As shown in Supplementary Fig. 21, the intracellular iNOS concentrations of GL261 cancer cells at densities of 103, 104, 105 and 106 cells mL−1 were approximately 2.0, 4.1, 9.8, and 17.3 μM, and the intracellular O2·- were approximately 4.4, 11.6, 36.0 and 63.9 nM, respectively, similar to the concentrations reported in other literatures35. This evidence concerns the gene NOS2 and cancer.