PDK4 Inhibition Ameliorates Melatonin Therapy by Modulating Cerebral Metabolism and Remyelination in an EAE Demyelinating Mouse Model of Multiple Sclerosis

We recently showed that melatonin ameliorates the severity of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. However, efficiency of melatonin therapy was associated with side effects, manifested by slowing down of remyelination, through increasing the inhibitory effects of brain pyruvate dehydrogenase kinase-4 (PDK-4) on pyruvate dehydrogenase complex (PDC), a key enzyme in fatty acid (FA) synthesis during remyelination. In this study, we investigated the metabolic profile of FA synthesis using combination therapy of melatonin and diisopropylamine dichloroacetate (DADA), a PDK4 inhibitor, in EAE mice. Disease progression was monitored by recording the disability scores. Immunological, oligodendrogenesis and metabolic factors were also evaluated. Results showed that combination therapy of melatonin and DADA significantly reduced EAE disability scores, compared to melatonin, whereas DADA alone did not have any effect. In addition, co-therapy inhibited pro-inflammatory while increasing anti-inflammatory cytokines, significantly better than melatonin alone. Moreover, administration of combination drugs recovered the declined expression of oligodendrocytic markers in EAE, more potently than melatonin. Furthermore, co-therapy affected cerebral energy metabolism by significantly reducing lactate levels while increasing N-acetylaspartate (NAA) and 3-hydroxy-3-methyl-glutaryl-coenzyme-A reductase (HMGCR) levels. Finally, while melatonin increased lactate and PDK4 expression levels and greatly reduced PDC activity, co-therapy significantly restored PDC function while reducing the lactate levels. In summary, administration of melatonin with DADA increased the efficiency of melatonin treatment by eliminating the inhibitory effects of PDK4 on PDC’s function, a critical step for proper FA synthesis during remyelination.

Superior anti-tumor efficacy of diisopropylamine dichloroacetate compared with dichloroacetate in a subcutaneous transplantation breast tumor model

Dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase, has anti-tumor properties in various carcinoma models. Diisopropylamine dichloroacetate (DADA), an over-the-counter drug for chronic liver disease, is a derivative of DCA. To date, few studies have evaluated the anticancer potential of DADA in breast cancer. In this study, MDA-MB-231 cells, a breast adenocarcinoma cell line, were used in in vitro and in vivo experiments to evaluate the anti-tumor efficacy of DADA and DCA. The half maximal inhibitory concentration (IC50) of DADA (7.1 ± 1.1 mmol/L) against MDA-MB-231 cells was significantly lower than that of DCA (15.6 ± 2.0 mmol/L); 100 mg/kg (0.0004 mol/kg) DADA was better than 100 mg/kg (0.0008 mol/kg) DCA at suppressing the growth of subcutaneous transplantation breast tumor at the same dose after 24 days intervention. Histological examination showed that both DCA and DADA interventions led to necrosis, inflammation, and fibrosis of tumor tissue in a mouse subcutaneous transplantation breast tumor model. DADA treatment inhibited Ki67 expression in tumor tissue. In vitro experiments showed that DADA could inhibit lactic acid production and glucose uptake in MDA-MB-231 cells at 10 mmol/L and these effects were stronger than DCA. DADA administration also induced complete autophagy during early treatment stages and incomplete autophagy and cell death at later treatment stages. In conclusion, DADA showed better anti-tumor efficacy than DCA in a breast cancer model.

Diisopropylamine dichloroacetate enhances radiosensitization in esophageal squamous cell carcinoma by increasing mitochondria-derived reactive oxygen species levels

Radiotherapy is generally applied in the treatment of esophageal squamous cell carcinoma (ESCC). However, the radioresistance of ESCC still remains an obstacle for the curative effect of this treatment. We hypothesized that diisopropylamine dichloroacetate (DADA), an inhibitor of pyruvate dehydrogenase kinase (PDK), might enhance radiosensitizationin resistant ESCC. The clonogenic survival assay revealed that DADA sensitized ESCC cells to radiotherapy in vitro; furthermore, the combination of DADA and radiotherapy increased the expression of γ-H2AX, which is a hallmark of DNA double-strand breaks. Arrest at G2/M phase as well as the induction of apoptosis of ESCC cells were also observed in the cells treated with the combination of DADA and radiotherapy. Notably, xenograft tumor growth was significantly suppressed in vivo by combined radiotherapy and DADA administration. It has been proven that glycolysis is highly correlated with radioresistance, which could be reversed by the shift from glycolysis to mitochondrial oxidation. In our present study, we found that DADA could modulate oxidative phosphorylation as well as increase the intracellular levels of reactive oxygen species (ROS). Collectively, we concluded that DADA-induced intracellular ROS accumulation was identified as the key factor of radiotherapy sensitization of ESCC.