1-Adamantanamine hydrochloride: inhibition of Rous and Esh Sarcoma viruses in cell culture.

I-Adamantanamine hydrochloride, added to chick embryo cells, inhibited focus production upon subsequent inoculation of the cells with Rous and Esh sarcoma viruses. Addition of the chemical to suspensions of Rous and Esh viruses before they were added to chick cell cultures did not inactivate the viruses; and the addition to chick cells did not prevent plaque formation following their inoculation with Newcastle disease virus. This indicates that cells treated with 1-adamantanamine hydrochloride are capable of supporting viral replication, and these observations suggest that the drug inhibits growth of two oncogenic viruses by prevention of virus penetration, but not by a virucidal effect or cell intoxication.

Dimethyl-10,12-benz(a)acridine; evidence for differential effects on the synthesis of RNA of mammalian or avian fibroblasts and some RNA viruses.

We have studied the differential effect of dimethyl-10,12-benz(a)acridine (DBMAcr) on the synthesis of RNA of chicken or mouse fibroblasts in culture and that of some RNA-containing viruses such as Rous sarcoma virus and Mengovirus. DMBAcr at low concentrations blocks the cell multiplication of both normal and Rous sarcoma virus-transformed chicken fibroblasts in culture; it affects transformed cells more than normal ones. The cell growth inhibiting effect of DMBAcr is reversible after short periods of incubation. DMBAcr depresses the synthesis of cellular DNA and RNA in parallel. Concurrently the synthesis of protein proceedes at a relatively high rate in DMBAcr-treated cultures. Its inhibitory effect on cellular RNA synthesis is mostly due to a block in the formation of 28 S and 18 S ribosomal RNA species; in contrast, the synthesis of 45 S ribosomal RNA precursor is proceeding at almost control rate. Also, the synthesis of heterogeneous nuclear RNA is not blocked by DMBAcr. The production of Rous sarcoma virus in transformed fibroblasts is not affected by DMBAcr. Since this is correlated with persisting high rates of protein and heterogenous nuclear RNA synthesis, the effects of DMBAcr suggest that the synthesis of Rous sarcoma virus-RNA shares the specificity of messenger and heterogeneous nuclear RNA. DMBAcr inhibits the synthesis of viral RNA of Mengovirus under conditions where the synthesis of total cellular RNA is not appreciably depressed, suggesting its differential effect on the DNA-directed and the RNA-directed RNA synthesis.

Effect of antabuse (disulfiram) on Rous sarcoma virus and on eukaryotic cells.

Antabuse (disulfiram) is widely used in the treatment of chronic alcoholism. We have examined the effect of this drug on malignant transformation by Rous sarcoma virus, on eukaryotic cell synthesis, and on nucleic acid binding. It was found that: (1) Disulfiram inhibits the activity of the RNA dependent DNA polymerase of Rous sarcoma virus and inactivates the ability of the virus to malignantly transform chick embryo cells. The monomer of disulfiram, diethyldithiocarbamate does not affect the virus. (2) Disulfiram induced the synthesis of four proteins in normal chick embryo and human foreskin cells. The monomer diethyldithiocarbamate, induced these proteins also. Cellular DNA synthesis is more sensitive to disulfiram than are RNA and protein synthesis. (3) Disulfiram binds to neither DNA or RNA in the presence or absence of copper. However, diethyldithiocarbamate in the presence of, but not in the absence of, copper binds to HeLa cell DNA and to Rous sarcoma virus 70 S genome RNA. These results indicate that this compound, which causes no symptoms in people who do not consume alcohol, may have significant effects on a cellular level.

Ascorbate stabilizes the differentiated state and reduces the ability of Rous sarcoma virus to replicate and to uniformly transform cell cultures.

In primary avian tendon cells, Rous sarcoma virus can coexist or completely take over the cell. Infection, at high multiplicity or under conditions that promote high virus production (no ascorbate and high serum concentrations), results in almost complete oncogenic transformation of the culture. This is indicated in part by a radical change in morphology, growth at high cell density, and a dramatic drop in the production of procollagen from approximately 50% to approximately 3% of total protein synthesis. In contrast, infection at low multiplicity, infection with a replication defective virus, or the presence of ascorbate restrict the ability of the virus to transform the culture. Thus, there appears to be a balance between the normal and transformed states of the cell that can be shifted depending on the cellular environment and the level of infection. Ascorbate stabilizes the normal state by reducing virus production and promoting the synthesis of differentiated proteins.

Optimization of the Schiff bases of N-hydroxy-N'-aminoguanidine as anticancer and antiviral agents.

Hydroxyurea, hydroxyguanidine, and some thiosemicarbazones have been shown to have anticancer and antiviral activities. One of their possible sites of action is the enzyme ribonucleotide reductase (RR). Combination of the structural features of these compounds led to the design and synthesis of the Schiff bases of N-hydroxy-N'-aminoguanidine. Synthesis and structure-activity studies of some of these compounds point to increased size and lipophilicity as important factors for activity. To optimize the activities of this series of compounds, 13 derivatives of high lipophilicity and molecular size have been synthesized and their biological activities studied. The most active anticancer compounds against L1210 in vitro (compounds 9 and 12) are about 7 times more active than hydroxyguanidine and hydroxyurea. The most active antiviral compounds against Rous sarcoma virus transformation of chick fibroblasts in vitro (7, 9) are about 40 times more active than hydroxyguanidine. One of the compounds (4) shows promising activity in vivo (% T/C = 140 against P388 leukemia in mice) and is undergoing further studies by the National Cancer Institute (NCI). Studies of the inhibition of transformation of chick embryo cells by Rous sarcoma virus show that all these compounds inhibit transformation while some compounds inhibit viral replication as well.

Synthesis of 3-deazaneplanocin A, a powerful inhibitor of S-adenosylhomocysteine hydrolase with potent and selective in vitro and in vivo antiviral activities.

The neplanocin A analogue 3-deazaneplanocin A (2b) has been synthesized. A direct SN2 displacement on the cyclopentenyl mesylate 3 by the sodium salt of 6-chloro-3-deazapurine afforded the desired regioisomer 4 as the major product. After deprotection, this material was converted to 3-deazaneplanocin A in two steps. X-ray crystallographic analysis confirmed the assigned structure. Consistent with its potent inhibition of S-adenosylhomocysteine hydrolase, 3-deazaneplanocin A displayed excellent antiviral activity in cell culture against vesicular stomatitis, parainfluenza type 3, yellow fever, and vaccinia viruses. Antiviral activity was also displayed in vivo against vaccinia virus by using a mouse tailpox assay. The significantly lower cytotoxicity of 3-deazaneplanocin A, relative to its parent compound neplanocin A, may be due to its lack of conversion to 5'-triphosphate and S-adenosylmethionine metabolites.

Alteration of phenotype of 'regressor' avian sarcoma cells following treatment with phorbol ester.

Tumor cells which are cultured from the regressor phase of avian sarcoma virus (ASV)-induced tumor growth are deficient with respect to ability to produce progeny transforming virus. In addition, such cells are relatively unreactive with anti-viral antibody and are unable to elaborate, into the medium, antigens which are stimulatory to the sensitized lymphocytes of virus-injected hosts. These deficits can be overcome by treatment of the cells with the tumor promoter, phorbol myristate acetate (PMA).

Characterization of a naphthalene derivative inhibitor of retroviral integrases.

The retroviral integrase protein (IN) is essential for virus replication and, therefore, an attractive target for the development of inhibitors to treat human immunodeficiency virus (HIV) infection. Diverse classes of compounds that are active against this protein have been discovered using in vitro assays. Here we describe the synthesis of a novel compound, 3,8-dibromo-7-amino-4-hydroxy-2-naphthalenesulfonic acid (2BrNSA), which inhibits the in vitro activities of the full-length HIV-1 and avian sarcoma virus (ASV) integrases, and the isolated catalytic core fragment of the ASV protein (residues 52-207). The compound also inhibits retroviral reverse transcriptase in vitro, but the IC(50) for the HIV-1 enzyme is almost two orders of magnitude higher than for HIV-1 integrase. The inhibitor was found to be active in cell culture, preventing reporter gene transduction of HeLa cells by both ASV and HIV-1 vectors. Neither viral attachment nor uptake into cells appeared to be affected in these transfections, whereas accumulation of vector DNA and its joining to host DNA were both drastically reduced in the presence of the inhibitor. Propagation of two different strains of replication-competent HIV-1 in human peripheral blood mononuclear cells (PBMCs) was also reduced by the inhibitor, allowing survival of a substantial number of cells in the treated cultures. Based on these and other results we speculate that binding of 2BrNSA to integrase in infected cells interferes not only with its catalytic activity but also with critical interactions that are required for the formation or function of the reverse transcriptase complex. Its activity in cell culture suggests that this inhibitor may provide a valuable new lead for further development of drugs that target early steps in the HIV life cycle.

Inhibitory activity of the new adamantane derivative N,N'-bis(ethylene)-P(1-adamantyl)-phosphonic diamide against Rous sarcoma virus.

A new adamantane derivative N,N'-bis (ethylene)P(1-adamantyl)-phosphonis diamide, was found to inhibit Rous sarcoma virus replication in much the same manner as reported for the parent compound, 1-adamantanamine hydrochloride.

Antiretroviral activities of anthraquinones and their inhibitory effects on reverse transcriptase.

Alizarin complexone (AC), alizarin Red S (ARS) and various other anthraquinones were evaluated for their inhibitory effects on Rous-associated virus 2 reverse transcriptase (RAV-2 RT). Some 1,2-dihydroxyanthraquinones were active against this enzyme and AC was the most potent inhibitor among these compounds [50% inhibitory concentration (IC50): 3.8 micrograms/ml]. AC slightly inhibited Rous sarcoma virus RT (RSV RT) and human immunodeficiency virus type 1 RT (HIV-1 RT) (IC50: 100 micrograms/ml and 45 micrograms/ml, respectively). However, AC efficiently inhibited focus formation by Rous sarcoma virus (RSV) and cytopathogenicity of human immunodeficiency virus type 1 (HIV-1). Simultaneous administration of AC with RSV to newborn chickens also delayed tumor induction by RSV.

Inactivation and inhibition of Rous sarcoma virus by copper-binding ligands: thiosemicarbazones, 8-hydroxyquinolines, and isonicotinic acid hydrazide.

We have shown that three types of copper-binding ligands, thiosemicarbazones, 8-hydroxyquinolines, and isonicotinic acid hydrazide and their copper complexes, inactivate the transforming ability of RSV and inhibit its RNA-dependent DNA polymerases. Three other compounds, 2-pyridine thiosemicarbazone, 1-formyl isoquinoline thiosemicarbazone, and diphenyl thiocarbazone inhibit transformation by RSV intracellularly. Most but not all of these compounds bind to nucleic acids in the presence of copper, which may be important in their mode of action.

Induction of retrovirus gene expression by selenium compounds.

Sodium selenite, sodium selenate, selenium oxide, selenophypoxanthine, selenopurine, selenocysteine, selenoethionine and selenomethionine were tested for their ability to induce endogenous retrovirus expression in cultured AKR mouse embryo fibroblasts. All except selenoethionine were highly toxic to the cells. Only selenomethionine however, had the ability to induce virus expression under the conditions used. The level of virus induction (plaque-forming-units/10(5) cells) was roughly proportional to dose over the range of concentrations from 0.25 mM to 5.0 mM. Induction was best observed when a treatment duration of 48 h was used and required the treatment of actively dividing cells. The induction and the cytotoxic effects of selenomethionine could be abrogated by simultaneous treatment with methionine. A ratio of methionine to selenomethionine of 1:10 inhibited induction by approx. 60% while equivalent amounts of methionine inhibited selenomethionine-mediated induction by greater than 96%, indicating that methionine was more efficiently recognized by the cells than was selenomethionine. A possible mechanism for selenomethionine induction involving the production of undermethylated DNA is presented.

Sparoxomycins A1 and A2, new inducers of the flat reversion of NRK cells transformed by temperature sensitive Rous sarcoma virus. I. Taxonomy of the producing organism, fermentation and biological activity.

Streptomyces sparsogenes SN-2325 isolated from a soil sample collected in Hokkaido, was found to produce sparoxomycins A1 and A2, new modulators of proliferation of mammalian cells. Sparoxomycins A1 and A2 reverse the morphology of temperature-sensitive mutant Rous sarcoma virus-infected NRK cells (src(ts)-NRK cells) from the transformed phenotype to the normal phenotype at the permissive temperature.

Induction by herbimycin A of contact inhibition in v-src-expressed cells.

Herbimycin A, an inhibitor of pp60src tyrosin kinase, caused src oncogene-expressed cells to become sensitive to contact inhibition, but did not affect ras oncogene-expressed cells. The cell lines tested were temperature sensitive v-src- and temperature sensitive v-ras-integrated nontransformed rat kidney cell line (NRK) (srctsNRK and rastsNRK, respectively) and a wild-type v-src-integrated NIH3T3 (src3T3). srctsNRK cells in densely populated cultures (plated at 1.25 x 10(4) cells/cm2), grown at 33 degrees C in the presence of 0.45 micrograms/ml of herbimycin A, ceased the cell cycle at the G0-G1 stage within 2 days, and the cells showed normal morphology. Upon removal of herbimycin A, the quiescent cells resumed the cell cycle in concert with morphological alteration from 'normal' to 'transformed', and proceeded through the S and M stages successively in a synchronized manner. Cells in the late S stage, compared with those in other stages of the cell cycle, were more sensitive to the killing effect of 5-fluorodeoxyuridine. Such synchronism of the cell cycle was not observed with sparsely populated cultures (2.5 x 10(3) cells/cm2); the cells resumed their asynchronous growth after removal of herbimycin A, although their morphology returned to 'transformed' as in the experiment with the densely populated cultures. The induction by herbimycin A of contact inhibition in densely populated cultures was also observed with src3T3 (grown at 37 degrees C) but not with rastsNRK (grown at 33 degrees C).

An in vitro screening method for antitumor and/or antitumorigenic substances involving the transformation of chick embryo fibroblasts infected with Rous sarcoma virus.

An efficient in vitro screening method for antitumor and/or antitumorigenic substances was established. The method is based on determining inhibitory effect of a compound on an RSV-induced tumorigenic process and the growth of the established tumor cells in a single assay system in the presence of normal cells. These effects were determined by inhibition of focus formation in a culture of chick embryo fibroblasts, while the nonspecific cytotoxic effect was determined by inhibition of the protein content of the same culture. The efficiency of this method in screening drugs was confirmed by testing various clinical and preclinical compounds.

Preparation of new 7-hydroxyguanine derivatives and their biological activities.

We prepared new 7-hydroxyguanine derivatives, 7-hydroxyguanosine 5'-monophosphate and N2-tetrahydropyranyl-7-hydroxyguanine, and compared biological activities of 7-hydroxyguanine derivatives including nucleosides acquired previously. 7-Hydroxyguanine and its nucleotide inhibited the focus formation of Rous sarcoma virus. Antitumor activities of these derivatives against mouse leukemia L1210 were not so different from one another. Anti-proliferative activities of the derivatives on various human cell lines were significantly different from one another.

BrdU-induced changes in the provirus of PR-RSV in mammalian cells.

Previously we demonstrated differences in the organization and methylation pattern of integrated Rous sarcoma proviral sequences in helper-dependent virogenic rat TWERC cells. In the present study we attempted to induce changes in the integrated viral genome of TWERC cells using 5-bromodeoxyuridine (BrdU). Four clones (A, B, C, and F) derived from the parental cell line were treated for 10 months with different concentrations of BrdU. Restriction enzyme analysis of the parental cell line and its clones showed that the cells contained in their genomic DNA two copies of deleted provirus. In TWERC cells, the PR-RSV provirus lost the whole env gene and part of the 3' end of the pol gene. The proviral sequences in DNA from the TWERC-derived clones were found to be hypermethylated. A slightly different situation was seen in clone C where demethylation of the provirus in the 3' region and in the 5' end of the genome was found. The level of mRNA expression both in the parental cells and in the clones correlated with the methylation pattern of the PR-RSV provirus. Clone C was less methylated and expressed more virus-specific RNA. The possible role of BrdU in these events is discussed.

Treatment of RSV-transformed "poorly" virogenic and non-virogenic mammalian cell lines with inhibitors of protein synthesis: failure to potentiate RSV rescue.

Treatment of the RSV-transformed "poorly" virogenic rat clones LW13-RsK4 and LW13-RsK4 R1 with cycloheximide or puromycin before fusion with chick embryo fibroblasts did not lead to RSV rescue. Neither was RSV rescued from the RSV-transformed non-virogenic mouse line RVP3 treated with 5-bromodeoxyuridine and cycloheximide or puromycin before fusion.

The study of the rous virus synthesis in mammalian embryonic tissues growing in vitro.

The genome of Rous sarcoma virus was found in mouse and hamster embryo cells growing in vitro shortly after the infection and long before cell transformation occurred. The virus genome was not detected in embryo cells when they were treated with actinomycin D or when the temperature of incubation was lowered to +20 degrees C. This suggested that the synthesis of Rous virus genome could have taken place de novo in the cells investigated. Furthermore, the experiments showed that the life cycle of Rous virus in mammalian and avian cells had at least one phase in common, i.e., that sensitive to the action of actinomycin D.

Effect of glucosamine on phenotype mixing of vesicular stomatitis virus with avian sarcoma virus.

The effect of glucosamine on phenotypic mixing between vesicular stomatitis virus (VSV) and avian sarcoma virus (ASV) was studied. Phenotypic mixing decreased with increase in glucosamine concentration, and, in the presence of 20 mM glucosamine, was no longer detectable. In the presence of 20 mM glucosamine, cells still produced 10(2)--10(3) focus forming units (FFU) of ASV and 10(6) plaque forming units (PFU) of VSV per milliliter. These results suggest that cells producing a relatively large amount of ASV (more than 10(3) FFU/ml) are essential for phenotypic mixing of VSV with ASV.