PARP inhibitors

Poly (ADP-ribose) polymerase inhibitors, also called PARP inhibitors, are targeted therapies that are used to treat cancer. PARP is a protein that has a role in cellular growth, regulation, and cell repair and it helps cancer cells repair themselves and survive. A PARP inhibitor stops cancer cells being repaired which causes the cells to die and reduces tumor growth.

How they work

DNA damage and mutation occurs naturally and can lead to cancer. If there is a small amount of DNA damage, the body can repair the DNA and the cell will survive. If there is too much damage, then the cell triggers its own death. The body repairs damaged DNA by using tumor suppressor genes (for example, the BRCA gene) and a protein called PARP. This system usually works well together. Any DNA damage is fixed by the tumor suppressor gene and by PARP, so the result is repaired DNA - meaning the cell survives, or, if there is too much damage to the DNA, the cell can't be repaired and it dies.

In cancers where the tumor suppressor gene is faulty, cancer cells are only repaired by PARP. The PARP repair is incomplete, which means the DNA is repaired to a point where it just has a small amount of damage and the cancer cells are able to able to grow and divide. If the PARP did not repair the DNA then the cancer cells would have too much damage and would trigger their own death. PARP inhibitors stops the DNA of cancer cells being repaired by PARP, and cell death is triggered. This inhibits the growth of the tumor.

What they treat

PARP inhibitors are used to treat cancers that have mistakes in their DNA repair genes (such as a BRCA mutation). Examples of cancers PARP inhibitors are used to treat include:

• ovarian cancer
• fallopian tube cancer
• peritoneal cancer
• breast cancer
• prostate cancer.