Towards development of Nav1.7 channel modulators for pain treatment: A comparison of mexiletine effect in two cell models by automated patch clamp

The Nav1.7 voltage-gated sodium channel recently emerged as a candidate target for developing analgesic drugs due to its contribution to nociception and association with different pain disorders. Despite extensive research, no selective modulator of Nav1.7 has been put into clinic yet. Meanwhile, some non-selective sodium channel blockers, such as lidocaine and mexiletine (Mex), have been used for treating peripheral neuropathy and Nav1.7-related pain syndromes. The development of selective molecules targeting Nav1.7 channels requires robust preclinical tests integrating efficient electrophysiological screening with proper cell models. Here, we used the automated patch clamp platform, Patchliner (Nanion Technologies), and two different cell lines, the human rhabdomyosarcoma TE671 cells endogenously expressing Nav1.7 and HEK293 cells stably expressing heterologous human Nav1.7, to compare the biophysical properties and state-dependent effect of Mex on Nav1.7 channels. Our results show that in voltage-dependent conditions, Mex similarly blocked sodium currents in both cell lines (IC₅₀: 226 ± 16 and 227 ± 14 μM, at -140 mV; 15 ± 1 and 12 ± 1 μM, at -70 mV, for TE671 and HEK293 cells). Likewise, Mex exerted a comparable tonic (0.3 Hz) and use-dependent (20 Hz) block in TE671 and in HEK293 cells (IC₅₀: 96 ± 4 vs 114 ± 9 μM; IC₅₀: 22 ± 2 and 18 ± 2 μM, at 0.3 Hz and 20 Hz). Moreover, Mex negatively shifted the voltage-dependence of inactivation of Nav1.7 channels in a dose-dependent manner in both cell lines. In conclusion, we confirmed the state-dependency of Mex block on Nav1.7 using automated patch clamp and validated two cell lines expressing Nav1.7 as suitable models for drug screening. This approach can help developing Nav1.7 modulators for the treatment of pain disorders.