Scientists have puzzled for years over how exactly aspirin works to ward off cancer. Most think it has to do with the drug's inflammation-lowering effects. 

Now Veterans Affairs (VA) researchers and colleagues in Texas have a new theory, tested in mice and cell cultures. It has to do with aspirin's effects on platelets, which form clots to stop bleeding. The findings (“Unlocking Aspirin's Chemopreventive Activity: Role of Irreversibly Inhibiting Platelet Cyclooxygenase-1”) appear in Cancer Prevention Research. 

Along with clotting, platelets also play a role in forming new blood vessels. That action is normally beneficial, such as when a new clot forms after a wound and new vessels are needed to redirect blood flow. But the same action can help tumors grow. It's this process that aspirin can interrupt, say the researchers. Their lab tests showed how aspirin blocked the interaction between platelets and cancer cells by shutting down the enzyme cyclooxygenase-1 (COX-1), thereby curbing the number of circulating platelets and their level of activity. 

Some of the experiments used regular aspirin from a local drug store. In another phase, the researchers used a special preparation of aspirin combined with phosphatidylcholine, a type of lipid. The molecule is a main ingredient in soy lecithin. The product, known as Aspirin-PC/PL2200, now in development by Houston-based PLx Pharma, is designed to ease the gastrointestinal risk associated with standard aspirin. 

The enhanced aspirin complex was even stronger against cancer than the regular aspirin, according to the researchers who wrote that “These results suggest that aspirin's chemopreventive effects may be due, in part, to the drug blocking the pro-neoplastic [supporting new, abnormal growth, as in cancer] action of platelets; and [they support] the potential use of Aspirin-PC/PL2200 as an effective and safer chemopreventive agent for colorectal cancer and possibly other cancers.” 

Lenard Lichtenberger, Ph.D., who led the research, has a financial stake in PLx Pharma, the company developing the new lipid-based aspirin under the brand name Aspertec. None of the other authors reported potential conflicts of interest. Dr. Lichtenberger is a professor of integrative biology and pharmacology at the University of Texas Health Sciences Center. 

The VA leader in the group was Vinod Vijayan, Ph.D., a research health scientist at the DeBakey VA Medical Center and an expert in platelet biology. He is with the site's Center for Translational Research on Inflammatory Diseases. Dr. Vijayan is also an associate professor at Baylor College of Medicine. 

The group says they plan to test the lipid–aspirin complex for safety and efficacy in people at high risk for colorectal cancer in a collaboration with researchers at MD Anderson Cancer Center in Houston. Meanwhile, they say their results so far “support the use of low-dose aspirin for chemoprevention.” They add that Aspirin-PC/PL2200 has “similar chemopreventive actions to low-dose aspirin and may be more effective.” 

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