Combining the sleep hormone melatonin with breast cancer drugs makes the drugs more effective at killing cancer cells, says a study from Tabriz University of Medical Sciences in Iran. The new therapy could mean patients could be given lower doses which would decrease side effects.

The hormone is delivered via tiny bubbles called nanostructured lipid carriers (NLCs). Researchers say it made tamoxifen, the leading medication used to treat breast cancer, stronger.

Although tamoxifen is widely used, it can cause serious side effects, including an increased risk of uterine cancer, stroke, pulmonary embolism, and vision problems. More common side effects include irregular menstruation, hot flushes and weight loss.

Cancer cells can also become resistant to tamoxifen — called chemoresistance — which makes it less effective and will eventually stop working altogether.

Previous research found that the sleep hormone melatonin can help cancer cells die, so the researchers involved in the new study wanted to see if they could use it to help tamoxifen kill cells more effectively, and reduce the incidence of side effects.

"We tried to solve both issues by putting melatonin into nanostructures so they can help the chemotherapeutic agent kill more cells," said Dr. Nasser Samadi. "By doing this, you can decrease the dose of tamoxifen needed, reducing the severity of the side effects."

Melatonin is a naturally occurring hormone produced in the body. It is important for sleep and growth, and the development of different tissues, but it also helps cancer cells die. However, melatonin is not very stable and it breaks down quickly in the body, so it needs to be re-injected or taken again every few hours.

To overcome its short survival time, the researchers developed tiny bubbles called nanostructured lipid carriers (NLCs) that can release melatonin slowly over a period of time. Essentially, this means the treatment can kill the cancer cells continuously, without needing to take new doses of melatonin.

When they tested the structures on cells in the lab, they found that melatonin-loaded NLCs inhibited the growth of breast cancer cells more effectively than melatonin alone. They also tested the empty NLCs and found that they did not kill the breast cancer cells without the melatonin and were not toxic to surrounding tissue.

"Lots of nanostructures these days are toxic to the body or to other cells, but we found no significant toxicity in the empty NLCs," said Samadi. "The characteristics are very suitable for applying to these kinds of treatments."

The team plans to test their NLCs on other cancer cells and treatments before moving to animal models and, eventually, clinical trials.