Cardiotoxic effects of local anesthetics (LAs) involve inhibition of NaV1.5 voltage-gated Na+ channels. Metastatic breast and colon cancer cells also express NaV1.5, predominantly the neonatal splice variant (nNaV1.5) and their inhibition by LAs reduces invasion and migration. It may be advantageous to target cancer cells while sparing cardiac function through selective blockade of nNaV1.5 and/or by preferentially affecting inactivated NaV1.5, which predominate in cancer cells. We tested the hypotheses that lidocaine and levobupivacaine differentially affect (1) adult (aNaV1.5) and nNaV1.5 and (2) the resting and inactivated states of NaV1.5.METHODS:
The whole-cell voltage-clamp technique was used to evaluate the actions of lidocaine and levobupivacaine on recombinant NaV1.5 channels expressed in HEK-293 cells. Cells were transiently transfected with cDNAs encoding either aNaV1.5 or nNaV1.5. Voltage protocols were applied to determine depolarizing potentials that either activated or inactivated 50% of maximum conductance (V½ activation and V½ inactivation, respectively).RESULTS:
Lidocaine and levobupivacaine potently inhibited aNaV1.5 (IC50 mean [SD]: 20  and 1 [0.6] μM, respectively) and nNaV1.5 (IC50 mean [SD]: 17  and 3 [1.6] μM, respectively) at a holding potential of −80 mV. IC50s differed significantly between lidocaine and levobupivacaine with no influence of splice variant. Levobupivacaine induced a statistically significant depolarizing shift in the V½ activation for aNaV1.5 (mean [SD] from −32 [4.6] mV to −26 [8.1] mV) but had no effect on the voltage dependence of activation of nNaV1.5. Lidocaine had no effect on V½ activation of either variant but caused a significantly greater depression of maximum current mediated by nNaV1.5 compared to aNaV1.5. Similar statistically significant shifts in the V½ inactivation (approximately −10 mV) occurred for both LAs and NaV1.5 variants. Levobupivacaine (1 μM) caused a significantly greater slowing of recovery from inactivation of both variants than did lidocaine (10 μM). Both LAs caused approximately 50% tonic inhibition of aNaV1.5 or nNaV1.5 when holding at −80 mV. Neither LA caused tonic block at a holding potential of either −90 or −120 mV, voltages at which there was little steady-state inactivation. Higher concentrations of either lidocaine (300 μM) or levobupivacaine (100 μM) caused significantly more tonic block at −120 mV.CONCLUSIONS:
These data demonstrate that low concentrations of the LAs exhibit inactivation-dependent block of NaV1.5, which may provide a rationale for their use to safely inhibit migration and invasion by metastatic cancer cells without cardiotoxicity.