Characteristics of SnO2-based 68Ge/68Ga generator and aspects of radiolabelling DOTA-peptides. 2011

Erik de Blois, and Ho Sze Chan, and Clive Naidoo, and Deidre Prince, and Eric P Krenning, and Wouter A P Breeman
Department of Nuclear Medicine, Erasmus MC Rotterdam, Rotterdam, The Netherlands.

OBJECTIVE PET scintigraphy with (68)Ga-labelled analogs is of increasing interest in Nuclear Medicine and performed all over the world. Here we report the characteristics of the eluate of SnO(2)-based (68)Ge/(68)Ga generators prepared by iThemba LABS (Somerset West, South Africa). Three purification and concentration techniques of the eluate for labelling DOTA-TATE and concordant SPE purifications were investigated. METHODS Characteristics of 4 SnO(2)-based generators (range 0.4-1 GBq (68)Ga in the eluate) and several concentration techniques of the eluate (HCl) were evaluated. The elution profiles of SnO(2)-based (68)Ge/(68)Ga generators were monitored, while [HCl] of the eluens was varied from 0.3-1.0 M. Metal ions and sterility of the eluate were determined by ICP. Fractionated elution and concentration of the (68)Ga eluate were performed using anion and cation exchange. Concentrated (68)Ga eluate, using all three concentration techniques, was used for labelling of DOTA-TATE. (68)Ga-DOTA-TATE-containing solution was purified and RNP increased by SPE, therefore also 11 commercially available SPE columns were investigated. RESULTS The amount of elutable (68)Ga activity varies when the concentration of the eluens, HCl, was varied, while (68)Ge activity remains virtually constant. SnO(2)-based (68)Ge/(68)Ga generator elutes at 0.6 M HCl >100% of the (68)Ga activity at calibration time and ±75% after 300 days. Eluate at discharge was sterile and Endotoxins were <0.5 EU/mL, RNP was always <0.01%. Metal ions in the eluate were <10 ppm (in total). Highest desorption for anion purification was obtained with the 30 mg Oasis WAX column (>80%). Highest desorption for cation purification was obtained using a solution containing 90% acetone at increasing molarity of HCl, resulted in a (68)Ga desorption of 68±8%. With all (68)Ge/(68)Ga generators and for all 3 purification methods a SA up to 50 MBq/nmol with >95% incorporation (ITLC) and RCP (radiochemical purity) by HPLC ±90% could be achieved. Purification and concentration of the eluate with anion exchange has the benefit of more elutable (68)Ga with 1 M HCl as eluens. The additional washing step of the anion column with NaCl and ethanol, resulted in a lower and less variable [H(+)] in the eluate, and, as a result the pH in the reaction vial is better controlled, more constant, and less addition of buffer is required and concordant smaller reaction volumes. Desorption of (68)Ga-DOTA-TATE of SPE columns varied, highest desorption was obtained with Baker C(18) 100 mg (84%). Purification of (68)Ga-DOTA-TATE by SPE resulted in an RNP of <10(-4)%. CONCLUSIONS Eluate of SnO(2)-based (68)Ge/(68)Ga generator, either by fractionated elution as by ion exchange can be used for labelling DOTA-peptides with (68)Ga at a SA of 50 MBq/nmol at >95% incorporation and a RCP of ±90%. SPE columns are very effective to increase RNP.

UI MeSH Term Description Entries
D007553 Isotope Labeling Techniques for labeling a substance with a stable or radioactive isotope. It is not used for articles involving labeled substances unless the methods of labeling are substantively discussed. Tracers that may be labeled include chemical substances, cells, or microorganisms. Isotope Labeling, Stable,Isotope-Coded Affinity Tagging,Isotopically-Coded Affinity Tagging,Affinity Tagging, Isotope-Coded,Affinity Tagging, Isotopically-Coded,Isotope Coded Affinity Tagging,Labeling, Isotope,Labeling, Stable Isotope,Stable Isotope Labeling,Tagging, Isotope-Coded Affinity,Tagging, Isotopically-Coded Affinity
D010455 Peptides Members of the class of compounds composed of AMINO ACIDS joined together by peptide bonds between adjacent amino acids into linear, branched or cyclical structures. OLIGOPEPTIDES are composed of approximately 2-12 amino acids. Polypeptides are composed of approximately 13 or more amino acids. PROTEINS are considered to be larger versions of peptides that can form into complex structures such as ENZYMES and RECEPTORS. Peptide,Polypeptide,Polypeptides
D011868 Radioisotopes Isotopes that exhibit radioactivity and undergo radioactive decay. (From Grant & Hackh's Chemical Dictionary, 5th ed & McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Daughter Isotope,Daughter Nuclide,Radioactive Isotope,Radioactive Isotopes,Radiogenic Isotope,Radioisotope,Radionuclide,Radionuclides,Daughter Nuclides,Daugter Isotopes,Radiogenic Isotopes,Isotope, Daughter,Isotope, Radioactive,Isotope, Radiogenic,Isotopes, Daugter,Isotopes, Radioactive,Isotopes, Radiogenic,Nuclide, Daughter,Nuclides, Daughter
D005710 Gallium Radioisotopes Unstable isotopes of gallium that decay or disintegrate emitting radiation. Ga atoms with atomic weights 63-68, 70 and 72-76 are radioactive gallium isotopes. Radioisotopes, Gallium
D005857 Germanium A rare metal element with a blue-gray appearance and atomic symbol Ge, atomic number 32, and atomic weight 72.63.
D006573 Heterocyclic Compounds, 1-Ring Organic compounds that contain a ring structure made up of carbon and one or more additional elements such as nitrogen and oxygen. Heterocyclic Cpds, 1-Ring,1-Ring Heterocyclic Compounds,1-Ring Heterocyclic Cpds,Heterocyclic Compounds, 1 Ring,Heterocyclic Cpds, 1 Ring
D049268 Positron-Emission Tomography An imaging technique using compounds labelled with short-lived positron-emitting radionuclides (such as carbon-11, nitrogen-13, oxygen-15 and fluorine-18) to measure cell metabolism. It has been useful in study of soft tissues such as CANCER; CARDIOVASCULAR SYSTEM; and brain. SINGLE-PHOTON EMISSION-COMPUTED TOMOGRAPHY is closely related to positron emission tomography, but uses isotopes with longer half-lives and resolution is lower. PET Imaging,PET Scan,Positron-Emission Tomography Imaging,Tomography, Positron-Emission,Imaging, PET,Imaging, Positron-Emission Tomography,PET Imagings,PET Scans,Positron Emission Tomography,Positron Emission Tomography Imaging,Positron-Emission Tomography Imagings,Scan, PET,Tomography Imaging, Positron-Emission,Tomography, Positron Emission
D052616 Solid Phase Extraction An extraction method that separates analytes using a solid phase and a liquid phase. It is used for preparative sample cleanup before analysis by CHROMATOGRAPHY and other analytical methods. Extraction, Solid Phase,Extractions, Solid Phase,Solid Phase Extractions
D017971 Tin Compounds Inorganic compounds that contain tin as an integral part of the molecule. Compounds, Tin
D019275 Radiopharmaceuticals Compounds that are used in medicine as sources of radiation for radiotherapy and for diagnostic purposes. They have numerous uses in research and industry. (Martindale, The Extra Pharmacopoeia, 30th ed, p1161) Radiopharmaceutical

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