Toward photodynamic detection and photodynamic therapy of tumours over-expressing carbonic anhydrase IX with a phosphorescent organometallic iridium( <scp>iii</scp> ) antibody conjugate

Antibody conjugates with phosphorescent organometallic iridium(iii) complexes attached to tumour targeting antibodies have the potential to be used as emissive probes to guide surgical resection of tumours and for tumour-targeted photodynamic therapy. In this work, a bidentate 2-pyridyl-1,2,3-triazole ligand with a polyethylene glycol linker and a squaramide ethyl ester functional group has been used as an ancillary ligand to make phosphorescent iridium(iii) complexes. The excitation and emission energies for the iridium(iii) complexes were tuned to lower energy by increasing the aromatic conjugation in the cyclometalating ligands. The squaramide ethyl ester functional group is used to attach the iridium(iii) complexes to girentuximab, an antibody that binds to carbonic anhydrase IX (CAIX). Over-expression of carbonic anhydrase IX is a characteristic of several tumour types, including clear cell renal cell carcinoma, glioblastoma, triple-negative breast cancer, ovarian cancer, and colorectal cancer. The squaramide ethyl ester functional group reacts with lysine residues in girentuximab to attach the iridium(iii) complexes through stable vinylogous amide linkages. The cellular uptake of one iridium(iii)-girentuximab conjugate was demonstrated using confocal microscopy and the conjugate is not toxic to HT-29 cells that over express CAIX, but irradiation with visible light results in dose dependent cytotoxicity. The iridium(iii)-girentuximab conjugate described here could be of use for emissive detection of carbonic anhydrase IX positive tumour tissue to guide surgical resection as well as carbonic anhydrase IX targeted photodynamic therapy. The approach described here could be used with other tumour targeting antibodies.