(S022) Experimental Insight Into the Preferential Cytotoxicity of Cancerous vs Noncancerous Cells of Metformin

Derek Isrow, MD, PhD, Karen Lapanowski, Andrew Kolozsvary, Stephen Brown, PhD, Jae Ho Kim, MD, PhD; Henry Ford Hospital

PURPOSE AND OBJECTIVE: Metformin is known to produce direct cancer cell cytotoxicity, inhibit tumor growth, radioprotect normal tissues, and radiosensitize cancer cells. However, the underlying mechanism behind the anticancer activity is not yet understood. This study was designed to investigate the biochemical effect of metformin on cancerous and noncancerous cells under varying conditions from the perspective of reactive oxygen species (ROS).

MATERIALS AND METHODS: A549 (lung cancer), MCF-7 (breast cancer), and MCF-10A (normal breast) cell lines were maintained in cell culture and exposed to 5 mM metformin for 4–6 hours in environments in which oxygen and glucose concentrations varied. The level of ROS production was measured using a standard dihydroethidium (DHE) fluorescence reagent and flow cytometric spectroscopy. Oxygen levels were maintained with atmospheric oxygen or a mixture of carbon dioxide/nitrogen gas. Clonogenic and MTT assays were used to assess cellular response to radiation therapy.

RESULTS: Metformin consistently and significantly increased ROS levels at least 2-fold in A549 and 3-fold in MCF-7 cell lines. ROS levels in MCF-10A cells were only moderately affected. Hypoxic A549 cells treated with metformin showed a 137% increase in ROS levels over baseline hypoxic cells without metformin (165% at 6 hr). Oxygenated A549 cells treated with metformin showed a 117% ROS increase compared with control cells without metformin (139% at 6 hr). When A549 cells were placed in glucose-free medium (GFM) and exposed to metformin, ROS levels were 203% greater than A549 cells in GFM without metformin. Hypoxic A549 cells in GFM with metformin produced a ROS level 120% greater than cells in hypoxic GFM without metformin. Cellular response studies confirmed the ROS results. Increased cytotoxicity to radiation in the presence of metformin was observed with A549 cells by clonogenic assay and with MCF-7 cells by MTT assay. In agreement with the ROS studies, no increased radiosensitization or cytotoxicity was observed in MCF-10A cells using metformin.

CONCLUSIONS: Metformin was demonstrated to increase ROS levels, cytotoxicity, and radiosensitization in A549 and MCF-7 cancer cells under oxic, hypoxic, glucose-full, and glucose-free conditions. Normal MCF-10A cells did not show increased toxicity with metformin. The preferential metformin-induced increase in ROS levels found in cancer cells, particularly hypoxic cells, may provide some explanation for the therapeutic benefit seen in diabetic patients taking metformin while undergoing cancer treatment. Further studies are underway in the hope of translating these findings into clinical practice.

Proceedings of the 97th Annual Meeting of the American Radium Society- americanradiumsociety.org