Melatonin helps to fight breast cancer, according to a study

Hormone is secreted naturally by the pineal gland located in the brain and participates in the regulation of sleep and wake cycle.

By Karina Toledo

Agência FAPESP – A study conducted in the São José do Rio Preto School of Medicine (Famerp) indicates that melatonin – the hormone with the main function of regulating sleep – can also fight breast cancer.

The experiments were conducted in the Laboratory for Molecular Cancer Research (LIMC) under the coordination of Professor Debora Aparecida Pires de Campos Zuccari and funded by FAPESP. The substance was found cut the average growth of tumors in mice by half.

The results were presented on June 13 during the Next Frontiers to Cure Cancer Congress, which was organized in São Paulo by A.C. Camargo Cancer Center.

“There is evidence in the scientific literature about the beneficial effects of melatonin against several types of tumors, and we decided to test it in breast cancer, which is one of the laboratory’s older lines of research,” commented Zuccari.

Melatonin is secreted naturally by the pineal gland located in the brain and participates in the regulation of sleep and wake cycle in all mammals. The substance can also be found in pharmacies in the form of a food supplement in some countries, but its sale in Brazil has not been authorized by the National Health Surveillance Agency.

According to Zuccari, previous studies have indicated that melatonin acts as an antioxidant, helping to eliminate the free radicals that can cause damage to DNA when taken in therapeutic doses that are higher than the levels normally found in an organism. Furthermore, melatonin inhibits the activity of telomerase, an enzyme that has more prominent expression in malignant cells, favoring their proliferation.

“Several studies have shown that tumors are often capable of manipulating the organism’s defenses, making even pro-inflammatory cytokines work in their favor. Melatonin appears to modulate this immune response, impeding malignant cells from multiplying freely,” explained Zuccari.

Before testing the action of melatonin in mice, the group lead by Zuccari evaluated the effect of different doses of the substance in two in vitro models of breast cancer. The experiments were part of the doctoral studies of Bruna Victorasso Jardim, who received a FAPESP fellowship.

“We used two different strains of cellular tumors. The first, an invasive ductal carcinoma, mimics the type of tumor that is most common in women, rarely causes metastasis and generally has a good prognosis. The other model represents the worst type of tumors, also known as triple negative because it does not respond to anti-estrogen treatment or chemotherapy. These latter types are more undifferentiated and have metastatic tendencies,” Zuccari explained.

The objective of the experiment was to determine the impact of melatonin on cell viability, or rather, on the proliferation capacity of cells in culture.

“When the tumor enters a process of exponential growth, part of the tissue begins to suffer hypoxia (a lack of oxygen), and this stimulates gene expression that is responsible for the formation of new blood vessels, mainly vascular endothelial growth factor, to increase the supply of nutrients to the location,” explained the researcher.

To stimulate hypoxia in vitro, the researchers applied cobalt chloride to the cell cultures; this substance consumes oxygen from the medium and stimulates gene expression to produce new blood vessels. The presence of HIF-1-alfa and VEGF were used as markers that the cells did, in fact, begin the process of angiogenesis.

A portion of the cultures were treated with doses of melatonin that varied between 0.5 and 10 millimoles (mmol). In metastatic cell lines, 1 mmol was the dose that showed the greatest benefit, reducing cell viability by 50% when compared to the control.

“In the invasive ductal carcinoma lines, all the doses were capable of reducing cell viability by more than 50%. We believe that the benefit is due to the fact that this type of tumor is sensitive to estrogen and that melatonin binds to the estrogen receptors. However, the interaction mechanism still has not been established in the case of metastatic cells, and more investigation is needed,” said Zuccari.

In vivo tests

The next step was to transplant the line of metastatic cells into the backs of immunosuppressed mice to evaluate whether treatment with melatonin would be capable of inhibiting the growth of the tumor.

“We used immunosuppressed animals because the immunological system of normal animals would destroy foreign cells, and the tumor would not be capable of developing. We also opted to use the lines of metastatic cells because they are more aggressive. The other tumor model would take a long time to grow and would not have as significant results,” stated Zuccari.

The rodents were split between two groups. One half received 1 milligram of melatonin daily for 21 days, starting from the moment when the tumor cells were transplanted. The other half received only a placebo in an attempt to maintain the same level of stress as the other group.

“We did not use larger doses in the animal model to avoid the possible neurotoxic effects of melatonin, which could compromise treatment, “said Zuccari.

The animals treated with melatonin presented significantly smaller tumors than the control animals after 21 days of treatment – on average 144.89 mm3 (± 38.37 mm3) versus 282.03 mm3 (± 88.52 mm3).

The average tumor volume among the control animals increased significantly between the 14th and 21st days, from 118.90 mm3 (± 40.17 mm3) to 282.00 mm3 (± 88.53 mm3), which was not observed in the animals treated with melatonin.

Furthermore, there was a regression of the tumor in one of the animals treated with melatonin – from 27.38 mm3 on day 7 to 8.79 mm3 on day 14 and 4.8 mm3 on day 21 – that was not observed in the control animals. “We are now performing protein expression analyses to understand why the benefit was greater in this animal,” explained Zuccari.

Jardim conducted the in vivo experiments at Henry Ford Hospital in the United States through an FAPESP Research Fellowship Abroad (BPE).

Zuccari currently supervises another post-doctoral study at the Henry Ford Hospital conducted by Thaiz Ferraz Borin, with the objective of evaluating the efficacy of melatonin in the prevention of metastasis.

“In this model, the cells in the metastatic lines are injected in the veins of the mouse’s tail. We evaluated whether treatment with melatonin managed to impede the fixation of malignant cells in other tissue,” explained the researcher.

The LIMC group is also conducting in vitro research on the action of melatonin on tumors in the head, neck and liver. According to Zuccari’s assessment, there is enough evidence to conduct clinical trials in women with breast cancer.

“In the beginning, however, we will have to attempt this treatment with patients with the worse prognosis, as there is no alternative therapy. This is because, in patients with a good prognosis, we run the risk of melatonin, which is considered to be an alternative drug, interfering with the efficacy of the standard treatment,” she added.