A combinatorial preclinical in vitro strategy against human glioblastoma cells. specific targeting of protein kinases, histone deacetylases and glycolysis

Effective treatment of malignant gliomas remains one of the great challenges in neurooncology. The incidence of malignant gliomas is 5 to 10 per 100.000 persons, and the outcome is always fatal with a mean survival of less than one year. Tumor location and invasiveness into normal brain tissues are the two main obstacles for surgical cure. Resistance to conventional chemo- and radiotherapy is a consequence of high genetic instability leading to countless mutations. The presence of the bloodbrain barrier makes drug targeting difficult. Nevertheless, mechanisms of gliomagenesis are becoming better understood. Among the key cellular pathways, those controlling apoptosis, proliferation, repair and invasion are most frequently disrupted due to alterations in TP53, p16/p14, RB, PTEN, EGFR and PDGFR. In addition, many regulatory genes are epigenetically silenced by methylation and acetylation. A cardinal feature of malignant gliomas, as well as many other cancers, is a high rate of ATP consumption via upregulation of glycolysis. All these pathways represent potential targets for interference with specific drugs. Recently, small lipo-soluble molecules were designed as a new class of drugs more specifically targeting those altered cancer pathways. These drugs were applied to human GBM cells for induction of apoptosis as a readout of drug efficacy. Single applications of the PKIs, AEE788, Glivec and RADOO1 or the glycolytic inhibitor, 2-DG, were not able to induce cell death, but only a cytostatic effect at clinically meaningful dose ranges. In contrast, cytotoxic drugs like the microtubule inhibitor EPO906 or HDAC inhibitors (HDIs) like trichostatin A, sodium butyrate and LAQ824 were able to efficiently trigger apoptosis, but are known to lead to toxicity with increased dose ranges in mice and humans. We therefore tested combinations of low doses of cytotoxic drugs with cytostatic drugs and indomethacin. Since p21 was shown to be re-expressed upon HDIs and to protect cancer cells against apoptotic stimuli, 2-DG was used as a sensitizer for HDIs-induced apoptosis. 2-DG strongly inhibits protein expression. Synergistic induction of apoptosis was observed in glioma and other cancer cell lines upon this combined treatment. Thus, drug combination that inflict a cytotoxic stress to cancer cells and simultaneously impair the p21-regulated response of the stressed cells to halt the cell cycle machinery may be a new way to treat cancer in the future.