Exploring gefitinib to enhance endocytosis of antibodies and nucleic acid aptamers targeting EGFR in glioblastoma

Active targeting in drug delivery involves the binding of ligands to receptors present on the surface of targeted cells. Several conjugates are already in use or under development for active targeting of tumors, the most widely known being antibody-drug conjugates (ADC). They combine the specificity of monoclonal antibodies with the cytotoxicity of chemotherapeutic molecules. Nucleic acid based aptamers belong to another promising family of ligands able to deliver conjugated drugs, like cytotoxic compounds or siRNAs, by active targeting of tumor cells. The therapeutic efficacy of most conjugates largely depends on their endocytosis and vesicular trafficking. While combinatorial pharmacological and other strategies to enhance conjugate endocytosis have been and remain an active area of investigation, additional studies are necessary to fully unlock their therapeutic potential. In recent studies, we showed that gefitinib, a tyrosine kinase inhibitor directed against the epidermal growth factor receptor EGFR, induces a massive, non-physiological endocytosis of EGFR, known as gefitinib-mediated endocytosis (GME), in different glioblastoma cell lines. We thus hypothesized that besides promoting endocytosis of EGFR, gefitinib could also promote endocytosis of its ligands. In this study, we proved by quantitative fluorescence bioimaging, that gefitinib is indeed able to strengthen the endocytosis of fluorophore-conjugated EGFR-specific antibodies or aptamers. We also showed that the GME potentiates the toxicity of an antibody-drug conjugate (ADC) and the efficacy of an aptamer-siRNA conjugate (AsiC) in vitro. Our results underline the potential for developing new therapeutic combination with gefitinib, to enhance the delivery of ADC, AsiC and likely other conjugates targeting EGFR in glioblastoma, while limiting side effects on non-targeted cells. However, in vivo data emphasize the need for further optimization of combinatorial strategies to achieve meaningful clinical outcomes.