Triethylenetetramine Synergizes with Pharmacologic Ascorbic Acid in Hydrogen Peroxide Mediated Selective Toxicity to Breast Cancer Cell

Breast cancer is characterized by overexpression of superoxide dismutase (SOD) and downregulation of catalase and more resistance to hydrogen peroxide (H(2)O(2)) than normal cells. Thus, relatively high H(2)O(2) promotes breast cancer cell growth and proliferation. However, excessive intracellular H(2)O(2) leads to death of breast cancer cells. In cancer cells, high level ascorbic acid (Asc) is able to be autoxidized and thus provides an electron to oxygen to generate H(2)O(2). In the present study, we demonstrated that triethylenetetramine (TETA) enhances Asc autoxidation and thus elevates H(2)O(2) production in MCF-7 cells. Furthermore, Asc/TETA combination significantly impaired cancer cell viability, while having much milder effects on normal cells, indicating Asc/TETA could be a promising therapy for breast cancer. Moreover, SOD1 and N-acetyl-L-cysteine failed to improve MCF-7 cells viability in the presence of Asc/TETA, while catalase significantly inhibited the cytotoxicity of Asc/TETA to breast cancer cells, strongly suggesting that the selective cytotoxicity of Asc/TETA to cancer cells is H(2)O(2)-dependent. In addition, Asc/TETA induces RAS/ERK downregulation in breast cancer cells. Animal studies confirmed that Asc/TETA effectively suppressed tumor growth in vivo. In conclusion, TETA synergizes pharmacologic Asc autoxidation and H(2)O(2) overproduction in breast cancer cells, which suppresses RAS/ERK pathway and results in apoptosis.