Targeting EGFR Endocytosis and Signaling for Cancer Drug Delivery and Cancer Treatment.

The epidermal growth factor receptor (EGFR) was the first receptor tyrosine kinase identified soon after v-Src was recognized as a tyrosine kinase. EGFR signaling begins when EGF binds to EGFR at the cell surface, inducing receptor dimerization, activation, and autophosphorylation. The resulting phosphotyrosine sites recruit downstream effectors that activate signaling cascades such as the RAS-RAF-MEK-ERK and PI3K-Akt pathways, thereby regulating cell growth, proliferation, and survival. EGF binding also promotes EGFR endocytosis, which can direct the receptor to lysosomal degradation. Aberrant EGFR activity is associated with many cancers, and the receptor has been therapeutically targeted using small-molecule tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs). Furthermore, EGFR endocytosis has been exploited for the targeted delivery of anticancer agents into EGFR-expressing cancer cells through antibody-drug conjugates (ADCs) and antibody-nanoparticle conjugates (ANCs). Although ADCs and ANCs both utilize mAbs as homing mechanisms to recognize cancer-associated antigens, they further harness EGFR endocytosis to deliver therapeutic payloads directly into target cells. In this review, we briefly discuss EGFR structure, activation, signaling, and endocytosis, as well as the mechanisms underlying EGFR function in cancer development. We then focus on current advances and future perspectives in using EGFR endocytosis pathways to improve targeted cancer drug delivery and therapy, particularly in the context of ANCs.