Technetium-99m radiolabelled diethylene triamine pentaacetic acid diester and process for the preparation of technetium-99m diethylene triamine penta-acetic acid diester

Abstract: The present invention relates a technetium-99m radiolabelled diethylene triamine pentaacetic acid diester kit for the diagnosis of renal disorders. Accordingly, the present invention provides a technetium-99m radiolabelled diethylene triamine pentaacetic acid diester kit for the diagnosis of renal disorders wherein technetium-99m diethylene triamine pentaacetic acid dimethyl ester has Rf value = zero in silica gel / acetone TLC system and Rf value = 1 in silica gel / acetonitrile water (1:1) TLC system and technecium-99m diethylene triamine pentaacetic acid dimethyl ester movement is of the order of half of the distance as compared to the standard compound (technecium-99m diethylene triamine pentaacetic acid) on conducting paper electrophoresis. The process for the preparation of a technetium-99m radiolabelled diethylene triamine pentaacetic acid diester kit for the diagnosis of renal disorders comprises: (a) Adding appropriate amount of stannous ion to a dilute aqueous solution of diethylene triamine pentaacetic diester prepared by known methods (b) Keeping the resultant solution abtained in step (a) in an evacuated rubber sealed injection vial flushed with nitrogen; (c) lyophilising the said kit and storing the lyophilised product an obtained in step (b) at 4°C; (d) radiolabelling the said lyophilised product with Tc-99m by allowing the kit to attain the room temparature before addition of 99m TcO 4 ; (e) shaking the kit vigorously to obtain the radiolabelled product available for use within a period of an hour.

Description: The present invention relates to a technetium-99m radiolabelled diethylene triamine pentaacetic acid dimethylester kit for the diagnosis of renal disorders. For accurate evaluation of degree of renal disorder estimation rate of transfer of some specified substances such as technetium-99m diethylene triamine pentaacetic acid and iodine-131 orthoiodo-hippurate from blood to urine are to be determinded. These compounds can be eliminated from blood either by glomerular filtration or by renal tubular secretion. In article "Coordination Compounds in Nuclear Medicine" published in magazine CHEMICAL REVIEW, vol. 93, no. 3, May 1993, pp. 1137 - 1156, S. Jurisson describes in general a the use of Technetium-based Radiopharmaceuticals. As a compound 99m Tc-penetat is stated. Such compounds show a very high toxity and can, therefore, hardly be used as radiopharmaceutical. The WO-A86/02005 discloses diester-DTPA derivates labeled with a paramagnetic metal for MRI imaging. Compounds with Te-99 are not described. These contrast agents are versatile and lower homologs with 1-4 carbons in the ester moiety are kidney selective and are therefore used for diagnosis of renal disorders. Due to theester water of hydration, these derivates have a higher paramagnetic effect compared to the free DTPA, as well as high stability and low toxicity. The problem of glomerular versus tubular extraction is not adressed here. Technetium-99m diethylene triamine pentaacetic acid which is widely available and used for above said estimation, but since it is cleared by glomerular filtration, the extraction efficiency is only 20 %. Therefore while using this reagent, a low target to background ratio is produced and in many cases non-diagnostic images are obtained with patients having impaired renal function. Orthoiodo-hippurate labeled either with iodine-131 or with iodine-123 which is also used for the above said estimation, is eliminated mainly by renal tubular secretion and therefore, has a very high extraction efficiency (87 %). This compound is extremely useful for patients with poor renal function. However, iodine-131 not only imparts a high radiation dose to patients but shows a poor spatial resolution, this is due to its non-optimal energy characteristics. On the other hand, iodine-123 has an ideal energy but is very expensive and not available widely. These problems led to the search for an agent which will have similar renal property of orthoiodo-hippurate but labeld with a radionucleide of optimal energy characteristics such as technetium-99m. After a decade of research in this area a compound technetiuum-99m mercaptoacetylglycylglycylglycine was offered for clinical use. However, this compound deviated considerably from the nearly optimal renal properties of iodine-131 orthoiodo-hippurate in the following way: 1. Renal extraction of technetium-99m mercaptoacetylglydylglycylglycine was only 53 % compared to that of iodine-131 orthoiodo-hippurate which was 79 %. 2. High protein binding (77 %) of technetium-99m mercaptoacetylglycylglycylglycine compared to a moderate value (32 %) of iodine-131 orthoiodo-hippurate. 3. Technetium-99m mercaptoacetylglycylglycylglycine is prohibitively expensive and not available in this country. 4. Technetium-99m mercaptoacetylglycylglycylglycine kit needs considerable skill to reconstitute or otherwise it may produce variable results. 5. Unwanted accumulation in hepatobiliary system is observed for technetium-99m mercaptoacetylglycylglycylglycine unlike that of iodine-131 orthoiodo-hippurate. To solve these difficulties we developed a new compound, viz., technetium-99m diethylene triamine pentaacetic acid dimethylester and a process for the preparation of this compound. Accordingly, the present invention provides a technetium-99m radiolabelled diethylene triamine pentaacetic acid dimethylester kit for the diagnosis of renal disorders wherein technetium-99m diethylene triamine pentaacetic acid dimethyl ester has Rf value=zero in silica gel/acetone TLC system and Rf value - 1 in silica gel/acetonitrile water (1:1) TLC system and technecium-99m diethylene pentaacetic acid dimethylester movement is of the order of half of the distance as compared to the standard compound (technecium-99m dithelene triamine pentaacetic acid) on conducting paper electrophoresis. The invention further provides a process for the preparation of a technetium-99m radiolabelled diethylene triamine pentaacetic acid dimethylester kit for the diagnosis of renal disorders which comprises: (a) Adding appropriate amount of stannous ion to a dilute aqueous solution of diethylene triamine pentaacetic acid diester prepared by known methods. (b) Keeping the resultand solution obtained in step (a) in an evacuated rubber sealed injection vial flushed with nitrogen; (c) lyophilising the said kit and storing the lyophilised product as obtained in step (b) at 4°C; (d) radiolabelling the said lyophilised product obtained with Tc-99m by allowing the kit to attain the room temperature before addition of 99m TcO 4 ; (e) shaking the kit vigorously to obtain the radiolabelled product available for use within a period of one hour Diethylene triamine pentaacetic acid diester used is prepared as know from by Journal of Pharmaceutical Sciences Vol 68, No 2, February 1979, pp 194-196 [a] esterifying dianhydride of diethylene triamine pentaacetic acid by conventional methods, [b] evaporatin the resulting semi-solid mass. [c] triturating with an organic solvent to get the crude diester, and [d] preparing the crude diester by recrystallisation from alcohol. In another embodiment esterification is effected by heating dianhydride of diethylene triamine pentaacetic acid with methanol in the presence of a solvent. In a further embodiment of the present invention, the solvent used is selected from pyridine, piperidine, picoline and the like. In yet another embodiment the solvent used for trituration is selected from petroleum ether, benzene, toluene and the like. In yet another embodiment the alcohol used for crystallization is selected from methanol, ethanol, propanol, isopropanol and the like. Further, in the preparation of the technetium-99m radiolabelled diethylene triamine pentaacetic acid dimethylester kit for the diagnosis of renal disorders stannous are introduced by using stannous chloride prepared by dissolving stannous chloride in dihydrate in HCI diluted nitrogen purged water. Detailed description of the invention: The invention is further described with refrence to the details and the examples which should not be construed to limit the scope of the invention. Technetium 99m diethylene triamine pentaacetic acid dimethylester is prepared by: 1. Esterification of the dianhydride of diethylene triamine pentaacetic acid. 2. formulation of frozen kit containing diethylene triamine pentaacetic acid dimethylester and stannous ion for easy radiolabeling, and 3. Radiolabeling of the above frozen kit with 99m TcO 4 . Diethylene triamine pentaacetic acid dianhydride is prepared form diethylene triamine pentaacetic acid and acetic anhydride according to the procedure of W.C. Eckelman et al. (J. Pharm.Sci. 64 , 704-706, 1975). Diethylene Triamine Penaacetic Acid Diester Diethylene triamine pentaacetic acid dianhydride was converted to diethylene triamine pentaacetic acid diester by heating it with alcohol in presence of a solvent. Usually eighteen to twenty hours of reaction period is sufficient. The mixture was then evaporated and the semisolid mass was triturated with a solvent to furnish the crude diester. This was then purified by recrystallising form aqueous alcohol to furnish the desired material which was characterized by melting point determination, elemental analysis and proton magnetic resonance spectroscopy. A kit for radiolabeling diethylene triamine pentaacetic acid dimethyl was prepared from a dilute aqueous solution of the above ligand to which appropriate amount of stannous ion was added. The kits vials were then lyophilized and stroed at 4°C. While radiolabeling with technetium-99m, the kit was allowed to attain room temperature and desired amount of aqueous 99m-TcO 4 was injected into the kit vial. The radiolabeled product thus obtained was characterised by thin layer chromatography and paper electrophoresis and was consumed in a short while. An Example of the process: [a] Preparation of diethylene triamine penttaacetic acid dimethylester: To a solution of diethylene triamine pentaacetic acid dianhydride (7,2 g) in dry pyridine (120 ml) was added dry methanol (3 ml) and the mixture was heated under reflux for 18 hours. The material was then evaporated and the residual semisolid mass was triturated with diethylether to furnish solid crude ester (7 g). This was then purified by recrystallisation from ethanol-water (1:1) to furnish the pre material m.p. 176-178°. PMR (D 2 O) 3.20-3.56 (br.8H, >N-CH 2 -CH 2 -N-C H 2 -C H 2 -N <): 3.48(S.6H, 2xCO 2 CH 3 ) : 3.94-4.28 (m, 1 OH, 3xC H 2 CO 2 H and 2xCH 2 -CO 2 CH 3 ) Anal. calculated from C 16 H 27 N 3 O 10 . C, 45.60, H, 6.46, N, 9.97 found C, 45.34; H, 6.78, N, 9.76 %). [b] Kit formulation of diethylene triamine pentaacetic acid dimethylester for radiolabeling: To evacuated rubber sealed injection vials flushed with nitrogen was added a solution of diethylene triamine pentaacetic acid dimethylester (10 mg) in water (1 ml) to which sodium hydroxide solution was added just to dissolve the material which was adjusted to pH 4 by hydrochloric acid and then stannous chloride solution (50 µl) was added which was prepared by dissolving stannous chloride dihydrate (10 mg) in hydrochloric acid (6N, 50 µl) diluted with N 2 purged water (10 ml) and the pH was readjusted to 4 and lyophilized. [c] Technetium-99m-radiolabeling of diethylene triamine pentaacetic acid dimethylester kit: The kit as prepared above was allowed to attain room temperature and technetium-99m pertechnetate (99m TcO 4 ) (2.20 mCi in 0.1-0.2 ml of water) was added, shaken vigorously and used within an hour. Complete Chemical and Biological Specification of Technetium-99m-diethylene triamine pentaacetic acid dimethylester: [a] Thin Layer Chromatography Two TLC systems were used (a) silica gel/acetone and [b] silica gel/acetonitrile-water (1:1). In these two systems, technetium-99m diethylene triamine pentaacetic acid dimethylester showed Rf values of 0 and 1 respectively. [b] Paper Electrophoresis : This was conducted on Whatman paper strip (61 cm x 26 cm) soaked in bicarbonate buffer (0.01 M, pH 7) on which technetium-99m-diethylene triamine pentaacetic acid dimethylester was spotted along with technetium-99m-diethylene triamine pentaacetic acid as standard A potential difference of 3.000 volts was applied across the paper and the system was allowed to run for 60 min. Technetium-99m diethylene triamine pentaacetic acid dimethylester moved 8 cm and the standard compound moved 16 cm, both towards anode unter the above experimental condition. Biological evaluation of technetium-99m diethylene triamine pentaacetic acid diester by comparative biodistribution with iodine-131 orthoiodo-hippurate and technetium-99m mercaptoacetylglycylglycylglycine. The comparative biodistribution experiment was undertaken in mice and rats. In mice either technetium-99m diethylene triamine pentaacetic acid diester ot technetium-99m mercaptoacetylglycylglycylglycine were injected via the tail vein along with iodine-131 orthoiodo-hippurate. Rats were anaesthetised with urethane and the above radiochemicals were injected via the femoral vein. After predetermined time interval the animals were sacrificed and the organs were taken in the counting vial. Considerable care were exercised not to loose any urine during the process. The biodistribution results were summarised in Table 1. Plasma Clearance Renal plasma clearance of technetium-99m diethylene triamine pentaacetic acid dimethylester was studied in rats by single injection method. Two plasma samplers were collected at 20 and 30 min time point. The clearance was calculated using a single compartment model. Iodine-131 orthoiodo-hippurate was coinjected as standard. This experiment was also performed with technetium-99m mercaptoacetylglycylglycylglycine. The clearance values were 1.39 and 1.45 ml / min / 100 g for the above two compounds respectively and the value of iodine-131 orthoiodo-hippurate was 2.68 ml / min / 100 g. The corresponding values in dog (10-12 kg) for technetium-99m diethylene triamine pentaacetic acid dimethylester and technetium-99m mercaptoacetylglycylglycylglycine along with coinjected hippurate were 72, 80 and 157 ml / min. These values are much higher than technetium-99m diethylene triamine pentaacetic acid in rats (0.82 ml / min / 100 g) or dogs (43 ml / min). Scintigraphic studies on dogs To dogs anaesthetised by pentothal sodium, either of the compounds were introduced via femoral vein while the animal was placed under the computerised gammacamera. Serial images were recorded using appropriate window on a computer tape. The time activity curve was generated from the above frames by placing the area of interest around kidney. The area of interest curves are shown in Fig. 1 and Fig. 2 indicating a comparable clearance of radioactivity from kidney for the above two radiopharmaceuticals. From the biodistribution in rats or mice or from the scintigraphic experiments on dog it appears that technetium-99m diethylene triamine pentaacetic acid dimethylester is a superior renal function agent than currently available (only in western countries) technetium.99m mercaptoacetylglycylglycylglycine, since there is no hepatobiliary accumulation of technetium-99m diethylene triamine pentaacetic acid dimethylester whereas appreciable amount of technetium-99m mercaptoacetylglycylglycylglycine accumulate in those organs. Moreover, diester of diethylene triamine pentaacetic acid could be easily synthesised compared to the tripeptide derivative mercaptoacetylglycylglycylglycine, therefore, making the former more affordable for clinical use. Again labeling of diester of diethylene triamine pentaacetic acid with technetium-99m is much simpler than mercaptoacetylglycylglycylglycine and is expected to produce a uniform labeled product easily like that of its precursor diethylene triamine pentaacetic acid. On the contrary, variation in biological results of technetium-99m mercaptoacetylglycylglycylglycine is well documented.

Claims: A technetium-99m radiolabeled diethylene triamine pentaacetic acid dimethylester kit for the diagnosis of renal disorders wherein technetium-99m diethylene triamine pentaacetic acid dimethylester has Rf value - zero in silica gel/acetone TLC system and Rf value = 1 in silica gel/acetonitrile water (1:1) TLC systen and technecium-99m diethylene triamine pentaacetic acid dimethyl ester movement is of the order of half of the distance as compared to the standard compound (technetium-99m diethylene triamine pentaacetic acid) on conducting paper electrophoresis. A process for the preparation of a technetium-99m radiolabelled diethylene triamine pentaacetic acid dimethylester kit for the diagnosis of renal disorders which comprises: (a) Adding appropriate amount of stannous ion to a dilute aqueous solution of diethylene triamine pentaacetic acid dimethylester prepared by known methods (b) Keeping the resultant solution abtrained in step (a) in an evacuated rubber sealed injection vial flushed with nitrogen; (c) lyophilising the said kit and storing the lyophilised product as obtained in step (b) at 4°C; (d) radiolabelling the said lyophilised product obtained with Tc-99m by allowing the kit to attain the room temperature before addition of 99m TcO 4 ; (e) shaking the kit vigorously to obtain the radiolabeled product available for use within a period of one hour. A technetium-99m radiolabelled diethylene triamine pentaacetic acid dimethylester kit according to claim for the diagnosis of renal disorders wherein stannous ions are introduced by using stannous chloride prepared by dissolving stannous chloride in dihydrate in HCI diluted with nitrogen purged water.

Inventors: BANERJEE SOME NATH, CHATTERJEE MITA, SEN KARABI, BANERJEE, SOME NATH, CHATTERJEE, MITA, SEN, KARABI
Applicants: COUNCIL SCIENT IND RES, COUNCIL OF SCIENTIFIC ANDINDUSTRIAL RESEARCH
Application year: 1998
Main classification: A61K51
IPC codes: A61K51, C07F13