Typical intracellular metabolite levels associated with PPP in MCF-7 MCLs (A), MCF-7 spheroids (B) and MCF-7 xenografted tumours (C) along with culture time. Metabolites were determined and identified by GC-MS and LC-Q/TOF-MS. For relative comparison, the peak areas were integrated and further weighted by internal standard and protein concentration, which were presented as intensity. The results are presented as the mean ± S.E. *p < 0.05, **p < 0.01, ***p < 0.001 vs the 3-day group.