Simultaneous quantification of four hormone therapy drugs by LC-MS/MS: Clinical applications in breast cancer patients.

Introduction: Aromatase inhibitors such as anastrozole, letrozole, exemestane and selective estrogen down-regulator (SERD) fulvestrant are used mostly to treat breast cancer estrogen receptor positive in post-menopausal women. These drugs are given either through the oral route or by intramuscular injection. They have shown great inter-individual variability with a risk of cardiometabolic disorders. Hence the importance of their therapeutic drug monitoring not only for exposure-efficacy but also exposure-toxicity. We describe here a LC-MS/MS method for the simultaneous quantification of anastrozole, letrozole, exemestane and fulvestrant in human plasma.

Material And Methods: Plasma samples were prepared by a single-step protein precipitation. The liquid chromatography system was paired with a triple quadrupole mass spectrometer. Quantification were achieved in Multiple Reactions Monitoring mode and the electrospray ionization was in positive mode.

Results: The method demonstrated consistent analytical performance across various parameters, including linearity, specificity, sensitivity, matrix effect, upper and lower limits of quantification, extraction recovery, precision, accuracy, hemolysis effect, dilution integrity, and stability under different storage conditions, in accordance with established guidelines. The analysis time for each run was 4 min. Calibration curves exhibited linearity within the 1-100 ng/mL range, with correlation coefficients > 0.99 for the four analytes. Plasma concentrations from 42 patients were integrated into the selected calibration. Stability assessments indicated that the four drugs remained stable at - 20 °C for three months, 15 days under refrigeration, up to 7 days at room temperature, and after three freeze-thaw cycles.

Conclusion: We have developed and validated this quantitative method for therapeutic drug monitoring of those four hormone therapy drugs:anastrozole, letrozole, fulvestrant and exemestane. This method can be also used for future clinical pharmacokinetics /pharmacodynamics studies.