We previously demonstrated that alkyl gallates coupled to triphenylphosphine have a selective and efficient antiproliferative effect by inducing mitochondrial uncoupling in vitro due to the increased mitochondrial transmembrane potential of tumor cells. Therefore, in this work, the in vivo antitumor activities of alkyl gallate triphenylphosphonium derivatives (TPP+C8, TPP+C10 and TPP+C12) were evaluated in a syngeneic murine model of breast cancer. We found that TPP+C10 increased the cytosolic ADP/ATP ratio and significantly increased the AMP levels in a concentration-dependent manner in TA3/Ha murine mammary adenocarcinoma cells. Interestingly, TPP+C10 induced a decrease in the levels of cellular proliferation markers and promoted caspase-3 activation in tumor-bearing mice. Additionally, TPP+C10 inhibited tumor growth in the syngeneic mouse model. Importantly, 30days of intraperitoneal (i.p.) administration of the combination of TPP+C10 (10mg/kg/48h) and the antibiotic doxycycline (10mg/kg/24h) completely eliminated the subcutaneous tumor burden in mice (n=6), without any relapses at 60days post-treatment. This enhancement of the individual activities of TPP+C10 and doxycycline is due to the uncoupling of oxidative phosphorylation by TPP+C10 and the inhibition of mitochondrial biogenesis by doxycycline, as demonstrated by loss of mitochondrial mass and overexpression of PGC1-α as an adaptive response. Moreover, i.p. administration of TPP+C10 (10mg/kg/24h) to healthy mice did not produce toxicity or damage in organs important for drug metabolism and excretion, as indicated by hematological, biochemical and histological assessments. These findings suggest that the combination of TPP+C10 with doxycycline is a valuable candidate therapy for breast cancer management.

Clinical and Molecular Pharmacology Program Institute of Biomedical Sciences Faculty of Medicine University of Chile Av Independencia 1027 Santiago 8380453 Chile

Department of Chemistry Faculty of Basic Sciences Metropolitan University of Educational Sciences Av José Pedro Alessandri 774 Santiago 7760197 Chile

Department of Organic and Physical Chemistry Faculty of Chemical and Pharmaceutical Sciences University of Chile Santos Dumont 964 Santiago 8380494 Chile

Institute of Biotechnology Czech Academy of Sciences Průmyslová 595 Vestec 25250 Prague Czech Republic

Program of Anatomy and Developmental Biology Institute of Biomedical Sciences Faculty of Medicine University of Chile Av Independencia 1027 Santiago 8380453 Chile

School of Medicine Faculty of Health Sciences University of Tarapacá Av General Velásquez 1775 Arica 1000007 Chile

References provided by Crossref.org

Complex Mitochondrial Dysfunction Induced by TPP+-Gentisic Acid and Mitochondrial Translation Inhibition by Doxycycline Evokes Synergistic Lethality in Breast Cancer Cells