The enhancement of oxidative DNA damage by anti-diabetic metformin, buformin, and phenformin, via nitrogen-centered radicals

Abstract

Metformin (N,N-dimethylbiguanide), buformin (1-butylbiguanide), and phenformin (1-phenethylbiguanide) are anti-diabetic biguanide drugs, expected to having anti-cancer effect. The mechanism of anti-cancer effect by these drugs is not completely understood. In this study, we demonstrated that these drugs dramatically enhanced oxidative DNA damage under oxidative condition. Metformin, buformin, and phenformin enhanced generation of 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG) in isolated DNA reacted with hydrogen peroxide (H₂O₂) and Cu(II), although these drugs did not form 8-oxodG in the absence of H₂O₂ or Cu(II). An electron paramagnetic resonance (EPR) study, utilizing alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide as spin trapping agents, showed that nitrogen-centered radicals were generated from biguanides in the presence of Cu(II) and H₂O₂, and that these radicals were decreased by the addition of DNA. These results suggest that biguanides enhance Cu(II)/H₂O₂-mediated 8-oxodG generation via nitrogen-centered radical formation. The enhancing effect on oxidative DNA damage may play a role on anti-cancer activity.

Keywords:

• 8-OHdG
• biguanide
• cancer
• EPR
• oxidative stress

Acknowledgments

S. Ohnishi would like to thank Prof. K. Tatsumi and Dr. Y. Maeda in Research Center for Materials Science in Nagoya University and Administrative Director Dr. T. Matsumoto in Institute of Transformative Bio-Molecules in Nagoya University, for use of EPR.

Disclosure statement

No potential conflicts of interest were disclosed.

Funding information

This work was partly supported by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant Numbers 15K08787, 26460813).