In vivo antiviral efficacy and safety of 5-hydroxymethyltubercidin against DENV2 and SARS-CoV-2.

Several newly emerging and re-emerging viral infections significantly affect human health and the global economy each year. As many of these viruses lack treatment options other than symptomatic management, the development of effective preventive and therapeutic measures is urgently needed. We previously identified 5-hydroxymethyltubercidin (HMTU) as a broad-spectrum antiviral ribonucleoside analog and demonstrated its in vitro potent antiviral activity against positive-sense single-stranded RNA viruses, including dengue virus (DENV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this study, we evaluated the in vivo efficacy, pharmacokinetics, and safety of HMTU. Pharmacokinetic analysis revealed that effective concentrations of HMTU were maintained in the plasma and lung tissues of mice following intravenous and intramuscular administration. In a DENV2 infection model using AG129 mice, prophylactic administration of HMTU provided 100% protection against lethal infection. Similarly, in a SARS-CoV-2 infection model using BALB/c mice, HMTU significantly reduced viral titers in the lungs and improved the survival rates versus those in vehicle-treated mice. Furthermore, mutagenicity assessments using the Ames and HPRT tests demonstrated that HMTU did not exhibit mutagenic activity under the tested conditions. Our findings highlight HMTU as a broad-spectrum antiviral candidate potentially offering a promising therapeutic approach for dengue, COVID-19, and other infectious diseases caused by emerging orthoflaviviruses and coronaviruses.