Veraguamide E, a Marine Cyanobacterial Depsipeptide Targeting σ ₂ R/TMEM97: Chemical and Neurobiological Characterization

The human sigma-2 receptor/transmembrane protein 97 (σ₂R/TMEM97) has been identified as a promising target to modulate neuronal excitability in chronic pain and address the unmet need for nonopioid therapeutics. We report the chemical and biological characterization of the cyclic depsipeptide, veraguamide E (Ver E), isolated from a Panamanian marine cyanobacterial collection, as a novel σ₂R/TMEM97 ligand and modulator of calcium in neurons. Ver E's structure was confirmed using 1D and 2D-NMR, HRMS, and MS/MS molecular networking analyses. NMR titration and computational docking confirmed direct, saturable, and tight binding of Ver E to σ₂R/TMEM97. Functional calcium imaging in primary mouse sensory neurons revealed that Ver E increases intracellular Ca²⁺ levels without modulating store-operated calcium entry (SOCE). Multiwell microelectrode array experiments using human induced pluripotent stem cell (hiPSC) nociceptors showed that Ver E reduced neuronal activity at physiological temperatures, but not under heat-stress. Ver E exhibited no cytotoxicity in HEK293 cells, and immunocytochemistry confirmed it does not alter phosphorylated eIF2α (p-eIF2α) expression, indicating a mechanism distinct from integrated stress response modulators. Collectively, these findings position Ver E as a nontoxic σ₂R/TMEM97 ligand capable of selectively modulating neuronal excitability, creating a starting point for developing novel pain therapeutics.