Effects of Melatonin and Doxorubicin on Primary Tumor And Metastasis in Breast Cancer Model

Background: Melatonin exerts oncostatic effects on breast cancer via immunomodulation and antioxidation. Doxorubicin is an effective chemotherapeutic agent, but parallel studies also provide ample evidence of an off-target effect of Doxorubicin in breast cancer patients. Objective: Combinatorial use of doxorubicin and melatonin has not been comprehensively analyzed in breast cancer models. We hypothesized that the anti-oxidative, anti-proliferative and anti-inflammatory effects of melatonin could ameliorate the off-target effects of doxorubicin in breast cancer patients and enhance the anti-tumoral effects of doxorubicin. The goal of the study is to test this hypothesis in cancer cell lines and xenografted mice. Methods: The effects of Melatonin and doxorubicin on the cell viability were evaluated in 4T1-Brain Metastatic Tumor (4TBM). Furthermore, the effects of melatonin and doxorubicin on the primary tumors and systemic metastasis were evaluated in the xenografted mice. Lung and liver tissues were removed and metastasis analyses were performed. The levels of p65, phospho-STAT3, CD11b+, GR1+, Ki67, and cleaved caspase-3 proteins were determined with immunohistochemistry and western blot analysis. We examined the effects of melatonin and Melatonin+Doxorubicin combination therapy on 4TBM cells. Results: Our results showed that doxorubicin inhibited the proliferation of metastatic breast cancer cells while melatonin did not affect cells. Tumor growth and metastasis were markedly suppressed in melatonin alone and in combination with doxorubicin. The expression of CD11b+ and GR1+ proteins, which are indicators of myeloid-derived suppressor cells (MDSCs), were noted to be reduced in both primary tumor and metastatic tissues in melatonin and doxorubicin groups. Conclusion: The combination of melatonin with doxorubicin reduced primary tumor growth and distant metastasis. Based on these results, melatonin is a promising candidate for combinatory use with conventional chemotherapeutics for breast cancer treatment.