Synergism between recombinant human interferon and nucleoside antiviral agents against herpes simplex virus: examination with an automated microtiter plate assay

Inhibition of respiratory syncytial virus fusion by the small molecule VP-14637 via specific interactions with F protein

Human respiratory syncytial virus (RSV) is a major cause of respiratory tract infections worldwide. Several novel small-molecule inhibitors of RSV have been identified, but they are still in preclinical or early clinical evaluation. One such inhibitor is a recently discovered triphenol-based molecule, VP-14637 (ViroPharma). Initial experiments suggested that VP-14637 acted early and might be an RSV fusion inhibitor. Here we present studies demonstrating that VP-14637 does not block RSV adsorption but inhibits RSV-induced cell-cell fusion and binds specifically to RSV-infected cells with an affinity corresponding to its inhibitory potency. VP-14637 is capable of specifically interacting with the RSV fusion protein expressed by a T7 vaccinia virus system. RSV variants resistant to VP-14637 were selected; they had mutations localized to two distinct regions of the RSV F protein, heptad repeat 2 (HR2) and the intervening domain between heptad repeat 1 (HR1) and HR2. No mutations arose in HR1, suggesting a mechanism other than direct disruption of the heptad repeat interaction. The F proteins containing the resistance mutations exhibited greatly reduced binding of VP-14637. Despite segregating with the membrane fraction following incubation with intact RSV-infected cells, the compound did not bind to membranes isolated from RSV-infected cells. In addition, binding of VP-14637 was substantially compromised at temperatures of < or =22 degrees C. Therefore, we propose that VP-14637 inhibits RSV through a novel mechanism involving an interaction between the compound and a transient conformation of the RSV F protein.

Combination of benzo[a]phenothiazines with acyclovir against herpes simplex virus

The combined antiviral effects of some benzo[a]phenothiazines and 9-[2-hydroxy(ethoxy)methyl]guanine (acycloguanosine, acyclovir, ACV) on the multiplication of herpes simplex virus type 2 (HSV-2) were studied using Vero cells. The antiviral effect of ACV on a wild strain of HSV-2 was enhanced in the presence of 5-oxo-5H-benzo[a]phenothiazine and 6-methyl-5-oxo-5H-benzo[a]phenothiazine in a yield reduction test. A mathematical formula was used to interpret the drug interaction and a synergistic effect was found with a combination of ACV and benzo[a]phenothiazines. The effect of simultaneous application of two benzo[a]phenothiazines on the multiplication of HSV-2 strain during serial passages was also investigated. The combinations of 5-oxo-5H-benzo[a]phenothiazine or 6-methyl-5-oxo-5H-benzo[a]phenothiazine with ACV at a low concentration using serial passages of a plaque-purified ACV sensitive HSV-2 strain, reduced the infective virus population. A similar effect was also found on the activity of other benzo[a]phenothiazine derivatives. When the two most effective derivatives of 5-oxo-5H-benzo[a]phenothiazine or 6-methyl-5-oxo-5H-benzo[a]phenothiazine were simultaneously used with ACV against a wild type HSV-2 strain during consecutive passages, the infective virus titres were decreased, but their effect was only moderate. These results suggest that a combination of some benzo[a]phenothiazines with ACV might enhance their antiviral activity probably by reduction of the mutagenic rate in the virus populations.

Effect of recombinant human interferon alpha B/D (rHu-IFN-alpha B/D) in combination with acyclovir in experimental HSV-1 encephalitis

The efficacy of recombinant human interferon alpha B/D in experimental HSV-1 encephalitis was investigated in the murine system. Recombinant Hu-IFN-alpha B/D significantly reduced the mortality in a mouse encephalitis model (about 30%, P = 0.021), whereas natural mouse interferon was inactive. Combination of acyclovir with Hu-IFN-alpha B/D had an additive effect.

Combined effects of interferon-alpha and acyclovir on herpes simplex virus type 1 DNA polymerase and alkaline DNase

Treatment of cells with combinations of human interferon-alpha (IFN-alpha) and the nucleoside analog, acyclovir (ACV), leads to the synergistic inhibition of herpes simplex virus type 1 (HSV-1) replication. We have examined the effect of these agents on the replication of HSV-1 DNA and the synthesis of early viral enzymes to understand the mechanism(s) responsible for this synergistic activity. Combination treatment with 100 IU/ml IFN-alpha and 5 microM ACV led to HSV-1 DNA levels more than 8-fold lower than in cells treated with ACV alone, while IFN-alpha treatment alone had no detectable effect on viral DNA synthesis. Steady state levels of DNA polymerase were reduced approximately 50% by IFN-alpha and 25% by ACV, but combination treatment did not decrease enzyme levels to an extent greater than the sum of these effects. In contrast, the activity of another early viral enzyme, alkaline DNase, was reduced less than 20% by IFN-alpha alone or combination treatment and was unaffected by ACV treatment. No decrease in the level of mRNA encoding either enzyme was detected in IFN-alpha-treated cells although ACV treatment reduced polymerase mRNA levels. These studies suggest that the synergistic anti-HSV activities of IFN-alpha with ACV could be mediated, in part, through some post-transcriptional mechanism induced by IFN-alpha treatment, leading to the reduction in production of viral early enzymes, especially DNA polymerase.

Efficacy of A-73209, a potent orally active agent against VZV and HSV infections

A-73209 is a novel oxetanocin derivative with potent in vitro and in vivo activity against VZV, HSV-1, and HSV-2. A-73209 was two logs more potent than acyclovir against five thymidine kinase positive (TK+) strains of VZV in vitro (mean EC50 0.01 vs. 1.22 micrograms/ml). The activity of A-73209 was one log more potent than acyclovir against TK+ HSV-1 strains in vitro (EC50 = 0.03 vs. 0.32 micrograms/ml). A-73209 yielded a mean EC50 of 2.2 micrograms/ml compared to a mean EC50 of 0.37 micrograms/ml for acyclovir against a panel of TK+ HSV-2 strains in vitro. The in vitro activity of A-73209 against thymidine kinase negative or deficient strains of VZV, HSV-1 and HSV-2 was much lower than for the corresponding TK+ strains. A-73209 produced efficacy superior to acyclovir against lethal systemic or intracerebral HSV-1 infections in mice. The greater efficacy of A-73209 relative to acyclovir was especially apparent with oral dosing. Against HSV-2 infections in mice, the efficacy of A-73209 ranged from equal to 1.7 times less active relative to acyclovir with oral dosing. A-73209 was orally bioavailable in mice, with maximal serum concentrations well in excess of in vitro inhibitory concentrations. A-73209 appears to be a potent and selective agent against varicella-zoster virus and herpes simplex virus infections.

Synergistic inhibition of human immunodeficiency virus type 1 (HIV-1) replication in vitro by 1-[(2-hydroxyethoxy)methyl]-6-phenylthiothymine (HEPT) and recombinant alpha interferon

1-[(2-Hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) has recently proved to be a potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1) in vitro. Combinations of HEPT and recombinant alpha interferon (IFN-alpha) synergistically inhibit the replication of HIV-1 in MT-4 cells at non-toxic concentrations. Synergistic inhibition of HIV-1 replication has also been observed in peripheral blood lymphocytes. These results indicate that the combination of HEPT with IFN-alpha should be further pursued in the treatment of retrovirus infections [i.e. acquired immune deficiency syndrome (AIDS)].

Combined anti-herpes virus activity of nucleoside analogs and interferon

Addition of interferon (IFN) to nucleoside analog therapy for herpetic keratitis has been shown to significantly increase the efficacy of therapy compared to nucleoside alone. We have analysed several nucleoside analogs and recombinant IFN-alpha 2 to determine which combinations have increased anti-herpes simplex virus type 1 (HSV) activity. Synergistic anti-HSV activity between IFN-alpha 2 and the acyclic guanosine analogs, acyclovir (ACV) and ganciclovir (DHPG), was demonstrated in cytopathic effect reduction assay in human corneal cell cultures as well as in Vero cells. In this assay system IFN-alpha 2 alone had little detectable antiviral activity at titers of greater than or equal to 2,000 IU/ml, however, treatment of cells with about 100 IU/ml of IFN-alpha 2 for 24 hrs prior to infection decreased the ED50 of ACV approximately 2- to 3-fold and of DHPG approximately 5- to 6-fold in Vero cells. Combinations of IFN-alpha 2 with bromovinyldeoxyuridine (BVdU) in Vero cells or human corneal stromal cells did not increase the antiviral activity of BVdU. Combinations of IFN-alpha 2 with trifluorothymidine (TFT) also did not increase the effective antiviral activity of this nucleoside and resulted in decreased uptake of TFT from the medium. These studies document that combinations of acyclic nucleoside analogs, ACV and DHPG, with IFN-alpha 2 resulted in synergistic anti-HSV activities in both Vero and human corneal stromal cells, while the pyrimidine analogs, TFT and BVdU, were not synergistic with IFN-alpha 2. IFN-alpha 2 treatment of cells induced modifications of nucleoside (e.g., thymidine and TFT), but not nucleobase (e.g., ACV) uptake. These studies suggest that selective inhibition of nucleoside versus nucleobase uptake may contribute to the mechanism of IFN/nucleobase synergy in the inhibition of HSV replication.

The role of tumour necrosis factor-alpha in acquired immunodeficiency syndrome

Tumour necrosis factor-alpha (TNF) is a primary mediator in the pathogenesis of infection, tissue injury and inflammation. It is synthesised by various activated, phagocytic and non-phagocytic cells, and a wide variety of infectious or inflammatory stimulae are capable of triggering TNF biosynthesis. Recent studies indicate that overproduction of TNF in septicaemia is a critical step in triggering septic shock and multiple organ damage. Intravenous administration of recombinant human TNF induced the same types of derangement in cardiovascular homatologic, inflammatory and metabolic homeostasis that are found with endotoxic or septic shock. Chronic TNF production causes a potentially lethal syndrome of cachexia, anaemia, and protein and lipid wasting. Several investigators have recently demonstrated elevated levels of serum TNF in patients with acquired immunodeficiency syndrome (AIDS), these levels being closely correlated with the severity of the disease. This review discusses the role of TNF in the pathophysiology of AIDS and of several disorders associated with the latter. In addition, it discusses the interactions between TNF and several agents used in AIDS therapy, and suggests the use of TNF-antagonists in combination as a therapeutic regimen for AIDS patients.

The effect of indomethacin, prostaglandin E2 and interferon on the multiplication of herpes simplex virus type 1 in human lymphoid cells

The control of latency and reactivation of herpesvirus (HSV) infection is poorly understood. The activation of latent HSV is usually associated with a local or systemic rise in prostaglandins (PGs). It is possible that PGs may act indirectly by suppressing the inhibitory effect of interferon (IFN) on HSV replication. IFN has also been shown to decrease the number of herpetic recurrences and to speed up the healing of lesions. We investigated the effect of indomethacin (IND: a non-steroid anti-inflammatory drug which inhibits PGE2), PGE2, IFN-alpha and various combinations thereof on HSV-1 replication in established human lymphoid cells: Raji and Raji-HSV (a persistently infected subpopulation of Raji cells which continuously produces HSV-1 particles). We found that, in contrast to exogenous PGE2, IND suppressed HSV-1 replication in both cell lines. Attempts to overcome the inhibitory effect of IND by addition of PGE2 were unsuccessful. IFN also inhibited HSV-1 replication when a low multiplicity of infection was used. Moreover, the inhibition of HSV-1 multiplication was more marked in cultures treated with IFN in the presence of IND. PGE2 did not decrease or reverse the protective effect of IFN. Our results also suggest that the effects of PGE2, IND and IFN on HSV-1 replication depend on the multiplicity of infection. Further, the present observations together with previously published data would indicate that the inhibitory effect of IND on HSV-1 replication is independent of cell type or origin, while the enhancing effect of PGE2 on virus growth may depend on these factors.

Ganciclovir. A review of its antiviral activity, pharmacokinetic properties and therapeutic efficacy in cytomegalovirus infections

Ganciclovir is a nucleoside analogue with antiviral activity in vitro against members of the herpes group and some other DNA viruses. It has demonstrated efficacy against human cytomegalovirus infections and should be considered a first-line therapy in the treatment of life- or sight-threatening cytomegalovirus infection in immunocompromised patients. Clinical efficacy varies with the underlying aetiology of immunocompromise and the site of disease, and prompt diagnosis and early treatment initiation appear to improve the response. In patients with cytomegalovirus pneumonia, particularly bone marrow transplant recipients, concomitant administration of cytomegalovirus immune globulin may significantly improve clinical outcome. Maintenance therapy to prevent recurrence is usually required by bone marrow transplant recipients until the recovery of adequate immune function, whereas AIDS patients may require indefinite ganciclovir maintenance therapy to prevent disease progression, as ganciclovir (like other antivirals) does not eradicate latent viral infection. Haematological effects occur relatively frequently during ganciclovir administration but are usually reversible. Ganciclovir has not been directly compared with other antiviral drugs because of the absence until recently of other effective treatments. However, comparative studies with foscarnet, particularly in cytomegalovirus retinitis, will be of considerable interest. Thus, ganciclovir represents a major advance in the therapy of severe cytomegalovirus infections in immunocompromised patients. Comparative studies, and investigation of ways of reducing toxicity (intravitreal administration; concomitant use of stimulants of haematopoiesis; use in conjunction with other antivirals with differing mechanisms of action), may further expand its eventual role.

Antiviral Activity of Mixtures of Compounds against Herpesviruses

A simple method for investigating the antiviral activity of mixtures of two antiviral compounds against herpes simplex virus (HSV) is described; the technique involves a modification of the dye-uptake technique for measuring antiviral activity, and the results are analysed by two methods for evidence of synergy or additive or antagonist effects. The antiviral activity of combinations of four antiviral compounds against HSV-1 and HSV-2 were investigated. The results indicate that interferon-alpha (IFN-α) with acyclovir or ara-A shows synergy, but IFN-α with ribavirin shows an additive effect. Ribavirin shows no synergism with any of the three compounds tested, and ara-A shows marginal synergy with acyclovir. The pattern of these results does not allow any prediction of which mixtures may show synergy. With the present limited number of antiviral compounds, all new combinations should be tested; and these further results may allow future predictions.

Combined effects of acyclovir and human interferon-alpha on herpes simplex virus replication in cultured neural cells

The combined effects of Acyclovir [9-(2'-hydroxyethoxymethyl)guanine; ACV] and human interferon-alpha (IFN-alpha) on replication of the herpes simplex virus type I (HSV-1) were determined in human neural cell lines, neuroblastoma (IMR), glioblastoma (118MGC), and glioma (U251MG). HSV-1 grew well in all these cells, with final yields of more than 1 x 10(6) PFU/ml. In terms of virus-yield reduction, ACV was found to be highly effective in IMR, moderately effective in U251MG, but ineffective in 118MGC. By contrast, IFN-alpha reduced the virus yield significantly in 118MGC and in U251MG, but did not in IMR. Combined application of ACV and IFN-alpha strongly inhibited the virus replication in all three cell lines with various degrees of synergism or additive effect. These results were also confirmed by immunofluorescent examinations. The sensitivity of HSV-1 to ACV or IFN-alpha was found to be different among the three different cell types. By combining the two agents, the virus growth was strongly suppressed in all the cells. These results suggest the importance of combination therapy for severe type of herpes simplex encephalitis in clinical practice.

Rapid and accurate viral diagnosis

In recent years, there has been increased recognition of the importance of viral infections. In addition, new antiviral agents have become available. These factors have led to a marked increase in utilization of viral diagnostic services. In this review, both conventional and rapid methods for viral diagnosis are presented, with emphasis on recent advances. The antiviral agents currently available and the major drugs under investigation are also briefly discussed. It is hoped that this review will serve as a useful adjunct for the management of patients with virus infections.

Protection against herpes simplex virus infection in mice by recombinant murine interferon-beta in combination with antibody

A recombinant murine interferon -beta (rMuIFN-beta) was used to suppress the development of skin lesions and death of mice after challenge with herpes simplex virus (HSV) type 1 (HSV-1). Depilated female BALB/c mice were inoculated intradermally with HSV-1, Hayashida strain, and were administered various concentrations of interferon (IFN) intraperitoneally 3 h later. The treatment with IFN was given once a day for 10 successive days. Under the conditions in which almost all control mice died after development of severe zosteriform skin lesions, the mortality of mice treated with IFN (8 X 10(5) or 8 X 10(4) U/mouse) was less than 50% (9/20 and 4/10, respectively), though all mice treated with a lower dose of IFN (8 X 10(3) U/mouse) died. Titration revealed that there was no significant suppression of virus growth by IFN in the skin or dorsal root ganglia, but it was significantly suppressed in the brain. The protective effect of IFN was enhanced when it was used in combination with human anti-HSV antibody having a neutralizing titer (NT) of 1:16. All mice treated with IFN (8 X 10(5) U/mouse) and antibody (NT, 1:16) survived, and only 40% of them developed slight zosteriform skin lesions. The effect of the combination was observed even when both IFN and antibody were diluted 1:10. The protective effect of IFN was also observed when athymic nude mice were used as the host. In this system, though the IFN-treated nude mice survived significantly longer than the controls, they finally died. In antibody- or acyclovir (ACV)-treated nude mice, there was also a prolongation of survival time as compared with control mice. The effect of antibody was enhanced by the addition of IFN, but IFN did not potentiate the effect of ACV.

Synergistic inhibition of human immunodeficiency virus in vitro by azidothymidine and recombinant alpha A interferon

Both recombinant alpha A interferon and azidothymidine inhibit the replication of human immunodeficiency virus in peripheral blood mononuclear cells. Combinations of recombinant alpha A interferon and azidothymidine at concentrations that are easily achievable in patients synergistically inhibit human immunodeficiency virus in vitro with minimal toxicity. Combinations of antiretroviral compounds that act by different mechanisms may prove useful in the treatment of acquired immunodeficiency syndrome-related disorders.

Interferon in the prevention of genital herpes recurrence

Patients with genital herpes were treated three times weekly for 12 weeks with 3 X 10(6) IU of alpha 2b interferon (20 patients) or placebo (17 patients) administered by subcutaneous injection in a double-blind trial. Interferon had minimal effects on the suppression of recurrences and moderate toxicity (chills, fever, fatigue, and leukopenia), suggesting that this route and dosage of interferon may not be clinically useful for this indication.