August 13, 2014
Welcome to the first installment of a periodic series of P-values posts by guest authors. We’ll be featuring scientists, advocates and implementers from around the world. If you’ve got a point of view you’d like to share or a topic you’re expert in and would like to explain, Let us know.
This post is the first of what will be a series of posts from scientists working on cure research. Dr. David Margolis and Karine Dubé of The Martin Delaney Collaboratory of AIDS Researchers for Eradication explain one strategy being pursued by scientists as a possible way to cure HIV. After reading this, if you want to learn more check out this video on related research.
Highly active antiretroviral therapy (HAART) is a true miracle of modern science and has contributed to saving millions of lives worldwide. HAART can successfully reduce plasma HIV-1 levels in adherent HIV-positive patients to below the detection limit of clinical assays. As wonderful as HAART is, it does not clear HIV from the human body, but can only suppress it. HIV remains dormant or latent in around 1 out of every million white blood cells in suppressed patients in the form of HIV provirus that becomes integrated within the human genome (also called the reservoir).
There are several approaches to eradicating latent HIV infection that have been proposed by the Martin Delaney Collaboratories, including, but not limited to: intensification of HIV treatment in the acute phase of infection, gene therapy and stem cell transplantation research as well as latency reserving agents. Latency reversing agents are small pharmacological molecules that would help uncover where HIV is hiding in the cells of HIV-infected patients whose viral load has been suppressed.
The Collaboratory of AIDS Researchers for Eradication – CARE – endorses the approach of small pharmacological molecules to finding a cure for HIV infection. We believe that this method represents the safest, most scalable, and accessible strategy to eradicating HIV in the future. By using established drug discovery tools, we hope to launch a pipeline of small pharmacological molecules to be used in human studies. These small molecules would induce the expression of the replication-competent latent HIV proviral genomes within resting CD4+ T cells and make them susceptible to the immune clearance and the effect of HAART. In the literature, this is also called the “shock and kill” strategy or “induction and clearance.” This method relies on reactivating the rare remaining reservoirs while patients take their HAART.
Our priority is to discover new molecules that are safe and can act alone or in synergy with other drugs to reactivate HIV virus transcription. We screened over 10,000 new pharmacological molecules and we are examining their mechanisms of action. As these new compounds have various levels of potency and toxicity, it is important to evaluate them carefully using cell models and animal models before advancing them into clinical testing. Experiments are being conducted in vitro (in artificial laboratory cell models), ex vivo (in patient’s cells studied in the laboratory) and in vivo (in animal models or real human patients) using various cell lines and animal models, included humanized mice and non-human primates.
The small pharmacological molecules being proposed would act as inducing agents to disrupt the state of proviral latency. Examples of small molecules that have been studied include inhibitors of histone deacetylase (HDAC) that play a role in maintaining HIV in a transcriptionally silent state. For example, Dr. Archin and colleagues demonstrated in a proof-of-concept study that a single dose of the drug vorinostat, an HDAC inhibitor, can disrupt HIV latency in HIV-positive patients on HAART. HDAC inhibitors have several advantages compared to other latency reversing agents. Because they have also been studied extensively as part of anticancer trials, we know more about their toxicological and pharmacological effects at this time.
Studying small pharmacological molecules also means that we need to carefully examine the regulatory pathways for these drugs. For example, the positive transcription elongation factor b (P-TEFb) plays an important role in regulating HIV transcription. When P-TEFb is active, this means that HIV viral transcription is stimulated. Another protein required for HIV expression is NF-κB, which is an activating regulatory protein needed for the transcription of many genes.
We are also studying molecules that induce signaling using the protein kinase C (PKC) pathway. Some of the PCK agonists under investigation include prostatin (which can induce transcription of latent HIV-1 in J-Lat cells and peripheral blood mononuclear cells (PBMCs) from HIV-positive patients on HAART). Two other PKC agonists under study include bryostatin and ingenol; however less is more about these compounds’ ability to safely induce HIV expression in vivo.
At this time, we cannot predict which compounds or combination of compounds may be effective at inducing expression of proviral DNA. We hope to investigate synergy both mechanistically and mathematically. Ideally, the chosen pharmacological molecules will reactivate latent HIV provirus without inducing a global activation of T cells. We also hope to get around the problem of toxicity by using low concentrations of the most effective inducing agents.
Once the HIV provirus is being expressed, the immune system needs to kill the infected cells. It will thus be important to re-invigorate the immune system of HIV-infected patients to ensure an effective immune response, so latency reversing agents can be used with immune-based therapies. For example, some of the immune cells could be expanded ex vivo and then be re-infused into HIV-infected patients.
Scientists within the Collaboratory are also working on ways to improve measures of the HIV reservoir. As of now, the quantitative viral outgrowth assay is the gold standard in terms of measuring replication-competent proviruses from resting CD4+ T cells. We are also using digital droplet PCR testing to quantify HIV DNA.
We are excited about the prospect of studying new latency reversing agents – as well as combinations of agents – that would be capable of aborting the state of HIV proviral quiescence. This strategy offers a diversity of options for the advancement of new compounds into clinical trials. It is also the safest way forward. We believe that small molecules represent the big picture for curing HIV infection.
If you have any questions, please send them to: