The unveiling of the Warburg effect and the inscribed innovative approach to a radical non toxic anticancer therapy

The purpose of this research has been deciphering the Warburg paradox, the biochemical enigma unsolved since 1923. This paradox consists of the aerobic pyruvate conversion to lactate brought about by anaplastic cancer, through the metabolic pathway known as aerobic glycolysis. This pathway implies a heavy energetic waste. We solved the enigma by demonstrating that its specific character, i.e. the forced aerobic lactate exportation, represents a crucial metabolic device to counteract the cytotoxic effect produced by an excess of pyruvate at the connection of glycolysis with the Krebs cycle. This solution was verified by exposing cancer cells of different histogenesis to pyruvate concentrations higher than the physiological ones, after showing that these concentrations are totally innocuous when injected into mice. The molecular aspects for this cancer selectivity has been explored in vitro and in vivo, providing the following information: i) the growth of highly anaplastic cancers, including melanoma and leukemia cell lines, was up to 90% inhibited by the addition of 10-20 mM pyruvate, while substantially unaffected resulted the bone marrow cells (BMC) and the clonogenic lymphocytes; ii) the metastatic diffusion of the A375 melanoma cells injected into nude mice was drastically inhibited by pre-treatment with pyruvate, which produced the progressive massive cancer apoptosis. The pathophysiological aspects of the pyruvate cytotoxicity were deciphered through the following series of biochemical achievements: the cytotoxicity is a linear function of the rate of its commitment to the respiratory chain through the Krebs cycle, i.e. to the rate of O2 consumption. This commitment engages, up the saturation, the respiratory chain in its function other than the cristae-dependent oxidative phosphorylation. This function is the disposal of the cytosolic reducing equivalents, a crucial step in the regulation of the cytosolic NADP/NADPH ratio. The latter gears all the NADP-dependent dehydrogenations implicated in the multiple metabolic networks, including the conversion of methylene-tetrahydrofolate to methenyl-tetrahydrofolate, whose product is an integral component of the purine ring. On these bases, the mechanism of the pyruvate cytotoxicity relies on the saturation of the respiratory chain, leading to a negative shift of the cytosolic NADP/NADPH ratio and the consequent restriction of the purine synthesis and the related cell apoptosis. The reducing equivalents generated by glycolysis and by cytosolic metabolism compete each other for their disposal trough the respiratory chain; this makes it that the cytotoxicity of pyruvate is inversely related to the mitochondrial number and efficiency of various cell types. Thus, the cytotoxicity is high in anaplastic cancer stem cells, whose mitochondria are extremely few and immature (cristae-poor); on the contrary, no inhibition is brought about in adult differentiated cells, physiologically rich of mature mitochondria. All this generates the pyruvate anticancer selectivity, together with the lack of a general toxicity, making pyruvate represent an ideal candidate for a radical non toxical anticancer treatment.