The Synthesis of BODIPY-TKI Conjugates and Investigation of Their Ability to Target the Epidermal Growth Factor Receptor

Abstract

A near-IR BODIPY was covalently conjugated via its isothiocyanate groups to one or two Erlotinib molecules, a known tyrosine kinase inhibitor (TKI), via triethylene glycol spacers, to produce two novel BODIPY-monoTKI and BODIPY-diTKI conjugates. The ability of these conjugates to target the intracellular domain of the epidermal growth factor receptor (EGFR) was investigated using molecular modeling, surface plasma resonance (SPR), EGFR kinase binding assay, time-dependent cellular uptake, and fluorescence microscopy. While both the BODIPY-monoTKI and the BODIPY-diTKI conjugates were shown to bind to the EGFR kinase by SPR and accumulated more efficiently within human HEp2 cells that over-express EGFR than BODIPY alone, only the BODIPY-monoTKI exhibited kinase inhibition activity. This is due to the high hydrophobic character and aggregation behavior of the BODIPY-diTKI in aqueous solutions, as shown by fluorescence quenching. Furthermore, the competition of the two Erlotinibs in the diTKI conjugate for the active site of the kinase, as suggested by computational modeling, might lead to a decrease in binding relative to the monoTKI conjugate. Nevertheless, the efficient cellular uptake and intracellular localization of both conjugates with no observed cytotoxicity suggest that both could be used as near-IR fluorescent markers for cells that over-express EGFR.