Abstract Hypoxia develops at sites of rapid cancer growth near sites of poorly organized vasculature. Heparin binding growth factors (HBGFs) support neoangiogenesis of tumors. We examined the effect of culturing bone-targeted, metastatic C4–2B prostate cancer cells and bone stromal derived HS27a cells under hypoxic conditions on expression of vascular endothelial growth factor (VEGF) family members. A sealed chamber infused with 1% (hypoxic) or 20% (normoxic) O 2 was used. Both cell lines produced VEGF-A in normoxia, but little or no HB-EGF, an- other HBGF. HS27a cells produced low levels of FGF- 2 and HGF, but little or none was secreted by C4–2B cells. Levels of VEGF-A in conditioned medium (CM) from both cell lines doubled when cultured in hypoxia. Similar changes in VEGF-A mRNA levels were seen. Receptor expression was unchanged by hypoxia. Changes in VEGF-A expression during hypoxia were preceded by nuclear accumulation of hypoxia inducible factor-1a (HIF-1a). Bone marrow endothelial (BME) cells express high levels of VEGFR2/flk-1, and are targets of VEGF-A induced neovascularization. BME cells proliferated in response to treatment with HS27a CM, but not C4–2B CM. BME cells formed tube-like angiogenic structures on growth factor reduced Ma- trigel Ò in response to CM from HS27a or C4–2B cells. This response was greater when CM was produced under hypoxia, and was reduced by VEGF-A or FGF-2 neutralizing antibodies. We conclude that hypoxia triggers a physiologically relevant increase in VEGF-A by prostate cancer and bone marrow stromal cells which involves a paracrine loop that recruits and acti- vates BME to support tumor neovascularization-re- lated processes. Keywords Prostate cancer Æ Hypoxia Æ Heparin binding growth factors Æ Bone marrow Æ Endothelial cells Æ VEGF Introduction Metastatic prostate cancer cells preferentially adhere to bone marrow endothelial (BME) cells, a phenom- enon associated with underlying stromal cell factors that facilitate bone homing [1–3]. Following extrava- sation, bone marrow provides a fertile microenviron- ment for growth and progression of prostate tumors, which in turn release factors that alter the bone marrow microenvironment [4, 5]. Functional interac- tions among extracellular matrix (ECM), abundant bone growth factors, and cellular receptors on pros- tate cancer cells, support cancer cell attachment, invasion, and growth in bone [4]. Some growth factors such as vascular endothelial growth factor-A (VEGF- A), fibroblast growth factor-2 (FGF-2), hepatocyte growth factor (HGF), and heparin binding epidermal Support: This work was supported by the NIH/ NCI P01 CA098912 (to LWKC and MCF-C). LWKC is the recipient of a Georgia Cancer Coalition Distinguished Scientist Award. C. Muir Æ D. D. Carson Æ M. C. Farach-Carson (&) Department of Biological Sciences, University of Delaware, Room 326 Wolf Hall, Newark, DE 19716, USA e-mail: farachca@udel.edu L. W. K. Chung Molecular Urology and Therapeutics Program, Department of Urology and Winship Cancer Institute, Emory University School of Medicine, Atlanta, GA 30322, USA Clin Exp Metastasis DOI 10.1007/s10585-006-9021-2 123 ORIGINAL PAPER Hypoxia increases VEGF-A production by prostate cancer and bone marrow stromal cells and initiates paracrine activation of bone marrow endothelial cells Caroline Muir Æ Leland W. K. Chung Æ Daniel D. Carson Æ Mary C. Farach-Carson Received: 21 February 2006 / Accepted: 14 May 2006 Ó Springer Science+Business Media B.V. 2006