Abstract 1418: Stromal cells of prostate, not the bone marrow, facilitate prostate cancer osteoblastic tumor growth in bone

Abstract

Abstract Stromal cells promote prostate cancer initiation and progression. Metastasized prostate cancers form osteoblastic bone lesions. The prostate cancer associated stroma expresses alpha-smooth muscle actin (alpha-SMA). Additionally, 69% of human prostate cancer tissues lost stromal TGFbeta type II receptor (Tgfbr2) expression. Conditional stromal knockout of the Tgfbr2 mouse model developed prostate adenocarcinoma. In parallel to the primary site, we observed human prostate cancer associated stroma in bone metastasis gained the expression of androgen receptor and alpha-SMA, which were negative in the normal bone marrow. Tgfbr2 expression was also lost in prostate cancer associated stroma in bone marrow, compared to its high expression in the normal bone marrow. This led us to question whether the stromal cells from the primary site or the bone marrow contribute the prostate cancer osteoblastic bone lesion development. In vitro, the conditioned media from Tgfbr2-flox or Tgfbr2-KO mouse prostate stromal cells (PSC) or bone marrow stromal cells (BMSC) were incubated on the C42B prostate cancer epithelia. Expressions of PTHrP, RANKL osteolytic factors and ET1, RUNX2, BMP2 osteoblastic factors by C42B cells were analyzed by qRT-PCR. The Tgfbr2-flox PSC conditioned media significantly increased the C42B cell expression of all the osteolytic and osteoblastic factors examined compared to C42B cells without conditioned media. However, the Tgfbr2-KO PSC conditioned media decreased the expression of PTHrP and RANKL, while further increased the expression of osteoblastic factors, ET1, RUNX2 and BMP2 by C42B cells by at least 2-fold. Conditioned media of Tgfbr2-flox and Tgfbr2-KO BMSC increased the expression of C42B cells on osteolytic factors (10-fold PTHrP and 2-fold RANKL), but neither has significant effect on expression of osteoblastic factors. Importantly, Tgfbr2-KO PSC and BMSC conditioned media increased C42B proliferation similarly by 2-fold over that of respective Tgfbr2-Tgfbr2-flox conditioned media. We found that the reduced PTHrP and RANKL expression was associated with respective promoter methylation, when C42B cells were incubated with Tgfbr2-KO PSC, but not BMSC. Epigenetic silencing of such osteolytic genes, would suggest for the first time, that the prostate stroma could influence osteoblastic tumor at a distant site. So, GFP labeled C42B cells, following pre-incubation with PSC or BMSC conditioned media, were injected into the tibia of SCID mice. X-rays of the bone lesions and fluorescence imaging of GFP-expressing tumor growth were measured. The data suggested, that the stromal cells from primary prostates, but not from the second metastasis site of bone marrow, promotes prostate cancer growth in the bone and osteoblastic bone lesion development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1418.