Targeted therapy is a treatment that targets specific targets. There are different types of targeted therapy and they all work differently. They can be categorized by size and/or effect.
The active substance is the part of the drug that will cause the effect by binding to the target. This often concerns a target that is also present in normal cells, but which occurs in much greater quantities in the cancer cell. The targeted treatments therefore mainly have an effect on the cancer cells. Each cell is surrounded by a cell membrane, and large active substances cannot pass through it. Large active substances must therefore have their target outside the cell or on the cell, while the small drugs can have their target inside the cell because they can pass through the membrane.
When it comes to large drugs, one usually speaks of antibodies. You can recognize these products by their substance name. The name of these remedies ends in “-mab”. That stands for “monoclonal antibody”. These antibodies can bind to their target on the cell membrane of cancer cells themselves or bind to structures in the environment of the cancer cells that help the cancer cells survive.
A 'Small active substance' is also referred to as a small molecule. They can pass through the cell membrane and therefore bind a target that is inside the cell.
There are many drugs that can pass through the cell membrane and not all of them are targeted treatments. When we talk about targeted therapy, we often refer to agents that block a certain function of the cell and whose name ends in '-ib', which stands for 'inhibition'.
An example of such inhibition/interference treatment are tyrosine kinase inhibitors (TKI). Tyrosine kinases are enzymes that stimulate the growth of cancer cells by disturbing certain signaling pathways (meaning: the signal for tumour growth is continuously ‘ON’). By inactivating these enzymes, cellular growth can be suppressed.
This treatment type can also cause side effects to cells that are dividing in a normal way, such as cells of the gastro-intestinal tract or immune system. Currently, two tyrosine kinase inhibitors (Masivet®, Palladia®) are registered for the treatment of dogs with mast cell tumours. They are also used for other tumour types, but this use is off-label.
Tyrosine kinase inhibitors are given orally (e.g. tablets or capsules) and administered at home by the owner.
After the targeted drug binds to the target, a number of effects can occur:
