The clinical significance of antiviral drug resistance

Lethal mutagenesis: targeting the mutator phenotype in cancer

The evolution of cancer and RNA viruses share many similarities. Both exploit high levels of genotypic diversity to enable extensive phenotypic plasticity and thereby facilitate rapid adaptation. In order to accumulate large numbers of mutations, we have proposed that cancers express a mutator phenotype. Similar to cancer cells, many viral populations, by replicating their genomes with low fidelity, carry a substantial mutational load. As high levels of mutation are potentially deleterious, the viral mutation frequency is thresholded at a level below which viral populations equilibrate in a traditional mutation-selection balance, and above which the population is no longer viable, i.e., the population undergoes an error catastrophe. Because their mutation frequencies are fine-tuned just below this error threshold, viral populations are susceptible to further increases in mutational load and, recently this phenomenon has been exploited therapeutically by a concept that has been termed lethal mutagenesis. Here we review the application of lethal mutagenesis to the treatment of HIV and discuss how lethal mutagenesis may represent a novel therapeutic approach for the treatment of solid cancers.

Evaluation of antiretrovirals in animal models of HIV infection

Animal models of HIV infection have played an important role in the development of antiretroviral drugs. Although each animal model has its limitations and never completely mimics HIV infection of humans, a carefully designed study allows experimental approaches that are not feasible in humans, but that can help to better understand disease pathogenesis and to provide proof-of-concept of novel intervention strategies. While rodent and feline models are useful for initial screening, further testing is best done in non-human primate models, such as simian immunodeficiency virus (SIV) infection of macaques, because they share more similarities with HIV infection of humans. In the early years of the HIV pandemic, non-human primate models played a relatively minor role in the antiretroviral drug development process. Since then, a better understanding of the disease and the development of better drugs and assays to monitor antiviral efficacy have increased the usefulness of the animal models. In particular, non-human primate models have provided proof-of-concept for (i) the benefits of chemoprophylaxis and early treatment, (ii) the preclinical efficacy of novel drugs such as tenofovir, (iii) the virulence and clinical significance of drug-resistant viral mutants, and (iv) the role of antiviral immune responses during drug therapy. Ongoing comparison of results obtained in animal models with those observed in human studies will further validate and improve these animal models so they can continue to help advance our scientific knowledge and to guide clinical trials. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Antiviral activity of the volatile oils of Melissa officinalis L. against Herpes simplex virus type-2

Melissa officinalis L. (Lamiaceae) has been used in a variety of practical applications in medical science. Our objective in the current study was to determine the effects of the volatile oil components of M. officinalis on Herpes simplex virus type 2 (HSV-2) replication in HEp-2 cells. Four different concentrations (25, 50, 100, 150 and 200 microg/ml) of volatile oils were examined. Experiments were carried out using HEp-2 cells. M. officinalis volatile oil was found to be non-toxic to HEp-2 cells up to a concentration of 100 micro/ml. It was, however, found to be slightly toxic at a concentration over of 100 microg/ml. The antiviral activity of non-toxic concentrations against HSV-2 was tested. The replication of HSV-2 was inhibited, indicating that the M. officinalis L. extract contains an anti-HSV-2 substance.

Management of neonatal herpes simplex virus infection

Herpes simplex viruses (HSV) are ubiquitous pathogens which can be transmitted vertically causing significant morbidity and mortality in neonates. Neonatal HSV infection is infrequent with an incidence ranging from 1 in 3,500 to 1 in 20,000, depending on the population. Neonatal HSV infection is much more frequent in infants born to mothers experiencing a primary HSV infection with an incidence approaching 50%, while infants born to mothers experiencing recurrent HSV infection have an incidence of less than 3%. Neonatal infections are clinically categorised according to the extent of the disease. They are: (i) skin, eye and mouth (SEM) infections; (ii) central nervous system infection (encephalitis)--neonatal encephalitis can include SEM infections; and (iii) disseminated infection involving several organs, including the liver, lung, skin and/or adrenals. The central nervous system may also be involved in disseminated infections. Caesarean section, where the amniotic membranes are intact or have been ruptured for less than 4 hours, is recommended for those women who have clinical evidence of active herpes lesions on the cervix or vulva at the time of labour. This procedure significantly decreases the risk of transmission to the infant. Diagnosis of neonatal infection requires a very high level of clinical awareness as only a minority of mothers will have a history of genital HSV infection even though they are infected. Careful physical examination and appropriate investigations of the infant should accurately identify the infection in the majority of cases. Treatment is recommended where diagnosis is confirmed or there is a high level of suspicion. The current recommendation for treatment is aciclovir 20 mg/kg 3 times daily by intravenous infusion. Careful monitoring of hydration and renal function as well as meticulous supportive care of a very sick infant is also required. The newer anti-herpes agents, valaciclovir and famciclovir, offer no advantage over aciclovir and are not recommended for neonatal HSV infection. Prognosis is dependent upon the extent of disease and the efficacy of treatment, with highest rates of morbidity and mortality in disseminated infections, followed by central nervous system infection and the least in SEM infection. However, SEM infection is associated with poor developmental outcome even in infants who do not have encephalitis. Studies to improve the outcome of SEM infection are in progress. Neonatal HSV infections, although being relatively uncommon, are associated with significant morbidity and mortality if unrecognised and specific treatment is delayed. Diagnosis relies on a high level of clinical suspicion and appropriate investigation. With early therapy, the prognosis for this infection is considerably improved.

Resistance to antivirals

The ability of viruses to develop resistance to antiviral agents is already a major concern with respect to HIV. This article reviews mechanisms and clinical correlates of antiviral resistance and alternative drugs for treatment of infections due to resistant strains of HIV, herpes simplex virus, cytomegalovirus, varicellazoster virus, and influenza A.