Ingrilimine, a novel marine cytotoxic and apoptotic cyclic imine toxin with a high affinity and dual activity on human α7 nicotinic acetylcholine receptor

Cyclic imine toxins are fast acting neurotoxins produced by dinoflagellates that are bioaccumulated by shellfish, which in turn, vectorize them to humans. Most cyclic imine toxins are potent antagonist of muscle and neuronal nicotinic acetylcholine receptors being able to cross the brain blood barrier. We report the discovery of ingrilimine, a novel cyclic imine toxin purified from Vulcanodinium rugosum (strain IFR-VRU-01). Its structure was determined by NMR, HRMS MS/MS and IR-spectroscopy. Ingrilimine bears a six-membered spirocyclic imine imbibed in a 13-carbon macrocycle (C 24 H 35 O 2 N; M r 369.2663) and it is the smallest cyclic imine toxin described to date. Ingrilimine belongs to a novel emergent class of cyclic imines exhibiting potent cytotoxic and pro-apoptotic activities against human cancer cell lines. It also shows a high affinity for the human α7 nicotinic acetylcholine receptor displaying an intriguing dual activity: a concentration-dependent antagonist/agonist activity. Boltz-modeling of ingrilimine binding to human α7 nicotinic acetylcholine receptor rationalizes ingrilimine antagonist behavior, predicting at the same time the interaction of ingrilimine with the transmembrane domain of the receptor. Voltage clamp experiments using L247T and M253L receptor mutants indicate that Met253 located in transmembrane domain-2 may be essential for the ingrilimine-induced activation of α7 nicotinic acetylcholine receptor channel. Singular molecules like ingrilimine represent novel plausible routes for the treatment of neurodegenerative disorders and cancer where α7 nicotinic acetylcholine receptor plays a pivotal role. Harmful algal blooms are neglected sources of bioactive compounds with original scaffolds that can be used as drug leads for the treatment of human diseases.