e22028 Background: Frequent activation of the PI3K/Akt/mTOR pathway and aberrations of tumor suppressor gene p53 are associated with therapeutic resistance in lung cancer. Nevertheless, the possibility of the variants of p53 genotype to affect response to mTOR inhibitor combined with irradiation therapy remains still unclear. Methods: Human non-small lung cancer cell line H1299 with p53 null genotype, was transfected with wild type or mutated p53 gene (H1299/wtp53 (WT), H1299/mp53 (MT)). Both cell survival and cell proliferation were estimated by colony formation assay to assess differences between WT and MT in sensitivity to rapamycin and ability of rapamycin to enhance radiation sensitivity. Cells were treated according to the individual study; DMSO (control), rapamycin (100 nM for 1 hour), irradiation (IR) (increasing doses), combination (RR) (rapamycin followed by irradiation). Changes in the cell cycle were also analyzed by flow cytometry. Results: Rapamycin decreased cell survival only in WT (P < 0.01, vs. control). MT was resistant to rapamycin exhibiting slightly inhibited cell proliferation. Compared with IR, RR with no less than 6 Gy radiation enhanced inhibitory effects on both cell survival and proliferation independent of p53 genotype (P < 0.01 in WT and P < 0.01 in MT, respectively), that indicating additive interaction. Cell cycle analysis demonstrated rapamycin induced G1 cell cycle arrest in both types of cells compared with controls (P < 0.01 in WT and P < 0.05 in MT, respectively) at 24 hours after treatment. Enhancement of G1 arrest by RR was observed in both WT (P < 0.01, vs. IR) and MT (P < 0.01, vs. IR) at the same time point. In addition, RR caused a greater reduction of cells in S phase than that of IR regardless of p53 gene status (P < 0.01 in WT and P < 0.01 in MT, respectively). Conclusions: Rapamycin is an effective radiosensitizer in a p53 independent manner, in which increased G1 cell cycle arrest and decrease in S phase cells are responsible for increased growth inhibitory effect. It will enable us to provide more appropriate treatment to patients with mutated p53 gene. No significant financial relationships to disclose.
Ifosfamide, etoposide, and thoracic irradiation therapy in 163 patients with unresectable small cell lung cancer