Intranasal administration of broad-spectrum macrocyclic peptide inhibitor protects against SARS-CoV-2 Omicron variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to cause significant morbidity and mortality despite the end of its pandemic phase. The emergence of highly mutated SARS-CoV-2 variants of concern highlights the requirement of broad-spectrum antiviral countermeasures which possess both prophylactic and therapeutic efficacies. Here, we obtain a macrocyclic peptide, 6L3-3P11K, that effectively inhibits a wide range of SARS-CoV-2 variants and subvariants. Structural studies show that 6L3-3P11K forms homotrimers that lock the spike protein (S) trimer into a “closed” conformation by engaging a conserved non-receptor binding motif (non-RBM) of S. This interaction disrupts the binding between S and ACE2 receptor. Structure-guided modifications result in a thermostable and trypsin-resistant macrocyclic peptide, 6L3-1F3P11hR, that exhibits prophylactic and therapeutic effects against SARS-CoV-2 infection in a male hACE2 transgenic mouse model after intranasal administration. Our results provide a drug candidate for the control and prevention of COVID-19 and may stimulate further research on macrocyclic broad-spectrum anti-coronavirus drug development. Newly emerging SARS-CoV-2 variants underscore the need for broad-spectrum antiviral solutions. This study shows a macrocyclic peptide inhibitor that locks the SARS-CoV-2 spike trimer into a “closed” conformation by engaging a conserved region, and demonstrates that intranasal administration of the peptide inhibitor protects against Omicron variants.