Dichloroacetate is an effective treatment for sarcoma models in vitro and in vivo

Background

Sarcomas are cancers that arise from tissues of mesenchymal origin and there has been limited improvement in treatments over the last 30 years. The Warburg effect is a widespread metabolic phenotype of cancer, where glycolysis is favoured despite the presence of oxygen. Dichloroacetate (DCA) is a pyruvate dehydrogenase kinase (PDK) inhibitor in clinical use that can reverse the Warburg effect, inhibiting growth and enhancing apoptosis in a range of cancers. We have investigated its effectiveness against sarcoma cells in vitro and in vivo.

Materials and methods

Three cell lines (mouse fibrosarcoma S180, mouse osteosarcoma K7M2 and human fibrosarcoma HT1080-luc2) were examined for cell viability after DCA treatment in vitro (neutral red uptake assay), alone and in combination with doxorubicin. In vivo, K7M2 cells were injected s.c. into Rag1^-/- mice (2 sites per mouse, 7-9 mice per group) and established tumours were treated with DCA in the drinking water (0, 0.5, 1.0 and 1.5 g/L, delivering 0, 70, 125 and 165 mg/kg/day, respectively). Tumour growth was monitored with callipers. Plasma was collected on d1 and d15 for measurement of DCA levels (LC-MS).

Results

DCA significantly reduced the total viable cell number after 48 h of treatment in the mouse sarcoma lines (~15% at 0.5 mM DCA, and 30-40% at 5 mM DCA), however HT1080-luc2 cells showed only a 10% reduction in cell number with 5 mM DCA. There was no morphological indication of apoptosis, suggesting DCA was decreasing proliferation. Chronic treatment of the mouse cells (5 mM DCA for 2 weeks) resulted in significantly slower growth rates as measured over 48 h (7 and 13% total cell number compared to untreated S180 and K7M2 cells, respectively). DCA did not synergise with doxorubicin but was additive at lower concentrations of doxorubicin. In vivo, 1.0 and 1.5 g/L DCA significantly reduced tumour growth (33.0 and 33.1% reduction in tumour size on d13, p=0.001 and 0.01 respectively). Plasma DCA was undetectable on d1 of treatment, but by d15, 1.0 and 1.5 g/L DCA delivered 2-44 uM. Tumour DCA concentrations were also measured and found to be in the range of 25-470 uM, much lower than those typically used in in vitro studies.

Conclusions

DCA was effective against an in vivo sarcoma model, with tumour DCA concentrations in the micromolar range. These concentrations are achievable clinically, thus DCA warrants further investigation for sarcoma treatment.