A new study is reporting that small daily doses of Viagra reduced the number of polyps by half in animal models predisposed to develop colorectal cancer. This intriguing off-label use adds a possible new chapter to the life of a drug famously known for treating erectile dysfunction.

Viagra, also known as sildenafil, was initially developed in the 1990s for hypertension but early clinical studies revealed it wasn't particularly effective as a heart disease treatment. Many of the trial volunteers were also reporting side effects of unexpected erections. This led to the drug being approved in 1998 by the FDA to treat erectile dysfunction.

Over the last twenty years Viagra has been investigated for a number of unexpected alternative uses from an anti-obesity drug to a potential treatment for jet-lag. Now a team of researchers suggest the drug could protect against colorectal cancer.

The research centers on the idea that increased levels of a chemical called cyclic GMP has been seen to suppress some intestinal cancers by reducing excessive cell proliferation in the gut. Viagra is known to inhibit an enzyme found in colon cells called PDE5. This enzyme breaks down cyclic GMP, so Viagra can indirectly help increase levels of cyclic GMP in the colon, subsequently reducing the volume of proliferating cells which then reduce the potential of abnormal mutations resulting in polyps that can lead to cancer.

In a mouse model, engineered with a mutation designed to cause large numbers of polyps, the animals administered with small doses of Viagra displayed a remarkable 50 percent reduction in the number of polyps they developed. A second drug called linaclotide was also trialled in the study and it was found to reduce the number of polyps even more significantly. Unfortunately linaclotide, used to treat irritable bowel syndrome patients with constipation, is not a fantastic target for a long-term human treatment due to its major side effect of diarrhea.

The next stage of the research is to undertake a human clinical trial of Viagra in subjects at high risk of developing colorectal cancer. The scientists suggest this drug could be a very viable treatment for high risk patients. And even better, Viagra is almost off patent, and a cheap generic version of the drug is already available.

The new research was published in the journal Cancer Prevention Research.

Source: Augusta University