An evaluation of common pharmaceutical solvents in the in vitro micronucleus assay

The in vitro micronucleus (IVMN) assay is a genetic toxicity assay routinely conducted in early drug development to evaluate clastogenicity and aneugenicity. At this discovery stage, synthetic routes for potential active pharmaceutical ingredients (API) are not optimized, which can lead to incomplete purification or solvation. API in genetic toxicity screens often contain residual solvent(s) in higher quantities than will be present in the GMP material. Understanding when solvents used either in API synthesis or as a vehicle may interfere with genetic toxicity screening results of APIs is important. In this work, twenty solvents commonly used in API synthesis were analyzed in the IVMN assay. These twenty solvents include acetonitrile, formic acid, anisole, dichloromethane, heptane, isopropyl amine, dimethyl sulfoxide, sodium hexafluorophosphate, N,N-Dimethylethylamine, N,N-Dimethylformamide, cyclopentyl methyl ether, 2-propanol, 1-butanol, 1-Methyl-2-pyrrolidinone, methanol, tetrahydrofuran, 2-Methyltetrahydrofuran, ethyl acetate, trifluoroacetic acid, and 2,6-Di-tert-butyl-4-methylphenol. When the in vitro data was correlated to available in vivo genotoxicity data published in the literature, only 5 of the 14 positively correlated. However, when a 10 mM limit of exposure was applied to the solvents, 13 of the 14 correlated to the in vivo literature results. While the results do not consider vehicle interaction within the assay, the data demonstrates that residual solvent carryover from API or other sources is generally not of concern. The 10 mM limit also reduces the false-positive risk of this assay. Baseline cytotoxicity and micronucleus formation from the solvents in this system provide a ranking on which solvents may produce confounding results in the assay.