Effect of pentoxifylline on radiation-induced G2-phase delay and radiosensitivity of human colon and cervical cancer cells.

Cells of three adherent cell lines with mutated p53 (WiDr and C33-A) and disrupted p53 (C4-I) were used to investigate the effect of pentoxifylline (PTX) on radiation-induced ${\rm G}_{2}\text{-}\text{phase}$ block and its relationship to radiosensitivity. Postirradiation exposure to 0.25-1.0 mM PTX resulted in an increase in radiosensitivity in a concentration-dependent manner as determined by a clonogenic assay. The change in radiation sensitivity was quantified by calculating the enhancement ratio (ER) at a clinically relevant dose of 2 Gy; the ER for WiDr cells was 1.23 ± 0.03 and 1.39 ± 0.15 for 0.5 and 1.0 mM PTX, respectively. For C33-A cells, the ER ranged from 1.04 ± 0.04 to 1.99 ± 0.17 for 0.25-1.0 mM PTX, whereas for C4-I cells the values were 1.29 ± 0.04 and 1.76 ± 0.17 for 0.25 and 0.5 mM PTX. In asynchronous WiDr, C33-A and C4-I cells, flow cytometry analysis showed a dose-dependent accumulation of cells in G2/ M phase which was detectable at 6 h and peaked at 12 h after...