L-189

L-189 is a DNA ligase I, III and IV inhibitor (IC₅₀ values are 5, 9 and 5 μM respectively) that blocks DNA binding (Ki= 5 μM for DNA ligase I). L-189 inhibits base excision repair (BER) and non-homologous end joining (NHEJ). L-189 specifically sensitizes cancer cells to DNA damage and increases the cytotoxicity of DNA-damaging agents.