Tilorone Hydrochloride: Lack of Correlation Between Interferon Induction and Viral Protection

Abstract

The protection of mice against MM virus infection and the induction of circulating interferon by tilorone hydrochloride were determined. Whereas protection was evident with doses of 0.15 and 1.5 mg/kg, interferon was not detected with doses lower than 150 mg/kg. Protection was apparently not dependent on interferon induction.Tilorone hydrochloride, the orange, watersoluble dihydrochloride salt of 2,7-bis[2-(diethylamino) ethoxy] fluoren-9-one, is a broadspectrum antiviral agent (5). In mice, it is effective against Semliki Forest virus by the oral, subcutaneous, and intraperitoneal treatment routes. It has also been shown to be effective against intranasal infection by vesicular stomatis virus (VSV; 2). Its mode of action is presumably interferon stimulation (2, 6). We have investigated the protection elicited by different doses of tilorone given intraperitoneally against MM virus infection in mice. At the same time, the amount of circulating interferon induced by each dose of tilorone was determined.Female Swiss Webster mice weighing about 14 g were treated intraperitoneally with different doses of tilorone diluted in Hanks balanced salt solution. Ten mice from each group were bled at 6, 12, and 24 hr after the administration of tilorone. The blood was pooled, and the plasma was collected and assayed for interferon activity. At 24 hr after the injection of tilorone, the mice remaining in each group were challenged intraperitoneatly with about 100 plaque-forming units of MM virus (2 LD50). Deaths were recorded daily for 20 days. The results (Table 1) show that, in terms of mortality and mean survival time, a tilorone dose of 7.5 mg/kg was sufficient to protect mice. They also suggest that doses as low as 0.15 and 1.5 mg/kg can have a protective effect, although at these doses the results were variable. Circulating interferon, however, was not detected with tilorone doses of less than 150 mg/kg. As these data show, in our system there was no correlation between the protection of mice against MM virus infection and the amount of circulating interferon induced by tilorone.These results are not in agreement with those of De Clercq and Merigan (2), who reported that the degree of protection of mice against intranasal infection with VSV was directly related to the titers of interferon induced by different doses of tilorone. Their interferon titers in response to tilorone were much higher than those in the present study. Since the 50% reduction in plaque count as a method for assay of interferon is more sensitive when MM virus is the challenge agent than when VSV is used (1), we must conclude that the differences in interferon titers in the two studies are real. This discrepancy could be due to a genotypic difference in the animals.

Antiviral effect of interferon on influenza virus infection in mice.

“…These findings suggest that the amount of IFN in the lung has an important role in the defense against influenza virus infection in mice. Similar results showing that the amounts of IFN in virus propagating tissues, but not in circulating IFN titers correlate to the resistance to viral diseases have been reported with pyran and poly I:C on mengovirus infected mice (Merigan et al 1970) and with tilorone hydrochloride on MM virus infected mice (Giron et al 1972).…”

Inhibition of Herpesvirus Deoxyribonucleic Acid and Protein Synthesis by Tilorone Hydrochloride

“…2). However, the presence of tilorone (10 ug/ml) did not affect significantly the rate of adsorption of the two virus preparations tested (Fig. 2).…”

“…Tilorone hydrochloride at a concentration of 10 ,ug/ml very efficiently inhibited herpes simplex virus growth in BSC1 cells when the virus is infected at a low multiplicity of infection. The adsorption of the virus was not affected by the drug, and the penetration of the deoxyribonucleic acid of the input virus into the cytoplasm and nuclei proceeded normally when tilorone hydrochloride was present.…”

Evaluation of Various Analogues of Tilorone Hydrochloride Against Venezuelan Equine Encephalitis Virus in Mice

“…Giron et al (3) reported that protection of mice with tilorone hydrochloride against MM virus is apparently not dependent on interferon induction. In their studies, circulating interferon was not detected with i.p.…”

“…Giron et al (3) concluded that determination of circulating interferon concentration is of limited value in assessing antiviral activity, since protection can be demonstrated without the simultaneous detection of interferon. In contrast, others report that protection of mice against intranasal infection with VSV is directly related to the concentrations of interferon induced by different doses of tilorone (1).…”