SARS-CoV-2 uses human angiotensin-converting enzyme 2 (ACE2) as the primary receptor to enter host cells and initiate the infection. The critical binding region of ACE2 is an ∼30-amino-acid (aa)-long helix. Here, we report the design of four stapled peptides based on the ACE2 helix, which is expected to bind to SARS-CoV-2 and prevent the binding of the virus to the ACE2 receptor and disrupt the infection. All stapled peptides showed high helical contents (50 to 94% helicity). In contrast, the linear control peptide NYBSP-C showed no helicity (19%). We have evaluated the peptides in a pseudovirus-based single-cycle assay in HT1080/ACE2 cells and human lung cell line A549/ACE2, overexpressing ACE2. Three of the four stapled peptides showed potent antiviral activity in HT1080/ACE2 (50% inhibitory concentration [IC50]: 1.9 to 4.1 μM) and A549/ACE2 (IC50: 2.2 to 2.8 μM) cells. The linear peptide NYBSP-C and the double-stapled peptide StRIP16, used as controls, showed no antiviral activity. Most significantly, none of the stapled peptides show any cytotoxicity at the highest dose tested. We also evaluated the antiviral activity of the peptides by infecting Vero E6 cells with the replication-competent authentic SARS-CoV-2 (US_WA-1/2020). NYBSP-1 was the most efficient, preventing the complete formation of cytopathic effects (CPEs) at an IC100 of 17.2 μM. NYBSP-2 and NYBSP-4 also prevented the formation of the virus-induced CPE with an IC100 of about 33 μM. We determined the proteolytic stability of one of the most active stapled peptides, NYBSP-4, in human plasma, which showed a half-life (T1/2) of >289 min. IMPORTANCE SARS-CoV-2 is a novel virus with many unknowns. No vaccine or specific therapy is available yet to prevent and treat this deadly virus. Therefore, there is an urgent need to develop novel therapeutics. Structural studies revealed critical interactions between the binding site helix of the ACE2 receptor and SARS-CoV-2 receptor-binding domain (RBD). Therefore, targeting the entry pathway of SARS-CoV-2 is ideal for both prevention and treatment as it blocks the first step of the viral life cycle. We report the design of four double-stapled peptides, three of which showed potent antiviral activity in HT1080/ACE2 cells and human lung carcinoma cells, A549/ACE2. Most significantly, the active stapled peptides with antiviral activity against SARS-CoV-2 showed high α-helicity (60 to 94%). The most active stapled peptide, NYBSP-4, showed substantial resistance to degradation by proteolytic enzymes in human plasma. The lead stapled peptides are expected to pave the way for further optimization of a clinical candidate.

We previously reported a milestone in the optimization of NBD-11021, an HIV-1 gp120 antagonist, by developing a new and novel analogue, NBD-14189 (Ref1), which showed antiviral activity against HIV-1 HXB2 , with a half maximal inhibitory concentration of 89 nM. However, cytotoxicity remained high, and the absorption, distribution, metabolism, and excretion (ADME) data showed relatively poor aqueous solubility. To optimize these properties, we replaced the phenyl ring in the compound with a pyridine ring and synthesized a set of 48 novel compounds. One of the new analogues, NBD-14270 (8), showed a marked improvement in cytotoxicity, with 3-fold and 58-fold improvements in selectivity index value compared with that of Ref1 and NBD-11021, respectively. Furthermore, the in vitro ADME data clearly showed improvements in aqueous solubility and other properties compared with those for Ref1. The data for 8 indicated that the pyridine scaffold is a good bioisostere for phenyl, allowing the further optimization of this molecule.

Human angiotensin-converting enzyme 2 (ACE2) is the primary receptor of SARS-CoV-2 to enter the host cells and start the infection process. Therefore, it is prudent to design therapeutics based on the critical binding region of ACE2, which is a ~30 aa long helix with a kink in the middle. However, the small peptide in solution may lose its helical conformation and subsequently lose its binding potential to the SARS-CoV-2 RBD, which it utilizes to bind to that helical region. Here we report the design of four stapled peptides based on that helix, which is expected to bind to SARS-CoV-2 with high affinity and prevent the binding of the virus to the ACE2 receptor and disrupt the infection. All stapled peptides showed high helical contents (50 - 94% helicity). On the contrary, the linear control peptide NYBSP-C showed no helicity (19%). We have evaluated the peptides in a pseudovirus based single-cycle assay in HT1080 and human lung cells, A549. Three of the four stapled peptides showed potent antiviral activity in HT1080 (IC50: 1.9 – 4.1 μ) and A549 cells (IC50: 2.2 – 2.8 μ). It is noteworthy that the stapled peptide, NYBSP-3, which showed the least helical content, also had the lowest antiviral activity in both cell lines. The linear peptides NYBSP-C and SBP1, reported recently to bind SARS-CoV-2 with KD of ~47nM affinity, showed no antiviral activity. Most significantly, none of the stapled peptides show any appreciable cytotoxicity at the highest dose tested. We determined the proteolytic stability of one of the most active stapled peptides, NYBSP-4, in human plasma, which showed a half-life (T1/2) of >289 min.

We report the discovery of several highly potent small molecules with low-nM potency against severe acute respiratory syndrome coronavirus (SARS-CoV; lowest half-maximal inhibitory concentration (IC50: 13 nM), SARS-CoV-2 (IC50: 23 nM), and Middle East respiratory syndrome coronavirus (MERS-CoV; IC50: 76 nM) in pseudovirus-based assays with excellent selectivity index (SI) values (>5000), demonstrating potential pan-coronavirus inhibitory activities. Some compounds showed 100% inhibition against the cytopathic effects (CPE; IC100) of an authentic SARS-CoV-2 (US_WA-1/2020) variant at 1.25 µM. The most active inhibitors also potently inhibited variants of concern (VOCs), including the UK (B.1.1.7) and South African (B.1.351) variants and the Delta variant (B.1.617.2) originally identified in India in pseudovirus-based assay. Surface plasmon resonance (SPR) analysis with one potent inhibitor confirmed that it binds to the prefusion SARS-CoV-2 spike protein trimer. These small-molecule inhibitors prevented virus-mediated cell–cell fusion. The absorption, distribution, metabolism, and excretion (ADME) data for one of the most active inhibitors, NBCoV1, demonstrated drug-like properties. An in vivo pharmacokinetics (PK) study of NBCoV1 in rats demonstrated an excellent half-life (t1/2) of 11.3 h, a mean resident time (MRT) of 14.2 h, and oral bioavailability. We expect these lead inhibitors to facilitate the further development of preclinical and clinical candidates.

We report the discovery of a series of benzoic acid-based inhibitors that show highly potent pancoronavirus activity. Some compounds also show complete inhibition of CPE (IC100) at 1.25 μM against an authentic SARS-CoV-2 (US_WA-1/2020). Furthermore, the most active inhibitors also potently inhibited variants initially identified in the UK and South Africa. We confirmed that one of the potent inhibitors binds to the prefusion spike protein trimer of SARS-CoV-2 by SPR. Besides, we showed that they inhibit virus-mediated cell-cell fusion. The ADME data show druglike characteristics, and in vivo PK in rats demonstrated excellent half-life (t½) of 11.3 h, mean resident time (MRT) of 14.2 h, and orally bioavailable. Despite the presence of ene-rhodamine moiety, we conclusively demonstrated that these inhibitors target the viral spike protein and are not promiscuous or colloidal aggregators. We expect the lead inhibitors to pave the way for further development to preclinical and clinical candidates.