Cystamine potently suppresses in vitro HIV replication in acutely and chronically infected human cells.

We have investigated the effects of cystamine on the replication of human immunodeficiency virus (HIV) in human lymphocytes and macrophages, the natural targets of HIV in vivo. Treatment of chronically infected macrophages with cystamine, at a concentration (500 microM) that did not show any cytotoxic or cytostatic effects, strongly decreased (> 80%) HIV-p24 antigen production and completely abolished the production of infectious viral particles. Cystamine does not affect viral transcription, translation or protein processing; indeed, all HIV proteins are present in a pattern similar to that of nontreated cells. Instead, cystamine interferes with the orderly assembly of HIV virions, as shown by electron microscopy analysis, that reveals only defective viral particles in treated cells. Moreover, suppression of HIV replication, due to the inhibition of proviral DNA formation was observed in acutely infected lymphocytes and macrophages pretreated with cystamine. These results show that cystamine potently suppresses HIV replication in human cells by contemporaneously blocking at least two independent steps of the viral life cycle, without affecting cell viability, suggesting that this compound may represent a new possibility towards the treatment of HIV-1 infection.

Selective inhibition of HIV replication by adriamycin in macrophages but not in lymphocytes.

Adriamycin (ADR) is an anticancer drug commonly used in the treatment of HIV-related cancers. Due to its effect on DNA metabolism, ADR might be able to modulate HIV replication in monocyte-macrophages (M/M), resting cells potentially less sensitive to the toxic effect of this drug. Thus, we assessed the efficacy of ADR against HIV replication in both lymphocytes and M/M. We further investigated the mechanism(s) of action of ADR and its potential synergistic activity with zidovudine (AZT) or alpha-interferon (IFN alpha). ADR consistently inhibited viral replication in M/M: 50% viral inhibition was obtained with 0.005 micrograms/ml ADR, while greater 90% viral inhibition was obtained with 0.05 micrograms/ml ADR. No cell toxicity was seen in M/M at concentrations up to 0.5 micrograms/ml. No anti-HIV activity was shown by ADR in lymphocytes at concentrations up to 0.05 micrograms/ml, that is also the toxic dose 50% (TCID50 for these cells). ADR neither inactivates HIV virions nor affects HIV binding with CD4 receptors. No inhibition of HIV reverse transcriptase by ADR was found at concentrations at least 2,000-fold greater than the 50% HIV inhibitory concentration in M/M. Molecular analysis by polymerase chain reaction (PCR) suggests that ADR substantially affects virus DNA production at concentrations that inhibit viral replication. Finally, late stages of HIV replication were not affected by ADR. At least additive effects of the association ADR + AZT and ADR + IFN alpha were obtained against de novo HIV infection of M/M.(ABSTRACT TRUNCATED AT 250 WORDS)

Low concentrations of suramin can reduce in vitro infection of human cord blood lymphocytes with HTLV-I during long-term culture.

In vitro infection of human cord blood lymphocytes (CBL) with human T-cell leukemia/lymphoma virus type I (HTLV-I) was found to be reduced by suramin treatment at a concentration ranging from 10-100 micrograms/ml. At higher concentrations (500 micrograms/ml) suramin was toxic to the cells and even resulted in an increased percentage of cells positive for the p19 viral core protein. Suramin treatment at the onset of the CBL coculture with a lethally irradiated HTLV-I donor cell line (MT-2) reduced virus transmission, evaluated as number of p19+ cells, and the consequent amount of integrated provirus in the host genome. The amount of viral RNA transcripts was not reduced in CBL cocultures. On the other hand, suramin affected HTLV-I replication in infected MT-2 cells, when used at a concentration of 50 micrograms/ml, and this might contribute to the reduced infectivity of suramin-treated MT-2 cells. In addition to its antiviral effects, suramin exerted a modest positive regulation on the natural killing activity of CBL and their early proliferative response in mixed lymphocyte/tumor cell culture.

Modulation of the cell-mediated immune function by interferon alpha, beta or gamma can partially reverse the immunosuppression induced by human T-cell leukemia virus I in human cord blood cultures.

Infection with human T-cell leukemia virus type I (HTLV-I) is associated in vitro and in vivo with a remarkable depression of cell-mediated immune functions. In the present report it is shown that early events following virus-induced suppression of the cell-mediated immune response of freshly isolated cord blood mononuclear cells (CBL) infected with HTLV-I can be partially counteracted by treatment with interferons alpha, beta or gamma (IFN). All three types of IFN exerted a protective effect on CBL cultures exposed to the virus. This resulted in: (a) a reduced number of virus-positive cells until 4 weeks of culture; (b) delay in the clonal expansion of infected cells (IFN alpha and gamma); (c) increased natural killer cell activity of CBL, 1 week post-infection (p.i.), mediated by IFN gamma; (d) increase of allospecific recognition of infecting and priming HTLV-I donor MT-2 cells by CBL in a cytotoxic-T-lymphocyte-like response, mediated by IFN and particularly by IFN gamma; (e) phenotype distribution of CBL subpopulations, tested 4 days p.i., more similar to that of non-infected CBL cultures. In contrast, the overall CBL proliferation, that is profoundly depressed during the first week p.i., was not restored by IFN treatments, suggesting that boosting of the cell-mediated killing induced by IFN might involve the maturation of undifferentiated precursor cells rather than stimulation of their proliferation. The improvement of the efficiency of the antiviral immune response induced by treatment with IFN is likely to contribute to the clearance of virus-positive cells during the early phase of infection. This would provide experimental evidence to support an immunopharmacological approach contributing to the conversion of HTLV-I carriers from positive to negative.

Immunopotentiation of anticancer chemotherapy by Candida albicans, other yeasts and insoluble glucan in an experimental lymphoma model.

Several yeast species in the genera Candida, Saccharomyces and Cryptococcus showed powerful immunoadjuvant, chemotherapy-synergic effects against a histocompatible, virus-induced murine lymphoma. Sensitizing and booster intraperitoneal injections of 2 x 10(7) yeast cells on days -14 and +1 (with respect to tumor challenge on day 0) followed by treatment with antiblastic drugs (on day +5) were required to elicit optimum activity. The antitumor effect was not markedly influenced by the morphological growth form of merthiolate-inactivated C. albicans nor by the nature of the carbon source in the growth medium, except for C. albicans cells grown in a medium containing stearic acid, which were not effective. These cells had a higher ratio of soluble to insoluble cell wall components, as compared to glucose-grown cells, but this finding alone could hardly explain the lack of antitumor effects. Previous observations, suggesting that the alkali-acid insoluble beta-glucan (in the form of cell wall ghosts) is the only component of yeast cell walls endowed with antitumor activity comparable to that of whole cells, were confirmed and extended; the soluble mannan and glucan-protein fractions were unable to replace whole cells and glucan ghosts even as sensitizers or as boosting agents.

Suppression of Friend leukemia cell-induced tumours by cellular preparations of Candida albicans.

Inactivated cellular preparations and cell wall materials of Candida albicans (CA) were tested for their capacity to suppress the growth of Friend Leukemia Cell (FLC)-induced tumours and the infection by Friend Leukemia Virus (FLV) in histocompatible mice. Factors affecting the inhibition of tumor growth by CA cellular preparations were: i) the schedule of agent administration; ii) the method of cell inactivation; iii) the FLC load. In particular, mice given 10(7) yeast cells, inactivated by cold alkali, on days -14 and +1 with respect to 10(4) FLC challenge on day 0 did not develop tumors. A crude cell wall fraction derived from cells extracted with hot alkali was still effective in reducing (but not suppressing) tumour growth whereas a purified, particulate glucan fraction (glucan "ghosts", essentially consisting of beta 1,3-1,6 glucan) was ineffective. No cellular preparation or cell wall fraction exerted anti-FLV effects (as shown by splenomegaly measurements) nor did any CA material induce interferon-like activity in the serum of animals injected with either FLC or FLV. Therefore, the observed antitumor activity by CA was not mediated by antiviral effects but possibly due to an "adjuvant-type", nonspecific, immunopotentiation of host antitumor response, as documented in other animal tumor models.

Inhibition of the protease of human immunodeficiency virus blocks replication and infectivity of the virus in chronically infected macrophages.

Because of the importance of monocytes/macrophages (M/M) as an in vivo reservoir of human immunodeficiency virus (HIV), a study was done to investigate whether viral replication in chronically infected macrophages (HIV M/M) could be inhibited by various drugs, including U-75875, an inhibitor of HIV protease. HIV replication in M/M and in chronically infected T cells was dramatically decreased by U-75875, while other drugs, including zidovudine, interferon-alpha, and an antisense oligodeoxynucleotide against the rev gene, were effective antiviral agents only in de novo-infected cells. Virus titer in HIV M/M was reduced approximately 10(5)-fold by nontoxic concentrations of U-75875, while no effect on HIV DNA or virus antigen expression on cell membrane was achieved in M/M infected either chronically or de novo. Thus, U-75875 essentially worked against late stages of viral replication. These data support the use of protease inhibitors, alone or in combination, in the therapy of HIV-infected patients.

Macrophage colony-stimulating factor enhances the susceptibility of macrophages to infection by human immunodeficiency virus and reduces the activity of compounds that inhibit virus binding.

The effects of macrophage colony-stimulating factor (M-CSF) on CD4 receptor expression, susceptibility to human immunodeficiency virus type 1 (HIV) infection, and anti-HIV activity of dextran sulfate and soluble-CD4 were studied in cultured, human primary macrophages. M-CSF stimulated macrophage cells to express the CD4 receptor, and this resulted in an increase of both the number of CD4+ cells and the density of the receptor on the cell surface. M-CSF also significantly enhanced the susceptibility of macrophage cells to HIV infection. Interestingly, the anti-HIV activity of dextran sulfate and soluble-CD4 (two compounds that interfere with HIV-CD4 binding with different mechanisms) was reduced 100-fold and fivefold, respectively, in M-CSF-treated macrophages. Human blood concentrations of M-CSF are reported to be similar to those used in this work (1,000 U/mL); thus, it is conceivable that also in vivo this cytokine may modify the susceptibility of macrophages to HIV and the ability of dextran sulfate and soluble CD4 to inhibit HIV replication. These results suggest that the in vitro study in M-CSF-treated macrophages of promising drugs inhibitors of HIV-CD4 binding could provide further insights into the potential efficacy of these compounds in patients.