ABSTRACT
Translation of carbon-11 labeled PET tracers to clinical settings is currently impeded by the technical difficulties associated with [11C]CO2 conversion into the highly reactive methylating agents [11C]CH3I and [11C]CH3OTf using automated modules relying on stationary valves. Here we describe development of the first in its kind "[11C]kit" for production of carbon-11 radiotracer using disposable manifolds. This method proved to be very reliable and allows for consecutive production of PET tracers with minimal intervals between the syntheses.
Subject(s)
Carbon Radioisotopes/isolation & purification , Isotope Labeling/methods , Positron-Emission Tomography/methods , Radiopharmaceuticals/isolation & purification , Automation/instrumentation , Automation/methods , Carbon Radioisotopes/chemistry , Equipment Design , Equipment Reuse , Humans , Isotope Labeling/instrumentation , Radiopharmaceuticals/chemical synthesis , Radiopharmaceuticals/chemistryABSTRACT
N-Succinimidyl 3-(di-tert-butyl[(18)F]fluorosilyl)benzoate ([(18)F]SiFB), a novel synthon for one-step labeling of proteins, was synthesized via a simple (18)F-(19)F isotopic exchange. A new labeling technique that circumvents the cleavage of the highly reactive active ester moiety under regular basic (18)F-labeling conditions was established. In order to synthesize high radioactivity amounts of [(18)F]SiFB, it was crucial to partially neutralize the potassium oxalate/hydroxide that was used to elute (18)F(-) from the QMA cartridge with oxalic acid to prevent decomposition of the active ester moiety. Purification of [(18)F]SiFB was performed by simple solid-phase extraction, which avoided time-consuming HPLC and yielded high specific activities of at least 525 Ci/mmol and radiochemical yields of 40-56%. In addition to conventional azeotropic drying of (18)F(-) in the presence of [K(+)â2.2.2.]C(2)O(4), a strong anion-exchange (SAX) cartridge was used to prepare anhydrous (18)F(-) for nucleophilic radio-fluorination omitting the vacuum assisted drying of (18)F(-). Using a lyophilized mixture of [K(+)â2.2.2.]OH resolubilized in acetonitrile, the (18)F(-) was eluted from the SAX cartridge and used directly for the [(18)F]SiFB synthesis. [(18)F]SiFB was applied to the labeling of various proteins in likeness to the most commonly used labeling synthon in protein labeling, N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). Rat serum albumin (RSA), apo-transferrin, a ß-cell-specific single chain antibody, and erythropoietin were successfully labeled with [(18)F]SiFB in good radiochemical yields between 19% and 36%. [(18)F]SiFB- and [(18)F]SFB-derivatized RSA were directly compared as blood pool imaging agents in healthy rats using small animal positron emission tomography. Both compounds demonstrated identical biodistributions in healthy rats, accurately visualizing the blood pool with PET.
Subject(s)
Fluorine Radioisotopes/chemistry , Organosilicon Compounds/chemical synthesis , Oxalic Acid/chemistry , Silicon/chemistry , Staining and Labeling/methods , Succinimides/chemical synthesis , Animals , Apoproteins/chemistry , Chromatography, High Pressure Liquid , Erythropoietin/chemistry , Fluorine Radioisotopes/analysis , Fluorine Radioisotopes/isolation & purification , Fluorine Radioisotopes/pharmacokinetics , Molecular Structure , Organosilicon Compounds/chemistry , Organosilicon Compounds/isolation & purification , Organosilicon Compounds/pharmacokinetics , Rats , Serum Albumin/chemistry , Single-Chain Antibodies/chemistry , Solid Phase Extraction , Succinimides/chemistry , Succinimides/isolation & purification , Succinimides/pharmacokinetics , Tissue Distribution , Transferrin/chemistryABSTRACT
INTRODUCTION: The central benzodiazepine receptor (cBZR)-gamma-aminobutyric acid (GABA(A)) receptor complex in the human brain plays an important role in many neurological and psychiatric disorders. (18)F-Labeled flumazenil ([(18)F]FZ) provides a potentially useful tracer to investigate those disorders by means of positron emission tomography (PET). METHODS: [(18)F]Flumazenil was synthesized from its nitro-precursor Ro 15-2344 in DMF at high temperatures between 150 degrees C and 160 degrees C. Other solvents like acetonitrile and dimethylsulfoxide were also investigated as reaction media. A new HPLC method for the final purification of [(18)F]FZ was developed to circumvent some difficulties associated with a previously published procedure sometimes led to a contamination of [(18)F]FZ with Ro 15-2344. The final purification of the radiotracer was achieved using a Waters Symmetry Prep C18 HPLC column with elution with 0.05 M sodium acetate (NaOAc) buffer (pH 5)/THF/MeOH (80:10:10). RESULTS: [(18)F]FZ could be synthesized in reproducible radiochemical yields (RCYs) of 15-20% (decay corrected to EOB) after 80 min overall synthesis time. The synthesized [(18)F]FZ was applied for the first time in a human PET study in a patient with ischemic right middle cerebral artery stroke using the HRRT high-resolution research scanner (Siemens Medical Solution, Knoxville, TN, USA). CONCLUSIONS: [(18)F]FZ is a potentially useful GABA receptor-binding PET ligand. A modified procedure for its preparation in reproducibly high radiochemical yields has been described and the [(18)F]FZ thus produced has been used successfully in a pilot clinical study.
