LM Rodrigues, S Uribe-Lewis, B Madhu, DJ Honess, M Stubbs, JR Griffiths
BACKGROUND: Ketone bodies have both metabolic and epigenetic roles in cancer. In several studies, they showed an anti-cancer effect via inhibition of histone deacetylases; however, other studies observed faster tumour growth. The related molecule butyrate also inhibits growth of some cancer cells and accelerates it in others. This "butyrate paradox" is thought to be due to butyrate mediating histone acetylation and thus inhibiting cell proliferation in cancers that preferentially utilise glucose (the Warburg effect); whereas in cells that oxidise butyrate as a fuel, it fails to reach inhibitory concentrations and can stimulate growth. METHODS: We treated transgenic mice bearing spontaneous MMTV-NEU-NT mammary tumours with the ketone body β-hydroxybutyrate (β-OHB) and monitored tumour growth, metabolite concentrations and histone acetylation. In a cell line derived from these tumours, we also measured uptake of β-OHB and glucose, and lactate production, in the absence and presence of β-OHB. RESULTS: β-OHB administration accelerated growth of MMTV-NEU-NT tumours, and their metabolic profile showed significant increases in ATP, glutamine, serine and choline-related metabolites. The β-OHB concentration within the treated tumours, 0.46 ± 0.05 μmol/g, had no effect on histone acetylation as shown by western blots. Cultured tumour cells incubated with 0.5 mM β-OHB showed β-OHB uptake that would be equivalent to 54% of glycolytic ATP phosphorylation and no significant change in glucose consumption or lactate production. CONCLUSIONS: These results suggest that a β-OHB paradox may occur in these mammary tumours in a manner analogous to the butyrate paradox. At low β-OHB concentrations (<1 mM, as observed in our tumour model post-treatment), and in the absence of a Warburg effect, β-OHB is consumed and thus acts as an oxidative energy source and not as an epigenetic factor. This would explain the increase in tumour growth after treatment, the metabolic profiles and the absence of an effect on histone H3 acetylation.