(T1430-03-20) A Rationally Designed Orally Active Peptidomimetic-Targeting EGFRs for Non-Small Cell Lung Cancer

Purpose: According to the American Cancer Society, in 2025, lung cancer is projected to account for 11.1% of new cancer cases and 20.2% of cancer-related deaths in the United States (US).¹ The five-year survival rate (2015-2021) for Non-small cell lung cancer (NSCLC) is 28.1%.¹ NSCLC accounts for 85% of the lung cancer cases.² Current therapies for early-stage treatment of NSCLC include surgery and chemotherapy.³ However, these therapies are helpful only in the early stages of cancer. Hence, novel approaches such as targeted therapies are vital against NSCLC. Epidermal growth factor receptors (EGFRs), and importantly HER2, are well-validated oncogenic drivers for NSCLC.⁴ Oncogenic mutation in HER2 is identified in 2-4% of NSCLC, which identifies HER2 as a possible target for Targeted therapies.⁴ Current HER2-targeted antibodies (trastuzumab and pertuzumab) block receptor dimerization and intracellular signaling.⁵ However, these molecules lack oral bioavailability and suffer from poor patient compliance.^{6, 7} Alternatively, small molecule inhibitors like tyrosine kinase inhibitors (TKIs) are effective in treating NSCLC; however, TKIs are prone to resistance and unwanted side effects, necessitating novel approaches for targeted therapies against HER2+ NSCLC.⁷ Our goal is to develop an orally active peptidomimetic based inhibitor for HER2 extracellular domain to inhibit downstream signaling and cancer progression. In our lab, we designed a cyclic peptidomimetic compound (Compound 18) that could inhibit HER2-positive NSCLC cells at a concentration of 18nM. Furthermore, to enhance the stability of the peptide, we grafted the essential amino acid residue from compound 18 into the Sunflower Trypsin Inhibitor (SFTI) framework, which made the peptidomimetic thermally and enzymatically stable. In our previous study, SFTI-G5 showed a significant reduction in viability compared to control.

Methods: The calu-3 subcutaneous mouse xenograft model was treated with SFTI-G5 via oral route at two concentrations (30 and 50mg/kg) for 4 weeks, and tumor volume was measured compared to vehicle alone (negative control) and combination of pertuzumab and trastuzumab (positive control). The immunohistochemistry staining of Ki67 was done from the tumor sections to measure cell proliferation. Similarly, EGFRs expressions were quantified using immunohistochemistry. Proximity ligation assay (PLA) was used to measure the ability of SFTIG5 to inhibit EGFR: HER2 and HER2:HER3 dimerization. Serum analysis and H&E are used for toxicological analysis. Similarly, to determine the specificity of SFTI-G5, it was tested on Patient-derived xenograft models.

Results: Oral administration of SFTIG5 at 30mg/kg dose didn’t show any significant decrease in the rate of tumor growth progression compared to vehicle control. The rate of tumor progression decreased nearly fivefold after 2^nd week of treatment with oral administration of SFTIG5 50mg/kg twice a week. Similar effects were seen in antibody combinations. Based on Immunohistochemistry results from Ki67 staining, both SFTI-G5 and antibody combination significantly reduced the cell proliferation by around 25%. However, a significant 8-fold decrease in EGFR: HER2 dimerization and a two-fold decrease in HER2:HER3 dimerization is observed by PLA quantification, indicating the ability of SFTI-G5 to decrease HER2 heterodimerization. Serum ALT (42.66±17.95 U/L), ALP (52±10.44 U/L), BUN (29.66±3.21 mg/dL), and Creatinine levels ( < 0.2mg/dL) were not significantly affected by SFTI-G5, indicating a lack of toxicity at the therapeutic dose. H & E staining was done on the vital organs collected from the mice, showing no toxicity at therapeutic doses. Furthermore, the change in body weight did not decrease significantly in the control and SFTIG5-treated groups. HER2 knockdown and HER2 overexpressed Patient-derived xenograft models of mice were treated with SFTI-G5. In the HER2 knockdown mice models, SFTI-G5 didn’t inhibit tumor proliferation when administered IV at 6mg/kg dose twice a week. In the case of the HER2 overexpression model, the tumor is reduced by almost half

Conclusion: Extracellular domains of EGFRs can be targeted by peptides and peptidomimetics. Stable peptides can be designed using templates such as sunflower trypsin inhibitor peptide. Oral peptidomimetics-based therapy (SFTI-G5) can be an effective way of treating EGFR/HER2-specific NSCLC.

References: (1) Siegel, R. L.; Kratzer, T. B.; Giaquinto, A. N.; Sung, H.; Jemal, A. Cancer statistics, 2025. CA: A Cancer Journal for Clinicians 2025, 75 (1), 10-45. DOI: https://doi.org/10.3322/caac.21871.
(2) Molina, J. R.; Yang, P.; Cassivi, S. D.; Schild, S. E.; Adjei, A. A. Non-small cell lung cancer: epidemiology, risk factors, treatment, and survivorship. Mayo Clin Proc 2008, 83 (5), 584-594. DOI: 10.4065/83.5.584 From NLM.
(3) Guo, Q.; Liu, L.; Chen, Z.; Fan, Y.; Zhou, Y.; Yuan, Z.; Zhang, W. Current treatments for non-small cell lung cancer. Front Oncol 2022, 12, 945102. DOI: 10.3389/fonc.2022.945102 From NLM.
(4) Uy, N. F.; Merkhofer, C. M.; Baik, C. S. HER2 in Non-Small Cell Lung Cancer: A Review of Emerging Therapies. Cancers (Basel) 2022, 14 (17). DOI: 10.3390/cancers14174155 From NLM.
(5) Hubalek, M.; Brantner, C.; Marth, C. Role of pertuzumab in the treatment of HER2-positive breast cancer. Breast Cancer (Dove Med Press) 2012, 4, 65-73. DOI: 10.2147/bctt.S23560 From NLM. Nahta, R.; Esteva, F. J. HER2 therapy: molecular mechanisms of trastuzumab resistance. Breast Cancer Res 2006, 8 (6), 215. DOI: 10.1186/bcr1612 From NLM.
(6) Quartino, A. L.; Hillenbach, C.; Li, J.; Li, H.; Wada, R. D.; Visich, J.; Li, C.; Heinzmann, D.; Jin, J. Y.; Lum, B. L. Population pharmacokinetic and exposure-response analysis for trastuzumab administered using a subcutaneous "manual syringe" injection or intravenously in women with HER2-positive early breast cancer. Cancer Chemother Pharmacol 2016, 77 (1), 77-88. DOI: 10.1007/s00280-015-2922-5 From NLM.
(7) Shyam Sunder, S.; Sharma, U. C.; Pokharel, S. Adverse effects of tyrosine kinase inhibitors in cancer therapy: pathophysiology, mechanisms and clinical management. Signal Transduction and Targeted Therapy 2023, 8 (1), 262. DOI: 10.1038/s41392-023-01469-6.

Acknowledgements: This research was supported by funding from the National Cancer Institute of the National Institutes of Health, Grant/Award Number: 5R01CA255176- 04 (SJ & DB).


Figure 1: Docking of SFTIG5 (highlighted as Pink) to HER2 domain IV (surface representation). Note: Trastuzumab (yellow) binding site is similar to SFTI-G5 (pink) binding site. (PDB 1N8Z)


Figure.2: Oral administration of SFTIG5 (50mg/kg) twice a week showed decrease tumor proliferation. Pertuzumab and Trastuzumab Intraperitoneal injections (12mg/kg loading dose and 6mg/kg maintenance dose once a week showed significant inhibition of tumor proliferation. (N=10). Statistical analysis using Ordinary one-way Anova *p < 0.05, **p < 0.01