Pharmacokinetics and absolute bioavailability of oral foscarnet in human immunodeficiency virus-seropositive patients

Optimizing Antiviral Dosing for HSV and CMV Treatment in Immunocompromised Patients

Herpes simplex virus (HSV) and cytomegalovirus (CMV) are DNA viruses that are common among humans. Severely immunocompromised patients are at increased risk of developing HSV or CMV disease due to a weakened immune system. Antiviral therapy can be challenging because these drugs have a narrow therapeutic window and show significant pharmacokinetic variability. Above that, immunocompromised patients have various comorbidities like impaired renal function and are exposed to polypharmacy. This scoping review discusses the current pharmacokinetic (PK) and pharmacodynamic (PD) knowledge of antiviral drugs for HSV and CMV treatment in immunocompromised patients. HSV and CMV treatment guidelines are discussed, and multiple treatment interventions are proposed: early detection of drug resistance; optimization of dose to target concentration by therapeutic drug monitoring (TDM) of nucleoside analogs; the introduction of new antiviral drugs; alternation between compounds with different toxicity profiles; and combinations of synergistic antiviral drugs. This research will also serve as guidance for future research, which should focus on prospective evaluation of the benefit of each of these interventions in randomized controlled trials.

Anti-herpes virus activity of the carnivorous botanical, Sarracenia purpurea

Herpes simplex virus type-1 (HSV-1), one of the most widely spread human viruses in the Herpesviridae family, causes herpes labialis (cold sores) and keratitis (inflammation of the cornea). Conventional treatment for HSV-1 infection includes pharmaceutical drugs, such as acyclovir and docosonal, which are efficacious but maintain the potential for the development of viral drug resistance. Extracts from the carnivorous pitcher plant, Sarracenia purpurea, have previously been shown to inhibit the replication of HSV-1. In this study, we demonstrate that S. purpurea extracts can inhibit the replication of HSV-1 by two distinct mechanisms of action. These extracts directly inhibit extracellular virions or viral attachment to the human host cell as well as inhibiting the expression of viral immediate-early, early and late genes when added at various times post-infection. This botanical has previously been shown to inhibit the replication of poxviruses through the inhibition of early viral gene transcription. These results support a broader anti-viral activity of S. purpurea extracts against both pox and herpes viruses.

High extracellular phosphate increases platelet polyphosphate content

Platelet-derived extracellular polyphosphate (PolyP) is a major mediator of thrombosis. PolyP is a linear chain of inorganic phosphate (P_i) and is stored in platelet dense granules. P_i enters cells from the extracellular fluid through phosphate transporters and may be stored as PolyP. Here we show that high extracellular P_i concentration in vitro increases platelet PolyP content, in a manner dependent on phosphate transporters, IP6K and V-type ATPases. The increased PolyP also enhanced PolyP-dependent coagulation in platelet-rich plasma. These data suggest a mechanistic link between hyperphosphatemia, PolyP and enhanced coagulation, which may be important in pathologies such as chronic kidney disease.

New Developments in the Management of Cytomegalovirus Infection After Transplantation

Cytomegalovirus (CMV) continues to be one of the most important pathogens that universally affect solid organ and allogeneic hematopoietic stem cell transplant recipients. Lack of effective CMV-specific immunity is the common factor that predisposes to the risk of CMV reactivation and clinical disease after transplantation. Antiviral drugs are the cornerstone for prevention and treatment of CMV infection and disease. Over the years, the CMV DNA polymerase inhibitor, ganciclovir (and valganciclovir), have served as the backbone for management, while foscarnet and cidofovir are reserved for the management of CMV infection that is refractory or resistant to ganciclovir treatment. In this review, we highlight the role of the newly approved drug, letermovir, a viral terminase inhibitor, for CMV prevention after allogeneic hematopoietic stem cell transplantation. Advances in immunologic monitoring may allow for an individualized approach to management of CMV after transplantation. Specifically, the potential role of CMV-specific T-cell measurements in guiding the need for the treatment of asymptomatic CMV infection and the duration of treatment of CMV disease is discussed. The role of adoptive immunotherapy, using ex vivo-generated CMV-specific T cells, is highlighted. This article provides a review of novel drugs, tests, and strategies in optimizing our current approaches to prevention and treatment of CMV in transplant recipients.

Polypharmacology in HIV inhibition: can a drug with simultaneous action against two relevant targets be an alternative to combination therapy?

HIV infection still has a serious health and socio-economical impact and is one of the primary causes of morbidity and mortality all over the world. HIV infection and the AIDS pandemic are still matters of great concern, especially in less developed countries where the access to highly active antiretroviral therapy (HAART) is limited. Patient compliance is another serious drawback. Nowadays, HAART is the treatment of choice although it is not the panacea. Despite the fact that it suppresses viral replication at undetectable viral loads and prevents progression of HIV infection into AIDS HAART has several pitfalls, namely, long-term side-effects, drug resistance development, emergence of drug-resistant viruses, low compliance and the intolerance of some patients to these drugs. Moreover, another serious health concern is the event of co-infection with more than one pathogen at the same time (e.g. HIV and HCV, HBV, herpes viruses, etc). Currently, the multi-target drug approach has become an exciting strategy to address complex diseases and overcome drug resistance development. Such multifunctional molecules combine in their structure pharmacophores that may simultaneously interfere with multiple targets and their use may eventually be more safe and efficacious than that involving a mixture of separate molecules because of avoidance or delay of drug resistance, lower incidence of unwanted drug-drug interactions and improved compliance. In this review we focus on multifunctional molecules with dual activity against different targets of the HIV life cycle or able to block replication, not only of HIV but also of other viruses that are often co-pathogens of HIV. The different approaches are documented by selected examples.

Permeation thresholds for hydrophilic small biomolecules across microvascular and epithelial barriers are predictable on basis of conserved biophysical properties

Purpose

Neutral small hydrophiles are permeable to varying degrees, across the aqueous pores of phospholipid bilayer protein channels, with their potential for permeation into cells being predictable, on the basis of hydrophilicity and size. Here, it is hypothesized that permeation thresholds for small hydrophiles, across capillary zona occludens tight junction and inter-epithelial junction pore complexes are predictable, on the basis of predicted hydrophilicity in context of predicted molecular size and charge distribution, as are those of cations and anions, on the basis of predicted ionization in context of predicted atomic size.

Methods

Small hydrophiles are categorized by charge distribution. 2-dimensional plots of predicted hydrophilic octanol-to-water partition coefficient (HOWPC; unitless) and predicted van der Waals diameter (vdWD; nm) are generated for each category. The predicted HOWPC-to-vdWD ratio (nm^-1), and vdWDs for permeable hydrophile at the maximum and minimum HOWPC-to-vdWD, vdWD @ MAXimum HOWPC-to-vdWD and vdWD @ MINimum HOWPC-to-vdWD are determined. For cations and anions, the ionization-to-atomic diameter ratios (CI or AI-to-AD ratios; nm^-1) are determined.

Results

Per sizes of mixed and pure polyneutral hydrophiles, the permeation size maximum for hydrophiles across tight junction pore complexes is >0.69 ≤ 0.73 nanometers and across inter-epithelial junction pore complexes is ≥ 0.81 nanometers. For hydrophiles with anionicity or cationicity, the vdWDs @ MAXimum HOWPC-to-vdWD are less than those of mixed and polyneutral hydrophiles across both tight and inter-epithelial junctions, ranges specific to category and junction type. For cations, the permeation threshold across tight junctions is between the CI-to-AD ratio of Na+ (+2.69 nm^-1) and CH3-Hg+ (+2.36 nm^-1), with CH3-Hg+ and K+ (+2.20 nm^-1) being permeable; and for divalent cations, the threshold across inter-epithelial junctions is between the CI-to-AD ratio of Mg2+ (+6.25 nm^-1) and Ca2+ (+5.08 nm^-1) , Ca2+ being semi-permeable. For anions, the permeation threshold across tight junctions is between the AI-to-AD ratio of Cl- (-4.91 nm^-1) and Br- (-4.17 nm^-1), and the threshold across inter-epithelial junctions is between the AI-to-AD ratio of F- (-7.81 nm^-1) and Cl- (-4.91 nm^-1).

Conclusions

In silico modeling reveals that permeation thresholds, of small molecule hydrophiles, cations and anions across junctional pore complexes, are conserved in the physiologic state.

Electronic supplementary material

The online version of this article (doi:10.1186/s40203-015-0009-y) contains supplementary material, which is available to authorized users.

HIV-1 reverse transcriptase inhibitors: beyond classic nucleosides and non-nucleosides

Reverse transcriptase (RT) of HIV-1 remains an important target in current treatments of HIV-1 infection. Clinically available inhibitors of HIV-1 RT include nucleoside analog RT inhibitors and non-nucleoside RT inhibitors. Nucleoside analog RT inhibitors compete with the natural dNTP substrate and act as chain terminators, while non-nucleoside RT inhibitors bind to an allosteric pocket, inhibiting polymerization noncompetitively. In addition to these two classes of approved drugs, there are a number of RT inhibitors that target the enzyme in different ways. These include nonobligate chain terminators, nucleotide-competing RT inhibitors, pyrophosphate analogs and compounds that inhibit the RT-associated RNase H activity. Here, we review the mechanisms of action associated with these compounds and discuss opportunities and challenges in drug discovery and development efforts.

Synthesis and biochemical evaluation of phosphonoformate oligodeoxyribonucleotides

Phosphonoformate oligodeoxyribonucleotides were prepared via a solid phase synthesis strategy. The first step in the preparation of appropriate synthons was condensation of bis(N,N-diisopropylamino)phosphine and diphenylmethylsilylethyl chloroformate in the presence of sodium metal to yield formic acid, [bis(N,N-diisopropylamino)phosphino]-beta-(diphenylmethylsilylethyl) ester. The product of this reaction was then condensed with appropriately protected 2'-deoxynucleosides using 4,5-dicyanoimidazole to yield the 3'-O-phosphinoamidite reactive monomers. The exocyclic amines of cytosine, adenine, and guanine were protected with 9-fluorenylmethyloxycarbonyl, and oligodeoxyribonucleotides were synthesized on controlled pore glass using the hydroquinone-O,O'-diacetic acid linker. Synthons were sequentially added to this support using tetrazole as an activator, oxidized to phosphonoformate, and the transient 5'-protecting group was removed with acid. Following total synthesis of an oligomer, protecting groups were removed with TEMED.HF and products purified by HPLC. These analogues were resistant to nucleases, formed duplexes with complementary RNA (A-form), and, as chimeric oligomers containing phosphate at selected sites, stimulated RNase H1 activity.

Emerging therapies for herpes viral infections (types 1 – 8)

There are eight members of the herpesviridae family: herpes simplex virus-1 (HSV-1), HSV-2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, human herpes virus-6, human herpes virus-7 and human herpes virus-8. The diseases caused by viruses of the herpesviridae family are treated with and managed by systemic and topical antiviral therapies and immunomodulating drugs. Because these viruses establish a latent state in hosts, antiherpetic agents, such as nucleoside analogues, only control symptoms of disease or prevent outbreaks, and cannot cure the infections. There is a need for treatments that require less frequent dosing, can be taken even when lesions are more advanced than the first signs or symptoms, and can treat resistant strains of the viruses without the toxicities of existing therapies. Immunomodulating agents, such as resiquimod, can act on the viruses indirectly by inducing host production of cytokines, and can thereby reduce recurrences of herpes. The new helicase primase inhibitors, which are the first non-nucleoside antiviral compounds, are being investigated for treatment of HSV disease, including infections resistant to existing therapy.

The targeting of primary effusion lymphoma cells for apoptosis by inducing lytic replication of human herpesvirus 8 while blocking virus production

Primary effusion lymphoma (PEL) is a B-cell lymphoma in which human herpesvirus-8 (HHV-8) is found within all tumor cells and represents a target for selectively destroying tumor cells. HHV-8 is latent in most PEL cells and, hence, resistant to antiviral agents that inhibit lytic replication. We demonstrate that PEL cell lines containing HHV-8 without and with coinfection with Epstein-Barr virus responded to the antiseizure medication valproate with entry into the lytic cascade and production of infectious virus. Minimal cell death occurred when noninfected BL-41 cells were incubated with valproate, whereas apoptosis occurred in response to valproate in PELs that supported lytic replication of HHV-8. The anti-viral agents ganciclovir and phosphonoformic acid (PFA) blocked valproate-induced production of infectious virus without blocking entry into the lytic cascade, and apoptosis occurred at levels that were as high as when virus production was not blocked. Ganciclovir and PFA also prevented most valproate-induced expression of the late lytic viral transcript open reading frame 26 (ORF-26), but they did not block the induction of either viral interleukin-6 (vIL-6) or viral G protein-coupled receptor (vGPCR). These studies provide evidence that incubation of PELs with valproate in the presence of ganciclovir or PFA can selectively target tumor cells for apoptosis without increasing viral load.

Hybrids of [TSAO-T]−[Foscarnet]: The First Conjugate of Foscarnet with a Non-nucleoside Reverse Transcriptase Inhibitor through a Labile Covalent Ester Bond

This paper describes the first example of combination of non-nucleoside reverse transcriptase inhibitors such as TSAO derivatives and foscarnet (PFA) in a single molecule through a labile covalent ester bond. The essential criteria in the design of these hybrids [TSAO-T]-[PFA] was to explore if the conjugation of foscarnet with the highly lipophilic TSAO derivative may facilitate the penetration of the conjugates through the cell membrane and if the hybrids escape extracellular hydrolysis and regenerate the parent inhibitors intracellulary. Several [TSAO-T]-[PFA] conjugates proved markedly inhibitory to HIV-1. Some of them also showed potent activity against PFA-resistant HIV-1 strains but fewer had detectable inhibitory activity against TSAO-resistant HIV-1 strains. These results indicated a pivotal role of the TSAO component of the hybrid but not the PFA component in the activity of the conjugates. Moreover, stability studies of the [TSAO-T]-[PFA] conjugates demonstrated that the compounds were stable in PBS whereas some of the conjugates regenerated the parent inhibitors in extracts from CEM cells.

Cytomegalovirus treatment options in immunocompromised patients

Cytomegalovirus (CMV) infection was recognised in congenitally infected infants in the first half of the 20th century. Following the increased use of immunosuppressive regimens for bone marrow and solid organ transplantation, various manifestations of CMV disease were recognised. Milder symptoms included fever, anorexia and malaise but severe symptoms included pneumonitis, hepatitis, gastrointestinal ulceration, choreoretinitis and encephalopathy, all with a high morbidity or mortality. With the onset of the AIDS epidemic, manifestations of CMV became evident, predominantly retinitis. Ganciclovir used intravenously has been the principal anti-CMV agent investigated. However, ganciclovir has problems with suboptimal efficacy, toxicity, poor oral bioavailability and evolution of resistant strains. Additional studies have been performed on foscarnet and cidofovir, although the use of both have been limited by their nephrotoxicity. Combination therapy with ganciclovir and foscarnet for resistant strains has been used. There are promising newer drugs like the methylenecyclopropane nucleoside analogues and benzimidazole. The most novel compound is the antisense oligonucleotide fomivirsen that has been evaluated principally in CMV retinitis. The role of immunotherapy with either immunoglobulin prophylaxis or the novel adoptive immunotherapy needs further evaluation.

Neoglycolipid conjugates of foscarnet with enhanced antiviral activity in cells infected with human cytomegalovirus and herpes simplex virus type 1

The synthesis of a series of neoglycolipid conjugates of foscarnet as potential drug targeting forms or lipophilic prodrugs of foscarnet is described. The compounds were obtained from suitably protected neoglycolipids, in which the lipid chain consisted of 12 to 20 carbon atoms, by ethoxycarbonylphosphonylation at the 6-hydroxyl or 4-hydroxyl group followed by deprotection. The in vitro antiviral activity of the compounds was determined in human foetal lung cells infected with human cytomegalovirus (HCMV) or herpes simplex virus type 1 (HSV-1). Compounds in which the lipid chain consisted of 14 to 20 carbon atoms showed pronounced antiviral activity against HCMV and HSV-1, the highest activity being shown by trans-9-octadecen-1-yl 6-O-carboxyphosphonyl-alpha-D-glucopyranoside against HCMV (approximately 50 times that of foscarnet) and by eicosyl 6-O-carboxyphosphonyl-beta-D-galactopyranoside against HSV-1 (approximately 15 times that of foscarnet). Cytotoxicity was determined by assessing the capability of mitochondrial enzymes to metabolise MTT and gave TC50 values for the compounds that were 30 to 350 times higher than their IC50 values against HCMV and 5 to 15 times higher than their IC50 values against HSV-1. Foscarnet was not liberated on incubation of n-tetradecyl 6-O-carboxyphosphonyl-alpha-D-glucopyranoside with rat liver or intestine homogenate, neither could the neoglycolipid conjugate nor foscarnet be detected in rat plasma following oral administration. Further metabolic and pharmacokinetic studies are required in order to determine whether neoglycolipid conjugates of foscarnet can find a use as drug targeting forms of foscarnet.