Treating respiratory viral infections remains challenging, necessitating exploration of novel therapeutic approaches. Alternative strategies, such as drug repurposing or combinations, are essential for treating them. This study evaluated the in vitro activities of the antivirals ribavirin, favipiravir, and oseltamivir, and the mucolytic drugs N-acetylcysteine (NAC) and erdosteine, alone or in combination, against Human Parainfluenza Virus (HPIV) and Respiratory Syncytial Virus (RSV). HPIV-2 and RSV were cultured in VERO and HEp-2 cell lines, respectively. Antiviral efficacy was assessed by calculating IC50 values using MTT and plaque reduction assays. For combination studies, synergy scores were analyzed using the SynergyFinder program. We investigated potential interactions underlying the synergistic activities using an in silico approach, that combined virtual screening and molecular docking. The IC50 values of ribavirin, favipiravir, and oseltamivir against HPIV-2 and RSV ranged from 4.46 to 14.1 µg/mL, and the results from both methods were highly similar. All three antivirals' cytotoxicity was well above their C-max, and SIs were 12.43-36.69 for HPIV-2 and 15.88-38.12 for RSV. The ribavirin-oseltamivir combination synergy scores of 13.35 for HPIV-2 and 17.98 for RSV indicate clear synergism, while other combinations were additive. Docking analysis identified potential molecular interactions that may contribute to the antiviral activity of the ribavirin-oseltamivir combination against RSV and HPIV-2. Ribavirin, favipiravir, and oseltamivir showed good activity against HPIV-2 and RSV, and the ribavirin-oseltamivir combination exhibited strong synergistic interactions, suggesting promising therapeutic potential.

Nucleoside analogues are among the most promising broad-spectrum antiviral agents. We developed a high-throughput synergistic screening system to identify US Food and Drug Administration-approved drugs that enhance the effectiveness of nucleoside analogues. Unlike conventional combination approaches, this strategy does not require boost agents to have direct antiviral activity; instead, they can enhance antiviral agent's effect through novel synergistic mechanisms. We identified mycophenolate mofetil (MMF), which significantly boosts ribavirin's (RBV) antiviral efficacy against influenza A virus, even at concentrations where MMF alone shows minimal activity. MMF enhances RBV by inhibiting IMPDH (inosine-5'-monophosphate dehydrogenase) and reducing cellular GTP levels, potentially increasing RBV incorporation and its antiviral potency. This mechanism was confirmed by adding exogenous GTP, which reversed the synergy. In a mouse model, MMF also enhanced RBV's effectiveness against PR8 in vivo. Moreover, MMF showed synergistic effects against other influenza subtypes and RNA viruses including ZIKV and HCoV-OC43, demonstrating the potential wide applicability of this strategy. Our study introduces a new screening system and identifies novel RBV combinations, offering a promising approach for developing effective broad-spectrum antiviral combinations against emerging viral threats.

Background/Objectives: Endemic viral respiratory illnesses caused by influenza, RSV, and coronaviruses impose a global disease burden of hundreds of millions of infections and hundreds of thousands of deaths annually. Chronic hepatitis B and C infections persist in 254 million and 58 million people worldwide, respectively. No approved therapy addresses these viruses simultaneously. MDL-001 is an oral, direct-acting, broad-spectrum antiviral targeting the Thumb-1 allosteric site of viral polymerases. Methods: Here, we evaluated the antiviral activity of MDL-001 in vitro in influenza A/B, RSV, SARS-CoV-2, endemic human coronaviruses, and hepatitis B/C/D. We next evaluated MDL-001 antiviral activity in vivo in H1N1, SARS-CoV-2, HCV, and HBV. MDL-001's in vivo efficacy was compared head-to-head versus standards of care including oseltamivir, remdesivir, sofosbuvir, and tenofovir alafenamide, or through the literature comparison with nirmatrelvir and molnupiravir. Lastly, we evaluated the pharmacokinetics, metabolism, tolerability, and safety profile of MDL-001. Results: Here, we report that MDL-001 inhibits influenza A/B, RSV, SARS-CoV-2, endemic human coronaviruses, and hepatitis B/C/D viruses with nanomolar EC90 potency in vitro. MDL-001 demonstrated equivalent in vivo efficacy to oseltamivir against mouse-lethal influenza A virus infection, reducing lung viral load by 2.6 log10 and preventing weight loss and mortality. MDL-001 demonstrated equivalent symptom reduction to subcutaneous remdesivir after SARS-CoV-2 infection. MDL-001 reduced SARS-CoV-2 lung viral titers by 2.9 log10, superior to the literature-reported 1.4 log10 and 1.0 log10 reductions for nirmatrelvir and molnupiravir, respectively. MDL-001 reduced HCV viremia by 3.3 log10, equivalent to sofosbuvir. Oral MDL-001 reduced plasma HBV surface antigen by 2.5 log10, superior to tenofovir alafenamide from Day 8 through Day 21. MDL-001 demonstrated an in vitro EC50 of 79.4 nM against infection with RSV strain A2, which is a 416-fold improvement over literature-reported ribavirin. Oral pharmacokinetics studies demonstrate that MDL-001 is rapidly absorbed and partitioned into lung (Kp = 39-52) and liver (Kp = 71-104) tissues. MDL-001 produced no treatment-related tolerability adverse events across 376 animals and showed no hERG, Ames genotoxicity, or micronucleus safety issues. Conclusions: These findings support MDL-001 as a broad-spectrum, direct-acting non-nucleoside antiviral clinical candidate.

Cancer cells hijack RNA metabolism, including splicing, polyadenylation, nuclear export and translation, to change both the amount and the form of the proteins they produce. This creates therapeutic vulnerabilities beyond the mutations and translocations that have guided drug development in acute myeloid leukemia (AML), where outcomes remain poor. Using AML as a paradigm, this review focuses on two nodes of RNA metabolism: the eukaryotic translation initiation factor eIF4E, a cap-chaperone that escorts mRNAs through processing, export and translation, and CRM1/XPO1, the major nuclear exporter of proteins and select RNAs that partners with eIF4E for specific mRNA export activity. We describe the RNA biology dysregulated in patients, the mechanisms of the inhibitors that target these pathways, and their pre-clinical and clinical data across AML and other malignancies. Indeed, early-stage clinical trials in AML and other malignancies show promise, including the use of CRM1/XPO1 inhibitors (selinexor, eltanexor) and eIF4E inhibitors (including ribavirin and tomivosertib). We discuss how selecting patients by eIF4E status, confirming on-target activity, and designing rational combinations could improve next-generation therapies.

SUMMARYHepatitis E virus (HEV) is an important cause of viral hepatitis globally. Historically considered an acute and self-limiting illness, HEV has emerged as a significant pathogen in various immunocompromised patient groups in the last 15 years. Vulnerable patients include transplant recipients, people living with advanced HIV infection, and patients with hematological malignancies, rheumatological disorders, or autoimmune diseases. These individuals are vulnerable to chronic hepatitis and extrahepatic manifestations due to HEV. These risks are also relevant to emerging modalities of immunosuppression such as new targeted drug therapies and chimeric antigen receptor T-cell therapies. Besides unique clinical implications, immunocompromised hosts have also been at the center of new developments in the hepatitis E field on zoonotic reservoirs, transmission routes, disease models, and pathogenesis. In this review, we present a comprehensive integrative summary of the epidemiology, clinical manifestations, pathogenesis, diagnosis, and management strategies of HEV infections in immunocompromised hosts.

Enteroviruses are the primary cause of hand, foot, and mouth disease (HFMD). The absence of broad-spectrum antivirals, due to high serotypic and genetic diversity, greatly hampers effective treatment. In this study, we developed a novel type of acylthiourea-based proteolysis-targeting chimeras (PROTACs) to induce targeted protein degradation. Compound X14 was identified as a potent candidate. X14 showed strong anti-EV71 activity by inhibiting viral replication. It directly binds to the EV71 3D polymerase with higher affinity than ribavirin and causes proteasome-dependent degradation of the 3D protein. X14 demonstrated broad-spectrum activity against representative EV-A, EV-B, EV-C, and EV-D enteroviruses and exhibited superior in vivo efficacy compared to the parent compound. X14 is a PROTAC targeting EV71 3D polymerase, making it a promising antiviral candidate and chemical tool for HFMD.

Feline infectious peritonitis virus (FIPV) causes a fatal disease in cats that remains challenging to treat due to the absence of effective vaccines and limited antiviral therapies. Given its central role in viral replication and transcription, RNA-dependent RNA polymerase (RdRp) represents a highly promising and strategic target for antiviral drug development. To enable live-cell monitoring of RdRp activity without external substrates or cell disruption, we developed a biologically validated, cell-based dual-fluorescent reporter assay using green fluorescent protein and red fluorescent protein to evaluate RdRp-dependent reporter activity. Following validation with the well-characterized RdRp inhibitor ribavirin, the dual-reporter platform achieved a Z-factor of 0.54 and a Z'-factor of 0.61. The system was further utilized to assess the antiviral potential of fifteen alkaloid compounds. Among compounds evaluated, lycorine and lycorine hydrochloride exhibited potent inhibition of RdRp-dependent reporter activity and yielded IC50 values of 2.83 ± 0.45 μM and 1.58 ± 0.20 μM, respectively. Further evaluation revealed that both compounds significantly reduced FIPV replication in infected cell. These findings identify lycorine and lycorine hydrochloride as promising anti-FIPV candidates and support further investigation of lycorine-class alkaloids as anti-coronaviral scaffolds. Together, the validated cell-based screening platform and whole-virus antiviral activity provide a foundation for advancing RdRp-targeted antiviral discovery against FIPV.

Crimean-Congo hemorrhagic fever (CCHF) is a potentially fatal tick-borne viral zoonosis with a wide geographic distribution, a significant case-fatality rate, and a risk of healthcare-associated transmission. Although CCHF commonly presents with nonspecific febrile illness followed by hemorrhagic manifestations, neurological symptoms may occur and can mimic acute stroke, creating diagnostic challenges in the emergency department. We report the case of a 72-year-old male farmer in the United Arab Emirates who presented with acute slurred speech, confusion, and right-sided facial droop, prompting stroke-code activation. Initial neuroimaging showed no acute intracranial hemorrhage, established infarction, or large-vessel occlusion. The patient subsequently developed worsening tachypnea, severe metabolic acidosis, thrombocytopenia, profound coagulopathy, mucocutaneous bleeding, acute kidney injury, and multiorgan failure. CCHF was confirmed by polymerase chain reaction testing. Despite maximal supportive care, including mechanical ventilation, vasopressor support, continuous renal replacement therapy, blood product transfusion, correction of coagulopathy, ribavirin therapy, and high-level isolation precautions, the patient developed refractory hemorrhagic shock and died later the same day. This case highlights CCHF as a rare but important stroke mimic. Emergency clinicians should consider CCHF in patients with acute neurological symptoms when accompanied by fever, bleeding manifestations, thrombocytopenia, coagulopathy, metabolic acidosis, renal dysfunction, shock, or relevant zoonotic exposure. Early epidemiological history, repeated clinical reassessment, prompt implementation of infection-control precautions, and multidisciplinary management are essential to reduce diagnostic delays and the risk of healthcare-associated transmission.

Hantavirus fevers (HF) are caused by pathogenic orthohantaviruses and are classified into two clinical forms: hemorrhagic fever with renal syndrome (HFRS), reported in Eurasia, and hantavirus pulmonary syndrome (HPS), reported in the Americas. HF are characterised by an acute course with predominant involvement of internal organs: HFRS is mainly associated with kidney damage, while HPS is characterised by severe lung injury. Both diseases may also affect the central nervous and endocrine systems. In addition, hantavirus fevers are marked by severe complications during the acute phase and a prolonged recovery period. Currently, there is neither a WHO-approved vaccine nor any effective etiotropic anti-hantavirus therapy. The development of antiviral treatment strategies focuses on preventing orthohantavirus entry into cells or suppressing their intracellular replication. One of the main directions in the search for effective anti-hantavirus therapy is the low-molecular-weight compounds development and testing, many of which have demonstrated pronounced antiviral activity against orthohantaviruses through direct or indirect effects on viral RNA polymerase function. The review shows that new antiviral nucleoside compounds development and study has promising potential, as well as their combined use for effective etiotropic, pathogenetic and symptomatic treatment of hantavirus fevers.