Computational de novo design using Rosetta created two heterochiral macrocyclic peptides (PD-i3, PD-i6) that bind PD-1 and block the PD-1/PD-L1 immune checkpoint interaction, with NMR-confirmed structures.
De novo designed PD-1 blockersComputer-designed cyclic peptides that block the same immune checkpoint as pembrolizumab (Keytruda) — potentially cheaper and more accessible
What the researchers found
Two de novo designed heterochiral macrocyclic peptides (PD-i3, PD-i6) bind PD-1 and block the PD-1/PD-L1 interaction. NMR elucidation confirmed computational structure predictions. The Rosetta framework enables generalizable design of target-specific cyclic peptides.
Why it matters
Current PD-1 checkpoint inhibitors are expensive antibodies requiring IV infusion. Small cyclic peptides could potentially be cheaper, more stable, and potentially orally available — democratizing access to cancer immunotherapy.
The numbers in context
2 lead peptides (PD-i3, PD-i6); heterochiral D/L design; Rosetta framework; NMR-confirmed structures; block PD-1/PD-L1
How the study worked
Computational de novo design using Rosetta with large-scale backbone sampling, side-chain composition, and energy scoring. Heterochiral (D/L) cyclic peptide synthesis. Biophysical evaluation of PD-1 binding and PD-L1 blocking. NMR structure confirmation.
Who was studied
In silico design and in vitro biophysical validation
What this study cannot tell us
Biophysical binding data only — no cell-based or in vivo anti-tumor efficacy testing. Binding affinity compared to antibody checkpoint inhibitors not reported. Oral bioavailability and stability in biological fluids not assessed.
How to read the evidence
Low evidence grade: computational design with biophysical validation only. No biological activity or anti-tumor efficacy data.
When this study was published
Published 2021. Computational peptide design and cyclic peptide checkpoint inhibitors are rapidly advancing fields.
The bigger picture
This demonstrates that computational platforms can now design bioactive cyclic peptides targeting specific protein surfaces — a capability that could accelerate drug discovery across oncology, autoimmunity, and infectious disease by making "undruggable" targets accessible.
Questions still open
- Can these cyclic peptides activate anti-tumor immunity in animal cancer models?
- How does their PD-1 binding affinity compare to approved antibody checkpoint inhibitors?
- Could this design framework be applied to other immune checkpoints like CTLA-4 or LAG-3?
Common questions
What is PD-1 and why target it?
Can computers really design new drugs from scratch?
Read the original research
Target-templated de novo design of macrocyclic d-/l-peptides: discovery of drug-like inhibitors of PD-1.
Chemical science, 12(14), 5164-5170
Citation
Guardiola, Salvador; Varese, Monica; Roig, Xavier; Sánchez-Navarro, Macarena; García, Jesús; Giralt, Ernest. (2021). Target-templated de novo design of macrocyclic d-/l-peptides: discovery of drug-like inhibitors of PD-1.. Chemical science, 12(14), 5164-5170. https://doi.org/10.1039/d1sc01031j