Toward a digital analysis of environmental impacts on rodent mammary gland density during critical developmental windows

Benzophenone-3 alters expression of genes encoding vascularization and epithelial-mesenchymal transition functions during Trp53-null mammary tumorigenesis

Benzophenone-3 (also referred to as oxybenzone) is a putative endocrine disrupting chemical and common ingredient in sunscreens and other personal care products. We previously showed that benzophenone-3 was promotional for epithelial tumorigenesis in mice fed adult high-fat diet, while protective against the incidence of more aggressive spindle cell tumors in the same treatment group. In this study, we show that benzophenone-3 reduces epithelial to mesenchymal transition in the epithelial tumors of these mice. This reduction in epithelial to mesenchymal transition is associated with altered expression of several genes involved in regulation of angiogenesis and epithelial to mesenchymal transition. Among the genes altered in expression, Timp1 is of particular interest because benzophenone-3 suppressed both migration and Timp1 expression in a mammary tumor cell line that displays epithelial to mesenchymal transition characteristics. These alterations in gene expression plausibly stabilize the vasculature of epithelial carcinomas and contribute to benzophenone-3 promotion of epithelial tumors, while at the same time suppress epithelial to mesenchymal transition and suppress incidence of spindle cell tumors.

Chemical Effects on Breast Development, Function, and Cancer Risk: Existing Knowledge and New Opportunities

Population studies show worrisome trends towards earlier breast development, difficulty in breastfeeding, and increasing rates of breast cancer in young women. Multiple epidemiological studies have linked these outcomes with chemical exposures, and experimental studies have shown that many of these chemicals generate similar effects in rodents, often by disrupting hormonal regulation. These endocrine-disrupting chemicals (EDCs) can alter the progression of mammary gland (MG) development, impair the ability to nourish offspring via lactation, increase mammary tissue density, and increase the propensity to develop cancer. However, current toxicological approaches to measuring the effects of chemical exposures on the MG are often inadequate to detect these effects, impairing our ability to identify exposures harmful to the breast and limiting opportunities for prevention. This paper describes key adverse outcomes for the MG, including impaired lactation, altered pubertal development, altered morphology (such as increased mammographic density), and cancer. It also summarizes evidence from humans and rodent models for exposures associated with these effects. We also review current toxicological practices for evaluating MG effects, highlight limitations of current methods, summarize debates related to how effects are interpreted in risk assessment, and make recommendations to strengthen assessment approaches. Increasing the rigor of MG assessment would improve our ability to identify chemicals of concern, regulate those chemicals based on their effects, and prevent exposures and associated adverse health effects.