Toronto (Sept. 1, 2020) — Targeting breast cancer cells that change and adapt to evade chemotherapy in order to survive and grow could be a new way to treat the often deadly triple-negative breast cancer, according to Princess Margaret Cancer Centre researchers.

Triple-negative breast cancer accounts for 15 per cent to 20 per cent of all yearly diagnosed breast cancers, but is responsible for a large portion of breast cancer deaths because it is so aggressive, and is more likely to have spread to other parts of the body and recur after treatment.

A study published in Cancer Discovery on Sept. 1, and led by senior author Dr. Mathieu Lupien, discovered changes in metabolism and epigenetics between chemotherapy-resistant and chemotherapy-sensitive cells, illuminating a major shift in understanding of the mechanisms driving drug-resistance – with the potential to identify a new druggable target.

"Our discovery is transformative because we found that non-genetic changes drive chemotherapy resistance, and these can provide more precise and druggable targets," says Dr. Lupien, Senior Scientist, Princess Margaret Cancer Centre. "We demonstrate that the metabolism of chemotherapy-resistant cells induces a unique epigenetic state that allows cells to thrive in the presence of chemotherapy."

Traditionally, cancer has been characterized as a genetic disease, but increasingly scientists have come to realize that epigenetic abnormalities are in fact key in initiating tumour development.

Building on rapid advances showing just how extensive alterations are in the epigenetic machinery of a cancer cell, major laboratories around the world are vying to understand the intricate nature of these epigenetic abnormalities which – unlike genetic mutations – are potentially reversible.

Emerging field of epigenetics

This has given rise to an emerging and massive global field of epigenetic therapy which seeks to reverse or restore the cell to a normal state – making this one of the most novel and important therapeutic avenues of cancer research.

In the laboratory, researchers at the Princess Margaret used patient-derived triple-negative breast cancer cells to identify epigenetic changes between two groups of cells: those that are chemotherapy-resistant and those that are chemotherapy-sensitive.

They found that specific epigenetic differences in drug-resistant cells were triggered by the metabolic stress induced by chemotherapy.

Specifically, these epigenetic changes or abnormalities in the chemo-resistant cells block a cellular viral mimicry response – a mechanism that normally prevents growth when cells sense viral infections, and that is activated by chemotherapy.

"Unblocking this viral mimicry response in chemo-resistant cells with drugs was our primary goal," says Dr. Lupien, "and we found that epigenetic therapy could unblock the viral mimicry response to complement chemotherapy in preclinical studies."

Dr. Lupien is also an Associate Professor in the Department of Medical Biophysics, University of Toronto. His lab’s tagline is "Decoding cancer through epigenetics."

Triple-negative breast cancer is more likely to occur before age 40 or 50, rather than after age 60 – which is more typical for other breast cancer types.

Researchers are working to find the best ways of treating triple-negative breast cancer, as there are no targeted therapies available to treat it. It is usually treated with chemotherapy or radiation therapy.

Funding for this study was provided by: Terry Fox Research Institute, Canadian Cancer Research Society, Ontario Institute for Cancer Research, Canadian Institute for Health Research, Princess Margaret Cancer Foundation, Ontario Ministry of Health, Quebec Breast Cancer Foundation, Gattuso-Slaight Personalized Cancer Fund, Canadian Cancer Society Breast Cancer Dream Team Research Funding, Stand Up to Cancer Canada, American Association for Cancer Research International.

About Princess Margaret Cancer Centre

Princess Margaret Cancer Centre has achieved an international reputation as a global leader in the fight against cancer and delivering personalized cancer medicine. The Princess Margaret, one of the top five international cancer research centres, is a member of the University Health Network, which also includes Toronto General Hospital, Toronto Western Hospital, Toronto Rehabilitation Institute and the Michener Institute for Education at UHN. All are research hospitals affiliated with the University of Toronto.

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