NQO1 and colon carcinoma: FaDu human pharynx squamous carcinoma cells had a high level of NQO1 activity, 557.6 ± 120.3 nmol.min−1.mg protein−1, while HCT116 human colon carcinoma cells had a level of NQO1 activity that was close to the average for human tumors, 230.4 ± 31 nmol.min−1.mg protein−1 (Fig. 2).