Acyclovir: a new use for an old drug

Viral Infection and Antiviral Treatments in Ocular Pathologies

Ocular viral infections are common and widespread globally. These infectious diseases are a major cause of acute red eyes and vision loss. The eye and its nearby tissues can be infected by several viral agents, causing infections with a short course and limited ocular implications or a long clinical progression and serious consequences for the function and structure of the ocular region. Several surveillance studies underline the increased emergence of drug resistance among pathogenic viral strains, limiting treatment options for these infections. Currently, in the event of resistant infections, topical or systemic corticosteroids are useful in the management of associated immune reactions in the eye, which contribute to ocular dysfunction. Many cases of viral eye infections are misdiagnosed as being of bacterial origin. In these cases, therapy begins late and is not targeted at the actual cause of the infection, often leading to severe ocular compromises, such as corneal infiltrates, conjunctival scarring, and reduced visual acuity. The present study aims at a better understanding of the viral pathogens that cause eye infections, along with the treatment options available.

A common anti-cytomegalovirus drug, ganciclovir, inhibits HIV-1 replication in human tissues ex vivo

BACKGROUND

Cytomegalovirus (CMV) is a common HIV-1 copathogen. Since CMV infection is an important contributor to immune activation, the driving force of HIV disease, an anti-CMV strategy might be beneficial to HIV-infected patients. Shin et al. (J Acquir Immune Defic Syndr 2014; 65:251-258) reported that anti-CMV therapy with valganciclovir in coinfected individuals results in a decrease of HIV viral load that is not accompanied by a decrease of immune activation. This suggests an alternative mechanism for HIV inhibition other than suppression of CMV-mediated inflammation.

METHOD

We evaluated the anti-HIV activity of ganciclovir (GCV), the active form of valganciclovir, on HIV replication in human tissues ex vivo.

RESULTS

We show that GCV has a direct suppressive activity on HIV replication in human tissues ex vivo, including laboratory strains, drug-resistant and primate HIV-1 isolates. We deciphered the mechanism of this inhibition and showed that GCV-TP is incorporated in the nascent DNA chain and acts as a delayed chain terminator.

CONCLUSION

Our results suggest that anti-CMV strategy using valganciclovir in HIV-1-infected individuals may reduce HIV-1 viral load not only indirectly by decreasing CMV-mediated immune activation but also directly by inhibiting HIV-1 reverse transcriptase.

Antivirals against animal viruses

Antivirals are compounds used since the 1960s that can interfere with viral development. Some of these antivirals can be isolated from a variety of sources, such as animals, plants, bacteria or fungi, while others must be obtained by chemical synthesis, either designed or random. Antivirals display a variety of mechanisms of action, and while some of them enhance the animal immune system, others block a specific enzyme or a particular step in the viral replication cycle. As viruses are mandatory intracellular parasites that use the host's cellular machinery to survive and multiply, it is essential that antivirals do not harm the host. In addition, viruses are continually developing new antiviral resistant strains, due to their high mutation rate, which makes it mandatory to continually search for, or develop, new antiviral compounds. This review describes natural and synthetic antivirals in chronological order, with an emphasis on natural compounds, even when their mechanisms of action are not completely understood, that could serve as the basis for future development of novel and/or complementary antiviral treatments.

SAMHD1 enhances nucleoside-analogue efficacy against HIV-1 in myeloid cells

SAMHD1 is an intracellular enzyme that specifically degrades deoxynucleoside triphosphates into component nucleoside and inorganic triphosphate. In myeloid-derived dendritic cells and macrophages as well as resting T-cells, SAMHD1 blocks HIV-1 infection through this dNTP triphosphohydrolase activity by reducing the cellular dNTP pool to a level that cannot support productive reverse transcription. We now show that, in addition to this direct effect on virus replication, manipulating cellular SAMHD1 activity can significantly enhance or decrease the anti-HIV-1 efficacy of nucleotide analogue reverse transcription inhibitors presumably as a result of modulating dNTP pools that compete for recruitment by viral polymerases. Further, a variety of other nucleotide-based analogues, not normally considered antiretrovirals, such as the anti-herpes drugs Aciclovir and Ganciclovir and the anti-cancer drug Clofarabine are now revealed as potent anti-HIV-1 agents, under conditions of low dNTPs. This in turn suggests novel uses for nucleotide analogues to inhibit HIV-1 in differentiated cells low in dNTPs.

Human Herpesviruses as Copathogens of HIV Infection, Their Role in HIV Transmission, and Disease Progression

Of eight human herpesviruses (HHVs), often, only herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) find mention in medical literature as both of these viruses are commonly associated with genital lesions and oral ulcers, commonly known as cold sores. However, role of human herpesviruses as copathogens and in aggravation and in the transmission of other human diseases, especially the Acquired immunodeficiency syndrome (HIV/AIDS) has only very recently been recognized. Therefore, screening and treating subclinical HHV infections may offer slowing of HIV infection, disease progression, and its transmission. Beside HSV-1 and HSV-2, HHV-3 a causative agent of herpes zoster remained one of the first manifestations of HIV disease before the era of highly active antiretroviral therapy (HAART). HHV-5 also known as human Cytomegalovirus infection remains a significant risk factor for HIV-associated mortality and morbidity even in HAART era. It is proposed that Cytomegalovirus viremia could be a better predictor of HIV disease progression than CD4+ T-lymphocyte count. The role of HHV-4 or Epstein-Burr virus and HHV-6, HHV-7, and HHV-8 is still being investigated in HIV disease progression. This review provides insight into the current understanding about these 8 HHVs, their co-pathogenesis, and role in HIV/AIDS disease progression. The review also covers recent literature in favor and against administering anti-HHV treatment along with HAART for slower AIDS progression and interrupted sexual transmission.

Herpes simplex virus and HIV: genital infection synergy and novel approaches to dual prevention

Sexual transmission of HIV-1, in the absence of co-factors, is poorly efficient. Data support that herpes simplex virus type-2 (HSV-2) may increase a woman's susceptibility to HIV-1. Potential mechanisms by which HSV-2 serves as an HIV-1 enhancing co-factor include (1) initiation of a clinical or subclinical mucosal inflammatory response, (2) alteration of innate mucosal immunity and (3) weakening or breaching the protective genital epithelia. No clinical trial has examined prevention of primary HSV-2 infection to eliminate the major morbidities of this recurrent disease and as a strategy to reduce HIV-1 transmission. Topical administration of potent antivirals can achieve local concentrations that are orders of magnitude higher than those obtained with oral administration. This paper reviews major advances in oral and topical pre-exposure prophylaxis of HIV-1 and HSV-2 and, based on these data, hypothesizes that simultaneous prevention of sexual acquisition of HSV-2 and HIV-1 via topical antiretroviral agents will have a synergistic impact on both epidemics.

It takes more than two for this tango

A paper in this issue by Ogawa et al. (2013) shows that HSV-2-infected keratinocytes in human skin explants release a protein that enhances HIV-1 infection of Langerhans cells in vitro. This may explain the in vivo observation that HSV-2 infection facilitates HIV-1 acquisition.

Microbicides: still a long road to success

The development of efficient microbicides, the topically applied compounds that protect uninfected individuals from acquiring HIV-1, is a promising strategy to contain HIV-1 epidemics. Such microbicides should of course possess anti-HIV-1 activity, but they should also act against other genital pathogens, which facilitate HIV-1 transmission. The new trend in microbicide strategy is to use drugs currently used in HIV-1 therapy. The success of this strategy is mixed so far and is impaired by our limited knowledge of the basic mechanisms of HIV-1 transmission as well as by the inadequacy of the systems in which microbicides are tested in preclinical studies.

Exploiting the anti-HIV-1 activity of acyclovir: suppression of primary and drug-resistant HIV isolates and potentiation of the activity by ribavirin

Multiple clinical trials have demonstrated that herpes simplex virus 2 (HSV-2) suppressive therapy using acyclovir (ACV) or valacyclovir in HIV-1/HSV-2-infected persons increased the patient's survival and decreased the HIV-1 load. It has been shown that the incorporation of ACV-monophosphate into the nascent DNA chain instead of dGMP results in the termination of viral DNA elongation and directly inhibits laboratory strains of HIV-1. We evaluated here the anti-HIV activity of ACV against primary HIV-1 isolates of different clades and coreceptor specificity and against viral isolates resistant to currently used drugs, including zidovudine, lamivudine, nevirapine, a combination of nucleoside reverse transcriptase inhibitors (NRTIs), a fusion inhibitor, and two protease inhibitors. We found that, at clinically relevant concentrations, ACV inhibits the replication of these isolates in human tissues infected ex vivo. Moreover, addition of ribavirin, an antiviral capable of depleting the pool of intracellular dGTP, potentiated the ACV-mediated HIV-1 suppression. These data warrant further clinical investigations of the benefits of using inexpensive and safe ACV alone or in combination with other drugs against HIV-1, especially to complement or delay highly active antiretroviral therapy (HAART) initiation in low-resource settings.

Meta-analysis of randomized trials on the association of prophylactic acyclovir and HIV-1 viral load in individuals coinfected with herpes simplex virus-2

OBJECTIVE

To summarize the randomized evidence regarding the association between acyclovir use and HIV-1 replication as measured by plasma HIV-1 RNA viral load among individuals coinfected with herpes simplex virus (HSV)-2.

DESIGN

Meta-analysis of seven randomized trials conducted between 2000 and 2009. Inclusion criteria composed of acyclovir or valacyclovir use as prophylaxis among individuals coinfected with HIV-1 and HSV-2 who were ineligible for highly active antiretroviral therapy. HIV-1 viral load was the outcome.

METHODS

Random-effects summarization was used to combine treatment effect estimates. Stratified and meta-regression analyses were used to compare estimated treatment effects by characteristics of trials and participants.

RESULTS

The summary treatment effect estimate was -0.33 (95% confidence interval: -0.56, -0.10, 95% population effects interval: -0.74, 0.08) log(10) copies, an approximate halving of plasma viral load. However, there was marked heterogeneity (P < 0.001). Older median age, valacyclovir, higher compliance, earlier publication, and shorter study length were associated with a larger decrease in viral load as compared with their counterparts.

CONCLUSION

Current evidence suggests a range of favorable effects of acyclovir on plasma HIV-1 viral load among persons coinfected with HSV-2.

HIV-associated immune activation: from bench to bedside

HIV infection is associated with a state of chronic, generalized immune activation that has been shown in many studies to be a key predictor of progression to AIDS. Consistent with this model, nonpathogenic SIV infections of natural hosts, such as the sooty mangabeys, are characterized by low levels of immune activation during the chronic phase of infection. The molecular, cellular, and pathophysiological mechanisms underlying the HIV-associated immune activation are complex and still poorly understood. There is, however, growing consensus that both viral and host factors contribute to this phenotype, with emphasis on the role played by the mucosal immune dysfunction (and consequent microbial translocation) as well as the pattern of in vivo-infected CD4(+) T cells. The observation that antiretroviral therapy (ART)-induced suppression of HIV replication does not fully resolve immune activation provided the rationale for a number of exploratory studies of potential immune modulatory treatments to be used in HIV-infected individuals in addition to standard ART. This review provides an update on the causes and consequences of the HIV-associated immune activation, and a summary of the immune modulatory approaches that are currently under clinical investigation.

Interactions of HIV, other sexually transmitted diseases, and genital tract inflammation facilitating local pathogen transmission and acquisition

Despite several decades of clinical trials assessing the impact of etiological treatment of sexually transmitted diseases (STDs) to decrease HIV acquisition and transmission, almost all of these trials have not proven to be efficacious. Increasing evidence suggests that specific STD treatment alone may not be sufficient to alter the genital tract inflammatory milieu that is created by STDs. This paper examines the associations between STDs and HIV susceptibility and infectiousness, and considers the role of chronic and refractory inflammation to create an environment that potentiates HIV and STD transmission and acquisition by reviewing biological, observational, and clinical trial data.

Contribution of sexually transmitted infections to the sexual transmission of HIV

PURPOSE OF REVIEW

We review recent evidence about the link between sexually transmitted infections (STI) and HIV transmission and consider implications for control programmes.

RECENT FINDINGS

New studies and meta-analyses confirm the association of HIV acquisition and transmission with recent STIs, although there is considerable heterogeneity between organisms and populations. Much of the recent evidence relates to herpes simplex virus type 2 (HSV-2), for which the population-attributable risk percentage (PAR%) for HSV-2 is between 25 and 35 in Africa. Mathematical models show how transmission attributable to STI varies with HIV epidemic phase, and HSV-2 becomes increasingly important as the epidemic matures. HSV-2 suppressive therapy reduces HIV concentrations in plasma and the genital tract in people coinfected with HSV-2, in part due to direct inhibition of HIV reverse transcriptase. Recent trials of HSV-2 suppressive therapy have not shown an impact on the risk of HIV acquisition, nor in controlling transmission from dually infected people to their serodiscordant heterosexual partners.

SUMMARY

Although there is a plausible link between STI and HIV risk, intervention studies continue to be disappointing. This fact does not disprove a causal link, but mechanisms of action and the design and implementation of interventions need to be better understood.