Identification and structural characterization of potential degraded impurities of ribociclib by time of flight -tandem mass spectrometry, and their toxicity prediction

The US FDA and EMA approved Ribociclib (RIBO) to treat metastatic breast cancers in 2017. Formation of impurities during storage of any drug can significantly contribute to its overall toxicity and therapeutic efficacy, which ultimately leads to a safety concern. Over the period, it has been observed that impurities sometimes cause serious unwanted toxicity, which can even lead to withdrawal of a drug from market. Therefore, complete characterization of potential impurities is extremely important to identify molecular hot spots regarding structural changes. To the best of our knowledge, till date, the potential degraded impurities of RIBO are unknown. No study reported in literature on the structural characterization of the degradation impurities of RIBO. In this study, an ICH recommended comprehensive stress study under hydrolytic, oxidative, photolytic and thermolytic conditions was performed on RIBO. The degradation products were characterized by tandem mass spectrometry utilising time of flight mass analyzer majorly after electrospray ionisation. The atmospheric pressure chemical ionisation mode was employed in characterization of the N-oxide degradation products where Meisenheimer rearrangement occurred. A degradation product was synthesized in house and fully characterized with the help of NMR (1H NMR, 13C NMR, DEPT, 2D NMR and D2O exchange experiments). The source of formylation for the generation of degradation products was investigated employing different solvent systems. The degradation pathways were delineated by explaining the putative mechanism of degradation in various conditions. The in silico toxicity of the degradation impurities was evaluated with the help of ProTox-II toxicity prediction platform.