POLYPHENOLS: NATURE HERITAGE TO DISCOVER NEW ANTI-HIV-1 AGENTS?

The urgent need for new anti-HIV drugs is a global concern. Side effects and the emergence of drug resistance have limited the therapeutic usefulness of anti-HIV drugs, and new targets for anti-retrovirals are explored. Our attention has recently focused on an emerging and promising target, HIV-1 Nucleocapsid protein (NC), a nucleic acid chaperone. Compounds able to impair NC activities would lead to inhibition of viral replication since the protein is critically implied in several steps of the HIV-1 life cycle.[1] Its strict conservation goes with the fact that all the known mutations in the protein sequence are lethal for the virus and raises the possibility that HIV-1 will be unable to generate NC mutants resistant to drugs.[2] For all these reasons the NC protein is an attractive candidate for drug development. NC acts as a nucleic acids chaperone that destabilizes stable nucleic acid structures and then promotes the formation of the annealed nucleic acid helices, substrate for Reverse Transcriptase after strand transfers. We focused our attention on the minus strand transfer, the first of the two obligatory strand transfer. This event involves the annealing of the Trans Activation Responsive (TAR) region of the viral RNA to the complementary sequence (cTAR) at the 3’-end of the DNA template. Although thermodynamically favored, the reaction does not occur extensively in the absence of NC, being cTAR and TAR sequences highly structured and stable. Compounds able to inhibit NC activity were discovered by high throughput screening and did not show common structural features.[3] The screening of libraries of different molecules is therefore valid to identify potential anti-NC agents as lead compounds suitable for the development of more powerful derivatives. To this aim, we developed and optimized a simple, fast and reliable assay to test the inhibitory activity of a large number of molecules on the NC-mediated nucleic acid helix-destabilizing activity. We screened a library of natural and synthetic polyphenols and identified highly active hits. The hits did not stabilize the TAR or cTAR structure and did not compete with NC for the binding to nucleic acids. Instead, they interacted directly with NC, resulting to be inhibitors of the NC protein with a mechanism of action distinct from that of zinc ejectors developed in past years. The effective impairment of the NC-mediated melting of TAR and cTAR led to a corresponding reduction of the TAR-cTAR hybrid formation analyzed in vitro on the NC-assisted annealing of TAR with cTAR. Compounds active in vitro showed also activity in HIV-1 infected cells. This approach would ultimately bring new insights into the development of compounds acting through NC targeting. As it has always been the case, “mother nature” offers great promises, and natural bioactive compounds and their derivatives could be excellent sources for the development of new anti-HIV therapeutics.