Effects of the ruthenium-based drug NAMI-A on the roles played by TGF-β1 in the metastatic process

The ruthenium-based drug NAMI-A, characterized by its selectivity against solid tumour metastases, promotes TGF-β1-dependent fibrosis and the reduction of the release of MMPs in the primary tumour. The aim of the study was to examine the interaction of NAMI-A with TGF-β1 in the process of metastasis formation. NAMI-A i) affects the secretion of TGF-β1 in metastatic MDA-MB-231 cells rather than in non-tumorigenic HBL-100 cells, ii) prevails over TGF-β1 with regard to the invasive capacity of the treated cells, and iii) contrasts integrin-dependent migration stimulated by TGF-β1. It thus appears that the effects of NAMI-A on cell invasion and migration are best summarized as an interference with TGF-β1 and a reduction of its activity in these events. At a molecular level, the similar activity of NAMI-A and TGF-β1 on RhoA GTPase supports its interaction with cell surface integrins while TGF-β1 can activate it by interaction with its TGFβR receptor. The inhibition of TGF-β1-induced migration of MDA-MB-231 cells by NAMI-A cannot simply be attributed to a modulation of the Smad2 and p38MAPK pathways. In conclusion, the effects of NAMI-A on the biological role of TGF-β1 in cancer metastasis are insufficient to attribute the responsibility for the anti-metastatic activity of the ruthenium-based drug to this target alone.