Davids, Claudia Ruby (2017-03)
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.
AFRIKAANSE OPSOMMING : PET beelding met gallium-68 (68Ga) word deesdae algemeen aangewend as gevolg van die beskikbaarheid van 68Ge/68Ga generators en DOTA-afgeleide peptied ligande vir radiomerking. Die doelstelling van hierdie studie was om die eluate van twee iThemba LABS 68Ge/68Ga generators oor ‘n 12 maande periode te moniteer om vas te stel of al die gehalteparameters van die 68Ga eluaat stabiel bly. ‘n Verdere doelstelling was om verskillende analitiese metodes vir bepaling van die radiochemiese suiwerheid van 68Ga-gemerkte peptiede te bekragtig. Twee 1850 MBq (50 mCi) generators is daagliks met 0.6M HCl ge-elueer en bepalings van metaalonsuiwerhede, 68Ge deurbraak, 68Ga opbrengste, pH, steriliteit en endotoksien konsentrasie is maandeliks herhaal. Die radiochemiese suiwerhede van 68Ga-gemerkte peptiede is met behulp van hoȅdoeltreffendheid- vloeistofchromatografie (HDVC) en kits dunlaag chromatografie of sg. instant thin layer chromatography (iTLC) bepaal. iTLC eksperimente is uitgevoer met beide gedroogde en ongedroogde iTLC papier. iTLC is ook uitgevoer op gemerkte peptied monsters wat doelbewus met klein hoeveelhede 68GaCl3 gekontamineer is. Hierdie resultate is vergelyk met HDVC resultate van dieselfde monsters. Die 68Ga opbrengste, totale metaalonsuiwerhede, steriliteit en endotoksien konsentrasie het na ‘n periode van 12 maande binne die grense van die Europese Farmakopee gebly. Die 68Ge deurbraak het toegeneem met veroudering van die generator maar dit kan beperk word deur gefraksioneerde eluering of prosessering van die eluaat met behulp van anioon- of katioon-uitruilchromatografie. Skeiding tussen 68GaCl3 en 68Ga-gemerkte peptiede is verkry met die gebruik van beide 0.1 M sitraat buffer pH 5 (mobiele fase 1) en 1 M ammonium asetaat : metanol (1:1) (mobiele fase 2). Die resultate het getoon dat die verspreiding van radioaktiwiteit op ‘n iTLC strook met behulp van ‘n dosiskalibreerder bepaal kan word wanneer ‘n TLC skandeerder nie beskikbaar is nie. Die eksperimente met vooraf gedroogde sowel as ongedroogde iTLC strokies het getoon dat, ten spyte van statisties betekenisvolle verskille tussen die resultate, beide in praktyk gebruik kan word. In gevalle waar gesuiwerde 68Ga-gemerkte peptiede doelbewus gekontamineer is met 2% 68GaCl3, is skeiding tussen die twee spesies verkry in beide HDVC en iTLC analises. 68GaCl3 inhoud is egter onderskat met iTLC en oorskat met HDVC. Die metode waarin mobiele fase 2 gebruik is, was in staat om kolloidale 68Ga onsuiwerhede te skei van die 68Ga-gemerkte peptiede, terwyl mobiele fase 1 en die HDVC metodes dit nie kon doen nie. Ter samevatting, die iThemba LABS 68Ge/68Ga generator kan as stabiel beskou word en vir ‘n periode van tot een jaar na vervaardiging gebruik word. Beide die HDVC en iTLC metodes kon 68Ga hoeveelhede van minder as 2% bepaal. Die Europese Farmakopee skryf voor dat 68Ga laer as 3 % moet wees met iTLC en laer as 2 % met HDVC. Gedroogde of ongedroogde iTLC papier kan gebruik word en indien ‘n iTLC radioskandeerder nie beskikbaar is nie, kan iTLC stroke wat met mobiele fase 1 ontwikkel is, ‘n geskikte afstand vanaf die oorsrong deurgesny word en die aktiwiteit op elke deel in ‘n dosiskalibreerder gelees word. iTLC met ammonium asetaat/metanol as mobiele fase, blyk die optimale sisteem vir roetine-analise van 68Ga-gemerkte peptiede te wees, omdat dit beide 68GaCl3 en kolloidale 68Ga onsuiwerhede van die gemerkte peptiede kan skei en ook ‘n vinnige en maklike tegniek is.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100825
Masters Degrees (Nuclear Medicine)