Cross-Species Transcriptomic Analysis of Mouse and Rat Lung Exposed to Chloroprene

β-Chloroprene (2-chloro-1,3-butadiene), a monomer used in the production of neoprene elastomers, is of regulatory interest due to the production of multiorgan tumors in mouse and rat can-cer bioassays. A significant increase in female mouse lung tumors was observed at the lowest exposure concentration of 12.8 ppm, whereas a small, but not statistically significant increase was observed in female rats only at the highest exposure concentra-tion of 80 ppm. The metabolism of chloroprene results in the gen-eration of reactive epoxides, and the rate of overall chloroprene metabolism is highly species dependent. To identify potential key events in the mode of action of chloroprene lung tumorigenesis, dose-response and time-course gene expression microarray meas-urements were made in the lungs of female mice and female rats. The gene expression changes were analyzed using both a tradi-tional ANOVA approach followed by pathway enrichment analysis and a pathway-based benchmark dose (BMD) analysis approach. Pathways related to glutathione biosynthesis and metabolism were the primary pathways consistent with cross-species differences in tumor incidence. Transcriptional BMD values for the pathway were more similar to differences in tumor response than were estimated target tissue dose surrogates based on the total amount of chloroprene metabolized per unit mass of lung tissue per day. The closer correspondence of the transcriptional changes with the tumor response is likely due to their reflection of the overall balance between metabolic activation and detoxication reactions, whereas the current tissue dose surrogate reflects only oxidative metabolism.