Targeting cancer cells

WORLD CANCER DAY : By focusing on molecular and cellular changes that are specific to cancer, targeted cancer therapy may prove to be effective against the disease, says Dr Shekar Patil.

Cancer, the dreaded C-word, is most often related to pain and inevitable death. But modern medicine is far advanced and new treatments have enabled doctors to treat it, reduce side effects and thus improve the quality of life of a patient. Target therapy is opted as the first line of treatment for most cancer diseases and has yielded positive results.

What is targeted cancer therapy?

Targeted cancer therapy uses drugs that block the growth and spread of cancer.

They interfere with specific molecules involved in carcinogenesis (the process by which normal cells become cancer cells) and tumour growth. As  scientists prefer to call these molecules  molecular targets, this form of therapy is called molecularly-targeted therapy. By focusing on molecular and cellular changes that are specific to cancer, targeted cancer therapy may be more effective than current treatments and less harmful to normal cells.

Most targeted cancer therapies are in preclinical testing (research with animals), but some are in clinical trials (research studies) or have been approved by the US Food and Drug Administration (FDA). Targeted cancer therapies are being studied for use alone, in combination with each other, and in combination with other cancer treatments, such as chemotherapy.

What are the cellular changes that lead to cancer?

Normally, cells grow and divide to form new cells as and when the body needs them.

When cells grow old, they die, and new cells take their place. Sometimes this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumour. The cells in malignant (cancerous) tumours are abnormal and divide without control or order. They can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumour and spread to other parts of the body.

Normal cell growth and division are largely under the control of a network of chemical and molecular signals that give instructions to cells. Genetic alterations (changes) can disrupt the signaling process so that cells no longer grow and divide normally, or no longer die when they should. Alterations in two types of genes can contribute to the cancer process. Proto-oncogenes are normal genes that are involved in cell growth and division. Changes in these genes lead to the development of oncogenes, which can promote or allow excessive and continuous cell growth and division.

Tumour suppressor genes are normal genes that slow down cell growth and division. When a tumour suppressor gene does not work properly, cells may be unable to stop growing and dividing, which leads to tumour growth.

To use the metaphor of a car, the presence of an oncogene is like having a gas pedal that is stuck to the floorboard, causing cells to continually grow and divide.

Tumour suppressor genes act like a brake pedal. The loss of a functioning tumor suppressor gene is like having a brake pedal that does not work properly, allowing cells to continually grow and divide.

Genetic changes that are not corrected by the cell can lead to the production of abnormal proteins. Normally, proteins interact with each other as a kind of relay team to carry out the work within a cell. For example, when molecules called growth factors (GFs) attach to their corresponding growth factor receptors (GFRs) on the surface of the cell, a process, carried out by proteins, signals the cell to divide.

Damaged proteins may not respond to normal signals, and may over-respond to normal signals, or otherwise fail to carry out their functions. Cancer develops when abnormal proteins inside a cell causes it to reproduce excessively and allow that cell to live longer than normal cells.

How does the targeted therapy work?

Targeted cancer therapy interferes with cancer cell growth and division in different ways and at various points during the development, growth, and spread of cancer.

Many of these therapies focus on proteins that are involved in the signaling process.

By blocking the signals that tell cancer cells to grow and divide uncontrollably, targeted cancer therapy can help to stop the growth and division of cancer cells.

What impact will targeted therapy have on cancer treatment?

Targeted cancer therapy will give doctors a better way to treat cancer. Eventually, treatments may be individualised based on the unique set of molecular targets produced by the patient’s tumour. Targeted cancer therapy also holds the promise of being more selective, thus harming fewer normal cells, reducing side effects, and improving the quality of life.

(The author is Medical Oncologist at HCG Hospital.)