Abstract 2720: Toll-like receptor 4 immunoreactivity in mammary tumors chemically induced in female Sprague-Dawley rats
Authors: Zapaterini Joyce Regina , Varuzza Muriele Bertagna , Moura Nelci Antunes , Rodrigues Maria Aparecida Marchesan , Barbisan Luis Fernando 
Published: August 2015

Toll-like receptors (TLRs) are essential type I transmembrane glycoproteins that play a major role in inflammation and innate immune system. TLRs have been investigated in cancer research due to their dual role in tumor progression. The TLRs signaling pathways can promote survival, cell proliferation and apoptosis and its stimulation may either enhance or inhibit tumor growth and metastasis. The role of TLR4 in cancer biology has been studied but the direct relation between TLR4 and development of many cancer types, including breast cancer, is still obscure. Thus, more studies about TLR4 expression in breast cancer can help to better understanding the involvement of TLR4 in this disease. The aim of this study was to investigate the expression of TLR4 in a rat mammary carcinogenesis model.

At 51 days of age, female Sprague-Dawley rats were allocated into three groups: Groups 1 and 2 (n = 12 each) were initiated for mammary carcinogenesis by a single i.g. dose of 7,12-dimethylbenz[a]anthracene (DMBA) (80mg/kg) and Group 3 (n = 6) received a single i.g. dose of sesame oil (DMBA vehicle, 1 ml/kg). Also, group 2 received five s.c. injections per week of Tamoxifen (100 μg/kg) and groups 1 and 2 received similar injections of sesame oil (Tamoxifen vehicle, 0.5 ml/kg) during 12 weeks. At week 13, the animals were euthanized and mammary tumor (groups 1 and 2) and non-altered mammary glands (group 3) were collected and processed for histophatological analysis and TLR4 expression by immunohistochemistry. The TLR4 expression was classified as weak, moderate or strong and the incidence of intensity scores in tumor samples/group was analyzed by Fisher's exact test. Significant differences when p&lt;0.05.

Most of mammary tumors were classified as adenocarcinomas with tubular, papillary, cribriform or mixed patterns. Also, the tumors presented an expansive growth pattern with local invasive areas but without metastasis. Besides, a tumor inflammatory response was more intensively observed in G2. The immunoreactivity for TLR4 was significantly stronger in non-altered alveolar and ductal epithelial cells (G1) than in mammary tumor epithelial cells (groups 1 and 2) (p&lt; 0.001 and p = 0.007, respectively). The TLR4 immunoreactivity was more intense in mammary tumor epithelial cells from tamoxifen-treated group than in positive control group (G1), but without a significant difference. In the tumor stroma the positivity for TLR4 was observed mainly in mononuclear inflammatory cells, showing a strong positivity for this marker in groups G1 and G2 when compared to the stromal cells from non-altered mammary tissue (G1, p = 0.028, p&lt; 0,001).

This present study show that there is a significant reduction in TLR4 expression in tumor epithelial cells when compared to the normal compartment in this rat DMBA-induced mammary carcinogenesis model. Besides, the intensity of the inflammatory response in the tumor microenvironment can alter the immunoreactivity for TLR4.

Citation Format: Joyce Regina Zapaterini, Muriele Bertagna Varuzza, Nelci Antunes Moura, Maria Aparecida Marchesan Rodrigues, Luis Fernando Barbisan. Toll-like receptor 4 immunoreactivity in mammary tumors chemically induced in female Sprague-Dawley rats. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2720. doi:10.1158/1538-7445.AM2015-2720