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Modifying tumour electrical properties reduces breast cancer metastasis

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Amiodarone, an ion channel blocker approved for the treatment of other diseases, could significantly inhibit tumour cell invasion.

Researchers at Tufts University have found that manipulating voltage patterns in tumour cells using ion channel blockers, already FDA-approved as treatments for other diseases, can significantly reduce tumour cell invasion in a dish and metastasis in an animal model of breast cancer.

Madeleine Oudin, assistant professor of biomedical engineering at Tufts University School of Engineering and corresponding author of the study said the fact that the drugs are already approved for other conditions could lead to an expedited path to approval for the treatment of cancer.

“This is very much an unexplored, but highly opportunistic strategy for the treatment of cancer.

“Ion channels, which regulate the bioelectrical properties of cells, are the second-most common target for existing pharmaceuticals, so we have a relatively large set of ready-to-use drugs that could be repurposed for cancer therapy.”

To test their therapeutic strategy, the research team focused on triple-negative breast cancer (TNBC), a subtype of the disease which accounts for approximately 15 per cent of all breast cancer cases.

The likelihood of metastasis for TNBC is greater than all other subtypes of breast cancer, and because TNBC is associated with a poor five-year prognosis, scientists are focusing efforts on counteracting it.

Cells in the body create a natural voltage across their membranes, caused by ion channels that actively push or passively allow positive and negative ions into and out of the cell.

The researchers were able to show that manipulating the voltage properties of breast cancer cells can have a significant effect on their progression to metastasis, reducing the number of metastatic sites in mouse lungs by about 50 per cent.

There are currently no clinically available treatments that specifically target the process of metastasis, which remains the leading cause of death in cancer patients.

In normal cells, electrical voltage patterns provide a blueprint for orderly growth. But with cancer, the opposite happens.

Marked by a breakdown in the normal electrical patterns generated by the cells, they lose their specialized functions, start expanding into a tumour and spread into and disrupting the function of other tissues, metastasis.

While there are a variety of channels that drive the movement of positively charged sodium, calcium, and potassium ions, as well as negatively charged chloride ions, potassium ion channels tend to dominate in generating the voltage across the cell membrane.

When the Tufts researchers genetically over-expressed the potassium ion channels in tumour cells, the inside of the cells became more negatively charged, and the imbalance in voltage led to increased tumour growth and metastasis, both in plated cells and animal models.

The researchers’ therapeutic strategy took the opposite approach, blocking the potassium ion channels led to a restoration of more normal voltages for the cells, decreased tumour cell invasion and significantly reduced metastasis.

Four FDA-approved potassium ion channel blockers were screened, and all had similar effectiveness in killing tumour cells.

One drug, amiodarone, had the largest effect on normalising cell voltages and was selected to see how well it would work in treating breast cancer in mice.

The researchers found that the drug, approved for use in treating heart rhythm disorders, cut back on the tumours’ ability to spread as cells broke off and move to other parts of the body.

By looking at the genes that were triggered by the voltage shift, they found a number of molecular pathways involved in the movement of cells.

The effects of the ion channel blocking drug were consistent with limiting the movement of the cell, so they don’t break off and grow new tumours.

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