title: Biochemistry and biology of 2'-Fluoro-2'-deoxythymidine (FT), a putative highly selective substrate for thymidine kinase type 2 (TK2).
abstract: 2'-Deoxy-2'-fluorothymidine (FT) is a bioisostere of both thymidine (TdR), in which F replaces H at C-2' in the ribosyl configuration, and methyluridine, in which F replaces OH at C-2' in the ribosyl configuration. Fluorine is bioisosteric with H with respect to atomic radius and is bioisosteric with OH with respect to polarity and H-bonding as an H acceptor. The consequences of this C-2' F for H substitution on cytotoxicity, nucleoside transporter affinity, phosphorylation by thymidine kinases (TK1, TK2), cell uptake and biodistribution of FT in a murine tumor model are now reported. FT toxicity against a bank of murine and human cells was seen only at very high (˜1 mM) concentrations, although the cellular uptake of [3H]FT in these cells was comparable to that of [3H]TdR over a 24 h period. Human equilibrative nucleoside transporters (hENT1, hENT2) displayed weaker affinity for FT than for TdR, but the concentrative transporters (hCNT1, hCNT2, hCNT3) had much higher affinities for FT. FT was phosphorylated by both mitochondrial thymidine kinase (TK2) (58 % of TdR) and cytosolic thymidine kinase (TK1) (39 % of TdR). Preliminary in vivo imaging with [18F]FT in mice bearing implanted KBALB and contralateral KBALB-STK tumors showed highly selective uptake, with a tumor:blood ratio of 33 in a small herpes simplex type 1 (HSV-1 TK) expressing tumor. In conclusion, [18F]FT appears to be a strong candidate for PET imaging of viral TK transgene imaging, based on its TK1:TK2 phosphorylation differential, its selective uptake by an HSV-TK expressing murine tumor model, its interaction with nucleoside transporters and its low toxicity.
authors.affiliation: Division of Oncological Imaging, Edmonton. leonard.wiebe@ualberta.ca
authors.forename: Leonard I
authors.initials: LI
authors.lastname: Wiebe
authors.forename: William
authors.initials: W
authors.lastname: Sun
authors.forename: Aihua
authors.initials: A
authors.lastname: Zhou
authors.forename: Jennifer
authors.initials: J
authors.lastname: Yang
authors.forename: Elena V
authors.initials: EV
authors.lastname: Sjuvarsson
authors.forename: Staffan
authors.initials: S
authors.lastname: Eriksson
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Paproski
authors.forename: Carol E
authors.initials: CE
authors.lastname: Cass
authors.forename: Piyush
authors.initials: P
authors.lastname: Kumar
authors.forename: Edward E
authors.initials: EE
authors.lastname: Knaus
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001345:Autoradiography; D001859:Bone Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D020128:Inhibitory Concentration 50; D026901:Membrane Transport Proteins / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D012516:Osteosarcoma / Q000188:drug therapy* / Q000378:metabolism; D010766:Phosphorylation; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D013936:Thymidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013937:Thymidine Kinase; D019076:Transgenes
chemical_list: D000970:Antineoplastic Agents; D026901:Membrane Transport Proteins; D019275:Radiopharmaceuticals; C065171:cif nucleoside transporter; C068636:2'-fluorothymidine; C105339:thymidine kinase 2; D013937:Thymidine Kinase; D013936:Thymidine