Background: While p53 protein plays an important role in the regulation of radiosensitivity and chemosensitivity in many tumors, the role of p53 in the combined management of tumors that harbor mutations in the p53 gene have not been fully defined. This study was undertaken to evaluate the impact of wild-type or mutant p53 status on the synergistic effects of 5-Fluorouracil (5-FU) and radiation (XRT) in pancreatic tumors.
Materials and methods: Three pancreatic tumor cell lines, one containing wild-type functional p53 (Capan-2) and two containing mutant p53 (Panc-1 and MIA PaCa-2), were used in this study. Radiation-induced p53 and p21(waf1/cip1) protein expression was determined by Western blot analysis. Radiation induced Thymidylate Synthase (TS) mRNA expression was determined by 32P-RT-PCR. The effect of 5-FU, radiation, and radiation +5-FU on the growth and colony-forming ability of Capan-2, Panc-1 and MIA PaCa-2 was determined by clonogenic assays respectively.
Results: Radiation elevated p53 and p21(waf1/cip1) levels in Capan-2 cells. No elevation of p53 and p21(waf1/cip1) was evident in Panc-1. MIA PaCa-2 cells showed down-regulation of p21(waf1/cip1) with no elevation of p53 protein. Clonogenic assays showed enhanced radiosensitizing effect when 5-Fluorouracil was added to cell lines lacking functional p53. In wild-type p53 Capan-2 cells, radiation up-regulated TS mRNA levels. High basal levels of TS mRNA were detected in p53 mutant cell lines with no evident induction by radiation.
Conclusion: Our results confirm that p53 status has a significant impact on radiation sensitivity with wild-type p53 cells being significantly more radiosensitive than mutant cell lines. When XRT and 5-FU were combined, this led only to an additive effect in wild-type cell lines and a synergistic effect in mutant cell lines.