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Diets high in n-6 fatty acids are associated with an increased risk of bone metastasis from prostate carces (PCa). The molecular mechanism underlying this phenomenon is largely unknown. Arachidonic acid (AA) and its precursor linoleic acid can be metabolized to produce pro-inflammatory cytokines that act as autocrine and paracrine regulators of cancer behavior. We and other authors have previously reported that factors released by PCa cells excite an aberrant response in bone marrow stromal cells (BMSCs). We planned to study how AA may modulate in vitro the interaction between PCa cells and human BMSCs. First, we observed that AA is a potent mitogenic factor for PCa cells through the production of both 5-lipoxygenase (5-LOX) and cyclooxygenase-2 (COX-2) metabolites. While 5-LOX controls cell survival through the regulation of the Bcl-2/Bax ratio, COX-2 activity stimulates the release of transforming growth factor-alpha (TGF-alpha) and pro-inflammatory cytokines. The blockade of COX-2 activity through a specific inhibitor is sufficient to repress AA-induced gene transcription. The over-expression of transforming growth factor -alpha (TGF-alpha), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) by AA-primed PCa cells resulted particularly effective in modifying cell behavior of cultured human BMSCs. In fact, we observed an increment in the cell number of BMSCs, due prevalently to the action of TGF-alpha, the number of osteoblasts, and the production of receptor activator for nuclear factor kappa B ligand (RANKL), events mainly controlled by inflammatory cytokines. These findings provide a possible molecular mechanism by which dietary n-6 fatty acids accumulating in bone marrow may influence the formation of PCa-derived metastatic lesions and indicate new molecular targets for the therapy of metastatic PCa.

The activation of epidermal growth factor receptor (EGF-R) plays a key role in the promotion of proliferation and invasion in prostatic carcinoma (PCa). Gefitinib (Iressa; ZD1839), an orally active EGF-R tyrosine kinase inhibitor, has shown an important anti-proliferative activity in tumors expressing EGF-R both in vitro and in vivo. Our aim was to elucidate the role of gefitinib in the modulation of the metastatic spread of PCa cells. The therapeutic role of gefitinib was investigated by evaluating the proliferative and invasive ability of the PCa cell line PC3 and of its high metastatic sub-line, PCb2, by in vitro assays and intracardiac injection in nude mice. The inhibitory effect of gefitinib was tested in vivo by injecting PCa cells subcutaneously or in the left ventricle of nude mice and by administrating daily 150 mg/kg of gefitinib. While xenograft growth was equally reduced in all PCa lines (about 50%), the bone metastasis formation was inhibited especially for the high metastatic PCb2 sub-line (81%) in comparison to PC3 cells (47%). The comparative in vitro analysis among PCa cell lines showed that PCb2 cells were more sensitive to the inhibitory effect of gefitinib in their invasive ability compared to parental PC3 cells but not in their proliferation rate. Moreover, PCb2 cells demonstrated an increased invasive ability in vitro in response to bone stromal cell conditioned medium (BCM). The simultaneous presence of 0.1 ng/ml gefitinib was sufficient to reduce the number of invaded cells in the presence of both EGF and BCM. The molecular characterization of the highly aggressive PCa sub-lines demonstrated that this phenomenon was associated with an increment in uPA/uPAR axis but not in EGF-R expression. In conclusion, our data suggest that the use of gefitinib as a therapeutic agent may be indicated in the control of PCa spreading to bone.