Glen J. Dixon

Purine analogs as potential anticytomegalovirus agents.

Summary The activity of 25 purine analogs was determined against human cytomegalovirus in vitro. Nineteen compounds were considered to have a degree of antiviral activity with seven of them markedly inhibiting both virus-induced cytopathogenic effects in WI-38 cells and the development of detectable virus. These seven compounds were 2-amino-9-β-d-ribofuranosyl-9H-purine-6-thiol, 2-aminopurine-6-thiol, 9-β-d-arabinofuranosyladenine, purine-6-thiol hydrate, purine-6-carboxaldehyde thiosemicarbazone, 2-amino-6-[(1-methyl-4-nitroimidazol-5-yl) thio] purine, and 9-β-d-ribofuranosyl-9H-purine-6-thiol. The active thiopurines protected the cells from virus infection if allowed to incubate with the cells 1 hr prior to addition of the virus. None of the compounds had demonstrable virucidal activity.

INDIRECT INHIBITION OF PROTEIN SYNTHESIS

Although a number of agents have been known for some time that will inhibit certain viruses in in vivo and in vitro systems,’ it was not until Rightsel and co-workers* in this country and Loddo3 in Italy demonstrated that guanidine hydrochloride markedly inhibited polio virus in various cell culture systems, that any extensive mechanism of action studies was carried out with virus inhibitory compounds. The virus inhibitory effect of guanidine was first detected in a cell culture screening system employing the plastic panel procedure described by Rightsel et al.* and mentioned in this Anna1 by Ehrlich. To review briefly the antiviral activity of guanidine, our first observations were made using the guanidine salt of hydroxyaminomethylene malonitrile. It was soon learned, however, that the guanidine moiety of the molecule was responsible for the antipolio activity and subsequent studies were carried out with guanidine hydrochloride. Antiviral test data on guanidine were collected in our laboratories and in the Parke, Davis laboratories on a number of different viruses in cell culture. It was found that many viruses in the picornavirus group were inhibited by guanidine but no virus from any other group studied was inhibited. The viruses studied that were not inhibited by guanidine are listed in TABLE 1. Loddo5 studied many of the same viruses as we did and obtained essentially the same results. In addition, he studied Newcastle disease virus; adenovirus 1, 5 , and 6; and foot and mouth disease (FMD) virus, which were unaffected by guanidine.* FMD virus is classified in the large group of picornaviruses but it is not in the subgroup of enteroviruses into which all of the guanidine-sensitive viruses fall. Viruses that we found to be inhibited by the drug are listed in TABLE 2a. TABLE 26 lists all strains of viruses that have been found to be inhibited by guanidine. Loddo5 tested ECHO 1, 2, 6, 7, 11, 12, 13, and 15 and Coxsackie B1, 2, 3, 4, and 5 and found that all types of ECHO and Coxsackie viruses studied were inhibited by guanidine. We are in agreement with the observations of Ueda and co-workers,E except for their reported inhibitory activity of guanidine against measles virus. In a series of tests with measles virus in H. Ep.-2 cells (the cell line used by Ueda et u l . ) , we were never able to demonstrate any antimeasles activity under the experimental conditions employed. Since the antipolio activity of guanidine was first reported, literally dozens of papers have appeared dealing with guanidine and its effect on poliovirus. In our earlier work we reported* that treatment of virus-infected cells with guanidine up to 48 hours following virus infection resulted in protection of cells from extensive virus damage. Forty-eight hours after infection of cells with 100 CCID50 of polio virus, one sees considerable cytopathogenicity (CPE) ; however, addition of guanidine at this time will protect the remaining cells and clear the virus from some damaged cells enough to allow “recovery.” Addition of drug up to 24 hours following virus infection results in virtually complete protection of cells from the virus. TABLE 3 shows the effect of guanidine added to cell

Kinetics of the effect of vincristine sulfate on the reproductive integrity of proliferating cultured leukemia L1210 cells.

Summary When proliferating cultured L1210 cell populations were exposed to effective concentrations of VCR or colchicine, the kinetics of the reduction in the number of viable cells did not occur at a first-order rate (the fraction of cells killed per unit of time was not constant). The minimum effective concentration of VCR required to produce an effect on the reproductive integrity of L1210 populations was < 0.01 but > 0.001 μg/ml. If the duration of drug exposure was 24 hours, extensive cell killing could be produced by VCR concentrations which were relatively low when compared to the theoretical maximum concentration attainable in the body fluids of a mouse. The kinetics of the lethal action of VCR on proliferating cultured L1210 populations indicate that this agent has cell cycle specificity.

Role of virucides in controlling virus dissemination by fabrics.

Vaccinia virus, a lipophilic agent containing deoxyribonucleic acid, and poliovirus, a hydrophilic ribonucleic acid virus, persisted on wool and cotton fabrics for varying periods up to 20 weeks, which was of sufficient duration to be of epidemiological significance. The length of persistence of each virus varied with the type of fabric, humidity and method of exposure to the virus. A group of quaternary ammonium salts and bromosalicylanilides were evaluated quantitatively for virucidal activity against these viruses in a cell culture system. None of the compounds was active against poliovirus, but three of the quaternary ammonium compounds significantly inactivated vaccinia virus. Impregnation of wool and cotton fabrics with one of these compounds resulted in a marked decrease in vaccinia virus persistence. Both polio and vaccinia viruses persisted for less than five days on a cotton fabric finished with a modified triazone resin to impart a wash-and-wear property. Cotton fabric contaminated with vaccinia or with poliovirus was laundered with an anionic detergent and a nonionic detergent. This laundering reduced but did not eliminate the virus. Sterile fabric was contaminated with virus when laundered with the virus-containing fabrics. Drying the fabrics for 20 hr after laundering reduced the virus titers to below detectable limits.

Effect of Host Weight Loss on Friend Leukemia Virus Infections in Swiss, DBA/2, and BALB/c Mice.

Summary Caloric restriction studies in Swiss, DBA/2, and BALB/c mice infected with Friend leukemia virus (FLV) have indicated that loss of host weight can markedly affect the extent of virus-induced splenomegaly, but does not noticeably affect the titer of recoverable virus in plasma or spleens from these animals. It was concluded that host weight change is important and should be considered when using FLV-induced splenomegaly in chemotherapy trials. The effect on FLV-induced splenomegaly of 2 compounds, porfiromycin and 1-methyl-1-nitrosourea, were evaluated in the light of these findings.

Effect of vidarabine in dimethyl sulfoxide vehicle on type 1 herpesvirus-induced cutaneous lesions in laboratory animals

Vidarabine (9-beta-D-arabinofuranosyladenine) prepared in a 70% dimethyl sulfoxide vehicle was applied topically to type 1 herpesvirus-induced cutaneous lesions on guinea pigs and athymic nude mice. Treatments were 3 or 5 times daily for 7 days beginning 24 h after virus exposure. Against infections in guinea pigs induced by a thymidine kinase-positive virus strain, either treatment schedule effectively inhibited mean lesion score, lesion size, appearance of new lesions, and reduced lesion virus titers. Therapy was similarly effective against infections in guinea pigs induced by a thymidine kinase-negative virus strain, except that lesion virus titers were somewhat increased in animals treated 3 times daily. Treatment 5 times daily was most efficacious against both virus strains. Treatment 3 times daily of mice infected with a thymidine kinase-negative virus was not effective, but treatment 5 times daily significantly inhibited lesion score and size and reduced lesion virus titer by 37%. Toxicity controls exhibited no signs of skin irritation, although guinea pigs treated 5 times daily experienced some transient weight loss.

HADACIDIN POTENTIATION OF LETHAL ACTION OF IONIZING IRRADIATION. I. EFFECT OF MAMMALIAN TUMOR CELLS IN CULTURE.

Summary The lethal effects of ionizing irradiation (X-ray) on Ca755, KB, and HeLa (S-3) cells were potentiated by hada-cidin. Under similar experimental conditions, no potentiation of the lethal effect was seen with Sal 80 cells and the results with H. Ep-2 cells were inconsistent and equivocal. With Ca7SS, KB, and HeLa (S-3) cells, the degree of potentiation was related to the dose of both X-ray and hadacidin.