Reversible inhibition of herpes simplex virus replication by hydroxyurea

Oral disease-modifying antirheumatic drugs and immunosuppressants with antiviral potential, including SARS-CoV-2 infection: a review

There have been several episodes of viral infection evolving into epidemics in recent decades, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the latest example. Its high infectivity and moderate mortality have resulted in an urgent need to find an effective treatment modality. Although the category of immunosuppressive drugs usually poses a risk of infection due to interference of the immune system, some of them have been found to exert antiviral properties and are already used in daily practice. Recently, hydroxychloroquine and baricitinib have been proposed as potential drugs for SARS-CoV-2. In fact, there are other immunosuppressants known with antiviral activities, including cyclosporine A, hydroxyurea, minocycline, mycophenolic acid, mycophenolate mofetil, leflunomide, tofacitinib, and thalidomide. The inherent antiviral activity could be a treatment choice for patients with coexisting rheumatological disorders and infections. Clinical evidence, their possible mode of actions and spectrum of antiviral activities are included in this review article.

LAY SUMMARY

Immunosuppressants often raise the concern of infection risks, especially for patients with underlying immune disorders. However, some disease-modifying antirheumatic drugs (DMARDs) with inherent antiviral activity would be a reasonable choice in the situation of concomitant viral infections and flare up of autoimmune diseases. This review covers DMARDs of treatment potential for SARS-CoV-2 in part I, and antiviral mechanisms plus trial evidence for viruses other than SARS-CoV-2 in part II.

Herpes simplex virus type 1 single strand DNA binding protein and helicase/primase complex disable cellular ATR signaling

Herpes Simplex Virus type 1 (HSV-1) has evolved to disable the cellular DNA damage response kinase, ATR. We have previously shown that HSV-1-infected cells are unable to phosphorylate the ATR substrate Chk1, even under conditions in which replication forks are stalled. Here we report that the HSV-1 single stranded DNA binding protein (ICP8), and the helicase/primase complex (UL8/UL5/UL52) form a nuclear complex in transfected cells that is necessary and sufficient to disable ATR signaling. This complex localizes to sites of DNA damage and colocalizes with ATR/ATRIP and RPA, but under these conditions, the Rad9-Rad1-Hus1 checkpoint clamp (9-1-1) do not. ATR is generally activated by substrates that contain ssDNA adjacent to dsDNA, and previous work from our laboratory has shown that ICP8 and helicase/primase also recognize this substrate. We suggest that these four viral proteins prevent ATR activation by binding to the DNA substrate and obstructing loading of the 9-1-1 checkpoint clamp. Exclusion of 9-1-1 prevents recruitment of TopBP1, the ATR kinase activator, and thus effectively disables ATR signaling. These data provide the first example of viral DNA replication proteins obscuring access to a DNA substrate that would normally trigger a DNA damage response and checkpoint signaling. This unusual mechanism used by HSV suggests that it may be possible to inhibit ATR signaling by preventing recruitment of the 9-1-1 clamp and TopBP1.

DNA viruses that replicate in the nucleus have been shown to both activate and inactivate various components of the cellular DNA damage response (DDR). Previous reports from our laboratory and others have demonstrated that Herpes Simplex Virus (HSV) utilizes some aspects of the DDR while inactivating others. Paradoxically, HSV utilizes the DDR kinase ATR to complete its life cycle while at the same time disabling the kinase from activating DDR signaling. In this report we provide detail describing the mechanism of ATR inactivation. ATR is normally activated in response to single strand DNA (ssDNA), which serves as a scaffold to recruit several proteins required for complete ATR activation. In this paper we provide evidence that the HSV encoded ssDNA binding protein and helicase/primase complex function to mask the DNA substrate that recruits the ATR kinase activator. This represents the first example of viral DNA replication proteins masking a DNA substrate that could be sensed by the cell as damaged DNA and activate checkpoint signaling. It also explains how ATR can be recruited to sites of viral DNA replication in the absence of checkpoint signaling.

Amazing results with hydroxyurea therapy in chronic hepatitis B: a preliminary report

BACKGROUND AND AIMS

To introduce the possible role of hydroxyurea (HU), a well-characterized antineoplastic drug with established antiviral effects, in the treatment of chronic hepatitis B.

METHODS

Four antiretroviral-naïve patients with chronic hepatitis B were enrolled in this limited pilot trial, and given 1000 mg/day of hydroxyurea for 4 weeks; then, the administration of the drug was suspended for 4 weeks. A clinical study and laboratory safety assessments and measurements of viral load were made at baseline, after drug therapy, and after one month suspension of the treatment

RESULTS

All 4 patients showed a significant decrease in viral load after 4 weeks of hydroxyurea therapy and the viral load of 2 patients increased again after a 4-week suspension of hydroxyurea

CONCLUSIONS

Our data demonstrate that the old low-cost antineoplastic drug, hydroxyurea, efficiently blocks hepatitis B virus (HBV) replication. We suggest that HU will play an important role in the treatment of chronic hepatitis in the foreseeable future. Further studies including those that evaluate optimal dosing in long-term use will continue to define the role of HU in the treatment of HBV infection alone or in combination with other antiviral drugs.

Rationale for the use of hydroxyurea as an anti-human immunodeficiency virus drug

Hydroxyurea has been extensively used in medical practice, mainly for treating chronic myelogenous leukemia, sickle cell anemia, and other diseases. In light of its ability to inhibit DNA synthesis and to induce cell cycle arrest through inhibition of ribonucleotide reductase, the effects of hydroxyurea on replication of human immunodeficiency virus type 1 (HIV-1) have been investigated. In vitro hydroxyurea has been shown to block HIV-1 reverse transcription and/or replication in quiescent peripheral blood mononuclear cells (PBMC) and macrophages. Hydroxyurea was also found to be synergistic with the nucleoside reverse transcriptase inhibitor didanosine and to inhibit HIV-1 replication in activated PBMC; this inhibition may be due to a reduction in deoxynucleoside triphosphate pool sizes. Finally, hydroxyurea has been shown to sensitize didanosine-resistant mutants. Hydroxyurea may therefore be useful for limiting the spread of didanosine-resistant HIV-1 variants. The favorable toxicity profile of hydroxyurea and the lack of significant overlapping toxicities with some of the nucleoside reverse transcriptase inhibitors, as well as their distinct mechanisms of action, have provided further rationale for use of these agents in combination therapies.

Effects of antimetabolites on the production of tubular structures in Vero cells infected with herpes simplex virus type 2

Treatment of Vero cells infected with herpes simplex virus type 2 with the proper concentrations of hydroxyurea (HU) reduced the production of infectious virus and markedly increased the accumulation of tubular structures in the nuclei when the drug was added within 6 hours after infection. Similar accumulation of tubular structures in the infected nuclei was also observed when infected cells were treated with phosphonoacetic acid at proper concentrations. The release of HU-treated, herpes simplex virus type 2-infected cells from the drug-induced blocking of synthesis of infectious virus resulted in the marked decrease of tubular structures coincidentally with the beginning of production of infectious virus. The data suggest the possibility that the disappearance of tubular structures may be related to the active production of infectious virus.

A combined chemical-physical treatment for herpes simplex lesions in guinea pigs

Determination of the effectiveness of chemical treatments for Herpes simplex type 2 infections has generally relied on a reduction in the rate of mortality. A more natural progression of the disease is seen when non-progressive cutaneous lesions are induced. Treatment of characteristic cutaneous lesions with ultrasound alone, a cream compound designated Herpigon alone, or a combination of ultrasound and Herpigon were compared to determine the time required for lesions to heal and the amount of virus recoverable from treated lesions. Results indicate that the use of Herpigon alone or in combination with ultrasound resulted in a significant reduction in the time required for the lesions to heal. A comparison of the amount of virus present in treated lesions indicated that the combined treatment was most effective in reducing the amount of recoverable virus.

In vitro RNA synthesis in nuclei from herpes simplex virus infected cells: effects of ultraviolet-irradiated, defective and bromodeoxyuridine-resistant virus preparations

Transcription of virus DNA was detectable in vitro in nuclei isolated from cells infected with wild type and bromodeoxyuridine (BUdR)-resistant herpes simplex virus type 1 but was suppressed in nuclei of cells infected with ultraviolet irradiated or defective virus or cells treated with BUdR during infection.

Irreversible inhibition of herpes simplex virus replication in BSC-1 cells by zinc ions

Zinc sulfate added to the medium of herpes simplex virus-infected BSC-1 cells, at a concentration of 0.1 mM, inhibited the synthesis of infectious virus progeny by 95 to 96%. A concentration of 0.2 mM zinc sulfate inhibited herpes simplex virus synthesis by 99.8% as determined by centrifugation in sucrose gradients and by plaque assay on BSC-1 monolayers. The inhibition of herpes simplex virus replication in BSC-1 cells was found to be irreversible.