protease inhibitor
Meaning of protease inhibitor: The phrase covers two different things: proteins the body makes to protect itself, and a family of antiviral drugs named after them.
Definition of protease inhibitor
A protease inhibitor is a substance that blocks a protease, an enzyme that cuts proteins into shorter pieces. The body makes its own inhibitors to stop its cutting enzymes from damaging healthy tissue. The same name is used for a group of antiviral drugs that work by blocking a viral enzyme needed to finish assembling new infectious particles.
What do the body's own inhibitors do?
Protein-cutting enzymes are powerful and indiscriminate, so wherever the body deploys them it deploys something to switch them off as well. White cells release cutting enzymes to destroy bacteria, and alpha-1 antitrypsin circulates to neutralize the surplus before it digests lung tissue. People who inherit a faulty version of that inhibitor develop emphysema unusually early, which shows what the balance holds back. Clotting, digestion, inflammation and the immune cascade are all regulated by similar pairs of enzyme and inhibitor.
How do the antiviral drugs work?
Some viruses build their proteins as one long chain and then cut it into working pieces using an enzyme of their own. Blocking that enzyme leaves the chain uncut, and the particles assembled from it are complete in outline but unable to infect anything. Drugs of this kind transformed the treatment of HIV infection, and others form part of the combinations that cure most hepatitis C infection. A protease inhibitor is also a component of an oral treatment for COVID-19.
How does it differ from a proteasome inhibitor?
| Feature | Protease inhibitor | Proteasome inhibitor |
|---|---|---|
| Target | One protein-cutting enzyme | The whole protein disposal complex |
| Main use | Viral infection | Multiple myeloma |
| Source | Natural and manufactured | Manufactured drugs only |
The two names differ by three letters and are confused often. A proteasome inhibitor acts on a large assembly present in every cell, while this term usually points at a single enzyme belonging to a virus.
Is there a role in cancer?
The idea is long-standing but has not produced an established treatment. Because tumor cells use cutting enzymes to break through the scaffolding around them as they invade, blocking those enzymes was expected to limit spread, and compound after compound was tested on that basis. Trials of inhibitors aimed at the matrix-cutting enzymes did not show the hoped-for benefit, and claims that this class stops cancer from spreading are not supported.
Also known as
Used in a sentence
The regimen included a protease inhibitor boosted by a second agent.
Good to know
The term spans naturally occurring inhibitors such as alpha-1 antitrypsin and a manufactured antiviral class, and the older phrase AIDS virus protease inhibitor refers to what is now called an HIV protease inhibitor.
Word origin
Where “protease inhibitor” comes from
Protease combines protein, from the Greek proteios meaning primary, with the ending -ase that marks an enzyme.