The effect of the association of Gossypol and Lonidamine on the energy metabolism of Ehrlich ascites tumor cells

Assessment of the low inhibitory specificity of oxamate, aminooxyacetate and dichloroacetate on cancer energy metabolism

BACKGROUND

Exceedingly high therapeutic/experimental doses of metabolic drugs such as oxamate, aminooxyacetate (AOA) and dichloroacetate (DCA) are required to diminish growth, glycolysis and oxidative phosphorylation (OxPhos) of different cancer cells. To identify the mechanisms of action of these drugs on cancer energy metabolism, a systematic analysis of their specificities was undertaken.

METHODS

Hepatocarcinoma AS-30D cells were treated with the inhibitors and glycolysis and OxPhos enzyme activities, metabolites and fluxes were analyzed. Kinetic modeling of glycolysis was used to identify the regulatory mechanisms.

RESULTS

Oxamate (i) not only inhibited LDH, but also PYK and ENO activities inducing an increase in the cytosolic NAD(P)H, Fru1,6BP and DHAP levels in AS-30D cells; (ii) it slightly inhibited HPI, ALD and Glc6PDH; and (iii) it inhibited pyruvate-driven OxPhos in isolated heart mitochondria. AOA (i) strongly inhibited both AAT and AlaT, and 2-OGDH and glutamate-driven OxPhos; and (ii) moderately affected GAPDH and TPI. DCA slightly affected pyruvate-driven OxPhos and Glc6PDH. Kinetic modeling of cancer glycolysis revealed that oxamate inhibition of LDH, PYK and ENO was insufficient to achieve glycolysis flux inhibition. To do so, HK, HPI, TPI and GAPDH have to be also inhibited by the accumulated Fru1,6BP and DHAP induced by oxamate.

CONCLUSION

Oxamate, AOA, and DCA are not specific drugs since they inhibit several enzymes/transporters of the glycolytic and OxPhos pathways through direct interaction or indirect mechanisms.

GENERAL SIGNIFICANCE

These data explain why oxamate or AOA, through their multisite inhibitory actions on glycolysis or OxPhos, may be able to decrease the proliferation of cancer cells.

BNIP3 regulates AT101 [(-)-gossypol] induced death in malignant peripheral nerve sheath tumor cells

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive Schwann cell-derived sarcomas and are the leading cause of mortality in patients with neurofibromatosis type 1 (NF1). Current treatment modalities have been largely ineffective, resulting in a high rate of MPNST recurrence and poor five-year patient survival. This necessitates the exploration of alternative chemotherapeutic options for MPNST patients. This study sought to assess the cytotoxic effect of the BH3-mimetic AT101 [(-)-gossypol] on MPNST cells in vitro and to identify key regulators of AT101-induced MPNST cell death. We found that AT101 caused caspase-independent, non-apoptotic MPNST cell death, which was accompanied by autophagy and was mediated through HIF-1α induced expression of the atypical BH3-only protein BNIP3. These effects were mediated by intracellular iron chelation, a previously unreported mechanism of AT101 cytotoxicity.

Glycolysis in the african trypanosome: targeting enzymes and their subcellular compartments for therapeutic development

Subspecies of the African trypanosome, Trypanosoma brucei, which cause human African trypanosomiasis, are transmitted by the tsetse fly, with transmission-essential lifecycle stages occurring in both the insect vector and human host. During infection of the human host, the parasite is limited to using glycolysis of host sugar for ATP production. This dependence on glucose breakdown presents a series of targets for potential therapeutic development, many of which have been explored and validated as therapeutic targets experimentally. These include enzymes directly involved in glucose metabolism (e.g., the trypanosome hexokinases), as well as cellular components required for development and maintenance of the essential subcellular compartments that house the major part of the pathway, the glycosomes.

Gossypol inhibition of mitosis, cyclin D1 and Rb protein in human mammary cancer cells and cyclin-D1 transfected human fibrosarcoma cells

The antiproliferative effects of gossypol on human MCF-7 mammary cancer cells and cyclin D1-transfected HT-1060 human fibrosarcoma cells were investigated by cell cycle analysis and effects on the cell cycle regulatory proteins Rb and cyclin D1. Flow cytometry of MCF-7 cells at 24 h indicated that 10 microM gossypol inhibited DNA synthesis by producing a G1/S block. Western blot analysis using anti-human Rb antibodies and anti-human cyclin D1 antibodies in MCF-7 cells and high- and low-expression cyclin D1-transfected fibrosarcoma cells indicated that, after 6 h exposure, gossypol decreased the expression levels of these proteins in a dose-dependent manner. Gossypol also decreased the ratio of phosphorylated to unphosphorylated Rb protein in human mammary cancer and fibrosarcoma cell lines. Gossypol (10 microM) treated also decreased cyclin D1-associated kinase activity on histone H1 used as a substrate in MCF-7 cells. These results suggest that gossypol might suppress growth by modulating the expression of cell cycle regulatory proteins Rb and cyclin D1 and the phosphorylation of Rb protein.

Genetic toxicity studies of gossypol

Gossypol, a polyphenolic compound extracted from cotton plants, shows promise for use as a male contraceptive, as well as a treatment for gynecological disorders, cancer, and certain microbial diseases. Before gossypol can be considered safe for widespread human use, particularly by healthy people of childbearing age, its effect on normal genetic processes should be understood. Characterization of gossypol's genotoxic potential has not been approached systematically, although numerous clinical and laboratory studies have addressed issues relating to genetic effects of gossypol. This review summarizes results of relevant studies and offers recommendations for the emphasis of future efforts to understand gossypol's genotoxicity potential. Evidence suggesting that gossypol has any genotoxic effects in mammals under normal physiologic conditions so far is weak, at best. However, several unresolved issues that are important for establishing long-term genetic safety of gossypol were uncovered by this analysis. These include the need for a better understanding of the significance of weak increases in SCE frequency seen in a number of laboratory exposure studies, and more definitive, comprehensive animal tumor bioassay data.

Effect of rhein on the glucose metabolism of Ehrlich ascites tumor cells

The effect of rhein, 4,5-dihydroxyanthraquinone-2-carboxylic acid, on oxygen consumption and the rate of aerobic and anaerobic lactate production by Ehrlich ascites tumor cells has been investigated. The rate of oxygen uptake decreases with the increase of rhein concentration. Rhein also inhibits aerobic and anaerobic glycolysis. The rate of aerobic lactate production decreases with the drug concentration and the maximal effect was observed at 0.100 mM. Anaerobic lactate production is also inhibited and the maximum effect is reached at 0.220 mM. The possibility that the lactate production decrease was secondary to an effect on mitochondrial ATPase was excluded on the basis of the data with DNP and oligomycin. Rhein reduces the intracellular level of lactate, pyruvate and glucose-6-phosphate. Glucose utilization and 2-deoxy-D-glucose uptake are decreased to the same extent as the inhibition of aerobic lactate production, whereas glucose phosphorylation is unaffected. It is, therefore, concluded that the inhibition of glycolysis of Ehrlich ascites tumor cells by rhein is caused by an impairment of glucose uptake.

Modulation of adriamycin uptake by lonidamine in Ehrlich ascites tumor cells

The effect of Lonidamine, 1-(2,4 dichlorobenzyl)-1-H-indazol-3-carboxylic acid, on the uptake of Adriamycin by Ehrlich ascites tumor cells has been investigated. The uptake of Adriamycin is greatly stimulated by Lonidamine and the increase depends on the energy sources of the cell. In the presence of glucose the intracellular drug content is remarkably lower than that in its absence. This difference lies in the mechanism by which Lonidamine enhances the uptake of Adriamycin. The Adriamycin efflux is via an active transport process and, in the presence of glucose, both aerobic glycolysis and oxidative phosphorylation contribute to ATP synthesis. Although Lonidamine inhibits both these pathways, there is still sufficient ATP to extrude a certain amount of Adriamycin. The elevated intracellular concentration of Adriamycin depends not only on the Lonidamine-inhibited outward transport but also on higher membrane permeability which allows a low concentration of Adriamycin (18 microM) to interfere also with the oxidative metabolism of Ehrlich ascites tumor cells.

Membrane structural/functional perturbations induced by gossypol. Effects on membrane order, liposome permeability, and insulin-sensitive hexose transport

The effects of gossypol on membrane structure and membrane-associated functions were studied to explore possible reasons for the ability of gossypol to disrupt cellular processes, many of which involve intracellular and plasma membranes. The experiments reported here measured the effects of gossypol on membrane order, permeability, and hexose transport. Electron spin resonance (ESR) studies of I(12,3) nitroxide fatty acid spin-labeled unilamellar liposomes showed that exposure to 0.05 to 4 mM gossypol caused a dose-dependent increase in the polarity-corrected order parameter (S), indicating reduced motional freedom of the spin probe after exposure to gossypol. This observation is consistent with the idea that gossypol causes an ordering or "condensing" of the membrane lipid matrix. Gossypol-induced changes in order parameter in phosphatidylcholine:cholesterol liposomes varied depending on the liposome composition. Liposomes exposed to gossypol also showed increasing permeability to glycerol as the gossypol:phospholipid ratio increased up to 10 mole %. Higher concentrations of gossypol were less effective at enhancing permeability. In addition, basal and insulin-stimulated 2-deoxy-D-[3H]glucose transport were inhibited in freshly isolated rat adipocytes incubated with gossypol at 37 degrees. Half-maximal inhibition occurred at approximately 0.2 mM for uptake in both the presence and absence of 40 ng/ml insulin. Microscopic observation of the cells under low power (40 X) confirmed that diminished hexose transport was not simply due to breakage of the adipocyte plasma membrane, resulting in a decrease in intact cell population and decreased accumulation of label in the gossypol-treated cells. Gossypol produced no significant changes in numbers of intact cells or gross morphology at the concentrations tested. We suggest that ordering and increased permeability of the lipid regions of plasma and subcellular membranes may contribute to some of the toxic and pharmacologic properties of gossypol. Our results also support the idea that gossypol may exert more pronounced effects in cells that are most sensitive to variations in availability of glucose substrates for energy metabolism.

Effect of lonidamine on protein synthesis in neoplastic cells

The action of lonidamine, 1,(2,4 dichlorobenzyl)-1H-indazol-3-carboxylic acid, on protein synthesis of neoplastic cells growing both in vivo and in vitro has been investigated. Lonidamine decreases amino acid incorporation in all cells tested, although the inhibition is partially relieved by glucose. The inhibition of labeled precursors into acid-insoluble material cannot be ascribed to an impairment of amino acid uptake which, on the contrary, is enhanced by the drug. Tests on cell-free systems showed that lonidamine does not inhibit the tobacco mosaic virus (TMV)-mRNA-directed in vitro protein synthesis, thus indicating that protein synthetic machinery per se is not affected. The inhibition of the rate of protein synthesis achieved by lonidamine must be ascribed to an effect on energy-yielding processes with a mechanism similar to that observed in other metabolic inhibitors. Lonidamine, however, because of its capacity to inhibit both respiration and glycolysis in neoplastic cells, is effective at 10 to 20 times lower concentrations. DNP and oligomycin potentiate the inhibitory effect of lonidamine on the rate of protein synthesis. This finding substantiates the idea that neoplastic cells, including those growing in ascitic form, utilize mitochondrial oxidative phosphorylation as the main source of ATP for their biosynthetic processes.

The effect of gossypol and Lonidamine on electron transport in Ehrlich ascites tumor mitochondria

The effect of the association of gossypol and Lonidamine on the electron transport in Ehrlich ascites tumor mitochondria has been investigated by addition of drugs to isolated mitochondria. The results may be summarized as follows. (1) Low concentrations of gossypol increase the rate of oxygen consumption at the level of three energy-conserving sites of the respiratory chain. Higher concentrations result in an inhibition of oxygen consumption at (or near) both energy-conserving sites 1 and 2, while energy-conserving site 3 is unaffected. (2) Gossypol, at concentrations at which it exerts its uncoupling effect, stimulates ATPase activity. Higher concentrations inhibit the enzyme activity. (3) The addition of gossypol to mitochondria respiring on pyruvate plus malate or succinate induces a more oxidized state of NAD+ and cytochrome b, respectively. (4) Gossypol enhances the effect of Lonidamine on oxygen consumption. Lonidamine does not affect state 4 respiration, but in the presence of gossypol, it determines a marked decrease in the rate of oxygen consumption. The inhibition of oxidation of NAD-linked substrates is greater than that of FAD-linked substrates. (5) It may be concluded that gossypol is very effective in potentiating the effect of Lonidamine. Moreover, it may be suggested that the antitumor activity of Lonidamine is enhanced if it is used in combination with other drugs and/or treatments, such as hyperthermia, which modify the energy status of mitochondria.