Preparation and quality control of radiolabeled streptokinase for thrombosis imaging

In order to diagnose the site of thrombi, radiolabeled streptokinase can be prepared. The radiolabeled compound can be used in imaging of thrombi in many cardiovascular diseases. Streptokinase was successively labeled with [[67] Ga]-gallium chloride using cyclic DTPA-dianhydride. The conjugation with DTPA was optimized for concentration, time and temperature followed by size exclusion chromatography using G-50 Sephadex. The radiochemical purity of the tracer was checked using HPLC and ITLC methods. The biodistribution studies were performed in normal rats up to 167 h using tissue counting and preliminary SPECT studies up to 2h. The radiolabeled enzyme was prepared in 60 minutes after incubation at room temperature, with the radiochemical purity of >95% [HPLC] and >99% [ITLC] methods. The radioactivity was accumulated in lung, intestine and liver as shown by scarification and SPECT [Single Photon Emission Computer Tomography] methods. Radiolabeled Streptokinase was prepared in suitable radiochemical purity and its biodistribution is comparable to other radiolabeled proteins. Further studies are required to investigate the imaging properties of the tracer in appropriate animal mode

Preparation and biodistribution of [67Ga]-labeledoxytocin for SPECT purposes

Oxytocin [OT] is a paracrine hormone with various biological activities and many sex organs in both sexes, as well as many tumor cells have shown to have related receptors. In this study the development of a receptor imaging tracer for possible tumor imaging has been described. OT was successively labeled with [67Ga]-gallium chloride after conjugation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 ml of a OT pharmaceutical solution [2 mg/ml, in phosphate buffer, pH=8] to a glass tube pre-coated with DTPA-dianhydride [0.02 mg] at 25°C with continuous mild stirring for 30 min. Radiochemical purity [RCP] of the labeled compound was determined, using RTLC and ITLC followed by stability tests and animal biodistribution studies. Radiolabeling took about 60 minutes with a RCP higher than 98% at optimized conditions [specific activity = 1000 Ci/mM, labeling efficiency 80%]. The stability of the tracer at room temperature was significant, up to an hour. Preliminary in vivo studies in normal female rat model showed ovary/blood and ovary/muscle ratio uptake of the tracer in 60 minutes to be 4.53 and 9.18, respectively. The result was consistent with the reported OT receptor distribution in normal female mammals. The radiolabeled oxytocin, prepared in this study, was a possible fast acting tracer for OT receptor imaging; studies however, more studies are required to determine the best imaging conditions especially in larger mammal animals

Development of [201T1][III] oxinate complex for in vitro cell labeling

The incorporation of thallium-201 into 8-hydroxyquinoline was targeted for cell labeling due to interesting physical properties and wide availability of this nuclide as a single photon emission computed tomography [SPECT] radionuclide. Thallium-201 [T[1/2]=3.04 d] in Tl[+] form was converted to Tl[3+] cation in presence of O[3]/6M HCl and di-isopropyl ether, controlled by radiothin layer chromatography [RTLC] /gel electrophoresis methods. The final evaporated activity reacted with ethanolic 8-hydroxy-quinoline [oxine] solution in normal saline to yield [[201]Tl][III] oxinate at room temperature after 0.5 h, followed by solid phase extraction/purification using C18 Sep-Pak column and partition coefficient determination for water/lipid solubility. In vitro red blood cell [RBC] labeling was also performed. A radiochemical yield of more than 95% was obtained. Radiochemical purity of 92% was obtained using RTLC [>90% using HPLC] with specific activity of about 820 GBq/mmol. The tracer was stable in the final product and in presence of human serum at 37°C up to 6h. The partition coefficient of lopP=5.5 was obtained. The labeled compound was used in RBC labeling. The cell uptake ratio was 0.47 after 240 min. [[201]Tl][III] oxinate used in this study is a widely available agent for use in RBC labeling studies in biology, medicine and various other research areas