Evaluation of the in vivo mutagenicity of isopropyl methanesulfonate in acute and 28‐day studies

Abstract

Understanding the mutagenic dose response could prove beneficial in the management of pharmaceutically relevant impurities. For most alkyl ester impurities, such as isopropyl methanesulfonate (IPMS), little in vivo mutagenicity data exist for dose analysis. The likelihood of a sublinear dose response for IPMS was assessed by comparing the Swain Scott constant, the SN 1/SN 2 reaction mechanism and the O(6) :N(7) guanine adduct ratio to that of more well-known alkyl esters. Based on available information, IPMS was predicted to have a mutagenic profile most like ethyl nitrosourea. To test this hypothesis, mature male Wistar Han rats were administered IPMS using acute (single administration at 3.5 to 56 mg/kg) or subchronic (28 days at 0.125 to 2 mg/kg/day) exposures. The in vivo Pig-a mutation assay was used to identify mutant phenotype reticulocyte (Ret) and red blood cell (RBC) populations. The maximum mutant response occurred approximately 15 and 28 days after the last dose administration in the mutant Ret and RBC populations respectively in the acute study and on Day 29 and 56 in the mutant Ret and RBC populations, respectively, in the subchronic study. A comparison of RBC mutant frequencies from acute and subchronic protocols suggests a sublinear response; however, this was not substantiated by statistical analysis. A No Observed Effect Level (NOEL) of 0.25 mg/kg/day resulted in a Permitted Daily Exposure equivalent to the Threshold of Toxicological Concern. An estimate of the NOEL based on the previously mentioned factors, in practice, would have pre-empted further investigation of the potent mutagen IPMS.

Elusive Impurities—Evidence versus Hypothesis. Technical and Regulatory Update on Alkyl Sulfonates in Sulfonic Acid Salts

“…Coffing et al, 2015, reported a NOEL (no-observed-effect level) of 0.25 mg/kg/day for IMS in a 28-day in vivo Pig-a mutation assay in the rat. The authors determined a PDE of 2.5 μg using ICH Q3C methodology and an overall assessment factor of 5000.…”

Mutagenic Alkyl-Sulfonate Impurities in Sulfonic Acid Salts: Reviewing the Evidence and Challenging Regulatory Perceptions

“…Mutagenic potency is generally greatest for the iso esters (isopropyl, isobutyl, and isopentyl), being correlated (approximately) with rate of hydrolysis and inversely with Swain–Scott s constant, as shown in Table . [A low Swain–Scott s constant is associated with low alkylation selectivity, greater formation of O 6 -guanyl DNA adducts (compared to compounds with high Swain–Scott s constants that are selective in terms of alkylation at the more nucleophilic N 7 -position of guanine), and higher mutagenic/carcinogenic potency …”

“…The resulting PDE is 31.8 μg for a 50 kg patient. Coffing et al reported the results of a rat Pig-a assay on isopropyl mesilate (iPrMS) involving daily oral administration at doses of 0.125–2.0 mg/kg/day for 28 days. A threshold dose (NOAEL) of 0.25 mg/kg/day was established, from which a PDE of 2.5 μg can be determined for iPrMS.…”