Effect of reactive oxygen intermediates on the in vitro invasive capacity of tumor cells and liver metastasis in mice.

We studied the role of reactive oxygen intermediates (ROIs) in experimental liver metastasis induced in mice by the inoculation of COLON 26-M5 murine colon cancer cells, a highly metastatic variant of COLON 26 cells, and the effect of ROIs on the invasive capacity of the cells in an in vitro chemo-invasion assay model using reconstituted basement membrane matrigel. We also measured the release of ROIs from cells using electron spin resonance (ESR) spectrometry. Hydroxyl radicals (.OH) were constitutively released from the cells. This release was augmented by pre-treatment with phorbol 12-myristate 13-acetate (PMA). In experimental liver metastasis in CDF1 mice, the administration of recombinant human superoxide dismutase (r-hSOD) significantly increased the number of metastatic nodules, while administration of catalase significantly inhibited metastasis formation. In vitro pre-treatment of cells with PMA significantly increased the number of metastatic nodules. Invasive capacity of the cells was markedly augmented by pre-treatment with PMA. PMA-induced augmentation was significantly inhibited by the simultaneous addition of r-hSOD to the assay. Catalase had no significant effect. Our findings suggest that ROIs play an important role in tumor invasion and metastasis, and that hydrogen peroxide (H2O2) may contribute to the retention or extravasation of circulating tumor cells. Furthermore, the superoxide anion (O2-) released by tumor cells may play an important role in basement membrane degradation.