K. Durkan

Design and synthesis of 99mTc-citro-folate for use as a tumor-targeted radiopharmaceutical

Folate conjugates exhibit high affinity for folate receptor (FR) positive cells and tissues, such as those in tumors, making them attractive candidates and of interest in diagnostic tumor imaging. The aim of study was to synthesize a novel radiopharmaceutical based folate conjugate, (99m)Tc-citro-folate, and to evaluate its efficiency as a targeted agent for imaging tumors that over express FR. TLC, HPLC (1)H NMR and LC-MS/MS methods were used to check and confirm the synthesized citro-folate. Citro-folate was labeled with Tc-99m with high labeling efficiency (97±1.0%). Biodistribution of the radiolabeled conjugate (99m)Tc-citro-folate was investigated in vivo using two groups of rats: FR saturated and unsaturated. These experiments showed high uptake of (99m)Tc-citro-folate in FR rich tissues and demonstrated its sensitivity and specificity in imaging ovary and uterus. Based on the demonstrated good radiolabeling and biodistribution properties, the compound (99m)Tc-citro-folate may potentially be used as a radiopharmaceutical agent for imaging the FR-positive tumors.

In vitro evaluation, biodistribution in rats of radiolabeled raloxifene.

Raloxifene is a selective estrogen receptor modulator that produces both estrogen agonistic effects on bone and lipid metabolism and estrogen-antagonistic effects on uterine endometrium and breast tissue. In the present study, raloxifene was labeled with I-131 by iodogen method and investigated for its radiopharmaceutical potential. Radiolabeling yield is 91+/-0.7%, as determined by radio thin layer chromatography (RTLC). Results of in vitro study indicated (131)I-raloxifene has high stability (4h) in serum. Biodistribution study was carried out with Albino wistar female rats. The result has shown that the radioiodinated raloxifene has higher uptake in uterus than breast and ovarian.

In vitro evaluation of 99mTc-EDDA/tricine-HYNIC-Q-Litorin in gastrin-releasing peptide receptor positive tumor cell lines

Abstract Bombesin and its derivatives exhibit a high affinity for gastrin-releasing peptide receptor (GRPr), which is over-expressed in a variety of human cancers (prostate, pancreatic, lung, etc.). The aim of this study was to investigate the in vitro potential of the hydrazinonicotinamide (HYNIC)-Q-Litorin. 99mTc labeling was performed by using different co-ligands: tricine and ethylenediamine diacetic acid (EDDA). The radiochemical stability of radiolabeled peptide conjugates was checked at room temperature and in cysteine solution up to 24 h. The in vitro cell uptake of 99mTc-EDDA-HYNIC-Q-Litorin and 99mTc-tricine-HYNIC-Q-Litorin were evaluated on pancreatic tumor and control cell lines. Optimum specific activity and incubation time were determined for all the cell lines. The results showed that the cell uptake of the radiolabeled peptide conjugates in tumor cell lines were higher than in the control cell line. The findings of this study indicated the need for further development of in vivo study as a radiopharmaceutical for pancreatic tumor imaging.

Technetium-99m labeled Mebendazole and biodistribution in experimentally Trichinella spiralis-infected rats

The aim of this study was to localize the biodistribution of Technetium-99m (99mTc) Mebendazole in experimentally Trichinella spiralis (T. spiralis)-infected rats. Localizing and distinguishing the “T. spiralis” in body sites are very important and life saving processes. Scintigraphic detections may help to determine the sites of trichinellosis infection. Twelve healthy female Wistar rats were infected via oral administration of infected muscle containing 750 to 1000 larvae. In this study, the antibiotic was labeled with Tc-99m, and 99mTc-Mebendazole was assessed as an infection imaging agent in a rat model. 99mTc-mebendazole was examined for localizing the normal, and inflamed with trichinellosis in rat muscle tissues after administrated 99mTc-mebendazole via intravenous (IV) or oral gastric catheter, and also for differentiating them from each other. 99mTc labeled mebendazole was retained in infectious areas. It was established that 99mTc-mebendazole which was administrated via IV route has high organ restrain level. It was observed that 99mTc-mebendazole uptake was high in tongue and diaphragm muscles of T. spiralis-infected rats after administration of radiolabeled mebendazole via either oral or IV routes. This study may be viewed as a basement of future studies on diagnosis of T. spiralis infection.

Biodistribution of 99m technetium- labeled creatinine in healthy rats

The distribution of creatinine, one of the toxic guanidine compounds, in various tissues has not been studied in detail by using radiolabeled creatinine. Our objective was to investigate the biodistribution of creatinine labeled with 99m technetium (99mTc) by the stannous (II) chloride method in healthy male Wistar rats. Quality controls were carried out by radio thin layer chromatography, high-performance liquid chromatography, and paper electrophoresis. The labeling yield was 85 +/- 2% under optimum conditions (pH 7 and 100 microg stannous chloride). Rats (N = 12) were injected intravenously with 99mTc-creatinine and their blood and visceral organs were evaluated for 99mTc-creatinine uptake as percent of the injected dose per gram wet weight of each tissue (%ID/g). The lowest amount of uptake was detected in the brain and testis. When the rate of uptake was evaluated, only the kidney showed increasing rates of uptake of 99mTc-creatinine throughout the study. Kidneys showed the highest amount of uptake throughout the study (P < 0.001 compared to all other organs), followed by liver, spleen and lung tissue.

Preparation of 131I-Pyrimethamine and evaluation for scintigraphy of experimentally Toxoplasma gondii-infected rats

We aimed to assess the ability of 131I-Pyrimethamine scintigraphy to detect the lesions of Toxoplasma gondii infection. An experimental model of toxoplasmosis was developed. The presence of toxoplasmosis was confirmed 60 days after implantation. Pyrimethamine was radioiodinated with I-131. The radioligand was validated by the requisite quality control tests to check its radiolabeling efficiency, in vitro stability and radiochemical purity etc. 131I-Pyrimethamine (specific activity: 7.08 MBq/µmol) was injected intravenously into the tail vein of the control and infected rats. Static whole body images of the rats were acquired under the gamma camera at 5 min, 45 min, 2 h, 6 h, and 24 h following the intravenous administration of the radioactivity (3.7 MBq/rat). Then the scintigraphic data were analyzed both visually and semiquantitatively. Regions of interest (ROIs) were drawn over the organs (thyroid, stomach, liver, bladder, and soft tissues) to calculate the ratios of the radiotracer in infected vs. control rats. The mean ratio of radiotracer in infected/control rats in the liver and diaphragm was over 1 at 45 min which persisted till 24 h. In conclusion, 131I-Pyrimethamine may be useful agent for diagnosis toxoplasmosis especially involving liver and diaphragm, needs further preclinical validation before being extended for use in clinical applications.

Biodistribution of 99mTc-creatinine in rats with ablation nephropathy.

Creatinine is the anhydride of creatine and is formed by non-enzymatic dehydration of creatine phosphate in muscle [1]. It is not protein-bound in plasma, has a small molecular weight, and is totally cleared by the glomeruli. In addition, it is also cleared by the gastrointestinal system to a smaller extent [2]. Since the daily production and renal excretion of creatinine is constant in healthy mammals, its serum level is fairly stable [3]. Thus, serum creatinine remains the most widely used laboratory test for estimation of renal function both in asymptomatic persons and in patients suspected of having renal disease [2]. Serum creatinine must be interpreted in light of the clinical information such as age, gender, weight, stability of renal function, muscle mass, and degree of catabolism. Serum creatinine concentration rises when more than 50% of renal function has been lost [2]. Although creatinine, as urea, is not generally considered to be an important uremic toxin, it has been shown experimentally that they are both toxic in acutely uremic rats [4]. Moreover, creatinine is one of the guanidine compounds contributing to uremic encephalopathy. The level of guanidine compounds including creatinine increases greatly in serum, cerebrospinal fluid, and brain of uremic patients. Uremic guanidine compounds have excitatory effects on the central nervous system [5]. A radioactive labeled form of creatinine has been used in the past to examine creatinine exchange between mother, fetus and amniotic fluid in rhesus monkeys [6]. However, its distribution at various tissues and the factors affecting this biodistribution has yet not been studied in detail by using radiolabeled creatinine. Recently, we labeled creatinine with Technetium by SnCl2 method [7, 8]. We aimed to compare the biodistribution of Tc-creatinine in healthy rats and in rats with ablation nephropathy. Male Wistar rats underwent either sham operation [9] (Sh, n = 6) or subtotal nephrectomy (Nx, n = 6). After 8 weeks, all were given Tc-creatinine IV. Then three rats at a time in each group were sacrificed at the 2nd and 4th hours. Their blood and visceral organs were obtained and evaluated for specific activity of Tc-creatinine as the percent-injected dose per gram of each tissue (%ID/g). Sh and Nx groups were compared for the relative uptake of Tc-creatinine by their tissues. Statistical analyses were performed by Univariate Analysis of Variance. The level of significance was considered as \0.05. Fatma Yurt Lambrecht, Osman Yılmaz—these authors contributed equally to this work.