Table 1.
In Vitro Characterization of Influenza A Viruses Used in This Study
| Predicted Amino Acid Substitution vs Controlaa |
Virus Titer, AUC8-72 Mean ± SE (%Difference)e |
||||||
|---|---|---|---|---|---|---|---|
| Subtype | Virus | PA Proteinb | Other Proteins | Sequence Accessionc EPI_ISL_ | Baloxavir EC50, nM, Mean ± SD (Fold Increase vs Control)d | MDCK | MDCK-SIAT1 |
| H1N1pdm09 | A/Illinois/08/2018 | Control | Control | 315855 | 1.82 ± 0.39 (1) | 364.6 ± 8.5 | 334.8 ± 13.4 |
| I38Tf | HA: K119N | 348120 | 92.00 ± 12.00 (51) | 321.8 ± 15.5 (−12)* | 316.0 ± 4.1 (−6) | ||
| I38Sf | - | 365522 | 94.13 ± 9.82 (52) | 327.8 ± 9.4 (−10)* | 300.5 ± 4.7 (−10) | ||
| A/Illinois/37/2018 | I38L | PA-X: E209G | 315856 | 16.69 ± 6.41 (9) | 382.2 ± 4.3 (+5) | 350.0 ± 6.8 (+5) | |
| H3N2 | A/Louisiana/50/2017 | Control | Control | 315857 | 1.31 ± 0.35 (1) | 342.6 ± 11.8 | 358.5 ± 11.4 |
| A/Louisiana/49/2017 | I38M | - | 315858 | 13.58 ± 2.59 (10) | 317.8 ± 11.6 (−7) | 323.6 ± 7.0 (−10)* | |
| A/Bangladesh/3007/2017g | Control | Control | 340421 | 1.33 ± 0.39 (1) | 212.5 ± 9.8 | 238.8 ± 6.8 | |
| I38T | NA: T71I | 340405 | 153.82 ± 15.90 (116) | 185.0 ± 9.5 (−13) | 218.7 ± 4.6 (−8)* | ||
Abbreviations: AUC8–72, area under the curve for 8–72 hours postinfection; EC50, 50% effective concentration; HA, hemagglutinin; MDCK, Madin-Darby canine kidney cells; NA, neuraminidase; PA, polymerase acidic protein; PA-X, PA-X protein; SD, standard deviation; SE, standard error.
Comparison of the codon-complete genome sequences of a PA-I38-substituted virus and its respective control virus. Only amino acid substitutions are shown.
PA and PA-X proteins share the same amino acid at residue 38; only additional changes in PA-X are shown in Table 1.
Genome sequences deposited to Global Initiative on Sharing All Influenza Data ([GISAID] https://www.gisaid.org/); PA-I38-substituted viruses have 1–4 silent nucleotide changes compared with the genomes of their respective control viruses.
Baloxavir EC50 results are shown as mean ± SD of at least 3 independent tests. The fold increase was determined by comparing the EC50 of PA-substituted virus with the respective control virus.
The percentage difference was determined by comparing the mean AUC value of PA-substituted virus with that of the respective control virus (set at 100%).
indicates statistical significant (P < .05) difference between AUC8–72 for PA-I38-substituted virus and its control.
Viruses carrying I38T and I38S were selected in MDCK cells in the presence of baloxavir and purified by limiting dilution.
A/Bangladesh/3007/2017 virus isolate (GISAID ID: S2 isolate EPI_ISL_286069; original specimen EPI_ISL_282881) contained viral subpopulations with I38 or I38T in PA protein, which were separated by limiting dilution.