Purpose: The aim of the study was to investigate the intracellular location of [methyl-(3)H]choline in MCF7 tumour cells and to determine the relationship between [methyl-(3)H]choline incorporation and proliferation.
Methods: Tumour cells were incubated with [methyl-(3)H]choline for 10 min, and then in cold medium to simulate the rapid blood clearance of [methyl-(11)C]choline. Labelled metabolites were then extracted from cells by treating them with organic and aqueous solvents to determine the distribution of tracer between phospholipid and water-soluble metabolite pools. Aqueous extracts were subjected to thin-layer chromatography, ion exchange chromatography and a choline extraction procedure to identify (3)H-containing metabolites. Procedures were carried out on fast- and slow-growing populations of MCF7 cells to determine the relationship between choline incorporation and proliferation.
Results: Only about 5% of [methyl-(3)H]choline was present as phospholipid. [methyl-(3)H]choline incorporation was found to be related to S-phase fraction. In another experiment, [methyl-(14)C]choline incorporation was found to be correlated with [methyl-(3)H]thymidine incorporation. The V(max) of choline uptake was found to be increased whilst K(m) was decreased in populations of MCF7 cells with higher proliferative fractions, compared with populations having lower proliferative fractions.
Conclusion: Choline incorporation into tumour cells under conditions that simulate rapid blood clearance of [methyl-(11)C]choline is correlated with proliferation. Most of the activity (about 95%) was in the non-lipid fraction of the cell.