Through the screening of a drug repositioning library from KCB, pyrimethamine was identified as a hit chemical for the treatment of lung cancer, selectively inhibiting DX2 over AIMP2 (IC50 > 100 μM) with an IC50 value of 0.73 μM in A549 cells expressing nanoluciferase-tagged DX2. The gene discussed is AIMP2; the disease is lung carcinoma.