Antivirals Acting on Viral Envelopes with a Biophysical Mechanism of Action

• Author / Creator

  Speerstra, Sietske

• Most antivirals target viral proteins and are specific for only one virus, or even one viral genotype. Whereas viral proteins are encoded in the plastic viral genome, virion lipids are not and their rearrangements during fusion of the virion envelope to cellular membranes are conserved among otherwise unrelated enveloped viruses. Antivirals that inhibit these lipid rearrangements could thus pose a high barrier to resistance and have broad-spectrum activities. Fusion occurs through a hemifusion stalk in which only the outer leaflets are fused, bent with their polar heads forming a smaller radius than their hydrophobic tails (negative curvature). Outer leaflets enriched in phospholipids with head groups of larger cross sections than their lipid tails (“inverted cone”) disfavor this negative curvature, inhibiting fusion. The rigid amphipathic fusion inhibitors (RAFIs) are synthetic compounds of inverted cone molecular geometry. They inhibit the infectivity of otherwise unrelated enveloped viruses. The leading RAFI aUY11 has an ethynyl-perylene hydrophobic and an uracil-arabinose polar moiety. aUY11 intercalates in viral envelopes to directly inhibit virion-to-cell fusion. Previous studies showed that amphipathicity, rigidity, and inverted cone molecular geometry are required. My hypothesis is that the inverted cone molecular geometry of the RAFIs increases the energy barrier for the hemifusion stalk, inhibiting fusion. Then, chemically distinct compounds with similar amphipathicity, rigidity, and inverted cone shape would have similar antiviral potencies, regardless of specific chemical groups. Alternatively, the perylene group exposed to visible light may induce viral lipid peroxidation. Then, the perylene group and absorbance at visible spectrum would be required. I evaluated the activities of twenty-five chemically distinct RAFIs with similar amphipathicity, rigidity, and inverted cone shape. The perylene moiety and absorption at visible spectrum were not required, but a minimum length of the hydrophobic moiety of 10.3 Å was. The arabino moiety could be modified or replaced by other groups. Cytidine replacement for uracil was not tolerated, indicating the O8 carbonyl group is required. Bilayer intercalation was required but not sufficient. The vast majority of RAFIs had no overt cytotoxicity (CC50 > 20 μM; TI > 250−1200). Carbonyl or butylamide substitutions for arabino or cytidine replacement for uracil, increased cytotoxicity. Cytotoxicity was mainly determined by the polar moiety and there was no correlation between antiviral and cytostatic activities. The definition of the effects of shape and chemical groups on the activity of the RAFIs opens the possibility for rational design of lipid-acting antivirals active against a broad spectrum of enveloped viruses.

• Subjects / Keywords

  • Antiviral
  • Viral entry
  • Structure activity relationship
  • Biophysical mechanism
  • HSV
  • Fusion inhibitors
  • RAFIs

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3SJ1B527

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.