Detection of DNA synthesis in intact organisms with positron-emitting (methyl- 11 C)thymidine.

(11)CO(2) produced in the Brookhaven 152-cm cyclotron was converted to formaldehyde, which in turn was used for the enzymatic conversion of deoxyuridine-5'-phosphate to [(11)C]thymidylate. Enzymatic treatment of the nucleotide with alkaline phosphatase gave [(11)C]thymidine.The preparation of [(11)C]thymidine from cyclotron-generated (11)CO(2) required 110 min (about 5 half-lives): 35 min for the synthesis of H(11)CHO, 25 min for the enzymatic conversion to [(11)C]thymidylate, 20 min for column chromatography, 5 min for phosphatase treatment, 10 min for evaporation, 2 min for filtration through an anion-exchange resin, and 13 min for miscellaneous manipulations.Positron-emitting [(11)C]thymidine and [(11)C]thymidylate were used for in vivo tracer studies of DNA synthesis in mice for periods of up to 3 hr. Findings with carbon-11 were consistent with earlier studies in which carbon-14 and tritium-labeled thymidine were used. For example, 3 hr after injection of [(11)C]thymidine, spleen DNA was labeled to a much greater extent than was liver DNA.