Abstract
Skeletal uptake of radiolabeled‐1, 4, 7, 10‐tetraazacyclododecane‐1, 4, 7, 10‐tetramethylene phosphoric acid (e.g., 177Lu‐DOTMP) complex, is used for bone pain palliation. The moderate energy of β‐emitting 177Lu (T1/2=6.7 d,Eβmax=497 keV) has been considered as a potential radionuclide for development of the bone‐seeking radiopharmaceutical. Since the specific activity of the radiolabeled carrier molecules should be high, the “no‐carrier‐added radionuclides” have significant roles in nuclear medicine. Many researchers illustrated no‐carrier‐added 177Lu production; among these separation techniques such as ion exchange chromatography, reversed phase ion‐pair, and electrochemical method, extraction chromatography has been considered more capable than other methods. In order to optimize the conditions, some effective factors on separation of Lu/Yb were investigated by EXC. The NCA 177Lu, produced by this method, was mixed with 300μ1 of DOTMP solution (20 mg in 1 mL of 0.5 M NaHCO3, pH=8) and incubated under stirring at room temperature for 45 min. Radiochemical purity of the 177Lu‐DOTMP complex was determined using radio‐thin‐layer chromatography (RTLC) method. The complex was injected to wild‐type rats and biodistribution was then studied for seven days. The NCA 177Lu was produced with specific activity of 48 Ci/mg and with a radinuclidic purity of 99.99% through irradiation of enriched 176Yb target (1 mg) in a thermal neutron flux of 4×1013 n.cm−2.s−1 for 14 days. 177Lu‐DOTMP was obtained with high radiochemical purities (>98%) under optimized reaction conditions. The radiolabeled complex exhibited excellent stability at room temperature. Biodistribution of the radiolabeled complex studies in rats showed favorable selective skeletal uptake with rapid clearance from blood along with insignificant accumulation within the other nontargeted organs.PACS number(s): 87.57.un, 87.57.uq
Highlights
129 Salek et al.: 177Lu (NCA)—DOTMP ligands has an important role in palliating pain of bone metastases due to the numerous limitations of the other therapeutic methods.[5]
Phosphonates carriers, such as EDTMP(diethylenetriamine penta(methylene phosphonic acid)), DOTMP(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylene phosphonic acid), APD(1-hydroxy-3- amino propylidene-diphosphonic acid), TTHMP(Triehtylenetetramine hexamethylene phosphonate), are being used for the other radiopharmaceuticals that are sitespecific for skeletal lesions.[6,7,8,9,10,11,12,13,14,15,16,17] Low-energy β--emitting radionuclides, such as 177Lu, 153Sm, 175Yb, and 186Re, are used for palliation of bone pain, whereas radionuclides with higher energies including 166Ho, 90Y, and 188Re are recommended for bone marrow ablation
Two alternative production routes are applied to obtain 177Lu: namely, the direct route is based on the neutron irradiation of lutetium targets, and the indirect route is based on the neutron irradiation of ytterbium targets followed by radiochemical separation of 177Lu from ytterbium isotopes.[26]. Formation of a small amounts of long-lived 177mLu (t1/2 = 160.5 d) is the main drawback of the direct route
Summary
129 Salek et al.: 177Lu (NCA)—DOTMP ligands has an important role in palliating pain of bone metastases due to the numerous limitations of the other therapeutic methods.[5]. Two alternative production routes are applied to obtain 177Lu: namely, the direct route is based on the neutron irradiation of lutetium targets, and the indirect route is based on the neutron irradiation of ytterbium targets followed by radiochemical separation of 177Lu from ytterbium isotopes.[26] Formation of a small amounts of long-lived 177mLu (t1/2 = 160.5 d) is the main drawback of the direct route Using this method, the product will contain macro quantities of nonradioactive isotopes of Lu and, has a comparatively low specific activity.[27,28] With the indirect route, it is feasible to separate 177Lu from 176Yb due to their chemical differences, which leads to produce a “no-carrier-added” (NCA) therapeutic radioisotope of 177Lu without any nonradioactive isotope. NCA 177Lu has been produced by EXC procedure and its suitability for the preparation of radiochemical agents has been determined by preparing 177Lu-DOTMP complexes as bone pain palliation agents
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