Inhibitory Activity of Flavonoid Scaffolds on SARS-CoV-2 3CLpro: Insights from the Computational and Experimental Investigations.

The emergence of the COVID-19 situation has become a global issue due to the lack of effective antiviral drugs for treatment. Flavonoids are a class of plant secondary metabolites that have antiviral activity against SARS-CoV-2 through inhibition of the main protease (3CLpro). In this study, 22 flavonoids obtained from natural sources and semisynthetic approaches were investigated for their inhibitory activity against SARS-CoV-2 3CLpro, along with cytotoxicity on Vero cells. The protein-ligand interactions were examined using molecular dynamics simulation. Moreover, QSAR analysis was conducted to clarify the structural effects on bioactivity. Accordingly, the in vitro investigation demonstrated that four flavonoids, namely, tectochrysin (7), 6″,6″-dimethylchromeno-[2″,3″:7,8]-flavone (9), panduratin A (19), and genistein (20), showed higher protease inhibitory activity compared to the standard flavonoid baicalein. Finally, our finding suggests that genistein (20), an isoflavone discovered in Millettia brandisiana, has potential for further development as a SARS-CoV-2 3CLpro inhibitor.

Sperm can act as vectors for HIV-1 transmission into vaginal and cervical epithelial cells.

PROBLEM: Sperm are the major cells in semen. Human sperm possess a number of HIV-1 gp120 binding ligands including sulfogalactosylglycerolipid (SGG). However, the mechanisms of how sperm capture HIV-1 onto their surface are unclear. Furthermore, the ability of sperm to deliver HIV-1 to vaginal/cervical epithelial cells lining the lower female reproductive tract, as a first step in HIV-1 transmission, needs to be determined. METHOD OF STUDY: Sperm from healthy donors were incubated with dual-tropic HIV-1CS204 (clinical isolate), and virus capture was determined by p24 antigen ELISA. The involvement of SGG in HIV-1 capture was assessed by determining Kd values of HIV-1 gp120-SGG binding as well as computational docking of SGG to the gp120 V3 loop. The ability of sperm-associated HIV-1 to infect peripheral blood mononuclear cells (PBMCs) and TZM-bl indicator cells was determined. Lastly, infection of vaginal (Vk2/E6E7), ectocervical (Ect1/E6E7), and endocervical (End1/E6E7) epithelial cells mediated by HIV-1-associated sperm was evaluated. RESULTS: Sperm were able to capture HIV-1 in a dose-dependent manner, and the capture reached a maximum within 5 minutes. Captured HIV-1, however, could be removed from sperm by Percoll-gradient centrifugation. Affinity of gp120 for SGG was substantial, implicating sperm SGG in HIV-1 capture. Sperm-associated HIV-1 could productively infect PBMCs and TZM-bl cells, and was capable of being transmitted into vaginal/cervical epithelial cells. CONCLUSION: Sperm are able to capture HIV-1, which remains infectious and is able to be transmitted into vaginal/cervical epithelial cells, a result indicating the importance of sperm in HIV transmission.