ObjectiveTo investigate the radiosensitizing effect of 3-(5'-hydroxy-2'-furyl)-1-benzyl indazole ( YC-1 ) on hypoxic human adenocarcinoma cell line A549.MethodsMTT assay was used to test the inhibitory effect of YC-1 on proliferation of A549 cells.Clonogenic assay was performed to determine the radiosensitizing effect of YC-1 on hopxic A549 cells.Single-hit multi-target model was used to plot survival curve and calculate sensitization enhancement ratio (SER).The cell cycle and apoptosis were measured by flow cytometry.ResultsThe proliferation of A549 cells was inhibited by YC-1 in a time-dose-dependent manner.In normoxic and hypoxic cells,the IC20 was 16.7 μmol/L and 39.2 μmol/L at 24 h,respectively.In the group of hypoxia plus YC-1,SERD0 and SERDq were 1.11 and 1.26,respectively.In hypoxia,YC-1combined with 2 Gy irradiation could induce cell apoptosis and prolong G2 + M phase arrest ( ( 30.17 ±1.21 )％ ∶ ( 15.44 ±0.96) ％,P =0.000; (21.56 ±0.47 )％ ∶ (6.16 ±0.16)％,P =0.000).Concinsions YC-1 could enhance the radiosensitivity of hypoxic A549 cells.