F. Al-Saeedi, A. E. Welch, T. A. D. Smith



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European Journal of Nuclear Medicine and Molecular Imaging

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Purpose: The aim of the study was to investigate the intracellular location of [methyl-H-3]choline in MCF7 tumour cells and to determine the relationship between [methyl-H-3]choline incorporation and proliferation. Methods: Tumour cells were incubated with [methyl-H-3]choline for 10 min, and then in cold medium to simulate the rapid blood clearance of [methyl-(11)pC]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 H-3-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-H-3]choline was present as phospholipid. [methyl-H-3]choline incorporation was found to be related to S-phase fraction. In another experiment, [methyl-C-14]choline incorporation was found to be correlated with [methyl-H-3]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-C-11]choline is correlated with proliferation. Most of the activity (about 95%) was in the non-lipid fraction of the cell.