Abstract 1478: Bone marrow mesenchymal stem cells suppress tumor cell apoptosis and are selectively recruited to early-stage tumors

Abstract

Abstract Bone marrow mesenchymal stem cells (BMMSC) are recruited to primary tumors and have been reported to display pro-tumorigenic as well as anti-tumorigenic activities. However, the mechanisms behind their effect on tumor development are still unclear. We have isolated murine bone marrow aspirates and plated them on fibronectin/collagen I, which allows expansion of an adherent stromal cell population in 3-6 weeks. These cells express the CD44 hyaluronic acid receptor in the absence of hematopoietic (CD34), myeloid (CD45), and endothelial (CD31/VEGFR2) markers and display both spontaneous and inducible adipogenesis/ osteoblastogenesis in culture. 3D matrigel cultures of murine 4T1 mammary carcinoma cells revealed enhanced generation of tumor spheroids in the presence of BMMSC or their conditioned media. Conditioned media from BMMSC also increased 4T1 cell expansion in 2D monolayer cultures, with loss of this phenomenon after heat inactivation suggesting the presence of protein-based signaling. Cell cycle analysis of 4T1 cells treated with BMMSC conditioned media revealed no statistically significant change in mitotic potential in either growth (serum present) or growth-arrest (serum depleted) phase, as determined by PI staining and BrdU uptake. However, analysis of apoptosis in 4T1 cells treated with BMMSC conditioned media showed increased percentages of live cells by PI uptake and AnnexinV staining, as well as a reduction in caspase-3 and caspase-9 activation by colorimetric assay, as the cells entered growth arrest phase. Furthermore, treatment with BMMSC conditioned media preserved viability in 4T1 cells exposed to paclitaxel under no-serum conditions. Complementary studies of BMMSC tumor-directed migration indicate that BMMSC show preferential in vitro recruitment by murine tumor cell lines which generate reactive stroma (4T1, LL/2 lung carcinoma) vs. no stroma (B16 melanoma). In vivo recruitment of BMMSC by early-stage/slow-growing subcutaneous 4T1 tumors was also visualized by bioluminescent imaging, red fluorescence, and magnetic resonance imaging of BMMSC labeled with iron-nanoparticles. These results were confirmed by immunohistochemical evaluation of iron deposits by Prussian blue stain and by immunofluorescent detection of PKH26-labeled BMMSC. Overall, our data identify BMMSC as an important mediator of tumor cell survival/treatment resistance and reveal an enhanced tropism of BMMSC toward early 4T1 tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1478. doi:1538-7445.AM2012-1478