In a new study from the University of Illinois Urbana-Champaign, researchers found a new approach to treating breast cancer kills 95-100% of cancer cells in mouse models of human estrogen-receptor-positive breast cancers and their metastases in bone, brain, liver, and lungs.
The newly developed drug, called ErSO, quickly shrinks even large tumors to undetectable levels.
The team found even when a few breast cancer cells do survive, enabling tumors to regrow over several months, the tumors that regrow remain completely sensitive to retreatment with ErSO.
It is striking that ErSO caused the rapid destruction of most lung, bone, and liver metastases and dramatic shrinkage of brain metastases since tumors that have spread to other sites in the body are responsible for most breast cancer deaths.
The activity of ErSO depends on a protein called the estrogen receptor, which is present in a high percentage of breast tumors.
When ErSO binds to the estrogen receptor, it upregulates a cellular pathway that prepares cancer cells for rapid growth and protects them from stress. This pathway spurs the production of proteins that protect the cell from harm.
The team says ErSO is a small molecule that had powerful anticancer properties without detectable side effects in mice.
The unique thing about this compound is that it doesn’t touch cells that lack the estrogen receptor, and it doesn’t affect healthy cells—whether or not they have an estrogen receptor. But it’s super-potent against estrogen-receptor-positive cancer cells.
ErSO is nothing like the drugs that are commonly used to treat estrogen-receptor-positive cancers, which are therapeutically used to block estrogen signaling in breast cancer.
Even though it binds to the same receptor that estrogen binds to, it targets a different site on the estrogen receptor and attacks a protective cellular pathway that is already turned on in cancer cells.
Since about 75% of breast cancers are estrogen-receptor positive, ErSO has potential against the most common form of breast cancer.
The amount of estrogen receptor needed for ErSO to target breast cancer is very low, so ErSO may also work against some breast cancers not traditionally considered to be ER-positive.
Further analysis in mice showed that exposure to the drug had no effect on their reproductive development.
ErSO also worked quickly, even against advanced, human-derived breast cancer tumors in mice. Often within a week of exposure to ErSO, advanced human-derived breast cancers in mice shrank to undetectable levels.
The team found many of these breast cancers shrink by more than 99% in just three days. ErSO is fast-acting and its effects on breast cancers in mice are large and dramatic.
The pharmaceutical company Bayer AG has licensed the new drug and will explore its potential for further study in human clinical trials targeting estrogen-receptor-positive breast cancers
If you care about breast cancer, please read studies about blood pressure drugs that may increase breast cancer death risk and what women need to know about breast cancer and heart disease.
For more information about breast cancer and your health, please see recent studies about a major cause of deadly breast cancer and results showing that this discovery may help stop breast cancer’s deadly spread.
The study is published in Science Translational Medicine. One author of the study is biochemistry professor David Shapiro.
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