Cancer growth blockers

This page is about cancer growth blockers (cancer growth inhibitors). They are a type of biological therapy and include tyrosine kinase inhibitors, proteasome inhibitors, mTOR inhibitors, PI3K inhibitors and histone deacetylase inhibitors. You can find information about

Growth factors
What cancer growth blockers are
Types of cancer growth blockers
Possible side effects of cancer growth blockers

Growth factors are natural body chemicals that control cell growth. There are many different types of growth factors and they all do different things. Some tell cells what type of cells they should become (how they should specialise). Some make cells grow and divide into new cells. Some tell cells to stop growing or to die. Growth factors work by plugging in to receptors on the cancer cell. This sends a signal to the inside of the cell, which sets off a chain of chemical reactions. These signalling systems are very complicated and no single growth factor works on its own.

There are a number of different growth factors. Examples include

Epidermal growth factor (EGF) – controls cell growth
Vascular endothelial growth factor (VEGF) – controls blood vessel development
Platelet derived endothelial growth factor (PDGF) – controls blood vessel development and cell growth
Fibroblast growth factor(FGF) – controls cell growth

Each growth factor has a corresponding receptor on the cancer cell. For example, EGF has epidermal growth factor receptor (EGFR).

A cancer growth blocker blocks the growth factors that trigger the cancer cells to divide and grow. Scientists are looking at different ways of doing this such as

Lowering levels of the growth factor in the body
Blocking the growth factor receptor on the cancer cell
Blocking the signals inside the cell that start up when the growth factor receptor is triggered

Most of the treatments developed so far work by blocking the signalling process that cancer cells use to divide.

Cancer cells are often very sensitive to growth factors. So if we can block them, we may be able to stop cancers from growing and dividing. Growth factor blockers (inhibitors) are an exciting new way of treating cancer. Scientists are working on developing new inhibitors for different types of growth factors.

It isn’t easy to group biological therapies into different types and so the groups often overlap. This can get very confusing. Some cancer growth blockers also block blood vessel growth to the growing cancer (anti angiogenic drugs). Others are also monoclonal antibodies. We have more explanation about the different types of biological therapies in this section.

There are different types of cancer growth blockers. They are named after the type of chemical that they block. Some of the main types are

Tyrosine kinase inhibitors
Proteasome inhibitors
mTOR inhibitors
PI3K inhibitors
Histone deacetylase inhibitors
Hedgehog pathway blockers

Tyrosine kinase inhibitors

Tyrosine kinase inhibitors are often called TKIs. They block chemical messengers (enzymes) called tyrosine kinases. They are part of the signalling process within cells. Blocking this process stops the cell growing and dividing. Cancer growth blockers can block one signal, a single TKI, or more than one signal, a multi TKI.

Single TKI

Multi TKI

TKIs in use or in clinical trials include

The links above take you to more information about these drugs. You take these TKIs as tablets or capsules, usually once or twice a day.

Recently, the National Institute for Health and Clinical Excellence (NICE) approved a tyrosine kinase inhibitor called pazopanib (Votrient) for use in advanced renal cell cancer.

Proteasome inhibitors

Proteosomes are found in all cells. They help break down proteins that the cell doesn't need. The proteosomes break the proteins into smaller parts so that the cell can use them to make new proteins that it does need. Blocking proteasomes leads to a build up of proteins in the cell, which makes the cancer cells die.

Bortezomib (Velcade) is a proteasome inhibitor used to treat myeloma. You have it as an injection through a tube into a vein. There is more information about bortezomib in the section about treating myeloma.

mTOR inhibitors

mTOR is a kinase protein. It can make cells produce chemicals such as cyclins that trigger cell growth. It may also trigger cells to produce proteins which trigger the development of new blood vessels that cancers need in order to grow. In some types of cancer mTOR is switched on, which makes the cancer cells grow and produce new blood vessels. mTOR inhibitors are a new type of cancer growth blocker being used to try to stop the growth of some cancers. mTOR inhibitors include temsirolimus (Torisel), everolimus (Afinitor) and deforolimus.

PI3K inhibitors

PI3Ks are a group of closely related kinase proteins. Their full name is phosphoinositide 3-kinases. They do a number of different things in cells. For example they turn on other proteins such as mTOR (see above). When this is switched on it signals to the cell to grow and multiply. PI3K proteins also help cells to move around and trigger the development of blood vessels.

In some cancers PI3K is permanently switched on, which means that the cancer cells grow and reproduce uncontrollably. Researchers are developing new treatments that block (inhibit) PI3K. They hope this will stop the cancer cells growing and make them die. This type of cancer growth blocker is only available within a clinical trial. It will be some time before we know how well it works in treating cancer.

Histone deacetylase inhibitors

Histone Deacetylase inhibitors are also called HDAC inhibitors or HDIs. They block the action of a group of enzymes that remove chemicals called acetyl groups from particular proteins. This can stop cancer cells from growing and dividing and can sometimes kill them.

HDACs used in cancer treatment or in clinical trials include vorinostat (SAHA), belinostat, panobinostat, entinostat and mocetinostat.

Hedgehog pathway blockers

Hedgehog pathway blockers are drugs that stop the production of particular proteins within cells. The proteins trigger a cell to divide and grow to form a cancer. The proteins are controlled by a gene called the hedgehog gene. The hedgehog gene is one of a group of genes that control how body tissues grow and develop in the embryo. They make sure that the cells grow in the right place and in the right way. They also control the growth of blood vessels and nerves within the body tissues.

In adults the hedgehog gene is not usually active. But in some people a change (mutation) happens in the hedgehog gene in some cells. The gene change triggers the cell to produce proteins that make the cell divide and grow. Many basal cell skin cancers have this gene change. Some other types of cancer also have this change, including some pancreatic cancers and some brain tumours called medulloblastomas. Hedgehog pathway blockers used in cancer treatment or in clinical trials include vismodegib (Erivedge) and GDC-0449.

All treatments can cause side effects. While there are general side effects for a type of treatment, they vary for each individual drug. In general, cancer growth blockers can cause