Background

The growth of solid tumours is accompanied by pathological remodelling of the native tissue (Cox and Erler, 2011; Bonnans et al., 2014). During progression, the local tissue environment experiences physical as well as biological changes, resulting in increased tissue stiffness (elastic modulus) (Humphrey et al., 2014). Alterations in the extracellular matrix lead to the generation of new tissue properties, which activate mechano-signalling pathways within tumour cells (DuFort et al., 2011). This outside-in signalling leads to altered behaviour, cell morphology, differentiation, proliferation, migration and stemness. In preclinical animal models of cancer, these changes have been shown to drive malignant progression and metastatic spread (Erler et al., 2006; Levental et al., 2009; Bonnans et al., 2014). Thus, as a result, the targeting of matrix remodelling and in particular stiffening has received substantial attention in recent years, and several clinical trials have been initiated (Barker et al., 2012; Baker et al., 2013; Cox et al., 2013; Miller et al., 2015; Madsen et al., 2015; Cox and Erler, 2016; Kai et al., 2016).

The mechanical properties of the tumour microenvironment can readily be examined using approaches such as atomic force microscopy (AFM) and nanoindentation (Akhtar et al., 2009). These approaches provide nanometre resolution and concurrent measurement of the applied force with picoNewton resolution (Kasas and Dietler, 2008). However, AFM is not applicable to understand the elastic properties of larger 3D samples. The mechanical properties of bulk 3D tumour samples can be more accurately examined using shear rheology (Picout and Ross-Murphy, 2003). Rheology is the study of how a material deforms when forces are applied to them. Thus applying shear stress to a 3D matrix can determine the elastic modulus (stiffness) as well as viscous properties of a bulk 3D tumour tissue. In this protocol, we describe a method to measure changes on tumour stiffness by shear rheology.