Abstract
During antiviral drug discovery, it is critical to distinguish molecules that selectively interrupt viral replication from those that reduce virus replication by adversely affecting host cell viability. In this report we investigate the selectivity of inhibitors of the host chaperone proteins cyclophilin A (CypA) and heat-shock protein 90 (HSP90) which have each been reported to inhibit replication of hepatitis C virus (HCV). By comparing the toxicity of the HSP90 inhibitor, 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) to two known cytostatic compounds, colchicine and gemcitabine, we provide evidence that 17-AAG exerts its antiviral effects indirectly through slowing cell growth. In contrast, a cyclophilin inhibitor, cyclosporin A (CsA), exhibited selective antiviral activity without slowing cell proliferation. Furthermore, we observed that 17-AAG had little antiviral effect in a non-dividing cell-culture model of HCV replication, while CsA reduced HCV titer by more than two orders of magnitude in the same model. The assays we describe here are useful for discriminating selective antivirals from compounds that indirectly affect virus replication by reducing host cell viability or slowing cell growth.
Highlights
Intensive efforts are underway to develop new therapies for hepatitis C virus (HCV)
We show that 17-AAG inhibits HCV replication through slowing cellular replication, while cyclosporin A (CsA) has a specific antiviral effect
The reduction in HCV titer caused by 17-AAG, may at least in part, result from the modest toxicity observed in the nondividing monolayers at the concentrations used. 17-AAG treatment reduced the number of cells to 74% of the DMSO-treated control, but neither CsA nor BILN 2061-treatment decreased the number of cells in the non-dividing monolayers
Summary
Intensive efforts are underway to develop new therapies for hepatitis C virus (HCV). HCV drugs can be broadly classified into two groups by target: (1) direct acting antivirals (those that inhibit the virus by directly interacting with viral proteins) or (2) hosttargeted antivirals (drugs that indirectly inhibit the virus by modulating host protein function). Inhibitors of two host factor targets, Cyclophilin A (CypA) and heat-shock protein 90 (HSP90), have shown selective antiviral activity with a high barrier to resistance. Clinical trials of 17-AAG demonstrated safety and tolerability [12,13] Together, these data suggest that HCV inhibitors targeting CypA or HSP90 have the potential to be well tolerated with a high barrier to resistance. To further complicate interpretation of toxicity measurements in cultured cell lines, various end-point assays (e.g., tetrazolium salts, Calcein AM, and luciferase-coupled assays) are often employed interchangeably despite measuring distinct surrogate markers for cell health or viability (mitochondrial reduction potential, intracellular esterase activity, and intracellular ATP concentrations, respectively) This creates the possibility that a putative antiviral molecule may exert its effect indirectly by inducing a partial or unobserved cellular toxicity (i.e., a cytostatic effect). Our work describes specific assays to distinguish between compounds that selectively inhibit viral replication from those which indirectly inhibit viral replication by slowing cellular growth
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
