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, which promotes metastatic progression. Pharmacological inhibition of VGSCs by specific channel blockers, such as ranolazine (RAN), results in antimetastatic behavior. Independently, epidermal growth factor signaling has been shown (1) to enhance VGSC activity and (2) to also promote TNBC progression. Here, we aimed to test whether cotreatment of a model TNBC cell line, MDA-MB-231, with an epidermal growth factor receptor inhibitor (AG1478 [AG]) and RAN would produce a synergistic effect on invasiveness. Two different concentrations of AG (5 and 10 μM) were used, whereas RAN was used at a clinically relevant concentration (<5 μM) under hypoxia (1% O2). Excess 'over bliss score' was determined quantitatively to evaluate possible synergy. Indeed, both RAN and AG individually suppressed Matrigel invasion dose dependently without altering proliferative activity. Clear synergy was observed at low-concentration combinations. Specifically, combined with 5 μM AG, RAN was clearly synergistic at 1.25 μM (excess over bliss = +38.7%). In contrast, higher concentrations produced little or no synergy. We concluded that the inhibitory effect of RAN on TNBC invasiveness can be made more effective by combination with an inhibitor of epidermal growth factor receptor/tyrosine kinase inhibitor at low concentrations. Furthermore, because functional VGSCs occur in several carcinomas and receptor tyrosine kinases commonly promote their invasiveness, the results could have broader application, including via drug repurposing. SIGNIFICANCE STATEMENT: Triple-negative breast cancer is a highly aggressive malignancy with limited therapeutic options. Ranolazine, an antianginal drug and an inhibitor of the voltage-gated sodium channel persistent current, inhibited cells' invasiveness at clinically relevant concentrations. Efficacy was enhanced by combination with an epidermal growth factor receptor inhibitor (AG1478). Synergy occurred specifically at low concentrations. These findings raise the possibility of treating triple-negative breast cancer nontoxically while reducing the chance of developing drug resistance. The results are also potentially applicable to multiple carcinomas.