in vitro Key words F N CONH2 Fig. 1. Structure of Favipiravir.

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1 in vitro Key words I F N CNH2 N H Fig. 1. Structure of.

2 25 RNA synthesis ( 1 5 cpm) Cont RTP Ribavirin-TP Fig. 2. Inhibitory effects of favipiravir-rtp and ribavirin-tp on influenza virus RNA polymerase activity. Results are means standard deviations (n 3)., results significantly different from those for the controls by the Tukey test (P.1). Table 1. Effects of favipiravir-rtp on DNA or RNA polymerases Polymerase Species Type IC5 ( mol/l) RNA polymerase Influenza virus RdRp.341 DNA polymerase Human DdDp 1, DNA polymerase Human DdDp 1, DNA polymerase Human DdDp 1, RNA polymerase II Human DdRp 95 RdRp: RNA-dependent RNA polymerase, DdDp: DNA-dependent DNA polymerase, DdRp: DNA-dependent RNA polymerase This table compares the IC5 of favipiravir-rtp for influenza virus RNA polymerase, human DNA polymerase () and human RNA polymerase II. ne unit each of human DNA polymerase and and human RNA polymerase II were incubated for 1 hr with reaction mixture containing 3 H-dGTP or 3 H-GTP 34). II in vitro μ μ

3 Adsorption Uncoating Protein synthesis F N CNH2 Incorporation N H Replication Assembly Phosphoribosylation H P H P H P H F N N CNH2 Release Phosphorylation H H -RTP Active form Fig. 3. Schematic representation of the activation mechanism of favipiravir. is incorporated into cells, and converted to favipiravir ribofuranosyl phosphates by host cell enzymes. The triphosphate form, favipiravir-rtp, inhibits the influenza virus RNA polymerase activity. α β γ III in vitro in vitro

4 Table 2. In vitro anti-viral activities of favipiravir Group Family Virus EC5( g/ml) Reference RNA ( ) strand RNA ( ) strand rthomyxoviridae Influenza A (seasonal).1.94 Furuta, Y. et al. 22 7) Sleeman, K. et al ) Influenza A (H5N1) Sidwell, R.W. et al ) Sleeman, K. et al ) Influenza A (H1N1) pdm Sleeman, K. et al ) Influenza A (H7N9) 1.4 Watanabe, T. et al. 213 ) Influenza B.4.8 Furuta, Y. et al. 22 7) Sleeman, K. et al ) Influenza C.3.6 Furuta, Y. et al. 22 7) Bunyaviridae La Crosse 5 Gowen, B.B. et al ) Punta Toro Gowen, B.B. et al. 27, 21 16,17) Rift Valley fever Gowen, B.B. et al. 27, 21 16,17) Sandfly fever Gowen, B.B. et al. 27, 21 16,17) Dobrava Buys, K.K. et al ) Maporal 1 Buys, K.K. et al ) Crimean Congo hemorrhagic fever 1.1 estereich, L. et al ) Prospect Hill 1 Buys, K.K. et al ) Severe fever thrombocytopenia syndrome Tani, H. et al ) Arenaviridae Junin.8 3. Gowen, B.B. et al. 27, 21 16,17) Mendenhall, M. et al ) Pichinde Gowen, B.B. et al. 27, 21 16,17) Tacaribe Gowen, B.B. et al. 27, 21 16,17) Guanarito 2.4 Mendenhall, M. et al ) Machupo 2.2 Mendenhall, M. et al ) Lassa (EC9) Safronetz, D. et al. 2 22) estereich, L. et al ) Filoviridae Ebola 1.5 estereich, L. et al ) Smither, S.J. et al ) Rhabdoviridae Rabies Yamada, K. et al ) Paramyxoviridae Human metapneumovirus (EC9) Jochmans, D. et al ) Respiratory syncytial virus 41 Furuta, Y. et al. 22 7) Flaviviridae West Nile 53 Morrey, J.D. et al ) Yellow fever 42 Julander, J.G. et al ) Zika virus Zmurko, J. et al ) Togaviridae Western equine encephalitis 1.2, 49 (EC9) Delang, L. et al ) Julander, J.G. et al ) Venezuelan equine encephalitis 1.7 Delang, L. et al ) Eastern equine encephalitis 2.8 Delang, L. et al ) Barmah forest 2.8 Delang, L. et al ) Ross river.5 Delang, L. et al ) Mayaro 2.5 Delang, L. et al ) Chikungunya Delang, L. et al ) Picornaviridae Polio 4.8 Furuta, Y. et al. 22 7) Rhino 29 Furuta, Y. et al. 22 7) Enterovirus Wang, Y. et al ) Caliciviridae Noro Rocha-Pereira, J. et al )

5 Strain [Infectious Dose] A/Victoria/3/75 (H3N2) [LD] b A/saka/5/7 (H3N2) [3 1 3 PFU/mouse] A/Duck/MN/25/81 (H5N1) [LD] b A/Duck/MN/25/81 (H5N1) [LD] b Table 3. Therapeutic effects of favipiravir in the mice infection model Treatment Dose (mg/kg/day) Survivors/Total a Control (Placebo) /2 1 /1 3 /1 1 1/1 3 7/1 1/1 3 1/1 Regimen Every 6 hrs seltamivir 1 c 5/1 Twice daily Control (Placebo) /1 1 1/1 3 9/1 9/1 Control (Placebo) /2 3 /1 1 2/1 3 8/1 1/1 3 1/1 Control (Placebo) /2 33 1/1 1/1 3 1/1 Twice daily Twice daily Every 6 hrs seltamivir 2 c 2/1 Twice daily a Number of survival mice to day 21 b % lethal infectious dose c Reduced oseltamivir dose p.1, p.1, compared to control group (Yates-corrected Chi-square test). p.1, compared to control group (Kaplan-Meier method, Log-rank test).

6 (A) Dose response 3 mg/kg/day, b mg/kg/day, a Survival (%) 4 2 Treatment Placebo Ribavirin 5 mg/kg/day Days post infection (B) Treatment beginning time treatment start day 5, day 7 treatment start day 9 Survival (%) 4 2 Placebo Days Days post post infection infection Fig. 4. Treatment of lethal Lassa virus infection in guinea pigs with favipiravir. (A) Treatment was beginning 48 hours after challenge. Groups of six guinea pigs were challenged with a lethal dose of guinea pig adapted-lassa virus (GPA-LASV) and treated subcutaneously once daily for two weeks with favipiravir ( or 3 mg/kg/ day), ribavirin (5 mg/kg/day) or vehicle placebo. (B) Groups of six guinea pigs were challenged with a lethal dose of GPA-LASV. Beginning on days 5, 7, and 9 post-challenge, favipiravir treatment (3 mg/kg/day, once daily subcutaneously for 14 consecutive days) was initiated in the respective group of animals. Each study followed survival for up to 42 days post-infection. p.5, p.1, p.1 compared to placebo; a: p.5 and b: p.1 compared to ribavirin. IV

7 Relative weight (%) Survival (%) Relative weight (%) Survival (%) Placebo days to 4 T-75 3 mg/kg/day days 3 to T-75 3 mg/kg/day days 1 to Days post infection Days post infection Days post infection 1 T-75 3 mg/kg/day days 4 to T-75 3 mg/kg/day days 5 to 9 T-75 3 mg/kg/day days 2 to 6 1 Fig. 5. Influence of the time from challenge to the initiation of the favipiravir treatment on SFTSV infections in IFNAR / mice. Six or 1 male mice in each group were inoculated subcutaneously with TCID5 of SFTSV (SPL1). Mice were treated with favipiravir at a dose of 3 mg/kg/day. Treatment was commenced 1, 2, 3, 4, or 5 days post-infection. was administered once daily until death or. Survival was determined using a Kaplan-Meier analysis and GraphPad Prism 6. Significance was determined relative to results for the placebo group:, P.1;, P.1;, P.5. Relative weight is shown as means with standard deviations.

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