Our previous results have suggested that increasing aggressiveness of breast tumour cells is associated with the down-regulation of the expression of nitric oxide synthase (NOS). As increasing aggressiveness is associated with a propensity for metastasis, this study aimed to investigate whether our theory applied to the processes of motility and invasion. Although the well-established dual roles of nitric oxide (NO) were evident, most of the results are consistent with our theory. We demonstrated that basal motility is higher in the MCF-7-ADR multidrug-resistant variant cell line compared to the MCF-7 parent cell line and that treatment with NOS inhibitors increased motility in MDA-MB-231 and T47D cells. Exogenous NO was associated with a trend to increase adhesion in the MCF-7 and MDA-MB-231 cell lines. These results are consistent with the theory that loss of NOS expression may be associated with the progression of breast cancers via increase in motility and loss of adhesion.

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