January 2006


Cancer is a group of similar diseases that have sickened people and frustrated healers since the dawn of human history. Many types of treatments--or therapies--have been developed in an effort to control and cure cancers. Many of these have been successful and cancer researchers are busy developing new, effective therapies all the time.

One form of cancer therapy, known as chemotherapy, or just "chemo," uses chemical compounds to fight cancer. Chemotherapy, especially when used in combination with other therapies, has become an important tool in modern cancer treatment. Doxorubicin (pronounced docks-e-roo-bi-sin) hydrochloride is an example of a popular chemotherapy drug that is made with chlorine.

The Biology of Cancer

Cells are the tiny building blocks of all living things. An adult person is made up of some 60-90 trillion cells, while bacteria are single-celled organisms. Today's powerful microscopes reveal the world of cells to scientists along with huge clues about cancer. Cancer, scientists tell us, is a disorder of some of the cells of the human body.

Normal cells have a life cycle: they form, they function, and finally they die off and are replaced by newly formed cells. Normal cells grow by a kind of controlled splitting or dividing of cells, known as mitosis (my-TOE-sis). Cancer cells, however, grow and divide uncontrollably. You might think of cancer as similar to a stuck key on a computer keyboard that won't stop printing a letter (eeeeeeeeeeeeeee.) on a screen.

The Main Parts of a Cell
All living beings are made up of cells.

Cancerous cells divide uncontrollably because their DNA is damaged. DNA is a substance in the nucleus of a cell that acts as a cell's brain, telling it how to function. The figure above shows the cell nucleus as one of the three main parts of a cell.

Amazingly, the DNA in our cell nuclei ("nuclei" is the plural of "nucleus") contains all of the information necessary for our survival. If you could see your DNA, you might describe it as shaped like two intertwined spiral staircases. In the past few decades, scientists have made amazing discoveries about DNA and how it determines who we are.

Doxorubicin Hydrochloride Zeros in on Fast-dividing Cells

Left: unaltered DNA Right: DNA affected by chemotherapy drug (Image created by Karol Langner (2005) and released into the public domain.)

Chemotherapy drugs such as doxorubicin hydrochloride target fast-dividing cells, putting a stop to the out-of-control growth of cancer cells. Doxorubicin hydrochloride actually zeros in on the DNA in the nuclei of these fast-growing cells. The goal is to disable the "DNA brains." One of the ways doxorubicin hydrochloride does this is by injecting itself into some of the empty spaces in the DNA molecule. This damages the DNA, causing a bit of unwinding of the spiral staircases, making it impossible to form new cancer cells.

Unfortunately, chemotherapy drugs cannot yet be designed to target only cancer cells, and so chemotherapy has side-effects--unwanted results. Besides cancer cells, chemo may also target other types of human cells that grow and divide rapidly. For example, cells responsible for hair growth, naturally fast dividers, are also affected by chemotherapy. For that reason, temporary hair loss is a side-effect of chemotherapy. Many patients solve this problem by wearing hats, scarves or wigs.

Derived from Bacteria

Many life-saving drugs are derived from chemical compounds found in nature. For example, it is estimated that 40 percent of all drugs in use today contain at least one plant-derived ingredient. Doxorubicin is produced from the bacterium, Streptomyces peucetius, found in soils. Scientists think that soil bacteria produce chemicals like doxorubicin to kill off other types of soil bacteria in the naturally competitive soil environment. To harvest this compound for chemotherapy, scientists remove doxorubicin chemically from Streptomyces peucetius using hydrogen chloride.

It is truly amazing and wonderful that from a microscopic organism found in soil, scientists have managed to produce a life-saving chemotherapy drug!

Follow-up Activities:

  1. Use the Internet to explore different types of cells. Find out how and why plant cells differ from animal cells. Draw diagrams to show these differences.

  2. Microscopes give us a peak into a fascinating world. Explore the image gallery at: http://askabiologist.asu.edu/pages/gallery.html to see what some common objects look like under the powerful gaze of the microscope.

  3. Learn about mitosis, the process by which one cell becomes two, which has been captured in micro-photography at this site: http://micro.magnet.fsu.edu/micro/gallery/mitosis/mitosis.html.

For a list of previous "Chlorine Compound of the Month" features, click here.


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