title: N(3)-Substituted thymidine analogues V: synthesis and preliminary PET imaging of N(3)-[(18)F]fluoroethyl thymidine and N(3)-[(18)F]fluoropropyl thymidine.
abstract: BACKGROUND
  [(18)F]-Labeled analogues of thymidine have demonstrated efficacy for PET imaging of cellular proliferation. We have synthesized two [(18)F]-labeled N(3)-substituted thymidine analogues, N(3)-[(18)F]fluoroethyl thymidine (N(3)-[(18)F]-FET) and N(3)-[(18)F]fluoropropyl thymidine (N(3)-[(18)F]-FPrT), and performed preliminary PET imaging studies in tumor-bearing mice.
  
  
  METHODS
  Thymidine was converted to its 3',5'-O-bis-tetrahydropyranyl ether, which was then converted to the N(3)-ethyl and propyl-substituted mesylate precursors. Reactions of these mesylate precursors with n-Bu(4)N[(18)F] or K[(18)F]/kryptofix followed by acid hydrolysis and HPLC purification yielded N(3)-[(18)F]-FET and N(3)-[(18)F]-FPrT, respectively. Subcutaneous (sc) xenografts of H441 human non-small cell lung cancer were established in two groups of mice (each n=6). Micro-PET images of the tumor-bearing animals were acquired after intravenous injection of N(3)-[(18)F]-FET or N(3)-[(18)F]-FPrT (3700 KBq/animal).
  
  
  RESULTS
  The radiochemical yields were 2-12% (d.c.) for N(3)-[(18)F]-FET and 30-38% (d.c.) for N(3)-[(18)F]-FPrT. Radiochemical purity was >99% and calculated specific activity was >74 GBq/mumol at the end of synthesis. The accumulation of N(3)-[(18)F]-FET and N(3)-[(18)F]-FPrT in the tumor tissue at 2 h postinjection was 1.81+/-0.78 and 2.95+/-1.14 percent injected dose per gram (%ID/g), respectively; tumor/muscle ratios were 5.57+/-0.82 and 7.69+/-2.18, respectively; the unidirectional influx rates (K(i)) were 0.013 and 0.018 ml/g per minute, respectively.
  
  
  CONCLUSIONS
  Two novel [(18)F]- N(3)-substituted thymidine analogues have been synthesized in good yields, high purity and high specific activity. Preliminary in vivo studies demonstrated the efficacy of these [(18)F]- N(3)-substituted thymidine analogues for PET imaging of tumors.
authors.affiliation: Department of Experimental Diagnostic Imaging, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Uday
authors.initials: U
authors.lastname: Mukhopadhyay
authors.forename: Suren
authors.initials: S
authors.lastname: Soghomonyan
authors.forename: Hsin Hsien
authors.initials: HH
authors.lastname: Yeh
authors.forename: Leo G
authors.initials: LG
authors.lastname: Flores
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Shavrin
authors.forename: Andrei Y
authors.initials: AY
authors.lastname: Volgin
authors.forename: Juri G
authors.initials: JG
authors.lastname: Gelovani
authors.forename: Mian M
authors.initials: MM
authors.lastname: Alauddin
mesh_terms: D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009928:Organ Specificity; D010865:Pilot Projects; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D013936:Thymidine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
chemical_list: C532426:N(3)-fluoropropylthymidine; C117289:O-(2-fluoroethyl)tyrosine; D019275:Radiopharmaceuticals; D014443:Tyrosine; D013936:Thymidine