Expression and activity of G6PD in MCF-7 MCLs, spheroids and xenografted tumours. Relative expressions of G6PD in the formation of MCF-7 MCLs (A) and spheroids (C) along with culture time, or in the growth of MCF-7 xenografted tumours (E) along with tumour volume were assayed by qPCR. Gene expression was normalized to the housekeeping gene β-actin. The enzyme activities of G6PD in the formation of MCF-7 MCLs (B) and spheroids (D) along with culture time, or in the growth of MCF-7 xenografted tumours (F) along with tumour volume were assayed by a Glucose-6-Phosphate Dehydrogenase Activity Assay Kit according to the manufacturer's instructions. The results are presented as the mean ± S.E. *p < 0.05, **p < 0.01, ***p < 0.001 vs the 3-day group or small volume group.