Monitoring Py8119 breast cancer cell proliferation in direct cocultures with osteoblasts and osteoclasts.

The intricate interaction among breast cancer (BrCa) cells, stromal/osteoblastic cells, and osteoclasts in the osseous microenvironment drives a vicious cycle that accelerates both osteolysis and tumor progression. Elucidating how these bone cells directly modulate BrCa cell proliferation is of paramount importance. Due to a lack of intrinsic background of luminescence signal in the body, the luciferase/luciferin assay enables sensitive, in vivo monitoring of tumor progression. However, this technique has not yet been utilized to monitor tumor cell proliferation during direct coculture with bone cells. In this study, we generated an Py8119 BrCa cell line stably expressing luciferase (luc). We demonstrated that the bioluminescence intensity of Py8119-luc cells strongly correlates with cell proliferation at various time periods, validated by both cell counts and BrdU assays. Utilizing this system, we found that both dual cocultures (with osteoblasts) and triple cocultures (with osteoblast and osteoclasts) promote Py8119-luc cell growth. Notably, a receptor activator of nuclear factor-κB ligand (RANKL)-neutralizing monoclonal antibody suppressed Py8119-luc proliferation in direct cocultures with both osteoblasts and osteoclasts, but not with osteoblasts alone, thereby confirming the feasibility of these cell models. In summary, our in vitro model for luciferase/luciferin assay effectively quantifies tumor cell proliferation in direct dual and triple cocultures with bone cells. These findings highlight the potential of this direct coculture model for screening and evaluating novel therapeutics targeting bone-metastatic breast cancer.