Our understanding of the impact that fibroblasts have on
cancer cell behavior in vivo has been limited by the complexities of in vivo tumor microenvironments, which contain many distinct cell populations that influence
tumor growth and survival. Herein, we describe a novel, three-dimensional (3D), in vitro, fluorometric,
Tumor Growth Assay (TGA) that allows for non-invasive measurements of
cancer cell expansion in the presence of multiple
tumor-associated cell types or soluble factors, while embedded in Cultrex or
Matrigel Basement Membrane Extract (BME). Using this assay, we investigated the direct biological impact of primary human bone marrow stromal cells (hMSC) on the growth rates of a panel of metastatic
breast cancer cell lines. Human MSC can be readily isolated from bone marrow, a principle site of
breast cancer metastasis, and were found to significantly enhance the growth rate of MCF-7 (P-value<0.0001), an
estrogen receptor-alpha (
ERalpha) positive
breast cancer cell line, in a soluble factor-dependent manner. MSC paracrine factors also enhanced the growth of other
ERalpha positive
breast cancer cell lines including T47D, BT474, and ZR-75-1 (P-value<0.05). In contrast, the
ERalpha negative cell line MDA-MB-231 was unaffected by hMSC and the growth rate of another
ERalpha negative cell line MDA-MB-468 was elevated in the presence of hMSC, albeit to a lesser extent than MCF-7 or the other
ERalpha positive cell lines tested.