Entry inhibitor


Entry inhibitors, also known as fusion inhibitors, are a class of antiviral drugs that prevent a virus from entering a cell, for example, by blocking a receptor. Entry inhibitors are used to treat conditions such as HIV and hepatitis D.

HIV entry

cell schematic.png|right|thumb|An HIV virion binds to a CD4+ human cell. The two bottom pictures depict two proposed models of HIV fusion with the cell.]
They are used in combination therapy for the treatment of HIV infection. This class of drugs interferes with the binding, fusion and entry of an HIV virion to a human cell. By blocking this step in HIV's replication cycle, such agents slow the progression from HIV infection to AIDS.

Proteins

There are several key proteins involved in the HIV entry process.

Binding, fusion, entry sequence

HIV entry into a human cell requires the following steps in sequence.
  1. The binding of HIV surface protein gp120 to the CD4 receptor
  2. A conformational change in gp120, which both increases its affinity for a co-receptor and exposes gp41
  3. The binding of gp120 to a co-receptor either CCR5 or CXCR4
  4. The penetration of the cell membrane by gp41, which approximates the membrane of HIV and the T cell and promotes their fusion
  5. The entry of the viral core into the cell
Entry inhibitors work by interfering with one aspect of this process.

Approved agents

  • Maraviroc binds to CCR5, preventing an interaction with gp120. It is also referred to as a "chemokine receptor antagonist" or a "CCR5 inhibitor."
  • Enfuvirtide binds to gp41 and interferes with its ability to approximate the two membranes. It is also referred to as a "fusion inhibitor."
  • Ibalizumab, a monoclonal antibody that binds to domain 2 of CD4 and interferes with post-attachment steps required for the entry of HIV-1 virus particles into host cells and prevents the viral transmission that occurs via cell-cell fusion.
  • Fostemsavir, an attachment inhibitor that interferes with the interaction of CD4 and gp120 by binding with gp120.

Investigational agents

Other agents are under investigation for their ability to interact with the proteins involved in HIV entry and the possibility that they may serve as entry inhibitors.