The utilisation of glutamine and glucose by a 3-D tumour model trapped in quiescence

Solid tumours modify their metabolic strategy to ensure sufficient biomass and energy to maintain a high rate of proliferation. However, solid tumours are characterised by a high proportion of quiescent cells and little is known about their metabolic profile. A tumour spheroid model with DLD1 cells was used to investigate the influence of a quiescent state on the cellular utilisation of glucose and glutamine. Quiescent DLD1 spheroids displayed increased depletion of both nutrients from the bathing medium compared to their proliferative counterparts and displayed highly active overall metabolism. A combination of biochemical and metabolomics approaches demonstrated that glucose utilisation resulted in an increased production of the 3-carbon intermediates lactate and alanine in quiescent spheroids. In addition, glutamine metabolism was directed to anabolic pathways; including the "reverse TCA cycle" to produce citrate for fatty-acid synthesis. These adaptations in DLD1 spheroids may propose a metabolic altruism of quiescent regions in solid tumours to provide biosynthetic intermediates required to sustain tumour growth, angiogenesis and metastasis.