Na(v)1.5 regulates breast tumor growth and metastatic dissemination in vivo

Voltage-gated Na(+) channels (VGSCs) mediate action potential firing and regulate adhesion and migration in excitable cells. VGSCs are also expressed in cancer cells. In metastatic breast cancer (BCa) cells, the Na(v)1.5 α subunit potentiates migration and invasion. In addition, the VGSC-inhibiting antiepileptic drug phenytoin inhibits tumor growth and metastasis. However, the functional activity of Na(v)1.5 and its specific contribution to tumor progression in vivo has not been delineated. Here, we found that Na(v)1.5 is up-regulated at the protein level in BCa compared with matched normal breast tissue. Na(+) current, reversibly blocked by tetrodotoxin, was retained in cancer cells in tumor tissue slices, thus directly confirming functional VGSC activity in vivo. Stable down-regulation of Na(v)1.5 expression significantly reduced tumor growth, local invasion into surrounding tissue, and metastasis to liver, lungs and spleen in an orthotopic BCa model. Na(v)1.5 down-regulation had no effect on cell proliferation or angiogenesis within the in tumors, but increased apoptosis. In vitro, Na(v)1.5 down-regulation altered cell morphology and reduced CD44 expression, suggesting that VGSC activity may regulate cellular invasion via the CD44-src-cortactin signaling axis. We conclude that Na(v)1.5 is functionally active in cancer cells in breast tumors, enhancing growth and metastatic dissemination. These findings support the notion that compounds targeting Na(v)1.5 may be useful for reducing metastasis.