Purpose: The combined effect of natural Interferon-beta (n-IFN-beta) and ionizing radiation was tested in vitro on 5 different tumor cell lines and 1 embryonal lung fibroblast cell line.
Materials and methods: The following cell lines were used: A549 (lung cancer), MCF-7 (breast cancer), CaSki (cervical cancer), WiDr (colon cancer), ZMK-1 (head and neck cancer), and MRC-5 (embryonal lung fibroblast line). Cells were incubated with n-IFN-beta (30 I.U./ml to 3000 I.U./ml) 24 h before irradiation. Irradiation was given as single dose between 1 and 6 Gy. Cell survival was evaluated using a standard colony-forming assay.
Results: Incubation with n-IFN-beta enhanced the effect of radiation in all tumor cell lines tested. The maximum sensitizing enhancement ratios (SER) at the 37% survival level were: 1.66 for A549 cells, 1.47 for CaSki cells, 1.56 for MCF-7 cells, 1.40 for WiDr cells, and 1.57 for ZMK-1 cells. In the nonneoplastic MRC-5 cell line, no radiosensitizing effect of n-IFN-beta could be demonstrated. The linear quadratic fit of the survival curves showed an increase of the alpha-component for all tumor cell lines treated with n-IFN-beta.
Conclusions: IFN-beta enhanced the effect of radiation in the tumor cell lines, but not in the nonmalignant lung fibroblasts. The increase of the alpha component in the survival curves indicates that impaired radiation repair or the accumulation of sublethal damage might play a role for the radiosensitizing effect of n-IFN-beta.