Identification of bis-benzylisoquinoline alkaloids as SARS-CoV-2 entry inhibitors from a library of natural products in vitro

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major public health issue. To screen for antiviral drugs for COVID-19 treatment, we constructed a SARS-CoV-2 spike (S) pseudovirus system using an HIV-1-based lentiviral vector with a luciferase reporter gene to screen 188 small potential antiviral compounds. Using this system, we identified nine compounds, specifically, bis-benzylisoquinoline alkaloids, that potently inhibited SARS-CoV-2 pseudovirus entry, with EC50 values of 0.1-10 M. Mechanistic studies showed that these compounds, reported as calcium channel blockers (CCBs), inhibited Ca2+-mediated membrane fusion and consequently suppressed coronavirus entry. These candidate drugs showed broad-spectrum efficacy against the entry of several coronavirus pseudotypes (SARS-CoV, MERS-CoV, SARS-CoV-2 [S-D614, S-G614, N501Y.V1 and N501Y.V2]) in different cell lines (293T, Calu-3, and A549). Antiviral tests using native SARS-CoV-2 in Vero E6 cells confirmed that four of the drugs (SC9/cepharanthine, SC161/hernandezine, SC171, and SC185/neferine) reduced cytopathic effect and supernatant viral RNA load. Among them, cepharanthine showed the strongest anti-SARS-CoV-2 activity. Collectively, this study offers new lead compounds for coronavirus antiviral drug discovery.

Stability of the COVID-19 virus under wet, dry and acidic conditions

COVID-19 has become a pandemic and is spreading fast worldwide. The COVID-19 virus is transmitted mainly through respiratory droplets and close contact. However, the fecal-oral transmission of the virus has not been ruled out and it is important to ascertain how acidic condition in the stomach affects the infectivity of the virus. Besides, it is unclear how stable the COVID-19 virus is under dry and wet conditions. In the present study, we have shown that the COVID-19 virus is extremely infectious as manifested by the infection of Vero-E6 cells by one PFU (Plaque Forming Unit) of the virus. We then investigated the stability of the COVID-19 virus in wet, dry and acidic (pH2.2) environments at room temperature. Results showed that the COVID-19 virus could survive for three days in wet and dry environments, but the dry condition is less favorable for the survival of the virus. Our study also demonstrated that the COVID-19 virus at a relative high titer (1.2 x 103 PFU) exhibits a certain degree of tolerance to acidic environment at least for 60 minutes. When the virus titer was [≤]1.0 x 103 PFU, acid treatment (pH2.2) for 30 or 60 minute resulted in virus inactivation. It suggests that the virus at a high concentration may survive in the acidic environment of the stomach. The finding of the present study will contribute to the control of the spread of the COVID-19 virus.

Immunization with HBsAg-Fc fusion protein induces a predominant production of Th1 cytokines and reduces HBsAg level in transgenic mice / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>The Fc receptor associated pathway might improve the immune responses against hepatitis B virus (HBV) as previously described by us. In addition, the Flt3 ligand (FL) has been reported to potentiate antigen presenting cells in vivo and may act as a potential adjuvant to boost antigen-specific immune responses. In this study, the immune efficacies of a set of fusion proteins of HBsAg and Fc and/or FL were evaluated in HBsAg transgenic mice.</p><p><b>METHODS</b>The fusion proteins composed of HBsAg and the Fc domain of murine IgG1 (HBsAg-Fc) and/or the Flt3 ligand, and yeast-derived recombinant HBsAg were used as immunogen to immunize HBsAg transgenic mice, respectively. Serum and liver HBsAg levels, serum anti-HBsAg and cytokine profile, and the activities of alanine aminotransferase (ALT)/AST were investigated after immunization.</p><p><b>RESULTS</b>After six injections, the most pronounced decrease in serum and liver HBsAg levels was observed in the HBsAg-Fc immunized group. In addition, serum Th1 cytokines and ALT/AST activities were highest in this group, indicating an effective induction of a favorable cellular immune response. Interestingly, the fusion protein containing HBsAg-Fc and the Flt3 ligand stimulated an alternative Th1-type immune response featured with high level productions of tumor necrosis factor α (TNF-α) and monocyte chemoabstractant protein 1 (MCP-1), causing a more severe cytotoxicity in hepatocytes while showed less effective in reducing serum HBsAg level.</p><p><b>CONCLUSION</b>HBsAg-Fc is effective in eliciting both the humoral and cellular immune responses against HBsAg in HBsAg transgenic mice, which makes it a potential immunogen for the immunotherapy of chronic hepatitis B.</p>

Cloning and expression of Streptococcus salivarius urease gene in Escherichia coli / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To clone Streptococcus salivarius (Ss) 57. I urease gene, which can express ureolytic activity in Escherichia coli (Ec) without adding extra nickel ions.</p><p><b>METHODS</b>Urease gene was cloned by polymerase chain reaction in three separate parts. The three separate plasmids were digested by specific restriction enzymes and ligated together. The expression of the complete urease gene in Ec was detected by phenol red assay and pH analysis.</p><p><b>RESULTS</b>Urease gene of Ss 57.I was eventually cloned and proved correct. Urease activity of the obtained clone was positive in Ec. Without adding extra NiCl(2), the recombinant Ec could hydrolyze urea to produce ammonia, resulting in the increase of pH value.</p><p><b>CONCLUSIONS</b>The clone of Ss urease gene obtained in this study could express ureolytic activity in Ec without adding extra nickel ions. The current clone can be used to construct ureolytic effector strain used in replacement therapy in caries prevention.</p>