Modifications of the radiosensitivity of a renal cancer cell line as a consequence of polyunsaturated fatty acid supplementation

We investigated the ability of arachidonic acid (20:4 [n-6], AA), eicosapentanoic acid (20:5 [n-3], EPA), and docosahexenoic acid (22:6 [n-3], DHA) to modulate DNA damage and cell killing by low-dose γ-radiation and whether this modulation interfered with the transcriptional regulation of the matrix metalloproteinase-2 gene (MMP-2) in a renal cancer cell line. Caki-1 cells were treated with subcytotoxic concentrations of AA, EPA, or DHA (10-30 μmol/L) either alone or in combination with ionizing radiation (0-10 Gy). Ten micromolars of AA, 30 μmol/L EPA, or 30 μmol/L DHA-supplemented Caki-1 cells sustained significantly higher levels of DNA damage at doses between 5 and 10 Gy relative to that seen with radiation alone as assessed by the alkaline Comet assay. The radiosensitizing effect of AA, EPA, and DHA was accompanied by large decreases in the survival fraction of the Caki-1 cell line and significant increases in the α-parameter of the linear-quadratic fit. Finally, there was a differential effect between n-3 and n-6 fatty acids on the expression and activity of MMP-2 after γ-radiation at doses between 5 and 8 Gy as measured by real-time reverse transcription-polymerase chain reaction (RT-PCR) and gelatin zymography. Thirty micromolars of EPA or 30 μmol/L DHA markedly reduced MMP-2 mRNA and protein levels 24 hours postirradiation relative to the effects induced by radiation alone. Conversely, 10 μmol/L AA up-regulated MMP-2 expression and activity under the same conditions. These findings suggest 2 of the roles exerted by AA, EPA, and DHA in this tumor cell line, both as important effectors of cell killing and major determinants of MMP-2 activity when used in combination with low-dose γ-radiation.