Tumour hypoxia is associated with resistance to therapy and with increased invasion and metastatic potential. Recent studies in our laboratory have shown that the hypoxic up-regulation of tumour cell invasiveness and chemoresistance is in part due to reduced nitric oxide (NO) signaling. Using B16F10 murine melanoma cells, we demonstrate here that the increased metastatic potential associated with exposure to hypoxia is mediated by a reduction in cGMP-dependent NO-signaling. Pre-incubation of B16F10 cells in hypoxia (1% vs. 20% O(2)) for 12 hr increased lung colonization ability by over 4-fold. This effect of hypoxia on metastasis was inhibited by co-incubation with low concentrations of the NO-mimetic drugs glyceryl trinitrate (GTN) and diethylenetriamine NO adduct (DETA/NO). In a manner similar to hypoxia, pharmacological inhibition of NO synthesis resulted in a significant increase in lung nodule formation, an effect that was prevented by co-incubation with GTN. An important NO-signaling pathway involves the activation of soluble guanylyl cyclase and the consequential generation of cGMP. Culture in the presence of a non-hydrolysable cGMP analogue (8-Br-cGMP) abrogated the hypoxia-induced lung nodule formation, suggesting that the effects of NO on metastasis are mediated via a cGMP-dependent pathway. These findings suggest that a novel mechanism whereby hypoxia regulates metastatic potential involves a downstream inhibition of cGMP-dependent NO signaling.
Copyright 2004 Wiley-Liss, Inc.