Autogenous immunity to endogenous RNA tumor virus. Identification of antibody reactivity to select viral antigens.

The viral antigenic determinants recognized in an autogenous immune response in mice against their endogenous C-type virus have been identified by SDS-polyacrylamide gel electrophoresis of immune precipitates between various sera and H(3)-labeled intact or disrupted AKR leukemia virus. Normal B6C3F(1) [(C57BL/6 x C3H/Anf)F(1)] serum reacts with viral envelope antigens having mol wt of approximately 68,000, 43,000, and 17,000. In addition, minor reactions with viral antigens having mol wts of approximately 19,000 and 15,000 are demonstrable. The 68,000 and 43,000 mol wt antigens can be labeled with [(3)H]glucosamine and may correspond to the major viral envelope antigens M(2) and M(1), respectively. The antigens recognized by autogenous immune sera do not differ with respect to age of the animal, nor are they significantly different in sera from various strains of mice (BALB/c, C57BL/6, and C3H/Anf). These results suggest that the age-asociated and strain variations in the autogenous immune response, as determined by radioimmune precipitation assays against intact virus, are due to quantitative and qualitative alterations of antibody levels against common antigens.

Effects of streptovaricins and their degradation products on infectivity of Rauscher leukemia virus.

The virucidal effects of streptovaricin (Sv) A, SvC, SvD, streptoval (Sval) C, Sval Fc, and streptovarone were evaluated by incubation of the drug with Rauscher leukemia virus (RLV) at 37 degrees C for 60 minutes prior to dillution and addition to cells (in vitro assay) or before ip injection into animals (in vivo assay). The in vitro and in vivo assays were plaque formation and splenomegaly, respectively. A dose-related effect was observed with all six compounds with the in vitro assay. On an equimolar basis, the Sv degradation products, i.e., Sval C, Sval Fc, and streptovarone were most inhibitory, followed by SvD; SvA and SvC were least active. At 0.0625 mumoles, the three Sv degradation products inactivated over 90% of the RLV. Similar results were obtained through the in vivo assay. At 0.06 mumoles, streptovarone, Sval C, and SvD showed 78,62, and 29% inhibition of splenomegaly, respectively; SvA and SvC were essentially inactive. A direct relationship was observed between inhibition on RNA-directed DNA polymrase of RLV by these compounds and their virucidal effects. No drug given at the time of injection, however, showed any significant effect on virus infective processes in vitro or in vivo. The reason for the lack of therapeutic effects of these compounds is discussed.

Stimulation of Rauscher leukemia virus DNA polymerase DNA-directed DNA synthesis by cationic trypanocides and polyamines.

Activated DNA-directed DNA synthesis catalyzed by Rauscher leukemia virus (RLV) and other type C mammalian retroviral DNA polymerases is uniquely stimulated by biologically active polyamines. Cationic trypanocides may act as antagonists of polyamine function. As described here, several cationic trypanocides stimulate RLV polymerase-catalyzed DNA-directed DNA synthesis at concentrations significantly inhibiting eukaryotic DNA polymerases. Such stimulation is negated by polyamines. Kinetic analysis of the stimulation of RLV DNA polymerase by three structurally dissimilar cationic trypanocides (Antrycide, Burroughs-Wellcome Compound 64A, and Bayer Compound 1694) suggests that such stimulation is, in part, due to a drug:DNA structural interaction resembling the polyamine:DNA structural complex recognized by the RLV DNA polymerase.

Thymic hormone modulation of leukemogenic virus replication.

The effect of purified calf thymus extract, thymosin, on infection with murine leukemia virus (MuLV) (Rauscher) was studied in adult thymectomized BALB/c mice. The course of infection was determined by virus titer in the blood plasma, by enumeration of spleen cells replicating MuLV (i.e., infectious centers), and by the examination of cells for expression of virus-induced cell membrane antigen. Thymectomy (performed 1 week prior to the virus injection) decreased MuLV infection by all three parameters. However, administration of thymosin (500 mug, given in equal doses 2 days before and at the time of injection of virus) caused a marked increase of plasma titer of virus, as well as an increased number of spleen cells generating MuLV as compared to controls treated either with purified spleen fraction or with diluent (buffered salt solution). More than two doses of thymic extract (up to nine, given every 2 days after infection) had no further effect on plasma virus titer or number of splenic infectious centers. Furthermore, treatment of mice with either thymic or splenic extracts increased the incidence of virus related membrane antigen appearing on the surface of spleen cells, as compared to diluent-treated control animals. These results indicate that thymosin may enhance infection by or replication of murine oncornaviruses.

Effects of hydroxyurea on murine type C virus-specific DNA synthesis in newly infected cells.

Cell transformation and replication of the Rauscher pseudotype of Moloney murine sarcoma virus in mouse embryo fibroblasts were inhibited by hydroxyurea within a critical time period of 30 to 90 min postinfection. In cells infected by Rauscher leukemia virus, treatment with 1mM hydroxyurea during the critical time period resulted in the accumulation of minus-strand DNA (molecular weight, 3 x 10(6)) in association with the parental viral genoma RNA. This 5 to 6 x 10(6) dalton RNA:DNA hybrid was found in the cytoplasm. Positive-strand DNA of genomic or smaller size was not detected in the presence of hydroxyurea, but virus-specific DNA was found in the nucleus 30 min after removal of drug.

Interferon-alpha and 3'-azido-3'-deoxythymidine are highly synergistic in mice and prevent viremia after acute retrovirus exposure.

This study was undertaken to calculate the in vivo drug interactions between recombinant human interferon-alpha A/D (rHuIFN-alpha A/D) and 3'-azido-3'-deoxythymidine (AZT) in a quantitative model for retroviral viremia. When given as single agents, both AZT and rHuIFN-alpha A/D suppressed virus-induced splenomegaly in a dose-dependent fashion in mice inoculated with Rauscher murine leukemia virus (RLV). However, suppressive doses of single-agent AZT caused anemia after 20 days of therapy. Combining rHuIFN-alpha A/D with AZT allowed drastic dose reductions for each agent while maintaining greater than or equal to 93% inhibition of splenomegaly. No clinically significant toxicity was seen. Computer analysis with the isobologram technique and combination index method showed that these combination regimens were highly synergistic. A 20-day course of AZT + rHuIFN-alpha A/D started 4 h after virus exposure was protective against RLV viremia and disease. After cessation of therapy, the animals were resistant to rechallenge with fully infectious RLV. We conclude that prompt initiation of effective combination therapy after retroviral exposure prevented viremia and disease and led to protective immunity.

In vivo analysis of castanospermine, a candidate antiretroviral agent.

Castanospermine (1,6,7,8-tetrahydroxyoctahydroindolizine), an inhibitor of glycoprotein processing, has been shown to inhibit the human immunodeficiency virus type 1 (HIV-1) with acceptable toxicity in cultured cells. In contrast to reverse transcriptase inhibitors, castanospermine targets host enzymes. We have analyzed castanospermine in murine systems, using cultured cells as well as live animals. Plaque formation by Rauscher murine leukemia virus (RLV) was inhibited with a median inhibitory concentration (IC50) of 2 micrograms/ml. RLV-exposed BALB/c mice treated with a 20 day course of castanospermine starting 4 h postinoculation showed a dose-dependent inhibition of splenomegaly. Oral castanospermine therapy given to chronically RLV-infected mice prolonged median survival from 36 to 94 days when compared to untreated controls (p = 0.007). Castanospermine was better tolerated orally than intraperitoneally at the same dose. Toxic effects included weight loss, lethargy, and dose-dependent thrombocytopenia. At the highest intraperitoneal dose, lymphoid depletion occurred in thymus, spleen, and lymph nodes. We conclude that castanospermine is an active antiviral agent in animals and that prolonged oral administration is tolerable; however, when compared to 3'-azido-3'-deoxythymidine in the same murine system, castanospermine was less active and more toxic.

Castanospermine vs. its 6-O-butanoyl analog: a comparison of toxicity and antiviral activity in vitro and in vivo.

Inhibitors of glycoprotein processing, such as castanospermine (1,6,7,8-tetrahydroxyoctahydroindolizine), have been shown previously to inhibit human immunodeficiency virus type 1 (HIV-1) with acceptable toxicity in cultured human cells. In prior experiments, we have tested the toxicity and antiviral efficacy of castanospermine in mice infected with the Rauscher murine leukemia virus (RLV). When compared with 3'-azido-3'-deoxythymidine (AZT, zidovudine), castanospermine was less effective and more toxic. Since the 6-O-butanoyl analog of castanospermine was previously found to have a more favorable activity profile than the parent compound against HIV-1 in cultured cells, we compared the antiviral efficacy of both compounds in parallel in vitro and in vivo in the RLV system. Plaque formation in the XC assay was inhibited with a 50% inhibitory concentration (IC50) of 2.4 microM for the 6-O-butanoyl analog of castanospermine, as compared to 9 microM for castanospermine. For both compounds, concentrations resulting in significant cytotoxicity were about ten times higher. Both compounds significantly decreased HIV-1 env-induced syncytium formation in a novel in vitro assay. In RLV-exposed mice, the 6-O-butanoyl analog showed no advantage over the parent compound: both curves for toxicity as well as antiviral efficacy were super-imposable. We conclude that the 6-O-butanoyl analog of castanospermine as well as castanospermine itself are active antiviral agents in mice and that prolonged oral administration is tolerable. However, in comparison to AZT, their antiviral activity profiles are less favorable.

Synthesis and antiviral activity of several 2,5'-anhydro analogues of 3'-azido-3'-deoxythymidine, 3'-azido-2',3'-dideoxyuridine, 3'-azido-2',3'-dideoxy-5-halouridines, and 3'-deoxythymidine against human immunodeficiency virus and Rauscher-murine leukemia virus.

Several 2,5'-anhydro analogues of 3'-azido-3'-deoxythymidine (AZT), 3'-azido-2'3'-dideoxyuridine (AZU), 3'-azido-2'3'-dideoxy-5-bromouridine, 3'-azido-2',3'-dideoxy-5-iodouridine, and 3'-deoxythymidine and the 3'-azido derivative of 5-methyl-2'-deoxyisocytidine have been synthesized for evaluation as potential anti-HIV (human immunodeficiency virus) agents. These 2,5'-anhydro derivatives, compounds 13-17, demonstrated significant anti-HIV-1 activity with IC50 values of 0.56, 4.95, 26.5, 27.1, and 48 microM, respectively. Compared to that of the parent compounds AZT and AZU, the respective 2,5'-anhydro analogues, compounds 13 and 14, were somewhat less active. Whereas AZT was cytotoxic with a TCID50 of 29 microM, the toxicity of the 2,5'-anhydro derivative of AZT, compound 13, was reduced considerably to a TCID50 value of greater than 100 microM. The 2,5'-anhydro analogue of 5-methyl-2'-deoxyisocytidine also demonstrated anti-HIV-1 activity with an IC50 value of 12 microM. These compounds were also evaluated against Rauscher-Murine leukemia virus (R-MuLV) in cell culture. Among them, AZT, 3'-azido-2',3'-dideoxy-5-iodouridine, 3'-azido-2',3'-dideoxy-5-bromouridine, and 2,5'-anhydro-3'-azido-3'-deoxythymidine (13) were found to be most active, with IC50 values of 0.023, 0.21, 0.23, and 0.27 microM, respectively.

Unsaturated and carbocyclic nucleoside analogues: synthesis, antitumor, and antiviral activity.

A series of unsaturated analogues of nucleosides were prepared and their cytotoxic, antitumor, and antiviral activities were investigated. Alkylation of cytosine with (E)-1,4-dichloro-2-butene gave chloro derivative 2f, which was hydrolyzed to alcohol 2h. Cytosine, adenine, 2-amino-6-chloropurine, thymine, and (Z)-1,4-chloro-2-butene gave compounds 4c-f, which, after hydrolysis, afforded alcohols 4a, 4b, 4g, and 4h. Alkenes 4d and 4e were cyclized to heterocycles 12 and 13. Alkylation of 2,6-diaminopurine with 1,4-dichloro-2-butyne led to chloro derivative 6a, which was hydrolyzed to alcohol 6b. Allenic isomerization of 6b gave compound 5c. Chloro derivatives 2e-g, 4c-f, 5d, and 6c-e as well as pyrimidine oxacyclopentenes 9c and 9d are slow-acting inhibitors of murine leukemia L1210 of IC50 10-100 microM. The most active were analogues 4c, 4d, 4e, and 6e (IC50 10-20 microM). The corresponding hydroxy derivatives were less active of inactive. Inhibition of macromolecular synthesis with compounds 4c, 4d, 6e, 9c, and 9d follows the order: DNA greater than RNA greater than or equal to protein. Cytotoxic effects of 4c, 6e, and 9d are not reversed with any of the four basic ribonucleosides or 2'-deoxyribonucleosides. Inhibitory activity of cytosine derivative 9c is reversed with uridine and 2'-deoxyuridine but not with the corresponding cytosine nucleosides. Zone assays in several tumor cell lines show that active compounds are cytotoxic agents with little selectivity for tumor cells. Analogue 6c showed 16.7% ILS in leukemia P388/o implanted ip in mice at 510 and 1020 mg/kg, respectively. Cytallene (5b) and 6'beta-hydroxyaristeromycin (10) exhibited significant activity against Friend and Rauscher murine leukemia viruses. The rest of the hydroxy derivatives, with the exception of 4a, were moderately effective or inactive as antiviral agents. None of the chloro derivatives or oxacyclopentenes exhibited an antiviral effect at noncytotoxic concentrations. Z-Olefin 4b and 2-aminoadenallene (5c) are substrates for adenosine deaminase.

Effects of tamoxifen, droloxifene and 17 beta-estradiol on Rauscher mouse leukemogenesis.

The effects of tamoxifen (TAM), its 3-hydroxy congener droloxifene (DROL) and 17 beta-estradiol were investigated on leukemogenesis induced in BALB/c mice by Rauscher murine leukemia virus (RLV). Multiple applications of each compound, in a dose-dependent manner, resulted in reduced virus titer in the serum, delayed onset of splenomegaly and significant prolongation of survival. Although 17 beta-estradiol proved most effective, prevention of disease was not achieved either by short- or long-term treatment with any of the drugs tested.

Suramin: a potent inhibitor of the reverse transcriptase of RNA tumor viruses.

Suramin--a well-known antitrypanosomal agent--was found to exert a strong inhibitory effect on the RNA-directed DNA polymerase (reverse transcriptase) activity of several oncornaviruses such as Moloney murine leukemia virus, murine Rauscher leukemia viruses, Moloney murine sarcoma virus and avian myeloblastosis virus. Inhibition of enzyme activity was obtained with both endogenous viral RNA and (A)n . oligo(dT) as the template-primer. Suramin effected a 50% inhibition of the reverse transcriptase activity of oncornaviruses at a concentration range of 0.1--1 microgram/ml. In this aspect it compared favorably to ethidium bromide, another trypanocide drug which is considered as one of the most powerful inhibitors of oncornaviral DNA polymerases. The inhibition of reverse transcriptase activity by suramin was competitive with the template-primer, (A)n . oligo(dT), suggesting that the drug may interact with the template-primer binding site of the enzyme.

Antileukemic activity of Viva-Natural, a dietary seaweed extract, on Rauscher murine leukemia in comparison with anti-HIV agents, azidothymidine, dextran sulfate and pentosan polysulfate.

An antileukemic activity of partially purified polysaccharide of an edible seaweed. Viva-Natural, against Rauscher murine retrovirus-induced erythroleukemia has been demonstrated. This antileukemic effect is compared with standard anti-human immunodeficiency virus (HIV) agents, azidothymidine (AZT), dextran sulfate and pentosan polysulfate. Pretreatment with Viva-Natural, as an immunomodulator, on day 3 prior to the virus inoculation demonstrated definite prophylactic activity, while pretreatment with the other three anti-HIV agents showed no prophylactic activity. The replication of Rauscher virus in BALB/3T3 cell cultures accompanied by direct cytopathic effect (syncytia formation) was suppressed in the presence of Viva-Natural or the other anti-HIV agents in the culture medium. In spite of the antiviral potentials of the four agents in vitro, only Viva-Natural and AZT demonstrated therapeutic efficacy against Rauscher leukemia in mice.

Differential antiviral activity of two TIBO derivatives against the human immunodeficiency and murine leukemia viruses alone and in combination with other anti-HIV agents.

R82913 and R86183, two derivatives of tetrahydroimidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)-thione (TIBO), were found to potently and selectively inhibit the replication and cell killing effects of a panel of biologically diverse laboratory and clinical strains of HIV-1. The two compounds exhibited significant activity in all human cell lines tested, as well as in fresh human peripheral blood lymphocytes and macrophages. One of these two compounds (R82913) was found to significantly inhibit the replication of a murine retrovirus (Rauscher murine leukemia virus) in both UV-XC plaque formation and virus yield reduction assays. R86183, despite differing from R82913 only in the positioning of a single chlorine molecule, was not active against the murine retrovirus but was 10-fold more potent in inhibiting HIV-1 replication. Combination antiviral assays with other reverse transcriptase inhibitors, including AZT, ddC, and carbovir, yielded synergistic anti-HIV activity with both TIBO derivatives. Additive to slightly synergistic results were obtained in combinations with ddI and phosphonoformic acid whereas additive to antagonistic activity was detected in combination with dextran sulfate.

Lead aggravates viral disease and represses the antiviral activity of interferon inducers.

Lead acetate was administered continuously in the drinking water to CD-1 male mice beginning at 4 weeks of age. An LD(10-20) of the lytic viruses or 300 plaque-forming units of RLV was inoculated intrapertioneally at 6 weeks of age. Lead increased the response of the mice to all classes of viruses against which it was tested: an RNA picornavirus-encephalomyocarditis (EMCV), a DNA herpesvirus-pseudoribies, an RNA leukemia-virus-Rauscher leukemia (RLV), an RNA arbovirus B-St. Louis encephalitis, and an RNA arbovirus A-western encephalitis. Most studies were performed between lead and EMCV. Increases in EMCV mortality in lead treated mice over controls ranged from 2x at a lead level of 0.004M to 7x (100% mortality) at a 0.1M lead level. Splenomegaly with spleens 800 to 1100 mg in weight containing high titers of RLV occurred in lead (0.03M)-treated mice 3 and 6 weeks after RLV inoculation; spleens or RLV controls were normal in weight (200 mg) and were free of virus. Lead did not reduce the protective effect of mouse interferon (IF) against the lethal action of EMCV, but it did repress the EMCV antiviral effect of poly I/poly C (PIC) and of Newcastle disease virus (NDV) against EMCV mortality. These data indicate several new facts concerning adverse effects lead may have on an animal: (1) lead aggravates viral disease, most likely in part, through reduced IF synthesis; (2) lead represses the anti-EMCV protective effects of both PIC and of NDV, which, in other reports, were shown to induce IF in radioresistant macrophages (PIC) or in radiosensitive lymphocytes (NDV); (3) lead may then be said to repress IF induction in two kinds of cells; (4) however, lead does not inhibit IF action.

In vitro and in vivo enhancement of ddI activity against Rauscher murine leukemia virus by ribavirin.

Ribavirin has been reported to enhance the activity of ddI against HIV. We explored this enhancement of antiviral activity in Rauscher murine leukemia virus (RMuLV) models in vitro and in vivo. The significant finding in these studies was that combinations of the drugs exhibited virus titer reductions that were greater than would be expected if the drug interactions were simply additive. These effects were designated synergistic by the method of Prichard and Shipman (Prichard, M.N. and Shipman, C., Jr. (1990). A three-dimensional model to analyze drug-drug interaction, Antiviral Res. 14, 181-206). In addition to the antiviral synergy, we also observed some synergistic toxicity in the animal model.

Disparate response of encephalomyocarditis virus and MM virus to interferon in JLS-V9R cells.

JLS-V9R cells, a Balb/c mouse bone marrow cell line chronically infected with Rauscher leukemia virus, were treated with mouse interferon and inoculated with several different lytic viruses. Relatively low interferon concentrations protected the cells against Sindbis virus, vesicular stomatitis virus and MM virus. In contrast, encephalomyocarditis virus replication was inhibited by less than 1 log even with an interferon concentration of 1000 U/ml. These findings provide further evidence that interferon-induced antiviral effects are mediated through multiple mechanisms and demonstrate that even viruses which are classified within the same family (MM and encephalomyocarditis virus) can exhibit differential interferon sensitivities.

Effects of SKF 108922, an HIV-1 protease inhibitor, on retrovirus replication in mice.

Rationally designed synthetic inhibitors of retroviral proteases inhibit the processing of viral polypeptides in cultures of human T lymphocytes infected with human immunodeficiency virus type 1 (HIV-1) and therefore suppress the infectivity of HIV-1 in vitro. We have previously reported the antiviral activity in vitro of HIV-1 protease inhibitors against the C-type retrovirus Rauscher murine leukemia virus (RMuLV) and the lentivirus simian immunodeficiency virus (SIV). The same compounds which blocked the infectivity of HIV-1 also inhibited the infectivity of RMuLV and SIV in vitro. This report extends these findings by testing the antiviral activity of HIV-1 protease inhibitors in vivo in the RMuLV model. RMuLV-infected mice were treated twice a day (bid) with either an active (SKF 108922) or inactive (SKF 109273) compound for fourteen days by the intraperitoneal (i.p.) route. Compared with excipient control, SKF 108922, formulated with hydroxypropyl-beta-cyclodextrin (HPB), reduced virus-induced splenomegaly, viremia, and serum reverse transcriptase (RT) levels, while SKF 109273 was inactive. The HPB vehicle by itself enhanced replication of RMuLV. The effects of changing the formulation and the route of administration were examined. SKF 108922, formulated in HPB, had similar antiviral activity when administered by the i.p. or subcutaneous (SC) routes. However, SKF 108922 administered as a colloidal suspension in cholesterol sulfate (CS) had no detectable antiviral effect. Measurements of the circulating levels of the protease inhibitor in plasma explained this result. Plasma concentrations of SKF 108922 exceeded 1000 nM within 10 min after SC administration of the compound solubilized in HPB, but SKF 108922 was not detected in plasma after SC administration of the same dose formulated with CS. Information on optimal conditions for administering these agents should prove useful in guiding their clinical application Therefore, RMuLV should provide a good model for the preclinical evaluation and development of this class of agents for the treatment of HIV.

Antiretroviral activity in a marine red alga: reverse transcriptase inhibition by an aqueous extract of Schizymenia pacifica.

An aqueous extract from the marine red alga, Schizymenia pacifica has been tested in a cell free system for its effect on reverse transcriptase from avian retrovirus (avian myeloblastosis virus), and mammalian retrovirus (Rauscher murine leukemia virus). The extract inhibited reverse transcriptase from both these retroviruses but showed almost no effect, if any, on the activity of cellular DNA polymerase alpha and RNA polymerase II in vitro. Consequently it is unlikely to have an adverse effect on the growth of cultured cell. The inhibitory activity of the extract was stable over a relatively wide pH range (pH 1-11) and was not lost after pronase digestion. Inhibitory activity of the extract was lost after boiling at 100 degrees C in 0.67 N HCl, and after treatment with 100 mM NaIO4. The active principle in the extract has an apparent molecular weight in excess of 100,000 daltons. This new reverse transcriptase inhibitor is probably a polysaccharide.

The inhibition of Rauscher leukemia virus and avian myeloblastosis virus DNA polymerases by anthracycline compounds.

Studies by other investigators have shown that adriamycin and daunorubicin exhibit antitumor and antiviral activity. A possible antiviral mechanism for the anthracycline compounds is the potent inhibition of viral DNA polymerases. Five anthracycline compounds were tested against purified Rauscher leukemia virus and avian myeloblastosis virus DNA polymerases. All compounds were found to be potent inhibitors of viral DNA polymerase activity. Inhibition was found to be primarily due to the planar ring structure (daunomycinone) common to all of these compounds. The degree of inhibition was dependent on the templates used: activated DNA, synthetic hybrids, poly(rA).dT12-18 and poly(rC).dG12-18, and the synthetic copolymer, poly(DA-dT). Alteration of the group substituent on the planar ring affected the degree of viral DNA polymerase inhibition. The inhibitory effects by anthracycline compounds appear to be relatively specific for viral polymerases.