Identification of inhibitors of the HIV-1 gp41 six-helix bundle formation from extracts of Chinese medicinal herbs Prunella vulgaris and Rhizoma cibotte.

An increasing portion of patients with HIV infection and/or AIDS cannot use currently FDA-approved anti-HIV drugs, including the reverse transcriptase and protease inhibitors, due to the adverse effects and the emergence of drug resistance. Thus, it is essential to develop new anti-HIV agents with a target different from the HIV reverse transcriptase and protease. Using a conformation-specific monoclonal antibody NC-1, we previously established a high throughput screening assay for identification of small molecular organic compounds that disrupt the HIV-1 gp41 six-helix bundle formation, a critical step of membrane fusion between the HIV and the target cell. In the present study, we used this assay to screen for inhibitors of the gp41 six-helix bundle formation from aqueous extracts of nine Chinese medicinal herbs with antiviral activity. We found that the extracts of two herbs, Prunella vulgaris and Rhizoma cibotte, showed potent inhibitory activity. The inhibitory activity of these two herb extracts significantly decreased after they were passed through polyamide resin mini-columns, which are able to bind polyphenols including tannin, an HIV-1 inhibitor with multiple mechanisms of action. The bound polyphenols were eluted from the polyamide columns and also showed potent inhibitory activity on the gp41 six-helix bundle formation. Tannin purchased from different commercial sources inhibited the gp41 six-helix bundle formation in a manner similar to the polyphenols isolated from the herb extracts. These results suggest that tannin may be one of major inhibitors of the HIV-1 gp41 six-helix bundle formation in the herb extracts and that tannin may inhibit HIV-1 entry by disrupting the gp41 six-helix bundle formation.