Development of a new precursor-minimizing base control method and its application for the automated synthesis and SPE purification of [(18) F]fluoromisonidazole ([(18) F]FMISO).

Bases such as potassium carbonate and potassium bicarbonate (KHCO3 ) are essential for the elution of trapped [(18) F]fluoride from ion exchange cartridges and for the prevention of [(18) F]fluoride adsorption on the silica glass vial during the preparation of radiopharmaceuticals for positron emission tomography imaging. However, these bases promote the chemical decomposition of precursor compounds and the creation of unwanted organic impurities. Thus, the goal of the current study was to develop a new method for synthesizing [(18) F]fluoride-labeled radiopharmaceuticals (e.g., [(18) F]fluoromisonizadole ([(18) F]FMISO)) that permits the fine control of base concentrations while minimizing adverse events. Non-decay-corrected radiochemical yields of 25.1 ± 5.0% and 13.3 ± 5.1% (n = 3) were achieved after solid-phase extraction purification using automatic synthesis with GE TRACERlab MX and KHCO3 at concentrations of 14.1 and 33.0 µmol, respectively, and 1 mg of precursor (1-(2'-nitro-1'-imidazolyl)-2-O-tetra-hydropyranyl-3-O-toluenesulfonyl propanediol (NITTP)). The newly developed synthesis protocol with fine base control and low precursor content permits high radiochemical yields with minimal impurities.

The possibility of a fully automated procedure for radiosynthesis of fluorine-18-labeled fluoromisonidazole using a simplified single, neutral alumina column purification procedure.

A novel fully automated radiosynthesis procedure for [(18)F]Fluoromisonidazole using a simple alumina cartridge-column for purification instead of conventionally used semi-preparative HPLC was developed. [(18)F]FMISO was prepared via a one-pot, two-step synthesis procedure using a modified nuclear interface synthesis module. Nucleophilic fluorination of the precursor molecule 1-(2'-nitro-1'-imidazolyl)-2-O-tetrahydropyranyl-3-O-toluenesulphonylpropanediol (NITTP) with no-carrier added [(18)F]fluoride followed by hydrolysis of the protecting group with 1M HCl. Purification was carried out using a single neutral alumina cartridge-column instead of semi-preparative HPLC. The maximum overall radiochemical yield obtained was 37.49+/-1.68% with 10mg NITTP (n=3, without any decay correction) and the total synthesis time was 40+/-1 min. The radiochemical purity was greater than 95% and the product was devoid of other chemical impurities including residual aluminum and acetonitrile. The biodistribution study in fibrosarcoma tumor model showed maximum uptake in tumor, 2h post injection. Finally, PET/CT imaging studies in normal healthy rabbit, showed clear uptake in the organs involved in the metabolic process of MISO. No bone uptake was observed excluding the presence of free [(18)F]fluoride. The reported method can be easily adapted in any commercial FDG synthesis module.

Fully automated one-pot synthesis of [18F]fluoromisonidazole.

A (18)F-labeled fluoromisonidazole (1H-1-(3-[(18)F]fluoro-2-hydroxypropyl)-2-nitroimidazole, [(18)F]FMISO) was prepared via a one-pot, two-step synthesis procedure using a modified commercial Tracerlab FX(F-N) synthesis module. Nucleophilic fluorination of the precursor molecule 1-(2'-nitro-1'-imidazolyl)-2-O-tetrahydropyranyl-3-O-toluenesulphonylpropanediol using no-carrier-added [(18)F]fluoride, followed by hydrolysis of the protecting group with 1 mol/L HCl and purification with Sep-Paks instead of HPLC, gave [(18)F]FMISO. The overall radiochemical yield with no decay correction was greater than 40%, the whole synthesis time was less than 40 min and the radiochemical purity was greater than 95%. The new automated synthesis procedure can be applied to the fully automated synthesis of [(18)F]FMISO using a commercial FDG synthesis module.

Influence of hypoxia on the metabolism and excretion of misonidazole by the isolated perfused rat liver--a model system.

The isolated perfused rat liver was evaluated as a model system for the characterization of misonidazole metabolism under hypoxic conditions. Misonidazole metabolism by livers perfused under aerobic conditions was also examined. The clearance of misonidazole was more than three times greater under anaerobic compared to aerobic conditions (4.94 +/- 1.56 vs 1.27 +/- 0.22 ml/min; means +/- S.D., N = 3). Misonidazole metabolites were detected only in the bile. Analysis of these metabolites by reverse-phase high performance liquid chromatography (HPLC) demonstrated that misonidazole metabolism was also qualitatively changed when anaerobic conditions were employed. Misonidazole beta-glucuronide was the major metabolite detected under aerobic conditions, but it was a minor metabolite in anaerobically perfused livers. The three major metabolites produced under anaerobic conditions were not characterized, but desmethyl misonidazole (RO-07-9963) and the 2-amino-imidazole derivative of misonidazole (1-[2-aminoimidazol-1-yl]-3-methoxy-2-propanol) were excluded as possible structures.