To develop patentiflorin A analogs as a broad spectrum of viral inhibitors against SARS-CoV-2

The current COVID-19 global epidemic caused by SARS-CoV-2 once again alerts us how severe harm a new virus can inflict on human civilization. Since the virus emerged in December of 2019, the viral infection has killed over 1,200,000 people among 47 million coronavirus infected cases. There are currently still no vaccines available to effectively prevent COVID-19. Remdesivir is the only US FDA approved drug that was found to just shorten the recovery time in hospitalized COVID-19 patients in some clinical trials. Fortunately, the nature has provided us a huge resource from where we may uncover therapeutic recipe to fight against the new vicious virus. For decades, we have dedicated ourselves to searching for new antiviral agents from plants to combat emerging viruses including coronavirus, which has led to discovery of some potent antiviral compounds. Among them, patentiflorin A (PTA) is determined to be a promising lead molecule that showed antiviral activities against a broad spectrum of viruses. PTA is an aryl naphthalide lignan glycoside isolated from two Justicia medicinal plants. It was demonstrated with potent inhibitory effects against H5N1 avian flu virus, SARS-CoV-2, HIV, Ebola virus, HCV, Dengue virus and Zika virus (IC50 values ranging from 20-100 nM). Our mechanism studies of PTA and its aglycone against Zika virus showed that they prevented acidification of endosomes of host cells and thereby blocked the viral fusion to infect the host cells, which revealed the antiviral potential of the lignan compounds against a broad spectrum of viruses. We totally synthesized the compound, and the subsequent structure-activity relationship study through synthesis of over 120 aryl naphthalide lignans determined that a sugar unit attached at C-7 of the lignan skeleton is a key functional group that can significanly contribute to the antiviral activity of a PTA analog. We thus hypothesize that further structure modification on the attached sugar units could significantly enhance the antiviral potency of this type of compounds. Because the potent antiviral properties of PTA as a broad spectrum inhibitor, it will be worthy to carry out in-depth chemical and biological studies of the compound to advance its analogs as therapeutic agents against SARS-CoV-2. To achieve this goal, we propose to:
1) chemically synthesize patentiflorin A (PTA) analogs through structure modification focusing on the sugar units;
2) determine the antiviral mechanism of action through identification of the antiviral target(s) of PTA and analogs. X-ray crystallography and binding assays will serve as efficient tools to identify the antiviral target(s) of the compounds;
3) assess the anti-SARS-CoV-2 activity of the synthetic compounds using a viral entry evaluation system, followed by confirmation of the antiviral activity of the active compounds using infectious SARS-CoV-2 virus; and to investigate the toxicity and pharmacokinetic properties of the confirmed active PTA analogs in animal models.

We expect to provide sufficient evidences for the further development of PTA analogs as potential antiviral drug candidates with strong therapeutic efficacy against SARS-CoV-2 upon completion of the proposed studies.