Poster Presentation The 16th Australian Peptide Conference 2025

LYTAPs: cyclic peptides that induce lysosomal degradation of EGFR and overcome resistance in NSCLC and CRC (#228)

Quach Truong 1 , Timothy J Mann 1 2 3 , Maria George Elias 1 2 , Mila Sajinovic 1 2 4 , Jun Zeng 1 5 , Paul De Souza 1 2 4 , Kieran F Scott 1 2 , Graham Kelly 1
  1. Filamon Limited, Sydney, New South Wales, Australia
  2. School of Medicine, Western Sydney University, Campbelltown, New South Wales, Australia
  3. School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
  4. Nepean Clinical School, Faculty of Medicine and Health, University of Sydney, Kingswood, New South Wales, Australia
  5. MedChemSoft Solutions, Scoresby, Victoria, Australia

Resistance to epidermal growth factor receptor (EGFR) inhibitors remains a major clinical challenge in treating non-small cell lung cancer (NSCLC) and colorectal cancer (CRC). We developed a novel class of cyclic peptides—Lysosome-Targeting Peptides (LYTAPs)—designed to bind the conserved extracellular domain of EGFR and induce its degradation via non-clathrin-mediated endocytosis (non-CME) and lysosomal degradation.

LYTAPs D1–D3 were derived from the parent peptide kesonotide, which binds EGFR but does not promote degradation. Structural modelling guided modifications that enabled D1–D3 to engage key EGFR residues (23-HFLSLQRM-30, 41-LETT-44, L17). In vitro assays revealed D1 to be the most potent, with an IC₅₀ of 166.4 µM in PC-3 prostate cancer cells, compared to 211.0 µM for kesonotide. Western blot analysis showed that D1, D2, and D3 reduced EGFR protein levels by 84%, 95%, and 97%, respectively, after 3–16 hours of treatment (100 µM), with D3 maintaining sustained EGFR depletion for >48 hours.

LYTAPs induced significant internalisation of EGFR into lysosomes in A549 NSCLC cells, confirmed via lysotracker co-localisation. In particular, D1 reduced membrane-associated EGFR by 56% (P < 0.0001), compared to DMSO control; and increased lysotracker intensity by 60% (P = 0.0005), consistent with enhanced lysosomal activity. Downstream signalling analysis showed D1 (100 µM) suppressed EGF-induced pERK levels by 83% (P < 0.0001).

D1 retained cytotoxic efficacy in both cetuximab-sensitive (SW48, IC₅₀ 126.5 µM) and resistant CRC line (SW48G12V, IC₅₀ 134.6 µM), as well as in erlotinib-sensitive (H3255, IC₅₀ 83.16 µM) and resistant NSCLC lines (H1975, IC₅₀ 150.9 µM). Notably, combination studies revealed strong synergy between D1 and cetuximab in CRC (SW48: CI = 0.54; SW48G12V: CI = 0.60) and with erlotinib in NSCLC (H3255: CI = 0.63; H1975: CI = 0.59)

These results establish LYTAPs as a promising peptide-based therapeutic platform for EGFR-driven cancers, with potential application as monotherapy or in synergistic combination with existing EGFR inhibitors.