Selective killing of human T cell lymphotropic virus type I-transformed cell lines by a damavaricin Fc derivative.

n-Pentyl ether of damavaricin Fc (n-pentyl DvFc) preferentially killed human T-cell lymphotropic virus type I (HTLV-I)-transformed cell lines. The mechanism of action of the drug was investigated using MT-4 cells. Cytotoxic action was diminished by the removal of n-pentyl DvFc from the culture or by the addition of sulfhydryl compounds such as 2-mercaptoethanol and dithiothreitol. The killing activity of n-pentyl DvFc was also diminished by membrane-acting agents including quinidine and diphenylhydantoin. Influx and subsequent efflux of Ca2+ were observed when either HTLV-I infected (MT-4 cells) or uninfected cells were treated with n-pentyl DvFc. An efflux of K+ was observed in HTLV-I infected MT-4 cells immediately after the exposure of the cells to n-pentyl DvFc. The K+ efflux, however, was not observed in the uninfected T cells. n-Pentyl DvFc seems to act primarily on the cell surface of MT-4 cells, leading to the perturbation of membrane function. The restoration of cell growth, however, is critically dependent on the presence of dithiothreitol and 2-mercaptoethanol, implying a role for a free sulfhydryl group in the killing activity.

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.

Immunosuppressant activity of the ansamycins.

The immunosuppressive effect of four analogues of rifampin and two streptovaracins on cell-mediated immunity has been determined. Tuberculin hypersensitivity in the footpads of immunized mice was inhibited by three of the rifampin analogues and by both streptovaracins. The observed in vivo immunosuppressive activity of the compounds tested was not correlated with their in vitro activity against mycobacterial growth but was associated with their toxicity in mice. These data indicate that some of the analogues of rifampin and the streptovaracins can significantly suppress cell-mediated immunity and suggest that other ansamycins may have significant immunosuppressant activity.

Inhibition by streptovaricins of Rauscher leukemia virus splenomegaly.

Streptovaricins (Sv), ansa macrolide antibiotics, inhibited Rauscher leukemia virus (RLV) splenomegaly by 25-50%. All streptovaricins tested were effective when administered orally either by diet ad lib or by intubation from infection to time of killing. When delivered by intubation, Sv was measurable in plasma for up to 6 h. SvC, at 300 mg/kg/day, reduced mean spleen weight of infected mice from 478 plus or minus 51 (SE) mg to 300 plus or minus 55 (SE) mg. Rifampicin, at 250 mg/kg/day, had no similar activity. Decrease in caloric intake and in body-weight gain also resulted in an inhibition of RLV splenomegaly; although Sv-treated mice gained weight, the increase was usually slightly less than controls. However, mice treated with a Sv diet for a week prior to infection, after an initial period of weight loss, gained at a rate equivalent to control group, and when killed had a marked reduction in splenomegaly. The selectivity of streptovaricins and specificity for viral events was suggested by several observations: (1) Splenomegaly and mortality, induced by L1210 or a non-infective transplantable tumor of RLV origin, was not inhibited. (2) No inhibition of normal hematopoietic spleen colonies was observed. (3) Host immune responses, including cellular and humoral immunity and interferon production and action, were not inhibited. Thus, although the effect of slightly decreased weight and intake could not be unequivocally established, the findings were most compatible with a selective inhibition of RLV splenomegaly by Sv.

Chemotherapeutic studies of mycobacterial infections in mice.

Of six antibiotics investigated, streptovaricin C had the most marked chemotherapeutic effect on Mycobacterium kansasii infections in mice. By the intraperitoneal route this antibiotic caused elimination of the pathogens from all organs. Kanamycin eliminated the pathogens from the lungs of all animals and from the spleens and livers of most of them. Bluensomycin also removed the pathogens from the lungs of all animals, and spectinomycin and lincomycin, from the lungs of the majority of the animals. The three latter antibiotics lowered the bacterial counts in liver and spleen. Streptovaricin C also decreased the bacterial counts in brain, spleen, and liver of mice inoculated intracerebrally with M. kansasii. In one experiment it completely eliminated this pathogen from the spleen and almost completely from the liver. The effect of streptovaricin C on the cerebral infection was more marked than that of streptovaricin complex. Respiratory and cerebral infections of mice with M. avium, serotypes I and II, were limited by streptovaricin C, and marked decreases of the bacterial counts in brain, lungs, spleen, and liver were observed.