Johns Hopkins Medicine scientists, who study a deadly type of breast cancer called triple negative, say they have identified important molecular differences between cancer cells that adhere to an original tumor and those that dare to grow distant tumors.
Research using mouse models and human tissue could pave the way for the development of new treatments that target such molecular variations.
A report of the results will be published on August 3rd Science Translational Medicine.
“We have long needed new treatment targets and options for triple-negative breast cancer,” says Andrew Ewald, Ph.D., Virginia DeAcetis Professor of Basic Research and Director of the Department of Cell Biology at Johns Hopkins University School of Medicine and co-leader of Cancer Invasion and Metastasis Program at the Johns Hopkins Kimmel Cancer Center. “These cancers often return within three years of diagnosis, and treatments used for other breast cancers don’t usually work in triple negative.”
An estimated 10-20% of the 280,000 breast cancers diagnosed in the US each year are triple negative, and the rate is higher in African American women, who are twice as likely as others to have this form of the disease.
The deadly nature of this cancer is characterized by the fact that its cells lack molecular flags on their surface associated with the hormones estrogen and progesterone and a cancer-promoting protein called Her2-neu. Many current breast cancer therapies work by targeting these flags, making them of little use to those with triple-negative tumors.
For the current study, the research team examined molecular differences between initial, or primary, triple-negative breast cancer sites and areas where it has spread, or metastatic sites, between three different types of cells: mouse models, human cancers implanted in mice, and samples from primary and metastatic Tissues from eight patients treated at Johns Hopkins Hospital.
Researchers used a combination of machine learning, cellular imaging and biochemical analysis to identify differences in genetic expression patterns of incipient and metastatic tumors.
“The bad news from our study is that cells from metastatic sites are super-optimized for migration and resist treatment,” says Ewald. “The good news is that we have identified several proteins called transcription factors that these cells need to meet the challenges of migrating and thriving at metastatic sites, and we may be able to develop new therapies that target these transcription factors.” “
More specifically, Ewald and Johns Hopkins postdoctoral researcher Eloïse Grasset, Ph.D., and other members of the research team found several unique properties in the cells of mice engineered to have the mouse version of triple-negative breast cancer and mice who have had tumors implanted from people with triple negative breast cancer.
The scientists found that when triple-negative breast cancer cells invade other tissues on their way to another part of the body, they acquire two cellular traits: better movement and better survival.
To do this, breast cancer cells receive a cellular skeletal protein called vimentin, which improves the ability of cells called mesenchymal cells, a type of cell typically found in bone and bone marrow, to migrate and form new cells.
Triple-negative breast cancer cells also gain survival benefits by producing a protein called E-cadherin, which is typically found in epithelial cells that line the ducts and coverings of organs and are often self-renewing.
When triple-negative breast cancer cells acquire such survival and migratory properties, scientists classify their cellular state as so-called hybrid epithelial mesenchymal (EMT) cells.
To study molecules involved in hybrid EMT states in more detail, the scientists sought the help of Elana Ready, Ph.D., department head and associate director of quantitative sciences and co-director of the Convergence Institute at the Johns Hopkins Kimmel Cancer Center to follow the molecular patterns of individual cells in cell assays that model invasion from the primary tumor and formation of a colony at a metastatic site.
Fertig’s computer team used machine learning techniques to find patterns in each cell’s RNA expression, a cousin of DNA involved in protein production. The scientists found that most metastatic cells transform into the more mobile, better surviving, hybrid EMT state. Ewald’s team then validated these conditions in samples from eight patients with triple-negative tumors, examining both primary tumors and tissue from metastases from the same patients.
At the molecular level, most metastatic cells produced five proteins called transcription factors (Grhl2, Foxc2, Zeb1, Zeb2, and Ovol1) that promote the manufacture of proteins involved in either cancer cell invasion or colony formation.
“The molecular differences between metastatic and primary tumors are probably the reason why metastatic tumor cells are so resistant to current treatments,” says Ewald.
His team is investigating ways to block transcription factor genes or resulting proteins to halt metastatic cancer growth, and whether the same molecular and cellular changes occur in other cancers such as colon, adrenal, stomach and small intestine.
Other Johns Hopkins researchers who contributed to the study include Matthew Dunworth, Gaurav Sharma, Melanie Loth, Joseph Tandurella, Ashley Cimino-Mathews, Melissa Gentz, Sydney Bracht, and Meagan Haynes.
The research was supported by the Breast Cancer Research Foundation, the Twisted Pink Foundation, Hope Scarves, the Jayne Koskinas Ted Giovanis Foundation, the Cindy Rosencrans Fund for Triple Negative Breast Cancer Research, and the National Cancer Institute of the National Institutes of Health (U01CA217846, U54CA268083 , 3P30CA006973, U01CA212007, U01CA253403).