The role of the collagen-dense tumor microenvironment in breast cancer 

The central focus of the Ponik lab is to understand the molecular mechanisms underlying breast cancer risk and progression due to increased breast density. Patients with mammographically dense breast tissue have a four to six-fold increased risk of developing breast carcinomas. In fact, 1/3 of all breast cancer cases are attributed to breast density, making it one of the greatest risk factors for carcinoma. Increased breast density is associated with a significant increase in the deposition of extracellular matrix (ECM) components, most notably the protein, collagen. Within the breast tumor microenvironment, regions of dense collagen that are associated with increased inflammatory signaling (COX-2) and presence of inflammatory macrophages provide a predictive biomarker patient outcome. Using a combination of in vitro and in vivo model systems, we hope to elucidate how increased collagen density promotes the progression of breast carcinoma and identify therapeutic targets to treat women with mammographically dense breast cancer. 

1. How do tumor cells sense and respond to alteration in ECM structure and composition? 

During oncogenic transformation, normal interactions with the ECM are profoundly altered, resulting in cells that lose their polarization and differentiation, lose anchorage dependent growth control, and acquire a migratory, invasive phenotype. To investigate the features of the ECM that are critical to these tumor-associated phenotypes, we use an in vitro 3D collagen gel model. Using this model, we determined that increasing the stiffness of the collagen matrix is sufficient to disrupt breast epithelial differentiation, increase cell proliferation and enhance invasion. However, the specific molecular players and signaling pathways that are regulated by ECM alterations, and how these pathways are involved in the progression of breast cancer is still relatively unknown. Therefore, part of the lab is focused on understanding how cells sense and respond to mechanical and compositional alterations of the extracellular matrix during cell invasion.

2. How does the collagen-dense tumor microenvironment enhance tumor progression in vivo?

Our ability to understand cancer progression has been significantly enhanced by the techniques of multiphoton microscopy and second harmonic generation imaging (SHG).  Applying these techniques in conjunction with rodent mammary imaging windows, allows us to study tumor formation, progression, and metastasis within live mammary tumors. The interactions between tumor cells and the matrix can be observed over time to capture in vivo cell migration events or to track changes in the same tumor repeatedly over multiple weeks to identify the timing of cell populations involved in disease progression. Additionally, we can utilize endogenous fluorescence to identify specific cell types and examine the interplay between the immune system and cancer. Ultimately, these experiments help us better understand how physical changes in the ECM drive cell phenotype and promote metastatic progression.

3. Does the collagen-dense matrix drive immune suppression?

Our investigation into mammary tumor progression identified inflammatory cytokines, metabolic alterations, and infiltration of immune populations, including macrophages and neutrophils, that are dramatically increased when tumors arise in a collagen dense microenvironment. Many of the factors that are upregulated in response to collagen density are known to promote immune evasion during tumor progression. However, it is unclear how underlying ECM cues drive immune suppressive signaling in breast cancer. Therefore, we seek to identify specific ECM signatures that drive immunosuppressive signaling and may serve as predictive biomarkers of immune suppression and resistance to immune checkpoint therapy.