644. In Vitro and In Vivo Resistance Potential to Circulating Influenza Viruses of Tizoxanide and Oseltamivir Carboxylate
Session: Poster Abstract Session: Oh, Those Pesky Viruses!
Thursday, October 27, 2016
Room: Poster Hall
Background: Tizoxanide (TIZ) is the active metabolite of nitazoxanide (NTZ) a thiazolide antiviral (AV) in late stage development for the treatment of influenza. These drugs exert their AV activity in a cell-specific manner as a selective protein folding enzyme inhibitor blocking replication of a broad range of RNA and DNA viruses in the Golgi and ER. Based on this MOA it has been hypothesized the potential for TIZ to induce AV resistance is low. The object of this study was to assess the development of AV resistance by flu viruses to TIZ, oseltamivir (OC) and TIZ+OC in vitro and in vivo.

Methods: MDCK cells grown in 6-well culture plates were inoculated with virus at an MOI of 0.1 PFU/cell. After removal of the virus inoculum, 2mL of medium containing TIZ, OC or TIZ+OC at the EC25 was added and cells were incubated. Once 70-80% destruction of the cell monolayer had occurred, cell culture supernatants were harvested and passaged into fresh MDCK cells with medium containing TIZ, OC, or TIZ+OC at EC25 for a total of 3 passages. Subsequently, drug concentrations were increased to EC50, EC75 and EC90 for an additional 3 passages each. Pre & post passage EC50 for TIZ and OC were calculated for each virus. To evaluate the potential for AV resistance development in vivo, antiviral sensitivities of flu viruses collected from patients at the beginning and end of a treatment course with either NTZ (n=7), OC (n=8) or NTZ+OC (n=11) were tested. Pre & post treatment EC50 for TIZ and OC were calculated for each isolate.

Results:Consistent with published data, flu viruses had an increase in post passage OC EC50 concentrations compared to baseline values, indicating development of in vitro OC resistance. No differences between pre & post passage TIZ EC50 were found in viruses passaged in the presence of TIZ, suggesting the absence of acquired AV resistance. Similarly, in vivo, no differences in pre & post treatment TIZ EC50 were found in viruses isolated from patients receiving NTZ. However, 2/8 (25%) of viruses recovered from patients receiving OC alone and 1/11 (9%) of virus isolates from patients receiving a combination of OC +NTZ demonstrated at least a 2 fold increase in OC EC50 between the start and end of treatment.

Conclusion: These results indicate that in contrast to OC, TIZ appears to have a high barrier for influenza AV resistance development.

Gabriele Landolt, DVM, PhD1, Lori Bentsen, BS1, Daniel Moezzi, DVM1, Matthew Bardin, PharmD, BCPS2 and Jean-Francois Rossignol, MD, PhD2, (1)Department of Clinical Sciences, Colorado State University- College of VMBS, Fort Collins, CO, (2)Romark, L.C., Tampa, FL


G. Landolt, Romark, L.C.: Investigator , Research support

L. Bentsen, Romark, L.C.: Research Assistant , Research support

D. Moezzi, None

M. Bardin, Romark, L.C.: Employee , Salary

J. F. Rossignol, Romark, L.C.: Board Member , Employee and Shareholder , Salary

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