In vitro radiosensitization by oxaliplatin and 5-fluorouracil in a human colon cancer cell line.

The current study was designed to compare the radiosensitizing effects of oxaliplatin and 5-fluorouracil (5FU) in a human colon cancer cell line. A human colon cancer cell line (S1) was treated with various doses of oxaliplatin, 5FU, radiation, and combinations thereof. Various clinically used schedules were mimicked. 5FU was either incubated during 1 h ("bolus") or 24 h ("continuous infusion"). When combining oxaliplatin and 5FU, an isobologram analysis revealed synergistic effects, regardless of 5FU schedule. The IC(10) and IC(50)-doses for the drugs where then combined with radiotherapy. With equitoxic drug doses (IC(50)), radiosensitization was observed in the following order: oxaliplatin > 5FU 24 h > 5FU 1 h exposure. The degree of potentiation corresponded to approximately 0.8 Gy, 0.7 Gy, and 0.2 Gy, respectively. In this experimental setting, oxaliplatin seemed to be a better radiosensitizer than 5FU, and longer incubation time with 5FU was better than short exposure.