Induction of cell death in hepatocellular carcinoma (HCC) via energy depletion

Background:

For a long time metabolism was considered a network of sequential reactions providing energy and building blocks in response to the needs of the cell. It is now appreciated that there is an intense crosstalk between metabolism and signaling cascades regulating cell survival, proliferation and differentiation. Dimethyl fumarate (DMF) is a pharmaceutical used for treatment of psoriasis (Fumaderm®) und multiple sclerosis (MS) (Tecfidera®). Recently, our group has shown that DMF application leads to suppression of NF κB, a transcription factor promoting cell survival and proliferation. In addition, treatment with DMF results in elevated glycolysis and reduced mitochondrial respiration. Tumor cells gain their energy mostly via glycolysis. Thus, DMF application increases cellular glucose dependency and most probably induces an energetic crisis. Thus, DMF-dependent induction of cell death via energy depletion could be a novel strategy to target solid tumors like HCC.

Methods:

Human liver tumor cell lines HepG2 und Huh7 were treated with DMF (12,5µM up to 100µM) or 2-desoxyglucose (2-DG) (1,1 mM up to 5,6 mM for HepG2 and 2,5 mM up to 12,5 mM for Huh7, depending on the glucose concentration in the medium) and cultivated for up to 72h. Induction of cell death was determined using a luminescence based viability assay. Characterization of DMF-induced cell death was performed by flow cytometry (FACS analysis) using DAPI/Annexin V staining.

Results:

Liver tumor cell lines HepG2 and Huh7 show no constitutive NF κB activation. Nevertheless, DMF application resulted in in a time- and dose-dependent induction of cell death. The strongest effect was gained after 72h at a concentration of 100µM DMF. Cell death induction was determined by luminescence based viability assays and FACS analysis. In addition, cells were treated with inhibitors of glycolysis. HepG2 and Huh7 cells were treated with 2 DG, an inhibitor of the Glucose-6-phosphat-isomerase. Cell viability/cell death was analyzed. Cell death in HepG2 and Huh7 was observed after 24h of treatment. The greatest impact in HepG2 was gained after 72h and a concentration of 5,6 mM 2-DG. In Huh7 the main effect was gained after 72h and a concentration of 12,5 mM. Huh7 cells were more effected than HepG2 by 2-DG.

Conclusion:

Solid tumors – especially HCC – display a rather high mortality rate compared to other malignant tumors. Here, we show that DMF is capable to induce cell death in HCC cell lines. DMF is already approved for treatment of psoriasis and MS showing minor side effects compared to anti-cancer drugs, hence, targeting cellular metabolism by substances like DMF should be regarded as a promising approach to develop novel therapeutic tools to treat solid tumors such as HCC.