Targeting voltage gated sodium channels for prevention of breast cancer metastasis

Voltage gated sodium channels (VGSC) are a recently identified drug target involved in the breast cancer invasion mechanism. VGSCs participate in the acidification of the perimembrane, activating the cysteine proteases, cathepsin B and S, thereby triggering the proteolysis of the extracellular matrix and the basement membrane, thereby promoting cell invasion. Highly aggressive, invasive breast cancer cells dramatically overexpress one subtype of VGSC, nNa_v1.5. Described here are the design, synthesis and in vitro evaluation of drug-like, small molecule blockers of nNa _v1.5 that are potential therapeutic agents for the prevention of breast cancer metastasis.

Initially, five compounds were designed and synthesized based on the predictions of a 3D-QSAR of VGSC blockers developed previously by our group. These compounds displayed nNa_v1.5 blockade in MDA-MB-231cells and the two best blockers inhibited the invasion activity of MDA-MB-231 cells at low micromolar concentrations.

In order to further optimize activities of these lead compounds, a systematic SAR study was carried out. Seventeen new compounds were synthesized by introducing independent variations on both “left” and “right” ends of the lead molecule. Three new nNa_v1.5 blockers were identified from these studies with inhibitory effects on both transient peak currents and persistent sodium currents in MDA-MB-231 cells. These results were corroborated by potent inhibition of invasiveness of MDA-MB-231 cells.

As a continuation of the SAR studies, a combinatorial library of twenty five compounds was synthesized using solution phase parallel synthesis. These studies resulted in the identification of two additional inhibitors with a potential for further optimization. Apart from this, several miscellaneous compounds were also synthesized and evaluated during the course of this project.

Based on these studies with MDA-MB-231 cells, the best candidates for consideration of further development had low cytotoxicity up to 25μM, inhibited persistent sodium currents and transient peak currents in whole cell patch clamp studies by 20% and 50% at 1μM, respectively, and inhibited invasiveness in an in vitro Matrigel^® invasion assay by up to 40% at 100 nM (the maximum theoretical inhibition based upon nNa _v1.5 knockout studies). These activities were considerably more potent than the known clinically used VGSC blockers (ranolazine and phenytoin) with non-cancer indications.