Question

Explain how acyclovir inhibits viral replication without affecting our own cells and why it is totally ineffective as a treatment for HIV

Answer 1

Acyclovir

Acyclovir is an Antiviral drug , that is usually used in the treatment of genital herpes. The mechanism of Action of the drug is the inhibition of viral DNA polymerase by Acyclovir triphosphate , there by preventing the viral DNA synthesis and thus the viral replication.  

Acyclovir is a Guanosine analog and it inhibits the Viral replication without affecting our own cells. Acyclovir can be monophosphorelated by virus encoded -thymidine kinase that is present in infected cells. Thymidine kinase present in the normal cell is not capable of monophosphorelation of Acyclovir. Subsequent reactions , are also catalysed by the host cell enzymes, like diphosphorelation, triphosphorelation may make the Acyclovir into Acyclovir triphosphate. When comparing with the normal cell , infected cells may have 100 times more amount of Acyclovir triphosphate concentration. Viral DNA synthesis can be prevented  by this Acyclovir triphosphate as it can inhibit the viral DNA polymerase . Thus Acyclovir inhibits viral replication without affecting our own host cells.

2. Acyclovir in HIV  treatment

Acyclovir is ineffective in HIV ( Human immunodeficiency Virus ) treatment. Herpes simplex virus , that is mainly treated with Acyclovir is a DNA virus and is multiplied by viral DNA replication with the help of DNA polymerase enzyme, whereas HIV is a RNA virus and is called retro virus . It stores it's genetic information in RNA not in DNA. Viral RNA polymerase is needed for its multiplication. The drug Acyclovir mainly act by inhibiting the DNA polymerase So the drug is not effective in HIV infection treatment.