Abstract 5675: Pathological crosstalk between osteocytes and breast cancer cells in bone metastasis

Abstract Bone provides an ideal niche for breast cancer cells (BCa) to reside and proliferate and is a frequent site of BCa metastasis. Osteocytes are the most abundant skeletal cells and permanent residents of bone. However, the role of osteocytes in BCa bone metastasis remains understudied. Here, we investigated the crosstalk between metastatic BCa cells and osteocytes. In vitro cultures revealed that conditioned media (CM) derived from metastatic E0771 BCa cells decreased by 50% the number of alive MLO-A5 and MLO-Y4 osteocyte-like cell lines. BCa cells modestly increased osteocyte apoptosis (2% vs. 6%, alone vs. exposed to BCa, respectively). Treatment with DEVD, a caspase 3 inhibitor, blocked osteocyte apoptosis but did not prevent the decrease in osteocytes induced by BCa. Thus, we studied osteocyte senescence, a process that causes irreversible cell cycle arrest and profound changes in gene expression. We found that BCa-CM upregulated the expression of markers of senescence markers (p16, p21) and senescence-associated secretory phenotype (Mmp13, Mmp9, Vcam-1) in osteocyte-like cell lines. Similarly, BCa-CM increased the expression of senescent markers in ex vivo bone organ cultures containing primary osteocytes. Osteocytes increased BCa cell proliferation by increasing cyclin D1 expression Through both cell-to-cell interactions and secretion of soluble factors., osteocytes increased BCa cell proliferation by increasing cyclin D1 expression. Moreover, osteocyte-derived CM stimulated BCa cells migration and invasion capabilities and upregulated the expression of genes involved in migration (Vcam-1 and N-cadherin). Co-culture with stromal cells also stimulated BCa cell proliferation, invasion, and migration. However, the increases induced by stromal cells were four-fold lower than those seen with osteocytes. Overall, our results suggest that BCa cells reprogram osteocytes, which acquire a senescent phenotype, whereas osteocytes produce factors that stimulate tumor growth, migration, and invasion. Together, these findings support the existence of a crosstalk between osteocytes and BCa cells in the metastatic niche that favors the progression of breast cancer in bone. Future studies are warranted to examine the contribution of osteocyte senescence and osteocytes-derived factors in animal models of breast cancer metastasis. Citation Format: Manish Adhikari, Hayley Sabol, Aric anloague, Sharmin Khan, Jesus Delgado-Calle. Pathological crosstalk between osteocytes and breast cancer cells in bone metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5675.