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Keywords:

  • radiopharmaceutical;
  • spectroscopy;
  • tumor imaging

99mTc-Diethylene triamine pentaacetic acid-bis (amide) conjugates have been synthesized and evaluated as a potential radiopharmaceutical for tumor imaging. The compounds were synthesized by the condensation reaction of DTPA bis(anhydride) with different l-amino acids (methyl tryptophan, and 5-hydroxy tryptophan) and were characterized on the basis of IR, NMR, and Mass spectroscopy. 99mTc-labeled compounds were found stable for about 24 h under physiological conditions with more than 95% radiolabeling yield. Blood kinetic studies of all these complexes showed a bi-exponential pattern as well as quick wash out from the blood circulation. The biological t1/2(F) and t1/2(S) were found to be 20 ± 0.001 min for DTPA-(Me-Trp)2 and 18 ± 0.001 min for DTPA-(5HT)2 and t1/2 (slow) 5 h 45 min ± 0.001, 5 h 30 ± 0.001 min for DTPA-(Me-Trp)2, and DTPA-(5HT)2, respectively. Imaging and biodistribution studies were performed in mice bearing Ehrlich ascites tumor (EAT) tumors in right thigh. Radioconjugate derived from l-5-hydroxytryptophan exhibited remarkable localization at tumor site; whereas radiotracer derived from l-methyl tryptophan shows relatively less accumulation at the tumor site. Tumor-to-muscles ratios were 5.07 ± 0.001, and 4.2 ± 0.001 at 1 and 4 h for 99mTc-DTPA-(Me trp)2 and 4.97 ± 0.001 and 5.8 ± 0.001 at 1 and 4 h after postinjection for 99mTc-DTPA-(5HT)2, respectively. The preliminary results with these amino acid based ligands are encouraging to carrying out further in vivo experiments for targeted tumor imaging.