Discovery of Retro-1 Analogs Exhibiting Enhanced Anti-vaccinia Virus Activity

Abstract

Orthopoxviruses (OPXVs) are an increasing threat to human health due to the growing population of OPXV-naive individuals after the discontinuation of routine smallpox vaccination. Antiviral drugs that are effective as postexposure treatments against variola virus (the causative agent of smallpox) or other OPXVs are critical in the event of an OPXV outbreak or exposure. The only US Food and Drug Administration-approved drug to treat smallpox, Tecovirimat (ST-246), exerts its antiviral effect by inhibiting extracellular virus (EV) formation, thereby preventing cell-cell and long-distance spread. We and others have previously demonstrated that host Golgi-associated retrograde proteins play an important role in monkeypox virus (MPXV) and vaccinia virus (VACV) EV formation. Inhibition of the retrograde pathway by small molecules such as Retro-2 has been shown to decrease VACV infection in vitro and to a lesser extent in vivo. To identify more potent inhibitors of the retrograde pathway, we screened a large panel of compounds containing a benzodiazepine scaffold like that of Retro-1, against VACV infection. We found that a subset of these compounds displayed better anti-VACV activity, causing a reduction in EV particle formation and viral spread compared to Retro-1. PA104 emerged as the most potent analog, inhibiting 90% viral spread at 1.3 µM with a high selectivity index. In addition, PA104 strongly inhibited two distinct ST-246resistant viruses, demonstrating its potential benefit for use in combination therapy with ST-246. These data and further characterizations of the specific protein targets and in vivo efficacy of PA104 may have important implications for the design of effective antivirals against OPXV.

Inhibition of vaccinia virus L1 N-myristoylation by the host N-myristoyltransferase inhibitor IMP-1088 generates non-infectious virions defective in cell entry

“…Viral spread assay. The viral spread assay was performed as previously described [50]. Briefly, IMP-1088 was serially diluted and mixed with VACV-WR-GFP virus diluted in DMEM-2.…”

A brief on new waves of monkeypox and vaccines and antiviral drugs for monkeypox

“… 17 So tecovirimat exerts its antiviral effect by inhibiting extracellular virus formation, and thereby preventing cell–cell and long-distance spread. 18 In infected cynomolgus macaques with tecovirimat treatment at 5, 6, 7, or 8 days following MPXV challenge, survival rate was 100%, 67%, 100%, and 50%, respectively. 19 Even with delayed administration for post–challenge therapy, tecovirimat is effective against MPXV infection.…”

“…Host Golgi-associated retrograde proteins play a role in EV formation from MPXV and vaccinia virus. 18 Inhibition of the retrograde pathway by small molecules, such as Retro-2, was found to be able to decrease vaccinia virus infection. 18 PA104, a new compound containing a benzodiazepine scaffold similar to that of Retro protein, could inhibit 90% viral spread at 1.3 μM with a high selectivity index.…”

“… 18 Inhibition of the retrograde pathway by small molecules, such as Retro-2, was found to be able to decrease vaccinia virus infection. 18 PA104, a new compound containing a benzodiazepine scaffold similar to that of Retro protein, could inhibit 90% viral spread at 1.3 μM with a high selectivity index. 18 PA104 strongly inhibited two distinct tecovirimat-resistant viruses, demonstrating its potential benefit for use in combination therapy with tecovirimat.…”

“… 18 PA104, a new compound containing a benzodiazepine scaffold similar to that of Retro protein, could inhibit 90% viral spread at 1.3 μM with a high selectivity index. 18 PA104 strongly inhibited two distinct tecovirimat-resistant viruses, demonstrating its potential benefit for use in combination therapy with tecovirimat. 18 Even with excellent antiviral effect in vitro , the effect of PA104 against MPXV in vivo needs more solid evidence.…”