Erik Sahai: Projects

The Tumour Cell Biology Group is focused on trying to understand why and how cancer cells spread through the body. In particular, we are interested in the role of stromal cells within the tumour and how cancer cells move through the extensively remodelled tumour extra-cellular matrix. Within the tumour microenvironment, cancer-associated fibroblasts (CAFs) provide a chemical and physical environment that favours tumour aggressiveness and dissemination. Thus, targeting CAFs represents an interesting alternative for therapeutic intervention to halt tumour progression.

Cancer-associated fibroblasts

To learn more about CAFs, Fernando Calvo isolated fibroblasts from different stages of breast cancer progression and analysed their function and gene expression. These analyses reveal that activation of the YAP transcription factor is a signature feature of CAFs. YAP function is required for CAFs to promote matrix stiffening, cancer cell invasion and angiogenesis. Matrix stiffening further enhances YAP activation, thus establishing a feed-forward loop. Once this feedback is established it can become self-sustaining, and this could explain the stability of the CAF phenotype in the absence cancer cells.

We also observed that actomyosin contractility and Src function are required for YAP activation by stiff matrices. Interestingly, Nil Ege was able to show that transient ROCK inhibition was able to disrupt the feed-forward loop, leading to a long-lasting reversion of the CAF phenotype.

Intravital imaging of melanoma cell

Endothelial cells are also a key component of the tumour microenvironment. Cerys Manning used intravital imaging to perform longitudinal imaging of melanoma vasculature in vivo. The tumour vasculature is a key part of the microenvironment, providing oxygen and metabolites to the tumour cells. However, current anti-angiogenic therapies have not performed as well as originally hoped in the clinic.

Using intravital imaging we identified three different vascular network morphologies within the tumour microenvironment; relatively well organised vessels within the tumour, sprouting networks at the tumour margin and more tortuous vessels further from the tumour. Our novel method for longitudinal imaging highlighted interesting transitions between these different vascular networks not previously observed in the conventional single time point analysis.

Given the poor clinical response to anti-angiogenic therapies, we used the clinically approved anti-angiogenic agent, Sunitinib, to test if the different vascular regions we identified responded differently to therapy. We showed that although treatment with Sunitinib reduced overall tumour vascular density and slowed tumour growth, Sunitinib had no significant effect on the angiogenic sprouting behaviour of the vasculature at the tumour margin. Therefore, we have demonstrated that within tumours that are broadly responsive to Sunitinib, there are pre-existing refractory microenvironments.

Furthermore we showed that these pre-existing refractory microenvironments were high in protease activity, CXCL12, FGF-2 and HGF. We propose that these micro-environments may account for the partial and heterogeneous response to anti-angiogenic therapy in the clinical setting.

Figure 1

Figure 1: Scanning Electron Microscopy of an A375 melanoma cell on a collagen-rich matrix. Filopodia are tinted yellow/orange and membrane blebs are tinted magenta/blue. (Click to view larger image)

Cytoskeletal factors required for migration

In the last few years there has been an increasing awareness of the role matrix geometry plays in determining how cells move and cytoskeletal factors required for migration. However, predicting migratory behaviour and the effect of experimental perturbation has proved difficult. Indeed, experiments have run ahead of our theoretical understanding of cell migration. To address this issue we collaborated with Melda Tozluoglu in the Biomolecular Modelling Group.

Figure 2

Figure 2. Inverted colour fluorescence image of a breast cancer cell (MDAMB231) moving on a flat substrate. F-actin is shown in magenta, myosin IIa is shown in blue, and ezrin in yellow. (Click to view larger image)

Melda developed a computational model that encompasses all key features of migrating cells and changing environments. Using the model, Melda first set up to identify the intracellular states that will provide fastest cell migration in different matrix geometries. This predicted the expected F-actin protrusion based migration strategies on unconfined surfaces, with the theoretical explanation for the roles of actin protrusions in maintaining contact with the surface and pulling the cell forward. Confined matrix geometries on the other hand, caused profound shifts in the relationship of adhesion and contractility to cell velocity.

The model predicted adhesion is dispensable in confined-discontinuous matrices and bleb driven migration will be an effective strategy. This provided explanation to the long lasting observation of adhesion-independent migration. We then tested our model with a highly challenging experimental context; the invasion of cancer cells in vivo.

Melda used the model to predict how cancer cells migrate into the discontinuous collagen matrix that surrounds tumours and the effect of different combinations of kinase inhibitors and integrin depletion in vivo. We used intravital imaging to test model predictions on bleb-driven migration, and predicted response to biochemical manipulations.

Strikingly, we could confirm the widespread use of bleb-driven cell migration in vivo and predict the effect of numerous experimental perturbations.

In addition to these studies, we are actively pursuing analysis of collective invasion of lobular breast cancers, the role of direct cell-cell contact between cancer cells and CAFs, intravital imaging of CAF signalling and the interplay between CAFs and chemotherapy. We hope that these studies will yield exciting insights into cancer biology and ultimately inform improved strategies for cancer therapy.

Erik Sahai

erik.sahai@crick.ac.uk
+44 (0)20 379 61322

  • Qualifications and history
  • 1998 PhD in Biochemistry, University College, London, UK
  • 1998 Postdoctoral Fellow, Institute of Cancer Research, UK
  • 2003 Postdoctoral Fellow, Albert Einstein College of Medicine, USA
  • 2004 Established lab at the London Research Institute, Cancer Research UK
  • 2015 Group Leader, the Francis Crick Institute, London, UK