NAMI-A, imidazolium trans-imidazoledimethylsulfoxidetetrachlororuthenate, is a ruthenium-based drug characterised by the selective activity against tumour metastases. Previously we have shown the influence of the hepatic microenvironment to direct the arrest of the metastatic cells of colorectal cancer. Here we used the experimental model of HCT-116 colorectal cancer cells in vitro to explore whether the interference with α5β1 integrin may mechanistically explain the anti-metastatic effect of NAMI-A. NAMI-A inhibits two important steps of the tumour metastatic progression of colorectal cancer, i.e. the adhesion and migration of the tumour cells on the extracellular matrix proteins. The fibronectin receptor α5β1 integrin is likely involved in the anti-adhesive effects of NAMI-A on the HCT-116 colorectal cancer cells during their interaction with the extracellular matrix. Mechanistically, NAMI-A decreases the α5β1 integrin expression, and reduces FAK (Focal Adhesion Kinase) auto-phosphorylation on Tyr397, an important signalling event, involved in α5β1 integrin activation. These effects were validated by siRNA-induced knock down of the α5 integrin subunit and/or by the use of specific blocking mAbs against the active site of the integrin. Our results demonstrate the relevance of α5β1 integrin for colorectal cancer. We also show that the anti-metastatic effect of NAMI-A depends on the modulation of this integrin. Thus, our data on NAMI-A support the new concept that metal-based drugs can inhibit tumour metastases through targeting of integrins and of other proteins which mediate tumour progression-related cell functions such as adhesion and migration.
