Nuclear Medicine

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Browsing Nuclear Medicine by Subject "(68)Ga-labelled DOTA-peptides"

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    Investigation into various aspects of radiolabelling somatostatin peptide derivatives with 68Ga eluted from a SnO2-based 68Ge/68Ga generator
    (Stellenbosch : Stellenbosch University, 2018-03) Prince, Deidre Mabel; Rubow, Sietske Margarete; Rossouw, Daniel Dutoit; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medical Imaging and Clinical Oncology. Nuclear Medicine.
    ENGLISH SUMMARY : 68Ge/68Ga generators ensure the supply of 68Ga for positron emission tomography (PET), for instance for somatostatin receptor imaging with 68Ga-DOTA-labelled somatostatin analogues. There are various generators available and their eluates are processed differently for radiolabelling of peptides. The objectives of this study were to investigate various aspects of the elution characteristics of the generator, to optimize labelling conditions using different eluate processing techniques such as fractionation and cation exchange chromatography and to develop user-friendly kit formulations. This study was approved by the Stellenbosch University Health Research Ethics Committee and permission was granted for the experimental work to be conducted at iThemba LABS. Elution efficiencies were determined using different HCl concentrations (0.2 M – 1.0 M). Metal analysis and 68Ge breakthrough determination were performed on eluates. Radiolabelling parameters were optimized, using fractionated eluates and different DOTA-peptide masses (15 to 50 μg) at pH 3.5 – 4.0 in sodium acetate buffer. Different heating times and heating methods and the influence of various periods of non-elution of the generator on radiolabelling results were investigated. Cationic resins were investigated for eluate processing. Radiolabelling parameters, using cationic resin-processed eluates, were optimized. Labelling was conducted at various pH values, using different quantities of buffer. DOTA-peptide kits for both fractionated and resin-processed eluates were developed and tested for sterility, endotoxin content and stability. Radiochemical yields, radiolabelling efficiency and radiochemical purity of 68Ga-DOTA-peptides were determined. The elution efficiency of the generator increased with an increase in the concentration of HCl eluent. The 68Ge breakthrough increased dramatically at 0.8 M HCl. Most metal contaminants were lowest when eluting with 0.2 M HCl and the Zn content increased with the increase in HCl concentration. The eluent of choice for the SnO2-based generator was confirmed to be 0.6 M HCl. For radiolabelling, 35 μg DOTA-peptide (9.2 – 9.4 μM) was the most favourable. Extended heating times and heating method did not significantly impact on the radiolabelling. The radiolabelling efficiencies were consistently above 90 % even after 3 weeks of non-elution of the generator, but radiochemical yields dropped after 7 days. DOTA-peptide kits for fractionated eluates were successfully developed and the radiolabelling quality was found to be superior over peptide stock solutions. A radiolabelling method using a cationic exchange resin was successfully adapted for the SnO2 generator. 68Ga was efficiently adsorbed on a Bond Elut SCX (100 mg) cartridge and desorbed by acidified solutions of NaCl. The SCX resin effectively removed about 98 % of deliberately “spiked” metals from the 68Ga eluate. An optimized labelling method based on the use of SCX-purified eluates was developed, producing radiochemical yields of almost 85 % and lead to the successful formulation of DOTATATE kits. The quality was found to be suitable over a 3-month period. In conclusion, a kit type labelling procedure, using cationic resin purified 68Ga eluates, provides the most practical method to produce 68Ga-labelled DOTA-peptides.
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    Monitoring various eluate characteristics of the iThemba LABS SnO2-based 68Ge/68Ga generator over time and validation of quality control methods for the radiochemical purity assessment of 68Ga-labelled DOTA peptide formulations
    (Stellenbosch : Stellenbosch University, 2017-03) Davids, Claudia Ruby; Rubow, Sietske Margarete; Rossouw, Daniel; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medical Imaging and Clinical Oncology. Nuclear Medicine
    ENGLISH SUMMARY : PET imaging with gallium-68 (68Ga) has become widely used due to the availability of 68Ge/68Ga generators and DOTA-derivatised peptide ligands for radiolabelling. The purpose of this study was to monitor the eluate of two iThemba LABS 68Ge/68Ga generators over a period of 12 months to ascertain whether all quality parameters of the 68Ga eluate remained stable and to validate different analytical methods used to determine the radiochemical purity of 68Ga-labelled peptides. Two 1850 MBq (50 mCi) generators were eluted daily with 0.6 M HCl and metal contaminants, 68Ge breakthrough, 68Ga yield, pH, sterility and endotoxin concentrations were determined on a monthly basis. The radiochemical purity of 68Ga-labelled peptides was ascertained using high performance liquid chromatography (HPLC) and instant thin layer chromatography (iTLC). iTLC experiments were performed using both dried and undried iTLC plates. iTLC was also carried out on labelled peptide solution that was spiked with 68GaCl3. These results were also compared with those using HPLC. After 12 months the 68Ga yields, total metal contaminants, sterility and endotoxin concentration remained within European Pharmacopoeial limits. The 68Ge breakthrough increased as the generator aged. This can however be minimised by fractionated elution and post-labelling processing of the eluate by anion or cation exchange chromatography. Separation between 68GaCl3 and 68Ga-labelled peptides was obtained using both 0.1 M citrate buffer pH 5.0 (mobile phase 1) and 1 M ammonium acetate : methanol (1:1) (mobile phase 2). The results also showed that the distribution of radioactivity on the iTLC strip could be determined using a dose calibrator when a TLC scanner is not available. Experiments performed using both undried and dried iTLC-SG chromatography paper, demonstrated that despite the statistically significant difference between the sets of results, in practice either undried or dried iTLC may be used. When purified 68Ga-labelled peptides were spiked with 2% of 68GaCl3, separation between the two was obtained on both HPLC and iTLC. However, iTLC underestimated and HPLC overestimated 68GaCl3 content. Of the two iTLC methods investigated, the method using mobile phase 2 was able to separate colloidal 68Ga impurities from the 68Ga-labelled peptides while the method using mobile phase 1 and the HPLC method could not. In conclusion, the iThemba LABS 68Ge/68Ga generator can be considered stable and of use for up to one year after its manufacture. Both the iTLC method and the HPLC method could detect 68GaCl3 amounts less than 2%. The pharmacopoeia states that 68Ga must be less than 3 % on iTLC and less than 2 % on HPLC. Either dried or undried iTLC strips can be used and if a radio-TLC scanner is not available, the iTLC strips developed with mobile phase 1 can be cut at a suitable distance from the origin and the activity on each section can be read in a dose calibrator. iTLC chromatography using ammonium acetate/methanol seems to be the optimal system for routine analysis of 68Ga labelled DOTA-peptides, as it separates both 68GaCl3 and colloidal impurities from the labelled peptides and is a fast and easy technique.