comparison of the Bland-Altman plots of the currently developed method and the previous method revealed no significant difference between the two methods (mean bias, -2.02%; 95% CI, -7.81-3.78). The values obtained using ACMIA were significantly higher than those obtained using the current method by 13.87% (95% CI, 6.49-21.25) owing to cross-reactivity. The degrees of cross reactivities in LAM patients and in organ transplant patients were similar, and our LC/ESI-MS/MS method precisely measured the blood concentrations of sirolimus.

Estimation of Blood Sirolimus Concentration Based on Tacrolimus Concentration/Dose Normalized by Body Weight Ratio in Lung Transplant Patients.

BACKGROUND: Sirolimus and tacrolimus require accurate drug dosing based on their target blood levels to produce better clinical outcomes, specifically, the avoidance of drug-induced adverse effects and the maintenance of efficacy. However, because the ideal dose of sirolimus and the schedule for measuring its blood levels are unclear in lung transplant patients, an index is required for estimating sirolimus blood concentrations. The aim of this work is to study the correlation between the trough concentration/dose normalized by body weight (C0/D) ratios of sirolimus and tacrolimus in lung transplant patients. METHODS: Thirteen lymphangiomyomatosis patients who underwent lung transplantation and were treated with sirolimus and tacrolimus from February 2015 to July 2018 were divided into 2 groups, one receiving twice-daily (TD, n = 6) and the other once-daily (OD, n = 7) tacrolimus formulations. The correlation between the C0/D ratio of sirolimus and patient background was evaluated using Spearman's rank correlation coefficient. Correlations between sirolimus and tacrolimus C0/D ratios or doses were analyzed by single regression analysis. RESULTS: Significant correlations were found between the C0/D ratios of sirolimus and tacrolimus. The regression equations from the initial data of TD and OD groups at steady state were y = 1.880x + 32.636 (adjusted R = 0.743, P = 0.017) and y = 1.684x + 38.816 (adjusted R = 0.919, P < 0.001), respectively. In addition, the regression equations from all data of TD and OD groups were y = 1.883x + 4.170 (adjusted R = 0.546, P < 0.001) and y = 1.950x + 43.188 (adjusted R = 0.898, P < 0.001), respectively. A significant correlation between the dosage of sirolimus and tacrolimus was observed only in the OD group, with relatively low accuracy. CONCLUSIONS: Blood sirolimus concentrations can be estimated using the C0/D ratio of tacrolimus, suggesting that the C0/D ratio of tacrolimus is an index of required sirolimus dosage and the frequency of blood sirolimus concentration measurements.