Hexachlorobenzene enhances tumor growth, metalloprotease expression and metastasis in breast cancer models

PONTILLO C, ROJAS P, CHIAPPINI F, SEQUEIRA G, COCCA C, CROCCI M, COLOMBO L, LANARI C, KLEIMAN DE PISAREV D AND RANDI A

Lisboa

Congreso; • International Congress of Environmental Health (ICEH 2012); 2012

Hexachlorobenzene (HCB) is an organochlorine pesticide considered as a probable human carcinogen. This pollutant was found in puerperal mother milk and in samples of bovine milk for human consumption. It is a dioxin-like compound and a weak ligand of the aryl hydrocarbon receptor (AhR), which is a transcription factor that modulates processes as apoptosis, proliferation and cell migration. In previous studies, we found that HCB induced c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways and cell migration and invasion in estrogen receptor alpha (-) MDA-MB-231 breast cancer cell line. We also observed that HCB stimulated metalloproteases (MMPs) 2 and 9 expression, as well as MMP9 secretion and activity. c-Src, HER1 and AhR were involved in all these HCB-induced effects in MDA-MB-231. HER1 and c-Src tyrosine kinases are overexpressed in a high percentage of human breast cancers, and they cooperate in tumor formation and progression, promoting processes like cell migration and invasion, MMPs activities and metastasis. The aim of our study was to investigate the HCB action on tumor growth, MMP2 and MMP9 expression, c-Src/HER1 signaling pathway activity and metastasis using animal models of spontaneous and experimental metastasis. We used three different experimental models: a) MDA-MB-231 cells xenotransplanted s.c. into NU/NU mice, b) C4-HI mammary carcinomas transplanted s.c into BALB/c mice (syngeneic hormone receptor positive tumors) and c) LM3 cells inoculated i.v. into BALB/c mice, a syngeneic hormone receptor negative model of experimental metastasis. Animals were treated with HCB (0.3, 3 and 30 mg/kg b.w.) dissolved in corn oil or with vehicle. In the xenograft model, HCB stimulated tumor growth at 0.3 and 3 mg/kg b.w. (p<0.001), whereas the pesticide also increased c-Src, HER1, ERK1/2 and STAT5b activities, as well as MMP2 (95 %, p<0.05) and MMP9 (178 %, p<0.01) protein levels in mammary tumors at all assayed doses. Similarly, we found that HCB (0.3 and 3 mg/kg b.w.) enhanced C4-HI mammary tumor growth (p<0.001), as well as the number of lung (190%, p<0.05 and 230% p<0.001) and liver (200%, p<0.05 at 0.3 mg/kg b.w) micrometastasis. Furthermore, we observed that the pesticide (3 mg/kg b.w.) enhanced the size of the LM3 lung metastasis (185%, p<0.05).In conclusion, in the present work we demonstrate that HCB promotes tumor growth and/or metastasis in three different experimental models in vivo of breast cancer irrespective to the hormone receptor status of the tumors. This enhance correlated with an increased activation of the c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways, as well as MMP2 and MMP9 expression as observed in the MDA-MB-231 xenograft model. These results highlight the promoting effect that this pesticide exerts on breast cancer progression.