Small Molecule Compound 5HN Flushes Out Latent HIV in Reservoir CD4 T-cells

A newly identified compound known as 5HN appears to "flush out" HIV from latent T-cells, potentially making the virus susceptible to eradication from the body, according to research published in the October 1, 2009 advance online edition of Journal of Clinical Investigation.

Current antiretroviral drugs do a good job of stopping HIV replication in the blood, but they cannot reach the latent "reservoir" of virus hidden in long-lived inactive CD4 T-cells. Furthermore, as long as this virus remains hidden, it can evade immune surveillance and rebound rapidly if treatment is interrupted.

Researchers have proposed various strategies for activating these cells and thereby releasing the sequestered virus, but complete eradication -- a cure -- has proven elusive.

In the present study, Robert Siliciano from Johns Hopkins University and colleagues aimed to find a better method of re-activating latent HIV, since non-specific or global activation of T-cells has unacceptable adverse effects associated with cytokines (chemical messengers) that trigger a systemic inflammatory response.

The researchers developed a novel in vitro model of HIV-1 latency. In a laboratory study, human primary CD4 T-cells were transduced with the "pro-survival" protein Bcl-2, which inhibits apoptosis, or "cell suicide," through the interleukin-7 (IL-7) signalling pathway. The resulting cells over-expressed Bcl-2, allowing them to mimic the sustained "quiescent" or inactive state of resting CD4 cells in the body.

The investigators then used this model system to search for agents that could reverse viral latency, screening some 2400 small-molecule compounds.

Results

• 17 compounds were identified that stimulated HIV re-activation and replication.
• The most active compound -- 5-hydroxynaphthalene-1,4-dione (5HN), derived from the black walnut tree -- reactivated latent HIV without causing global T-cell activation.
• Unlike previously described latency-reversing agents, 5HN activated latent HIV-1 through reactive oxygen species (ROS) and nuclear factor kappa-B (NF-kappa-B).
• The new compound, however, did not affect nuclear factor of activated T-cells (NFAT) or protein kinase C theta (PKC-theta).

These results, the study authors wrote, demonstrate that T-cell receptor signalling pathways "can be dissected and utilized to purge latent virus."

"Our study expands the number of classes of latency-reversing therapeutics and demonstrates the utility of this in vitro model for finding strategies to eradicate HIV-1 infection," they concluded.

"Because of the high cost and potential toxicities of long-term HAART and the disappointing results from the clinical trials of HIV-1 vaccines and microbicides, there is still a pressing need for pursuing the goal of eradication," the researchers elaborated in their discussion.

"To cure HIV-1 infection is exceptionally challenging and will likely require combining HAART with agents that can purge latent virus," they continued. "Although the toxicities of 5HN raise concerns for its clinical application, this is a proof of concept for this approach to finding novel strategies to reactivate latent HIV-1 without inducing global T-cell activation."

On a cautionary noted, Siliciano pointed out that recent research indicates that there appears to also be a second, not yet identified, HIV reservoir, and achieving a cure may require finding ways to target this reservoir as well.

Department of Medicine and Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD; Department of Biology, Calvin College, Grand Rapids, MI; Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD; Howard Hughes Medical Institute, Baltimore, MD.

10/16/09

Reference

HC Yang, S Xing, L Shan, and others. Small-molecule screening using a human primary cell model of HIV latency identifies compounds that reverse latency without cellular activation. Journal of Clinical Investigation. October 1, 2009(epub ahead of print). Free full text.