Exceptionally selective voltage-sensor trapping of Na_V1.5 channels by Mg-protoporphyrin impairs cancer cell migration

The human voltage-gated sodium channel hNa_V1.5 is essential for cardiac excitability. Though underrecognized, Na_V1.5 is also expressed in multiple cancers, promoting cell migration and malignancy. hNa_V1.5 is a therapeutic target but limited pharmacological isoform specificity presents a risk of side effects via neuronal and skeletal muscle Na_V channels. Here we identify Mg²⁺-protoporphyrin IX (MgPpIX), a Mg-containing tetrapyrrole and intermediate in chlorophyll biosynthesis, as a potent inhibitor of hNa_V1.5 (IC₅₀ of 1 nM). The activity profile of various metal protoporphyrins correlates with the electrostatic potential at the metal center of the compounds. MgPpIX is specific to hNa_V1.5, as no inhibition of other hNa_V isoforms (hNa_V1.2, 1.4, 1.7, 1.8) was detected. A mutagenesis study and structural modeling reveals that MgPpIX stabilizes the domain-II voltage sensor in the deactivated conformation, with residues E795 and N803 being relevant determinants. MgPpIX also inhibits native Na_V channels in breast cancer MDA-MB-231 and colorectal carcinoma SW-480 cell lines, and suppresses cell migration. MgPpIX is an exceptionally potent and specific inhibitor of hNa_V1.5 and may serve as a lead compound in anti-cancer drug development.