3-Cyclic amine derivatives of rifamycin: strong inhibitors of the DNA polymerase activity of RNA tumor viruses

Rifapentine is an entry and replication inhibitor against yellow fever virus both in vitro and in vivo

Yellow fever virus (YFV) infection is a major public concern that threatens a large population in South America and Africa. No specific anti-YFV drugs are available till now. Here, we report that rifapentine is a potent YFV inhibitor in various cell lines by high-throughput drugs screening, acting at both cell entry and replication steps. Kinetic test and binding assay suggest that rifapentine interferes the viral attachment to the target cells. The application of YFV replicon and surface plasmon resonance assay indicates that rifapentine suppresses viral replication by binding to the RNA-dependent RNA polymerase (RdRp) domain of viral nonstructural protein NS5. Further molecular docking suggests that it might interact with the active centre of RdRp. Rifapentine significantly improves the survival rate, alleviates clinical signs, and reduces virus load and injury in targeted organs both in YFV-infected type I interferon receptor knockout A129^−/− and wild-type C57 mice. The antiviral effect in vivo is robust during both prophylactic intervention and therapeutic treatment, and the activity is superior to sofosbuvir, a previously reported YFV inhibitor in mice. Our data show that rifapentine may serve as an effective anti-YFV agent, providing promising prospects in the development of YFV pharmacotherapy.

Curing viruses in Pleurotus ostreatus by growth on a limited nutrient medium containing cAMP and rifamycin

Oyster mushroom spherical virus (OMSV) and oyster mushroom isometric virus (OMIV) are the causative agents of a fruiting body deformation disease in the edible mushroom Pleurotus ostreatus. The curing of these mycoviruses was facilitated by a serial transfer of infected mycelia onto a limited nutrient medium containing 1mM of cAMP and 75 μg/ml of rifamycin (cAMP-rifamycin plate). The mycelia were grown on cAMP-rifamycin plates for 5 successive passages. ELISA and RT-PCR showed that the amount of mycoviruses inside the mycelia decreased significantly with increasing numbers of passages. The mycelia became free of viruses after 5 successive passages. Cultivation of the virus-cured mycelia on a mushroom compost medium produced a normal harvest, whereas the spawn infected with viruses failed to produce any fruiting bodies.

Study of ansamycin inhibition of a ribonucleic acid-directed deoxyribonucleic acid polymerase by an immobilized template assay

A series of structurally related ansamycins have been analyzed, in a new immobilized template assay, to determine the mechanism by which they inhibit a ribonucleic acid-directed deoxyribonucleic acid (DNA) polymerase from Moloney murine leukemia virus. By this assay, we can better correlate specific structures of these drugs with inhibitory mechanisms. Using an immobilized template, we were also able to observe drug effects on the stability of complexes formed between the polymerase, a template (polyadenylic acid-agarose), and a primer, as well as to monitor the synthesis of DNA in the presence of drug. For each drug, we determined the complex (intermediate in DNA synthesis) which was primarily affected and whether the effect was due to a destabilization process. Although the activity and specificity of the unsubstituted ansamycins (streptovaricins and rifamycin SV) were modulated by conformation of the molecule and electron density of the aromatic ring, the principal mode of inhibition is, apparently, drug binding to a polymerase-template complex; the drug binds in a manner which prevents subsequent formation of a polymerase-template-primer complex. However, some derivatives of rifamycin SV, when substituted at carbon-3 with bulky or hydrophobic side chains, displayed markedly different modes of action. For example, demethyl dimethyl rifampin prevented the formation of polymerase-template complexes, whereas rifazacyclo 16 acted by promoting the dissociation of polymerase-template-primer complexes.

Differential susceptibility of spleen focus-forming virus and murine leukemia viruses to ansamycin antibiotics

The streptovaricin complex (SvCx) and rifamycin SV derivatives display potent antiviral activity against the polycythemic strain of Friend leukemia virus (FV-P), as measured by a reduction in the number of spleen foci produced in mice. Such reductions may be explained by inactivation of functions of (i) the spleen focus-forming virus (SFFV), (ii) its "helper" murine leukemia virus (MuLV), or (iii) both viruses normally present in FV-P. We noted that preincubation of FV-P with fractionation products of SvCx, or derivatives of rifamycin SV, at low concentrations (3 to 5 mug/ml) reduces the number of spleen foci 80 to 97%, whereas titers of MuLV (from the same inoculum) remain unaffected (MuLV titers were measured by XC, S(+)L(-), and "helper activity" assays). Our findings indicate a remarkable biological selectivity of ansamycins, as well as nonansamycin components of SvCx, against the transforming and defective spleen focus-forming virus as compared to MuLV. Thus, the drugs might be useful in distinguishing other types of oncornaviruses.

Interruption of oncornavirus replication by modified rifamycin antibiotics

Thirteen rifamycin SV derivatives containing 3'-alkylaminomethyl substituents fail to inhibit the activities of the simian sarcoma virus Type 1 DNA polymerase, and of cellular DNA, RNA, and poly(A) polymerases prepared from NIH Swiss mouse embryos. These compounds show a range in their toxicities for NIH Swiss mouse 3T3 cells and in their capacities to inhibit production of foci of morphologically altered cells by murine sarcoma virus (MSV). Three compounds--the N-methyl-N-hydroxyethylaminomethyl, the N,N-dimethyl-aminomethyl, and the N4-methylpiperazinomethyl rifamycin derivatives--are comparable to adenine arabinoside and ribavirin in their toxicity for 3T3 cells, but these compounds show superior focus inhibition. These compounds inhibit oncornavirus production apparently by exacerbation of a delay in growth that results from infection of 3T3 cells with MSV.

DNA-polymerase inhibitors. Rifamycin derivatives

Ten new derivatives of the antibiotic rifamycin with variable side chains at position 3 were synthesized. The inhibitory activity of these derivatives against DNA-polymerases isolated from avian myeloblastosis virus, E. coli and calf thymus were studied at various conditions. 3-(2,4,6-trinitrophenylhydrazone-(methyl) rifamycin SV is a strong inhibitor for all the polymerases tested and belongs to the C class inhibitors of reverse transcriptase. 3-(monoallylhydrazone-(methyl) rifamycin SV possesses a selective action on polymerases: at 0.1 mg/ml concentration it almost completely inhibits the reverse transcriptase and less than half of the bacterial and eukaryotic enzymes. A drug is found which strongly inhibits the DNA-polymerases from E. coli and calf thymus and weakly the viral enzyme. The inhibitory effect on reverse transcriptase is independent of the choice of template-primer; it could be overcome by the addition of excess enzyme but not of excess template-primer; the inhibition could be completely reversed by dilution of the drug-enzyme mixture. From Lineweaver-Burk analysis, the inhibition is noncompetitive with respect to the template-primer and, thus the drugs bind to the site different from the active site for the template-primer. From protective action of the template-primer and other data it might be suggested that the rifamycin derivatives act at an early step(s) in DNA synthesis catalyzed by reverse transcriptase. The obtained data are in agreement with the results for other derivatives of rifamycin SV described in literature.

Inhibition of infectious Rous sarcoma virus production by rifamycin derivative

A new rifamycin derivative, rifazone-82 (R-82), an inhibitor of viral RNA-dependent DNA polymerase, is selectively toxic to transformed chicken cells in culture. R-82 has now been shown to possess antiviral activity as well. The relatively nontoxic properties of R-82 to nontransformed cells have permitted the execution of experiments examining the effect of a rifamycin derivative on virus reproduction. Addition of low concentrations of R-82 (15 mug/ml) to cultures soon after Rous sarcoma virus infection prevents the spread of infection thoroughout the culture. This inhibition is not dependent on concomitant cellular transformation as identical results were obtained with cells infected with a transformation-defective Rous sarcoma virus. Addition of R-82 to cultures in which all the cells are infected does not substantially affect the yield of physical particles as measured by RNA-dependent DNA polymerase activity and by (3H) uridine incorporation into viral RNA. However, the infectivity of the progeny virus, as measured by focus-forming ability, is decrreased 95 to 99% by R-82 treatment.

Immunological and chemotherapeutic prevention and control of oncogenic viruses

Computed tomographic (CT) and surgical findings were correlated retrospectively in 51 patients with preoperative diagnoses of prolactin-secreting pituitary microadenomas. Twenty-four had microadenomas at surgery. Twenty-eight had identifiable discrete lesions. Of these, 18 had microadenomas and 10 did not; these two groups could not be distinguished reliably. Six patients with proven microadenomas had normal CT scans. Focal hypodense lesions, sellar floor erosion, infundibulum displacement, gland height greater than 8 mm, and an abnormal diaphragma sellae configuration are neither sensitive nor specific findings of microadenoma. A significant number of patients with proven microadenomas had few or none of these abnormalities. Thus, recognition of prolactin microadenoma is seldom possible by CT alone, even with high-resolution direct coronal imaging.

The specificity of dimethylbenzylrifampicin as an inhibitor of viral induced transformation

The effect of 2',6'-dimethyl-N(4')-benzyl-N(4')- [desmethyl]rifampicin on viral transformation induced by two unrelated oncogenic viruses was compared. Transformation of Balb/3T3 cells by the small, DNA-containing papova virus simian virus 40 was completely normal under conditions where transformation by the large, RNA-containing oncornavirus murine sarcoma virus was inhibited more than 150-fold. For these experiments a resistant variant of Balb/3T3 was selected that grows well in high concentrations of the drug, is not dependent on the drug for growth, and is probably not blocked at the level of drug uptake. These data show that dimethyl-benzylrifampicin specifically inhibits oncornavirus-induced transformation rather than nonspecifically inhibiting cellular growth or transformation.

Preferential inhibition of the growth of virus-transformed cells in culture by rifazone-82, a new rifamycin derivative

Rifazone-8(2), a new rifamycin derivative, is shown to preferentially inhibit the growth of virus-transformed chick cells in culture. Macromolecular synthesis and glucose uptake of transformed cells are also appreciably decreased in the presence of low concentrations of rifazone-8(2) where the normal cells appear unaffected. While rifazone-8(2) is shown to be a selective inhibitor of RNA-directed DNA polymerase in vitro, its action on the growth of transformed cells may involve some other mechanism.

Inhibition of three nucleotide polymerases by rifamycin derivatives

It is possible to design rifamycin derivatives which can distinguish between viral RNA-instructed DNA polymerase and other nucleotide polymerases.

Detergent effects on a reverse transcriptase activity and on inhibition by rifamycin derivatives

A reverse transcriptase activity, extracted from virus-transformed cells, is activated by very low concentrations of nonionic detergents. These same detergents also significantly reduce the effectiveness of certain rifamycin derivatives as inhibitors of the polymerase activity when the detergents are present at micelle-forming concentrations.