T-705 (favipiravir) activity against lethal H5N1 influenza A viruses

Abstract

The neuraminidase inhibitors oseltamivir and zanamivi are used to treat H5N1 influenza. However, oseltamivir-resistant H5N1 viruses have been isolated from oseltamivir-treated patients. Moreover, reassortment between H5N1 viruses and oseltamvir-resistant human H1N1 viruses currently circulating could create oseltamivir-resistant H5N1 viruses, rendering the oseltamivir stockpile obsolete. Therefore, there is a need for unique and effective antivirals to combat H5N1 influenza viruses. The investigational drug T-705 (favipiravir; 6-fluoro-3-hydroxy-2-pyrazinecarboxamide) has antiviral activity against seasonal influenza viruses and a mouse-adapted H5N1 influenza virus derived from a benign duck virus. However, its efficacy against highly pathogenic H5N1 viruses, which are substantially more virulent, remains unclear. Here, we demonstrate that T-705 effectively protects mice from lethal infection with oseltamivir-sensitive or -resistant highly pathogenic H5N1 viruses. Furthermore, our biochemical analysis suggests that T-705 ribofuranosyl triphosphate, an active form of T-705, acts like purines or purine nucleosides in human cells and does not inhibit human DNA synthesis. We conclude that T-705 shows promise as a therapeutic agent for the treatment of highly pathogenic H5N1 influenza patients.

Effect of an Asparagine-to-Serine Mutation at Position 294 in Neuraminidase on the Pathogenicity of Highly Pathogenic H5N1 Influenza A Virus

“…2A, C, E, and G and 3) compared to those of the oseltamivir-sensitive counterpart. In contrast, consistent with the mouse data (19,22,32), the ferret pathogenicity of VN1203 virus was not significantly altered by introducing the NA N294S substitution (Fig. 4).…”

“…Highly pathogenic H5N1 influenza virus A/Hanoi/30408/ 2005 oseltamivir-sensitive clone 7 (HN30408 virus), oseltamivir-resistant clone 3 possessing an asparagine-to-serine substitution at position 294 in the NA protein (HN30408-N294S virus), and oseltamivir-resistant clone 9 possessing a histidineto-tyrosine substitution at position 274 in the NA protein (HN30408-H274Y virus) were isolated from an oseltamivir-treated influenza patient by using plaque purification in Madin-Darby canine kidney (MDCK) cells, which were maintained in Eagle's minimal essential medium supplemented with 5% newborn calf serum (see reference 23 for details). Wild-type A/Vietnam/1203/04 (H5N1; VN1203 virus) and its two oseltamivir-resistant variants, one possessing the histidine-to-tyrosine substitution at position 274 (VN1203-H274Y virus) and the other possessing the asparagine-to-serine substitution at position 294 (VN1203-N294S virus) in the NA protein, were generated by using reverse genetics (13) as described previously (19,22) in 293T cells, which were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum. Cells were cultured at 37°C in 5% CO 2.…”

“…In contrast, the NA H274Y and N294S substitutions were detected in fatal cases, even though drug treatment was initiated early (i.e., within 48 h of onset of symptoms) (9), suggesting the potential virulence of H5N1 virus variants with these NA mutations for oseltamivir resistance. In fact, A/Vietnam/1203/04 (H5N1)-based recombinant viruses possessing either the NA H274Y or N294S substitution exhibited lethality similar to that of the wild-type virus in a mouse model (19,22,32).…”

T-705 (Favipiravir) Induces Lethal Mutagenesis in Influenza A H1N1 Viruses In Vitro

“…T-705 demonstrated inhibitory activity against viruses of different families that utilize viral RNA-dependent RNA polymerase (RdRP) for genomic replication (7). The agent showed potent activity in vitro against flaviviruses (8), bunyaviruses (9), arenaviruses (9, 10), noroviruses (11), seasonal influenza A (H1N1, H2N2, and H3N2), B, and C viruses (6), and influenza A (H5N1) viruses (12,13). Importantly, viruses resistant to both oseltamivir and amantadine were susceptible to T-705 (6,14).…”

Broad-spectrum antiviral that interferes with de novo pyrimidine biosynthesis

“…Nevertheless, the mechanism of T-705 is not fully understood. It does not affect the synthesis of cellular DNA or RNA (13,14), and may therefore target viral RNAdependent RNA polymerases directly or may be preferentially incorporated into viral RNA, thereby causing hypermutations. Brequinar was described as a broad-spectrum antiviral agent capable of inhibiting both negative-and positive-strand RNA viruses (15), and leflunomide and a derivative, FK778, have been reported to inhibit human cytomegalovirus (HCMV) and herpes simplex virus 1 (HSV-1) (16)(17)(18)(19).…”