Abstract 3191: The role of rigidity in myeloid-tumor cell interactions in bone

Bone is one of the most common metastatic sites for breast cancer, where nearly 70% of patients that die from disease develop skeletal metastases. Skeletal metastases can cause hypercalcemia, fractures, and pain. With the use of 2D polyurethane films (PUR) that mimic tissue rigidity ranging from the basement membrane (10 MPa) to bone (2600 MPa), we have previously published that bone rigidity increases expression of Parathyroid hormone-related protein (PTHrP). This factor is important in tumor-induced bone disease in several cancer cell lines that metastasize to bone. Current in vivo studies implanting 3D scaffolds seeded with the bone metastatic breast cancer cells MDA-MB-231 GFP into athymic nude mice indicate that cells from the microenvironment infiltrate into the scaffolds, suggesting that these cells may play a role in tumor response to rigidity. Myeloid cells, which have been implicated in promoting tumor progression by altering the tumor microenvironment, are one of major infiltrating populations as determined by flow cytometry. Specifically CD11b+ myeloid cells made up 15% of overall cells within the scaffold, with the remaining population being mostly GFP+ tumor cells. Since few studies have examined the effect of rigidity on myeloid cells, we hypothesize that the physical rigidity of the bone promotes myeloid secretion of pro-tumorigenic factors that lead to an increase in tumor-expression of factors important in bone metastasis. In order to determine how rigidity influences myeloid cell differentiation and their effect on tumor progression, we seeded the macrophage/osteoclast cell line, RAW 264.7 cells on 2D PUR films. Differentiation of cells was monitored and conditioned media collected and used to treat MDA-MB-231 cells seeded on 2D PUR films. Surprisingly, we found that the conditioned media from RAW cells that were seeded onto the rigid films (bone-micking) decreased expression of PTHrP in tumor cells seeded on both rigid and soft films using RT-PCR. This effect was not seen from conditioned media from RAW cells seeded on soft films. Additionally, RAW cells seeded on soft films upregulate their expression of TGF-β, a factor important in regulating the expression of PTHrP, by 6-fold as compared to cells seeded on a rigid film. In contrast, PTHrP expression increases on rigid scaffolds in the absence of RAW conditioned media. Together these results suggest that myeloid cells sense changes in rigidity and alter their signaling profile accordingly to aid bone metastasis. Importantly, these studies highlight the need to perform studies that include more diverse cell populations, since the presence of myeloid cells or other cell types can alter gene expression within tumor cells. The use of 3D scaffolds will allow us to include multiple cell types and examine the interactions between tumor cells and cells in the bone microenvironment. Better understanding this interaction will help identify new therapeutic targets for the inhibition of tumor-induced bone disease. Citation Format: Denise Buenrostro, Ushashi Dadwal, Scott Guelcher, Julie Sterling. The role of rigidity in myeloid-tumor cell interactions in bone. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3191. doi:10.1158/1538-7445.AM2015-3191