Low-Dose Viagra Could Keep Colorectal Cancer at Bay

A daily dose of sildenafil (Viagra) was found to substantially reduce the risk of developing colorectal cancer in mice models of the disease, according to a study recently published by Cancer Prevention Research.

Notably, a small, daily dose of sildenafil reduced polyp formation by 50% in mice. Since these cells can turn cancerous, this finding could have significant implications for colorectal cancer prevention.

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Commonly known as a treatment for erectile dysfunction, sildenafil has also been evaluated for other conditions in various doses and age groups, including in infants with pulmonary hypertension, according to the authors.

When administered in drinking water, sildenafil was found to prevent the development of polyps in mice engineered to develop hundreds of the growths, according to the study.

"Giving a baby dose of Viagra can reduce the amount of tumors in these animals by half," said researcher Darren D Browning, PhD.

The researchers also found that sildenafil increases levels of the cyclic GMP chemical, which is known to be involved with the epithelium.

Although much is still unknown, the authors noted that increased cyclic GMP can suppress cell proliferation occurring in the gut and increase normal cell differentiation. This process also ramps up apoptosis, according to the study.

"When we give Viagra, we shrink the whole proliferating compartment," Dr Browning said. "Proliferating cells are more subject to mutations that cause cancer."

However, existing polyps were not affected by sildenafil treatment, which highlights its potential as a preventive therapy.

The authors noted that these results are likely because sildenafil inhibits the PDE5 enzyme, which breaks down cyclic GMP so it’s available to reduce proliferation and increase differentiation.

The study also investigated the efficacy of linaclotide, a drug known to increase cyclic GMP. Although low-dose linaclotide was able to inhibit polyp formation, the adverse event of diarrhea may prevent it from being widely adopted, according to the authors.

In comparison, there are no known adverse events associated with low-dose sildenafil, according to the study.

Future studies should focus on implementing the therapy among patients at a high-risk of colorectal cancer, including those with familial history, previous polyps, and intestinal inflammation, according to the authors.