Metabolism of 3'-deoxy-3'-[F-18]fluorothymidine in proliferating A549 cells: validations for positron emission tomography.
3'-Deoxy-3'-[F-18]fluorothymidine (FLT) is under clinical evaluation as a metabolic probe for imaging cell proliferation in vivo using positron emission tomography (PET). As part of our validation effort, we followed the short-term metabolism of FLT in exponentially growing tumor cells to demonstrate the enzyme activities within the DNA salvage pathway that influence retention of radioactivity. In A549 cells, thymidine kinase-1 (TK1) activity produced FLTMP, which dominated the labeled nucleotide pool. Subsequent nucleotide phosphorylations by thymidylate kinase (TMPK) and nucleotide diphosphate kinase (NDPK) led to FLTTP. After 1h, the cellular metabolic pool contained approximately 30% FLTTP. A putative deoxynucleotidase (dNT), which degrades FLTMP to FLT, provided the primary mechanism for tracer efflux from cells. In contrast, FLTTP was resistant to degradation and highly retained. The uptake and retention characteristics of FLT were also compared to those of thymidine, FMAU (2'-arabino-fluoro-TdR) and FIAU (2'-arabino-fluoro-5-iodo-2'-dexoyuridine). Despite the fact that FLT lacks the 3'-hydroxy necessary for its incorporation into DNA it out performed both FMAU and FIAU in terms of uptake and retention.
Department of Radiology, University of Washington, Seattle, WA 98195-6004, USA. grierson@u.washington.edu
John R
JR
Grierson
Jeffery L
JL
Schwartz
Mark
M
Muzi
Robert
R
Jordan
Kenneth A
KA
Krohn
D000230:Adenocarcinoma / Q000000981:diagnostic imaging* / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015224:Dideoxynucleosides / Q000493:pharmacokinetics*; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D008657:Metabolic Clearance Rate; D009367:Neoplasm Staging / Q000379:methods; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics
D015224:Dideoxynucleosides; D019275:Radiopharmaceuticals; C002854:alovudine