Proguanil Suppresses Breast Tumor Growth In Vitro and In Vivo through Mitochondrial Dysfunction

Breast cancer is a serious disease and the second leading cause of cancer-related death among women in the U.S. New treatments for this aggressive disease are urgently needed. Repurposing FDA-approved drugs for cancer treatment is an alternative that saves time and lowers the costs needed for drug development. In this study, we investigated the effects of proguanil, an anti-malarial drug, in breast cancer cells. Proguanil exhibited a significant cytotoxic effect on breast cancer cell lines including patient derived cell lines. Proguanil caused apoptosis through increased production of ROS and consequent decrease of mitochondrial membrane potential, mitochondrial respiration, and ATP production rates. ROS generation by proguanil was up to 3-fold higher when compared to the control. Proguanil treatment increased the expression of Bax, p-H2AX, cleaved-caspase 9, cleaved PARP, and down-regulated bcl-2 and survivin in breast cancer cell lines. The enlargement of 4T1 breast tumors in female Balb/c mice was suppressed by 55% through daily oral administration of 20mg/kg of proguanil. Western blot analyses of proguanil- treated tumors showed increased levels of p-H2AX, Bax, c-PARP, and c-caspase3 compared to control. Proguanil proved to be an efficient in vitro and in-vivo inhibitor of breast cancer cells, hence should be considered further for clinical investigation against breast cancer.