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Copper bis(thiosemicarbazone) complexes as hypoxia imaging agents: structure-activity relationships
Jason L J Dearling1, Jason S Lewis, Gregory E D Mullen
1Biosciences Department, University of Kent, Canterbury CT2 7NJ, UK.
Summary
New copper radiopharmaceuticals show promise for hypoxia imaging. Structure-activity studies reveal that ligand modifications influence redox potential, enhancing selectivity for hypoxic tissues.
Area of Science:
- Radiopharmaceutical chemistry
- Medical imaging
- Biomedical research
Background:
- Copper bis(thiosemicarbazone) complexes are effective radiopharmaceuticals for imaging blood flow and hypoxic tissues.
- Understanding structure-activity relationships is crucial for designing improved hypoxia imaging agents.
Purpose of the Study:
- To identify structure-activity relationships in copper bis(thiosemicarbazone) analogues.
- To design improved hypoxia imaging agents with enhanced selectivity.
- To elucidate mechanisms of hypoxia selectivity.
Main Methods:
- Synthesis and spectroscopic/electrochemical characterization of thirteen copper bis(thiosemicarbazone) complexes.
- In vitro study of Cu-64 labelled complex uptake in EMT6 tumor cells under normoxic and hypoxic conditions.
- Correlation analysis between cellular uptake, redox potential, and ligand structure.
Main Results:
- All synthesized complexes showed efficient cellular uptake.
- Several complexes exhibited strong hypoxia selectivity, correlated with Cu(II/I) redox potential.
- Low redox potentials were essential for hypoxia selectivity, influenced by alkyl substitution patterns on the diimine backbone.
Conclusions:
- Ligand structure, particularly alkyl group number on the diimine backbone, significantly impacts redox potential and hypoxia selectivity.
- Several complexes warrant further investigation as potential hypoxia imaging agents.
- A model for hypoxia-selective intracellular trapping is proposed based on radioactivity uptake/release behavior.