DCK knockdown reduces levels of ddCTP. (A) DCK was knocked down in TEX cells using shRNA. Levels of DCK were measured in whole-cell lysates by immunoblotting 7 days posttransduction. A representative immunoblot is displayed. (B-C) Quantification of total intracellular ddC and ddCTP by LC-MS/MS in DCK knockdown or control shRNA TEX cells following treatment with 1 µM ddC for 4 days. ddC and ddCTP levels were normalized to 10⁶ cells input. Data are shown as mean ± SD of 2 biological replicates performed at least in triplicate. NS, not significant.