Dormant breast cancer micrometastases reside in specific bone marrow niches that regulate their transit to and from bone

Abstract

Breast cancer metastatic relapse can occur years after therapy, indicating that disseminated breast cancer cells (BCCs) have a prolonged dormant phase before becoming proliferative. A major site of disease dissemination and relapse is bone, although the critical signals that allow circulating BCCs to identify bone microvasculature, enter tissue, and tether to the microenvironment are poorly understood. Using real-time in vivo microscopy of bone marrow (BM) in a breast cancer xenograft model, we show that dormant and proliferating BCCs occupy distinct areas, with dormant BCCs predominantly found in E-selectin- and stromal cell-derived factor 1 (SDF-1)-rich perisinusoidal vascular regions. We use highly specific inhibitors of E-selectin and C-X-C chemokine receptor type 4 (CXCR4) (SDF-1 receptor) to demonstrate that E-selectin and SDF-1 orchestrate opposing roles in BCC trafficking. Whereas E-selectin interactions are critical for allowing BCC entry into the BM, the SDF-1/CXCR4 interaction anchors BCCs to the microenvironment, and its inhibition induces mobilization of dormant micrometastases into circulation. Homing studies with primary BCCs also demonstrate that E-selectin regulates their entry into bone through the sinusoidal niche, and immunohistochemical staining of patient BMs shows dormant micrometastatic disease adjacent to SDF-1(+) vasculature. These findings shed light on how BCCs traffic within the host, and suggest that simultaneous blockade of CXCR4 and E-selectin in patients could molecularly excise dormant micrometastases from the protective BM environment, preventing their emergence as relapsed disease.

Bone-in-culture array as a platform to model early-stage bone metastases and discover anti-metastasis therapies

“…4d). These results support that the peri-vascular niche regulates metastasis dormancy2021. Our previous studies demonstrated that the osteogenic niche promotes cancer cell proliferation13.…”

Hallmarks of Bone Metastasis

“…A major impetus to the dormancy field has been the lack of a standardized definition of a dormant tumor cell. In general, a non-proliferative (e.g., Ki67 or BrdU negative) disseminated tumor cell that has not grown into a micrometastasis is often considered dormant [17–21], but there are several potential models for dormant tumor cell behavior: (1) very slow growing, (2) proliferative, but dying off at an equal rate, or (3) non-replicative until reactivated by the tumor microenvironment (e.g., angiogenic switch, immune surveillance) [22]. Importantly, these models may not be mutually exclusive; a slow-growing tumor cell may eventually be reactivated by the tumor microenvironment.…”

Confocal/two-photon microscopy in studying colonisation of cancer cells in bone using xenograft mouse models

“…One advantage of using these lipophilic dyes is being able to detect dormant cells as these cell membrane dyes are diluted to undetectable concentrations in proliferating cells. [20][21][22]24,25 Cancer cells are firstly washed with phosphate-buffered saline (PBS), trypsinised by 0.15% Trypsin-EDTA for 3-5 min, at 37 1C, 5% CO 2 . Cells are neutralised with appropriate media containing 10% FBS and centrifuged for 5 min at 200 g. The cell pellet is resuspended at a concentration of 1 Â 10 6 cells per ml in serum free medium for Vybrant DiD labelling or in Hanks 0 balanced salt solution (HBSS) for Vybrant CM-DiI.…”