Preparation of Some Radiolabeled Phosphonates for Bone Imaging

This study is focused on the synthesis of two bisphosphonate derivatives, 1-hydroxy-2-(3-pyridyl) ethylidene bisphosphonic acid monosodium (sod. risedronate) and 1-hydroxy-2-(2-pyridyl) ethylidene bisphosphonic acid monosodium (HPEBP) from corresponding nitrile. The labeling of two compounds was studied with technetium-99m using two different reducing agents (SnCl2.2H2O and NaBH4) where NaBH4 gave a stable complex and high radiochemical yield more than SnCl2.2H2O. The radiochemical yield of 99mTc-risedronate and 99mTc-HPEBP were 99.2 ± 0.6 and 95.5 ± 3.5%, respectively, which more than that of the SnCl2.2H2O method (84.5 ± 3.5 and 83.9 ± 3%, respectively). Both radiolabeled complexes showed in vitro stability, up to 6 hours. The in vivo biodistribution studies, performed in mice, show highly selective uptake of both labeled compounds in the skeletal system and rapid elimination via the urinary pathway. The maximum value of the bone uptake after 30 min was 30.25 ± 3 and 31 ± 2 % ID/organ for risedronate and HPEBP, respectively.