LC/Q‐TOF‐MS‐based structural characterization of enasidenib degradation products and establishment of a stability‐indicating assay method: Insights into chemical stability

Abstract

RationaleEnasidenib (EDB) is an orally active selective mutant isocitrate dehydrogenase‐2 enzyme inhibitor approved by the U.S. Food and Drug Administration to treat acute myeloid leukemia. It lacks a reported forced degradation study and a stability‐indicating assay method (SIAM). This study addresses this gap by establishing a degradation profile in accordance with the International Council for Harmonisation Q1A and Q1B (R2) guidelines and developing a validated SIAM for EDB.MethodsEDB was exposed to forced degradation under various conditions (hydrolytic, photolytic, oxidative, and thermal stress). Degradation samples were analyzed using high‐performance liquid chromatography on an Agilent ZORBAX Eclipse Plus C18 column with a mobile phase consisting of 0.1% formic acid in Milli‐Q water and acetonitrile at a flow rate of 1 mL/min and detection at 270 nm. Liquid chromatography‐quadrupole time‐of‐flight‐high‐resolution mass spectrometry (LC/Q‐TOF HRMS) was used for the identification and characterization of degradation products. Nitrosamine risk assessment was conducted using a modified nitrosation assay procedure (NAP) test due to the presence of a secondary amine group in the drug, which is liable to forming nitrosamine drug substance–related impurities (NDSRI).ResultsThe drug exhibited significant degradation under acidic, basic, photolytic, and oxidative conditions in the solution state. A total of nine degradation products (DP) were formed (DP‐I, DP‐III, and DP‐IV: acidic conditions; DP‐I and DP‐III: basic conditions; DP‐II, DP‐V, DP‐VI, and DP‐VII: oxidative stress; and DP‐VII, DP‐VIII, and DP‐IX: photolytic conditions), which were separated and identified using reversed‐phase high‐performance liquid chromatography and characterized using liquid chromatography–tandem mass spectrometry. The mechanism behind the formation of EDB degradation products has been discussed, and this study was the first to develop a degradation pathway for EDB. In addition, the possibilities of NDSRI formation for EDB were studied using a modified NAP test, which can contribute to the risk assessment of the drug.ConclusionsForced degradation studies were conducted by establishing a SIAM for EDB. All the degradation products were characterized by mass spectral data obtained using LC/Q‐TOF‐HRMS.