Inhibition of Prostaglandins May Be Mechanism by Which Aspirin Protects Against Certain Cancers


New research suggests that the reason aspirin may protect against certain cancers is its ability to inhibit prostaglandins, chemicals naturally produced by the body that are suspected of playing a role in colorectal and lung cancer.

Prostaglandins are chemical messengers that send signals in the body, stimulating various activities, including blood clotting and neurotransmission. Prostaglandins are also immune suppressors, and their inhibition might improve the body's ability to fight cancer cells.

Scientists were led to study aspirin because anecdotal evidence has suggested that adults who take the drug on a regular basis for other maladies are less likely to die of colorectal cancer.

Now, preliminary research by Mack T. Ruffin IV, MD, of the University of Michigan Medical School, Ann Arbor, suggests that as little as 80 mg of acetylsalicylic acid (ASA), the dosage of a baby aspirin tablet, taken each day can lead to significant prostaglandin suppression. By comparison, a person with a headache might take two adult-strength tablets of approximately 325 mg ASA per tablet, as many as six times a day.

Speaking at the annual meeting of the American Association for Cancer Research (AACR), Dr. Ruffin described his study of 65 healthy adults given 14 days of a single daily dose of ASA or a placebo. The doses of ASA were 40, 80, 160, or 640 mg. Rectal tissue biopsies were taken to monitor changes in prostaglandin levels.

Dr. Ruffin said that 80 mg/day was the lowest effective dose and that prostaglandin production remained suppressed up to 3 days after the last dose. In addition, the research team observed that women produce significantly less prostaglandin than men. "Women also have a lower incidence of colorectal cancer," Dr. Ruffin said, suggesting a possible link.

Aspirin and Lung Cancer

In his AACR presentation, André Castonguay, PhD, of Laval University, Quebec City, Canada, reported on a study of the ability of various nonsteroidal anti-inflammatory drugs (NSAIDs) to suppress the development of lung cancer in mice given NNK, a powerful carcinogen found in cigarette smoke.

He found that mice who received unprocessed, nonformulated ASA had 60% fewer lung tumors, compared with the control group. In mice fed the aspirin form of ASA, tumors were reduced by 63%. Sulindac, an NSAID arthritis medication, suppressed tumor growth by 52%, he said, and buffered aspirin did not demonstrate any significant protection from tumors.

Avoid 'Cavalier' Use

Even though ASA is available over-the-counter, Dr. Ruffin warned that it should not be used in a cavalier manner, and should be considered an experimental cancer drug. ASA has many potential side effects, including stomach pain, bleeding ulcers, nausea, diarrhea, and vomiting.

As many as 4% of the population cannot tolerate normal doses of ASA because of side effects. In addition, some people are allergic to ASA, and the drug may interfere with other medications.

"It is ironic that in this era of high-tech medicine, researchers are taking a second look at this old standby," Dr. Ruffin said. "Scientists are rediscovering it, and may find that it has a potential impact beyond even what we speculate now."

Dr. Ruffin also stressed that ASA should not be used as a "magic bullet" to prevent cancer instead of following a healthy diet and lifestyle. Colorectal cancer is believed to be related to the high-fat, low-fiber North American diet, and he also suspects that there may be a relationship between prostaglandin levels and diet.

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