Pre-clinical evaluation of antiviral activity of nitazoxanide against Sars-CoV-2

To address the emergence of SARS-CoV-2, multiple clinical trials in humans were rapidly started, including those involving an oral treatment by nitazoxanide, despite no or limited pre-clinical evidence of antiviral efficacy. In this work, we present a complete pre-clinical evaluation of the antiviral activity of nitazoxanide against SARS-CoV-2. First, we confirmed the in vitro efficacy of nitazoxanide and tizoxanide (its active metabolite) against SARS-CoV-2. Then, we demonstrated nitazoxanide activity in a reconstructed bronchial human airway epithelium model. In a SARS-CoV-2 virus challenge model in hamsters, oral and intranasal treatment with nitazoxanide failed to impair viral replication in commonly affected organs. We hypothesized that this could be due to insufficient diffusion of the drug into organs of interest. Indeed, our pharmacokinetic study confirmed that concentrations of tizoxanide in organs of interest were always below the in vitro EC50. These preclinical results suggest, if directly applicable to humans, that the standard formulation and dosage of nitazoxanide is not effective in providing antiviral therapy for Covid-19.

SARS-CoV-2 20I/501Y.V1 variant in the hamster model

Late 2020, SARS-CoV-2 Alpha variant from lineage B.1.1.7 emerged in United Kingdom and gradually replaced the G614 strains initially involved in the global spread of the pandemic. In this study, we used a Syrian hamster model to compare a clinical strain of Alpha variant with an ancestral G614 strain. The Alpha variant succeeded to infect animals and to induce a pathology that mimics COVID-19. However, both strains replicated to almost the same level and induced a comparable disease and immune response. A slight fitness advantage was noted for the G614 strain during competition and transmission experiments. These data do not corroborate the epidemiological situation observed during the first half of 2021 in humans nor reports that showed a more rapid replication of Alpha variant in human reconstituted bronchial epithelium.

Replicative fitness SARS-CoV-2 20I/501Y.V1 variant in a human reconstituted bronchial epithelium

Since its emergence in 2019, circulating populations of the new coronavirus continuously acquired genetic diversity. At the end of 2020, a variant named 20I/501Y.V1 (lineage B.1.1.7) emerged and replaced other circulating strains in several regions. This phenomenon has been poorly associated to biological evidence that this variant and original strain exhibit different phenotypic characteristics. Here, we analyse the replication ability of this new variant in different cellular models using for comparison an ancestral D614G European strain (lineage B1). Results from comparative replication kinetics experiments in vitro and in a human reconstituted bronchial epithelium showed no difference. However, when both viruses were put in competition in a human reconstituted bronchial epithelium, the 20I/501Y.V1 variant outcompeted the ancestral strain. Altogether, these findings demonstrate that this new variant replicates more efficiently and could contribute to better understand the progressive replacement of circulating strains by the SARS-CoV-2 20I/501Y.V1 variant. ImportanceThe emergence of several SARS-CoV-2 variants raised numerous questions concerning the future course of the pandemic. We are currently observing a replacement of the circulating viruses by the variant from the United Kingdom known as 20I/501Y.V1 from B.1.1.7 lineage but there is little biological evidence that this new variant exhibit a different phenotype. In the present study, we used different cellular models to assess the replication ability of the 20I/501Y.V1 variant. Our results showed that this variant replicate more efficiently in a human reconstituted bronchial epithelium, which may explain why it spreads so rapidly in human populations.

Preclinical evaluation of Imatinib does not support its use as an antiviral drug against SARS-CoV-2

Following the emergence of SARS-CoV-2, the search for an effective and rapidly available treatment was initiated worldwide based on repurposing of available drugs. Previous reports described the antiviral activity of certain tyrosine kinase inhibitors (TKIs) targeting the Abelson kinase 2 against pathogenic coronaviruses. Imatinib, one of them, has more than twenty years of safe utilization for the treatment of hematological malignancies. In this context, Imatinib was rapidly evaluated in clinical trials against Covid-19. Here, we present the pre-clinical evaluation of Imatinib in multiple models. Our results indicated that Imatinib and another TKI, the Masitinib, exhibit an antiviral activity in VeroE6 cells. However, Imatinib was inactive in a reconstructed bronchial human airway epithelium model. In vivo, Imatinib therapy failed to impair SARS-CoV-2 replication in a golden Syrian hamster model despite high concentrations in plasma and in the lung. Overall, these results do not support the use of Imatinib and similar TKIs as antivirals in the treatment of Covid-19.

Favipiravir and severe acute respiratory syndrome coronavirus 2 in hamster model

Despite no or limited pre-clinical evidence, repurposed drugs are massively evaluated in clinical trials to palliate the lack of antiviral molecules against SARS-CoV-2. Here we used a Syrian hamster model to assess the antiviral efficacy of favipiravir, understand its mechanism of action and determine its pharmacokinetics. When treatment was initiated before or simultaneously to infection, favipiravir had a strong dose effect, leading to dramatic reduction of infectious titers in lungs and clinical alleviation of the disease. Antiviral effect of favipiravir correlated with incorporation of a large number of mutations into viral genomes and decrease of viral infectivity. The antiviral efficacy observed in this study was achieved with plasma drug exposure comparable with those previously found during human clinical trials and was associated with weight losses in animals. Thereby, pharmacokinetic and tolerance studies are required to determine whether similar effects can be safely achieved in humans.