Donations = Metastatic Breast Cancer Research: This is the second in a series of six reports, written by CJ, on the research grants METAvivor has thus far awarded.
Grant #3 went to Andrea Mastro, PhD, for her research on breast cancer metastases in bone.
2011 Grant Recipient: Andrea Mastro, Ph.D. is a Professor of Microbiology and Cell Biology at Huck Institutes of the Life Sciences at Penn State University, PA.
Research Project: Dr. Mastro received a METAvivor grant in January, 2012 for her research proposal: Dormancy or growth? A three dimensional in vitro system to study breast cancer metastases in bone.
Setting the Scene: Circulating tumor cells (CTC) or bone disseminated tumor cells (DTC) are present in most breast cancer survivors tested. There is no known way to selectively remove them. Does this finding mean that the individuals with these cells will suffer from recurring metastases? Not necessarily. Many tumor cells die, but others simply remain dormant. Unfortunately, some of these dormant cells can remain for years, even decades, and then awaken to become aggressively growing metastases.
What triggers this escape from dormancy? It is known that dormant cells often reside in the bone, so it is reasonable to expect that the bone microenvironment plays a key role; however, it is difficult to study metastases in the bone due to the nature of the organ. The bone is a complex organ made up of bones cells, called osteocytes, osteoblasts and osteoclasts, and an extracellular matrix [ECM]. Both the bone cells and the matrix produce signaling biomolecules for growth, as well as for inflammatory responses involving cytokines. These bioactive molecules are essential for normal bone growth and maintenance but can be hijacked by CTCs and DTCs to remodel the bone environment to suit metastatic cancer growth. How this is accomplished, and which biomolecules are specifically involved in “awakening” dormant breast cancer cells to establish metastatic growth, is poorly understood.
In the laboratory, most of the experimental bone metastasis models are mouse models. Their use has led to many important discoveries. Nonetheless, it is difficult to selectively manipulate individual cells and the host environment in animals. Furthermore, it is especially difficult to study dormant cells, precisely because they do not grow into large visible colonies.
Pre-application research: Prior to applying for the METAvivor research grant, Dr. Mastro’s team had developed a three dimensional growth chamber called a bioreactor. When seeded in this bioreactor, the bone building cells (osteoblasts) secrete a thick matrix (ECM) that mineralizes into actual bone! When metastatic human breast cancer cells were added to the osteoblast matrix culture, Dr. Mastro’s team found that the cancer cells behaved very similarly to cell growth in bones of experimental animals. They penetrated the matrix resulting in bone loss, and lined up as rows of single cells, reminiscent of metastatic cells observed in clinical samples by pathologists. These behaviors are rarely seen in standard tissue culture.
In contrast to the metastatic cells, called MDA231 cells, a metastasis-suppressed variant of this line, called MDA-231-BRMS1 cells, did not exhibit this behavior under the same growth conditions. The BRMS1 cells attached loosely and did not grow over time. This behavior is similar to that seen in vivo. In a mouse model these types of cells form primary tumors but do not metastasize. Some can be found in the bone marrow but they do not grow there. They remain dormant. Thus, in the bioreactor growth chamber, these dormant cells exhibited the same characteristics as dormant cells in animal models. Interestingly, as in the case of humans, or on rare occasions in animal experiments, the BRMS1 cells did indeed sometimes escape dormancy to expand and grow in the bone. Why are most of these cells dormant and why did a few cells break dormancy?
Objective: Dr. Mastro’s hypothesis was that the behavior and characteristics of the ECM (bone matrix), in conjunction with bone marrow cytokines (present during immune system responses), were critical for both breast cancer dormancy and escape to the proliferative disease state. The in vitro bone bioreactor system would provide a superior tool to study the impact of metastatic bone microenvironment molecules on the dormancy status of breast cancer cells. The objectives were to compare the behavior or three types of cell lines — metastatic, growing (MDA-MB-231 ER negative); dormant (MDAMB-231BRMS1); and non-metastatic MCF-7(ER positive) — in the bone model bioreactor. The aims were: first, to manipulate the microenvironment by adding cytokines and other factors that increase during periods of accelerated bone remodeling (such as post fracture or osteoporosis) or inflammatory incidents (such as arthritis or infection); and second, to simulate bone remodeling by adding and activating osteoclasts to cause cytokine release and also to modify the ECM. The cells were to be monitored microscopically to observe morphological changes that would indicate escape from dormancy.
Where does the research currently stand?
In order to study the effect of the bone cells, the bone matrix, and the dormant breast cancer cells on the remodeling of the bone microenvironment to suit metastatic growth, Dr. Mastro’s team cultured the dormant MDA231BRMS1 cells in their 3D bioreactors. Then they added cocktails of cytokines and growth factors to mimic (a) general inflammation (osteoarthritis and rheumatoid arthritis) and (b) bone remodeling post trauma (osteoclast-derived). Initial findings show that cytokines involved in inflammatory responses do not “wake-up” the dormant MDA231BRMS1 cells. In contrast, however, addition of bone-derived cytokines and growth factors, to mimic traumatic bone injury and subsequent bone-remodeling, has a marked effect on “waking-up” the dormant MDA231BRMS1 cells. These cells can now penetrate the matrix, destroy the bone, and line up in rows of cells as seen in pathological samples from patients with metastases. Dr. Mastro’s group is now trying to narrow down the specific components of the cytokine cocktail that help accomplish this escape from dormancy. They will also test whether these bone-derived cytokines act directly on the breast cancer cells and ECM or require further signaling from certain bone cells called osteoclasts.
We look forward to reporting on the final results once Phase II has been completed.
Why is this important to the patient?
The threat of metastases or re-occurance of metastases is a constant concern for a cancer survivor. One of METAvivor’s main goals is to fund research that would help transition MBC into a chronic manageable condition. Understanding what makes a breast cancer cell stay dormant in the secondary organ for years, and what triggers an escape from dormancy to help establish metastatic growth, is key to developing therapies that can arrest metastatic growth and prolong dormancy to improve patient quality of life. At this point, chemo and adjuvant therapies are largely directed at the primary tumor, but with little knowledge of effectiveness on dormant cells, except indirectly in long-term clinical trials. Thus, Dr. Mastro’s research to tease out the key players involved in escaping dormancy is crucial to this quest. The outcomes from this study will be instrumental in development of innovative approaches to the treatment of active and dormant metastatic breast cancer.
Dr. Mastro is also known for her previous research on the beneficial effect of exercise on boosting immunity in breast cancer patients who’ve had chemotherapy. An article and two interview audio clips are available at this link: Exercise after Chemotherapy Boosts T-cells
