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New therapies are needed for hormone refractory prostate cancer. Promising new treatments specifically target metastatic disease in the bone, the predominant site of spread in prostate cancer. Recent advances in the understanding of the biology of the tumor–bone microenvironment are leading to the development of new bone-targeted therapies. In this article, we review current and developing clinical strategies designed to control prostate-cancer bone metastases.

We previously showed that adhesion of myeloma cells to fibronectin (FN) by means of β1 integrins causes resistance to certain cytotoxic drugs. The study described here found that adhesion of U937 human histiocytic lymphoma cells to FN provides a survival advantage with respect to damage induced by the topoisomerase (topo) II inhibitors mitoxantrone, doxorubicin, and etoposide. Apoptosis induced by a topo II inhibitor is thought to be initiated by DNA damage. The neutral comet assay was used to determine whether initial drug-induced DNA damage correlated with cellular-adhesion–mediated drug resistance. Cellular adhesion by means of β1 integrins resulted in a 40% to 60% reduction in mitoxantrone- and etoposide-induced DNA double-strand breaks. When the mechanisms regulating the initial drug-induced DNA damage were examined, a β1 integrin–mediated reduction in drug-induced DNA double-strand breaks was found to correlate with reduced topo II activity and decreased salt-extractable nuclear topo IIβ protein levels. Confocal studies showed changes in the nuclear localization of topo IIβ; however, alterations in the nuclear-to-cytoplasmic ratio of topo IIβ in FN-adhered cells were not significantly different. Furthermore, after a high level of salt extraction of nuclear proteins, higher levels of topo IIβ–associated DNA binding were observed in FN-adhered cells than in cells in suspension. Together, these data suggest that topo IIβ is more tightly bound to the nucleus of FN-adhered cells. Thus, FN adhesion by means of β1 integrins appears to protect U937 cells from initial drug-induced DNA damage by reducing topo II activity secondarily to alterations in the nuclear distribution of topo IIβ.

Iron overload at the time of bone marrow transplantation has recently been associated with increased mortality. The mechanism by which iron overload negatively impacts survival is unclear. In an effort to better define iron overload and its potential role in the transplant setting, we examined 78 consecutive patients at risk for transfusion-related iron overload (AML, ALL, MDS, and aplastic anemia) undergoing either autologous or allogeneic stem cell transplant at our institution between 1999 and 2004. To estimate transfusion-related iron overload, we devised a novel scoring system based on routinely available laboratory variables obtained prior to transplant. In our scoring system, a single point was awarded for each of the following: number of red cell units transfused prior to transplantation > 25; serum ferritin > 1000 ng/ml; and a semi-quantitative bone marrow iron stain of 6+. The Transfusion Iron Overload Score (range of 0 to 3) predicted for overall survival in our patient sample (Fig. 1, p = 0.0003 by Kaplan-Meier log rank trend) and was more powerful than using serum ferritin alone (p = 0.02). The calculated score retained its significant association with overall survival while controlling for traditional risk factors (age, sex, diagnosis, transplant type, donor relation, and remission status), inflammation (c-reactive protein), and measures of organ damage (transaminases, total bilirubin, INR, and cardiac ejection fraction) (p = 0.04 by Cox proportional-hazards regression). The 27 patients (35%) with a high score (≥ 2) had a dramatically lower median survival of 5.0 months compared to 29.3 months in those with an iron score of less than two (unadjusted hazard ratio of 2.5; 95% CI of 1.6 to 6.3). The observed mortality seen in those with a high score was primarily attributable to treatment-related mortality (p = 0.018) rather than disease-related mortality (p = 0.48). This finding likely accounts for the significant survival impact of iron overload seen in the allogeneic (p = 0.006) but not the autologous (p = 0.48) subgroup. In conclusion, the Transfusion Iron Overload Score served as a strong independent predictor of survival in our stem cell transplant population, identifying patients at significant risk for early treatment-related mortality. Our results lend further support to the notion that iron overload is detrimental in the transplant setting, and for the first time suggest that transfusion-related iron overload increases mortality via a mechanism independent of pre-existing inflammation and end-organ dysfunction. Figure 1. Overall post-transplant survival by the Transfusion Iron Overload Score. Figure 1. Overall post-transplant survival by the Transfusion Iron Overload Score.

Human A1 a Bcl-2 related gene, has been reported to be induced by TNF-α in endothelial and hematopoietic cells. In this study, we investigate the effects of up- or down-regulation of A1 expression on TNF-α induced apoptosis. We use U937 leukemia cell line that was transfected with a retroviral vector containing A1 cDNA in the sense or antisense orientation, as well as U937 cells that overexpress Bcl-2 or manganese superoxide dismutase (MnSOD). The effects of TNF-α on A1 mRNA (by Northern analysis) and toxicity (by apoptosis using Annexin V/flow cytometry and colony assay) were measured. Our results show that TNF-α (10-1000 ng/mL) induces A1 mRNA in all experimental groups except for U937 cells overexpressing Bcl-2, and, to a lesser degree, cells overexpressing A1 antisense. Chronic exposure of wild type U937 cells to low concentration of TNF-α (2-3 ng/mL) lead to overexpression of A1 mRNA and promote full protection against TNF-α induced apoptosis. Cells overexpressing A1 in the sense orientation are resistant to TNF-α induced apoptosis while those expressing antisense are more sensitive. U937 cells overexpressing Bcl-2 or MnSOD were also protected against TNF-α toxicity despite total suppression of A1 mRNA expression in the Bcl-2 cells. The addition of 25-50 μg/mL cycloheximide during TNF-α incubation reverses the protective effects of A1 and MnSOD but not that of Bcl-2. These results suggest that A1 may be induced by TNF-α as part of a protective mechanism against TNF-α toxicity in certain cell types. Furthermore, our results suggest a negative regulatory mechanism for A1 may be activated in the presence of high levels of Bcl-2.