RNA-Directed DNA Polymerase and Virus-Induced Leukemia in Mice

Abstract

Rifamycin antibiotics, which inhibit RNAdirected DNA polymerase of Rauscher leuckemia virus, prevent the leukemogenic activity of the virus, and the effect of leukemogenesis correlates with the magnitude of inhibition of the purified enzyme. This inhibition of enzyme activity by rifamycin SV derivatives is due to a relatively tight binding between the enzymes and the inhibitors, yet the binding can be reversed by nonionic detergent. The results of this study suggest that RNAdirected DNA polymerase is essential for induction of leukemia by exogenous virus and correlate with the previous observation that the same derivatives block viral transformation in vitro.Leukemia can be induced in mice by inoculation with RNA leukoviruses, such as Rauscher leukemia virus (RLV) (1), These viruses contain RNA-directed DNA polymerase (2, 3). Some recent experiments have indicated that this enzyme is necessary for successful transformation of normal cells in culture (4-6). However, evidence of involvement of this enzyme in leukemic formation in animals is lacking.Hanafusa and Hanafusa (4) and Hanafusa et al. (5) reported that noninfectious RSV a (0) particles produced from a-type transformed cells did not contain RNA-directed DNA polymerase. To further demonstrate a relationship between RNA-directed DNA polymerase and infectivity, they showed that an infectious pseudotype RLV a (ALV) can be rescued by superinfection of the a-type transformed cells with avian leukosis virus (ALV) and the cells then transformed by RSV a (ALV) produced only RSV a (0) (4). Using different classes of rifamycin SV derivatives (with respect to potency of inhibition of activity of RNA-directed DNA polymerase), we reported that there is a direct correlation of inhibition of viral RNA-directed DNA polymerase and inhibition of focus formation by murine sarcoma virus (MSV) as well as infectivity by RLV (6). This experiment was performed by preincubation of the inhibitors with virus particles at 37°for 30 min in order to prevent cytotoxicity in culture (6, 7). These findings suggested that RNA-directed DNA polymerase was essential to viral transformation in culture. It is of interest, then, to extend these observations to an animal system; leukemia induced by RLV in mice was used. Splenomegaly is a useful index for a quantitative measurement of the development of leukemia in this system (8). Therefore, the degree of splenomegaly was used to measure the inhibitory effect of rifamycin SV derivatives on murine leukemogenesis. The result suggests that RNA-directed DNA polymerase is required for development of virus-induced leukemia. METHODS AND MATERIALSVirus and Animal System. 4-to 6-week-old NIH Swiss Mice of either sex were used. RLV from plasma and tissue culture were obtained through the Special Virus Cancer Program from Hazelton Laboratory (Vienna, Va.) and Electro-Nucleonics, Incorp. (Bethesda, Md.), respectively. Only one stock of plasma viruses (about 5 X 105 PFU/ml) was used for all of the animal experiments. The virus suspension was diluted wi...

Antivirion Effects of Streptovaricin Complex Against Friend Virus

“…The totality of these studies have suggested that SvCx inhibits an event(s) directly associated with the action of oncogenic viruses rather than with the proliferation of neoplastic cells (5). An inhibition might result from the direct interaction of streptovaricin with the virion, resulting in blockage of the virion-associated reverse transcriptase present in leukemogenic viruses, as has been postulated by Wu et al with other ansamycin compounds (16).…”

Activity of Pure Streptovaricins and Fractionated Streptovaricin Complex Against Friend Virus

“…More recently, SvCx has shown potent, and surprisingly selective, activity against functions of oncornaviruses both in cell culture (6) and mice (2). The mechanism of action of SvCx is not firmly understood, but it may be related to the known ability of SvCx to block the ribonucleic acid-dependent deoxyribonucleic acid polymerase present in ribonucleic acid tumor viruses (3,5,12,14); it is clear that blockade of bacterial and bacteriophage function is mediated at the level of polymerase function (4).…”

Differential Susceptibility of Spleen Focus-Forming Virus and Murine Leukemia Viruses to Ansamycin Antibiotics

“…Specific antiviral effects of ansamycins have been demonstrated on several different levels of biological organization, such as inhibition ofreverse transcriptase (6,10,11,19), activity apparently directed against the virus particle itself (13,14,28), inhibition of murine and avian sarcoma virus production and transformation in cell culture (3,8,16,20,27), reduction of splenomegaly in Rauscher disease in vivo (4,5), and cytotoxic activity against human leukemic blasts (22). The mechanism of action of these drugs on RNA tumor virus functions is not firmly understood, but in several instances it has been correlated apparently with an ability to inhibit the RNA-dependent deoxyribonucleic acid polymerase (6,10,11,18,19,28). It has, however, never been determined whether the replicationdefective transforming particles or the accompanying helper viruses are the primary drug targets.…”

“…Two compounds are derivatives of rifamycin SV, well characterized as to their potent inhibition of reverse transcriptase and activity against Rauscher virus-induced splenomegaly (25,28): compound no. 120, 2,6-dimethyl benzyl 4-demethyl rifampin ( (Fig.…”