Phosphorescent d6 iridium complexes are excellent candidates as fluorophores for biological imaging and therapeutic applications such as and fluorescent guided surgery and photodynamic therapy, due to their photostability, large Stokes shifts, long excited state lifetimes and efficient sensitisation of singlet oxygen generation.
In this work, water soluble phosphorescent iridium complexes incorporating a bidentate, polyethylene glycol functionalised triazole ligand were synthesised and their electronic properties characterised. Their light and dark cytotoxicity was measured before conjugation to girentuximab, a monoclonal antibody that binds selectively to carbonic anhydrase IX.
Carbonic anhydrase IX is a zinc metalloenzyme that is overexpressed by some cancers such as clear cell renal cell carcinoma. The binding affinity to CAIX as well as the light and dark cytotoxicity of the new conjugates was evaluated. The phosphorescent iridium-girentuximab conjugates were also used for imaging in live carbonic-anhydrase expressing cells using confocal microscopy.