Increased anti-tumour effects of doxorubicin and zoledronic acid in prostate cancer cells in vitro: supporting the benefits of combination therapy.

PURPOSE: Combination treatment using the chemotherapy drug doxorubicin and the anti-resorptive agent zoledronic acid has shown to be very effective in inducing apoptosis in breast cancer cells, and also to eradicate breast tumour growth in vivo. Here, we investigated whether apoptotic cell death is increased when zoledronic acid and doxorubicin are given in sequence or in combination in prostate cancer cells in vitro. METHODS: PC3, DU145 and LNCaP prostate cancer cells were treated with zoledronic acid or doxorubicin alone, in sequence or in combination, and apoptosis was measured by evaluation of nuclear morphology following staining with Hoechst and PI. The involvement of the mevalonate pathway in the induction of apoptosis was assessed through the addition of the mevalonate pathway intermediate geranylgeraniol. RESULTS: Both agents induced PC3 cell death, with 5 microM zoledronic acid inducing 1.73% apoptosis and 50 nM doxorubicin 3.60% apoptosis following 24 h of exposure. In contrast, sequential exposure (doxorubicin followed by zoledronic acid) caused 8.87% apoptosis. Doxorubicin followed by zoledronic acid induced 4.77% apoptosis in LNCaP cells, compared to 1.53% caused by zol alone, 2.23% by dox alone and 2.5% following the reverse sequence (P < 0.001 in all cases). In DU145 cells doxorubicin followed by zoledronic acid induced 5.73% apoptosis, compared to 1.8% following zol alone, 2.93% by dox alone, and 3.20% following the reverse sequence (P < 0.001 in all cases). CONCLUSIONS: This is the first detailed study to show that an increased anti-tumour effect is generated when doxorubicin and zoledronic acid are given in sequence in both hormone-sensitive and insensitive prostate cancer cells in vitro. Our results suggest that combined treatment with these agents is superior to single agent therapy, and should be explored in a tumour model of prostate cancer.

Breast cancer cells stimulate osteoprotegerin (OPG) production by endothelial cells through direct cell contact.

BACKGROUND: Angiogenesis, the sprouting of capillaries from existing blood vessels, is central to tumour growth and progression, however the molecular regulation of this process remains to be fully elucidated. The secreted glycoprotein osteoprotegerin (OPG) is one potential pro-angiogenic factor, and clinical studies have demonstrated endothelial cells within a number of tumour types to express high levels of OPG compared to those in normal tissue. Additionally, OPG can increase endothelial cell survival, proliferation and migration, as well as induce endothelial cell tube formation in vitro. This study aims to elucidate the processes involved in the pro-angiogenic effects of OPG in vitro, and also how OPG levels may be regulated within the tumour microenvironment. RESULTS: It has previously been demonstrated that OPG can induce tube formation on growth factor reduced matrigel. In this study, we demonstrate that OPG enhances the pro-angiogenic effects of VEGF and that OPG does not stimulate endothelial cell tube formation through activation of the VEGFR2 receptor. We also show that cell contact between HuDMECs and the T47D breast cancer cell line increases endothelial cell OPG mRNA and protein secretion levels in in vitro co-cultures. These increases in endothelial cell OPG secretion were dependent on alphanubeta3 ligation and NFkappaB activation. In contrast, the pro-angiogenic factors VEGF, bFGF and TGFbeta had no effect on HuDMEC OPG levels. CONCLUSION: These findings suggest that the VEGF signalling pathway is not involved in mediating the pro-angiogenic effects of OPG on endothelial cells in vitro. Additionally, we show that breast cancer cells cause increased levels of OPG expression by endothelial cells, and that direct contact between endothelial cells and tumour cells is required in order to increase endothelial OPG expression and secretion. Stimulation of OPG secretion was shown to involve alphanubeta3 ligation and NFkappaB activation.

Pathophysiological roles of osteoprotegerin (OPG).

Osteoprotegerin (OPG) is a secreted glycoprotein central to bone turnover via its role as a decoy receptor for the receptor activator of nuclear factor kappaB ligand (RANKL) and has traditionally been linked to a number of bone-related diseases. However, there is additional evidence that OPG can promote cell survival by inhibiting TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. As a result, a number of in vitro, in vivo and clinical studies have been performed assessing the role of OPG in tumourigenesis. Similar studies have been performed regarding vascular pathologies, resulting from observations of expression and regulation of OPG in the vasculature. This review aims to provide an update on this area and assess the potential protective or detrimental role of OPG in both vascular pathologies and tumourigenesis.