Tumor invasion as non-equilibrium phase separation

Abstract

TWO-SENTENCE SUMMARY: Using a multicellular spheroid embedded within an engineered threedimensional matrix, we show here the potential for coexistence of solid-like, fluid-like, and gas-like phases of the cellular collective described by a jamming phase diagram. Depending upon cell type and matrix density, moreover, invasion into matrix from the tumor periphery can switch from a continuous cellular collective that flows like a fluid to discrete cells that scatter individually like a gas. ASTRACT:The early malignant tumor invades surrounding extracellular matrix (ECM) in a manner that depends upon material properties of constituent cells and ECM. Biophysical mechanisms remain unclear, however. Using a multicellular spheroid embedded within an engineered three-dimensional matrix, we show here the potential for coexistence of solid-like, fluid-like, and gas-like phases of the cellular collective described by a jamming phase diagram. Depending upon cell type (MCF-10A vs. MDA-MB-231) and ECM density (1 to 4 mg/ml collagen), cancer cells within the spheroid display a variety of collective behaviors, including a nonmigratory jammed phase and a migratory unjammed phase. At a critical collagen density, unjammed cancer cells at the spheroid periphery transition in an almost switch-like fashion between distinct modes of invasion. In the case of MDA-MB-231, for example, we find that when ECM density is 2 mg/ml or smaller single cells and cell clusters scatter from the spheroid periphery in the form of discrete gas-like particles, but when ECM density is 3 mg/ml or greater these cells flow collectively from the spheroid periphery in continuous fluid-like invasive branches. These findings suggest coexistence within the spheroid mass of multiple material phases of the cellular collective -solid-like, fluid-like, and gas-like-in a manner that is superficially similar to common inanimate multiphasic systems at thermodynamic equilibrium, but here arising in living cellular systems, all of which are displaced far from thermodynamic equilibrium. We conclude that non-equilibrium phase separation based upon jamming dynamics may provide a new physical picture to describe cellular migratory dynamics within and invasion from a tumor mass.Quantum Photonics. D.R. acknowledges the Department of Defense (DoD grant W81XWH-15-1-0070). We also gratefully acknowledge Elizabeth Bartolak-Suki (Boston University) for expert assistance with spheroid histology, and Lauren O'Keeffe (Cornell University) for assistance with spheroid embedding and cell counting. METHODSCell lines and culture media. Non-tumorigenic MCF-10A and metastatic MDA-MB-231 breast epithelial cell lines were purchased from American Type Cell Culture Collection (ATCC) and cultured using standardized media and conditions [21,52]. MCF-10A cells were cultured in DMEM/F-12 (ThermoFisher, No. 11330032) supplemented with 5% horse serum (Invitrogen, No. 16050122), 20 ng/ml EGF (Peprotech, AF10015; ThermoFisher, No. 10605HNAE), 0.5 mg/ml hydrocortisone (Sigma-Aldrich, No. H0888), 100 ng/ml ...

Self-generated persistent random forces drive phase separation in growing tumors

“…We performed t-SNE on data generated using simulations of an expanding tumor spheroid model 15,18,29,30 . The results revealed massive dynamical heterogeneity that depends on the radial distance from the tumor center, which accords well with the conclusions in recent experiments [11][12][13] . t-SNE also resolves the dynamical phase space structure of cells in the core and periphery.…”

“…Previously we showed that the cell dynamics in a growing multicellular spheroid (MCS) is spatially heterogeneous 15,18 , which implies that cells in the core (periphery) exhibit sub-diffusive (super-diffusive) motion. These characteristics were first observed in imaging experiments tracking the displacement of cells moving in a collagen matrix, and recently in other studies as well 12,13 . However, characterizing the dynamics using conventional ensemble average measures, such as mean squared displacement or the self-intermediate scattering function, hide the rich dynamics, the cause of DITH.…”

“…Stochastic variations due to differences in cancer microenvironment, which results in vastly different dynamics of cells in distinct regions of an evolving solid tumor, could also give rise to ITH. Evidence for the dynamically-driven ITH have emerged recently from several imaging studies, which have mapped out the phenotypic properties (such as shape and size) in three dimensional tumors spheroids [10][11][12][13] . The growth of tumor spheroids are monitored by embedding them in a collagen matrix [10][11][12][13][14] .…”

“…Evidence for the dynamically-driven ITH have emerged recently from several imaging studies, which have mapped out the phenotypic properties (such as shape and size) in three dimensional tumors spheroids [10][11][12][13] . The growth of tumor spheroids are monitored by embedding them in a collagen matrix [10][11][12][13][14] . Direct imaging reveals that the dynamics of cells in the tumor core differs dramatically compared to cells in the periphery [11][12][13]15 , a clear signature of dynamical ITH, which we abbreviate as DITH.…”

“…The growth of tumor spheroids are monitored by embedding them in a collagen matrix [10][11][12][13][14] . Direct imaging reveals that the dynamics of cells in the tumor core differs dramatically compared to cells in the periphery [11][12][13]15 , a clear signature of dynamical ITH, which we abbreviate as DITH. A characteristic of DITH is that the material properties of the cells are unaltered, implying that heterogeneity arises solely from microenvironment fluctuations.…”