Zur trägerarmen Radiofluorierung von Peptiden und Proteinen über prosthetische Gruppen

Two complementary methods, $^{18}$F-fluoroacylation and $^{18}$F-fluoroamidation, were studied for n.c.a. labeling of peptides and proteins. Nucleophilic $^{18}$F-fluorination of suitable protected carboxylic acids such as small aliphatic $\alpha$-bromo acetic- or propionic acid esters or p-trimethylammonium triflatesubstituted benzoic acid esters was the common first step in the fluoroacylation methods. Following deprotection, formation of imidazolides, succinimide esters orp-nitrophenyl esters as reactive intermediates was investigated. In view of an automated synthesis for the production of $^{18}$F-fluoroacylation agents as keyintermediates, a route to p-nitrophenylesters via the corresponding $^{18}$F-fluorinated acid chloride was also developed. The reactivity of the $^{18}$F-labeled acylation agents towards a wide range of amines with different sterical hindrance and basicities was compared. Even with low reactive aniline derivatives almost quantitative formation of the corresponding $^{18}$F-fluorinated amides was observed. For pharmacolgical studies using positron emission tomography (PET), thesomatostatin analog octreotide was selectively $^{18}$F-fluoroacylated at the N-terminus of the cyclic octapeptide using the $\epsilon$-Lys-Boc protected precursor. Binding studies with the non radioactive fluoropropionylated standard compound and rat cortex membran es revealed high affinity (pK$_{i}$=8.6) to the somatostatin receptor and almost unchanged biological activity compared to the native octreotide. As alternative to $^{18}$F-fluoroacylation the inverse reaction, using $^{18}$F-fluorinated amines and unlabeled acylation agents, was investigated. For this purpose halogenated, Boc-protected amines were used as precursors in the n.c.a. nucleophilic fluorination step. 3-[$^{18}$F]Fluoropropylamine proved to be optimal for $^{18}$F-fluoroamidation with respect to radiochemical yield and reactivity towards acylation agents. Thus suitable derivatives of the vitamin Biotin could be labeled with high radiochemical yields using $^{18}$F-fluoroacylation as weil as $^{18}$F-fluoroamidation. Both methods led to labeled compounds with full biological activity as shown by their binding ability to the protein avidin. Avidin itself could be labeled using the $^{18}$F-fluoroacylation method. In this case affinity chromatography revealed preservation ofthe biological activity of the $^{18}$F-labeled compound

Use of a new tandem cation/anion exchange system with clinical-scale generators provides high specific volume solutions of technetium-99m and rhenium-188

In this paper the authors describe the first application of a simple and inexpensive post elution tandem cation-anion exchange column system which is based on generator elution with salts of weak acids such as ammonium acetate instead of saline solution to provide very high specific volume solutions of technetium-99m and rhenium-188 from clinical scale molybdenum-99/technetium-99m generator prepared from low specific activity (n,y) molybdenum-99, and tungsten-188/rhenium-188 generators, respectively. Initial passage of the bolus through a strong cation exchange cartridge converts the ammonium acetate to acetic acid which is essentially not ionized at the acidic pH, allowing specific subsequent amine type (QMA SepPak{trademark}) anion exchange cartridge column trapping of the microscopic levels of the pertechnetate or perrhenate. Subsequent elution of the anion cartridge with a small volume ( 500 mCi/mL) from the alumina-based tungsten-188/rhenium-188 generator

Zur traegerarmen Radiofluorierung von Peptiden und Proteinen ueber prosthetische Gruppen

Two complementary method, "1"8F-fluoroacylation and "1"8F-fluoroamidation, were studied for n.c.a. labeling of peptides and proteins. Nucleophilic "1"8F-fluorination of suitable protected carboxylic acids such as small aliphatic #alpha#-bromo acetic- or propionic acid esters or p-trimethylammonium triflate substituted benzoic acid esters was the common first step in the fluoroacylation methods. Following deprotection, formation of imidazolides, succinimide esters or p-nitrophenyl esters as reactive intermediates was investigated. The reactivity of the "1"8F-labeled acylation agents towards a wide range of amines with different sterical hindrance and basicities was compared. Even with low reactive aniline derivatives almost quantitative formation of the corresponding "1"8F-fluorinated amides was observed. As alternative to "1"8F-fluoroacylation the inverse reaction, using "1"8F-fluorinated amines and unlabeled acylation agents, was investigated. For this purpose halogenated, Boc-protected amines were used as precursors in the n.c.a. nucleophilic fluorination step. Both methods led to labeled compounds with full biological activity as shown by their binding ability to the protein avidin. Acidin itself could be labeled using the "1"8F-fluoroacylation method. In this case affinity chromatography revealed preservation of the biologicaly activity of the "1"8F-labeled compound. (orig./SR)SIGLEAvailable from TIB Hannover: RA 831(3136) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Availability of rhenium-188 from the alumina-based tungsten-188/Rhenium-188 generator for preparation of rhenium-188-labeled radiopharmaceuticals for cancer treatment

Rhenium-188 (β- = 2.2 MeV; γ- = 155 keV; T(1/2) 16.9 hours) is an attractive therapeutic radioisotope which is produced from decay of the reactor-produced tungsten-188 parent (T1/2 69 days) and thus conveniently obtained on demand by elution from the alumina-based tungsten-188/rhenium-188 generator system. The rhenium-188 is obtained as sodium perrhenate by elution of the generator with 0.9% saline. The post elution use of disposable tandem, ion-exchange columns is a simple method for the concentration of rhenium-188 saline solutions with specific volumes > 500 mCi/ml. This method can also extend the useful shelf-life of the generator, which can be as long as one year. The long useful shelf-life of the generator is expected to provide rhenium-188 at very reasonable costs for routine preparation of a variety of radiopharmaceuticals for the treatment of a variety of cancers

Nuclear medicine program progress report for quarter ending March 31, 1996

Biodistribution studies with the radioiodinated 3(R)- and 3(S)-BMIPP isomers in rats have shown that 3(R)-BMIPP has 20-25% higher heart uptake (15-180 min) than 3(S)-BMIPP, while uptake in other tissues examined is similar. To evaluate the possible differences in metabolic fate of the two isomers, a mixture of [I-125]-3(R)/[I-131]- 3(S)-BMIPP was administered to fasted female Fisher rats. Groups (n=3 rats per group) were sacrificed after 15, 60 and 180 min, and urine and feces collected from another group. Samples of blood, heart, liver, lungs, kidney, and urine were Folch-extracted. The distribution of I-125 and I-131 in the organic, aqueous, and pellet samples were determined. Organic samples were then analyzed by thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC). The relative distribution of I-125/I-131 in the lipid, aqueous, and pellet samples was similar for both isomers. Distribution of I-125/I-131 in the various components of the lipid extracts observed by TLC was similar, with principal incorporation into the free fatty acid (FFA) and triglyceride (TG) pools. HPLC analyses (Cl8) of the FFA fraction showed similar I-125/I-131 profiles, corresponding to BMIPP, and the {alpha}-methyl-C,4 (PIPA) and C12, Cl0 and C6 carbon chain-length catabolites. By TLC, urine I-125/I-131 chromatographed with hippuric acid. HPLC analyses (Cl 8) of acid-hydrolyzed urine gave a single I-125/I-131 component with the same RRT as 2-({beta}-iodophenyl)acetic acid, the final {alpha}/{beta}-oxidative BMIPP catabolite. Unexpectedly, HPLC of lipids from base hydrolyzed TG from the heart tissue, showed I-125/I-125 co-chromatographing with short-chain fatty acids, with only levels in BMIPP. These unexpected results demonstrate that the 3(R)-BMIPP and 3(S)-BMIPP isomers are metabolized similarly in rat tissues, and that the higher myocardial extraction observed for the 3(R)-BMIPP may reflect differences in the relative membrane transport of the two isomers

Nuclear medicine program progress report for quarter ending December 31, 1995

In this report we describe the first resolution of the 3R-(+)-and 3S- ({minus})-methyl BMIPP methyl-branched fatty acid stereoisomers and biodistribution of the radioiodinated isomers in rats to investigate the effects of the configuration of the 3({beta})-methyl group on the organ distribution and myocardial uptake and release kinetics. Synthesesis of 3R-(+)BMIPP was accompanied by initial acylation of the thiophene template with the acid chloride of ethyl 3R- methylglutarate. The amide of the synthetic 3R-BMIPP isomer prepared S-(-)-{alpha}-methylbenzylamine exhibited identical spectral and chromatographic properties with the chromatographically more polar isomer (TLC and HPLC) which was separated from the mixture of amides prepared from reaction of the acid chloride of racemic BMIPP with the S-(-)-{alpha}-methylbenzylamine. The second less chromatographically polar amide isomer was assigned the 3S-(-)-methyl configuration. The free acids were obtained by acid hydrolysis of the amides and converted to the radioiodinated analogues. While biodistribution studies in separate groups of rats demonstrated greater myocardial uptake of 3R-BMIPP compared with the 3S-isomer values for most other tissues evaluated (blood, lungs, kidneys and thyroid) were similar, whereas the 3S-BMIPP isomer consistently showed higher liver uptake. These results were confirmed in a [l-131]-3S-BMIPP/[l-125]-3R-BMIPP dual label study and both isomers had similar myocardial wash-out curves (5-180 min). These studies suggest that [l-123]-3R-BMIPP is a candidate for clinical evaluation and may show greater myocardial uptake than the 3S-isomer and thus may require a reduced injected dose compared to racemic BMIPP