Ca(2+)-ionophore A23187 and the Ca(2+)-mobilizing hormones serotonin, vasopressin, and bradykinin increase mitochondrially bound hexokinase in muscle

Inhibition of tumor growth and prolonged survival of rats with intracranial gliomas following administration of clotrimazole

OBJECT

Clotrimazole, an imidazole derivative and inhibitor of cytochrome P-450, inhibits the proliferation of cancer cells by downregulating the movement of intracellular Ca++ and K+ and by interfering with the translation initiation process. Clotrimazole inhibits the proliferation of human glioblastoma multiforme cells; it induces morphological changes toward differentiation and blocks the cell cycle in the G1/G1 phase. In vitro, clotrimazole enhances the antitumor effect of cisplatin by inducing wild-type p53-mediated apoptosis. The authors examined the effect of clotrimazole on tumor growth, sensitivity to cisplatin, and survival of rats with intracranial gliomas.

METHODS

Cultured C6 and 9L glioma cells were exposed to clotrimazole, and cell growth was assessed using the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide colorimetric assay. Clotrimazole produced a dose- and time-dependent inhibition of cell proliferation. The growth inhibitory effect of clotrimazole could not be overcome by exogenous stimulation with epidermal growth factor. Both C6 and 9L glioma cells were implanted into the rat brain and after 5 days, the animals were treated with a daily single dose of clotrimazole for 8 consecutive days. Clotrimazole treatment caused a significant inhibition of intracranial tumor growth. The survival of rats with 9L gliomas was analyzed after 10 days of treatment with clotrimazole, cisplatin, or a combination of clotrimazole and cisplatin. Rats treated with either drug displayed a significantly prolonged survival time; however, the combination treatment resulted only in an additional survival benefit.

CONCLUSIONS

Clotrimazole effectively inhibits cell proliferation and tumor growth, and prolongs survival of rats with intracranial gliomas. Clotrimazole may be considered a potential anticancer drug for treatment of intracranial gliomas.

Clotrimazole decreases glycolysis and the viability of lung carcinoma and colon adenocarcinoma cells

Glycolysis is known to be the primary energy source in most cancer cells. We investigated here the effect of clotrimazole (1-(alpha-2-chlorotrityl)imidazole), the antifungal azole derivative, which was recently recognized as calmodulin antagonist, on the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis, and on ATP content and cell viability in LL/2 Lewis lung carcinoma cells and CT-26 colon adenocarcinoma cells. We found that clotrimazole induced a significant, dose- and time-dependent reduction in the levels of glucose 1,6-bisphosphate, fructose 1,6-bisphosphate, ATP, and cell viability. These findings suggest that clotrimazole causes a reduction in glycolysis and ATP levels, which eventually leads to cell destruction after 3 h of treatment. Since cell proliferation was also reported to be inhibited by calmodulin antagonists, this substance is most promising agent in treatment of cancer by inhibiting both cell proliferation and the glycolytic supply of ATP required for cancer cell growth.

Ca2+-induced changes in energy metabolism and viability of melanoma cells

Cancer cells are characterized by a high rate of glycolysis, which is their primary energy source. We show here that a rise in intracellular-free calcium ion (Ca2+), induced by Ca2+-ionophore A23187, exerted a deleterious effect on glycolysis and viability of B16 melanoma cells. Ca2+-ionophore caused a dose-dependent detachment of phosphofructokinase (EC 2.7.1.11), one of the key enzymes of glycolysis, from cytoskeleton. It also induced a decrease in the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis. All these changes occurred at lower concentrations of the drug than those required to induce a reduction in viability of melanoma cells. We also found that low concentrations of Ca2+-ionophore induced an increase in adenosine 5'-triphosphate (ATP), which most probably resulted from the increase in mitochondrial-bound hexokinase, which reflects a defence mechanism. This mechanism can no longer operate at high concentrations of the Ca2+-ionophore, which causes a decrease in mitochondrial and cytosolic hexokinase, leading to a drastic fall in ATP and melanoma cell death. The present results suggest that drugs which are capable of inducing accumulation of intracellular-free Ca2+ in melanoma cells would cause a reduction in energy-producing systems, leading to melanoma cell death.

Effects of Ca(2+)-ionophore A23187 and calmodulin antagonists on regulatory mechanisms of glycolysis and cell viability of NIH-3T3 fibroblasts

We studied here, in NIH-3T3 fibroblasts, the effect of the Ca(2+)-ionophore A23187 (which is known to increase intracellular-free Ca(2+)) on the control of glycolysis and cell viability and the action of calmodulin antagonists. Time-response studies with Ca(2+)-ionophore A23187 have revealed dual effects on the distribution of phosphofructokinase (PFK) (EC 2.7.1.11), the rate-limiting enzyme of glycolysis, between the cytoskeletal and cytosolic (soluble) fractions of the cell. A short incubation (maximal effect after 7 min) caused an increase in cytoskeleton-bound PFK with a corresponding decrease in soluble activity. This leads to an enhancement of cytoskeletal glycolysis. A longer incubation with Ca(2+)-ionophore caused a reduction in both cytoskeletal and cytosolic PFK and cell death. Both the "physiological" and "pathological" phases of the Ca(2+)-induced changes in the distribution of PFK were prevented by treatment with three structurally different calmodulin antagonists, thioridazine, an antipsychotic phenothiazine, clotrimazole, from the group of antifungal azole derivatives that were recently recognized as calmodulin antagonists, and CGS 9343B, a more selective inhibitor of calmodulin activity. The longer incubation with Ca(2+)-ionophore also induced a decrease in the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two allosteric stimulatory signal molecules of glycolysis. All these pathological changes preceded the reduction in cell viability, and a strong correlation was found between the fall in ATP and cell death. All three calmodulin antagonists prevented the pathological reduction in the levels of the allosteric effectors, ATP and cell viability. These experiments may throw light on the mechanisms underlying the therapeutic action of calmodulin antagonists that we previously found in treatment of the proliferating melanoma cells, on the one hand, and skin injuries, on the other hand.

Influence of adrenergic agonists on the release of amino acids from rat skeletal muscle studied by microdialysis

The microdialysis technique was used to study the effects of adrenergic agonists on the release of amino acids from rat skeletal muscle. The release was monitored indirectly by measurements of interstitial concentrations. To distinguish metabolic from vasoactive effects, the adrenaline and isoprenaline results were compared with those of vasopressin, alpha-agonists and adenosine. As determined by the microdialysis ethanol technique, adrenaline, alpha-agonists and vasopressin induced vasoconstriction, whereas isoprenaline and adenosine induced vasodilatation. The lactate-to-pyruvate ratio increased fourfold with adrenaline (P < 0.001) and by 54% with isoprenaline (P < 0.05), whereas no change was observed with alpha-agonists and adenosine. Vasopressin induced a fivefold increase in the lactate-to-pyruvate ratio (P < 0.001), but with an unchanged pyruvate concentration, indicating that the effect may have been secondary to ischaemia. Adrenaline induced a twofold and vasopressin a 34% increase in the concentration of alanine (P < 0.001), whereas isoprenaline, adenosine and alpha-agonists had no significant effect. Adrenaline-perfusion induced an initial anabolic effect as evidenced by a reduced concentration of tyrosine. A significant decrease in the glutamate-to-glutamine ratio was observed with adrenaline and isoprenaline (22 and 27%, P < 0.01) whereas alpha-agonists, vasopressin and adenosine were without effect. In conclusion, the present study showed that adrenaline, via a beta-adrenergically mediated activation of glycogenolysis, possibly further stimulated by ischaemia, induced an increased release of alanine from skeletal muscle. The study indicates a beta-adrenergic stimulation on the glutamine synthetase step and a short lasting anabolic effect of adrenaline. Differences in the magnitude of the effects of adrenaline and isoprenaline could be related to their different vasoactive properties.

Clotrimazole and bifonazole detach hexokinase from mitochondria of melanoma cells

Cancer cells are characterized by a high rate of glycolysis. Hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1), the only glycolytic enzyme which binds to mitochondria, is exceptionally high in cancer cells, and believed to play a key role in regulating cell energy metabolism and cancer cell growth rate. We have previously found that clotrimazole (1-(alpha-2-chlorotrityl)imidazole) and bifonazole (1-(alpha-biphenyl-4-ylbenzyl)imidazole), the antifungal azole derivatives, which were recently recognized as calmodulin antagonists, are calmodulin antagonists which most effectively reduce glycolysis and ATP level in B16 melanoma cells. They act through allosteric regulation and detachment of glycolytic enzymes from cytoskeleton. Here we report of a novel, additional, mechanism of action of these drugs. We show that they induce a dose-dependent detachment of hexokinase from mitochondria of B16 melanoma cells. This effect preceded the decrease in cell viability. These results suggest that clotrimazole and bifonazole may be promising drugs in treatment of melanoma.

Calmodulin antagonists decrease glucose 1,6-bisphosphate, fructose 1,6-bisphosphate, ATP and viability of melanoma cells

Glycolysis is known to be the primary energy source in cancer cells. We investigated here the effect of four different calmodulin antagonists: thioridazine (10-[2-(1-methyl-2-piperidyl) ethyl]-2-methylthiophenothiazine), CGS 9343B (1,3-dihydro-1-[1-[(4-methyl-4H,6H-pyrrolo[1,2-a] [4,1]-benzoxazepin-4-yl)methyl]-4-piperidinyl]-2 H-benzimidazol-2-one (1:1) maleate), clotrimazole (1-(alpha-2-chlorotrityl)imidazole) and bifonazole (1-(alpha-biphenyl-4-ylbenzyl)imidazole), on the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis, and on ATP content and cell viability in B16 melanoma cells. We found that all four substances significantly reduced the levels of glucose 1,6-bisphosphate, fructose 1,6-bisphosphate and ATP, in a dose- and time-dependent manner. Cell viability was reduced in a close correlation with the fall in ATP. The decrease in glucose 1,6-bisphosphate and fructose 1,6-bisphosphate did not result from the cytotoxic effects of the calmodulin antagonists, since their content was already reduced before any cytotoxic effect was observed. These findings suggest that the fall in the levels of the two signal molecules of glycolysis, induced by the calmodulin antagonists, causes a reduction in glycolysis and ATP levels, which eventually leads to cell death. Since cell proliferation was also reported to be inhibited by calmodulin antagonists, these substances are most promising agents in treatment of cancer by inhibiting both cell proliferation and the glycolytic supply of ATP required for cell growth.

Effects of low-frequency stimulation on soluble and structure-bound activities of hexokinase and phosphofructokinase in rat fast-twitch muscle

Several glycolytic enzymes exist in muscle as free and structure-bound forms. A fraction of hexokinase (HK) is associated with the outer mitochondrial membrane. Phosphofructokinase (PFK) and aldolase (ALD) bind to F-actin, and AMP deaminase (AMPase) interacts with myosin. Using low-frequency stimulation (10 Hz, 24 h/d), we studied in rat fast-twitch muscle effects of contractile activity on soluble and structure-bound forms of these enzymes. Phosphoglucose isomerase (PGI), a soluble enzyme, was also examined. Fractional extraction was applied to study the intracellular distribution of soluble and bound enzyme activities 5 min, 1 h, 3 h, 1 d, and 7 d after the onset of stimulation. Confirming previous findings, total HK activity increased 7-fold in 7-d-stimulated muscles, whereas PFK, ALD, and PGI were reduced, ranging between 55% and 80% of their normal activities. AMPase activity was unaltered. At the time points studied, no changes were found in the extraction behavior of PGI and AMPase. The fraction of bound ALD increased slightly (12%). However, the distribution of HK and PFK was markedly altered. Bound PFK increased from 50% in the control to 85% in 7-d-stimulated muscles. Bound HK rose from 52% to 83% during the same time period. The increase in PFK binding was steep and occurred mainly within the first minutes and hours. The increase in HK binding occurred with some delay, but was significant in muscles stimulated for more than 1 h. In view of the altered kinetic properties of F-actin-bound PFK (alleviated allosteric inhibition by ATP) and bound HK (elevated catalytic activity), these changes are interpreted as early responses to match the metabolic demands during maximal contractile activity imposed on a muscle not programmed for sustained activity: Enhanced binding of PFK serves to accelerate glycolytic flux immediately after the onset of stimulation, whereas mitochondrial binding of HK facilitates the phosphorylation of exogenous glucose when glycogen stores have been depleted.

Rapid stimulatory effect of insulin on binding of glycolytic enzymes to cytoskeleton of C-6 glial cells, and the antagonistic action of calmodulin inhibitors

Insulin was shown in our previous experiments to induce an increase in binding of glycolytic enzymes to muscle cytoskeleton. We show here the same stimulatory effect of insulin in C-6 glial cells in culture. In these cells, like in muscle, a short time of incubation with insulin (1-10 min) induced an increase in cytoskeleton bound phosphofructokinase and aldolase. This stimulatory effect of insulin could be prevented by treatment with calmodulin antagonists trifluoperazine, thioridazine or CGS 9343 B (a potent and selective inhibitor of calmodulin activity), which strongly suggests that calmodulin is involved in this action of insulin. Our previous experiments have shown that growth factors and Ca(2+) also induce a rapid, calmodulin-mediated stimulation of binding of glycolytic enzymes to cytoskeleton. The present and previous results suggest that the rapid binding of glycolytic enzymes to cytoskeleton, may be a general mechanism, in different cells, in signal transduction of insulin, growth factors and other Ca(2+) -mobilizing hormones. The accelerated cytoskeletal glycolysis will supply local ATP, which is required for the rapid cytoskeletal-membrane rearrangements following the binding of hormone to its receptor.

Uncoupling of mitochondrial oxidative phosphorylation abolishes the stimulatory action of insulin on the binding of glycolytic enzymes to muscle cytoskeleton

1. We show here that treatment of diaphragm muscle with 2,4-dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, abolished the stimulatory action of insulin on binding of the glycolytic enzymes, phosphofructokinase (PFK) and aldolase, to muscle cytoskeleton. This effect was demonstrated with low concentration of DNP, which caused only a small decrease in ATP and did not affect the basic levels of cytoskeleton-bound glycolytic enzymes. 2. Higher concentrations of DNP, which induced a drastic decline in ATP content, caused a decrease in cytoskeleton-bound glycolytic enzymes and damage to myofibrils. 3. These results suggest that mitochondrial ATP is required for both the preservation of the basal levels of cytoskeleton-bound glycolytic enzymes and cell structure, as well as for the expression of the stimulatory action of insulin on glycolytic enzymes' binding to muscle cytoskeleton.