Macrocycles are a highly interesting modality to modulate difficult-to-drug targets, but often reside in chemical space where obtaining sufficient cell permeability and solubility is challenging. We have determined permeability across Caco-2 cells, aqueous solubility and log D for four series of semipeptidic macrocycles and one series of linear matched molecular pairs. By using X-ray crystallography, NMR spectroscopy, and computational chemistry, unexpected permeability differences between series and matched pairs were explained by differences in conformational preferences that determine the formation of intramolecular interactions. Macrocycles that formed intramolecular NH-π interactions and hydrogen bonds were more permeable than matched pairs unable to form such interactions. The elevated permeability of linear compounds was concluded to result from their greater conformational flexibility, allowing them to shield amide bonds and expose nonpolar groups to a greater extent than their macrocyclic matched pairs. Solubility was less dependent on specific intramolecular interactions and was predominantly low at log D >2.5.

Dengue is a global health emergency, with annually increasing case numbers that overwhelm healthcare systems, an ever-expanding range of the mosquito vector, and no antiviral or host-directed treatments proven to alter the course of disease. This article reports on a meeting of the Dengue Therapeutics Consortium, which included attendees from 19 countries with backgrounds in basic science, clinical research, drug development, industry, clinical trial methodology and policy. We summarise the current state of dengue therapeutics research and highlight the necessary steps to ensure that patients have equitable access to affordable and effective treatments. We review the antiviral pipeline, including novel and repurposed antiviral candidates, and we propose both human challenge and rate of viral clearance studies as methods to rapidly screen for antiviral activity prior to larger phase 3 clinical trials. We review ongoing phase 2 and phase 3 clinical trials to evaluate repurposed host-directed therapies for patients with moderate and severe disease, and we suggest considerations for future trial design, such as factorial randomisation and the use of a core outcome set to maximise efficiency and enable evidence synthesis by meta-analysis. We consider that multisectoral collaboration will be essential to achieve our aim of effective treatments for dengue. This will include drug development aligned to target product profiles, conduct of clinical trials with endpoints acceptable to both patients and regulators and sustained commitment from the pharmaceutical industry, non-profit initiatives and policymakers to ensure that effective treatments reach those who need them the most.

Applications of AI to the discovery of new treatments could have a large impact on the acceleration of drug discovery for neglected diseases such as Leishmaniasis. Taking advantage of a lead compound derived from a library of 1.8 million molecules screened against Leishmaniasis Infantum and a dataset used for further refining the lead compound potency and metabolic stability, we fine-tuned a foundational model MMELON (Multi-view Molecular Embedding with Late Fusion) to accurately predict these properties with high AUROCs of 0.90 and 0.87 respectively. Indeed, although the lead compound had many promising properties, such as high potency, low host cell toxicity, and excellent in vivo efficacy, high clearance and low bioavailability made it unfit for implementation in a clinical trial. In order to find new molecules with the desired properties, the fine-tuned MMELON was then used to generate new predictions, prospecting the 10,000 molecules from the Enamine library with most similarity to the lead compound. The purpose was to obtain a new diverse set of molecules with high potency and metabolic stability, to further explore clearance and bioavailability. A subset of 59 new compounds were chosen using fine-tuned MMELON predictions and sent for further experimental testing. Overall, 29 hits (49.2%) were correctly predicted to have high potency and 14 hits (23.7%) were correctly predicted to have low metabolic rate. The molecules were also quite distinct from the lead compound DNDI-6993, opening new avenues for the development and implementation of a new treatment for Leishmaniasis.

Chagas disease (CD), caused by the flagellate protozoan Trypanosoma cruzi, is a neglected tropical disease endemic in 21 countries. The only two antiparasitic drugs approved for its treatment, benznidazole and nifurtimox, have significant drawbacks. We present herein the optimization of a series of substituted indoles that were identified through phenotypic screening against T. cruzi. Early lead compounds with balanced potency and physicochemical properties were advanced to animal studies but showed limited plasma exposure. Medicinal chemistry strategies were used to improve metabolic stability and solubility, but unfortunately, this effort failed to yield compounds with improvements in both exposure and potency. Still, the best compound was progressed for a proof-of-concept efficacy study using acute and chronic mice models of Chagas disease. Despite showing antiparasitic activity in these in vivo studies, the optimization work with this series was stopped due to unfavorable drug metabolism and pharmacokinetic (DMPK) properties and a deprioritized mechanism of action (CYP51 inhibition).

The 2020 SARS-CoV-2 coronavirus pandemic highlighted the urgent need for novel small molecule antiviral drugs. (S)-x38 DNDI-6510 is a non-covalent SARS-CoV-2 main protease inhibitor developed by the open science collaboration COVID Moonshot. Here, we report on the metabolic and toxicologic optimization of the lead series previously disclosed by the COVID Moonshot Initiative, leading up to the selection of (S)-x38 DNDI-6510 as the preclinical candidate. We describe the thorough profiling of the series, identifying key risks such as formation of genotoxic metabolites and high clearance, which were successfully addressed during lead optimization. In addition, we disclose the in vitro and in vivo evaluation of (S)-x38 DNDI-6510 in pharmacokinetic and pharmacodynamic models, exploring multiple approaches to ameliorate rodent-specific metabolic clearance, and show that both co-dosing of (S)-x38 DNDI-6510 with an ABT inhibitor and utilizing a metabolically humanized mouse model (8HUM) achieve significant improvements in exposure. Through comparisons of ABT co-dosing and humanized mouse models in efficacy experiments, we demonstrate that continuous exposure over cellular EC90 is required for SARS-CoV-2 antiviral efficacy in vivo in an antiviral model using a mouse-adapted SARS-CoV-2 strain. Finally, (S)-x38 DNDI-6510 was assessed in maximum tolerated dose experiments in two species, demonstrating significant in vivo PXR-linked auto-induction of metabolism, leading to the discontinuation of this compound. In summary, we report the successful effort to overcome series-specific AMES liabilities in a lead development program. Downstream optimization of existing series will require in-depth optimization of rodent-specific liabilities and metabolic induction profile.

Dengue, caused by any one of four distinct virus serotypes, is the most rapidly spreading mosquito-borne viral disease worldwide. It is a primary arboviral infection with increasing global incidence, driven by climate change, urbanisation, and the expanding range of Aedes mosquito vectors. Despite growing research interest, outcome and measurement instrument heterogeneity in dengue clinical trials remains high, limiting comparability and evidence synthesis. This project aimed to develop a globally relevant Core Outcome Measurement Set (COMS) for use in dengue clinical trials through international consensus. This consensus study followed core outcome measures in effectiveness trials and Core Outcome Set-Standards for Development (COS-STAD) guidelines and was conducted in two phases. Phase 1 focused on developing a Core Outcome Set (COS) through four steps: (1) a systematic literature review; (2) qualitative interviews with people with lived experience of dengue; (3) review by the management group and steering committee; (4) a two-round modified Delphi survey and structured online consensus meetings to finalise the COS for hospitalised and early stages of dengue disease. Input from critical care experts informed recommendations for the intensive care unit (ICU) and high dependency unit COS. Phase 2 consisted of a further two steps: (1) targeted review of outcome measurement instruments; and (2) a hybrid international consensus workshop to finalise the COMS. The agreed COMS for hospitalised dengue included seven outcomes; the early stage dengue COS included these outcomes plus four more. For critical care trials, use of existing ICU-specific COS was recommended. Unified definitions were developed for nine clinician-reported outcomes. The DEN-CORE COMS provides a consensus-based framework for harmonising outcome selection and measurement in dengue trials, improving comparability and supporting policy and clinical decision making.

BackgroundThe current pipeline for new antibiotics fails to fully address the significant threat posed by drug-resistant Gram-negative bacteria that have been identified by the World Health Organization (WHO) as a global health priority. New antibacterials acting through novel mechanisms of action are urgently needed. We aimed to identify new chemical entities (NCEs) with activity against Klebsiella pneumoniae and Acinetobacter baumannii that could be developed into a new treatment for drug-resistant infections.MethodsWe developed a high-throughput phenotypic screen and selection cascade for generation of hit compounds active against multidrug-resistant (MDR) strains of K. pneumoniae and A. baumannii. We screened compound libraries selected from the proprietary collections of three pharmaceutical companies that had exited antibacterial drug discovery but continued to accumulate new compounds to their collection. Compounds from two out of three libraries were selected using “eNTRy rules” criteria associated with increased likelihood of intracellular accumulation in Escherichia coli.FindingsWe identified 72 compounds with confirmed activity against K. pneumoniae and/or drug-resistant A. baumannii. Two new chemical series with activity against XDR A. baumannii were identified meeting our criteria of potency (EC50 ≤50 μM) and absence of cytotoxicity (HepG2 CC50 ≥100 μM and red blood cell lysis HC50 ≥100 μM). The activity of close analogues of the two chemical series was also determined against A. baumannii clinical isolates.InterpretationThis work provides proof of principle for the screening strategy developed to identify NCEs with antibacterial activity against multidrug-resistant critical priority pathogens such as K. pneumoniae and A. baumannii. The screening and hit selection cascade established here provide an excellent foundation for further screening of new compound libraries to identify high quality starting points for new antibacterial lead generation projects.FundingBMBF and GARDP.

[This corrects the article DOI: 10.1371/journal.pgph.0002598.].

Macrocycles are prominent among drugs for treatment of infectious disease, with many originating from natural products. Herein we report on the discovery of a series of macrocycles structurally related to the natural product hymenocardine. Members of this series were found to inhibit the growth of Plasmodium falciparum, the parasite responsible for most malaria cases, and of four kinetoplastid parasites. Notably, macrocycles more potent than miltefosine, the only oral drug used for the treatment of the neglected tropical disease visceral leishmaniasis, were identified in a phenotypic screen of Leishmania infantum. In vitro profiling highlighted that potent inhibitors had satisfactory cell permeability with a low efflux ratio, indicating their potential for oral administration, but low solubility and metabolic stability. Analysis of predicted crystal structures suggests that optimization should focus on the reduction of pi-pi crystal packing interactions to reduce the strong crystalline interactions and improve the solubility of the most potent lead.

The SARS-CoV-2 pandemic has highlighted the need for broad-spectrum antiviral drugs to respond promptly to viral emergence. We conducted a preclinical study of molnupiravir (MOV) against SARS-CoV-2 to fully characterise its antiviral properties and mode of action. The antiviral activity of different concentrations of MOV was evaluated ex vivo on human airway epithelium (HAE) and in vivo in a hamster model at three escalating doses (150, 300 and 400 mg/kg/day) according to three different regimens (preventive, pre-emptive and curative). We assessed viral loads and infectious titres at the apical pole of HAE and in hamster lungs, and MOV trough concentration in plasma and lungs. To explore the mode of action of the MOV, the entire genomes of the collected viruses were deep-sequenced. MOV effectively reduced viral titres in HAE and in the lungs of treated animals. Early treatment after infection was a key factor in efficacy, probably associated with high lung concentrations of MOV, suggesting good accumulation in the lung. MOV induced genomic alteration in viral genomes with an increase in the number of minority variants, and predominant G to A transitions. The observed reduction in viral replication and its mechanism of action leading to lethal mutagenesis, supported by clinical trials showing antiviral action in humans, provide a convincing basis for further research as an additional means in the fight against COVID-19 and other RNA viruses.

Dengue is currently the most rapidly spreading mosquito-borne viral infection in the world, with half of the world's population at risk of becoming infected.1WHOGeographical expansion of cases of dengue and chikungunya beyond the historical areas of transmission in the Region of the Americas.https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON448Date: March 23, 2023Date accessed: June 12, 2023Google Scholar As a result of climate change, rapid urbanisation, and widespread international travel, the incidence of dengue is rapidly increasing, overwhelming health-care systems in many lower-income countries. Climate change has increased the burden of dengue in endemic countries and has also led to expansion of this infection to new territories in Europe and North America.2Colón-González FJ Sewe MO Tompkins AM et al.Projecting the risk of mosquito-borne diseases in a warmer and more populated world: a multi-model, multi-scenario intercomparison modelling study.Lancet Planet Health. 2021; 5: e404-e414Summary Full Text Full Text PDF PubMed Scopus (79) Google Scholar Dengue is estimated to infect approximately 390 million individuals annually, with 96 million infections being symptomatic.1WHOGeographical expansion of cases of dengue and chikungunya beyond the historical areas of transmission in the Region of the Americas.https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON448Date: March 23, 2023Date accessed: June 12, 2023Google Scholar So far, the only strategy adopted to reduce the burden of dengue is vector control. Although techniques such as using Wolbachia bacteria to reduce dengue transmission by Aedes mosquitoes look promising,3Utarini A Indriani C Ahmad RA et al.Efficacy of Wolbachia-infected mosquito deployments for the control of dengue.N Engl J Med. 2021; 384: 2177-2186Crossref PubMed Scopus (155) Google Scholar it is evident that vector control alone is unlikely to be adequate to reduce the burden of dengue. The currently available dengue vaccines (CYD-TDV and TAK-003) have been shown to reduce hospitalisations, especially in dengue-seropositive individuals, but lack efficacy against some dengue virus serotypes.4Biswal S Borja-Tabora C Martinez Vargas L et al.Efficacy of a tetravalent dengue vaccine in healthy children aged 4–16 years: a randomised, placebo-controlled, phase 3 trial.Lancet. 2020; 395: 1423-1433Summary Full Text Full Text PDF PubMed Scopus (99) Google Scholar Furthermore, CYD-TDV showed a higher incidence of severe dengue in dengue-naive vaccine recipients, and both vaccines show some degree of waning immunity with time, especially in seronegative individuals.5Thomas SJ Is new dengue vaccine efficacy data a relief or cause for concern?.NPJ Vaccines. 2023; 8: 55Crossref Scopus (2) Google Scholar, 6Hadinegoro SR Arredondo-García JL Capeding MR et al.Efficacy and long-term safety of a dengue vaccine in regions of endemic disease.N Engl J Med. 2015; 373: 1195-1206Crossref PubMed Scopus (772) Google Scholar Therefore, an integrated approach that comprises vector control, use of safe and effective vaccines, and an effective treatment is needed to face the growing challenges of dengue infection. Efforts focused on finding a treatment have been scarce, with some investigator-led clinical trials conducted, and a few performed by pharmaceutical companies.7Troost B Smit JM Recent advances in antiviral drug development towards dengue virus.Curr Opin Virol. 2020; 43: 9-21Crossref Scopus (48) Google Scholar, 8Biering SB Harris E A step towards therapeutics for dengue.Nature. 2021; 598: 420-421Crossref Scopus (3) Google Scholar The importance of developing a treatment for dengue has largely been ignored.9Palanichamy Kala M St John AL Rathore APS Dengue: update on clinically relevant therapeutic strategies and vaccines.Curr Treat Options Infect Dis. 2023; 15: 27-52Crossref Google Scholar The Drugs for Neglected Diseases initiative, which is focused on finding novel affordable treatment solutions for neglected tropical diseases since its inception in 2003, has recently formed a Global Dengue Alliance with several institutions in dengue-endemic countries, including the Faculty of Medicine at Siriraj Hospital, Mahidol University in Thailand; the Ministry of Health in Malaysia; the Translational Health Science and Technology Institute in India; the Oswaldo Cruz Foundation in Brazil; and the Federal University of Minas Gerais in Brazil. The mission of this alliance is to accelerate research and development and deliver dengue therapeutics through an inclusive partnership. It aims to deliver a new treatment for dengue, within 5 years, from repurposed drugs and combinations (including novel antivirals from pharmaceutical companies). This alliance is co-created, co-owned, and co-funded by dengue-endemic countries, with a tiered governance mechanism allowing collaborative decision making at different levels. The organisations have formed a preclinical working group, a clinical working group, and a translational working group for effective communication and scientific planning. All three working groups feed into the Joint Steering Committee, which is responsible for delivering on the vision and mission of the alliance. The partners of this alliance share knowledge, experience, technologies, and capabilities to jointly validate preclinical assays with the ambition in the initial phase to identify currently available drugs that can be repurposed for use as dengue therapeutics. In parallel, clinical trials for these drug candidates are being designed using the expertise of clinicians in these countries who have been treating patients with dengue for many years, with initiation planned by the end of 2023. Formation of this alliance is a major step towards developing a treatment for dengue, by aggregating resources from endemic countries, and ensuring engagement, scientific leadership, clinical guidance, and political interest in these countries. The different working groups and the steering committee coordinate efforts to address gaps in knowledge, such as epidemiology (specifically in Africa), biomarkers and diagnostics, clinical trials, and regulatory framework, while promoting open science. Although currently the alliance has a small number of partners, it is open to collaborations with new partners and key stakeholders in therapeutics and diagnostics. Working with and aligning many partners and stakeholders to deliver objectives in a new model of collaboration is challenging, as is filling the existing knowledge gaps and need for integration, and leveraging information from different geographies and epidemiological settings. Furthermore, doing clinical trials aimed at treating dengue disease is challenging due to the seasonal nature of the disease, and with climate change, disease patterns could become more unpredictable. Although this approach is likely to accelerate development of a treatment, funding remains a challenge. With climate change becoming more of a concern in high-income countries, there is an increasing possibility that many global funding organisations will acknowledge the true burden of dengue, the devastation it causes to health systems and patients in endemic countries, and, therefore, the importance of funding initiatives to accelerate the development of new treatments for dengue. We declare no competing interests.

Antimicrobial resistance (AMR) is widely acknowledged as one of the most serious public health threats facing the world, yet the private sector finds it challenging to generate much-needed medicines. As an alternative discovery approach, a small array of diarylimidazoles was screened against the ESKAPE pathogens (https://en.wikipedia.org/wiki/ESKAPE) and the results made publicly available through the Open Source Antibiotics (OSA) consortium (https://github.com/opensourceantibiotics). Of the 18 compounds tested (at 32 μg/mL), 15 showed >90% growth inhibition activity against MRSA alone. In the subsequent hit-to-lead optimization of this chemotype, 147 new heterocyclic compounds containing the diarylimidazole and other core motifs were synthesized, tested against MRSA and structure-activity relationships identified. While potent, these compounds have moderate to high intrinsic clearance and some associated toxicity. The best overall balance of parameters was found with OSA_975, a compound with good potency, solubility and reduced intrinsic clearance in rat hepatocytes. We have progressed towards the knowledge of the molecular target of these phenotypically active compounds, with proteomic techniques suggesting TGFRB1 is potentially involved in the mechanism of action. Further development of these compounds towards antimicrobial medicines is available to anyone under the licensing terms of the project.

The coronavirus disease 2019 (COVID-19) pandemic continues to cause significant morbidity and mortality worldwide. Since a large portion of the world’s population is currently unvaccinated or incompletely vaccinated and has limited access to approved treatments against COVID-19, there is an urgent need to continue research on treatment options, especially those at low cost and which are immediately available to patients, particularly in low- and middle-income countries. Prior in vitro and observational studies have shown that fluoxetine, possibly through its inhibitory effect on the acid sphingomyelinase/ceramide system, could be a promising antiviral and anti-inflammatory treatment against COVID-19. In this report, we evaluated the potential antiviral and anti-inflammatory activities of fluoxetine in a K18-hACE2 mouse model of SARS-CoV-2 infection, and against variants of concern in vitro, i.e., SARS-CoV-2 ancestral strain, Alpha B.1.1.7, Gamma P1, Delta B1.617 and Omicron BA.5. Fluoxetine, administrated after SARS-CoV-2 infection, significantly reduced lung tissue viral titres and expression of several inflammatory markers (i.e., IL-6, TNFα, CCL2 and CXCL10). It also inhibited the replication of all variants of concern in vitro. A modulation of the ceramide system in the lung tissues, as reflected by the increase in the ratio HexCer 16:0/Cer 16:0 in fluoxetine-treated mice, may contribute to explain these effects. Our findings demonstrate the antiviral and anti-inflammatory properties of fluoxetine in a K18-hACE2 mouse model of SARS-CoV-2 infection, and its in vitro antiviral activity against variants of concern, establishing fluoxetine as a very promising candidate for the prevention and treatment of SARS-CoV-2 infection and disease pathogenesis.

Not every life-threatening or debilitating disease has a sufficient armoury of therapies available nor a pipeline of future products to combat the remaining unmet areas of medical need. This is particularly so in the areas of infectious diseases affecting, disproportionately, those in low- and middle-income countries where market forces, namely the inability to recoup research and development costs through sales, disincentivises new discovery and product innovation. This is further exacerbated by the inevitable challenges of resistance to anti-infectious agents and thus their controlled and careful use only in cases of need. The Medicines for Malaria Venture (MMV), the Global Alliance for TB Drug Development (GATB) and Drugs for Neglected Diseases initiative (DNDi) are Product Development Partnerships that were created to address this market failure as donor-funded organisations seeking to deliver the medicines of the future for malaria, tuberculosis and many neglected tropical diseases. The science of drug discovery, despite the resource constraints, remains unchanged from commercial therapeutic areas and MMV, GATB and DNDi work with partners globally applying state-of-the-art medicinal chemistry and thinking to diseases that affect over 250 million symptomatic disease episodes each year. The discovery strategies in each disease will be illustrated with case studies that have progressed into clinical development.

Leishmaniasis is a collection of diseases caused by more than 20 Leishmania parasite species that manifest as either visceral, cutaneous, or mucocutaneous leishmaniasis. Despite the significant mortality and morbidity associated with leishmaniasis, it remains a neglected tropical disease. Existing treatments have variable efficacy, significant toxicity, rising resistance, and limited oral bioavailability, which necessitates the development of novel and affordable therapeutics. Here, we report on the continued optimization of a series of imidazopyridines for visceral leishmaniasis and a scaffold hop to a series of substituted 2-(pyridin-2-yl)-6,7-dihydro-5H-pyrrolo[1,2-a]imidazoles with improved absorption, distribution, metabolism, and elimination properties.

Dengue is the most rapidly emerging mosquito-borne infection and, due to climate change and unplanned urbanization, it is predicted that the global burden of dengue will rise further as the infection spreads to new geographical locations. Dengue-endemic countries are often unable to cope with such increases, with health care facilities becoming overwhelmed during each dengue season. Furthermore, although dengue has been predominantly a childhood illness in the past, it currently mostly affects adults in many countries, with higher incidence of severe disease and mortality rates in pregnant women and in those with comorbidities. As there is currently no specific treatment for dengue and no early biomarker to identify those who will progress to develop vascular leakage, all individuals with dengue are closely monitored in case they need fluid management. Furthermore, diagnosing patients with acute dengue is challenging due to the similarity of clinical symptoms during early illness and poor sensitivity and specificity of point-of-care diagnostic tests. Novel vector control methods, such as the release of Wolbachia- infected mosquitoes, have shown promising results by reducing vector density and dengue incidence in clinical trial settings. A new dengue vaccine, TAK-003, had an efficacy of 61.2% against virologically confirmed dengue, 84.1% efficacy against hospitalizations and a 70% efficacy against development of dengue haemorrhagic fever (DHF) at 54 months. While vaccines and mosquito control methods are welcome, they alone are unlikely to fully reduce the burden of dengue, and a treatment for dengue is therefore essential. Several novel antiviral drugs are currently being evaluated along with drugs that inhibit host mediators, such as mast cell products. Although viral proteins such as NS1 contribute to the vascular leak observed in severe dengue, the host immune response to the viral infection also plays a significant role in progression to severe disease. There is an urgent need to discover safe and effective treatments for dengue to prevent disease progression.

Upregulation of the transcription factor Nrf2 by inhibition of the interaction with its negative regulator Keap1 constitutes an opportunity for the treatment of disease caused by oxidative stress. We report a structurally unique series of nanomolar Keap1 inhibitors obtained from a natural product-derived macrocyclic lead. Initial exploration of the structure-activity relationship of the lead, followed by structure-guided optimization, resulted in a 100-fold improvement in inhibitory potency. The macrocyclic core of the nanomolar inhibitors positions three pharmacophore units for productive interactions with key residues of Keap1, including R415, R483, and Y572. Ligand optimization resulted in the displacement of a coordinated water molecule from the Keap1 binding site and a significantly altered thermodynamic profile. In addition, minor reorganizations of R415 and R483 were accompanied by major differences in affinity between ligands. This study therefore indicates the importance of accounting both for the hydration and flexibility of the Keap1 binding site when designing high-affinity ligands.

New antimalarial treatments with novel mechanism of action are needed to tackle Plasmodium falciparum infections that are resistant to first-line therapeutics. Here we report the exploration of MMV692140 (2) from the Pathogen Box, a collection of 400 compounds that was made available by Medicines for Malaria Venture (MMV) in 2015. Compound 2 was profiled in in vitro models of malaria and was found to be active against multiple life-cycle stages of Plasmodium parasites. The mode of resistance, and putatively its mode of action, was identified as Plasmodium falciparum translation elongation factor 2 (PfeEF2), which is responsible for the GTP-dependent translocation of the ribosome along mRNA. The compound maintains activity against a series of drug-resistant parasite strains. The structural motif of the tetrahydroquinoline (2) was explored in a chemistry program with its structure-activity relationships examined, resulting in the identification of an analog with 30-fold improvement of antimalarial asexual blood stage potency.

In the absence of drugs to treat or prevent COVID-19, drug repurposing can be a valuable strategy. Despite a substantial number of clinical trials, drug repurposing did not deliver on its promise. While success was observed with some repurposed drugs (e.g., remdesivir, dexamethasone, tocilizumab, baricitinib), others failed to show clinical efficacy. One reason is the lack of clear translational processes based on adequate preclinical profiling before clinical evaluation. Combined with limitations of existing in vitro and in vivo models, there is a need for a systematic approach to urgent antiviral drug development in the context of a global pandemic. We implemented a methodology to test repurposed and experimental drugs to generate robust preclinical evidence for further clinical development. This translational drug development platform comprises in vitro, ex vivo, and in vivo models of SARS-CoV-2, along with pharmacokinetic modeling and simulation approaches to evaluate exposure levels in plasma and target organs. Here, we provide examples of identified repurposed antiviral drugs tested within our multidisciplinary collaboration to highlight lessons learned in urgent antiviral drug development during the COVID-19 pandemic. Our data confirm the importance of assessing in vitro and in vivo potency in multiple assays to boost the translatability of pre-clinical data. The value of pharmacokinetic modeling and simulations for compound prioritization is also discussed. We advocate the need for a standardized translational drug development platform for mild-to-moderate COVID-19 to generate preclinical evidence in support of clinical trials. We propose clear prerequisites for progression of drug candidates for repurposing into clinical trials. Further research is needed to gain a deeper understanding of the scope and limitations of the presented translational drug development platform.

BackgroundTo 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.MethodsIn this work, we present a complete pre-clinical evaluation of the antiviral activity of nitazoxanide against SARS-CoV-2.FindingsFirst, 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.InterpretationThese 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.FundingThis work was supported by the Fondation de France “call FLASH COVID-19”, project TAMAC, by “Institut national de la santé et de la recherche médicale” through the REACTing (REsearch and ACTion targeting emerging infectious diseases), by REACTING/ANRS MIE under the agreement No. 21180 (‘Activité des molécules antivirales dans le modèle hamster’), by European Virus Archive Global (EVA 213 GLOBAL) funded by the European Union's Horizon 2020 research and innovation program under grant agreement No. 871029 and DNDi under support by the Wellcome Trust Grant ref: 222489/Z/21/Z through the COVID-19 Therapeutics Accelerator”.