Toward targeting the untargetable: A non-canonical EGFR-peptide–drug conjugate achieves potent antitumor activity in KRAS-mutant CRC

Colorectal cancer (CRC) harboring KRAS mutations remains a major therapeutic challenge, as resistance to EGFR directed signaling inhibitors persists despite receptor expression. We aimed to establish a delivery-based therapeutic strategy that bypasses EGFR signaling inhibition by exploiting the receptor as an internalization gate. We report the development of a peptide-drug conjugate (PDC) that exploits non-canonical EGFR engagement to enable tumor selective delivery of the cytotoxic payload SN38. Computational modeling demonstrates stable binding of the P6 peptide within a non-canonical extracellular cavity between domains I and III of EGFR, distinct from the classical EGF binding site, supporting a potential allosteric interaction mechanism. The resulting PDC exhibits preferential cellular uptake and cytotoxicity in KRAS mutant CRC cells compared with normal colon epithelial cells, despite EGFR expression in both, demonstrating tumor selective internalization driven by cellular context and receptor density. P6-SN38 significantly inhibits cancer cell migration in vitro, further supporting its anti-tumor activity beyond cytotoxicity. PDC treatment significantly suppresses tumor growth in in vivo KRAS mutant xenograft model, demonstrating superior efficacy compared with cetuximab-based regimens and controls, without observable body weight loss. This strategy uses EGFR as a delivery portal instead of a signaling target, enabling KRAS independent anti-tumor activity. These findings indicate a non-canonical EGFR mediated delivery approach with potential translational relevance for the treatment of therapy resistant CRC.