Toxicological and pharmacodynamic evaluation of Nixodine-S [(S)-6-Methylnicotine] relative to (S)-nicotine

6-Methylnicotine (6-MN) products are increasingly appearing on the US and global markets and are currently unregulated in the US. Nixodine-S is a flavorless concentrate containing (S)-6-MN for use as a 1:1 nicotine alternative in the manufacture of vape or oral products. Based on intravenous acute toxicity study results, it was formulated to be less acutely toxic than nicotine. Under volume-equivalent dosing conditions, the Nixodine-S formulation did not induce cytotoxicity in the neutral red uptake assay with BALB/c 3T3 cells, while nicotine was cytotoxic. Both Nixodine-S and nicotine were negative in micronucleus and Ames assays. In nAChR activation testing, Nixodine-S, as well as its salt, elicited similar activation of two nAChR subtypes that are implicated in nicotine reward pathways. Nixodine-S and its salt produced a response consistent with weak partial agonism (low intrinsic efficacy relative to acetylcholine) similar to nicotine but with much lower potency than nicotine, at the most nicotine-sensitive of the three receptors tested and a primary driver of phasic dopamine release in mesolimbic reward circuits. Collectively, these data support an exploratory receptor-referenced therapeutic index (rTI) for Nixodine-S that is comparable to that of nicotine at volume-equivalent doses, and a differential nAChR subtype profile.