Rufael Chekol - Academia.edu (original) (raw)
Papers by Rufael Chekol
Journal of Labelled Compounds and Radiopharmaceuticals, 2011
Journal of Labelled Compounds and Radiopharmaceuticals, 2011
The research work would not have been possible without the collaboration between different depart... more The research work would not have been possible without the collaboration between different departments: Department of Imaging and Pathology (KU Leuven) and Nuclear Medicine (UZ Leuven) for production of radiolabeled compounds (from radionuclide production to formulation and quality control), Nuclear Medicine and Molecular Imaging (MoSAIC, KU Leuven) for animal experiments, Department of Cardiovascular Sciences (KU Leuven) for providing transgenic mice, pig for PET study, TAC and LAD mice and their expert advice on cardiac hypertrophy, Discovery Sciences (Janssen Pharmaceutica) for determination of in vitro phosphodiesterase inhibitory activity of compounds discussed in this dissertation. I have to extend my acknowledgement and appreciation for aforementioned departments and organizations for their contribution to the success of this research work and the resulting manuscript. We (Nuclear Medicine, UZ Leuven and Radiopharmacy, KU Leuven) are truly two big and happy families. The collaboration is an amazing experience and an example to others. I would like to take this opportunity to express my gratitude to the members of this big family: Prof. Koen Van Laere (Head of Nuclear Medicine, UZ Leuven), Tjibbe De Groot and Marva Bex you were always willing to help me during radioisotope production despite the hectic situation during working hours. Tjibbe you were always forthright spoken and I like that character of yours! Bert Vanbilloen (thanks for the supervision during my first year in post graduate studies), Stef Verschoren (for the nice after-work hours :), Christelle Terwinghe; Nathalie Devolder; Mireille Heroes; Anja Wilberts; Mieke Steukers; Magdalena Sojka; Kim Serdons, Kim Deliege; Katrien Seré and Annemie Morel: thank you all for the help and nice time. Jan Cleynhens, thank you for your great work and help on the organic synthesis of molecules. Your presence in the lab made a big difference both scientifically and socially and you were the spice of the lab! Sofie thank you for valuable and practical input. Ivan, Julie and Jana: thank you for your technical assistance during animal experiments. Maarten, thank you for your help on microPET image processing and also for the great time we had while on lab trip (Parma, Amsterdam...). Ahamed, thank you for your help on organic synthesis and NMR elucidation. I greatly appreciate for forwarding links to job postings and also for little chitchats we had.
Molecular Pharmaceutics, 2019
Insulin growth factor receptor (IGF-1R) is overexpressed in many cancers of epithelial origin whe... more Insulin growth factor receptor (IGF-1R) is overexpressed in many cancers of epithelial origin where it confers enhance proliferation and resistance to therapies targeted at other receptors. Anti-IGF-1R monoclonal antibodies have not demonstrated significant improvements in patient outcomes in clinical trials. Humanized monoclonal antibody cixutumumab (IMC-A12) binds to IGF-1R with low nM affinity. In this study cixutumumab was conjugated with p-SCN-Bn-DOTA and radiolabeled with 111 In or 225 Ac for imaging or radiotherapy using a triple negative breast cancer (TNBC) model SUM149PT. The antibody conjugate showed low nM affinity to IGF-1R which was not affected by conjugation and radiolabeling procedures. Cixutumumab immunoconjugates was effectively internalized in SUM149PT and was cytotoxic to the cells with an EC 50 of 225 Ac-cixutumumab (0.02 nM) that was almost 5000-fold less than unlabeled cixutumumab (95.2 nM). MicroSPECT imaging of SUM149PT xenograft showed the highest tumor uptake occurred at 48 h post injection and was 9.9 ± 0.5 % injected activity per gram (%IA/cc). In radiotherapy studies, we evaluated the effect of specific activity of 225 Accixutumumab on efficacy following a tail vein injection of two doses (day 0 and 10) of the investigation agent or controls. Cixutumumab (2.5 mg/kg) prolonged the survival of SUM149PT tumor bearing mice with a median survival of 87 days compared to PBS control group (median survival of 62 days). Median survival of high specific activity 225 Ac-cixutumumab (8 kBq/µg, 225 nCi, 0.05 mg/kg) was 103.5 days compared to 122 days for low specific activity 225 Accixutumumab (0.15 kBq/µg, 225 nCi, 2.5 mg/kg). Additionally, low specific activity radioimmunoconjugate led to complete tumor remission in 2/6 mice. The data suggest that efficacy of cixutumumab can be enhanced by radiolabeling with 225 Ac at a low specific activity.
Journal of Nuclear Medicine, 2019
Epidermal growth factor receptor I (EGFR) is overexpressed in most cancers of epithelial origin. ... more Epidermal growth factor receptor I (EGFR) is overexpressed in most cancers of epithelial origin. Antibody drug conjugates (ADCs) with PEGylated-maytansine (PEG-DM1) show promise in vitro and in vivo. However, in vivo biodistribution data for ADCs with PEG-DM1 have not been reported. Development of methods to understand the real-time in vivo behavior of these ADCs is needed to move these compounds to the clinic. Methods: Here we have used noninvasive small-animal SPECT/CT imaging and ex vivo biodistribution to understand the in vivo behavior of PEG 6-DM1 ADCs. We developed nimotuzumab ADCs conjugated to PEG 6-DM1. We generated immunoconjugates with low (nimotuzumab-PEG 6-DM1-Low) and high (nimotuzumab-PEG 6-DM1-High) drug-to-antibody ratios. The drug-to-antibody of nimotuzumab-PEG 6-DM1-Low and nimotuzumab-PEG 6-DM1-High was 3.5 and 7.3, respectively. Quality control was performed using ultraviolet spectrophotometry, size-exclusion high-performance liquid chromatography, bioanalyzer, biolayer interferometry, and flow cytometry in EGFR-positive DLD-1 cells. These immunoconjugates were conjugated with DOTA and radiolabeled with 111 In. The in vitro binding and internalization rates of 111 In-nimotuzumab, 111 In-nimotuzumab-PEG 6-DM1-Low, and 111 In-nimotuzumab-PEG 6-DM1-High were characterized. Furthermore, the pharmacokinetics, biodistribution, and imaging characteristics were evaluated in normal and DLD-1 tumor-bearing mice. Results: Flow cytometry and biolayer interferometry showed a trend toward decreasing EGFR affinity with increasing number of PEG 6-DM1 on the antibody. Despite the lower overall cellular binding of the PEG 6-DM1 radioimmunoconjugates, internalization was higher for PEG 6-DM1 ADCs than for the non-PEGylated ADC in the following order: 111 In-nimotuzumab-PEG 6-DM1-High. 111 Innimotuzumab-PEG 6-DM1-Low. 111 In-nimotuzumab. Nuclear uptake of 111 In-nimotuzumab-PEG 6-DM1-High was 4.4-fold higher than 111 In-nimotuzumab. Pharmacokinetics and biodistribution showed that 111 In-nimotuzumab-PEG 6-DM1-High had the slowest blood and whole-body clearance rate. Uptake in DLD-1 tumors of 111 In-nimotuzumab was similar to 111 In-nimotuzumab-PEG 6-DM1-Low but was significantly higher than for 111 In-nimotuzumab-PEG 6-DM1-High. Tumor-to-background ratios for 111 In-nimotuzumab and 111 Innimotuzumab-PEG 6-DM1-Low were higher than for 111 In-nimotuzumab-PEG 6-DM1-High. Conclusion: The results show that conjugation of multiple PEG 6-DM1 reduces the affinity for EGFR in vitro. However, the reduced affinity is counteracted by the high internalization rate of constructs with PEG 6-DM1 ADCs in vitro. The decreased affinity resulted in low tumor uptake of 111 In-nimotuzumab-PEG 6-DM1-High, with a slow overall whole-body clearance rate. These data provide insights for evaluating the pharmacokinetics and normal-tissue toxicity and in determining dosing rate of PEGylated ADCs.
Journal of medicinal chemistry, Jan 23, 2016
The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) plays an impor... more The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) plays an important role in various pathologies including pulmonary arterial hypertension and cardiomyopathy. PDE5 represents an important therapeutic and/or prognostic target, but noninvasive assessment of PDE5 expression is lacking. The purpose of this study was to develop and evaluate pyridopyrazinone derivatives labeled with carbon-11 or fluorine-18 as PDE5-specific PET tracers. In biodistribution studies, highest PDE5-specific retention was observed for [(11)C]-12 and [(18)F]-17 in the lungs of wild-type mice and in the myocardium of transgenic mice with cardiomyocyte-specific PDE5 overexpression at 30 min postinjection. In vivo dynamic microPET images in rats revealed that both tracers crossed the blood-brain barrier but brain retention was not PDE5-specific. Both [(11)C]-12 and [(18)F]-17 showed specific binding to PDE5 in myocardium of transgenic mice; however [(18)F]-17 showed significantly hi...
Society of Nuclear Medicine Annual Meeting Abstracts, May 1, 2013
EJNMMI Research, 2013
Background To date, few PET tracers for in vivo labeling of red blood cells (RBCs) are available.... more Background To date, few PET tracers for in vivo labeling of red blood cells (RBCs) are available. In this study, we report the radiosynthesis and in vitro and in vivo evaluation of 11C and 18F sulfonamide derivatives targeting carbonic anhydrase II (CA II), a metallo-enzyme expressed in RBCs, as potential blood pool tracers. A proof-of-concept in vivo imaging study was performed to demonstrate the feasibility to assess cardiac function and volumes using electrocardiogram (ECG)-gated positron emission tomography (PET) acquisition in comparison with cine magnetic resonance imaging (cMRI) in rats and a pig model of myocardial infarction. Methods The inhibition constants (K i) of CA II were determined in vitro for the different compounds by assaying CA-catalyzed CO2 hydration activity. Binding to human RBCs was estimated after in vitro incubation of the compounds with whole blood. Biodistribution studies were performed to evaluate tracer kinetics in NMRI mice. ECG-gated PET acquisition ...
Nuclear Medicine and Biology, 2014
The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) is considered ... more The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) is considered to play an important role in various etiologies such as pulmonary arterial hypertension (PAH) and chronic heart failure. This PDE5 modulation represents an important prognostic and/or therapeutic target; however, there is currently no method to non-invasively evaluate the PDE5 expression levels in vivo. Radiolabeled tracers were prepared by N-alkylation of the corresponding precursors with [(11)C]methyl trifluoromethanesulfonate ([(11)C]CH3OTf) or 2-[(18)F]fluoroethyl trifluoromethanesulfonate ([(18)F]FEtOTf). Biodistribution of radiolabeled tracers was studied in NMRI mice and their specific binding to PDE5 was investigated by comparing their lung retention as the enzyme is abundantly expressed in this organ. The overall radiochemical yields ranged between 24% and 60% for labeled radiotracers with radiochemical purity of>99%. The highest retention in the lungs at 30min post injection was observed for vardenafil derivatives [(11)C]-7 and [(18)F]-11 and the retention of the ethoxyethyl pyrazolopyrimidine derivative [(11)C]-37 was moderate. The other investigated compounds [(11)C]-8, [(11)C]-14, [(11)C]-21 and [(11)C]-33 showed lower retention in lungs in agreement with their lower in-vitro affinity for PDE5. Among the different radiolabeled PDE5 inhibitors evaluated in this study, the vardenafil derivatives [(11)C]-7 and [(18)F]-11 are found to be promising tracers for in vivo visualization of PDE5.
Nuclear Medicine Communications, 2010
Objectives 68 Ga-Dotatoc has become the PET radiopharmaceutical of choice for the diagnosis and t... more Objectives 68 Ga-Dotatoc has become the PET radiopharmaceutical of choice for the diagnosis and treatment follow-up of neuroendocrine tumours. 68 Ga-Dotatoc is prepared on-site through a so-called magisterial preparation. The use of an appropriate buffer during the radiolabelling step is essential to maximize the labelling yield and the specific activity. Such a buffer should be nontoxic, able to buffer in the pH range of 3.5-5.0, not compete with gallium ions and preferentially have a weak metal complexing capacity to avoid the formation of colloidal gallium. In addition, the buffer should be allowed for human use. In view of the high radiation dose to the operator when manually handling 68 Ga, especially to the extremities, we also tested the buffers in a semi-automated system. Methods HEPES, acetate, succinate, Tris, glutamate, lactate, oxalate and tartrate were tested as potential buffers in the manual radiosynthesis of 68 Ga-Dotatoc. Temperature, heating time and substrate concentration were optimized. Results Buffers based on HEPES, acetate and succinate were found to be the most appropriate. Optimal labelling yields were achieved with a 5-min heating time for the manual synthesis and 8 min for a semi-automated system, whereas the optimal amount of Dotatoc was 30 and 40 lg, respectively. Conclusion Although the use of HEPES, acetate and succinate as buffering substances yielded comparable results, only acetate is currently recognized as a substance for pharmaceutical use and also for human use. Therefore, acetate buffer should be used for 68 Ga-Dotatoc synthesis. The semi-automated system allowed for a shorter radiosynthesis time, thereby increasing the overall yield. Nucl Med Commun 31:753-758
Journal of Labelled Compounds and Radiopharmaceuticals, 2011
Journal of Labelled Compounds and Radiopharmaceuticals, 2011
The research work would not have been possible without the collaboration between different depart... more The research work would not have been possible without the collaboration between different departments: Department of Imaging and Pathology (KU Leuven) and Nuclear Medicine (UZ Leuven) for production of radiolabeled compounds (from radionuclide production to formulation and quality control), Nuclear Medicine and Molecular Imaging (MoSAIC, KU Leuven) for animal experiments, Department of Cardiovascular Sciences (KU Leuven) for providing transgenic mice, pig for PET study, TAC and LAD mice and their expert advice on cardiac hypertrophy, Discovery Sciences (Janssen Pharmaceutica) for determination of in vitro phosphodiesterase inhibitory activity of compounds discussed in this dissertation. I have to extend my acknowledgement and appreciation for aforementioned departments and organizations for their contribution to the success of this research work and the resulting manuscript. We (Nuclear Medicine, UZ Leuven and Radiopharmacy, KU Leuven) are truly two big and happy families. The collaboration is an amazing experience and an example to others. I would like to take this opportunity to express my gratitude to the members of this big family: Prof. Koen Van Laere (Head of Nuclear Medicine, UZ Leuven), Tjibbe De Groot and Marva Bex you were always willing to help me during radioisotope production despite the hectic situation during working hours. Tjibbe you were always forthright spoken and I like that character of yours! Bert Vanbilloen (thanks for the supervision during my first year in post graduate studies), Stef Verschoren (for the nice after-work hours :), Christelle Terwinghe; Nathalie Devolder; Mireille Heroes; Anja Wilberts; Mieke Steukers; Magdalena Sojka; Kim Serdons, Kim Deliege; Katrien Seré and Annemie Morel: thank you all for the help and nice time. Jan Cleynhens, thank you for your great work and help on the organic synthesis of molecules. Your presence in the lab made a big difference both scientifically and socially and you were the spice of the lab! Sofie thank you for valuable and practical input. Ivan, Julie and Jana: thank you for your technical assistance during animal experiments. Maarten, thank you for your help on microPET image processing and also for the great time we had while on lab trip (Parma, Amsterdam...). Ahamed, thank you for your help on organic synthesis and NMR elucidation. I greatly appreciate for forwarding links to job postings and also for little chitchats we had.
Molecular Pharmaceutics, 2019
Insulin growth factor receptor (IGF-1R) is overexpressed in many cancers of epithelial origin whe... more Insulin growth factor receptor (IGF-1R) is overexpressed in many cancers of epithelial origin where it confers enhance proliferation and resistance to therapies targeted at other receptors. Anti-IGF-1R monoclonal antibodies have not demonstrated significant improvements in patient outcomes in clinical trials. Humanized monoclonal antibody cixutumumab (IMC-A12) binds to IGF-1R with low nM affinity. In this study cixutumumab was conjugated with p-SCN-Bn-DOTA and radiolabeled with 111 In or 225 Ac for imaging or radiotherapy using a triple negative breast cancer (TNBC) model SUM149PT. The antibody conjugate showed low nM affinity to IGF-1R which was not affected by conjugation and radiolabeling procedures. Cixutumumab immunoconjugates was effectively internalized in SUM149PT and was cytotoxic to the cells with an EC 50 of 225 Ac-cixutumumab (0.02 nM) that was almost 5000-fold less than unlabeled cixutumumab (95.2 nM). MicroSPECT imaging of SUM149PT xenograft showed the highest tumor uptake occurred at 48 h post injection and was 9.9 ± 0.5 % injected activity per gram (%IA/cc). In radiotherapy studies, we evaluated the effect of specific activity of 225 Accixutumumab on efficacy following a tail vein injection of two doses (day 0 and 10) of the investigation agent or controls. Cixutumumab (2.5 mg/kg) prolonged the survival of SUM149PT tumor bearing mice with a median survival of 87 days compared to PBS control group (median survival of 62 days). Median survival of high specific activity 225 Ac-cixutumumab (8 kBq/µg, 225 nCi, 0.05 mg/kg) was 103.5 days compared to 122 days for low specific activity 225 Accixutumumab (0.15 kBq/µg, 225 nCi, 2.5 mg/kg). Additionally, low specific activity radioimmunoconjugate led to complete tumor remission in 2/6 mice. The data suggest that efficacy of cixutumumab can be enhanced by radiolabeling with 225 Ac at a low specific activity.
Journal of Nuclear Medicine, 2019
Epidermal growth factor receptor I (EGFR) is overexpressed in most cancers of epithelial origin. ... more Epidermal growth factor receptor I (EGFR) is overexpressed in most cancers of epithelial origin. Antibody drug conjugates (ADCs) with PEGylated-maytansine (PEG-DM1) show promise in vitro and in vivo. However, in vivo biodistribution data for ADCs with PEG-DM1 have not been reported. Development of methods to understand the real-time in vivo behavior of these ADCs is needed to move these compounds to the clinic. Methods: Here we have used noninvasive small-animal SPECT/CT imaging and ex vivo biodistribution to understand the in vivo behavior of PEG 6-DM1 ADCs. We developed nimotuzumab ADCs conjugated to PEG 6-DM1. We generated immunoconjugates with low (nimotuzumab-PEG 6-DM1-Low) and high (nimotuzumab-PEG 6-DM1-High) drug-to-antibody ratios. The drug-to-antibody of nimotuzumab-PEG 6-DM1-Low and nimotuzumab-PEG 6-DM1-High was 3.5 and 7.3, respectively. Quality control was performed using ultraviolet spectrophotometry, size-exclusion high-performance liquid chromatography, bioanalyzer, biolayer interferometry, and flow cytometry in EGFR-positive DLD-1 cells. These immunoconjugates were conjugated with DOTA and radiolabeled with 111 In. The in vitro binding and internalization rates of 111 In-nimotuzumab, 111 In-nimotuzumab-PEG 6-DM1-Low, and 111 In-nimotuzumab-PEG 6-DM1-High were characterized. Furthermore, the pharmacokinetics, biodistribution, and imaging characteristics were evaluated in normal and DLD-1 tumor-bearing mice. Results: Flow cytometry and biolayer interferometry showed a trend toward decreasing EGFR affinity with increasing number of PEG 6-DM1 on the antibody. Despite the lower overall cellular binding of the PEG 6-DM1 radioimmunoconjugates, internalization was higher for PEG 6-DM1 ADCs than for the non-PEGylated ADC in the following order: 111 In-nimotuzumab-PEG 6-DM1-High. 111 Innimotuzumab-PEG 6-DM1-Low. 111 In-nimotuzumab. Nuclear uptake of 111 In-nimotuzumab-PEG 6-DM1-High was 4.4-fold higher than 111 In-nimotuzumab. Pharmacokinetics and biodistribution showed that 111 In-nimotuzumab-PEG 6-DM1-High had the slowest blood and whole-body clearance rate. Uptake in DLD-1 tumors of 111 In-nimotuzumab was similar to 111 In-nimotuzumab-PEG 6-DM1-Low but was significantly higher than for 111 In-nimotuzumab-PEG 6-DM1-High. Tumor-to-background ratios for 111 In-nimotuzumab and 111 Innimotuzumab-PEG 6-DM1-Low were higher than for 111 In-nimotuzumab-PEG 6-DM1-High. Conclusion: The results show that conjugation of multiple PEG 6-DM1 reduces the affinity for EGFR in vitro. However, the reduced affinity is counteracted by the high internalization rate of constructs with PEG 6-DM1 ADCs in vitro. The decreased affinity resulted in low tumor uptake of 111 In-nimotuzumab-PEG 6-DM1-High, with a slow overall whole-body clearance rate. These data provide insights for evaluating the pharmacokinetics and normal-tissue toxicity and in determining dosing rate of PEGylated ADCs.
Journal of medicinal chemistry, Jan 23, 2016
The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) plays an impor... more The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) plays an important role in various pathologies including pulmonary arterial hypertension and cardiomyopathy. PDE5 represents an important therapeutic and/or prognostic target, but noninvasive assessment of PDE5 expression is lacking. The purpose of this study was to develop and evaluate pyridopyrazinone derivatives labeled with carbon-11 or fluorine-18 as PDE5-specific PET tracers. In biodistribution studies, highest PDE5-specific retention was observed for [(11)C]-12 and [(18)F]-17 in the lungs of wild-type mice and in the myocardium of transgenic mice with cardiomyocyte-specific PDE5 overexpression at 30 min postinjection. In vivo dynamic microPET images in rats revealed that both tracers crossed the blood-brain barrier but brain retention was not PDE5-specific. Both [(11)C]-12 and [(18)F]-17 showed specific binding to PDE5 in myocardium of transgenic mice; however [(18)F]-17 showed significantly hi...
Society of Nuclear Medicine Annual Meeting Abstracts, May 1, 2013
EJNMMI Research, 2013
Background To date, few PET tracers for in vivo labeling of red blood cells (RBCs) are available.... more Background To date, few PET tracers for in vivo labeling of red blood cells (RBCs) are available. In this study, we report the radiosynthesis and in vitro and in vivo evaluation of 11C and 18F sulfonamide derivatives targeting carbonic anhydrase II (CA II), a metallo-enzyme expressed in RBCs, as potential blood pool tracers. A proof-of-concept in vivo imaging study was performed to demonstrate the feasibility to assess cardiac function and volumes using electrocardiogram (ECG)-gated positron emission tomography (PET) acquisition in comparison with cine magnetic resonance imaging (cMRI) in rats and a pig model of myocardial infarction. Methods The inhibition constants (K i) of CA II were determined in vitro for the different compounds by assaying CA-catalyzed CO2 hydration activity. Binding to human RBCs was estimated after in vitro incubation of the compounds with whole blood. Biodistribution studies were performed to evaluate tracer kinetics in NMRI mice. ECG-gated PET acquisition ...
Nuclear Medicine and Biology, 2014
The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) is considered ... more The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) is considered to play an important role in various etiologies such as pulmonary arterial hypertension (PAH) and chronic heart failure. This PDE5 modulation represents an important prognostic and/or therapeutic target; however, there is currently no method to non-invasively evaluate the PDE5 expression levels in vivo. Radiolabeled tracers were prepared by N-alkylation of the corresponding precursors with [(11)C]methyl trifluoromethanesulfonate ([(11)C]CH3OTf) or 2-[(18)F]fluoroethyl trifluoromethanesulfonate ([(18)F]FEtOTf). Biodistribution of radiolabeled tracers was studied in NMRI mice and their specific binding to PDE5 was investigated by comparing their lung retention as the enzyme is abundantly expressed in this organ. The overall radiochemical yields ranged between 24% and 60% for labeled radiotracers with radiochemical purity of>99%. The highest retention in the lungs at 30min post injection was observed for vardenafil derivatives [(11)C]-7 and [(18)F]-11 and the retention of the ethoxyethyl pyrazolopyrimidine derivative [(11)C]-37 was moderate. The other investigated compounds [(11)C]-8, [(11)C]-14, [(11)C]-21 and [(11)C]-33 showed lower retention in lungs in agreement with their lower in-vitro affinity for PDE5. Among the different radiolabeled PDE5 inhibitors evaluated in this study, the vardenafil derivatives [(11)C]-7 and [(18)F]-11 are found to be promising tracers for in vivo visualization of PDE5.
Nuclear Medicine Communications, 2010
Objectives 68 Ga-Dotatoc has become the PET radiopharmaceutical of choice for the diagnosis and t... more Objectives 68 Ga-Dotatoc has become the PET radiopharmaceutical of choice for the diagnosis and treatment follow-up of neuroendocrine tumours. 68 Ga-Dotatoc is prepared on-site through a so-called magisterial preparation. The use of an appropriate buffer during the radiolabelling step is essential to maximize the labelling yield and the specific activity. Such a buffer should be nontoxic, able to buffer in the pH range of 3.5-5.0, not compete with gallium ions and preferentially have a weak metal complexing capacity to avoid the formation of colloidal gallium. In addition, the buffer should be allowed for human use. In view of the high radiation dose to the operator when manually handling 68 Ga, especially to the extremities, we also tested the buffers in a semi-automated system. Methods HEPES, acetate, succinate, Tris, glutamate, lactate, oxalate and tartrate were tested as potential buffers in the manual radiosynthesis of 68 Ga-Dotatoc. Temperature, heating time and substrate concentration were optimized. Results Buffers based on HEPES, acetate and succinate were found to be the most appropriate. Optimal labelling yields were achieved with a 5-min heating time for the manual synthesis and 8 min for a semi-automated system, whereas the optimal amount of Dotatoc was 30 and 40 lg, respectively. Conclusion Although the use of HEPES, acetate and succinate as buffering substances yielded comparable results, only acetate is currently recognized as a substance for pharmaceutical use and also for human use. Therefore, acetate buffer should be used for 68 Ga-Dotatoc synthesis. The semi-automated system allowed for a shorter radiosynthesis time, thereby increasing the overall yield. Nucl Med Commun 31:753-758