Abstracts

Rationale: Lacosamide (R-2-acetamido-N-benzyl-3-methoxypropionamide) is a functionalized amino acid which has shown activity in a wide range of animal models for epilepsy and pain. Lacosamide is currently being evaluated in Phase III clinical trials for epilepsy and diabetic neuropathic pain. Since lacosamide did not bind with significant affinity to any of more than 100 receptors, enzymes, transporters or ion channels tested, the aim of the current experiments was to identify the molecular mode of action.Methods: Affinity fishhook experiments with biotinylated lacosamide analogues were performed to identify possible binding partners of lacosamide in rat brain fractions. Interaction of lacosamide with candidate proteins was assessed in binding experiments with radiolabeled drug and a functional assay in primary hippocampal neurons.Results: In the fishhook study putative binding partners of lacosamide were identified. Of special interest appeared collapsin response mediator protein 2 (CRMP-2, also identified as DRP-2, TOAD-64, Ulip2), a protein involved in neuronal differentiation and control of axonal outgrowth. In a radioligand binding experiment with CRMP-2 expressed in Xenopus oocytes binding of lacosamide to CRMP-2 was confirmed with an affinity of about 5 µM. In order to study the functional consequences of lacosamide’s interaction with CRMP-2, a cellular assay was used in which the effects of CRMP-2 modulation have been previously characterized: Lacosamide (1-100 µM) inhibited the effects of neurotrophins (BDNF, NT-3) on axonal outgrowth of primary hippocampal cells without effects on basal growth. This is in line with published findings that inhibition of CRMP-2 by siRNA attenuated neurotrophin induced axonal outgrowth of cultured neurons.Conclusions: The results of these studies show that CRMP-2 is one of the molecular targets of lacosamide. Together with the finding that lacosamide selectively enhances sodium channel inactivation (see corresponding abstract), these results suggest that lacosamide has a dual and novel mode of action. Given the important role of neurotrophic factors in the pathophysiology of epilepsy and chronic pain, the interaction of lacosamide with CRMP-2 might potentially have disease modifying effects. This, however, remains to be proven.