Edward L. Stephen

IMMUNE MODULATING EFFECTS OF POLY ICLC

This presentation will compare immune modulation brought about by interferon with those brought about by interferon inducers, particularly doublestranded RNA. If the only effect of the interferon inducer was the induction of interferon, then we would expect that interferon and its inducers would have the same effect in any given immune phenomenon, be it no effect, enhancement or inhibition. The fact that inducers can elicit a higher level of circulating interferon in vivo than is readily obtainable by administering exogenous interferon might modify this expectation in that large amounts of interferon might act differently from small amounts of interferon. However, within this limitation, interferon inducers might be expected to act like interferon. Indeed, there are many instances where this is the case. You will hear of them during this session. One such is the enhancement of natural killer cell activity by interferon and by poly

Aerosol therapy of influenza infections of mice and primates with rimantadine, ribavirin, and related compounds.

Ribavirin administered as small-article aerosols had significant therapeutic effect in the treatment of viral respiratory infections induced by influenza virus. The preliminary experiment using ribavirin to treat influenza infection in the squirrel monkey is encouraging. We expect to extend these experiments by initiating therapy at a later time to investigate the potential value of ribavirin in a clinical situation. Several derivatives of ribavirin are effective antiviral compounds. The tri-O-acetyl derivative appears to offer a potential advantage over ribavirin, although this cannot be stated with certainty since the data were obtained from separate experiments. Radiolabeling has been used as a means of measuring tissue concentration and clearance rates of various drugs. It is hoped that the use of labeled ribavirin and the tri-O-acetyl derivative will assist us in determining whether a depot of antiviral drug is created in pulmonary tissues after administration as a small-particle aerosol. These experiments are now in progress.

Interferon Induction in Cynomolgus and Rhesus Monkeys After Repeated Doses of a Modified Polyriboinosinic-Polyribocytidylic Acid Complex

Serum interferon activity was determined in 12 cynomolgus and 12 rhesus monkeys injected intravenously once daily for 10 days with from 0.1 to 6.0 mg of a stabilized polyriboinosinic acid · polyribocytidylic acid complex per kg, composed of polyriboinosinic acid · polyribocytidylic acid, poly-1-lysine, and carboxymethylcellulose [poly(ICLC)]. Interferon activity was detected 2 h after the first injection, with maximum activity occurring 8 h after the second injection. A period of hyporesponsiveness occurred after the third injection of poly(ICLC) in all monkeys and lasted until the sixth injection in the rhesus monkeys, when interferon activity again became more elevated. The delayed rebound was not as apparent in cynomolgus monkeys. Rhesus monkeys injected with 6 mg/kg did not exhibit serious side effects.

Treatment of Influenza Infection of Mice by Using Rimantadine Hydrochlorides by the Aerosol and Intraperitoneal Routes

Rimantadine hydrochloride was administered for 4 days in a small-particle (95% < 6.5 μm) aerosol (8.8 mg/kg per day) or intraperitoneally (40 mg/kg per day) to mice previously infected with influenza A/Aichi/2/68 (H3N2), mouse adapted. Mean time to death and incidence of survival were significantly increased in all treated groups of mice. The rate of eventual disappearance of virus from lung tissue was also accelerated by therapy. However, maximal mean virus titer per lung, and lung histopathology, did not reveal any difference between control and either group of treated mice. Aerosol therapy initiated at 72 h postinfection was as effective as that initiated at 6 h, even though lung virus titers of these mice had already peaked by 72 h. In contrast, intraperitoneal therapy initiated at 72 h was not effective in all studies.

Response of Influenza Virus-Infected Mice to Selected Doses of Ribavirin Administered Intraperitoneally or by Aerosol

The effects of graded doses of ribavirin administered either by aerosol or intraperitoneally were compared in influenza virus-infected mice. The median effective dose values (based upon percent survival) were 3.3 and 15.8 mg/kg per day for the aerosol and intraperitoneal routes, respectively. Lung lesion scores and titer of virus were lower after aerosol than intraperitoneal therapy.

Therapeutic Effects of Ribavirin Given by the Intraperitoneal or Aerosol Route Against Influenza Virus Infections in Mice

Ribavirin (1-β-d-ribofuranosyl-1,2,4-triazole-3-carboxamide) is an effective antiviral agent against type A influenza infection of mice. Therapy was most effective when administered as a small-particle aerosol early in the infection. Treatment was also effective by either the intraperitoneal or aerosol route in mice with histological evidence of pneumonia. Ribavirin increased the percent survival, lowered lung virus titers, and decreased the development of lung pathology when therapy was initiated at 6 h as a small-particle aerosol. There was no evidence of pulmonary toxicity or immunosuppressive effects. Images

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

The antiviral activity of tilorone hydrochloride and three of its analogues (11,002, 11,567, and 11,877) was assessed by oral and intraperitoneal (i.p.) administration to Venezuelan equine encephalitis (VEE) virus-infected mice. Significant increases in the percentage of survival (P < 0.01) were apparent after oral administration of tilorone and analogue 11,877 at dosages of 250 and 500 mg/kg. Neither tilorone nor 11,877 increased percentage of survival when dosages of 31.25 to 500 mg/kg were given by the i.p. route. Orally administered analogue 11,002 was effective against 100 mouse intracranial median lethal doses (MICLD50) of VEE virus at doses at 250 to 1,000 mg/kg; doses of 31.25 to 250 mg/kg given i.p. were effective against 10 MICLD50. Oral dosages of 250 to 1,000 mg of analogue 11,567 per kg were active against 100 MICLD50 of virus. By the i.p. route, 250 mg of 11,567 per kg protected mice against 1,000 MICLD50, and a dose of 125 mg/kg protected against 100 MICLD50. Oral treatment of VEE infection with analogue 11,567 24 h after subcutaneous inoculation of VEE virus resulted in no significant increase in the percentage of survivors. All survivors of these studies were susceptible to rechallenge 21 days after the first inoculation of virus.

Indirect Mouse Model for the Evaluation of Potential Antiviral Compounds: Results with Venezuelan Equine Encephalomyelitis Virus

An indirect mouse model was utilized to evaluate the antiviral activity of several compounds against Venezuelan equine encephalomyelitis (VEE) virus infection in mice. Mice were given various dosages of lysine-stabilized polyriboinosinic acid-polyribocytidylic acid, a tilorone analogue, kethoxal, or mepacrine before and/or shortly after receiving one of several dose levels of attenuated strain TC-83 VEE virus. Twenty-one days later, the same mice were rechallenged intracranially with virulent Trinidad donkey strain VEE virus. Susceptibility to rechallenge was interpreted as evidence of drug effectiveness in completely preventing the initial immunizing virus infection. In contrast, if a drug lacked antiviral effectiveness, the initial attenuated infection stimulated sufficient immunity to protect mice against the virulent rechallenge. Both of the interferon inducers, lysine-stabilized polyriboinosinic acid-polyribocytidylic acid and tilorone analogue 11,567, possessed significant (P < 0.01) antiviral activity based upon this indirect model, whereas mepacrine and kethoxal were inactive. Results using the indirect method were confirmed by using the conventional direct method for evaluating the effectiveness of potentially useful antiviral compounds. The indirect mouse model described should prove useful for studying drug efficacy against certain viruses that are lethal only by intracranial inoculation.

Systemic Metabolic Alterations Associated with Repeated Injections of a Modified Polyriboinosinic-Polyribocytidylic Acid Complex

Polyriboinosinic acid-polyribocytidylic acid complexed with poly-1-lysine and injected intramuscularly into rats (0.3 or 3.0 mg/kg) produced fever, altered leukocyte count, slightly depressed plasma zinc, increased amino acid uptake into liver, and increased plasma acute-phase globulins two- to threefold. It is suggested that these systemic metabolic alterations are indicative of a mild inflammatory response to this drug. The metabolic alterations may have to be taken into consideration when polyriboinosinic acid-polyribocytidylic acid complexed with poly-1-lysine is used in therapy.