Universiteit Leiden

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Division of Drug Discovery & Safety

Cancer Drug Target Discovery

In this research group, headed by Prof. Erik Danen, the aim is to unravel cellular signaling mechanisms in normal and diseased cells, with a long-standing interest in cell adhesion signaling. In complex multicellular organisms such as ourselves, a division of labor emerges where different tissues and organs are formed with their unique contributions to the organism as a whole. Progress in understanding how cells work together to form and maintain these building blocks in normal physiology and how these are corrupted in pathological situations, impacts on strategies for tissue engineering and the discovery of drugs to cure diseases. Mostly, our research has been in the context of cancer, not only trying to unravel mechanisms of signaling but also aimed at identification of novel drug targets in the areas of drug resistance and metastasis, the two major aspects of cancer contributing to mortality.

Questions in which we are interested with respect to cell signaling include the following: How do cells sense and integrate information from the environment to shape this into a cellular response? What are the mechanisms controlling whether cells survive and proliferate or die, whether they move or stay in the same place? How do cells respond to changes in their environment, including alterations in the surrounding extracellular matrix (ECM), proximity of other cell types, and exposure to harmful chemicals? How are these processes altered in cancer versus normal cells and how can we translate this knowledge into strategies for intervention?

Fig. 1: Breast cancer invading extracellular matrix in a 3D tissue culture model. See Science Signaling 7:ra15 for details.

Over the years, we have developed a pipeline of model systems to investigate these issues ranging from relatively simple 2D cultures to more elaborate multi cell-type 3D tissue culture models, and to in vivo models (Figure 1). This is combined with perturbations of gene expression and gene function followed by biochemical analyses, ‘omics’ approaches, and (real time) microscopy to unravel (adhesion) signaling pathways that control cell proliferation and cell migration. Several collaborations with on the one hand engineers, physicists, and computational biologists and on the other hand biotech and pharma companies and clinicians have been established for fundamental biology research, building of new models, and innovative drug research.

During our studies to find out how cells integrate information from the environment to regulate survival, proliferation, and motility, we were the first to show that the type of ECM glycoprotein that cells adhere to critically regulates cell cycle progression by modulating kinase and small GTPase signaling. Cell-ECM adhesions are mediated by integrin receptors and typically contain a mixture of different integrins.

We discovered that altering the integrin composition of adhesions dramatically impacts on cellular cytoskeletal architecture, activity of signaling cascades, and cell motility strategies. Together with the Schmidt lab in the Physics Institute (LION) of our Faculty we unraveled how shifts in integrin composition affect bidirectional force transmission in cell-ECM adhesions. We have also shown that even though oncogenically transformed cells are typically less dependent on ECM-anchorage for their growth, integrin signaling can in fact have a major impact on cancer cell proliferation, tumor growth, and therapy resistance, depending on the oncogenic context. There is now strong evidence from tissue culture and animal models that integrins can support cancer growth and therapy resistance directly or through their role in tumor angiogenesis. Nevertheless, clinical trials with integrin antibodies or peptide antagonists have thus far been disappointing.

Fig. 2: PBMC-derived NK cells (green) targeting tumor spheroid (blue) in a 3D ECM network.

Our own recent work and that of another group published at the same time indicates that tumor cells can adapt to the absence or inhibition of one class of integrins and activate alternative signaling pathways affecting cell motility and metastasis, which may in fact worsen disease outcome. We are currently further studying these important aspects of tumor cell plasticity. In addition, we have expanded our 3D tissue culture models to include fibroblasts, endothelial cells, and immune cells and we study the impact of tumor-induced ECM reorganization on tumor angiogenesis and immunity as well as aspects of fibrosis using real time microscopy (Figure 2). This work is also being implemented in organ-on-chip models through our participation in the hDMT Institute where engineers and biomedical researchers join forces to develop novel OoC technology.

Fig. 3: Bioinformatics prediction of WNT signaling network involved in the response to chemotherapy-induced DNA damage signaling. See Science Signaling 6:ra5 for details.

We have developed an unbiased screening approach to unravel how normal and cancerous cells cope with stresses such as those inflicted by chemotherapeutics. By combining RNA interference screens, global transcriptomics, and phospho-proteomics in a collaborative effort with the Leiden University Medical Center (LUMC) and University of Copenhagen, we extracted key chemotherapy-responsive signaling networks. Besides known DNA damage response factors, components of cell adhesion signaling and cytoskeletal rearrangement were affected, and a novel mechanism was identified in embryonic stem cells where activation of Wnt signaling counteracts p53-mediated apoptosis to tune the cellular response to chemotherapeutics (Figure 3).

One goal of this work was to discover means to sensitize cancer cells to genotoxic chemo- or radiotherapy. We investigated the top hits from the RNAi screen in a panel of cancer cell lines and identified a ubiquitin ligase that protects against chemotherapy by initiating a transient mRNA translation arrest. In an ongoing collaboration with the Van Attikum lab at LUMC and the Boffa lab at Yale Cancer Center, New Haven CT we further investigate the mechanism of action and clinical relevance of some of the DNA damage response-related hits from our identified networks. An additional interesting candidate drug target that we follow up on pharmacologically, is the Syk kinase in prostate cancer. We discovered this target through a screening pipeline using 3D cultures and zebrafish embryo xenografts and validated it in clinical samples and mouse models with colleagues from the Biology Institute of our Faculty (Snaar-Jagalska), LUMC (van der Pluijm), and Erasmus University, Rotterdam NL (Jenster; van Leenders). Lastly, we have a fruitful ongoing collaboration with the departments of Pathology (Hogendoorn, Bovee) and Clinical Oncology (Gelderblom) at LUMC where we use similar screening approaches and this has already led to several insights into signaling mechanisms underlying the notoriously chemoresistant nature of sarcomas.

Key publications