Drug designing strategies targeting S protein and its interactions
The RBD is targeted in many drug designing studies.[25] A peptide sequence with sequence similarity to the RBD of S protein hampered S1-RBD: ACE-2 interaction and prevented entry of SARS-CoV into Vero cells (IC50 around 40 μM).[254950]
A SARS-CoV RBD-specific antibody (FM6) failed to inhibit the occurrence of infection.[39]
OC43-HR2P, a peptide derived from heptad repeat 2 regions of S2 domain of HCoV-OC43 and its optimized form EK1, showed pan-CoV fusion inhibition property.[39] The structure (protein data bank [PDB] ID 5ZUV and 5ZVM) shows a stable 6-helix bundle structure with α-HCoV and long β-HCoV-HR1 domain.[39]
Chloroquine, an antimalarial agent, inhibits SERS-CoV by elevation of endosomal pH and alters the terminal glycosylation of ACE-2, which ultimately interferes with the virus receptor binding.[51]
Other inhibitors SSAA09E2 block the S-ACE2 interaction, SSAA09E1 inhibits the host protease cathepsin L (which is important for viral entry), and SSAA09E3 prevents fusion of host and viral cell membrane.[52]
Kao et al. identified 18 small molecules that targeted the S-ACE-2-mediated entry of virus into human cell.[53] In 293T cells expressing ACE-2, one of these agents (VE607) showed a significant inhibition of SARS-pseudovirus entry.[53] In Vero E6 cells, two other molecules tetra-O-galloyl beta-D-glucose and luteolin also inhibited SARS-pseudovirus and SARS-CoV infection.[53] In virus-infected Vero E6 cells, a siRNA against the S sequences of SARS-CoV inhibited SARS-CoV replication.[2554]
The S230 antibody (origin: memory B-cells of SARS-CoV-infected persons) neutralizes wide spectrum of isolates of SARS-CoV.[55] S230 antibody Fab fragment binds to the SARS-CoV complex to neutralize it, and their structures are also available (PDB IDs: 6NB6, 6NB7, and 6NB8.[55] The monoclonal antibody, m396, has a competitive role for RBD binding (PDB ID: 2DD8).[56]
Monoclonal antibody can be generated by immunizing the spike protein of SERS-CoV (transgenic mice) or from the B-cells of CoV-infected persons.[25] Spike-specific monoclonal antibodies 80R and CR301 block the S-ACE-2 interactions and thus neutralize infection by human SARS-CoV (HKu39849 and Tor2) and palm civet strain (SZ3).[25]
Mice vaccinated with SARS-n DNA showed T-cell immune response (both induction and proliferation),[57] and cytotoxic T-cell response was seen against SARS-DNA-transfected alveolar epithelial cells.