ORIGINAL ABSTRACT

Glyphosate and atrazine, two widely used herbicides, may induce subtle molecular changes even at low levels encountered in the drinking water of some populations. This study assessed structural and RNA expression changes in MCF-7 and MDA-MB-231 breast cancer cell lines after 72-h exposures to glyphosate (50 or 500 ppb) and atrazine (2 or 20 ppb). These doses are commonly found in drinking water and falls below or within the maximum residue levels recommended or allowed in the drinking water of populations in Brazil and the USA. Genome wide RNA sequencing detected differentially expressed genes (DEGs) at lower doses as well as highlighted dose-dependent responses at higher concentrations. For instance, MDA-MB-231 cells treated with 20 ppb atrazine exhibited 60 DEGs, while 500 ppb glyphosate exposure resulted in 39 DEGs, with notable overlap in gene expression profiles across pesticides and doses. Gene set enrichment analysis suggested alterations linked to DNA repair and replication, sterol metabolism, and cellular response to starvation, with specific pathways varying by pesticide and cell line. Significant changes were observed in DNA homologous repair genes for both pesticides and cell lines. Finally, fourier-transform infrared spectroscopy (FTIR) suggested dose- and pesticide-specific structural changes linked to lipid metabolism and nucleic acid modifications. Our findings indicate that low-level glyphosate and atrazine exposures induce subtle structural and transcriptomic changes without overt cytotoxicity. These results underscore the potential implications for chronic environmental herbicide exposures that may affect breast cancer cell development and progression. Our study highlight the need for monitoring exposure in certain populations and for further investigations into the long-term consequences of pesticide exposure for human health.