Metformin for Therapeutic Intervention In Acute Myeloid Leukemia

Abstract 4351

Metformin is a biguanide compound widely used for the treatment of type 2 diabetes. Several epidemiological studies have shown that metformin may reduce the risk of cancer in these patients and recent works in cancer suggest that this drug class may have anti-neoplastic activity. Metformin is known to have at least two mechanisms of action, which may be interrelated, inhibition of electron transport chain complex I and modulation of intracellular signal transduction pathways especially AMP Kinase. We hypothesized that acute myeloid leukemia (AML) cells may be sensitive to this agent and have studied its effects on cell survival and cellular metabolism in several AML cell lines.

Metformin consistently and markedly decreased oxygen consumption of six leukemic cell lines in a concentration-dependent manner. However, only MOLM14 cells showed significant apoptosis when treated with metformin alone or in combination with a conventional chemotherapeutic agent (cytosine arabinoside). In addition, only MOLM14 cells exhibit a significant increase of the extracellular lactate level (Pasteur effect) in response to metformin-induced inhibition of the mitochondrial electron transport chain complex I. By contrast, U937 cells, another AML cell line are insensitive to metformin with a marked decrease of the Pasteur effect, suggesting that intrinsic metabolic differences may contribute to the cytotoxic effect of metformin in vitro. Interestingly, we first observed highest glucose consumption and glutathione content as well as differentially expressed genes encoding several enzymes that catalyze glycolytic and anapleurotic reactions in metformin-insensitive U937 cells compared to metformin-sensitive MOLM14 cells. Accordingly, treatment of U937 cells with an inhibitor of glycolysis sensitized U937 cells to metformin while their treatment with an inhibitor of the glutathione synthesis did not abrogate their insensitivity. Finally, treatment of insensitive HL60 cells with activators of mitochondrial oxygen consumption and cell differentiation sensitized these cells to metformin.

Taken together, these findings suggest that a high glycolytic flux for production of ATP and biosynthetic precursors coupled to significant routing to the pentose phosphate pathway for NADPH for biosynthesis and GSH regeneration are key components which counterbalance the metformin-induced cytotoxic stress in U937 cells. Furthermore, based on these results, we can hypothesize that AML cell lines, and perhaps primary AML patient samples undergo a reprogramming of diverse metabolic pathways, which might be exploited by targeted therapies. Experiments on metabolic and signaling pathways as well as in vivo studies are in progress to better characterize alterations in different metabolic pathways which mediate the cytotoxic response of metformin in both AML cell lines and primary patient specimens, and thereby impact the therapeutic potential of metformin in vivo.