LAUSR

The development of cancer in humans is caused by irreversible modifications of the genome through genetic or epigenetic alterations resulting in the acquisition of multiple heritable abnormal cellular phenotypes. We have investigated DNA methylation and gene expression alterations in mammary glands of Sprague Dawley rats induced by treatment with the weight-loss drug lorcaserin, a drug that increased the cancer incidence in a human clinical trial (CAMELLIA-TIMI 61) and in rats. Female Sprague Dawley rats received lorcaserin by gavage 7 days/week for 12 weeks, at doses previously used in a 2-year rodent cancer bioassay (0, 30, and 100 mg/kg bw/day). DNA methylation changes were investigated in mammary glands, a target organ for lorcaserin carcinogenicity in rats, by reduced representation bisulfite sequencing. Gene expression changes were analyzed by RNA sequencing. Lorcaserin exposure resulted in dose-dependent DNA methylation alterations in the mammary glands, as evidenced by the presence of 1832 and 2352 significantly differentially methylated CpG (dmCpG) sites in the 30 and 100 mg/kg bw/day treatment groups, respectively, as compared to the control group, among which 593 sites were hypomethylated or hypermethylated in common. Similar to DNA methylation changes, lorcaserin treatment resulted in dose-dependent changes in gene expression. Pathway enrichment analysis of the dmCpG-containing genes demonstrated a strong representation of genes associated with cell morphology, cellular function and maintenance, and cellular growth and proliferation. Analysis of dmCpG sites indicated an increase in the number of hypermethylated sites compared to the number of hypomethylated sites in both 30 (1.9 fold) and 100 (2.6 fold) mg/kg bw/day treatment groups. Furthermore, while the number of hypomethylated CpG sites did not differ between treatment groups, the number of hypermethylated CpG sites in rats treated with 100 mg/kg bw/day of lorcaserin was 1.4 times greater than in rats treated with 30 mg/kg bw/day. By combining the analysis of differentially expressed genes and dmCpG sites, we identified 13 genes (11 hypermethylated and 2 hypomethylated) the expression of which was inversely correlated with DNA methylation in the mammary glands of rats treated with 100 mg/kg bw/day of lorcaserin. We also identified 41 hypermethylated and 17 hypomethylated genes containing more than two dmCpG sites. In summary, we have demonstrated that lorcaserin induces extensive DNA methylation and transcriptomic changes in mammary glands at early preneoplastic stages of lorcaserin-induced rat carcinogenesis. These findings suggest the importance of these non-genotoxic alterations in the carcinogenicity of lorcaserin. Citation Format: Volodymyr P. Tryndyak, Rose A. Willett, Todd Bourcier, Frederick A. Beland, Igor P. Pogribny. Exposure-related DNA methylation and gene expression changes in mammary glands of Sprague Dawley rats treated with lorcaserin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6017.