Inhibition of Tunneling Nanotubes between Cancer Cell and the Endothelium Alters the Metastatic Phenotype

The interaction of tumor cells with blood vessels is one of the key steps during cancer metastasis. Metastatic cancer cells exhibit phenotypic state changes during this interaction: (1) they form tunneling nanotubes (TNTs) with endothelial cells, which act as a conduit for intercellular communication; and (2) metastatic cancer cells change in order to acquire an elongated phenotype, instead of the classical cellular aggregates or mammosphere-like structures, which it forms in three-dimensional cultures. Here, we demonstrate mechanistically that a siRNA-based knockdown of the exocyst complex protein Sec3 inhibits TNT formation. Furthermore, a set of pharmacological inhibitors for Rho GTPase–exocyst complex-mediated cytoskeletal remodeling is introduced, which inhibits TNT formation, and induces the reversal of the more invasive phenotype of cancer cell (spindle-like) into a less invasive phenotype (cellular aggregates or mammosphere). Our results offer mechanistic insights into this nanoscale communication and shift of phenotypic state during cancer–endothelial interactions.