Towards clinical adherence monitoring of oral endocrine breast cancer therapies by LC-HRMS-method development, validation, comparison of four sample matrices, and proof of concept

Abstract

Oral endocrine therapies (OET) for breast cancer treatment need to be taken over a long period of time and are associated with considerable side efects. Therefore, adherence to OET is an important issue and of high clinical signifcance for breast cancer patients’ caregivers. We hypothesized that a new bioanalytical strategy based on liquid chromatography and highresolution mass spectrometry might be suitable for unbiased adherence monitoring (AM) of OET. Four diferent biomatrices (plasma, urine, fnger prick blood by volumetric absorptive microsampling (VAMS), oral fuid (OF)) were evaluated regarding their suitability for AM of the OET abemaciclib, anastrozole, exemestane, letrozole, palbociclib, ribociclib, tamoxifen, and endoxifen. An analytical method was developed and validated according to international recommendations. The analytical procedures were successfully validated in all sample matrices for most analytes, even meeting requirements for therapeutic drug monitoring. Chromatographic separation of analytes was achieved in less than 10 min and limits of quantifcation ranged from 1 to 1000 ng/mL. The analysis of 25 matching patient samples showed that AM of OET is possible using all four matrices with the exception of, e.g., letrozole and exemestane in OF. We were able to show that unbiased bioanalytical AM of OET was possible using diferent biomatrices with distinct restrictions. Sample collection of VAMS was difcult in most cases due to circulatory restraints and peripheral neuropathy in fngers and OF sampling was hampered by dry mouth syndrome in some cases. Although parent compounds could be detected in most of the urine samples, metabolites should be included when analyzing urine or OF. Plasma is currently the most suitable matrix due to available reference concentrations.