Question

Drugs against viruses are usually designed to affect viral genome replication.

Based on these mechanisms of replication, is it possible to design a drug that would affect all viruses, no matter what the mechanism of genome replication? If yes, explain what the drug would do. If no, explain why not.

Answer 1

Aany agent that is used in the treatment of an infectious disease caused by a virus is called antiviral drug.  Viruses consist of either DNA or RNA and a protein coat. Viruses are obligate parasites. They do not have the enzymes that are needed to manufacture cellular components. They must enter a cell for replication to occur which leads to an infectious virus.

In order to inhibit the virus, an antiviral agent interfere the viral replication cycle by the following steps.

(1) Attachment and penetration of the virus into the host cell. ie., attachment between viral capsid proteins and specific receptors on the host cellular surface and  enter the host cell through receptor-mediated endocytosis or membrane fusion.

(2) Removal of the protein coat and release of the nucleic acid (DNA or RNA) by degradation by viral or host enzymes or by simple dissociation.

(3) Synthesis of new viral components by the host cell as directed by the virus DNA. This is accomplished through synthesis of viral mRNA, viral protein synthesis and assembly of viral proteins and viral genome replication mediated by regulatory protein expression.

(4) Assembly of the protein coat and nucleic acids into new virus and

(5) Release of the new virus from the host cell by lysis.

For example drugs that are effective against herpesviruses interfere with DNA replication. The ntiviral drugs acyclovir and ganciclovir mimic the normal nucleoside and block the viral DNA polymerase enzyme, which is important in the formation of DNA. Acyclovir activated by a viral enzyme, so they are specific for the cells that contain viral particles. Another drug idoxuridine activated by cellular enzymes, so these have less specificity. Foscarnet, a non-nucleoside inhibitors of herpesvirus replication directly inhibits the viral DNA polymerase and thus blocks formation of new viral DNA.

Designing safe and effective antiviral drugs is difficult because viruses need for a host cell to support the multiplication. The major difficulty in developing antiviral drugs is due to viral variation.This makes it difficult to find targets for the drug without also harming the cells of host organism. Some factors account for the difficulty in developing antiviral agents are the difference in structure of each virus and periodic changes in the antigenic proteins of the virus.