A series of promising truncated antibacterial tripeptides derived from lactoferricin has been prepared, and their in vitro metabolic stability in the main metabolic compartments, plasma, liver, kidney, stomach, duodenum, and brain, has been investigated for the first time. The potential stabilizing effect of truncation, C-terminal capping, and introduction of the bulky synthetic amino acid biphenylalanine is also investigated. The drug-like peptides displayed large differences in half-lives in the different matrixes ranging from 4.2 min in stomach and duodenum to 355.9 min in liver. Kinetic analysis of the metabolites revealed that several different degrading enzymes simultaneously target the different peptide bonds and that the outcome of the tested strategies to increase the stability is clearly enzyme-specific. Some of the metabolic enzymes even prefer the synthetic modifications incorporated over the natural counterparts. Collectively, it is shown that the necessary antibacterial pharmacophore generates compounds that are not only potent antibacterial peptides, but excellent substrates for the main degrading enzymes. All the amide bonds are thus rapidly targeted by different enzymes despite the short peptidic sequences of the tested compounds. Hence, our results illustrate that several structural changes are needed before these compounds can be considered for oral administration. Strategies to overcome such metabolic challenges are discussed.

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Peptide drugs, as all types of pharmaceuticals, require adequate specifications (i.e. quality attributes, procedures and acceptance criteria) as part of their quality assurance to ensure the safety and efficacy of drug substances (i.e. active pharmaceutical ingredients) and drug products (i.e. finished pharmaceutical dosage forms). Compendial monographs are updated regularly to keep up with the most recent advances in peptide synthesis (e.g. reduced by-products) and analytical technology. Nevertheless, currently applied pharmacopoeial peptide specifications are barely harmonized yet (e.g. large differences between the European Pharmacopoeia and the United States Pharmacopeia), increasing the manufacturers' burden of performing analytical procedures in different ways, using different acceptance criteria. Additionally, the peptide monographs are not always consistent within a single pharmacopoeia. In this review, we highlight the main differences and similarities in compendial peptide specifications (including identification, purity and assay). Based on comparison, and together with additional information from peptide drug substance manufacturers and public evaluation reports on registration files of non-pharmacopoeial peptide drugs, a consistent monograph structure is proposed.

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27SARS-CoV-2 rapidly spread around the globe after its emergence in Wuhan in December 28 2019. With no specific therapeutic and prophylactic options available, the virus was able to 29 infect millions of people. To date, close to half a million patients succumbed to the viral disease, 30 COVID-19. The high need for treatment options, together with the lack of small animal models 31 of infection has led to clinical trials with repurposed drugs before any preclinical in vivo 32 evidence attesting their efficacy was available. We used Syrian hamsters to establish a model 33 to evaluate antiviral activity of small molecules in both an infection and a transmission setting. 34Upon intranasal infection, the animals developed high titers of SARS-CoV-2 in the lungs and 35 pathology similar to that observed in mild COVID-19 patients. Treatment of SARS-CoV-2-36 infected hamsters with favipiravir or hydroxychloroquine (with and without azithromycin) 37 resulted in respectively a mild or no reduction in viral RNA and infectious virus. Micro-CT scan 38 analysis of the lungs showed no improvement compared to non-treated animals, which was 39 confirmed by histopathology. In addition, both compounds did not prevent virus transmission 40 through direct contact and thus failed as prophylactic treatments. By modelling the PK profile 41 of hydroxychloroquine based on the trough plasma concentrations, we show that the total lung 42 exposure to the drug was not the limiting factor. In conclusion, we here characterized a hamster 43 infection and transmission model to be a robust model for studying in vivo efficacy of antiviral 44 compounds. The information acquired using hydroxychloroquine and favipiravir in this model 45 is of critical value to those designing (current and) future clinical trials. At this point, the data 46 here presented on hydroxychloroquine either alone or combined with azithromycin (together 47 with previously reported in vivo data in macaques and ferrets) provide no scientific basis for 48 further use of the drug in humans. 49

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Since its emergence in Wuhan, China in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread worldwide resulting in a global pandemic with >2 million deaths within a year of the emergence of the virus. In the search for small molecule inhibitors of SARS-CoV-2 Molnupiravir (EIDD-2801), an orally bioavailable nucleoside analog that was originally developed as an antiviral against influenza viruses but that exerts also activity against a number of other RNA viruses, including SARS-CoV2 and other coronaviruses. We here report on the effect of EIDD-2801 in a well-established Syrian hamster SARS-CoV-2 infection model. Oral treatment of SARS-CoV-2-infected hamsters with EIDD-2801 for four consecutive days, starting from the day of infection, significantly reduced infectious virus titers and viral RNA loads in the lungs and markedly improved lung histopathology in a dose-dependent manner when assessed at 4 dpi. When onset of treatment with 500 mg/kg/dose was delayed until 24h post-infection, a modest but significant antiviral effect was observed. When suboptimal doses of both favipiravir (300 mg/kg, BID) and EIDD-2801 (150 mg/kg, BID) were combined, a complete reduction (~5 log10) of infectious virus titers was observed in the lungs of most of the combo-treated animals whereas either compound alone resulted in a reduction of respectively 1.2 and 1.3 log10. The potential of EIDD-2801 for the treatment and/or prevention of SARS-CoV-2 alone or in combination with favipiravir deserves further attention.