G4s: the long sought-after targets for future HIV-1 treatment?
It’s all due to what you could call a design flaw in this virus that has been plaguing the world for decades. There is only one region of HIV-1’s DNA where gene transcription is initiated – its gene promoter – and the European Research Council (ERC)-funded project HIV LTR G-4 (G-quadruplexes in the HIV-1 genome: novel targets for the development of selective antiviral drugs) has recently found that region to be filled with G4s. This is true even for a virus in a latent state which, until now, has been completely invisible to immune cells and therapy. “This discovery is very important and has implications at different levels,” says Sara Richter, professor in Microbiology and Clinical Microbiology at the University of Padua and ERC grantee and principal investigator for the project. “It means that G4s are key for viral transcription and, since each G4 has its own peculiar structure, they are specifically targetable, it also means that we have identified a potential pathway to effectively target and eliminate the virus even when it’s in a latent state.”
New selective compounds
Richter found good starting points for her research in four different molecules displaying anti-HIV-1 activity. The first one is a G4 ligand inhibiting HIV-1 with effective concentration in the low micromolar range, from which she and her team synthesised a second class of molecules with effective potential against HIV-1 in the nanomolar range. The third molecule was found by screening a commercial library: it is selective for HIV-1 G4s but binds poorly to cellular G4s. Finally, the team focused on a fourth molecule called aptamer AS1411 – an anticancer agent found to inhibit HIV-1 entry by binding to a viral co-receptor on the cell surface. “The results of our research met our initial expectations. We identified some compound leads that target HIV G4 with a good level of selectivity and display antiviral activity. We also demonstrated how the G4-based centre of HIV transcription regulation is controlled by cellular proteins with an impressively fine-tuned network between G4s and cellular proteins. Moreover, we reported – at the nuclear magnetic resonance (NMR) resolution level – the structures of the most important HIV G4s. This allows for the rational design/optimisation of drug targeting,” Richter explains.
Promising results
Of course, there is still much work to be done before these findings can result in a new generation of anti-HIV drugs. But this ERC-funded team has recently published a paper showing how a peptide nucleic acid (PNA) strategy enables the delivery of G4-stabilising compounds to the exact HIV G4 location. Results of additional research from the same team were also recently submitted. They showcase the development of a high-throughput method that can be applied to search for drug-like molecules against any single G4 structure of choice. “In our case, this high-throughput sequencing (HTS) strategy enabled the identification of a family of drug-like compounds targeting the most important HIV G4 with a specific and unique type of interaction. The compounds have good antiviral activity and are not toxic for the cells. We are currently checking if the antiviral activity can be further improved by rationally modifying the family of compounds based on the NMR structural data that we provided,” Richter points out. Richter and her team are currently in touch with collaborators to test their compounds on animal models. Even though they still have to do this, their research has provided a whole new level of understanding of the HIV promoter structure and the regulation of viral transcription by G4 structures.
Keywords
HIV LTR G-4, HIV-1, G4, DNA, viral transcription, treatment, HIV, HTS, G-quadruplexes
