Inosiplex: an immunomodulation model for the treatment of viral disease

Measles, mumps, rubella, and human parvovirus B19 infections and neurologic disease

While the systemic disorders associated with measles, mumps, and rubella viruses and human parvovirus B19 tend to be mild, each virus can produce potentially life-threatening neurologic disease in human hosts, especially when these viruses infect young children. Two of the viruses, rubella and parvovirus B19, can be vertically transmitted to fetuses during maternal infection and cause congenital infection. Neurologic complications are common after intrauterine infection with the rubella virus, a condition known as the congenital rubella syndrome. Two, measles and rubella viruses, can induce "slow viral" infections, serious, disorders that can occur several years after the initial exposure to the virus and typically have fatal outcomes.

Oral proliferative verrucous leukoplakia (PVL); open trial of surgery compared with combined therapy using surgery and methisoprinol in papillomavirus-related PVL

Proliferative verrucous leukoplakia (PVL) is a unique oral white lesion in which human papillomavirus (HPV) may play a role. PVL behaves far more aggressively than other forms of leukoplakia with a high rate of recurrence after surgical excision, and relentless progression to verrucous hyperplasia and to verrucous or squamous cell carcinomas. The treatment of PVL is usually by surgery, but there is often early recurrence. This study was an open trial of surgery in 25 patients with oral HPV-positive PVL, compared with combined therapy using surgery and methisoprinol in another group of 25 patients with oral PVL. Six months postoperatively there was a significant difference, with 18 recurrences in the patients treated by surgery alone compared to only two recurrences in the patients treated also with methisoprinol (isoprinosine or inosine pranobex), a synthetic agent with immunomodulatory properties and some antiviral activity against HPV. Eighteen months postoperatively there were no further recurrences in the patients treated by surgery alone but another two recurrences in the patients treated with methisoprinol. Overall, by 18 months follow-up, there were 18 recurrences in the group treated by surgery alone, compared with four in those also receiving methisoprinol. The use of this antiviral agent appeared to offer a significant enhancement to the surgical management of PVL.

Effects of non-specific immunopotentiators in experimental Schistosoma mansoni infection. II. Corynebacterium parvum

The effects of Corynebacterium parvum on host protection, tissue reaction and "in vivo" chemotaxis in Schistosoma mansoni infected mice were studied. The C. parvum was given intraperitoneally using a dose of 0.7 mg, twice a week (for 4 weeks), thirty days before (prophylactic treatment) or after infection (curative treatment). The host protection was evaluated through the recovery of adult worms by liver perfusion and was lower in the prophylactic group as compared to the control group (p = 0.018), resulting in 44% protection. The "in vivo" leukocyte response in both prophylactic and curative groups was higher as compared to the infected/non treated group (p = 0.009 and p = 0.003, respectively). Tissue reactions were described in the experimental and control groups, but there were not remarkable differences among them. The possible biological implications and relevance of the findings for the defensive response of the host and control of schistosomiasis are discussed.

Effect of isoprinosine on IL-2, IFN-gamma and IL-4 production in vivo and in vitro

The effects of an immunopotentiating drug, isoprinosine, on the splenocytes of BALB/c mice to produce cytokines were investigated. Isoprinosine enhanced IL-2 production, upregulating the expression of IL-2 receptor in vitro. It also significantly increased the IFN-gamma secretion and decreased the IL-4 production in vivo. The significance of these findings in terms of immune regulation is discussed.

Chemically induced immunomodulation in domestic food animals

There is extensive research underway on development of chemical immunomodulators for use in humans. This research is primarily driven by the need for therapeutic immunomodulators for use in patients with cancer or AIDS. Currently, there are no chemicals approved as immunomodulators by the Food and Drug Administration for use in domestic food animals. There is considerable potential for applying the rapid advances in immunomodulation research to benefit domestic animals. In domestic food animals, immunomodulators have the greatest potential for prevention and perhaps therapy in early stages of infectious diseases associated with immunosuppression. There are many different causes for immunosuppression and many different molecular mechanisms responsible for defective function of immune cells. It is unlikely that any one immunomodulator will be capable of preventing or reversing all of these various causes of immunosuppression. Therefore, research is needed to understand the mechanisms of immunosuppression and the mechanism of action of immunomodulators so that rational approaches can be developed for their prophylactic and therapeutic use. Without this information and information on effective dosages and duration of action, attempts to use immunomodulators clinically are likely to produce discouraging results.

Effect of isoprinosine on lymphocyte proliferation and natural killer cell activity following thermal injury

The effect of in vivo administration of Isoprinosine (ISO) on, i) the proliferation of splenic lymphocytes in response to the T-cell mitogen, concanavalin-A (Con-A) and, ii) the natural killer (NK) cell cytotoxicity was studied following a full skin thickness burn injury in a rat model. Administration of ISO (100 mg/kg body wt/day) twice daily, resulted in significant augmentation of the proliferative responses of lymphocytes compared to non-treated burned animals, at 7 days post injury. However, it did not effect the lymphoproliferation at 14 days post injury, the time period at which a complete suppression of lymphocyte proliferation was observed in burned non-treated animals. Also, the proliferation of lymphocytes from normal nonburned animals was not affected by treatment with ISO. ISO treatment of the burned animals resulted in a significant increase in the NK cytotoxicity compared to non-treated burned animals. As with Con-A responses, ISO administered to control nonburned animals did not have any effect on NK cell cytotoxicity. Our studies thus indicate that ISO can be a potential immunomodulator of suppressed immune function following thermal injury, particularly in patients whose lymphocyte responses to T cell mitogen Con-A are not completely suppressed.

5-Fluorouracil and isoprinosine in the treatment of advanced colorectal cancer. A limited phase I, II evaluation

We studied the effects of 5-fluorouracil (5-FU) and isoprinosine (ISO) on 15 patients with previously untreated metastatic colorectal carcinoma. The patients were treated in a limited Phase I, II protocol. All patients received a fixed ISO dose of 4 g orally on days 1 through 5 of each cycle. Each cycle was repeated every 35 days. The first seven patients were treated with an initial 5-FU dose of 7.5 mg/kg intravenously (IV) on days 1 through 5, which was escalated to 11.5 mg/kg IV after the first course and to 13 mg/kg IV after the second course. The next eight patients were treated with an initial 5-FU dose of 11.5 mg/kg IV on days 1 through 5, which was escalated to 13 mg/kg IV on days 1 through 5. No major responses (complete or partial) were documented. Median survival for all evaluable patients was 33 weeks. Toxicity was predominantly gastrointestinal and hematologic and was considered moderate. Our data suggest that 5-FU and ISO, at the doses used, were ineffectual in the treatment of metastatic colorectal carcinoma.

The use of non-specific immunopotentiators in experimental Trypanosoma cruzi infection

The effects of levamisole, isoprinosine and Corynebacterium parvum on Trypanosoma cruzi (Y strain) experimental infection of mice were studied. In prophylactic treatment these drugs reduced the peak of parasitaemia, and had no apparent effect on mortality rate or on histopathological and electrocardiographic findings. Levamisole and isoprinosine had no effect when used after infection. Electrocardiograms were obtained from all chronic chagasic mice. The most frequent changes were left atrial overload and first degree atrio-ventricular block. These findings became more frequent the longer the animals survived. The net effect of the non-specific immunopotentiators seems to depend on several factors: host immune state, severity of infection, dose and timing of drug administration. This probably explains the variable published results and the paradoxical findings of different laboratories.

Influence of isoprinosine on bovine herpesvirus type-1 infection in cattle

A study was conducted to determine the in vivo efficacy of isoprinosine (ISO) in calves infected with bovine herpesvirus type-1 (BHV-1). Calves were infected with BHV-1 on day 0 and received ISO daily for 14 days. Clinical signs of disease, shedding of BHV-1, lymphocyte proliferative responses to mitogens, interleukin-2 production, and alveolar macrophage bactericidal activity were monitored during the study. Rectal temperatures were increased (P less than 0.05) in BHV-1 and ISO-BHV-1 calves at days 3 to 7 postinfection (PI). Isoprinosine did not influence BHV-1 shedding in calves. Lymphocyte proliferative responses to phytohemagglutinin (PHA) were lower (P less than 0.01) in BHV-1 calves when compared to control or ISO calves at day 4 PI, but ISO did not ameliorate this effect. Interleukin-2 activity was greater (P less than 0.05) in ISO-BHV-1 calves on days 4 and 8 PI in PHA-stimulated lymphocytes and on day 8 PI in concanavalin A-stimulated lymphocytes when compared to control, ISO or BHV-1 calves. Isoprinosine treatment of BHV-1-infected calves tended to decrease alveolar macrophage bactericidal activity. These data suggest that ISO does not reverse BHV-1 suppression of lymphocyte proliferation, but may enhance IL-2 production in BHV-1 infected calves.

Study of the inhibition of histamine release by inosine pranobex

The effects of Inosine pranobex and its parent compounds inosine and dimethylamino-2-propanol-p-acetamidobenzoic acid (DipPacBa) on the Concanavalin A (ConA)-induced histamine release from human adenoidal mast cells were investigated. Inosine pranobex inhibited the ConA-induced histamine release at concentrations greater than 10(-3) M. Inosine itself (10(-5)-10(-2) M) enhanced the ConA-induced histamine release whereas DipPacBa inhibited the release significantly at concentrations between 10(-6) and 10(-2) M. These results are consistent with the assumption that the effect of Inosine pranobex is due to the DipPacBa moiety.

Inosine pranobex. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Inosine pranobex is a synthetic compound formed from the p-acetamido benzoate salt of N-N dimethylamino-2-propanol and inosine in a 3:1 molar ratio. It has been reported to exert antiviral and antitumour activities in vivo which are secondary to an immunomodulating effect, and early results suggest beneficial clinical effects in several diseases and infections including mucocutaneous Herpes simplex infections, subacute sclerosing panencephalitis, genital warts, influenza, zoster, and type B viral hepatitis, as well as in homosexual men with persistent generalised lymphadenopathy. However, many of the studies have been preliminary in nature and deficient in design or in the reporting of their results. One must therefore conclude that while inosine pranobex may prove to be a valuable and innovative therapy for a number of diseases and infections for which no satisfactory therapy exist, further long term well controlled studies in larger numbers of patients are required before definitive conclusions about the efficacy of inosine pranobex in these disorders will be possible.

Griseofulvin-methisoprinol combination in the treatment of herpes zoster

A total of 57 herpes zoster patients (28 men and 28 women) were randomly assigned to one of the following four treatments: griseofulvin, 125 mg four times daily; methisoprinol, 1 g four times daily; griseofulvin plus methisoprinol (dosage schedules as above); placebo, four times daily. Griseofulvin had no effect at all, methisoprinol both significantly accelerated drying of vesicles and reduced pain, and the combination of griseofulvin and methisoprinol turned out to be significantly more effective in reducing pain than methisoprinol alone. The present results suggest a new effective treatment for herpes zoster disease.

Prophylaxis of Rift Valley fever with antiviral drugs, immune serum, an interferon inducer, and a macrophage activator

Rift Valley fever virus (RVFV), a member of the family Bunyaviridae, extended its range from sub-Saharan Africa into Egypt in 1977. Its clinical spectrum is recognized to include severe manifestations such as hemorrhagic fever and encephalitis. For these reasons, as well as the limited knowledge of specific therapy for Bunyaviridae infections, we investigated several prophylactic regimens for RVF in a mouse model. Rimantadine, thiosemicarbazone, and inosiplex were ineffective. Pretreatment with glucan was of some use, but the most encouraging results were obtained with the antiviral drug ribavirin, passive antibody, or an interferon inducer polyriboinosinic-polyribocytidylic acid complexed with poly-L-lysine and carboxymethylcellulose (poly[ICLC]). Ribavirin and poly(ICLC) were also shown to be efficacious in preventing disease in hamsters. Ribavirin (loading dose of 50 mg/kg followed by 10 mg/kg at 8-h intervals for 9 days) suppressed viremia in RVF-infected rhesus monkeys. Ribavirin also reduced virus yield in infected cell cultures; sensitivity varied markedly with cell type but not with virus strain. Immune mouse ascitic fluid, with a plaque reduction neutralization titer of 1:1024, was effective in a dose of 4 ml/kg, a volume approximately equivalent to administration of a unit of convalescent plasma to a human. Poly(ICLC) may well have functioned through interferon induction, since RVFV was shown to be sensitive to interferon in cell culture, and since another macrophage activator (glucan) was only marginally effective. These studies suggest that ribavirin, poly(ICLC), and convalescent plasma may have a role in prevention or therapy of human RVF.

Effect of isoprinosine on sialylation of interleukin-2

The effects of Isoprinosine (ISO) on interleukin-2 (IL-2) production by human peripheral blood mononuclear cells (PBMC) were investigated. Treatment (of human PBMC) with ISO enhanced IL-2 production by PBMC from 7 of 10 normal individuals. However, no augmentation of IL-2 production was observed when cultures of HUT-78 cells, a human leukemic T cell line, were treated with ISO. IL-2 purified from supernatants of human PBMC treated with ISO exhibited pI values of 5.5 and 6.4. IL-2 prepared from untreated PBMC exhibited a single pI value of 8.2. The pI value of IL-2 prepared from ISO-treated PBMC shifted to 8.2 after treatment with neuraminidase, demonstrating that the IL-2 molecules isolated from ISO-treated PBMC possessed sialic acid. The pI values of the IL-2 isolated from ISO-treated and untreated HUT-78 culture supernatants were identical (pI = 7.8) and were not modified by neuraminidase treatment. These results suggest that the increase in IL-2 production following treatment of PBMC with ISO may be mediated through the activation of a distinct subset of IL-2 producing cells. Furthermore, the sialylation of IL-2 may be of physiologic and immunopharmacologic importance.

Effects of isoprinosine in animal models of depressed T-cell function

Isoprinosine--a new drug possessing immunostimulating properties--was investigated for its ability to influence cell-mediated immune responsiveness in animal models of deficient T-cell function. In vitro isoprinosine strongly increased T-cell mitogenesis in spleen cells from normal rats, with only modest increases in B-cell mitogenesis and no effects on unstimulated cells. In vivo isoprinosine (50 mg kg-1 day-1 orally) had no effects on spleen cell responsiveness when administered to normal rats for 4 or 14 days. However, when the same dose of isoprinosine was administered to rats immunosuppressed with cyclophosphamide (5 mg kg-1 day-1 orally) a partial restoration of T-cell mitogenesis was observed after 14 days of treatment. In rats with adjuvant arthritis treated with isoprinosine for 14 days, depressed T-cell responsiveness was completely restored to the level of the nonarthritic animals. The involvement of different cell types in the observed effects of isoprinosine was further studied in arthritic rats. Removal of monocytes/macrophages from the cell suspensions prior to culture did not affect the increased T-cell response in isoprinosine-treated rats, suggesting a direct stimulatory effect of isoprinosine on T-cell functions. T-suppressor cell function, impaired in arthritic rats, was not restored by treatment with isoprinosine. These results suggest that isoprinosine may exert selective effects on specific T-cell subsets, a finding that may increase the therapeutic interest of the drug.

Comparative effects of an antiviral drug, inosiplex, and diphosphonates in Paget's disease of bone

The effects of the antiviral agent, inosiplex, were assessed in four patients with Paget's disease of bone. Treatment for 6 months did not suppress disease activity as judged by serum alkaline phosphatase and hydroxyprolinuria, and viral inclusions persisted in the one patient from whom a bone biopsy was taken. These results contrasted markedly with the suppressive effects of diphosphonate treatment in these same patients.

Modulation of T- and B-lymphocyte functions by isoprinosine in homosexual subjects with prodromata and in patients with acquired immune deficiency syndrome (AIDS)

Male prodromal homosexuals and patients with acquired immune deficiency syndrome (AIDS) exhibited similar immunological abnormalities but by different degrees. A reduction in the number of circulating T lymphocytes bearing the T-4 surface marker led to an altered ratio of Th to Ts subpopulations in both groups of subjects. Total numbers of suppressor cells (Ts) remained virtually similar in both study groups to that of the control subjects. Proliferative responses to T-cell mitogen (PHA) and T cell-dependent B-cell mitogen (PWM) were severely impaired in prodromal subjects and more so in the AIDS group. The response to PWM was unrelated to the total number of suppressor T cells but was associated with a significant decrease in helper T-cell number. The impaired lymphocyte functions of immunosuppressed subjects were potentiated by coincubation with isoprinosine in a selective fashion. While the percentage of upward modulation among homosexuals with normal lymphocyte functions was comparable to that obtained in control subjects, a higher degree of augmentation was achieved in AIDS patients and in prodromal subjects with impaired blastogenic responses. In none of the AIDS patients with severe immunodeficiencies, however, was the lymphocyte functions restored to the normal range established in the heterosexual controls. These results suggest the feasibility of eventual prophylactic utilization of isoprinosine in male homosexuals at high risk of developing AIDS.

Treatment of subacute sclerosing panencephalitis: an overview

Subacute sclerosing panencephalitis (SSPE) is a rare central nervous system degenerative disease that occurs primarily in children and adolescents. It is believed to be caused by a measles-like virus. Initial symptoms usually present as a variety of personality changes followed by myoclonus with progression of mental and motor deterioration, which leads to death within a few months to years. New experimental treatment with inosiplex has been shown to be helpful for patients stricken with this progressive neurological disease. A response to inosiplex therapy is best in patients with a slowly progressing form of the disease. Inosiplex treatment is safe with few adverse effects. The duration of treatment appears to be lifelong since many patients relapse when inosiplex therapy is discontinued. This article reviews the etiology, pathogenesis, and experimental treatment of SSPE.

Inosine biosynthesis in transfer RNA: a postulated role in immune regulation

A hypothesis is put forth describing a role in immune regulation for inosine biosynthesis in the anticodon of tRNA. The enzymatic insertion of hypoxanthine into the tRNA wobble base position is predicted to be a control point for the translation of proteins and peptides required for normal immune function. The substrate for inosine biosynthesis in tRNA, hypoxanthine, is an intermediate in the purine catabolic pathway, and defects in this pathway are associated with inherited immunodeficiency diseases. Therefore, a role for aberrant inosine biosynthesis in tRNA is postulated in causing the immunodeficient conditions, and it may be a relevant molecular defect in leukemia as well.

Immunostimulation. Clinical and experimental perspectives

Three classes of immunostimulating drugs are described, each representing a different approach to the problem of pharmacological immunostimulation. The rationale for the use of microbes or microbial agents as immunostimulators rests on the fact that some micro-organisms, especially those that replicate intracellularly, carry a special potential to activate macrophages. Clinically, the use of these agents in patients with tumors and infections has been disappointing; however, there have been positive exceptions like the responsiveness of melanomas and bladder carcinomas to the injection of BCG. Many of the inconclusive results may be due to insecurities in the dosage of microbial preparations and to a general lack in standardization. Some structures with high efficacy and low toxicity which have recently evolved from this field deserve further investigation. A number of structurally unrelated synthetic compounds was found to influence immune parameters. Levamisole can today be classified as an immunostimulating drug with limited utility in recurring infections and in chronic polyarthritis. Several immunostimulating drugs which have attracted interest contain a purine as the effective component. This is not surprising in view of the fact that many genetically determined immunodeficiencies can be traced to defects of enzymes which play a crucial role in purine biosynthesis. Finally, the potential role of lymphokines as stimulators of the immunosystem is briefly described. Some of these glycoproteins have recently become available for clinical trials. Others will be made available through genetic engineering. The therapeutic utility of these compounds is not yet clear; they will, however, be of great value as probes for the study of immune functions and for the development of immunopharmacology.

Potentiation of cytotoxic effects of 5-fluorouracil by inosiplex on cancer cells

The antitumor effect of 5-fluorouracil (5-FU) was significantly enhanced by inosiplex which has been developed as a drug possessing antiviral activity. The enhancement of antitumor effect of 5-FU was demonstrated by experiments both in vitro and in vivo, viz. depression of the colony formation rate in cultures of HeLa cells (an established cell line of human cervical carcinoma), and prolongation of the survival of mice bearing transplanted Ehrlich ascites tumor of murine mammary carcinoma origin. The HeLa cell colony formation was synergistically decreased in the presence of 0.5-2.0 micrograms/ml of 5-FU combined with 100 micrograms/ml of inosiplex. Inosiplex did not cause any appreciable inhibition of cell growth at this concentration when added alone to the culture. The mean duration of survival of tumor-bearing mice was 18.2, 20.3, 31.9 and 47.1 days in the control group and groups receiving inosiplex, 5-FU, or a combination of 5-FU and inosiplex, respectively; hence significantly prolonged in the combined therapy regimen group as compared with the control and the 5-FU treated group (P less than 0.01).

Effect of isoprinosine on natural killer cell activity of blood mononuclear cells in vitro and in vivo

Addition of isoprinosine to cultures of blood mononuclear cells was shown to inhibit natural killer (NK) cell activity against the K562 myeloid cells and melanoma cells. This appeared to be due to inhibitory influences of monocytes in that after removal of adherent cells isoprinosine appeared to stimulate NK activity. Similar effects were noted on T cells separated by E rosette procedures. Administration of isoprinosine in vivo had variable effects on NK activity during drug administration but there was a significant increase in NK activity 3 days after cessation of the drug. These changes in NK activity may reflect different threshold levels of the drug on suppressor and NK cell populations and the relative proportions of different lymphocyte populations in individual subjects. Further studies with a wider range of drug doses and more frequent monitoring of responses are required to further evaluate the effect of isoprinosine on NK activity.

Effect of isoprinosine on interleukin 1 and 2 production and on suppressor cell activity in pokeweed mitogen stimulated cultures of B and T cells

Isoprinosine appeared to potentiate the production of interleukin 1 and interleukin 2 in cultures of lipopolysaccharide stimulated human monocytes and phytohemagglutinin stimulated cultures of blood mononuclear cells respectively at pharmacological drug levels. Administration of the drug in vivo was associated with increased activity of radiation sensitive suppressor T cell activity against immunoglobulin production in pokeweed mitogen stimulated cultures of B and T cells. Addition of isoprinosine to the latter cultures in vitro appeared to enhance immunoglobulin production consistent with inhibition of suppressor cell activity or stimulation of helper activity. It is not clear from these studies whether the contrasting effects of the drug in vitro and in vivo represent different actions of metabolites or alteration of the proportion of lymphocyte subsets in the circulation. Further studies are required to answer these questions and to determine whether the changes persist with long term administration of the drug.

Immunoenhancing effect of flavonoid compounds on lymphocyte proliferation and immunoglobulin synthesis

Flavonoid compounds are lipophilic agents which can interact with membrane lipids and may affect responsiveness of immune cells. We therefore studied whether cianidanol ((+)-catechin), the O-methyl-derivative (+)-3-methoxy-5,7,3',4'-tetrahydroxyflavan and palmitoyl-derivative (+)-3-palmitoyl-5,7,3',4'-tetrahydroxyflavan influence T and B cell functions. In addition, immunomodulatory property of ubiquinone 50 was also investigated. As controls were used cyclosporin A and inosine which are known to inhibit or enhance immune responses, respectively. The in vitro spontaneous, antigen and mitogen induced proliferation as well as immunoglobulin synthesis of peripheral blood mononuclear cells from healthy individuals was determined in the presence of different concentrations of the agents. All flavonoid compounds and ubiquinone 50 significantly increased (p less than 0.05 - less than 0.01) the spontaneous lymphocyte transformation but hardly affected antigen, alloantigen and mitogen induced proliferative response. Only cianidanol and O-methyl-derivative enhanced significantly (p less than 0.05 - less than 0.01) spontaneous, pokeweedmitogen and Staphylococcus aureus Cowan I induced immunoglobulin synthesis while the palmitoyl-derivative and ubiquinone 50 had only minor influence on B cell function. In contrast, Staphylococcus aureus induced immunoglobulin production was neither increased by inosine nor suppressed by cyclosporin A. These studies show that especially cianidanol and the O-methyl-derivative can exert an immunoenhancing effect on T and B cell functions.

Restoration of immune responses of aging hamsters by treatment with isoprinosine

Immune competence declines with advanced age in hamsters, as in other laboratory mammals and in humans. We found significant alterations in the functional parameters of different populations of immunocytes (natural killer cells, T cells, monocytes, and suppressor cells) in aging hamsters, beginning at approximately 14 mo of age. Natural killer cytotoxicity, phytohemagglutinin-induced lymphocyte stimulation, and monocyte chemotaxis were decreased in aging Lak:LvG(Syr) outbred hamsters. When old hamsters were given a single injection (5 mg/kg body wt) of isoprinosine, a chemical immune potentiator, these three immune parameters increased almost to the levels found in young adult hamsters but returned to pretreatment levels after 7 d. Suppressor cell activity for the lymphocyte response to phytohemagglutinin, which increased with age, was decreased after treatment. In old hamsters treated with weekly injections of isoprinosine, these four immunological parameters remained at or near the levels found in young adults.

The immunomodulatory action of inosiplex in relation to its effects in experimental viral infections

The effect of inosiplex (Isoprinosine) on viral replication, experimental viral infections and host immune functions has been examined. Inosiplex was found to have a broad spectrum of antiviral activity, inhibiting the RNA viruses, influenza (INFV) and parainfluenza (PIV), as well as the DNA viruses, herpes simplex (HSV) and vaccinia (VACV). However, the antiviral effects were modest when compared to amantadine and adenine arabinoside (ARA-A). Inosiplex in vivo caused a statistically significant increase in survival of treated animals (hamster, mice) infected with RNA or DNA viruses. This effect of inosiplex was apparent in animals which were previously immunosuppressed. Inosiplex, at optimal dose, conferred total protection in treated mice against secondary influenza infection. Since this was accompanied by statistically significant increases in serum anti-hemagglutinin and anti-neuraminidase titers, an effect of inosiplex on host defenses against secondary viral infection was implicated. This effect was further demonstrated by passive transfer of protection by splenocytes from inosiplex-treated donors to untreated recipients. Inosiplex was found to enhance the mitogen- (PHA-, ConA and MLC-) induced blastogenesis of lymphocytes from untreated mice. The LPS response was not affected. Inosiplex added in vitro caused a dose-dependent increase in the primary immune anti-SRBC response in vitro, as determined by direct and indirect PFC; there was also a dose-dependent effect on the secondary in vitro direct and indirect PFC responses. Inosiplex in vivo enhanced the primary immune response to SRBC, as determined by direct PFC assay; this was also the case for immunosuppressed mice. The drug enhanced delayed type hypersensitivity to picryl chloride in the mouse. Macrophage function was also enhanced by inosiplex, as was apparent from phagocytosis of SRBC. Gamma interferon production from murine lymphocytes was augmented by inosiplex in vitro. Treatment with inosiplex had no effect on natural killer cells or on antibody dependent cellular cytotoxicity. Thus, the pronounced effect of inosiplex on secondary viral infections may result through two different mechanisms: a direct antiviral effect and an elevation of multiple parameters of host immunity, which are usually compromised during viral infection. The latter mechanism may be the more important.

Enhancement and restoration of contact sensitivity reactions by isoprinosine

Isoprinosine (50 mg/kg i.p.) increased the ear swelling reaction in mice sensitized with trinitro-chlorobenzene (picryl chloride) and challenged with the same agent. Enhancements were observed when the drug was administered either simultaneously to the sensitization or to the challenge with picryl chloride. Similar results were obtained when lymphoid cells from sensitized animals were transferred i.v. to normal animals which were then challenged with picryl chloride. Using the same cell transfer system, we found that treatment of cell donors with Isoprinosine (50 mg/kg/day, i.p.) counteracts the inhibition induced by cyclophosphamide. Isoprinosine (50 mg/kg/day, i.p.) inhibited also the generation of antigen-specific suppressor cells induced by picryl-sulfonic acid as shown by transfer to normal recipients of suppressor cells together with lymphoid cells from sensitized animals. These results indicate that Isoprinosine enhances normal contact sensitivity reactions and can counteract, under certain circumstances, antigen-specific as well as nonspecific immunosuppression.

Modulation of human T lymphocyte functions by isoprinosine

Isoprinosine was shown to alter certain T cell functions. In vitro, it has previously been shown to induce suppressor cell activity in both mouse and human lymphocytes. Our in vitro results suggest that Isoprinosine acts on immune balance by increasing the number of non-suppressor T cells and, at least partially blocks Con A induced suppressor activity. In vitro NK activity remained unaltered.

An in vitro study on the effects of isoprinosine on immune responses in cancer patients

The in vitro effects of ISO on the immune responses of cancer patients were investigated. Forty seven patients with primary tumors (26 lung carcinoma, 14 breast adenocarcinoma, 7 melanoma) were studied. Concanavalin A (ConA)-induced lymphocyte proliferation, natural killer cell (NK) activity, and monocyte chemotaxis were measured. In 40 of the 47 patients (85%), ConA-induced lymphocyte proliferation was depressed; NK activity was depressed in 32 (68%), and monocyte chemotaxis was found to be depressed in 36 (77%). For in vitro studies, an optimum concentration of ISO (100 micrograms/ml per 10(6) cells) was used to treat peripheral blood mononuclear cells. In the presence of ISO, all three parameters were restored to normal or near normal levels in those that were depressed. Under these preincubation conditions in vitro treatment of mononuclear cells from the peripheral blood of normal individuals with ISO had no effect on their activities in the three assays. Similar effects on these three immune parameters were observed when 24 h supernatants obtained from patients' mononuclear cells pretreated with ISO were employed in these assays.

Methisoprinol effect on enriched B and T lymphocyte populations stimulated with phytohemagglutinin

The Authors investigated the effect of methisoprinol (Inosiplex) on separated B and T lymphocytes from 8 healthy donors. B or T treated cells, recombined with T or B untreated cells, were subsequently mitogen stimulated. Proliferative response resulted significantly increased, in comparison to a control, when T lymphocytes were preincubated with the drug, while treating only B lymphocytes led to a decrement. These data confirm the hypothesis of a direct action of the drug on T lymphocytes, but are also consistent with its influence on B cells too, even though with an opposite effect.

In vitro lymphocyte sensitivity test to methisoprinol in different pathological conditions

The present paper describes an in vitro study with Methisoprinol, carried out by means of various lymphocyte sensitivity tests in different pathological conditions. Methisoprinol does not exert any effect--neither on responsiveness nor on lymphocyte function--in healthy subjects, while in subjects with immunodepressive pathology the drug is capable of increasing these parameters either alone (rosettes) or in conjunction with mitogens (rosetting) at doses between 50 and 100 micrograms/ml.

In vitro effect of inosiplex on T lymphocytes. I. Influence on T cells with receptors for IgG (T gamma)

Inosiplex, a complex of inosine and 2-hydroxypropyldimethyl ammonium-4-(acetylamino)benzoate, 1:3 molar ratio, originally developed for antiviral use, is now under wider investigation because of its immunopotentiating properties. This compound can have some actions on T cells at various stages of differentiation, thus promoting an enhancement of their blastogenic responses to varied mitogenic agents (PHA, Con A, PWM, MLC, tetanus toxoid, and viral antigens). Our studies demonstrated that under the influence of inosiplex human peripheral blood T lymphocytes bearing Fc IgG receptors have an augmented receptor avidity for SRBC which result in an increased E active rosette formation, and that T cells preincubated with the drug at the appropriate concentrations express more Fc IgG receptors. Even though T gamma cells exert "in vitro" immunoregulatory properties, the increase in percentage of T gamma lymphocytes do not correlate with a potentiation of the Con A-induced suppressor activity of T cells. Moreover, the lymphocytes treated with the substance in the absence of Con A exert helper functions, increasing the mitogenic responses of the second culture PHA--treated lymphocytes. These data appear to suggest a pro-proliferative inosiplex-induced effect which could mask a concomitant suppressor cell induction.

Ribavirin and inosiplex: a review of their present status in viral diseases

A considerable amount of information has accumulated during the past 10 years in the search for antiviral agents. Ribavirin and inosiplex are 2 interesting developments to come out of this search. Ribavirin, a synthetic nucleoside, has an unusually wide spectrum of antiviral activity, especially when tested in vitro. A large number of RNA and DNA viruses are sensitive, especially herpes viruses, poxvirus, influenza, parainfluenza, reovirus, togavirus, and RNA tumour viruses. The in vivo antiviral spectrum of activity is much narrower, with activity against herpes virus, influenza, parainfluenza, measles and adenoviruses. However, controlled clinical trials have not been uniformly successful in treating influenza, hepatitis, herpes simplex and herpes zoster. Inosiplex has been shown to have antiviral activity in vivo against influenza, herpes simplex, rhinovirus and vaccinia virus infections. However, antiviral activity has not been consistently demonstrated, and this observation led to further studies which revealed its immunomodulating effects. The accumulated evidence has indicated that inosiplex is more a prohost agent rather than an antiviral drug. Immune functions which are depressed during viral infection can be restored to normal by inosiplex therapy. At present, neither ribavirin nor inosiplex alone has been shown to be uniformly successful in the treatment of human viral diseases. Nevertheless, their potential place in chemotherapy should not be neglected, although further data are needed to determine what this place will be. Whether combining them with other antiviral agents such as interferon, acyclovir, Ara-A, and so on, would produce a potentiation of action and improved antiviral chemotherapy, will be an interesting area for further study.

Isoprinosine as an immunopotentiator in an animal model of human osteosarcoma

The effects of isoprinosine (ISO) on the immune responses (Con A-induced lymphocyte proliferation, monocyte chemotactic responsiveness, and "natural killer" cytotoxicity) of normal hamsters and hamsters with human osteosarcoma (OS) were investigated. Human osteosarcoma was induced in newborn inbred hamsters (LHX/SsLAK) after induction of tolerance in utero. In vitro, ISO increased Con A-induced proliferation of peripheral blood lymphocytes (PBL) from normal hamsters by 23.4-48.9% and from OS-bearing hamsters by 58.1-107.4% over controls (Con A alone). When ISO was administered in vivo by intraperitoneal injection. Con A-induced proliferation of PBL from both normal and OS-bearing recipients in vitro was increased by 50-55% at 1, 3 and 5 days after injection. The chemotactic responsiveness of monocytes from OS-bearing hamsters was also significantly increased (59.1-97.4%) at 1, 3 and 5 days after injection of ISO. Natural killer cytotoxicity was augmented at 1, 3 and 5 days after injection of ISO by 31.7-83.6% in normal hamsters and 54.6-184% in OS-bearing hamsters. These results indicate that ISO can produce a generalized enhancement of immune function in hamsters with OS.

Plaque inhibition assay for drug susceptibility testing of influenza viruses

The relative antiviral activities of four drugs against contemporary strains of influenza A and B viruses were determined in Madin-Darby canine kidney cell monolayers with a plaque inhibition assay. This assay proved to be a reliable, rapid method of determining 50% inhibitory concentrations that correlated well with clinically achievable drug levels and the results of clinical trials. Contemporary strains of influenza A viruses (subtypes H1N1, H3N2, HSW1N1) required amantadine hydrochloride and rimantadine hydrochloride 50% inhibitory concentrations in the range of 0.2 to 0.4 microgram/ml, whereas 50% inhibitory concentrations ranged from approximately 50 to 100 micrograms/ml against influenza B viruses. Ribavirin was approximately 10-fold less active than amantadine hydrochloride against influenza A viruses, and the ribavirin 50% inhibitory concentrations against both influenza A and B viruses ranged from 2.6 to 6.8 micrograms/ml. Inosiplex had no antiviral activity in this test system.