TP53 and malignant colon neoplasm: Notably, in a pair of isogenic tumors in mice derived from human colon cancer HCT116 cells (p53 or p53KO), PEPD KD by intratumor injection of siRNA inhibited the growth of p53 tumors by 79% with strong induction of p53 target proteins but had no effect on p53KO tumors7.