Step 3. Target Selection

Diseases occur when the normal body processes are altered or not functioning properly. When developing a medicine, it is important to understand in detail (at the level of the cells) what has gone wrong. This means that the abnormal process can then be ‘targeted’ and corrected. The ‘target’ may be a molecule that has been produced in excess interfering with normal body functions; or not being produced in normal amounts; or one that has an abnormal structure. For example, in cancer, there can be too much of a chemical messenger signalling the cells to grow abnormally; and in diabetes, there is a lack of insulin production, or the cells don’t respond to insulin.

Figure 2 shows a simple representation of a cell, with a nucleus and a receptor on the cell surface.

  • The nucleus acts as the control centre for the cell – it contains the genetic material.
  • The receptor allows chemical messengers to communicate with the cell.
When a chemical messenger, in this case the ‘growth factor’, combines with the growth factor receptor on the cell surface, a message is generated inside the cell. This then communicates with the nucleus and the cell is then stimulated to divide. When the signalling is uncontrolled, the cellular growth leads to cancer. Blocking the receptor in cancer cells will prevent transmission of the message and will prevent uncontrolled cell growth. If you can block the receptor in cancer cells, this will:
    stop the message being sent and
  • prevent uncontrolled cell growth.
The ‘target’, in this example, is therefore the growth factor receptor.

cells 1

cells 2

Figure 2: Cells, receptors and messengers.

In many cases, it is impossible to know in detail what has gone wrong. Often in a disease, there are several abnormalities or ‘targets’, but scientists cannot tell precisely which target is responsible for the disease, or these abnormalities have not caused the illness and therefore trying to correct them will not treat the disease. In this case, the development project might be pursuing the wrong target, and ultimately it will fail. Therefore, selecting the best target to work on in a project is crucial.