title: Metabolic stability of 6,7-dialkoxy-4-(2-, 3- and 4-[18F]fluoroanilino)quinazolines, potential EGFR imaging probes.
abstract: Epidermal growth factor receptors (EGFR), upregulated in many tumor types, have been a target for therapeutic development and molecular imaging. The objective of this study was to evaluate the distribution and metabolic characteristics of fluorine-18 labeled anilinoquinazolines as potential imaging agents for EGFR tyrosine kinase expression. Fluorine-18 labeled fluoronitrobenzenes were prepared by reaction of potassium cryptand [(18)F]fluoride with 1,2- and 1,4-dinitrobenzenes, and 3-nitro-N,N,N-trimethylanilinium triflate in 5min. Decay-corrected radiochemical yields of [(18)F]fluoride incorporation into the nitro-aromatic compounds were 81±2%, 44±4% and 77±5% (n=3-5) for the 2-, 3- and 4-fluoro isomers, respectively. Sodium borohydride reduction to the corresponding [(18)F]fluoroanilines was achieved with greater than 80% conversion in 5min. Coupling of [(18)F]fluoroaniline-hydrochlorides to 6,7-dimethoxy-4-chloro-quinazoline gave the corresponding 6,7-dimethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 31±5%, 17±2% and 55±2% radiochemical yield, respectively, while coupling to the 6,7-diethoxy-4-chloro-quinazoline produced 6,7-diethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 19±6%, 9±3% and 36±6% radiochemical yield, respectively, in 90min to end of synthesis from [(18)F]fluoride. Biodistribution of 2- and 4-[(18)F]fluoroanilinoquinazolines was conducted in tumor-bearing mice (MDA-MB-435 and MDA-MB-468 xenografts). Low tumor uptake (<1% injected dose per gram (ID/g) of tissue up to 3h postinjection of the radiotracers) was observed. High bone uptake (5-15% ID/g) was noted with the 4-[(18)F]fluoroanilinoquinazolines. The metabolic stabilities of radiolabeled quinazolines were further evaluated by incubation with human female cryopreserved isolated hepatocytes. Rapid degeneration of the 4-fluoro-substituted compounds to baseline polar metabolites was observed by radio-TLC, whereas, the 2- and 3-[(18)F]fluoroaniline derivatives were significantly more stable, up to 2h, corroborating the in vivo biodistribution studies. para-Substituted [(18)F]fluoroanilines, a common structural motif in radiopharmaceuticals, are highly susceptible to metabolic degradation.
authors.affiliation: Department of Radiotracer Development and Imaging Technology, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Neil
authors.initials: N
authors.lastname: Vasdev
authors.forename: Peter N
authors.initials: PN
authors.lastname: Dorff
authors.forename: James P
authors.initials: JP
authors.lastname: O'Neil
authors.forename: Frederick T
authors.initials: FT
authors.lastname: Chin
authors.forename: Stephen
authors.initials: S
authors.lastname: Hanrahan
authors.forename: Henry F
authors.initials: HF
authors.lastname: VanBrocklin
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000032:analysis*; D005260:Female; D005462:Fluorine Radioisotopes / Q000737:chemistry; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D051379:Mice; D011799:Quinazolines / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D005462:Fluorine Radioisotopes; D011799:Quinazolines; D019275:Radiopharmaceuticals; D066246:ErbB Receptors