THE ACCUMULATION OF MERCAPTOPURINE METABOLITES IN AGE FRACTIONATED RED-BLOOD-CELLS

1 Red blood cells from four children with lymphoblastic leukaemia were age fractionated on Percoll density gradients into 'young', 'middle-a ged' and 'old' cells. 2 The rates of accumulation of the mercaptopurin e (MP) metabolites thioguanine nucleotides (TGNs) and methylmercaptopu rine nucleotides (MeMPs) were measured in the cell fractions from the start of MP continuing chemotherapy. 3 TGNs and MeMP metabolites were present in all the red cell fractions after 3 days oral MP. There was no significant difference between the metabolite concentrations measur ed in either young, middle-aged or old cells (Mann-Whitney P = 1.0 to 0.12). 4 These observations suggest that MP metabolites do not enter r ed cells at the stem cell level at the start of therapy. 5 With respec t to the monitoring of therapy, these results suggest that the concent ration of TGNs after 7 to 10 days MP could be used to predict eventual steady-state concentrations using a simple model.