Before the COVID-19 pandemic, viruses were not a major priority for the scientific community. Today, many events have changed the world and the importance of studying viruses, vaccines, and antiviral drugs is fully appreciated. The development of effective vaccines was crucial to overcome the pandemic, but the continue emergence of new viruses could make vaccines inadequate.

Antiviral drugs are used to treat viral infections. They inhibit one step of the viral replication and generally they are specific for a single virus. Many viruses share the same target for their attachment ligand, i.e. the protein used by the virus for the initial attachment to the cell. Therefore, entry inhibitors, i.e. antivirals that bind to the receptor binding domain of the attachment ligand, are broad-spectrum of action when they mimic the glycans present on the cell membrane that are conserved as targets across many viruses. Unfortunately, their inhibition is reversible, a limitation that severely limits their use as drugs because they lose efficacy upon dilution.

In our group, to overcome this limitation, we created broad spectrum entry inhibitors with an irreversible inhibition. These compounds inhibit the entry into the cell and at the same time irreversibly disrupt the virus. They are composed of three parts, a multivalent core, gold nanoparticles or b-cyclodextrins, a long hydrophobic linker, and a glycan mimic. The linker is responsible for the interaction with the virus that eventually leads to its permanent disruption. Because of their virucidal mechanism some of these compounds have shown excellent in vivo properties with good efficacy and limited toxicity. Yet, all of them target the receptor binding domain of the viral attachment ligand, that unfortunately is the domain more prone to mutations.

In this thesis, we have addressed two key research questions to overcome these limitations. First, we set to investigate whether it was possible to design virucidal drugs that would target the virus with a moiety not based on a glycan mimic. We show here that it is possible to use virus-targeting peptides to achieve antivirals of comparable efficacy to the ones previously made. At the same time, we attempted to understand whether these antivirals would have an irreversible effect only when targeting the receptor binding domain of the viral attachment ligand or whether this was possible when targeting other (ideally more conserved) parts of the viral attachment ligand. We show in this thesis that our peptides are directed toward a region distinct from the receptor binding domain, confirming the possibility of inhibiting the viral activity through mechanisms beyond interference with receptor binding domain.

Specifically, we designed peptides to target hemagglutinin of influenza virus by extracting them from broad neutralizing antibodies. b-cyclodextrins based on these peptides irreversibly inhibited the viral replication in vitro (EC50 as low as 0.04 µg/mL). Finally, we investigated the inhibition of our best compounds on different strains of influenza virus with mutations on the receptor binding domain. They proved to be effective against all the tested mutants.