LAUSR

Simple Summary Despite the recent advances in the diagnosis and treatment of medullary thyroid cancer (MTC), it remains an understudied cancer type and continues to disproportionately contribute to thyroid-cancer-related mortality. In this manuscript, we report, for the first time, the overexpression of voltage-gated sodium channel subtype NaV1.7 in MTC cells and MTC patient samples, which is not expressed in normal thyroid cells and tissues. We establish the druggability of this channel by identifying a novel inhibitor (SV188) of this channel and investigate its mode of binding and ability to inhibit the INa current in NaV1.7. We also show that SV188 significantly inhibited the migration and invasion of aggressive MTC cells at doses lower than its cytotoxic concentration. Overall, our data suggest that the unique overexpression of NaV1.7 in MTC can be exploited for the discovery of novel small-molecule drugs to treat MTC metastasis. Abstract Our results from quantitative RT-PCR, Western blotting, immunohistochemistry, and the tissue microarray of medullary thyroid cancer (MTC) cell lines and patient specimens confirm that VGSC subtype NaV1.7 is uniquely expressed in aggressive MTC and not expressed in normal thyroid cells and tissues. We establish the druggability of NaV1.7 in MTC by identifying a novel inhibitor (SV188) and investigate its mode of binding and ability to inhibit INa current in NaV1.7. The whole-cell patch-clamp studies of the SV188 in the NaV1.7 channels expressed in HEK-293 cells show that SV188 inhibited the INa current in NaV1.7 with an IC50 value of 3.6 µM by a voltage- and use-dependent blockade mechanism, and the maximum inhibitory effect is observed when the channel is open. SV188 inhibited the viability of MTC cell lines, MZ-CRC-1 and TT, with IC50 values of 8.47 μM and 9.32 μM, respectively, and significantly inhibited the invasion of MZ-CRC-1 cells by 35% and 52% at 3 μM and 6 μM, respectively. In contrast, SV188 had no effect on the invasion of TT cells derived from primary tumor, which have lower basal expression of NaV1.7. In addition, SV188 at 3 μM significantly inhibited the migration of MZ-CRC-1 and TT cells by 27% and 57%, respectively.