18F-FLUCICLOVINE COMPOSITIONS IN CITRATE BUFFERS

Abstract

The present invention provides a pharmaceutical composition comprising [.sup.18F]FACBC having certain advantages over known compositions comprising [.sup.18F]FACBC. Also provided by the present invention is a method to obtain the composition of the invention.

Claims

1-21. (canceled)

22. A positron emission tomography (PET) tracer composition comprising anti-1-amino-3-.sup.18F-fluorocyclobutyl-1-carboxylic acid (.sup.18F-FACBC) having an end of synthesis (EOS) radioactive concentration (RAC) of at least 1,000 MBq/mL, and comprising no more than 150 ?g/mL hydroxyl-ACBC, wherein the composition is prepared without passing the reaction mixture through an alumina solid phase.

23. The PET tracer composition as defined in claim 22, wherein the composition has an end of synthesis (EOS) radioactive concentration (RAC) of at least 1500 MBq/mL.

24. The PET tracer composition as defined in claim 22, wherein the composition has no more than 80 ?g/mL hydroxyl-ACBC.

25. The pharmaceutical composition as defined in claim 22 comprising 50-100 mM citrate buffer.

26. The pharmaceutical composition as defined in claim 22 comprising 60-90 mM citrate buffer.

27. The pharmaceutical composition as defined in claim 22 comprising 75-85 mM citrate buffer.

28. The pharmaceutical composition as defined in claim 22 that has a pH of 4.0-5.0.

29. The pharmaceutical composition as defined in claim 22 that has a pH of 4.1-4.5.

30. The pharmaceutical composition as defined in claim 22 which comprises not more than 0.15 ?g/mL 1-amino-3-fluorocyclobutane-1-carboxylic acid (FACBC).

31. The pharmaceutical composition as defined in claim 22 which comprises not more than 0.10 ?g/mL FACBC.

32. The pharmaceutical composition as defined in claim 22 which comprises not more than 2.0 ?g/mL 1-amino-3-chloro-cydobutane-1-carboxylic acid (chloro-ACBC).

33. The pharmaceutical composition as defined in claim 22 which comprises not more than 1.0 ?g/mL chloro-ACBC.

34. A method of preparation of a PET tracer composition comprising (a) reacting in a reaction vessel a source of .sup.18F-fluoride with a precursor compound of Formula I: ##STR00008## wherein: LG is a leaving group; PG.sup.1 is a carboxy protecting group; and, PG.sup.2 is an amine protecting group; to obtain a reaction mixture comprising a compound of Formula II: ##STR00009## wherein PG.sup.1 and PG.sup.2 are as defined for Formula I; (b) carrying out removal of PG.sup.1 to obtain a reaction mixture comprising a compound of Formula III: ##STR00010## wherein PG.sup.1 is as defined for Formula I; (c) carrying out removal of PG.sup.2 to obtain a reaction mixture comprising .sup.18F-FACBC; and (d) purifying said reaction mixture comprising .sup.18F-FACBC by passing it through a hydrophilic lipophilic balanced (HLB) solid phase, wherein said purifying does not comprise passing the reaction mixture comprising .sup.18F-FACBC through an alumina solid phase.

35. The method as defined in claim 34 wherein LG is trifluoromethanesulfonic acid.

36. The method as defined in claim 34 wherein PG.sup.1 is ethyl.

37. The method as defined in claim 34 wherein PG.sup.2 is t-butoxycarbonyl.

38. The method as defined in claim 34 wherein PG.sup.1 is removed using NaOH.

39. The method as defined in claim 34 wherein PG.sup.2 is removed using HCl.

40. The method as defined claim 34 further comprising formulating said purified reaction mixture obtained in step (d) with citrate buffer.

Description

EXAMPLES

[0069] All reagents and solvents were purchased from Merck and used without further purification. The [.sup.18F]FACBC precursor; Syn-1-(N-(tert-butoxycarbonyl)amino)-3-[[(trifluoromethyl)sulfonyl]oxy]-cyclobutane-1-carboxylic acid ethyl ester was obtained from GE Healthcare. The Oasis HLB plus cartridge and the Sep-Pak cartridges: QMA light Plus (K.sub.2CO.sub.3 form), tC18 light, Alumina N light were purchased from Waters (Milford, Mass., USA). A Capintec NaI ion chamber was used for all radioactive measurements (model CRC15R). Radio-thin layer chromatography (radio-TLC) was performed on a Packard instant imager using pre-coated plates of silica gel (Merck 60F.sub.254).

Example 1

Synthesis and Formulation of [.SUP.18.F]FACBC Composition of the Invention

[0070] No-carrier-added [.sup.18F]fluoride was produced via the .sup.18O(p,n).sup.18F nuclear reaction on a GE PETtrace 6 cyclotron (Norwegian Cyclotron Centre, Oslo). Irradiations were performed using a dual-beam, 30 ?A current on two equal Ag targets with HAVAR foils using 16.5 MeV protons. Each target contained 1.6 ml of ?96% [.sup.18O]water (Marshall Isotopes). Subsequent to irradiation and delivery to a hotcell, each target was washed with 1.6 ml of [.sup.16O]water (Merck, water for GR analysis), giving approximately 2-5

[0071] Gbq in 3.2 ml of [.sup.16O]water.

[0072] All radiochemistry was performed on a commercially available GE FASTlab? with a single-use cassette. Each cassette is built around a one-piece-moulded manifold with 25 three-way stopcocks, all made of polypropylene. Briefly, the cassette includes a 5 ml reactor (cyclic olefin copolymer), one 1 ml syringe and two 5 ml syringes, spikes for connection with five prefilled vials, one water bag (100 ml) as well as various SPE cartridges and filters. Fluid paths are controlled with nitrogen purging, vacuum and the three syringes. The fully automated system is designed for single-step fluorinations with cyclotron-produced [.sup.18F]fluoride. The FASTlab was programmed by the software package in a step-by-step time-dependent sequence of events such as moving the syringes, nitrogen purging, vacuum, and temperature regulation. Synthesis of [.sup.18F]FACBC followed the three general steps: (a) [.sup.18F]fluorination, (b) hydrolysis of protection groups and (c) SPE purification.

[0073] Vial A contained K.sub.222 (156 ?mol), K.sub.2CO.sub.3 (60.8 ?mol) in 79.5% (v/v) MeCN.sub.(aq) (1105 ?l). Vial B contained 4M HCl. Vial C contained MeCN. Vial D contained precursor (123.5 ?mol) in its dry form (stored below ?5? C. until cassette assembly). Vial E contained 2 M NaOH (4.1 ml). The 30 ml product collection glass vial was filled with 200 mM citrate buffer (10 ml). Aqueous [.sup.18F]fluoride (1-1.5 ml, 100-200 Mbq) was passed through the QMA and into the .sup.18O-H.sub.2O recovery vial. The QMA was then flushed with MeCN and sent to waste. The trapped [.sup.18F]fluoride was eluted into the reactor using eluent from vial A (730 ?l) and then concentrated to dryness by azeotropic distillation with acetonitrile (80 ?l, vial C). Approximately 1.7 ml of MeCN was mixed with precursor in vial D from which 1.0 ml of the dissolved precursor (corresponds to 72.7 mmol precursor) was added to the reactor and heated for 3 min at 85? C. The reaction mixture was diluted with water and sent through the tC18 cartridge. Reactor was washed with water and sent through the tC18 cartridge. The labelled intermediate, fixed on the tC18 cartridge was washed with water, and then incubated with 2M NaOH (2.0 ml) for 5 min. The labelled intermediate (without the ester group) was eluted off the tC18 cartridge into the reactor using water. The BOC group was hydrolysed by adding 4M HCl (1.4 ml) and heating the reactor for 5 min at 60? C. The reactor content with the crude [.sup.18F]FACBC was sent through the HLB and Alumina cartridges and into the 30 ml product vial. The HLB and Alumina cartridges were washed with water (9.1 ml total) and collected in the product vial. Finally, 2M NaOH (0.9 ml) and water (2.1 ml) was added to the product vial, giving the purified formulation of [.sup.18F]FACBC with a total volume of 26 ml. Radiochemical purity was measured by radio-TLC using a mixture of McCN:MeOH:H.sub.2O:CH.sub.3COOH (20:5:5:1) as the mobile phase. The radiochemical yield (RCY) was expressed as the amount of radioactivity in the [.sup.18F]FACBC fraction divided by the total used [.sup.18F]fluoride activity (decay corrected). Total synthesis time was 43 min.