We found that the percentage of cells in G1 significantly increased, p ˂ 0.05 via Student’s t-test, from 58 to 68% and 63 to 74% in PC3 and C4-2 cells, respectively, indicating G1 arrest of prostate cancer cells in response to APE1/Ref-1 inhibition. The gene discussed is APEX1; the disease is prostate cancer.