Microenvironment Influences Cancer Cell Mechanics from Tumor Growth 5 to Metastasis Deepraj Ghosh and Michelle R. Dawson Abstract cell motility can easily be combined with anal- The microenvironment in a solid tumor in- ysis of critical cell fate processes, including cludes a multitude of cell types, matrix pro- adhesion, proliferation, and drug resistance, teins, and growth factors that profoundly in- to determine how changes in mechanics con- fluence cancer cell mechanics by providing tribute to cancer progression. This biophysical both physical and chemical stimulation. This approach can be used to systematically inves- tumor microenvironment, which is both dy- tigate the parameters in the tumor that control namic and heterogeneous in nature, plays a cancer cell interactions with the stroma and to critical role in cancer progression from the identify specific conditions that induce tumor- growth of the primary tumor to the develop- promoting behavior, along with strategies for ment of metastatic and drug-resistant tumors. inhibiting these conditions to treat cancer. In- This chapter provides an overview of the bio- creased understanding of the underlying bio- physical tools used to study cancer cell me- physical mechanisms that drive cancer pro- chanics and mechanical changes in the tumor gression may provide insight into novel thera- microenvironment at different stages of cancer peutic approaches in the fight against cancer. progression, including growth of the primary tumor, local invasion, and metastasis. Quan- titative single cell biophysical analysis of in- Keywords tracellular mechanics, cell traction forces, and Cell mechanics · Deformation · Microrheology · Traction force · Epithelial to D. Ghosh mesenchymal transition (EMT) · Motility · Department of Molecular Pharmacology, Physiology, and Adhesion · Metastasis Biotechnology, Brown University, Providence, RI, USA M. R. Dawson () Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, RI, USA Center for Biomedical Engineering, Brown University, Providence, RI, USA 5.1 Introduction School of Engineering, Brown University, Providence, RI, USA To improve cancer prevention and survival rates, e-mail: [email protected] the biology of cancer has been extensively an- © Springer Nature Switzerland AG 2018 69 C. Dong et al. (eds.), Biomechanics in Oncology, Advances in Experimental Medicine and Biology 1092, https://doi.org/10.1007/978-3-319-95294-9_5 70 D. Ghosh and M. R. Dawson alyzed to find molecular targets at genetic and The field of physical oncology is aimed at ex- epigenetic levels. Yet, cancer remains a leading ploring the role of mechanical forces in the tumor cause of death worldwide, with over 90% of microenvironment during growth and metastasis cancer-related deaths due to metastasis [1]. Phys- [2–4, 20–22]. Mechanical forces in the primary ical interactions of cells in the tumor microenvi- tumor are caused by solid stress that results from ronment, along with the mechanical forces that the rapid proliferation of tumor cells and the modulate them, play a critical role in cancer recruitment of host-derived stromal cells. Matrix metastasis [2–4]. The growth of metastatic tu- stiffening and high interstitial fluid pressure fur- mors is also highly dependent upon the recruit- ther contribute to this high-stress environment, ment of host-derived stromal cells, such as fi- which alters cells and the surrounding matrix to broblasts, mesenchymal stem cells (MSCs), and activate signaling pathways important in cancer immune cells, which secrete extracellular ma- [11, 23]. Mechanical forces are also critical in di- trix proteins, soluble factors, and proteases crit- recting cancer metastasis. In fact, cancer cells un- ical for tissue remodeling and tumor microen- dergo a cascade of biophysical changes through- vironment development [5]. Therapeutics target- out this process. First, cells undergo morpholog- ing non-cancer cells in the tumor microenviron- ical elongation with reduced cell-cell adhesion ment have emerged as adjuvants to traditional during EMT. Next, cells go through multiple chemotherapeutics [6, 7]. The complexity and deformations as they cross the tumor stroma and heterogeneity of cancer are major challenges to surrounding basement membrane, then migrate the development of successful treatments. In this through the bloodstream to the metastatic site, respect, our knowledge and understanding of and finally invade the tissue to form metastases the disease are incomplete, and new aspects are [2, 3, 21]. This chapter on cancer cell mechan- being researched more actively to influence the ics will explore changes in matrix mechanics, outcome of cancer. cytoskeletal and nuclear mechanics, cell traction Many of the hallmarks associated with cancer, forces, and motility at different stages of cancer including unlimited replicative potential, apop- progression, including growth of the primary totic evasion, and tissue invasion and metastasis, tumor, local invasion, and metastasis (illustrated can be linked to abnormal cytoskeletal or ma- in Fig. 5.1). trix mechanics—important biophysical parame- ters [8–10]. A common feature of these biophys- ical interactions is the transmission of force from 5.2 Mechanical Forces in Cancer the extracellular matrix (ECM) to the internal cytoskeleton, which forms the structure of the Quantitative analysis of intracellular mechanics, cell. Groundbreaking work from the Weaver lab surface traction, and matrix stiffness forces al- has demonstrated that mechanics play a criti- low us to probe the biomechanical properties cal role in cancer progression [3, 4, 11]. My of the tumor with an unprecedented level of lab also showed that increased traction forces detail. These biophysical techniques can be used (transmitted from the internal cytoskeleton to the to systematically investigate the parameters in external environment) correlate with increased the tumor that control cancer cell interactions cancer cell motility, proliferation, and chemore- with the stroma and to identify specific con- sistance; this was demonstrated in mechanosensi- ditions that induce tumor-promoting behavior, tive breast and ovarian cancer cells that respond along with strategies for inhibiting these condi- to changes in matrix stiffness [12, 13]andina tions to treat cancer. This section briefly outlines genetic model of induced epithelial to mesenchy- biophysical techniques and provides insight on mal transition (EMT) [14]. We also showed that how these techniques can be combined with cell paracrine factors exchanged between cancer and fate analysis to study cancer. stromal cells dramatically alter the mechanical properties of both cell types [15–19]. 5 Microenvironment Influences Cancer Cell Mechanics from Tumor Growth to Metastasis 71 Fig. 5.1 The progression of cancer from the develop- croenvironment, including extracellular matrix mechan- ment of the primary tumor, to the invasion of the sur- ics, cell and nuclear mechanics, cell traction forces, and rounding tissue, and the formation of distal metastases motility. This chapter will explore how these parameters are controlled by biophysical properties of the tumor mi- are measured and used to increase our understanding of metastatic cancer 5.2.1 Intracellular Mechanics of guanidine exchange factors (GEFs) leads to the activation of Rho-associated Actin and Rho GTPases kinases (ROCK) that block myosin light chain (MLC) phosphatase and activate Intracellular mechanical properties are myosin light chain kinase (MLCK) leading largely determined by structure of filamen- to MLC phosphorylation and actomyosin tous actin. Actin filaments can organize contractility. The actin cytoskeleton is in a myriad of hierarchical structures in a also connected to the nucleus via LINC cell: parallel bundling of actin results in complexes that transmit mechanical signals stress fiber formation to provide tensile to the nucleus to regulate transcription strength and strong contractile activity, factors [30, 31]. whereas cross-linking of actin filaments increase intracellular elasticity. Actin can interact with other structural complexes, During progression of cancer, the dynamic mi- like myosin motor proteins, to control croenvironment forces cancer cells to adapt and actomyosin contractility which plays a key modify their mechanical properties in response role in cell-generated forces [24]. The Rho to both chemical and mechanical stimulation. family of GTPases and its downstream Characterization of cancer cell mechanics using effectors play a pivotal role in regulating deformability, defined as the resistance to defor- the structural dynamics of actin, and these mation, at single-cell level has become increas- proteins are overexpressed in tumors ingly important to design new diagnostic tools [25–29]. In particular, activation of small and treatment methods. Intracellular mechani- Rho GTPases such as RhoA with the help cal properties are regulated by the cytoskeleton, a complex network of filamentous actin, mi- (continued) crotubules, and intermediate filaments extending 72 D. Ghosh and M. R. Dawson Fig. 5.2 Schematic of cellular components contributing in recruitment of multiple structural proteins to the in- to cell mechanics and mechanotransduction. Cytoskeletal tracellular tail domain to form focal adhesion complex proteins actin, microtubule, and intermediate filaments act that activates pathways such as ERK and Rho-ROCK as load-bearing components of the cells. Cells can sense signaling.