Host-targeting strategies for the development of novel therapeutics to fight viral infections

Viral infections impose a significant economic and healthcare burden on society, markedly contributing to mortality rates, especially in the case of newly emerging or re-emerging viruses with pandemic potential. The range of therapeutic options available to combat these threats mainly consists of vaccines and antivirals, which are, however, unevenly distributed and applicable; moreover, the availability of safe and effective interventions largely depends on the specific pathogen involved. To make the situation worse, the remarkable genomic plasticity of viruses allows them to evade therapeutic control by developing resistance to treatments. This PhD research focused on developing innovative approaches for antiviral therapy, notably emphasising host-targeting antivirals (HTAs). These compounds are an emerging therapeutic strategy aimed at targeting host proteins or cellular pathways essential for viral replication, thus providing broad-spectrum antiviral potential while minimising the risk of viral resistance. The project was structured into three main and complementary experimental lines. First, the study investigated endogenous oxysterols, body-produced molecules known for their promising although improvable HTA profiles. Through a medicinal chemistry-based approach, structural optimization of these compounds was pursued to enhance their antiviral efficacy and broaden their activity against different alpha-herpesviruses, such as herpes simplex virus type 2 (HSV-2) and varicella zoster virus (VZV). This research led to the definition of structural-refined compounds with a novel antiviral mechanism involving the oxysterol-binding protein (OSBP), a molecular target of antiviral therapy previously identified only for RNA viruses. Another line of research explored innovative pharmacological formulations designed either to improve the pharmacokinetic profile of existing antivirals or to produce molecules endowed with intrinsic antiviral potential as broad-spectrum agents. This approach integrated advanced drug-delivery strategies based on lipidic nanostructures loaded with 27-HC (i.e., an endogenous oxysterol with antiviral activity), and the discovery of new broad-spectrum activities of polymeric β-cyclodextrin (β-CD) formulations. Finally, a target-based approach using CRISPR/Cas9 technology was adopted to perform a whole-genome knockout screening to identify human genes involved in respiratory syncytial virus (RSV) replication. The identified genes represent promising host targets for the development of future broad-spectrum antiviral therapies, contributing to the understanding of host-virus interactions and the discovery of novel therapeutic targets. Overall, this thesis presents an integrated vision of antiviral research, where the combination of medicinal chemistry, drug delivery, and functional genomics approaches enables the identification and optimization of new cellular targets, paving the way for more effective and universal strategies to fight viral infections.