One-step quenching and extraction were applied as previously described to cell samples [14, 15]. Briefly, after the removal of cell culture medium, the cells were washed twice with ice-cold PBS, and then the pellets were quenched by 2 mL −20°C methanol (HPLC grade, Kermel Chemical Reagent, Tianjin, China). Afterwards, the cells were scraped and transferred into a 15-mL centrifugation tube, followed by adding 2 mL −20°C chloroform and ice-cold ddH2O (V/V/V 1:1:0.7). Cell lysates were mixed by vortex for 5mins and left stand for 15 mins, and then centrifuged with 14,000 g for 30 min at 4°C, generating two-phase extraction. The aqueous phase was lyophilized and then dissolved into 450 μL D2O with 50 μL buffer (1.5 M K2HPO4, 0.375 M NaH2PO4, 0.1% TSP, 0.2% NaN3, pH 7.4) . After being mixed with vortex, undissolved substances were removed by 14,000 × g centrifugation for 5 mins at 4°C and the supernatant was transferred into a 5-mm nuclear magnetic tube for NMR analysis.