Search

Many cancer cells share with yeast a preference for fermentation over respiration, which is associated with overactive glucose uptake and breakdown, a phenomenon called the Warburg effect in cancer cells. The yeast tps1Δ mutant shows even more pronounced hyperactive glucose uptake and phosphorylation causing glycolysis to stall at GAPDH, initiation of apoptosis through overactivation of Ras and absence of growth on glucose. The goal of the present work was to use the yeast tps1Δ strain to screen for novel compounds that would preferentially inhibit overactive glucose influx into glycolysis, while maintaining basal glucose catabolism. This is based on the assumption that the overactive glucose catabolism of the tps1Δ strain might have a similar molecular cause as the Warburg effect in cancer cells. We have isolated Warbicin® A as a compound restoring growth on glucose of the yeast tps1Δ mutant, showed that it inhibits the proliferation of cancer cells and isolated structural analogs by screening directly for cancer cell inhibition. The Warbicin® compounds are the first drugs that inhibit glucose uptake by both yeast Hxt and mammalian GLUT carriers. Specific concentrations did not evoke any major toxicity in mice but increase the amount of adipose tissue likely due to reduced systemic glucose uptake. Surprisingly, Warbicin® A inhibition of yeast sugar uptake depends on sugar phosphorylation, suggesting transport-associated phosphorylation as a target. In vivo and in vitro evidence confirms physical interaction between yeast Hxt7 and hexokinase. We suggest that reversible transport-associated phosphorylation by hexokinase controls the rate of glucose uptake through hydrolysis of the inhibitory ATP molecule in the cytosolic domain of glucose carriers and that in yeast tps1Δ cells and cancer cells reversibility is compromised, causing constitutively hyperactive glucose uptake and phosphorylation. Based on their chemical structure and properties, we suggest that Warbicin® compounds replace the inhibitory ATP molecule in the cytosolic domain of the glucose carriers, preventing hexokinase to cause hyperactive glucose uptake and catabolism.

Glioblastoma is a highly lethal grade of astrocytoma with very low median survival. Despite extensive efforts, there is still a lack of alternatives that might improve these prospects. We uncovered that the chemotherapeutic agent temozolomide impinges on fatty acid synthesis and desaturation in newly diagnosed glioblastoma. This response is, however, blunted in recurring glioblastoma from the same patient. Further, we describe that disrupting cellular fatty acid homeostasis in favor of accumulation of saturated fatty acids such as palmitate synergizes with temozolomide treatment. Pharmacological inhibition of SCD and/or FADS2 allows palmitate accumulation and thus greatly augments temozolomide efficacy. This effect was independent of common GBM prognostic factors and was effective against cancer cells from recurring glioblastoma. In summary, we provide evidence that intracellular accumulation of saturated fatty acids in conjunction with temozolomide based chemotherapy induces death in glioblastoma cells derived from patients.