BONEMETTNC

Evidence suggests that the progression of breast cancer depends on interactions between cancer cells and the surrounding microenvironment. Researchers in the BONEMETTNC project aim to dissect the role of the microenvironment in breast cancer metastasis, work which could open up new therapeutic avenues, as Dr Thordur Oskarsson explains

The most common form of cancer in women, accounting for around 25 percent of all female cases across the world, breast cancer causes more than 500,000 deaths a year. The vast majority of these deaths are caused by metastasis, the process by which malignant cells spread to distant organs, a topic that lies at the core of the BONEMETTNC project. “We are trying to dissect the role of the surrounding microenvironment in breast cancer metastasis,” says Dr Thordur Oskarsson, the project’s Principal Investigator. The consequences of mutations and other changes in cancer cells are frequently context-dependent, underlining the importance of research into the surrounding microenvironment, or metastatic niche, which supports the continued growth of the cancer. “Over the last few years we have focused in particular on the extracellular matrix, which is the non-cellular component of the microenvironment,” outlines Dr Oskarsson.

The extracellular matrix fills the space between cells within tissues and performs a number of key functions, including providing structural support and regulating cellular communication. In cancer, the extracellular matrix is distinct from healthy tissue and resembles the matrix that is produced during wound healing. The development of a cancer associated matrix is a complex process, however it is recognized that reactive stromal fibroblasts, a type of connective tissue cell, play a prominent role in matrix production and maturation. This is an area of great interest to Dr Oskarsson. “We aim to dissect the molecular cross-talk between these stromal cells and cancer cells,” he says.

These interactions are highly dynamic and the resulting extracellular matrix niche may not form instantaneously. Therefore, when disseminated cancer cells arrive at a distant site, the microenvironment may not be welcoming, leading to the elimination of most of the cancer cells. The continuous cross-talk

between cancer cells and stroma induces changes in the microenvironment, which may generate a supportive niche that promotes cancer growth. “Moreover, we have observed that the cancer cells that can bring their own niche components have a selective advantage in secondary organs,” explains Dr Oskarsson.

The extracellular matrix protein tenascin C (TNC), a type of matricellular protein, is an essential component of the metastatic niche in breast cancer. “We’ve observed that TNC is expressed in cancer cells that we isolated from the pleural fluids of breast cancer patients. These are patients with systemic metastasis, so we think that these samples may provide a window to look at the most aggressive cancer cells in metastasis,” says Dr Oskarsson. One of the reasons that Dr Oskarsson is interested in molecules like TNC and other matricellular proteins is that while they do not contribute significantly to the scaffolding structure of the extracellular matrix, they are important for cell regulation and the modulation of signalling pathways. “They can determine cell fate, particularly under stress, and we think that this is very important for the metastatic colonisation,” he outlines.

A second major reason for studying TNC and other matricellular proteins is their expression in the normal stem cell niches of a number of different tissues. This could indicate that TNC plays a role in regulating the properties of normal stem cells, properties which have increasingly been shown to be important in the development and progression of cancer. “In a tumour, stem cell attributes, such as self-renewal and the ability to resist stress, have essentially been hi-jacked by the cancer cells, and during metastatic progression, cancer cells express their

Tenascin-C expression in breast cancer. Immunostaining of tenascin-C protein in a primary breast tumour (left) and metastasis (above).

own TNC to maintain some of these properties,” explains Dr Oskarsson.

The interaction between the tumour cells and the metastatic niche continuously evolves as the metastasis grows, and cells manipulate the microenvironment to promote their own fitness. The project is investigating the role of TNC during this process, looking at the underlying mechanisms behind signalling and cell functions. “We are identifying the receptors that mediate TNC induced metastatic colonization. This is very important and may expand the possible strategies to target the TNC axis in metastasis,” outlines Dr Oskarsson. Another major area of research is the role of TNC in resistance to cancer therapy. “We generate tumours that are deficient in tenascin C, and treat with commonly used chemotherapy to look at whether we can sensitise cancer to the current therapeutic options by eliminating tenascin C,” continues Dr Oskarsson. “Moreover, using conditional knockdown methods, we can eliminate tenascin C at distinct stages during the progression of the disease, and compare different intervention strategies.”

Alongside their research into TNC, Dr Oskarsson and his colleagues are also starting to analyse other molecular components of the metastatic niche as well as the cells that produce these components. “We’re looking at the fibroblasts and endothelial cells that are recruited to metastatic foci, and analysing the molecular changes that occur during disease progression. We’re studying the cross-talk between these stromal - or niche - cells, and the cancer cells themselves,” he outlines. This will help researchers build a deeper understanding of metastatic process. “There are many things that we still need to dissect and analyse within the metastatic niche, a lot of work needs to be done in that area,” says Dr Oskarsson.

While at this stage the project is primarily focused on mechanistic analysis, the research holds important clinical implications, potentially offering insights that may help to inhibit metastatic relapse. “An important part of our work is to clinically validate any findings from the model systems that we are using, both 3-D cell culture models and mouse models,” continues Dr Oskarsson. The findings from these model systems can then be related back to clinical parameters. The project has access to clinical samples from partners in Heidelberg and Mannheim, from which researchers can then look to draw links and learn more about extracellular matrix proteins. “We can stain these extracellular matrix proteins in patient derived tumours and look to associate their expression with numerous clinical parameters,” explains Dr Oskarsson.

Analysis of Tenascin C function in breast cancer metastasis to bone (BoneMetTnc)

The aim of the project is to dissect the function and molecular mediators of the extracellular matrix protein tenascin C (TNC) within the metastatic niche in lung and bone. Furthermore, we want to identify and analyze the surface receptors to which TNC may bind and promote signaling and metastatic progression. Finally, we aim to analyze the potential role of TNC in resistance to cancer therapy.

Marie Curie Actions CIG Dietmar Hopp Foundation German Cancer Consortium (DKTK)

• Professor Andreas Schneeweiss, National Center for Tumor Diseases, University Hospital Heidelberg • Professor Marc Sütterlin, Department of Gynecology and Obstetrics, University Medical Center Mannheim • Dr Saskia Spaich, Department of Gynecology and Obstetrics, University Medical Center Mannheim • Professor Peter Sinn, Institute of Pathology, University Hospital Heidelberg

Thordur Oskarsson, PhD Heidelberg Institute for Stem Cell Technology and Experimental Medicine (HI-STEM gGmbH) German Cancer Research Center (DKFZ) Im Neuenheimer Feld 280 D-69120 Heidelberg, Germany T: + 49 (0) 6221/ 42-3903 E: t.oskarsson@dkfz.de W: http://www.hi-stem.de W: https://www.dkfz.de

Dr Thordur Oskarsson

Dr Thordur Oskarsson is a group leader at the Heidelberg Institute for Stem Cell Technology and Experimental Medicine (HI-STEM gGmbH) and the German Cancer Research Center (DKFZ). He received a PhD from the Swiss Institute for Experimental Cancer Research (ISREC) in Lausanne in 2006 and pursued a postdoctoral training at the Memorial Sloan-Kettering Cancer Center in New York, between 2006 and 2011. The research in the Oskarsson laboratory focuses on the role of the microenvironment in cancer metastasis and therapy resistance.