About 2,500 years ago, the ancient Phoenician people stumbled across a way to pull chemicals from the mucous of local sea snails to create a rich purple dye. Named Tyrian purple, the dye was rare, expensive and reserved for nobility.

In modern times, scientists have explored these compounds and others similar to them for a different kind of noble cause — treating cancer and other diseases.

Researchers now know that the compounds that make Tyrian purple are bromoindirubins, chemical relatives of indirubin, a naturally occurring chemical with known healing properties. One of the most common vehicles for these compounds today is a traditional Chinese medicine mixture called Dang Gui Long Hui Wan, which is used to treat a form of leukemia. Among its blend of 11 herbs and flowers is indigo — which contains indirubin. Scientists have shown indirubin’s activity against brain, lung and prostate cancers, as well.

Wanting to know more about how indirubin hampers cancer, Sangkil Nam, Ph.D., associate research professor in the Department of Molecular Medicine, and Richard Jove, Ph.D., Morgan and Helen Chu Director’s Chair of Beckman Research Institute, studied the chemical A compound found in ancient times may lead to a future cancer treatment and some of its derivatives. They found that the compounds interfere with a protein called STAT3, which promotes cancer growth and development and can protect tumor cells from the immune system.

More recently, a team led by Jove and Lucy Liu, Ph.D., a graduate of City of Hope’s Irell & Manella Graduate School of Biological Sciences, focused on another compound called 6-bromoindirubin-3’-oxime, or 6-BIO. It is a chemical derivative of the bromoindirubins found in the Phoenicians’ sea snails.

The researchers discovered that 6-BIO works by blocking a group of proteins that activate STAT3. By blocking the proteins, 6-BIO keeps STAT3 from encouraging cancer. It also helps push the cancer cells to kill themselves.

Of all of the compounds the group tested, 6-BIO was the most effective indirubin derivative, suppressing tumor cell growth more than three times as effectively as indirubin itself.

“Many times we find the active ingredient in a natural or traditional remedy is effective but can be improved with some modification,” Liu said.

Importantly, 6-BIO also suppressed tumor growth and demonstrated low toxicity in laboratory studies, suggesting the substance may have a future as an anti-cancer agent.

The researchers are continuing their studies with the aim of testing the compound or related molecules in clinical trials.