Degradation pathways and impurity profiling of the anticancer drug apalutamide by HPLC and LC-MS/MS and separation of impurities using Design of Experiments

Apalutamide, an androgen receptor inhibitor, is used to treat prostate cancer. A stability-indicating high-performance liquid chromatography method was developed for the estimation of assay and organic impurities of apalutamide in drug substance and in tablet dosages using Design of Experiments. The chromatographic separation was achieved within 30 min using Atlantis dC(18), 100 x 4.6 mm, 3.0 mu m and the binary gradient program (10 mm KH2PO4, pH 3.5; acetonitrile). The detection wavelength, flow rate, column temperature and injection volume used were 270 nm, 1.0 ml/min, 45 degrees C and 10 mu l, respectively. The interaction of independent variables (pH, column temperature and flow rate) and their influences on HPLC parameters were studied using a central composite design, and then the peak separation and elution behaviors between apalutamide and its seven impurities were determined. The method validation was performed for linearity, detection limit, quantitation limit, accuracy, precision and robustness as per the International Conference on Harmonization. A high-quality recovery with good precision (91.7-106.0%) and correlations (r(2) > 0.997) within a linear range of 0.12-2.24 mu g/ml (0.05-0.3%, w/w) were achieved consistently for assay and organic impurities of apalutamide. The stability-indicating characteristics of the proposed method were assessed through forced degradation and mass balance studies. An effort was made to figure out the chemical structures of newly formed degradation products (DP1-DP5) using LC-MS/MS.