Hiroo Toyoda

Triple-negative breast cancer (TNBC) is one of the most difficult subtypes of breast cancer to treat due to its aggressive, metastatic behavior, and a lack of a targeted therapy. Trivalent arsenic derivatives (arsenite, AsIII) with remarkable clinical efficacy in acute promyelocytic leukemia has been demonstrated to exhibit inhibitory effect against breast cancer cells. To provide novel insight into the development of new therapeutic strategies, antitumor activity of AsIII and tetrandrine (Tetra), a Chinese plant-derived alkaloid, against the TNBC cell line MDA-MB-231 in vitro and in vivo was investigated. Cytotoxicity was evaluated using cell viability, lactate dehydrogenase leakage and cell cycle assay. Alterations of genes related to cell proliferation and death were analyzed using western blotting. In vivo antitumor activity of AsIII alone or in combination with Tetra was studied using MDA-MB-231 xenografts in nude mice. Synergistic cytotoxic effects of two drugs were observed in the cells. In vivo study also showed that co-administration of AsIII and Tetra significantly reduced tumor volume and weight, directly supporting its in vitro antitumor activity. No deaths and reduction of body-weight were observed after a long-term co-administration, indicating its good tolerability. S-phase arrest associated with the upregulation of FOXO3a, p27 along with decreased Cyclin D1 expression was observed in the cells treated with the combined regimen. A substantial upregulated p21 expression and downregulated phospho-FOXO3a and Cyclin D1 expression was observed in the tumor tissues of mice co-administered with AsIII and Tetra. Autophagy induction was observed in the combination treatment in vitro and in vivo. The addition of wortmannin, a potent autophagy inhibitor, significantly rescued MDA-MB-231 cells from their cytotoxicity of AsIII and Tetra. S-phase arrest, autophagic and necrotic cell death contribute to the cytocidal effects of the combined regimen of AsIII and Tetra. Considering our previous study showing synergistic cytotoxic effects of the combined regimen in estrogen receptor-positive breast cancer cell line MCF-7, these results suggest that development of the combination regimen of AsIII plus Tetra may offer many benefits to patients with different types of breast cancer.