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Published on: February 3, 2015
Directional Engineering of Cyclic β-Hairpin Peptides for PET/CT Imaging of PD-L1
Can Liu1,2, Siqi Zhang1,2, Jianan Chen3,4
1State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100050, China.
Abstract:
Peptide-based radiopharmaceuticals represent an emerging drug modality for the noninvasive diagnosis and targeted radiotherapy of cancer. However, the de novo discovery of peptide ligands that combine high binding affinity with sufficient in vivo stability remains a formidable challenge. Conformation-oriented rational design has proven to be a robust strategy for identifying peptide binders to protein targets involved in protein-protein interactions (PPIs), particularly those mediated by well-defined secondary structures such as β-sheets or α-helices. Inspired by the highly structured β-sheet binding interface between programmed death ligand 1 (PD-L1) and its receptor PD-1, we applied a β-hairpin conformation-oriented evolution strategy to engineer high-affinity PD-L1 binders. Starting from a de novo discovered PD-L1-targeting peptide, TPP-1, as a β-hairpin prototype, we iteratively optimized the peptide by sequentially introducing various β-turn motifs, a tryptophan zipper (Trpzip) motif, and subsequently amide cyclization to "lock" the β-hairpin conformation. This process yielded TPP-10, a side-chain to tail cyclized peptide with a highly stabilized β-hairpin structure, as confirmed by circular dichroism (CD) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and molecular dynamics (MD) simulations. TPP-10 exhibited a significant improvement in binding affinity (KD) for PD-L1 compared with TPP-1, along with markedly enhanced in vivo stability. We further evaluated these peptides as radioligands using PET imaging with 68Ga and 64Cu. [68Ga]TPP-10 demonstrated significantly increased tumor uptake and retention in mouse models, and this performance improvement was even more pronounced when the longer-lived radionuclide 64Cu was employed. Collectively, these results identify TPP-10 as a promising clinical candidate for PD-L1 PET imaging and highlight β-hairpin-oriented peptide engineering as a powerful approach for developing radiopharmaceuticals targeting aberrant PPIs.
Insights
Researchers engineered TPP-10, a highly stable peptide binder for programmed death ligand 1 (PD-L1), using a β-hairpin design. This peptide shows promise for cancer imaging and therapy by improving tumor targeting and retention in PET scans.
Area of Science:
- Biochemistry and Molecular Biology
- Radiopharmaceutical Chemistry
- Cancer Therapeutics
Background:
- Peptide-based radiopharmaceuticals are crucial for noninvasive cancer diagnosis and therapy.
- Discovering high-affinity, stable peptide ligands for cancer targets like programmed death ligand 1 (PD-L1) is challenging.
- Conformation-oriented design is effective for developing binders to protein-protein interaction (PPI) targets.
Purpose of the Study:
- To engineer high-affinity and stable peptide binders targeting PD-L1 using a β-hairpin conformation-oriented strategy.
- To develop novel peptide-based radioligands for Positron Emission Tomography (PET) imaging of PD-L1.
- To assess the in vivo performance of engineered peptides for cancer detection and potential therapy.
Main Methods:
- Iterative optimization of a de novo peptide (TPP-1) by incorporating β-turn and Trpzip motifs, followed by amide cyclization to stabilize a β-hairpin structure, yielding TPP-10.
- Structural confirmation of the stabilized β-hairpin using circular dichroism (CD), nuclear magnetic resonance (NMR) spectroscopy, and molecular dynamics (MD) simulations.
- Evaluation of peptide binding affinity (KD) and in vivo stability, followed by radiolabeling with 68Ga and 64Cu for PET imaging in mouse models.
Main Results:
- TPP-10 demonstrated a highly stabilized β-hairpin structure with significantly improved binding affinity for PD-L1 compared to the prototype TPP-1.
- 68Ga-labeled TPP-10 ([68Ga]TPP-10) showed enhanced tumor uptake and retention in mouse models.
- The performance of [64Cu]TPP-10 was even more pronounced, indicating superior tumor targeting and retention with the longer-lived radionuclide.
Conclusions:
- TPP-10 is a promising clinical candidate for PD-L1-targeted PET imaging due to its enhanced stability and tumor targeting.
- The β-hairpin conformation-oriented peptide engineering strategy is a powerful approach for developing radiopharmaceuticals against aberrant PPIs.
- This work advances the development of targeted cancer diagnostics and therapeutics by optimizing peptide binders for specific protein targets.
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