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Synthesis, Biological Evaluation and Molecular Docking Studies of High-Affinity Bone Targeting N,N'-Bis (alendronate) Diethylenetriamene-N,N'-Triacetic Acid: A Bifunctional Bone Scintigraphy Agent



A bisphosphonate derivative DTPA-bis(alendronate) conjugate has been synthesized and evaluated as potential radiopharmaceutical for bone imaging. The compound was synthesized by the covalent coupling of DTPA-bis(anhydride) with alendronate and was char-acterized on the basis of IR, NMR and mass spectroscopy. It was labelled with 99mTc with 96% efficacy and was found stable for about 24 h under physiological conditions. Blood kinetic studies of 99mTc DTPA-bis(alendronate) showed a biexponential pattern as well as quick washout from the blood circulation. The biological t1/2(F) and t1/2(S) were found to be 50 min ± 0.001 and 6 h 30 min ± 0.005, respectively. Imaging and biodistribution studies showed a significant accumulation of 99mTc DTPA-bis(alendronate) conjugate at bone site. Bone-to-muscles ratios were 12.08 ± 0.001 at 1 h, 45.33 ± 0.001 at 4 h and 35.83 ± 0.001 at 24 h after post-injection, respectively. The receptor binding of the 99mTc-DTPA-bis (alendronate) was established on human bone cell line (Soas-2) revealed KD = 0.86 nm. The preliminary result of the 99mTc-DTPA-bis(alendronate) is encouraging to carrying out further in vivo experiment for targeted bone imaging because of good-bone-to-normal-organ contrast. Further docking analysis with molecular targets, farnesyl diphosphate synthase, geranylgeranyl pyrophosphate and osteocalcin revealed the high affinity of −17.419 and thus represents strong potential of bone-imaging agent.