BACKGROUND Severe acute respiratory syndrome corona virus (SARS-CoV-2) infection frequently causes severe and prolonged disease but only few specific treatments are available. We aimed to investigate safety and efficacy of a SARS-CoV-2-specific siRNA-peptide dendrimer formulation (MIR 19 ®) targeting a conserved sequence in known SARS-CoV-2 variants for treatment of COVID-19. METHODS We conducted an open-label, randomized controlled multicenter phase II trial (NCT05184127) evaluating safety and efficacy of inhaled MIR 19 ® (3.7mg and 11.1 mg/day: groups 1 and 2, respectively) in comparison with standard etiotropic drug treatment (group 3) in patients hospitalized with moderate COVID-19. The primary endpoint was the time to clinical improvement according to predefined criteria within 14 days of randomization. RESULTS Patients from group1 had a significantly reduced (median 6 days (95% confidence interval [CI]: 5-7, HR 1.75, P=0.0005) time to clinical improvement compared to patients from group 3 (8 days (95% CI: 7-10). Normalized oxygen saturation (SpO 2>94%) occurred quicker in the group 1 (median 5 days (95% CI: 4–5, HR 1.59, P=0.0033) than in the group 3 (6 days, 95% CI: 5–8). Treatment with MIR 19® was well tolerated and safe. CONCLUSIONS MIR 19 ®, a SARS-CoV-2-specific siRNA-peptide dendrimer formulation is safe and significantly reduces time to clinical improvement in hospitalized moderate COVID-19 patients compared to standard therapy in a randomized controlled trial. MIR 19 ® treatment targets a sequence which is identical in all SARS-CoV-2 variants known so far and hence should be applicable for all of them.

Background. First vaccines for prevention of Coronavirus disease 2019 (COVID-19) are becoming available but there is a huge and unmet need for specific forms of treatment. In this study we aimed to evaluate the potent anti-SARS-CoV-2 effect of siRNA both in vitro and in vivo. Methods. To identify most effective molecule out of a panel of 15 in silico designed siRNAs, an in vitro screening system based on vectors expressing SARS-CoV-2 genes fused with the firefly luciferase reporter gene and SARS-CoV-2-infected cells was used. The most potent siRNA, siR-7, was modified by Locked nucleic acids (LNAs) to obtain siR-7-EM with increased stability and was formulated with the peptide dendrimer KK-46 for enhancing cellular uptake to allow topical application by inhalation of the final formulation - siR-7-EM/KK-46. Using the Syrian Hamster model for SARS-CoV-2 infection the antiviral capacity of siR-7-EM/KK-46 complex was evaluated. Results. We identified the siRNA, siR-7, targeting SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) as the most efficient siRNA inhibiting viral replication in vitro. Moreover, we have shown that LNA-modification and complexation with the designed peptide dendrimer enhanced the antiviral capacity of siR-7 in vitro. We demonstrated significant reduction of virus titer and total lung inflammation in the animals exposed by inhalation of siR-7-EM/KK-46 in vivo. Conclusions. Thus, we developed a therapeutic strategy for COVID-19 based on inhalation of a modified siRNA-peptide dendrimer formulation.