Conversation before crossing: dissecting metastatic tumor-vascular interactions in microphysiological systems

Abstract

Tumor metastasis via the circulation requires crossing the vascular barrier twice: first, during intravasation when tumor cells disseminate from the primary site through proximal vasculature, and second, during extravasation, when tumor cells exit the circulation to form distant metastatic seeds. During these key metastatic events, chemomechanical signaling between tumor cells and endothelial cells elicits reciprocal changes in cell morphology and behavior that are necessary to breach the vessel wall. Existing experimental systems have provided a limited understanding of the diverse mechanisms underlying tumor-endothelial interactions during intravasation and extravasation. Recent advances in microphysiological systems have revolutionized the ability to generate miniaturized human tissues with tailored three-dimensional architectures, physiological cell interfaces, and precise chemical and physical microenvironments. By doing so, microphysiological systems enable experimental access to complex morphogenic processes associated with human tumor progression with unprecedented resolution and biological control. Here, we discuss recent examples in which microphysiological systems have been leveraged to reveal new mechanistic insight into cellular and molecular control systems operating at the tumor-endothelial interface during intravasation and extravasation.

Keywords: extravasation; intravasation; microphysiological system; organ-on-chip; tumor-vascular interaction.

Graphical abstract

Figure 1.

Microphysiological systems capture signaling and dynamic interactions at the tumor cell-endothelial interface during intravasation. A: example MPS device containing two separate fluidic channels embedded in 3-D ECM: one containing a perfused microvessel (top, pink) and the other containing primary tumor tissue (bottom, blue). Compartments are flanked by fluidic ports that control perfusion. B: zoomed-in view of MPS device, highlighting that PTCs may migrate collectively or individually to the endothelium for intravasation. C: bidirectional paracrine interactions between ECs and PTCs. Breast cancer (BC) cells secrete IL-6/8 to disrupt adherens junctions, actin cytoskeletal organization, and vascular glycocalyx, causing increased vascular permeability. ECs secrete CXCL12 to CXCR4 on PTCs, guiding chemotaxis toward the vasculature in GBM. D: luminal flow and interstitial fluid flow (IFF) regulated by ECs impacts PTC migration by i) generating autocrine chemokine gradients that guide PTC migration downstream; ii) stimulating TRPM7 channels, the expression level of which determines migration reversal or persistence; and iii) alignment of ECM fibers. E: mosaic vessel formation is one mechanism of PDAC intravasation and escape into circulation (iii), caused by i) PTC-mediated EC apoptosis and ii) PTC replacement of EC. F: maximum intensity projection images of endothelial vessels cultured nearby MCF10A ducts expressing empty vector (EV), constitutively active hemagglutinin (HA)-tagged PI3Kα H1047R (PIK3Cα^H1047R), or HA-tagged ErbB2 (ErbB2^amp) (12). PIK3Cα^H1047R duct causes a significant shift in endothelial actin organization from junction-associated to diffuse and cytoplasmic. Green = endothelial actin, cyan = epithelial actin, blue = nuclei; scale = 100 μm. F reprinted from Kutys et al. (12) with slight modifications to font sizes and text locations (Creative Commons CC BY license). BM, basement membrane; ECs, endothelial cells; ECM, extracellular matrix; GBM, glioblastoma multiforme; MPS, microphysiological system; PDAC, pancreatic ductal adenocarcinoma; PTC, primary tumor cell.

Figure 2.

Microphysiological systems capture signaling and dynamic interactions at the tumor cell-endothelial interface during extravasation. A: example MPS device containing a microvascular network (red) flanked by two parallel media compartments (pink). ΔP = pressure differential generated across the network. CTCs (blue) are perfused. B: zoomed-in view of microvascular network, highlighting key paracrine and juxtracrine steps during extravasation. C: CTC adherence to vessel walls. This occurs by adhesion signaling (EC E-selectin to CTC glycocalyx, EC glycocalyx to CTC CD44) and/or physical trapping where the CTC is wider in diameter than the microvessel. D: morphological behaviors in ECs and CTCs required for extravasation: i) ECs remodel their junctions in response to IL-6/8 to facilitate diapedesis, or remodel their apical membrane in response to luminal flow to facilitate CTC pocketing; ii) CTCs soften their cell body and nuclei, and elongate along the vessel surface to facilitate migration through ECs. E: CTCs utilize invadopodia and EC-mediated BM destruction to facilitate invasion. CTC-expressed IL-6/8 cause ECs to express MMP3. CTC invadopodia form focal adhesions with basement membrane via α_xβ₁, FAK, vinculin, and talin, the latter two facilitating local actin polymerization. Invadopodia recruit Tks5 and secrete MMP9 to cause BM destruction. F: MDA-MB-231 BC CTCs (red) adhered to endothelium (green) through interactions between CTC CD44 (red arrows) and streaks of HA atop ECs (blue). Dashed arrow indicates direction of flow. Scale bar 60 μm (16). G: time-lapse confocal imaging of MDA-MB-231 overexpressing fluorescent CD44 (gray) extravasating through endothelium. Red arrows indicate regions where CD44 binds ECM. T = 0 min is onset of CTC perfusion (16). F and G reprinted from Offeddu et al. (16) with no modifications (Creative Commons CC BY license). BC, breast cancer; BM, basement membrane; CTC, circulating tumor cell; EC, endothelial cell; ECM, extracellular matrix; GFP, green fluorescent protein; HA, hyaluronic acid; MPS, microphysiological system PDMS, polydimethylsiloxane; RFP, red fluorescent protein; TC, tumor cell.