Category Archives: Antiviral Drugs

Antiviral Drugs, Epidemics, Immunology, Molecular Virology

Luring HIV out of its latency may be the secret to developing an effective HIV cure

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Contributed by guest blogger: Steven Chan ‘12

The emergence of highly active antiretroviral therapy (HAART) in the treatment of HIV-infected individuals has certainly changed the outlook of an HIV diagnosis today, compared to what such an outlook looked like in the earliest years of the epidemic. Such a treatment regimen, if strictly adhered to, has the potential to suppress the levels of active circulating HIV in the infected individual to a level that is manageable, essentially halting the progression of the disease. It soon became clear however, that these treatments could not effectively clear the body of all HIV particles—the virus manages to stow itself away within the cellular genome of the memory CD4+ T-cells, and remain transcriptionally silent indefinitely. These latent reservoirs of HIV-infected cells prove to be undetectable for these antiretroviral therapies, since antiretroviral drugs can only target HIV-infected cells when they are replicating. And so, memory cells, which replicate infrequently, cannot be effectively targeted, making it impossible to clear HIV-infected bodies of all HIV-particles. “We’re never going to cure anybody unless we go for this latent pool,” says Robert Siliciano, the researcher at Johns Hopkins University that first identified the latent HIV memory-T cells.

A great deal of HIV-therapy research over the past decade has focused on finding a way to coax these infected cells out of their latency to make them detectable by antiretroviral drugs. The problem that has been persistently hounding researchers has been the difficulty in luring these cells out of their latency without triggering the immune system in an inflammation response that would end up doing more harm than good. David Margolis, MD, and his research team at UNC Chapel Hill, who have been working on this problem for a while now, have found success with a set of histone deacetylase inhibitors called Zolinza (vorinostat), a chemotherapeutic cancer drug that has been found to stimulate gene expression within the latent HIV-infected cells without inducing an overwhelming immune response. HDAC inhibitors accomplish this by inhibiting the activity of histone deacetylase, which removes the acetyl groups from the lysine residues in the core histones, resulting in the formation of a condensed and transcriptionally silenced chromatin. By inhibiting this activity, the core histones become less compact, and the chromatin becomes more transcriptionally active. After initial success with in vitro tests in cell cultures and in blood tissues, six HIV-positive men were recruited in a clinical trial pairing this treatment alongside consistent antiretroviral therapy. Each of the study volunteers had already been taking part in a robust antiviral regimen for an average of four years, and displayed undetectable viral loads and stable CD4+ T-cell counts. Post-exposure to Zolinza, HIV-RNA levels—a marker of viral activity—in these patients increased by an average of 4.8 times, ranging from a 1.5-fold increase in one patient to a 10.0-fold increase in another. The drug took effect in as little as 8 hours, inducing a two-fold increase in cellular and chromatin-bound histone acetylation within that time span. Increased expression made these cells susceptible to detection and eradication by the antiretroviral drugs, which proceeds just as efficiently as usual.

Margolis addresses the significance of this advancement, “This study provides first proof of concept, demonstrating disruption of latency, a significant step toward eradication.” Just how effective this drug is in teasing out the latent cells still remains to be seen—with nearly a ten-fold difference in one trial participant compared to the other, the efficacy of such a drug remains questionable. The limited sample size in this initial trial also doesn’t give us too much to go on. There are also concerns that the drug could induce some serious side effects such as blood clots in the legs and lungs, diabetes, fewer platelets and RBC count, as well as dehydration from nausea and vomiting, but at least in this trial, there were only mild adverse effects at worst. Little is known about the potential adverse effects of long-term use of the drug. Margolis et al.’s study design made use of a single dose of Vorinostat, but it is likely that repeated intermittent doses would yield the most optimal effects. “Vorinostat may not be the magic bullet, but this success shows us a new way to test drugs to target latency and suggests that we can build a path that may lead to a cure,” says Margolis. Further studies to assess Vorinostat’s safety and effectiveness, and the way it interacts with other HAART treatments, would certainly be crucial before it can be deployed as a component in future HIV treatment regimen.

 

Links:

Archin N, Liberty A, Kashuba A, Choudhary S, Kuruc J, Hudgens M, Kearney M, Eron J, Hazuda D, and Margolis D. “Administration of Vorinostat Disrupts HIV-1 Latency in Patients on ART,” HIV Persistence, Latency, and Eradication at 19th Conference on Retroviruses and Opportunistic Infections, March 8, 2012,              http://www.retroconference.org/2012b/Abstracts/45315.htm

Contreras X, Schwenwker M, Chen CS, McCune JM, Deeks SG, Martin J, Peterlin BM. Suberoylanilide Hydroxamic Acid Reactivates HIV from Latently Infected Cells, J. Biol. Chem., January 9, 2009, http://www.jbc.org/content/284/11/6782.full

Horn T. “Pathway to a Cure: Cancer Drug Helps Purge HIV From Resting Cells,”  AidsMeds, March 9, 2012, http://www.aidsmeds.com/articles/hiv_vorinostat_ cure_1667_22059.shtml

“Lymphoma Drug Wakes Up Dormant HIV,” AidsMeds, March 17, 2009,     http://www.aidsmeds.com/articles/hiv_zolinza_latent_1667_16307.shtml

Steven Chan is a senior at Vassar College, majoring in Science, Technology, and Society

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Antiviral Drugs, Epidemics

Highly Active Antiretroviral Therapy and Tenofovir: Lowering HIV Viral Loads, Raising the Risk of Renal Failure

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Contributed by guest blogger: Michael McManus ‘12

People undergoing anti-retroviral therapies, which target and interrupt the replicative processes of HIV, are living longer due to the relative success of treatments. Those with HIV are using these drug cocktails for longer periods of time, an important characteristic with results that could not be observed in short-term clinical studies.

Mortality for patients with HIV who are able to undergo highly active antiretroviral therapy (HAART) has shifted from higher rates, during the initial HIV scare, to relatively lower rates. HAART has been incredibly successful, increasing the quality of life for those who have access to it. For some, however, the effects of an HAART regimen, which combines up to four medications, can lead to renal failure within two weeks of regimen administration due to the toxic nature of some of the medications.

Renal failure, or loss of kidney function, can lead to organ failure and eventually death. The kidneys are normally responsible for filtering the blood. They maintain homeostasis by regulating electrolytes, regulating blood pressure, maintaining pH balances, and by removing and diverting waste from the blood into the urinary bladder, producing urine. The kidneys filter many things from the blood in order to retain them in the body, ranging from proteins to glucose. When the kidneys fail, proteins, glucose, and even blood become detectable in the urine. Glycosuria, proteinuria, and hematuria are all biological indicators of a lack of reabsorption and therefore renal failure.

In a recently published paper, Juliette Pavie et al. describe a case of renal failure in an HIV-positive patient after only two weeks of tenofovir therapy. Tenofovir is a nucleotide reverse transcriptase inhibitor associated with low risk of severe renal adverse events in clinical trials. However, tenofovir is in the same class of drugs such as adefovir and cidofovir, which have well-documented nephrotoxicity1,2.

The patient followed was a 46-year-old homosexual male of Scottish descent. His weight, CD4 cell count, plasma HIV RNA level, serum creatine, and urea levels were all taken before HAART regimen, which consisted of tenofovir, emtricitabine, atazanavir, and ritonavir, was started. During treatment, the patient did not take any nonsteroidal anti-inflammatory drugs (NSAIDs), which are known to lead to kidney dysfunction.

Fifteen days after treatment began levels were tested again: serum creatine and urea had increased 3-fold and 2.5-fold respectively. Five days later, the patient became unable to pass urine and levels were immediately measured again: serum creatine showed a 15-fold increase from the original amount, and urea a 12-fold increase. Urinalysis showed glycosuria and proteinuria, indicating loss of kidney function. Renal biopsy indicated necrosis of the kidneys and other abnormalities. After these observations, HAART was halted and hemodialysis was started to rescue lost kidney function. After three months of hemodialysis, HAART was resumed, but tenofovir was excluded from the treatment.

After one year of treatment, the patient showed signs of recovery. CD4 cell count increased to relatively normal levels, and serum creatine and plasma HIV RNA levels dropped. To this day, the patient is still undergoing the same HAART, with serum creatine and plasma HIV RNA levels remaining stable. However, the patient still suffers from moderate glycosuria and proteinuria, indicating that kidney function has not fully recovered.

Although this case only followed one individual undergoing a HAART regimen containing tenofovir, the observations and results are still crucial to studying renal failure resulting from HAART. The novel form of nephrotoxicity observed may serve as a model for other forms of nephrotoxicity caused by reverse transcriptase inhibitors. Although the nephrotoxicity studies1,2 only reported findings in one individual each, their findings should not be discredited, as this is the nature HIV symptom studies. For example, the emergence of Kaposi’s sarcoma as a symptom of HIV began with isolated incidents. The nature of HIV and its rapid mutation also obfuscates the relationship between HAART effectiveness and strain type. From this observation, one question out of many must be addressed: Did the combination of drugs used in the patient’s HAART regimen have an effect on nephrotoxicity?

Despite the emergence of renal failure as a threat, great strides have been made in the fight against HIV. The quality of life for those who are suffering from HIV and who have access to HAART is drastically improved compared to those who are unable to undergo HAART. However, now that HIV patients are living longer, research must switch from just targeting HIV to focusing on HIV and the complications created by decreased mortality. Nephropathy, or disease of the kidney, and subsequent nephrectomy, removal of a kidney, now contribute to the decrease in quality of life associated with the aging HIV population. When developing future treatments, scientists and doctors must analyze the nephrotoxicity of the products they are synthesizing, as renal failure is a clear and present danger for those undergoing HAART.

Article Links:

http://online.liebertpub.com/doi/abs/10.1089/apc.2011.0056

1Tanji, N., Tanji, K., Kambham, N., Markowitz, G. S., Bell, A., and D’Agati, V. D. (2001) Adefovir nephrotoxicity: Possible role of mitochondrial DNA depletion. Human Pathology. 32, 732-740.

2 Meier, P., Dautheville-Guibal, S., Ronco, P. M., and Rossert, P. (2001) Cidofovir-induced end-stage renal failure. Nephrology Dialysis Transplantation. 17, 148-149.

Michael McManus is a senior at Vassar College, majoring in Biochemistry

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Antiviral Drugs, Molecular Virology

Broad Spectrum Antiviral is an Effective Inhibitor of Viruses but Not Media Hype

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There have been a few important successes in antiviral drug development, but for the most part it is extremely difficult to find drugs to treat viral infections. Viruses are highly effective hijackers of cellular processes, and since drugs that target cellular processes are likely to be toxic, that leaves only a few potential virus specific targets. Further, because of the diversity of viruses most antiviral drugs are very specific for their target virus and are not effective against others. The holy grail of antiviral drugs would be something that inhibits replication of many viruses – a broad spectrum antiviral.

A new paper in PLOS One describes a creative approach to the problem of broadly targeting viral infections. The approach uses a recombinant protein that combines the properties of two natural antiviral response pathways in the cell. Almost all viruses generate long double stranded RNA (dsRNA) at some point in their replication cycle. But long dsRNA is not found in normal, healthy cells. So the presence of dsRNA triggers a response in the cell that shuts down gene expression, which can effectively shut down viral replication. Another response is apoptosis: an infected cell can trigger a cellular suicide pathway, destroying the infected cell and the virus along with it. In this new study, researchers fused parts of proteins from key mediators of both pathways to generate a new protein called DRACO that triggers apoptosis when it binds to dsRNA.

In cell culture, DRACOs induce apoptosis in cells only when dsRNA is present. The study goes on to test whether DRACOs can protect cells from infection. Cells pre-treated with DRACOs survive viral infection, while untreated cells don’t. And it protects against a large variety of different viruses; viruses from 7 different families were tested and DRACOs appear to be effective against all of them. But for an antiviral to be useful it has to also work in vivo, and DRACOs show some promise here too. 60-70% of mice pre-treated with DRACOs survive influenza virus challenge, while only 10% of untreated mice survive.

The results of this study are exciting and show promise but we must be cautious about over-extending the findings. It is a long and challenging process to go from an early stage development like this one to a clinically useful anti-viral drug. There will be some very significant hurdles to overcome to develop this further. In all the experiments, the cells (or animals) are pre-treated with DRACOs, but its not known if there is any post-exposure protection. The animal studies show that interperitoneal injection can protect animals, but the distribution of the drug in different tissues varies and in some tissues disappears before 24 hours, which could be a problem if it can’t reach the required concentrations in the target tissues. Also, being a protein, there will be challenges for effective delivery (since interperitoneal injection is not likely to be a favored route!). Many years of further testing, development, and clinical trials (if it gets that far) are needed. Despite the many challenges that lay ahead for further development of this broad spectrum anti-viral, it appears promising and worth pursuing.

As usual though, news reports describing this as a major breakthrough have missed the point that this is an interesting new development but that it is very much in its infancy. Since nearly every discovery is hailed as a breakthrough, the public gets a distorted idea of the way science proceeds. Media reports have also been misleading, including promoting it as a potential treatment for HIV or Hepatitis, which weren’t even among the viruses tested, or touting it as a possible cure for nearly all viral infections. Slow down a little, folks. There is a long way to go before those claims can be made. Perhaps someone can develop a treatment for the disease that makes headline writers distort information.

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Antiviral Drugs, Guest Blogger, Molecular Virology

A different alphabet, a different treatment?

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Contributed by Guest Blogger: Sean Koerner ’11

It’s easy to think of viruses as alien or lifeless – after all, they can’t reproduce on their own, eat anything, or even move around without assistance. However, viruses have evolved to use the same toolbox that human cells use, right down to the way their genes and proteins are encoded. One of the most problematic viruses for humans, HIV, works by putting its own information into our cells’ genomes, turning host cells into viral factories. This information is formed from two types of alphabets: strung-together sequences of deoxyribonucleotides, which exist intracellularly as deoxyribonucleotide triphosphate (dNTP) monomers in our own cells and ribonucletides, which form the HIV genome as well as existing independently as ribonucleotide triphosphate (rNTP) monomers within our own cells. In order to infect our cells, HIV uses a protein known as reverse transcriptase to generate the DNA that our cells are used to reading from the viral RNA genome. This reverse transcription of RNA to DNA has long been a target of anti-HIV drugs, since without this step, HIV cannot successfully infect our cells.

Recently, a team at the University of Rochester discovered a previously unknown characteristic of this process. Two of the cells most commonly infected by HIV, CD4+ lymphocytes and macrophages, displayed different levels of dNTPs and rNTPs after being infected by HIV, with the lymphocytes containing much less rNTPs and more dNTPs than the macrophages. After a biochemical analysis of the cells, the research team discovered that HIV’s reverse transcriptase is capable of using cellular rNTPs to generate RNA based upon the HIV genome, which is then reverse transcribed into cellular DNA while in the macrophage environment. This allows HIV to use the higher concentrations of rNTPs in macrophages to continue replicating efficiently, despite the relative dearth of dNTPs as compared to lymphocytes. Since HIV uses one method (dNTPs) in lymphocytes and one method (rNTPs) in macrophages, it may be possible to target HIV replication in macrophages specifically. Why care about the difference between the two cell types? Well, macrophages travel the body much more rapidly than lymphocytes; if we can stop HIV infecting them, we may be able to slow the progression of HIV infection throughout the body.

How could we do that? In short, by targeting the synthesis of rNTP strands with new drugs. Although we would likely experience side effects, they could be negligible compared with the repression of HIV. The research team at Rochester have already demonstrated that rNTP string inhibitors slow HIV’s infection of macrophages, so specific drugs targeted for this process might be able to halt it altogether.

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Antiviral Drugs, Immunology

A cell model of HIV latency for finding novel small-molecule therapeutics

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Contributed by Guest Blogger: Jack Bulat, ’11

Highly active antiretroviral therapy (HAART) has extended the quality and expectancy of life for people infected with HIV-1, but has been unsuccessful in leading to a cure for AIDS. This is because it proves ineffective at targeting the latent HIV-1 reservoir – a pool of memory CD4+ T cells in the quiescent phase of the cell cycle that harbor inactive integrated virus. Should an HIV-infected patient ever come off HAART, activation of this latent pool would cause the virus to re-emerge. Because HAART has become both expensive and toxic in the long-run, significant efforts have been directed at targeting HIV-1 latency for more effective treatment.

A considerable obstacle to studying HIV-1 latency in memory CD4+ T cells has been the lack of a latency cell model. Because only a small portion of CD4+ T cells infected with HIV-1 survive to become latently-infected memory cells, a resilient cell line mimicking latency has practical value for therapeutic screening. In a study, Yang and colleagues transduced primary CD4+ T cells with a lentiviral vector for constitutive expression of Bcl-2, an antiapoptotic signaling factor implicated in the generation and maintenance of memory CD4+ T cells. Upon confirming that the physical and biochemical properties of these Bcl-2-expressing cells are highly similar to those of freshly-isolated primary resting CD4+ T cells, they activated and infected the cells with an HIV-1 strain mutated to mitigate cytopathic effects. After establishing latency in the infected cells, the researchers screened more than 4400 drugs and natural products for the ability to activate the latent HIV-1 mutant. 5-hydroxynaphthalene-1,4-dione (5HN), a compound found in the leaves, roots, and bark of the black walnut tree, was a promising hit because it did not cause global T cell activation, which would be too dangerous for clinical use.

Despite this, it looks like 5HN will not be hitting the pharmacy shelves any time soon, since it is chemically reactive, affects several cellular proteins, and leads to the stimulation of inflammatory genes. Nevertheless, the study is significant for presenting a methodology for generating potentially useful cell lines modeling HIV-1 latency. A noteworthy criticism has been that a mutated strain, rather than wild-type virus, was used to infect the model cells. The scientists contended that the strain is suitable to study latency specifically because the genes implicated in HIV-1 activation were not modified.

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