Introduction: Lipophilic delocalized cations accumulate in tumor cell mitochondria due to their higher transmembrane potential. In this work, this strategy was adopted for the development of 99mTc tumor-targeted imaging agents.
Methods: Two tridentate ligands containing the triphenylphosphonium cation, L1 (S-cysteinyl) and L2 (N-iminodiacetate) as well as the respective 99mTc/ReL1 and 99mTc/ReL2 tricarbonyl complexes were synthesized. The effect of the ligands and the Re complexes on cell growth in U-87 MG glioblastoma cells was assessed. In vitro stability studies and measurement of logP of the 99mTc tracers was performed. The cellular and mitochondrial uptake of the 99mTc tracers in U-87 MG cells was evaluated. Biodistribution of 99mTcL1 and 99mTcL2 were performed on SCID mice bearing U-87 MG tumors.
Results: The ligands L1, L2 and the Re1 and ReL2 complexes were characterized spectroscopically. Single products 99mTcL1 and 99mTcL2, >90% stable in rat serum, were obtained. LogP was 0.40±0.14 for 99mTcL1 and -0.02±0.07 for 99mTcL2. L1, ReL1 and ReL2 caused no notable cytotoxicity and L2 was found to infer 40% inhibition of cellular growth at 10-5M as well as 80% cell death in culture at 10-4M. The cell uptake of 99mTcL1 and 99mTcL2 over 4h was 1.26±0.08% and 0.06±0.01% respectively, of which 13.41±3.63% and 18.61±6.19% was distributed in the mitochondria respectively. The initial tumor uptake in mice was found to be >1% ID/g for both 99mTc tracers.
Conclusions: In vitro mitochondrial and in vivo tumor targeting was observed, better in 99mTcL1, however these properties should be optimized in future studies. Advances in Knowledge and Implications for Patient Care: Continuous efforts in this direction may lead to a suitable mitochondrial-targeted 99mTc imaging agent for tumor detection.
Keywords: Mitochondrial targeting; Technetium; Tricarbonyl complexes; Triphenylphosphonium; Tumor imaging agents.
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