Molecular iodine exerts antineoplastic effects by diminishing proliferation and invasive potential and activating the immune response in mammary cancer xenografts

BACKGROUND: The immune system is a crucial component in cancer progression or regression. Molecular iodine (I(2)) exerts significant antineoplastic effects, acting as a differentiation inductor and immune modulator, but its effects in antitumor immune response are not elucidated. METHODS: The present work analyzed the effect of I(2) in human breast cancer cell lines with low (MCF-7) and high (MDA-MB231) metastatic potential under both in vitro (cell proliferation and invasion assay) and in vivo (xenografts of athymic nude mice) conditions. RESULTS: In vitro analysis showed that the 200 μM I(2) supplement decreases the proliferation rate in both cell lines and diminishes the epithelial-mesenchymal transition (EMT) profile and the invasive capacity in MDA-MB231. In immunosuppressed mice, the I(2) supplement impairs implantation (incidence), tumoral growth, and proliferation of both types of cells. Xenografts of the animals treated with I(2) decrease the expression of invasion markers like CD44, vimentin, urokinase plasminogen activator and its receptor, and vascular endothelial growth factor; and increase peroxisome proliferator-activated receptor gamma. Moreover, in mice with xenografts, the I(2) supplement increases the circulating level of leukocytes and the number of intratumoral infiltrating lymphocytes, some of them activated as CD8+, suggesting the activation of antitumor immune responses. CONCLUSIONS: I(2) decreases the invasive potential of a triple negative basal cancer cell line, and under in vivo conditions the oral supplement of this halogen activates the antitumor immune response, preventing progression of xenografts from laminal and basal mammary cancer cells. These effects allow us to propose iodine supplementation as a possible adjuvant in breast cancer therapy. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12885-019-5437-3) contains supplementary material, which is available to authorized users.