“Brain metastasis is a major problem for breast cancer patients, and most of the treatments that we have are not that effective. We have identified unique features of metastatic breast cancer cells that could serve as new targets,” said Srinivas Malladi, Ph.D., assistant professor of pathology and member of the Harold C. Simmons Comprehensive Cancer Center, who co-led the study with Pravat Kumar Parida, Ph.D., a postdoctoral fellow in the Malladi lab.
The brain is a common site for breast cancer metastasis, particularly for patients with a subtype of this disease known as HER2+. About half of patients with HER2+ breast cancers develop secondary tumors at some point after their primary tumor is diagnosed, Dr. Malladi explained, a phenomenon known as metachronous brain metastasis (M-BM).
Synchronous brain metastasis (S-BM), when secondary brain tumors are diagnosed at the same time as the primary breast tumor, are rarer – but patients with S-BM have a far worse prognosis, with a median overall survival of just six months after diagnosis.
HER2+ breast cancer patients with latent brain metastatic cells (Lat) are asymptomatic and likely to develop M-BM over variable lengths of time.
Using an animal model developed in the Malladi lab, Drs. Malladi, Parida, and their colleagues found significant differences in the metabolism of these different types of brain metastatic cells.
For example, while S-BM cells used glucose as a primary fuel source, M-BM and Lat cells used a related sugar called glutamine. Also, Lat cells secreted less lactate, a form of lactic acid, than M-BM and S-BM cells.
Lactate helps M-BM and S-BM cells to evade innate immune surveillance and hence can promote tumor survival.
Additionally, the researchers discovered higher amounts of a protein known as xCT, which mediates oxidative stress, in the M-BM and Lat cells compared to S-BM. Stemming the activity of this protein using genetic techniques and chemical inhibitors significantly reduced the metastatic activity of M-BM and Lat cells and made them more vulnerable to drugs that target HER2+ cells.
Dr. Malladi noted that the differences identified in the study suggest potential targets to attack brain metastasis in breast cancers and potentially other types of malignancies.
Because an xCT inhibitor is already being tested in clinical trials for multiple myeloma, he added, its use could represent a particularly promising strategy for attacking metabolic vulnerabilities of brain metastases.