Breast cancer progression and kynurenine pathway enzymes are induced by hexachlorobenzene exposure in a Her2-positive model.

Breast cancer is one of the leading cancers among women worldwide. Given the evidence that pesticides play an important role in breast cancer, interest has grown in pesticide impact on disease progression. Hexachlorobenzene (HCB), an aryl hydrocarbon receptor (AhR) ligand, promotes triple-negative breast cancer cell migration and invasion. Estrogen receptor ß (ERß) inhibits cancer motility, while G protein-coupled ER (GPER) modulates the neoplastic transformation. Tryptophan is metabolized through the kynurenine pathway by indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO), with kynurenine signaling activation often predicting worse prognosis in cancer. In this context, we examined the HCB (0.005; 0.05; 0.5 and 5 µM) effect on LM3 cells, a human epidermal growth factor receptor 2 (HER2)-positive breast cancer model. Results show that HCB increases IDO and TDO mRNA levels and promotes cell viability, proliferation and migration through the AhR pathway. Moreover, HCB boosts mammosphere formation, vascular endothelial growth factor and cyclooxygenase-2 expression and reduces IL-10 levels. For some parameters, U-shaped or inverted U-shaped dose-response curves are shown. HCB alters ER levels, reducing ERß while increasing GPER. These results demonstrate that exposure to environmentally relevant concentrations of HCB up-regulates the kynurenine pathway and dysregulates ERß and GPER levels, collaborating in HER2-positive breast cancer progression.

Extracellular acidosis stimulates breast cancer cell motility through aryl hydrocarbon receptor and c-src kinase activation.

A reduction in extracellular pH (pHe) is a characteristic of most malignant tumors. The aryl hydrocarbon receptor (AhR) is a transcription factor localized in a cytosolic complex with c-Src, which allows it to trigger nongenomic effects through c-Src. Considering that the slightly acidic tumor microenvironment promotes breast cancer progression in a similar way to the AhR/c-Src axis, our aim was to evaluate whether this pathway could be activated by low pHe. We examined the effect of pHe 6.5 on AhR/c-Src axis using two breast cancer cell lines (MDA-MB-231 and LM3) and mammary epithelial cells (NMuMG) and found that acidosis increased c-Src phosphorylation only in tumor cells. Moreover, the presence of AhR inhibitors prevented c-Src activation. Low pHe reduced intracellular pH (pHi), while amiloride treatment, which is known to reduce pHi, induced c-Src phosphorylation through AhR. Analyses were conducted on cell migration and metalloproteases (MMP)-2 and -9 activities, with results showing an acidosis-induced increase in MDA-MB-231 and LM3 cell migration and MMP-9 activity, but no changes in NMuMG cells. Moreover, all these effects were blocked by AhR and c-Src inhibitors. In conclusion, acidosis stimulates the AhR/c-Src axis only in breast cancer cells, increasing cell migration and MMP-9 activity. Although the AhR activation mechanism still remains elusive, a reduction in pHi may be thought to be involved. These findings suggest a critical role for the AhR/c-Src axis in breast tumor progression stimulated by an acidic microenvironment.

Angiogenesis signaling in breast cancer models is induced by hexachlorobenzene and chlorpyrifos, pesticide ligands of the aryl hydrocarbon receptor.

Breast cancer incidence is increasing globally and pesticides exposure may impact risk of developing this disease. Hexachlorobenzene (HCB) and chlorpyrifos (CPF) act as endocrine disruptors, inducing proliferation in breast cancer cells. Vascular endothelial growth factor-A (VEGF-A), cyclooxygenase-2 (COX-2) and nitric oxide (NO) are associated with angiogenesis. Our aim was to evaluate HCB and CPF action, both weak aryl hydrocarbon receptor (AhR) ligands, on angiogenesis in breast cancer models. We used: (1) in vivo xenograft model with MCF-7 cells, (2) in vitro breast cancer model with MCF-7, and (3) in vitro neovasculogenesis model with endothelial cells exposed to conditioned medium from MCF-7. Results show that HCB (3 mg/kg) and CPF (0.1 mg/kg) stimulated vascular density in the in vivo model. HCB and CPF low doses enhanced VEGF-A and COX-2 expression, accompanied by increased levels of nitric oxide synthases (NOS), and NO release in MCF-7. HCB and CPF high doses intensified VEGF-A and COX-2 levels but rendered different effects on NOS, however, both pesticides reduced NO production. Moreover, our data indicate that HCB and CPF-induced VEGF-A expression is mediated by estrogen receptor and NO, while the increase in COX-2 is through AhR and NO pathways in MCF-7. In conclusion, we demonstrate that HCB and CPF environmental concentrations stimulate angiogenic switch in vivo. Besides, pesticides induce VEGF-A and COX-2 expression, as well as NO production in MCF-7, promoting tubulogenesis in endothelial cells. These findings show that pesticide exposure could stimulate angiogenesis, a process that has been demonstrated to contribute to breast cancer progression.

Impact of endocrine disruptor hexachlorobenzene on the mammary gland and breast cancer: The story thus far.

Breast cancer incidence is increasing globally and exposure to endocrine disruptors has gained importance as a potential risk factor. Hexachlorobenzene (HCB) was once used as a fungicide and, despite being banned, considerable amounts are still released into the environment. HCB acts as an endocrine disruptor in thyroid, uterus and mammary gland and was classified as possibly carcinogenic to human. This review provides a thorough analysis of results obtained in the last 15 years of research and evaluates data from assays in mammary gland and breast cancer in diverse animal models. We discuss the effects of environmentally relevant HCB concentrations on the normal mammary gland and different stages of carcinogenesis, and attempt to elucidate its mechanisms of action at molecular level. HCB weakly binds to the aryl hydrocarbon receptor (AhR), activating both membrane (c-Src) and nuclear pathways. Through c-Src stimulation, AhR signaling interacts with other membrane receptors including estrogen receptor-α, insulin-like growth factor-1 receptor, epidermal growth factor receptor and transforming growth factor beta 1 receptors. In this way, several pathways involved in mammary morphogenesis and breast cancer development are modified, inducing tumor progression. HCB thus stimulates epithelial cell proliferation, preneoplastic lesions and alterations in mammary gland development as well as neoplastic cell migration and invasion, metastasis and angiogenesis in breast cancer. In conclusion, our findings support the hypothesis that the presence and bioaccumulation of HCB in high-fat tissues and during highly sensitive time windows such as pregnancy, childhood and adolescence make exposure a risk factor for breast tumor development.