Effect of -amanitin on adenovirus 5 multiplication

Optimization of piperazine-derived ureas privileged structures for effective antiadenovirus agents

In recent years, human adenovirus (HAdV) infections have shown a high clinical impact in both immunosuppressed and immunocompetent patients. The research into specific antiviral drugs for the treatment of HAdV infections in immunocompromised patients constitutes a principal objective for medicinal chemistry due to the lack of any specific secure drug to treat these infections. In this study, we report a small-molecule library (67 compounds) designed from an optimization process of piperazine-derived urea privileged structures and their biological evaluation: antiviral activity and cytotoxicity. The active compounds selected were further evaluated to gain mechanistic understanding for their inhibition. Twelve derivatives were identified that inhibited HAdV infections at nanomolar and low micromolar concentrations (IC₅₀ from 0.6 to 5.1 μM) with low cytotoxicity. In addition, our mechanistic assays suggested differences in the way the derivatives exert their anti-HAdV activity targeting transcription, DNA replication and later steps in the HAdV replication cycle. Furthermore, eight of the 12 studied derivatives blocked human cytomegalovirus (HCMV) DNA replication at low micromolar concentrations. The data provided herein indicates that the 12 thiourea/urea piperazine derivatives studied may represent potential lead compounds for clinical evaluation and development of new anti-HAdV drugs.

Viral RNA synthesis and levels of DNA-dependent RNA polymerases during replication of adenovirus 2

The rates of RNA synthesis in cultured human KB cells infected by adenovirus 2 were estimated by measuring the endogenous RNA polymerase activities in isolated nuclei. The fungal toxin alpha-amanitin was used to determine the relative and absolute levels of RNA polymerases I, II, and III in nuclei isolated during the course of infection. Whereas the level of endogenous RNA polymerase I activity in nuclei from infected cells remained constant relative to the level in nuclei from mock-infected cells, the endogenous RNA polymerase II and III activities each increased about 10-fold. These increases in endogenous RNA polymerase activities were accompanied by concomitant increases in the rates of synthesis in isolated nuclei of viral mRNA precursor, which was quantitated by electrophoretic analysis on polyacrylamide gels. The cellular RNA polymerase levels were measured with exogenous templates after solubilization and chromatographic resolution of the enzymes on DEAE-Sephadex, using procedures in which no losses of activity were apparent. In contrast to the endogenous RNA polymerase activities in isolated nuclei, the cellular levels of the solubilized class I, II, and III RNA polymerases remained constant throughout the course of the infection. Furthermore, no differences were detected in the chromatographic properties of the RNA polymerases obtained from infected or control mock-infected cells. These observations suggest that the increases in endogenous RNA polymerase activities in isolated nuclei are not due to variations in the cellular concentrations of the enzymes. Instead, it is likely that the increased endogenous enzyme activities result from either the large amounts of viral DNA template available as a consequence of viral replication of from replication or from functional modifications of the RNA polymerases or from a combination of these effects.

Replication process of the parvovirus H-1. I. Kinetics in a parasynchronous cell system

Parasynchronous cultures of hamster embryo cells were used to study some of the events in the replication process of the parvovirus H-1. Synthesis of viral DNA, viral hemagglutinating antigen, and infectious virus were examined. It was found that initiation of DNA synthesis, on which subsequent viral hemagglutinin synthesis was dependent, occurred at a specific time in late S-phase. Production of H-1 viral protein was shown to be sensitive to inhibition by alpha-amanitin. The implications of these findings are discussed.