Study reveals how cancer drug helps to restore immune system's ability to fight tumours

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A group led by scientists at The University of Texas at Austin has discovered a brand-new, bio-inspired medication that restores the capability of immune cells to combat cancer. The medication increases the effectiveness of immunotherapy and inhibits tumour growth in mice models of melanoma, bladder cancer, leukemia, and colon cancer.

The findings of the research published in the journal Cancer Cell and could be a game changer for many cancer patients.

A DNA segment known as 9p21, which is frequently deleted in tumours and occurs in 25 per cent - 50 per cent of various cancers such melanoma, bladder cancer, mesothelioma, and several brain cancers, is frequently deleted. Long-standing research has shown that malignancies with the 9p21 deletion have worse prognoses for patients and are more resistant to immunotherapies, which are cancer treatments that boost a patient's innate immune system.

The deletion helps cancer cells avoid getting detected and wiped out by the immune system, in part by prompting the cancer to pump out a toxic compound called MTA that impairs normal functioning of immune cells and also blocks the effectiveness of immunotherapies.

"In animal models, our drug lowers MTA back down to normal, and the immune system comes back on," said Everett Stone, a research associate professor in the Department of Molecular Biosciences and associate professor of oncology at Dell Medical School, who led the work. "We see a lot more T cells around the tumor, and they're in attack mode. T cells are an important immune cell type, like a SWAT team that can recognize tumor cells and pump them full of enzymes that chew up the tumor from the inside out."

Stone envisions the drug being used in combination with immunotherapies to boost their effectiveness.

The study's co-first authors are Donjeta Gjuka, a former UT postdoctoral researcher and currently a scientist at Takeda Oncology, and Elio Adib, formerly a postdoctoral researcher at Brigham and Women's Hospital and the Dana-Farber Cancer Institute, and currently a resident physician at Mass General Brigham.

The 9p21 deletion leads to the loss of some key genes in cancer cells. Gone are a pair of genes that produce cell cycle regulators -- proteins that keep healthy cells growing and dividing at a slow, steady rate. When those genes are lost, cells can grow unchecked. That's what makes them cancerous. Also deleted is a housekeeping gene that produces an enzyme that breaks down the toxin MTA. It's this loss, according to Stone, that lets cancer cells acquire a new superpower: the ability to deactivate the immune system.

"Cancer gets a two-for-one when it loses both of these genes," Stone said. "It loses the brakes that normally keep it from growing in an uncontrolled manner. And then at the same time, it disarms the body's police force. So, it becomes a much more aggressive and malignant kind of cancer."

To create their drug candidate, Stone and his colleagues started with the helpful enzyme that's naturally produced by the body to break down MTA and then added flexible polymers.

"It's already a really good enzyme, but we needed to optimize it to last longer in the body," Stone said. "If we injected just the natural enzyme, it would be eliminated within a few hours. In mice, our modified version stays in circulation for days; in humans it will last even longer."

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