Preparation and Quality Control of (68)Ga-Citrate for PET Applications.

OBJECTIVES: In nuclear medicine studies, gallium-68 ((8)Ga) citrate has been recently known as a suitable infection agent in positron emission tomography (PET). In this study, by applying an in-house produced (68)Ge/(68)Ga generator, a simple technique for the synthesis and quality control of (68)Ga-citrate was introduced; followed by preliminary animal studies. METHODS: (68)GaCl3 eluted from the generator was studied in terms of quality control factors including radiochemical purity (assessed by HPLC and RTLC), chemical purity (assessed by ICP-EOS), radionuclide purity (evaluated by HPGe), and breakthrough. (68)Ga-citrate was prepared from eluted (68)GaCl3 and sodium citrate under various reaction conditions. Stability of the complex was evaluated in human serum for 2 h at 370C, followed by biodistribution studies in rats for 120 min. RESULTS: (68)Ga-citrate was prepared with acceptable radiochemical purity (>97 ITLC and >98% HPLC), specific activity (4-6 GBq/mM), chemical purity (Sn, Fe<0.3 ppm and Zn<0.2 ppm) within 15 min at 500C. The biodistribution of (68)Ga-citrate was consistent with former reports up to 120 minutes. CONCLUSION: This study demonstrated the possible in-house preparation and quality control of (68)Ga-citrate, using a commercially available (68)Ge/(68)Ga generator for PET imaging throughout the country.

Production and Quality Control of [(67)Ga]-DOTA-trastuzumab for Radioimmunoscintigraphy.

Breast cancer radioimmunoscintigraphy targeting HER2/neu expression is a growing field of work in nuclear medicine research. In this study, trastuzumab was successively labeled with [(67)Ga] GaCl3 after conjugation with DOTA-NHS-ester. The conjugates were purified by molecular filtration, the average number of DOTA conjugated per mAb was calculated and total concentration was determined by spectrophotometric method. DOTA-Trastuzumab was labeled with (67)Ga. Radiochemical purity, integrity of protein after radiolabeling and stability of (67)Ga-DOTA-Trastuzumab were determined followed by biodistribution studies in wild-type rats (30 ± 5.5 µCi, 2, 4 and 24 h p.i.). The radioimmunoconjugate was prepared with a radiochemical purity of higher than 95% (RTLC). The average chelate to antibody ratio (c/a) for the conjugate used in this study was 5.8:1. The final compound was stable in presence of PBS at 37ºC and room temperature. The sample was showed to have similar patterns of migration in the gel electrophoresis similar to the native protein. The accumulation of the radiolabeled antibody in liver, spleen, kidney, heart and other tissues demonstrates. (67)Ga-DOTA-Trastuzumab was prepared as a surrogate for important clinically applicable radionuclides used in SPECT and PET including In-111 and Cu-64 as a model of radiolabeling. It is also a potential compound for molecular imaging of SPECT for diagnosis and treatment studies and follow-up of HER2 expression in oncology.

Development of a (68)Ga-Fluorinated Porphyrin Complex as a Possible PET Imaging Agent.

AIM: Due to the interesting pharmacologic properties of porphyrins, the idea of developing a possible tumor imaging agent using PET by incorporating (68)Ga into a suitable porphyrin ligand was investigated. METHODS: (68)Ga-labeled 5,10,15,20-tetrakis(pentafluoro-13 phenyl) porphyrin ((68)Ga-TFPP) was prepared using freshly eluted [(68)Ga]GaCl3 obtained from a 68Ge/68Ga generator developed in-house and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H2TFPP) for 60 min at 100°C. RESULTS: The complex was prepared with high radiochemical purity (>99% ITLC, >99% HPLC, specific activity: 13-14 GBq/mmol). Stability of the complex was checked in the final formulation and in human serum for 5 h. The partition coefficient was calculated for the compound (log P = 0.62). The biodistribution of the labeled compound in vital organs of Swiss mice bearing fibrosarcoma tumors was studied using scarification studies and SPECT imaging up to 1 h. The complex was mostly washed out from the circulation through kidneys and liver. The tumor-to-muscle ratio 1 h post injection was 5.13. CONCLUSION: The radiolabeled porphyrin complex demonstrated potential for further imaging studies in other tumor models.

Development of ga-67 maltolate complex as an imaging agent.

Due to the antitumor activity of Gallium MAL complex, as well as recent findings on new targeted biomolecules in malignant cells through this complex, the development of radiolabeled gallium complex for future imaging studies was targeted. Ga-67 labeled 3-hydroxy-2-methyl-4H-pyran-4-onate (Ga-67 MAL) was prepared using freshly prepared Ga-67 chloride and 3-hydroxy-2-methyl-4H-pyran-4-onate in a sodium salt form in 25 min at 40° C. The stability of the complex was checked in final formulation and human serum for 24 h followed by the administration in Swiss mice for biodistribution studies. The complex was prepared in high radiochemical purity (> 97% ITLC, > 98% HPLC) and specific activity of 13-14 GBq/mmol and was stable in the presence of serum for 48 h. The partition coefficient was calculated for the compound (log p = 0.40). A detailed comparative pharmacokinetic study was performed for Ga-67 cation and Ga-67-MAL. The complex is more rapidly washed out from the circulation through kidneys and liver compared to Ga-67 cation and can be an interesting tumor imaging agent due to the fact that the cold compound is undergoing clinical trials as a safe and potential therapeutic agent for cancer.

Preparation and evaluation of [(61)Cu]-thiophene-2-aldehyde thiosemicarbazone for PET studies.

BACKGROUND: [(61)Cu]Thiophene-2-aldehyde thiosemicarbazone ([(61)Cu]TATS) (4) was prepared according to an analogy of carrier copper compound with antitumor activity, for eventual use in PET. MATERIAL AND METHODS: [(61)Cu]TATS was prepared using copper-61 acetate and in-house made ligand (TATS) in one step. (61)Cu was produced via the (nat)Zn(p,x) (61)Cu nuclear reaction (180 mircoA, 22 MeV, 3.2 h) followed by a two-step chromatography method (222 GBq of (61)Cu(2+)). [(61)Cu]TATS preparation was optimized for reaction conditions (buffer concentration and temperature). The tracer was finally administered to normal rats for biodistribution studies. RESULTS: Total radiolabelling of the tracer took 30 minutes with a radiochemical purity of more than 90% (using HPLC and RTLC) and specific activity of about 250-300 Ci/mmol. The complex was stable in the presence of human serum for an hour. The biodistribution of copper cation and the tracer was checked in wild-type rats for up to 2 hours with significant spleen and lung uptake of the tracer. CONCLUSIONS: The production of (61)Cu via the (nat)Zn(p,x) (61)Cu is an efficient and reproducible method with high specific activity leading to the production and preliminary evaluation of [(61,)Cu]TATS, a potential PET tracer, was reported.

Evaluation of [67Ga]-insulin for insulin receptor imaging.

BACKGROUND: Radiolabelled human recombinant insulin can be used for the imaging of insulin receptors in some tumours where FDG has natural uptake and diminishes the value of its imaging. MATERIAL AND METHODS: Insulin was successively labelled with [(67)Ga]-gallium chloride after conjugation with freshly prepared cyclic DTPA-dianhydride (HPLC radiochemical purity assay > 96%) followed by biodistribution studies in normal rats, white blood cell labelling and preliminary SPECT studies. RESULTS: In vitro studies demonstrated the retention of radiolabelled insulin receptor affinity using freshly prepared human white blood cells at different blood sugar conditions. Preliminary in vivo studies in a normal rat model was performed to determine the biodistribution of the radioimmunoconjugate at up to 44 h. SPECT images revealed high uptake of the liver. CONCLUSION: Radiolabelled insulin is stable enough to be used in biological studies in order to image insulin receptors in diabetic conditions as well as possible tumour imaging applications. The data was consistent with other radiolabelled insulin studies.