CONICET | Buscador de Institutos y Recursos Humanos

Breast cancer is the second cause of death in women. Its incidence is increasing in the developing world and even though it is a treatable disease if detected early, there are a large number of deathsassociated with breast cancer, especially related to uncontrolled metastatic disease. It was previously demonstrated that the administration of the probiotic Lactobacillus (L.) casei CRL 431delayed the tumour growth in a murine breast cancer model. The aim of this work was to evaluate the effect of the administration of milk fermented by L. casei CRL 431on lung metastasis associatedto breast cancer in a mouse model. BALB/c mice were injected subcutaneously with the highly metastatic tumor cell line 4T1. When the tumours were measurable (7‐10 days), mice were dividedinto three groups: 1) Mice administered milk fermented by L. casei CRL431 (FM group), 2) mice given milk (M group), and 3) control mice without any special feeding (C group). Tumour volumewas calculated until day 35 (after tumour cells injection). Animals were sacrificed if presented loss of 20% of initial body weight and /or cachexia. The rest of the animals were sacrificed the day 70.Whole blood, lungs and liver were processed to count the number of colonies formed by tumoral cells. Blood serum was obtained for MCP1 chemokine determination by ELISA, lung tissues forhistological observations and tumour tissues for angiogenesis determination by immunohistochemistry. FM administration after tumour injection significantly decreased tumorgrowth, and increased the survival percentage of the animals at day 70, compared to C and M groups. The analysis of tumor angiogenesis showed a significant decrease of the area occupied byblood vessels in the mice from FM group compared to C and M groups. The tumoral cell culture assay from samples of blood, lung and liver showed a greater number of tumour cell colonies in theblood and lung samples obtained from mice of C and M groups than in the samples from FM group. No significant differences were observed in the livers. Metastasic areas in the lungs were also analyzed and it was observed that mice from FM group had a lower percentage of metastatic occupation compared to the C and M groups. Finally, considering the importance of the immunecell recruitment in the metastasic site, the chemokine MCP1 was determined in serum of all the mice. It was observed that MCP1 levels increased in mice with higher tumor volume and presenceof metastases and its concentration was lower in FM group. We can conclude that FM administration after the tumor was measurable, exerted protection against lung metastasis. In thepresent model, the protection was mainly through the influence on the tumour growth, diminishing the angiogenesis which decreased the concentration of circulating tumor cells and consequently the metastasis. The decrease of MCP1 circulating levels in the mice that received FM suggests that possible changes in the infiltrating immune cell and their activations at the metastasic site could be involved in the protection against metastasis.