Background: Glioblastoma multiform (GBM) tumors are the most aggressive and diffusely infiltrating brain tumors in human patients. Despite surgery, modern chemotherapy and anti-angiogenesis treatments, GBM tumors regrow rapidly and end patients’ lives in a relatively short time. GBM tumors aggressively invade and infiltrate adjacent normal brain tissues. GBM cells are driven by glycolysis
(glucose oxidation to produce ATP and lactate in cancer cells).
Materials and Methods: In this study, we cultured rat C6 GBM cells and human GBM cells (U373MG) to be treated using glycolysis inhibitors. Citrate is a natural product enormously available in citrus fruits and has many pharmacological uses e.g. to treat urate renal stones. Citric acid was recently reported to exert cardioprotective effects on myocardial ischemia/reperfusion injury. Serial doses of citrate
(glycolytic inhibitor of phosphofructokinase) were lethal to human GBM cell lines at relatively high doses (in millimolar range). Using the combination drug index, low effective doses of citrate (1, 3 and 5 mM) exerted a synergistic anticancer effect with low effective doses of 3- bromopyruvate (15 and 25 μM). Combination index was < 1 and denoted strong synergism between citrate and 3- bromopyruvate. As
3-bromopyruvate is another glycolysis inhibitor (hexokinase II inhibitor) in addition to citrate itself, double inhibition of glycolysis was evident when combining both citrate and 3-bromopyruvate. Both drugs benefited from tumor biology as citrate is acidic in solution and does better in acidic tumor microenvironment and same thing applies to 3-bromopyruvate that is also acidic in solution. In addition, 3- bromopyruvate is a structural analog and competitive antagonist of lactate (The Warburg effect) to deprive cancer cells of vital benefits of lactate. Lactate-based benefits to cancer cells include enhancing angiogenesis, metastasis, invasion, proliferation, migration,
chemoresistance, radioresistance and acidic tumor microenvironment.
Results: Our data confirmed that pharmacological glycolysis double inhibition significantly, maximally and synergistically distorted GBM cells morphology and reduced cellular viability.