Although melatonin oncostatic and cytotoxic effects have been described in
different types of cancer cells, the specific mechanisms leading to its antitumoral effects
and their metabolic context specificity are still not completely understood. Here, we
evaluated the effects of melatonin in P19 embryonal carcinoma stem cells (CSCs) and
in their differentiated counterparts, cultured in either high glucose medium or in a
galactose (glucose-free) medium which leads to glycolytic suppression and increased
mitochondrial metabolism. We found that highly glycolytic P19 CSCs were less
susceptible to melatonin antitumoral effects while cell populations relying on oxidative
metabolism for ATP production were more affected. The observed antiproliferative
action of melatonin was associated with an arrest at S-phase, decreased oxygen
consumption, down-regulation of BCL-2 expression and an increase in oxidative
stress culminating with caspase-3-independent cell death. Interestingly, the combined
treatment of melatonin and dichloroacetate had a synergistic effect in cells grown in
the galactose medium and resulted in an inhibitory effect in the highly resistant P19
CSCs. Melatonin appears to exert its antiproliferative activity in P19 carcinoma cells
through a mitochondrially-mediated action which in turn allows the amplification of
the effects of dichloroacetate, even in cells with a more glycolytic phenotype.
Although melatonin oncostatic and cytotoxic effects have been described indifferent types of cancer cells, the specific mechanisms leading to its antitumoral effectsand their metabolic context specificity are still not completely understood. Here, weevaluated the effects of melatonin in P19 embryonal carcinoma stem cells (CSCs) andin their differentiated counterparts, cultured in either high glucose medium or in agalactose (glucose-free) medium which leads to glycolytic suppression and increasedmitochondrial metabolism. We found that highly glycolytic P19 CSCs were lesssusceptible to melatonin antitumoral effects while cell populations relying on oxidativemetabolism for ATP production were more affected. The observed antiproliferativeaction of melatonin was associated with an arrest at S-phase, decreased oxygenconsumption, down-regulation of BCL-2 expression and an increase in oxidativestress culminating with caspase-3-independent cell death. Interestingly, the combinedtreatment of melatonin and dichloroacetate had a synergistic effect in cells grown inthe galactose medium and resulted in an inhibitory effect in the highly resistant P19CSCs. Melatonin appears to exert its antiproliferative activity in P19 carcinoma cellsthrough a mitochondrially-mediated action which in turn allows the amplification ofthe effects of dichloroacetate, even in cells with a more glycolytic phenotype.
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