Quantitation of the ATR inhibitor elimusertib (BAY-1895344) in human plasma by LC-MS/MS

Ataxia-telangiectasia mutated and Rad3-related (ATR) is master regulator of the DNA-damage response that, through multiple mechanisms, can promote cancer cell survival in response to replication stress from sources including chemotherapy and radiation. Elimusertib (BAY-1895344) is an orally available small molecule ATR inhibitor currently in preclinical and clinical development for cancer treatment. To support these studies and define elimusertib pharmacokinetics, we developed a high-performance liquid chromatography mass spectrometry method for its quantitation. A 50 μL volume of plasma was subjected to acetonitrile protein precipitation, followed by chromatographic separation using a Phenomenex Polar-RP column (4 μm, 2 x 50 mm) and a gradient mobile phase consisting of 0.1% formic acid in acetonitrile and water, during a 7 minute run time. Mass spectrometric detection was achieved using a SCIEX 4000 triple-stage mass spectrometer with electrospray positive-mode ionization. With a stable isotopic internal standard, the assay was linear from 30 to 5,000 ng/mL and proved to be both accurate (93.5-108.2%) and precise (