Oral Presentation 8th Venoms to Drugs 2023

Constrained Peptides as Viral Protease Inhibitors (#39)

Christoph Nitsche 1
  1. Australian National University, Canberra, ACT, Australia

Many pathogenic RNA viruses require proteases for viral replication. Protease inhibitors in clinical use are often modified peptide substrate analogues with chemical modifications such as electrophilic warheads or transition state mimetics. Examples are approved drugs against HIV, hepatitis C virus (HCV), and the recently approved SARS-CoV-2 main protease inhibitor nirmatrelvir. Our research aims to complement these efforts by exploring constrained peptides as viral protease inhibitors.

Constrained peptides fill an important area of chemical space between small molecule therapies and larger antibodies. Constraining a peptide by macrocyclization or stapling can (i) enhance metabolic stability by greater resistance towards proteolysis, (ii) promote biological uptake across cell membranes, and (iii) decrease the entropic penalty of binding by locking the peptide in the active conformation.

We have developed unnatural amino acids specifically designed for macrocyclization and stapling of peptides.1,2 Reactions usually proceed under biocompatible conditions in the presence of viral proteases, allowing for the identification of constrained protease inhibitors. Our unnatural amino acids can also be charged onto tRNA enabling their use in genetically encoded cyclic and bicyclic peptide libraries to identify new antiviral compounds.3

Bicyclic peptides can provide enhanced conformational rigidity, metabolic stability, and even antibody-like affinity and specificity. We investigated biocompatible chemical methods to generate bicyclic peptides, which exhibited plasma stability, conformational preorganization, and nanomolar inhibition of viral proteases. The incorporation of bismuth into peptides allowed for the in situ access to high-affinity bicyclic peptides during biochemical screening assays, as demonstrated for two viral proteases.5 Additionally, we successfully developed peptide-bismuth bicycles that can efficiently penetrate mammalian cell membranes, representing a novel class of highly efficient cell-penetrating peptides.6

  1. Morewood, R., Nitsche, C., A Biocompatible Stapling Reaction for in situ Generation of Constrained Peptides, Chem. Sci. 2021, 12, 669–674.
  2. Morewood, R., Nitsche, C., Bioinspired Peptide Stapling Generates Stable Enzyme Inhibitors, Chem. Commun. 2022, 58, 10817–10820.
  3. Liu, M., Morewood, R., Yoshisada, R., Pascha, M. N., Hopstaken, A. J. P., Tarcoveanu, E., Poole, D. A., de Haan, C. A. M., Nitsche, C., Jongkees, S. A. K., An N-Terminal Selective Thiazoline Peptide Macrocyclisation Compatible with mRNA Display and Efficient SPPS, ChemRxiv 2023, 10.26434/chemrxiv-2023-wdbkx.
  4. Ullrich, S., George, J., Coram, A. E., Morewood, R., Nitsche, C., Biocompatible and Selective Generation of Bicyclic Peptides, Angew. Chem. Int. Ed. 2022, 61, e202208400.
  5. Voss, S., Rademann, J., Nitsche, C., Peptide-Bismuth Bicycles: In Situ Access to Stable Constrained Peptides with Superior Bioactivity, Angew. Chem. Int. Ed. 2022, 61, e202113857.
  6. Voss, S., Adair, L. D., Achazi, K., Kim, H., Bergemann, S., Bartenschlager, R., New, E. J., Rademann, J., Nitsche, C., Cell-Penetrating Peptide–Bismuth Bicycles, ChemRxiv 2023, 10.26434/chemrxiv-2023-mgxdm.