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Updated: Feb 26, 2026
Using Phage Display to Develop Ubiquitin Variant Modulators for E3 Ligases
Published on: August 27, 2021
Phage Display Selection, In Vitro Characterization, and Correlative PET Imaging of a Novel HER3 Peptide
Benjamin M Larimer1, Nicholas Phelan2, Eric Wehrenberg-Klee2
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, 149 13th Street, Charlestown, MA, 02129, USA. blarimer@mgh.harvard.edu.
Purpose:
HER3 (ERBB3) is a receptor tyrosine kinase that is implicated in treatment resistance across multiple cancers, including those of the breast, lung, and prostate. Overexpression of HER3 following targeted therapy can occur rapidly and heterogeneously both within a single lesion and across sites of metastasis, making protein quantification by biopsy highly challenging. A global, non-invasive methodology such as positron emission tomography (PET) imaging can permit serial quantification of HER3, providing a useful approach to monitor HER3 expression across the entire tumor burden both prior to and following treatment. PET imaging of HER3 expression may permit a more personalized approach to targeted therapy by allowing for detection of HER3-mediated resistance, in addition to informing clinical trial patient selection for novel therapies targeting HER3.
Procedures:
Phage display selection targeting the HER3 extracellular domain was performed in order to develop a peptide with optimal blood clearance and highly accurate HER3 quantification.
Results:
The selection converged to a consensus peptide sequence that was subsequently found to bind HER3 with an affinity of 270 ± 151 nM. The peptide, termed HER3P1, was bound with high selectivity to HER3 over other similar receptor tyrosine kinases such as EGFR and HER2. Furthermore, HER3P1 was able to distinguish between high and low HER3-expressing cells in vitro. The peptide was radiolabeled with Ga-68 and demonstrated to specifically bind HER3 by in vivo PET imaging. Uptake of [68Ga]HER3P1 was highly specific for HER3-positive tumors, with tumor-to-background ratios ranging from 1.59-3.32, compared to those of HER3-negative tumors, ranging from 0.84-0.93. The uptake of [68Ga]HER3P1 also demonstrated high (P < 0.001) correlation with protein expression as quantified by Western blot and confirmed by biodistribution.
Conclusions:
HER3P1 accurately quantifies expression of HER3 by PET imaging and has potential utility as a clinical imaging agent.
Insights
A novel peptide, HER3P1, enables non-invasive quantification of HER3 (ERBB3) receptor tyrosine kinase expression using PET imaging. This approach aids in monitoring treatment resistance and personalizing cancer therapies.
Area of Science:
- Oncology
- Molecular Imaging
- Biotechnology
Background:
- HER3 (ERBB3) is a receptor tyrosine kinase implicated in treatment resistance in breast, lung, and prostate cancers.
- Rapid and heterogeneous HER3 overexpression post-therapy poses challenges for biopsy-based quantification.
- Non-invasive methods like PET imaging are needed for serial HER3 monitoring across tumor burden.
Purpose of the Study:
- To develop a peptide for accurate, non-invasive HER3 quantification using PET imaging.
- To enable monitoring of HER3 expression for personalized cancer therapy and clinical trial selection.
Main Methods:
- Phage display selection was used to identify a peptide targeting the HER3 extracellular domain.
- The peptide, HER3P1, was radiolabeled with Gallium-68 ([68Ga]) for PET imaging.
- In vitro and in vivo studies assessed HER3 binding affinity, selectivity, and tumor uptake.
Main Results:
- HER3P1 demonstrated high affinity (270 ± 151 nM) and selectivity for HER3 over EGFR and HER2.
- [68Ga]HER3P1 PET imaging showed specific uptake in HER3-positive tumors with high tumor-to-background ratios (1.59-3.32).
- Uptake of [68Ga]HER3P1 strongly correlated with HER3 protein expression (P < 0.001).
Conclusions:
- HER3P1 is a promising peptide for accurate HER3 quantification via PET imaging.
- This method can guide personalized targeted therapy and inform patient selection for HER3-targeted treatments.
