Bioengineered human bone-mimetic niche compositions regulatebreast cancer cell quiescence and therapy response

Disseminated tumor cells (DTCs) in the bone are widely regarded as the cellular seeds of late metastatic relapse in estrogen receptor-positive (ER+) breast cancer (BC). However, how distinct bone compartments influence BC cell quiescence and endocrine therapy response remains unclear. Mechanistic insight has been hindered by limited access to human bone samples and by the lack of relevant human models that permit controlled manipulation of stromal compartments. Here, we developed a fully human, 3D bone-mimetic system for modular, controllable assembly of engineered osteoblastic (eON), vascularized (eVN), and vascularized osteoblastic (eVON) niche compositions. These niches were generated by perfusion culture of human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) and/or human adipose tissue-derived stromal vascular fraction (hAT-SVF) cells within porous ceramic scaffolds. The resulting tissue microenvironments were then used as a substrate for the culture of an ER+ BC cell line, expressing a mutant reporter of p27 to monitor the quiescent status. We found that the eON enhanced BC cell proliferation, whereas the eVN was enriched in quiescent BC cells positive for NR2F1, a dormancy-associated transcription factor, and located near perivascular elements. Treatment with the selective ER degrader fulvestrant reduced BC cell numbers in vascularized niches (eVN and eVON) but not in eON, despite comparable receptor degradation. In summary, we developed a modular human platform for dissecting niche-specific regulation of BC quiescence, proliferation, and endocrine therapy response. The system can be further used to investigate perivascular niche-dependent mechanisms of BC cell dormancy and to guide the development of therapeutic strategies preventing recurrence in ER+ BC patients.