Inflammatory cell-mediated tumour progression and minisatellite mutation correlate with the decrease of antioxidative enzymes in murine fibrosarcoma cells

We isolated six clones of weakly tumorigenic fibrosarcoma (QR) from the tum origenic clone BMT-11 cl-9. The QR clones were unable to grow in normal C57 BL/6 mice when injected s.c. (1 x: 10(5) cells). However, they formed aggre ssive tumours upon co-implantation with a 'foreign body', i.e. a gelatin sp onge, and the rate of tumour take ranged from 8% to 58% among QR clones. Th e enhanced tumorigenicity was due to host cell-mediated reaction to the gel atin sponge (inflammation). Immunoblot analysis and enzyme activity assay r evealed a significant inverse correlation between the frequencies of tumour formation, by QR clones and the levels of manganese superoxide dismutase ( Mn-SOD, P<0.005) and glutathione peroxidase (GP chi, P<0.01) in the respect ive tumour clones. Electron spin resonance (ESR) revealed that superoxide-s cavenging ability of cell lysates of the QR clone with high [level of Mn-SO D was significantly higher than that with low level of the antioxidative en zyme in the presence of potassium cyanide, an inhibitor for copper-zinc sup eroxide dismutase (CuZn-SOD) (P<0.001). Minisatellite mutation (MSM) induce d by the inflammatory cells in tumour cells were investigated by DNA finger print analysis after QR clones had been cocultured with ge[gelatin-sponge-r eactive cells. The MSM rate was significantly higher in the subclones with low levels of Mn-SOD and GP chi (P<0.05) than in the subclones with high le vels of both enzymes. The MSM of the subclones with low levels of both enzy mes was inhibited in the presence of mannitol, a hydroxyl radical scavenger . The content of 8-hydroxydeoxyguanosine (8-OHdG) by which the cellular DNA damage caused by active oxygen species can be assessed was significantly l ow in the tumours arising from the QR clone with high levels of Mn-SOD and GP chi even if the clone had been co-implanted with gelatin sponge, compare d with the arising tumour from the QR clone with low levels of those antiox idative enzymes (P<0.001). In contrast, CuZn-SOD and catalase levels in the six QR clones did not have any correlation with tumour progression paramet ers. These results suggest that tumour progression is accelerated by inflam mation-induced active oxygen species particularly accompanied with declined levels of intracellular antioxidative enzymes in tumour cells.