New Means for Studying Cancer

by National Cancer Institute

(Page 7 of 9)

1982 -1985

BY USING TRANSGENIC ANIMALS, the role of specific cancer-causing oncogenes and tumor progression factors are studied. Researchers have shown that some oncogenes can be moved into specific animal tissues under certain conditions and produce cancer. Other experiments in retrovirus-tagged mutagenesis follow the insertion of a retrovirus near a cell's proto-oncogene to see if the proto-form converts to a cancer-causing oncogene.

Improved Diagnostic Techniques

Advances in computer technology in the 1980s transformed diagnostic imaging, now making it possible to visualize organs and soft tissues in a detail that had previously been available only with anatomical dissections.

Imaging techniques such as CT, PET, MRI and ultrasound provide additional windows into the body, allowing tumors or other abnormalities to be detected in areas not accessible with a physical examination or x-rays alone.

Another technique, immunodiagnosis, uses antibodies, linked to radioactive isotopes, which seek out and identify cancerous growths. These antibodies can be used to study cancer growth in the laboratory or be injected into the body as markers for tracking cancer cells.

Transplanting Cells and Genes

In the 1980s, scientists transformed the SCID mouse (a mouse lacking a functional immune system, a condition called Severe Combined Immunodeficiency Disease) with human immune cells and tissues, creating an in vivo model of the human immune system.

Transferring cells to mice with SCID enables researchers to explore the workings of the immune system and its complex relationship to cancer and to other diseases such as cystic fibrosis and atherosclerosis. Genetic engineering also makes possible the transfer of genes for human proteins such as insulin into organisms like yeast, bacteria, animals and plants. The organisms then serve as human protein "factories."

New Tools for Genetic Explorers

During the 1980s, geneticists gained several remarkable new tools. These include RFLPs, fragments of DNA as unique as an individual's fingerprints; PCR, a technique that makes it possible to take a speck of DNA and make billions of copies within hours; YACs, or yeast artificial chromosomes, which provide a vector to manipulate vast stretches of custom DNA; and FISH, a chromosome staining technique that uses fluorescent dyes to label specific chromosome regions.

DNA sequencing accelerated suddenly when Leroy Hood developed an automated sequencing machine that read 7,000 DNA "letters" in a day.

Cancer Research and AIDS

Just as NASA's space program generated unexpected benefits for industry and society, the National Cancer Program has produced spin-offs in medicine. A driving force in genetic engineering and other biotechnologies, cancer research has also yielded clues to the causes and treatments of other diseases such as acquired immunodeficiency syndrome (AIDS). In 1984, only three years after the AIDS epidemic was recognized, Robert Gallo of the NCI and Luc Montagnier of the Insitut Pasteur in France succeeded in identifying, isolating and growing HIV, the human immunodeficiency virus that causes AIDS. Ongoing research into the role of RNA viruses in causing cancer made this breakthrough possible.

New Drugs

The NCI screens thousands of drugs, natural and synthetic, each year for anticancer properties. Plants such as May apple, periwinkle and the yew tree have provided powerful and promising anticancer substances. For those answers not found in nature, researchers also use computer modeling systems to design molecules that may have the desired pharmaceutical effect on a targeted area of a cell.

Drug Resistance: The Drug Efflux Pump

The use of anticancer drugs, along with the standard treatments of surgery and radiation directed at tumors, ensures that roving cancer cells metastasizing into the bloodstream also come under attack. However, many common cancers develop a resistance to multiple anticancer drugs. In 1983 Victor Ling and his associates discovered a protein, P-glycoprotein, that resides in the cell membrane and is thought to pump anticancer drugs out of cancer cells along with other substances perceived as toxic. Identification of the human gene that encodes the drug pump has allowed researchers to consider possibilities for circumventing the pump and enhancing drug therapy.

About the Author

www.nci.nih.gov
The National Cancer Institute's research programs are extensive and contain many innovative initiatives. I invite you to explore our Web site to find out more about the exciting work being conducted here at NCI and by NCI-supported scientists throughout the country.