A Mechanoimmunological Basis for Metastatic Site Preference

Summary Antitumor immunosurveillance by cytotoxic lymphocytes is generally conceived as a biochemical process in which tumor specific markers are recognized by activating receptors on the lymphocyte surface. We have found, however, that cytotoxic T cells and natural killer cells also respond to the mechanical properties of cancer cells,

preferentially destroying targets that are physically stiffer. This mechanical form of immunosurveillance, which we call mechanosurveillance, appears to be particularly relevant during metastasis, when cancer cells remodel their cytoskeleton to invade new organs. In this proposal, we will investigate the interplay between

mechanosurveillance and the physical properties of the metastatic microenvironment. Cellular mechanics are modulated continuously by cell-extrinsic biophysical signals. A particularly important manifestation of this crosstalk, called mechanoreciprocity, induces cells in stiffer environments become stiffer themselves, and those

in softer locales to become softer. Whether environmentally-induced stiffening might sensitize cancer cells to mechanosurveillance in vivo, however, has not been explored. This an interesting question because metastatic microenvironments vary widely in their physical properties, ranging from very rigid (e.g. bone) to very soft (e.g.

lung). Enhanced mechanosurveillance in rigid microenvironments would establish a regime in which cytotoxic lymphocytes control the spectrum of metastatic site preference by disproportionately suppressing outgrowth in organs like the bone. Using a mouse model of metastasis, we have found that cancer cells colonizing the bone

are significantly stiffer than cancer cells colonizing the lung, and that the in vivo expansion of bone metastasis is exquisitely sensitive to cytotoxic lymphocytes. Building on these preliminary observations, we propose that microenvironmental stiffness dictates the efficacy of mechanosurveillance and that this relationship shapes both

metastatic site preference and the power of anti-tumor immunotherapy. We will investigate this hypothesis in three Specific Aims. Aim 1 will examine how distinct metastatic microenvironments affect cancer cell biomechanics and immune vulnerability in mice and humans. Aim 2 will determine if environmental stiffness can,

as an independent variable, control the efficiency of mechanosurveillance. Finally, Aim 3 will apply state-of-the- art rigidity dependent cell sorting technology to identify novel mechanoregulators of metastasis in vivo. Our proposed studies are organized around the conceptually innovative idea that crosstalk between environmental

mechanics and cellular cytotoxicity determines where metastases grow. In addition, we will employ highly innovative technologies, including suspended microchannel resonator (SMR) devices that rapidly measure cell deformability and sort cells based on stiffness. The successful completion of our Specific Aims could identify

biomarkers for guiding antitumor immunotherapy and aid development of novel strategies for treating metastatic growth in specific target organs. As such, this work is highly relevant to the NIH mission in that it will contribute to the advancement of knowledge that could improve human health.