Effect of COX-2 (PGE2) and IL-6 on Prostate Bone Metastases

Abstract

Abstract : We hypothesize that (1) prostate cancer cells that express cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2) and interleukin-6 (IL-6) display enhanced bone targeting and (2) the level of expression of COX-2, PGE2, and lL-6 in established bone metastases determines the overall bone response, with lower vs. higher cytokine levels inducing osteoblastic vs. osteolytic responses, respectively. We utilize two human prostate cancer cells lines (MDA-Pca 2b, osteoblastic response, low cytokine expression and PC-3ML, osteolytic response, high cytokine expression). Over the past year, we have established a subline of MDA-PCa-2b that stably expresses COX-2 and secretes high levels of PGE2,. Our data indicates that 1L6 stimulates PGE2 secretion significantly only in the COX-2+ transfected MDA-Pca-2b cells. We compared wtMDA-Pca2b vs. COX-2 + transfectants with regards to their ability to stimulate the Wnt signaling pathway (a key mediator of osteoblastic differentiation) in an autocrine and paracrine (osteoblast cell line M03T3). We demonstrate that forced expression of COX-2 and/or higher doses of exogenous PGE2 inhibits Wnt signaling in both MDAPCa2b cells and MC3T3 osteoblasts, whereas low PGE2 induces Wnt signaling. The mechanism of this dose-dependent effect of COX2/PGE2 involves modulation of Wnt receptor (LRP5/6), beta-catenin, and a natural Wnt inhibitor (DKK) expression in MC3T3 osteoblast cells grown in co-culture with MDA- PCa2b (wt vs. COX-2+) cells or with addition of varying doses of PGE2. The overall effect of COX-2/PGE2 was to stimulate Wnt signaling at low expression/dosing levels and inhibit Wnt signaling at high expression/dosing levels. A similar dose- response effect was observed with regards to BMP expression (another osteoblast stimulator) in that low COX-2/PGE2 stimulated BMP whereas high levels inhibited BMP in bone cells. We will continue our in vitro studies and begin in vivo studies in the coming year.