Even with its endemic transition, the COVID-19 pandemic remains a public health threat, particularly in the light of emerging variants of concern (VoCs) and the need for pandemic preparedness in the future. In November 2021, the SARS-CoV-2 VoC Omicron emerged and its subvariants BA.1, BA.2 and BA.5 became predominant. Although the protease inhibitor Paxlovid^® and the polymerase inhibitors Molnupiravir and Remdesivir were approved as specific antiviral treatment options for COVID-19 patients in the early stages after infection, effective prophylactically acting substances without adverse effects are not available yet. In a recent study, we demonstrated that iota-carrageenan, a sulfated polysaccharide extracted from red seaweed, efficiently inhibits the replication of the SARS-CoV-2 Wuhan Type and the VoCs Alpha, Beta, Gamma and Delta. Now, we extended this study by investigating the antiviral effects of iota-, lambda- and kappa-carrageenans on the VoC Omicron subvariants BA.1, BA.2 and BA.5. Using a VoC Omicron BA.1 spike pseudotyped murine leukemia virus (BA.1 MLV_OMVLP) as well as patient-derived SARS-CoV-2 Omicron isolates BA.1, BA.2 and BA.5 (SARS-CoV-2_{OM BA.1}, SARS-CoV-2_{OM BA.2} and SARS-CoV-2_{OM BA.5}), we demonstrate that iota-carrageenan exhibits similar antiviral activity against all analyzed Omicron subvariants. As with other VoCs shown before, the biologically inert iota-carrageenan was more efficient than kappa- and lambda-carrageenan. Altogether, these results confirm that, independent of the current and potential future variants, the physical barrier provided by iota-carrageenan might be applicable for prophylaxis and early treatment of SARS-CoV-2 infections.

Host-directed antivirals (HDAs) represent an attractive treatment option and a strategy for pandemic preparedness, especially due to their potential broad-spectrum antiviral activity and high barrier to resistance development. Particularly, dual-targeting HDAs offer a promising approach for antiviral therapy by simultaneously disrupting multiple pathways essential for viral replication. Izumerogant (IMU-935) targets two host proteins, (i) the retinoic acid receptor-related orphan receptor γ isoform 1 (RORγ1), which modulates cellular cholesterol metabolism, and (ii) the enzyme dihydroorotate dehydrogenase (DHODH), which is involved in de novo pyrimidine synthesis. Here, we synthesized optimized derivatives of izumerogant and characterized their antiviral activity in comparison to a recently described structurally distinct RORγ/DHODH dual inhibitor. Cell culture-based infection models for enveloped and non-enveloped DNA and RNA viruses, as well as a retrovirus, demonstrated high potency and broad-spectrum activity against human viral pathogens for RORγ/DHODH dual inhibitors at nanomolar concentrations. Comparative analyses with equipotent single-target inhibitors in metabolite supplementation approaches revealed that the dual-targeting mode represents the mechanistic basis for the potent antiviral activity. For SARS-CoV-2, an optimized dual inhibitor completely blocked viral replication in human airway epithelial cells at 5 nM and displayed a synergistic drug interaction with the nucleoside analog molnupiravir. In a SARS-CoV-2 mouse model, treatment with a dual inhibitor alone, or in combination with molnupiravir, reduced the viral load by 7- and 58-fold, respectively. Considering the clinical safety, oral bioavailability, and tolerability of izumerogant in a recent Phase I study, izumerogant-like drugs represent potent dual-targeting antiviral HDAs with pronounced broad-spectrum activity for further clinical development.

Starting in 2019, the spread of respiratory syndrome coronavirus 2 (SARS-CoV-2) and the associated pandemic of the corona virus disease (COVID-19) has led to enormous efforts in the development of medical countermeasures. Although innovative vaccines have scaled back the number of severe COVID cases, the emergence of the omicron variant (B.1.1.529) illustrates how vaccine development struggles to keep pace with viral evolution. On the other hand, while the recently approved antiviral drugs remdesivir, molnupiravir, and Paxlovid are considered as broadly acting anti-coronavirus therapeutics, only molnupiravir and Paxlovid are orally available and none of these drugs are recommended for prophylactic use. Thus, so far unexploited small molecules, targeting strategies, and antiviral mechanisms are urgently needed to address issues in the current pandemic and in putative future outbreaks of newly emerging variants of concern. Recently, we and others have described the anti-infective potential and particularly the pronounced antiviral activity of artesunate and related compounds of the trioxane/sesquiterpene class. In particular, the trimeric derivative TF27 demonstrated strong anti-cytomegalovirus activity at nanomolar concentrations in vitro as well as in vivo efficacy after oral administration in therapeutic and even prophylactic treatment settings. Here, we extended this analysis by evaluating TF27 for its anti-SARS-CoV-2 potential. Our main findings are as follows: (i) compound TF27 exerted strong anti-SARS-CoV-2 activity in vitro (EC₅₀ = 0.46 ± 0.20 µM), (ii) antiviral activity was clearly distinct from the induction of cytotoxicity, (iii) pretreatment with TF27 prevented virus replication in cultured cells, (iv) antiviral activity has likewise been demonstrated in Calu-3 human lung and Caco-2 human colon cells infected with wild-type, delta, or omicron SARS-CoV-2, respectively, and (v) analysis of TF27 combination treatments has revealed synergistic interaction with GC376, but antagonistic interaction with EIDD-1931. Combined, the data demonstrated the pronounced anti-SARS-CoV-2 activity of TF27 and thus highlight the potential of trioxane compounds for further pharmacologic development towards improved options for COVID-specific medication.