Endogenous oxysterols: a novel antiviral strategy against rhinovirus infections

Human rhinoviruses (HRVs) are non-enveloped viruses belonging to Picornaviridae family, mostly responsible for an acute and self-limiting respiratory disease in humans, i.e. the common cold, accounting for 50-70% of overall cases worldwide. Although the course of this disease is commonly positive, HRV infections can lead to more life-threatening conditions especially in those individuals who already deal with chronic respiratory diseases, such as cystic fibrosis (CF) patients, where it can cause exacerbations and recurrent worsening of their clinical picture. To date, large efforts to produce an effective drug able to counteract these infections have been frustrated by excessive toxicity, collateral effects, and tendency to generate viral resistant strains, making the available solutions unlikely to overcome the clinical trial rock. Considering these assumptions, we investigasted two enzymatic oxysterols, namely 25-hydroxycholesterol (25HC) and 27-hydroxycholesterol (27HC), as promising molecules endowed with antiviral activity against HRV infections. Enzymatic oxysterols represent an important family of physiologic molecules endogenously originated from cholesterol, acting as host-targeting, sterol-lipid effectors of innate immunity against viral infections. In the experiments described in this thesis, we demonstrate that both 25HC and 27HC are able to strongly counteract in vitro viral replication of two HRV strains, namely HRV serotype A1 (HRV A1) and HRV serotype B48 (HRV B48), with favourable selectivity indexes. The antiviral activity was further confirmed on 3D in vitro fully reconstituted human nasal and bronchial epithelia starting from samples of respiratory mucosa of CF patients. In this highly predictive system, we demonstrated that 27HC can significantly inhibit HRV replication, thus providing a solid proof of concept for the exploitability of 27HC as active ingredient of an antiviral drug. Interestingly, both oxysterols can block HRV replication mostly by targeting the earlier steps of viral infection, by hampering the HRV endocytosis inside the host cells. More importantly, by means of two independent approaches, we show that neither 25HC nor 27HC select drug-resistant strains, unlike direct-acting anti-HRV molecules such as pleconaril or rupintrivir, accounting for a safer usage in the medical field. Overall, these results clearly suggest that oxysterols of endogenous origin, and in particular 27HC, might be a primary host strategy to counteract HRV infection. In particular, given their anti-HRV activity, and their low potential to select resistant strains, 25HC and 27HC could be considered for the development of new therapeutic strategies against HRV.