Abstract:
The identification and development of novel antiviral drugs is one of the most important areas of current medical research. Such therapeutics may serve to control treatment resistant diseases as well as having the potential to contain viral epidemics that occur in the future. Compounds which are able to inhibit herpes simplex virus type 1 (HSV-1) merit thorough investigation as this is a human pathogen that is globally distributed, highly prevalent and capable of producing severe morbidity.
The HSV-1 infection cycle begins with the attachment of a virion to a suitable host-cell, this initial attachment is facilitated by binding between viral attachment proteins (VAPs) on the surface of the virion and a class of host polysaccharides known as heparan sulfate glycosaminoglycans (HS GAGs). Of the compounds currently being investigated as potential HSV therapeutics, many are functional mimetics of HS GAGs. These compounds (by enlarge) act by binding to HSV-1 VAPs in the place of HS GAGs and thereby block the virions ability to attach to host-cells. These compounds are of special interest to virologists as HS GAGs serve as attachment receptors for numerous viruses, including significant human pathogens such as hepatitis B virus (HBV), human immunodeficiency virus (HIV) and server acute respiratory syndrome coronavirus-2 (SARS Cov-2).
This study, completed as part of a MSc through the University of Auckland, examines four synthetic HS GAG mimetics developed by the Ferrier Research Institute (FRI) and assesses their ability to inhibit HSV-1 infection. Viral inhibition was measured via plaque inhibition assay, qPCR and yield reduction assays. The first two of these assays indicated that the compounds exerted varying levels of inhibition with the two compounds having tetrameric molecules showing promisingly high levels of HSV-1 inhibition corresponding with IC₅₀ values less than 1M. The yield reduction assay, while indicating some level of HSV-1 inhibition, failed to replicate the potent HSV-1 inhibition seen in the preceding assays.
The mode of action of the most efficacious of the four compounds was interrogated via experiments which measured the level of virion neutralisation (aka “virucidal effect”), attachment inhibition and entry inhibition produced by this compound. These assays revealed that the anti-HSV-1 effect of the compound could be entirely explained by its capacity to inhibit viral attachment. The compound in question also displayed an ability to inhibit virion entry to the host-cell cytoplasm, however there was no apparent correlation between the concentration of the compound and the degree of entry inhibition. Because of this it was inferred that the entry inhibition results were due to a down-stream effect of the binding between compound molecules and the HSV-1 VAPs (rather than being the direct result of interaction between the compound and the HSV-1 entry mechanism).
The observed disparity between the yield reduction results and other measures of compound efficacy were most unexpected. This anomaly may be partially due to the observed ability of HSV-1 infections from different MOIs to produce convergent yields at 24 hours post infection (24hpi). Additional possibilities are discussed in the final chapter of this thesis.