Recombinant interferons alpha and gamma: comparative antiviral activity and synergistic interaction in encephalomyocarditis virus infection of mice

Type I IFNs: A Blessing in Disguise or Partner in Crime in MERS-CoV-, SARS-CoV-, and SARS-CoV-2-Induced Pathology and Potential Use of Type I IFNs in Synergism with IFN-γ as a Novel Antiviral Approach Against COVID-19

Since the end of 2019, the emergence of novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has accelerated the research on host immune responses toward the coronaviruses. When there is no approved drug or vaccine to use against these culprits, host immunity is the major strategy to fight such infections. Type I interferons are an integral part of the host innate immune system and define one of the first lines of innate immune defense against viral infections. The in vitro antiviral role of type I IFNs against Middle East respiratory syndrome coronavirus (MERS-CoV) and SARS-CoV (severe acute respiratory syndrome coronavirus) is well established. Moreover, the involvement of type I IFNs in disease pathology has also been reported. In this study, we have reviewed the protective and the immunopathogenic role of type I IFNs in the pathogenesis of MERS-CoV, SARS-CoV, and SARS-CoV-2. This review will also enlighten the potential implications of type I IFNs for the treatment of COVID-19 when used in combination with IFN-γ.

Intranasal Treatment of Picornavirus and Coronavirus Respiratory Infections in Rodents Using 7-Thia-8-Oxoguanosine

Since common cold viruses are responsive to interferon, we developed two animal models to test the efficacy of the interferon inducer 7-thia-8-oxoguanosine: (i) an intranasal coronavirus infection in suckling rats; and (ii) an intranasal encephalomyocarditis (EMC) virus infection in adult mice. Concentrations of 0.3 and 1% 7-thia-8-oxoguanosine delivered intranasally to rats 24 and 18 hours before virus inoculation were highly protective against the otherwise lethal coronavirus infection. A 1% concentration of drug administered 4 and 8 hours after virus challenge increased mean survival times of rats but did not increase numbers of survivors. Intranasal treatment of an EMC infection produced moderate improvements in mean survival times and survival. Titrations of EMC virus indicated >300-fold reductions in nasal titres in drug-treated relative to placebo control animals on days 2–4 following virus challenge. The distribution of [14C]-7-thia-8-oxoguanosine was determined shortly after intranasal delivery to mice and rats. Approximately 50% of total doses were deposited in the inner noses and mouths of both species. Most of the rest was found on/in the outer noses, stomachs, tracheas, oesophagi, and lungs. By analogy, the infecting viruses were deposited on/in the same organs and tissues of each species. The results suggest that containment of the viruses primarily occurred in the nasopharyngeal area prior to their spread to the lungs (rat coronavirus) or the brain (EMC), where fatal pathologies were manifest. Intranasal application of an interferon-inducing nucleoside analogue represents a new approach for the study of treatment of the common cold.

Increased Sensitivity of Sars-Coronavirus to a Combination of Human Type I and Type II Interferons

There is currently an urgent need to identify effective antiviral agents that will prevent and treat severe acute respiratory syndrome coronavirus (SARS-CoV) infection. In this study, we have investigated and compared the antiviral effect of different interferons (IFNs) on SARS-CoV replication in the epithelial kidney monkey Vero cell line. The results showed that SARS-CoV grown in Vero cells is moderately sensitive to IFN-β and only weakly sensitive to IFN-α and IFN-γ, in comparison to other IFN-sensitive viruses, such as those for encephalomyocarditis, vesicular stomatitis and Newcastle disease. Simultaneous incubation of Vero cells with IFN-β and IFN-γ indicated that they may act synergistically against SARS-CoV replication. The IFN-induced MxA protein was detected in the IFN-treated Vero cells. The data, however, suggest that the antiviral activity of IFN against SARS-CoV virus is independent of MxA expression.

Immunoenhancing properties and antiviral activity of 7-deazaguanosine in mice

The nucleotide analog 7-deazaguanosine has not previously been reported to possess biological (antiviral or antitumor) properties in cell culture or in vivo. Up to 10(5) U of interferon per ml was detected in mouse sera 1 to 4 h following oral (200-mg/kg of body weight) and intraperitoneal (50-mg/kg) doses of the compound. 7-Deazaguanosine also caused significant activation of natural killer and phagocytic cells but did not augment T- and B-cell blastogenesis. Intraperitoneal treatments of 50, 100, and 200 mg/kg/day administered 24 and 18 h before virus inoculation were highly protective in mice inoculated with lethal doses of Semliki Forest or San Angelo viruses. Less but still significant survivor increases were evident in treated mice infected with banzi or encephalomyocarditis viruses. In most cases, the degree of antiviral activity was similar to that exhibited by the biological response modifier 7-thia-8-oxoguanosine. 7-Thia-8-oxoguanosine was more potent than 7-deazaguanosine against encephalomyocarditis virus in mice, however. Oral efficacy was achieved with 7-deazaguanosine treatments of greater than or equal to 100 mg/kg against all virus infections, whereas 7-thia-8-oxoguanosine is reported to be devoid of oral activity in rodents. Thus, 7-deazaguanosine represents the first reported orally active nucleoside biological response modifier exhibiting broad-spectrum antiviral activity against particular types of RNA viruses.

Broad-spectrum in vivo antiviral activity of 7-thia-8-oxoguanosine, a novel immunopotentiating agent

A novel immunopotentiating agent, 5-amino-3-beta-D-ribofuranosylthiazolo [4,5-d]pyrimidine-2,7(3H,6H)-dione (7-thia-8-oxoguanosine), lacks virus-inhibitory properties in vitro but induces interferon and potentiates immune functions, such as natural killer cell activity. It was evaluated in rodent models to determine the spectrum of antiviral activity and effective treatment regimens. At 50 to 200 mg/kg given as single or divided intraperitoneal (i.p.) doses 1 day before virus inoculation, significant protection was afforded to mice infected i.p. with Semliki Forest, San Angelo, banzi, and encephalomyocarditis viruses. Similarly, suckling rats were protected from an intranasal challenge with rat coronavirus. Against San Angelo virus, treatments could be delayed to 1 day post-virus inoculation and still show a beneficial effect. The compound was moderately effective in mice infected i.p. with herpes simplex virus type 2 or intranasally with vesicular stomatitis virus. No activity was seen against influenza B virus in mice when the analog was administered one time pre-virus inoculation or in multiple doses given before and after the virus inoculation. Nor was there a prophylactic effect against herpetic skin lesions on mice. This immune modulator may have promise for the treatment of a variety of virus infections.