Nitric oxide promotes murine mammary tumour growth and metastasis by stimulating tumour cell migration, invasiveness and angiogenesis

The contributory role of nitric oxide (NO) on tumour growth and metastasis was evaluated in a murine mammary tumour model. NO synthase (NOS) protein e xpression levels were examined in spontaneously arising C3H/HeJ mammary ade nocarcinomas and respective lung metastases, In addition, 2 clonal derivati ves of a single spontaneous tumour differing in metastatic phenotype (C3L5 and C10; highly and weakly metastatic, respectively) were utilised to inves tigate (i) the relationship between NOS expression levels and the biologica l behaviour of tumour cells (e.g., in vitro migratory and invasive capaciti es, in vivo tumour growth rate and metastatic and angiogenic capacities) an d (ii) whether tumour-derived NO stimulated the invasive, migratory and ang iogenic capacities of tumour cells. A heterogeneous pattern of endothelial NOS (eNOS) expression was observed in tumour cells in spontaneous primary t umours, and eNOS expression was higher in undifferentiated relative to diff erentiated tumour zones. However, tumour cells in lung metastatic sites wer e always strongly eNOS-positive, suggesting that eNOS expression facilitate d metastasis, Findings using clonal derivatives supported this notion; s.c. primary tumour growth race, efficiency of spontaneous metastasis and eNOS expression were higher for C3L5 relative to C10 cell lines. Nevertheless, l ung metastases derived from both tumour cell lines were always strongly and homogeneously eNOS-positive, C3L5 cells were more invasive than C10 cells in vitro, but che migratory capacities of the cell lines did not differ. Ho wever, migration and invasiveness of both cell lines were inhibited with L- NAME and restored with excess L-arginine. Tumour-associated angiogenesis, m easured in Matrigel implants inclusive of tumour cells, was higher for C3L5 relative to C10 cells, and C3L5-induced angiogenesis was reduced with chro nic L-NAME treatment of host animals. These findings suggest that tumour-de rived eNOS promoted tumour growth and metastasis by multiple mechanisms: st imulation of tumour cell migration, invasiveness and angiogenesis, Int. J. Cancer 86:30-39, 2000, (C) 2000 Wiley-Liss, Inc.