We recently published a preliminary assessment of the activity of a poly (ADP-ribose) polymerase (PARP) inhibitor, stenoparib, also known as 2X-121, which inhibits viral replication by affecting pathways of the host. Here we show that stenoparib effectively inhibits a SARS-CoV-2 wild type (BavPat1/2020) strain and four additional variant strains; alpha (B.1.1.7), beta (B.1.351), delta (B.1.617.2) and gamma (P.1) in vitro, with 50% effective concentration (EC50) estimates of 4.1 μM, 8.5 μM, 24.1 μM, 8.2 μM and 13.6 μM, respectively. A separate experiment focusing on a combination of 10 μM stenoparib and 0.5 μM remdesivir, an antiviral drug, resulted in over 80% inhibition of the alpha variant, which is substantially greater than the effect achieved with either drug alone, suggesting at least additive effects from combining the different mechanisms of activity of stenoparib and remdesivir.

New therapeutics are urgently needed in the fight against COVID-19. Repurposing drugs that are either already approved for human use or are in advanced stages of the approval process can facilitate more rapid advances toward this goal.

ABSTRACTBy late 2020, the coronavirus disease (COVID-19) pandemic, caused by SARS-CoV-2 has caused tens of millions of infections and over 1 million deaths worldwide. A protective vaccine and more effective therapeutics are urgently needed. We evaluated a new PARP inhibitor, stenoparib, which was recently advanced to Stage II clinical trials for treatment of ovarian cancer, for activity against human respiratory coronaviruses, including SARS-CoV-2,in vitro. Stenoparib exhibits dose-dependent suppression of SARS-CoV-2 multiplication and spread in Vero E6 monkey kidney and Calu-3 human lung adenocarcinoma cells. Stenoparib was also strongly inhibitory to the HCoV-NL63 human seasonal respiratory coronavirus. Compared to remdesivir, which inhibits viral replication downstream of cell entry, stenoparib impedes entry and post-entry processes as determined by time-of-addition (TOA) experiments. Moreover, a 10 μM dosage of stenoparib – below the approximated 25.5 μM half-maximally effective concentration (EC50), combined with 0.5 μM remdesivir suppressed coronavirus growth by more than 90%, indicating a potentially synergistic effect for this drug combination. Stenoparib as a standalone or as part of combinatorial therapy with remdesivir should be a valuable addition to the arsenal against COVID-19.ImportanceNew therapeutics are urgently needed in the fight against COVID-19. Repurposing drugs that are either already approved for human use or are in advanced stages of the approval process can facilitate more rapid advances toward this goal. The PARP inhibitor stenoparib may be such a drug, as it is currently in Stage II clinical trials for the treatment of ovarian cancer and its safety and dosage in humans has already been established. Our results indicate that stenoparib possesses strong antiviral activity against SARS-CoV-2 and other coronavirusesin vitro.This activity appears to be based on multiple modes of action, where both pre-entry and post-entry viral replication processes are impeded. This may provide a therapeutic advantage over many current options that have a narrower target range. Moreover, our results suggest that stenoparib and remdesivir in combination may be especially potent against coronavirus infection.