Ranolazine inhibits invasiveness of human breast cancer cells in combination with a tyrosine kinase inhibitor: Dose-dependent synergy

Voltage-gated sodium channels (VGSCs) have emerged as important promoters of the invasive phenotype in triple-negative breast cancer (TNBC), a clinically aggressive and therapeutically challenging subtype of breast cancer. Channel activity is enhanced by hypoxia that promotes metastatic progression. Pharmacological inhibition of VGSCs by specific channel blockers such as ranolazine results in anti-metastatic behaviour. Independently, epidermal growth factor (EGF) signalling has been shown (i) to enhance VGSC activity and (ii) to promote TNBC progression. Here, we aimed to test whether co-treatment of a model TNBC cell line, MDA-MB-231, with an inhibitor of EGF receptor (AG1478) and ranolazine would produce a synergistic effect on invasiveness. Two different concentrations of AG1478 (5 and 10 μM) were used whilst ranolazine was employed at clinically relevant concentration (< 5 μM) under hypoxia (1% O2). Excess over Bliss (EOB) score was determined quantitatively evaluate possible synergy. Indeed, both ranolazine and AG1478 individually suppressed Matrigel invasion dose dependently without altering proliferative activity. Clear synergy was observed at low-concentration combinations. Specifically, combined with 5 μM AG1478, ranolazine was clearly synergic at 1.25 μM (EOB= +38.7%). In contrast, higher concentrations did not produce any synergy. We concluded that the inhibitory effect of ranolazine on TNBC invasiveness can be made more effective by combination with an inhibitor of EGF receptor / tyrosine kinase inhibitor (TKI) at low concentrations. Furthermore, since functional VGSCs occur in several carcinomas and TKIs commonly promote their invasiveness, the results could have broader application including via drug repurposing.