Search

The prolonged treatment of immunosuppressed (IS) individuals with anti-influenza monotherapies may lead to the emergence of drug-resistant variants. Herein, we evaluated oseltamivir and polymerase inhibitors combinations against influenza A/H3N2 infections in an IS mouse model. Mice were IS with cyclophosphamide and infected with 3 × 103 PFU of a mouse-adapted A/Switzerland/9715293/2013 (H3N2) virus. Forty-eight hours post-infection, the animals started oseltamivir, favipiravir or baloxavir marboxil (BXM) as single or combined therapies for 10 days. Weight losses, survival rates and lung viral titers (LVTs) were determined. The neuraminidase (NA) and polymerase genes from lung viral samples were sequenced. All untreated animals died. Oseltamivir and favipiravir monotherapies only delayed mortality (the mean day to death (MDD) of 21.4 and 24 compared to 11.4 days for those untreated) while a synergistic improvement in survival (80%) and LVT reduction was observed in the oseltamivir/favipiravir group compared to the oseltamivir group. BXM alone or in double/triple combination provided a complete protection and significantly reduced LVTs. Oseltamivir and BXM monotherapies induced the E119V (NA) and I38T (PA) substitutions, respectively, while no resistance mutation was detected with combinations. We found that the multiple dose regimen of BXM alone provided superior benefits compared to oseltamivir and favipiravir monotherapies. Moreover, we suggest the potential for drug combinations to reduce the incidence of resistance. [ABSTRACT FROM AUTHOR]

Background Baloxavir marboxil (BXM), a cap-dependent endonuclease inhibitor, has been recently approved in the United States for the treatment of influenza infections. It is superior to oseltamivir for reducing the time of viral shedding but is reported to have a low barrier of resistance. We sought to evaluate the viral fitness of the predominant BXM-resistant I38T PA mutant in the A/H1N1 and A/H3N2 viral backgrounds. Methods Recombinant A/Quebec/144147/2009 (H1N1) and A/Switzerland/9715293/2013 (H3N2) influenza viruses and their respective I38T PA mutants were generated by reverse genetics. Standardized inoculums (500 PFUs) of wild-type (WT) and mutant mixtures were inoculated on α2,6 MDCK cells. On day 3 post-infection (pi), the supernatants were collected and the ratios of WT/mutant viruses were determined by droplet digital PCR using specific LNA probes. Single infections and competitive experiments were also performed in C56/BL6 mice with quantification of lung viral titers on days 3 and 6 pi. Results In vitro A/H1N1 studies showed similar total copy numbers for the WT and mutant viruses on day 3 pi (1.2 × 109 and 1.3 × 109 copies/mL, respectively). The initial 50%/50% mixture became 70%/30% (WT/mutant) after one passage in cells. For A/H3N2, the total copy numbers were 8.1 × 109 and 1.0 × 109 copies/mL for the WT and mutant viruses. The initial 50%/50% mixture became 94%/6% (WT/mutant) after one passage. The I38T mutants remained stable after 4 passages in α2,6 MDCK cells. In mice, the A/H1N1 WT and I38T mutant induced similar weight loss and generated comparable lung titers on days 3 and 6 pi. In contrast, the weight loss of the A/H3N2 mutant was greater than that of the WT between days 3 and 7 pi with comparable lung titers on days 3 and 6. Following infection with 50%/50% mixtures, the mutant virus predominated over the WT on day 3 pi (73% A/H1N1 and 58% A/H3N2). Conclusion The BXM-resistant I38T PA mutant replicates well both in vitro and in vivo in the A/H1N1 and A/H3N2 backgrounds. Surveillance for the emergence and transmission of such mutant in the community is required. Disclosures All Authors: No reported Disclosures. [ABSTRACT FROM AUTHOR]