A small-molecule SARS-CoV-2 inhibitor targeting the membrane protein (preprint)

The membrane (M) protein of betacoronaviruses is well-conserved and plays a key role in viral assembly. Here, we describe the discovery of JNJ-9676, a novel small molecule targeting the coronaviral (CoV) M protein. JNJ-9676 demonstrates in vitro nanomolar antiviral activity against SARS-CoV2, SARS-CoV, and sarbecovirus strains from bat and pangolin zoonotic origin. Using cryogenic electron microscopy, we determined a novel binding pocket of JNJ-9676 in the M protein's transmembrane domain. Compound binding stabilized the M protein in an altered conformational state between its long- and short-forms, preventing the release of infectious virus. In a pre-exposure Syrian golden hamster model, JNJ-9676 (25 mg/kg BID) showed excellent efficacy illustrated by a significant reduction in viral load and infectious virus in the lung by 3.5 log10 and 4 log10, respectively. Histopathology scores at this dose were reduced to baseline. In a post-exposure hamster model, JNJ-9676 was efficacious at 75mg/kg BID even when added at 48 h post-infection, when peak viral loads were observed. The M protein is an attractive novel antiviral target to block coronavirus replication with JNJ-9676 representing an interesting chemical series towards identifying clinical candidates addressing the current and future CoV pandemics.

Hybrid immunity to SARS-CoV-2 arises from serological recall of IgG antibodies distinctly imprinted by infection or vaccination (preprint)

We used plasma IgG proteomics to study the molecular composition and temporal durability of polyclonal IgG antibodies triggered by ancestral SARS-CoV-2 infection, vaccination, or their combination ("hybrid immunity"). Infection, whether primary or post-vaccination, mainly triggered an anti-spike antibody response to the S2 domain, while vaccination predominantly induced anti-RBD antibodies. Immunological imprinting persisted after a secondary (hybrid) exposure, with >60% of the ensuing serological response originating from the initial antibodies generated during the first exposure. We highlight one instance where hybrid immunity arising from breakthrough infection resulted in a marked increase in the breadth and affinity of a highly abundant vaccination-elicited plasma IgG antibody, SC27. With an intrinsic binding affinity surpassing a theoretical maximum (KD < 5 pM), SC27 demonstrated potent neutralization of various SARS-CoV-2 variants and SARS-like zoonotic viruses (IC50 ~0.1-1.75 nM) and provided robust protection in vivo. Cryo-EM structural analysis unveiled that SC27 binds to the RBD class 1/4 epitope, with both VH and VL significantly contributing to the binding interface. These findings suggest that exceptionally broad and potent antibodies can be prevalent in plasma and can largely dictate the nature of serological neutralization.