Explore the Pathogenesis and Drug Development of SARS-CoV-2 (II)

2 Drug screening for new coronavirus

1. 1 Virus targeted drugs, protease inhibitors, immunosuppressants

At present, medications for COVID-19 mainly focus on broad-spectrum virus-targeted drugs, protease inhibitors, viral spike protein-targeted drugs, targeted host drugs, and immunomodulators, by cutting off the binding of the virus to the host receptor, inhibiting virus replication, or anti-viral immune response, to achieve the purpose of controlling or eliminating the virus. The most common ones are Remdesivir, Chloroquine/Hydroxychloroquine, Kelizi, IL-6 Inhibitor, and Serum Tests for recovered patients. The binding of SARS-CoV-2 to the host depends on the cell surface receptor ACE-2, which can interfere with virus invasion by blocking the binding of S protein to ACE-2. At the cellular level, soluble recombinant human ACE-2 (hrsACE2), as a competitive inhibitor, can significantly inhibit the infection of SARS-CoV-2. The humanized ACE-2 protein drug APN01 (rhACE2) has entered Phase II clinical trials for the treatment of COVID-19. The small molecule drugs Nadide, Losartan, 9-Methyllithospermate B and Leonurine are potential therapeutic drugs, which can target the integrin formed by the binding of S protein and ACE2 to interfere with the binding of the virus to the host receptor. For ACE-2 combined with RBD, humanized epitope antibodies are also in the process of development. The clinical trial of CD147 monoclonal antibody Meplazumab confirmed that Meplazumab can block CD147 from interfering with the virus and help ACE2 to allow the virus to enter cells through CD147, improve the symptoms of COVID19 patients and shorten the time for viral nucleic acid to become negative.

After SARS-CoV-2 enters the host cell, the virus uses RNA-dependent RNA polymerase (RdRP) to transcribe and replicate RNA. Previous studies have shown that adenine or guanine derivatives in nucleoside analogs can target RNA-dependent RNA polymerase (RdRP) and block the invasion of viral RNA during the synthesis of most RNA viruses, including human coronaviruses. dye. For example, Favipiravir (T-705), a guanine analogue, can effectively inhibit RNA-dependent RNA polymerase and has been approved for the treatment of influenza viruses. In the latest study, the activity of SARS-CoV-2 in VeroE6 cells was reported (EC = 61.88μm), and the drug has now entered phase III clinical trials. In the two recent Favipiravir clinical trials, 240 randomized patients were treated with Favipiravir or Abidol. The study found that on the 7th day of taking Favipiravir, 71.43% of patients recovered clinically, and 55.86% of patients who took Arbidol recovered clinically, indicating that Favipiravir is more beneficial than Arbidol for improving clinical symptoms. The 80 patients enrolled in the group were treated with Fapiravir and inhaled IFNα, or Kelizi and inhaled IFNα. The study found that Favipiravir significantly improved the virus clearance rate and CT imaging performance, and the side effects of Favipiravir were smaller. However, neither of these two experiments has a non-treatment control group, and more randomized controlled experiments are needed to determine whether Favipiravir is effective.

The nucleoside analogue Remdesivir is a prodrug of adenine derivative phosphoramidate. In in vitro experiments, Remdesivir has broad-spectrum resistance against RNA virus. Compared with ribavirin and spray, Cyclovir has a lower dosage and is more medicinal. In addition, when screening anti-new coronavirus drugs in the Vero cell line, β-D-N4-hydroxycytidine (NHC) showed stronger activity than remdesivir. NHC's prodrug β-4-hydroxycytosine-5'-isopropyl ester (EIDD-2801) also showed antiviral activity when treating mice infected with SARS-CoV or MERS-CoV. EIDD -2801 can alleviate weight loss and lung hemorrhage in mice, while inhibiting virus replication in lung tissues and improving lung function of mice. In the currently revealed clinical trial report of Remdesivir, it may shorten the course of the disease and make the treatment patients recover faster, improve the hospital turnover rate, but not reduce the mortality rate. This may be due to the limited ability of Remdesivir to inhibit RNA polymerase activity to control virus replication and reduce viral load. Due to the high viral load base in severe patients, it cannot significantly reduce the mortality rate.

SARS-CoV-2 virus replicase needs to be cleaved by 3C-like protease (3CLpro /Mpro) and papain-like virus protease (PLVP) to function. The proliferation of the virus can be controlled by inhibiting the main protease during the synthesis and hydrolysis of viral RNA. Known enzyme protein inhibitors such as α-ketoamide inhibitor (α-ketoamide), ledipasvir (ledipasvir), velpatasvir (velpatasvir), drug Epclusa (Sofosbuvir/Vipatavir) and Harvoni (Sophibuvir/Retipavir), Indinavir (Indinavir), Nelfinavir (Nelfinavir), Atazanavir (Atazanavir), and the pyrimidine analog Camofur, and organic selenium molecule Ebselen, have a potential inhibitory effect on the 3C-like protease of SARS-CoV-2 main protease. Disulfiramand Cobicistat can inhibit papain-like proteases. Darunavirand Klitsch (lopinavir/ritonavir, Loponavir/ritonavir arbidol) have inhibitory effects on the endopeptidase C30 of coronavirus.

In addition, the use of CRISPR/Cas13d technology to design the GRNA of the virus's ORF1ab and S protein to knock out the viral genome can directly inhibit virus replication, but this treatment platform based on nucleic acid editing technology is not mature and requires more experiments supported by clinical data.

Host innate immunity is down-regulated, and cytokine storms and secondary infections caused by the mass production of inflammatory factors and chemokines are the main reasons that cause immunopathological conditions and worsen the patient's condition. Therefore, controlling the immune damage mediated by COVID-19 through immunosuppressive methods may improve the patient's condition. For example, Recombinant human type I IFN. rhIFNα Nasal Drops + Thymosin α 1 and SNG001 (inhaled interferon-β-1a) can activate type I IFN receptors, and small molecule drugs Olumiant baricitinib and Jakavi ruxolitinib can inhibit JAK1/2 for regulation Type I IFN pathway. IL-6 inhibitor Actemra tocilizumab (RoActemra), anti-GM-CSF antibody Lenzilumab, and mTOR inhibitor Sirolimus (rapamycin) can be used to control inflammation.

Chloroquine, an immunosuppressant, interferes with the binding of virus particles to their cell surface receptors by increasing the pH value of the virus or the endosome required by the virus, destroys the virus in the early stage of virus replication, and interferes with virus packaging through the pH-dependent endoplasmic reticulum mediated virus translation. Chloroquine can also act on the immune system through cell signal transduction and regulate pro-inflammatory cytokines. On the Vero cell line, chloroquine may have an anti-SARS-CoV effect by inhibiting the binding of virus surface receptors and angiotensinase In the three reported clinical trials of chloroquine/hydroxychloroquine, hydroxychloroquine treatment can shorten the clinical recovery period, relieve fever and cough symptoms, and significantly improve the performance of pneumonia.

Other immunosuppressive agents, such as the anti-IL-6R drug Tocilizumab, can reduce fever in severe patients, recover CPR, improve lymphopenia, and have a significant effect in improving the clinical symptoms of severe patients. However, the use of IL-6 inhibitors may exacerbate viral infections, and it is necessary to balance the negative effects of immunosuppressant drugs against the viral immune response and control the inflammatory response.

To be continued in Part III…