Pathophysiology of Bone Metastases in Prostate Cancer

Transcription

1 European Urology Supplements European Urology Supplements 3 (2004) 3 9 Pathophysiology of Bone Metastases in Prostate Cancer Per-Anders Abrahamsson* Malmö University Hospital, Malmö, Sweden Abstract Objective: Men with advanced prostate cancer are at high risk for bone metastases that result in significant skeletal morbidity. This review discusses the pathophysiology of bone metastases in prostate cancer. Methods: Relevant information was identified through searches of published studies, abstracts from scientific meetings, and review articles. Results: Bone metastases are common in patients with advanced cancer. Numerous growth factors present in the bone matrix are released during bone remodeling, potentially providing a fertile environment for the growth of tumor cells. Factors such as parathyroid hormone-related protein and interleukin-6 stimulate osteoclast-mediated bone resorption, thus enhancing the release of bone-derived growth factors. Prostate cancer cells secrete factors, including protease-activated receptor 1, that are involved in the multistep process of tumor cell detachment and migration to bone and factors that stimulate osteoblast-mediated bone formation, such as transforming growth factor-beta and bone morphogenetic proteins. In addition, prostate cancer cells produce endothelin-1, a peptide under intense investigation that stimulates the proliferation of osteoblasts and is thought to play a role in the development of osteoblastic bone lesions. These tumor-derived factors cause dysregulation of normal bone remodeling. Interactions between prostate tumor cells and the bone typically result in the formation of osteoblastic lesions characterized by increased osteolysis and uncoupled new bone formation. Preclinical evidence suggests that zoledronic acid has antitumor activity in animal models of prostate cancer. Conclusions: Bone metastasis is a complex process involving multiple molecular interactions between tumor cells and the bone microenvironment resulting in disruption of bone remodeling. In patients with prostate cancer, bone lesions are primarily osteoblastic, but are also associated with increased osteolytic activity, resulting in marked increases in bone turnover and clinically significant morbidity. # 2004 Elsevier B.V. All rights reserved. Keywords: Bisphosphonates; Zoledronic acid; Bone metastases; Prostate cancer 1. Introduction * Tel ; Fax: address: per-anders.abrahamsson@skane.se. The skeleton is the most common site of tumor metastasis, indicating that the bone microenvironment may provide fertile ground for tumor cell growth. Bone metastases occur in approximately 65% to 75% of patients with advanced prostate cancer, with bone lesions typically developing in the lumbar spine, ribs, and pelvis [1 3]. These lesions result in clinically important skeletal complications, including pathologic fracture, spinal cord compression, and debilitating bone pain. Skeletal morbidity is particularly problematic for patients with prostate cancer because the clinical course of bone metastases in these patients is relatively long; after diagnosis of bone metastases, patients with prostate cancer live for a median of 12 to 53 months, depending on hormonal status at presentation [1,4]. The mineralized bone matrix is rich in growth factors that are released during bone resorption, thus providing a fertile microenvironment for tumor cell metastasis. Normal bone remodeling is a dynamic process involving a delicate and coordinated balance between bone-resorbing osteoclasts and bone-forming osteoblasts, resulting in replacement of old bone with new, stronger bone [5]. This process is dependent on adequate amounts of vitamin D, calcium, and /$ see front matter # 2004 Elsevier B.V. All rights reserved. doi: /j.eursup

2 4 P.-A. Abrahamsson / European Urology Supplements 3 (2004) 3 9 phosphate. Mechanical stress stimulates bone remodeling through the activation of both osteoclasts and osteoblasts, resulting in the strengthening of bone at the sites of increased burden [6,7]. Bone resorption is also initiated in response to parathyroid hormone (PTH) and local factors such as interleukin (IL)-1 and IL-6 that stimulate osteoclast activity. PTH is responsible for regulating the release of calcium and phosphate from bone into the circulation, thereby maintaining the mineral homeostasis of the blood. Secretion of PTH by the parathyroid gland is dependent on serum calcium concentration; as the calcium concentration increases, PTH concentration decreases in a simple negative feedback loop. After osteoclasts degrade the bone, growth factors contained in the bone matrix, predominantly transforming growth factor-beta (TGF-b) and insulin-like growth factor (IGF)-II, are released from the bone and stimulate osteoblasts to repair the bone at the site of resorption. This coupled activity serves to maintain the homeostasis of the skeleton as well as the blood [5,8]. Bone metastases disrupt the normal bone remodeling process by increasing bone metabolism, which, in turn, might also facilitate the establishment of bone metastases. Preclinical studies have demonstrated that the activation of osteoclast-mediated bone resorption is an important first step in the formation of bone metastases [9,10]. In one study, mice rendered androgendeficient and inoculated with PC-3 prostate cancer cells (an androgen-refractory cell line) developed more bone metastases compared with control mice [9]. This was ascribed to the increased bone turnover elicited by androgen ablation (as evidenced by increased osteoclast numbers and increased bone loss). Importantly, the occurrence of bone metastases was effectively prevented by the addition of the bone resorption inhibitor zoledronic acid. Once tumor cells detach from the primary site and colonize the bone matrix, they produce soluble growth factors that stimulate osteoclastmediated bone resorption. In turn, activated osteoclasts release growth factors from the bone matrix that can stimulate tumor cell growth [8]. This interaction is likely to become cyclical, resulting in increased osteolysis and progression of tumor growth within the bone lesion. Bone metastases are classified according to radiographic appearance as osteolytic, osteoblastic, or mixed lesions [1]. Osteolytic lesions are characterized by excessive bone resorption around tumor sites with little new bone formation and appear as focal areas of profound osteopenia. Osteoblastic lesions are associated with increased bone formation and appear sclerotic. Bone lesions resulting from prostate cancer are primarily osteoblastic, but are also associated with increased bone resorption [8]. These lesions are characterized by increased bone formation around tumor cell deposits combined with unbalanced osteolytic activity and marked increases in bone turnover, resulting in significant bone loss. Moreover, excess bone formation may result in calcium entrapment in bone, leading to increases in serum PTH and development of a bone hunger syndrome characterized by generalized osteopenia [11]. Endothelin-1, a growth factor that is produced by the prostate epithelium and detected at increased levels in the circulation of patients with bone metastases from prostate cancer, is a potent stimulator of osteoblast proliferation and is thought to play a role in the development of the osteoblastic bone lesions in these patients [12 14]. Bisphosphonates are potent inhibitors of osteoclastmediated bone resorption and have demonstrated efficacy in the treatment and prevention of skeletal complications resulting from bone metastases from a variety of solid tumors [15]. Zoledronic acid, a newgeneration bisphosphonate, has demonstrated significant reduction in the incidence of skeletal complications and significant palliation of bone pain in patients with bone metastases from prostate cancer [16 18]. Furthermore, preclinical evidence indicates that zoledronic acid has antitumor effects and may prevent the formation of bone metastases (reviewed by Dr. Jonathan Green in this supplement) [9]. 2. Pathophysiology of bone metastases Bone metastasis occurs through a cascade of events that involves complex interactions between tumor cells and the bone [5,8]. Primary tumor cells penetrate the basement membrane and escape the confines of the primary tumor site by invading lymphatic or blood vessels. Subsequently, the tumor cells proliferate, migrate to distant capillary beds in the bone, and eventually escape the vasculature by extravasation. Prostate cancer cells can also migrate to the lumbar spine via the vertebral venous plexus (Batson s plexus): tumor cells traverse this low-pressure, high-volume system of vertebral veins and form metastatic tumor deposits in the lumbar vertebrae [19] Factors involved in metastasis Recent studies have identified stromal factors produced by prostate cancer cells that are involved in the multistep process of metastasis [20]. Most importantly, prostate cancer cells express high levels of proteaseactivated receptor 1 (PAR1; thrombin receptor), and

3 P.-A. Abrahamsson / European Urology Supplements 3 (2004) PAR1 activation promotes cell adhesion to matrix proteins, cell motility and migration, and matrix metalloproteinase (MMP) secretion [5,20 22]. Primary prostate cancer cell lines express higher levels of PAR1 than normal tissue, and prostate cancer cell lines derived from bone metastases express the highest levels of PAR1, suggesting that PAR1 may participate in tumor cell metastasis to bone [20]. Activation of PAR1 by proteolytic cleavage of the extracellular domain has been shown to alter the expression of cell adhesion molecules. Among the cell adhesion molecules, integrin a v b 3 appears to be critical for the metastatic process. Integrin a v b 3 is involved in the adhesion of prostate cancer cells to the vascular endothelium and is also necessary for osteoclastmediated bone resorption [23,24]. Expression of integrin a v b 3 on prostate cancer cells facilitates binding to blood vessel walls and extravasation into the surrounding tissue. Furthermore, studies have demonstrated that expression of integrin a v b 3 in tumor cells increases tumor cell invasion and development of osteolytic lesions in nude mice [25].PAR1 activation also induces secretion of MMPs, which degrade the extracellular matrix. Secretion of MMPs allows tumor cells to detach from their primary site, enter and exit the vasculature, and migrate into bone tissue [5,20]. Bisphosphonates can disrupt this metastatic process at several levels. In a recent study, zoledronic acid was shown to inhibit integrin a v b 3 -mediated tumor cell adhesion to the vascular endothelium [26]. In addition, bisphosphonates dose-dependently inhibit the activity and expression of a broad range of MMPs produced by tumor cell lines, and this inhibition correlates with reduced invasion in the Matrigel assay [27]. Specifically, zoledronic acid reduces the expression of MMP- 2 and MMP-9 in PC-3 prostate cancer cells [28] Activation of osteoclasts Tumor cells also secrete a variety of soluble growth factors that stimulate osteoclast activity and disrupt normal bone remodeling (Fig. 1) [29]. Many tumor cells secrete parathyroid hormone-related protein and IL-6, which stimulate osteoclastogenesis and bone resorption [8,30 32]. Evidence from several preclinical studies indicates that induction of bone resorption is an important first step in the formation of bone metastases. Studies with mice that lack the integrin a v b 3 have shown that osteoclast-mediated bone resorption requires integrin-mediated cell adhesion and signaling [10]. Consequently, these a v b 3 knock-out mice have a defect in normal bone resorption, and they are also protected from bone metastases [10]. Furthermore, in another study (also discussed in the introduction) mice Fig. 1. Pathophysiology of bone metastases. (A) In osteolytic bone disease, (1) metastatic tumor cells release humoral factors that stimulate osteoclastic recruitment and differentiation. (2) Osteoclasts begin to break down bone. (3) Bone resorption results in the release of growth factors that stimulate tumor-cell growth. (4) As the tumor proliferates, it produces substances that increase osteoclast-mediated bone resorption. (B) In osteoblastic bone disease, (1) metastatic tumor cells release growth factors that stimulate the activity of osteoclasts. (2) Tumor cells also secrete growth factors that stimulate the activity of osteoblasts. (3) Excessive new bone formation occurs around tumor-cell deposits. (4) Osteoclastic activity releases growth factors that stimulate tumor-cell growth. (5) Osteoblastic activation releases unidentified osteoblastic growth factors that also stimulate tumor-cell growth. PTHrP = parathyroid hormone-related protein; IL-6 = interleukin-6; TGF-b = transforming growth factor-beta; BMP = bone morphogenetic protein; IGF = insulin-like growth factor; FGF = fibroblast growth factor. Adapted from Saad and Schulman [29]. Copyright #2004, with permission from the European Association of Urology.

4 6 P.-A. Abrahamsson / European Urology Supplements 3 (2004) 3 9 rendered androgen deficient by surgical castration had increased osteoclast numbers and increased bone resorption; these mice also developed more bone metastases when inoculated with the PC-3 prostate cancer cell line compared with control mice [9]. Therefore, increased bone resorption may stimulate bone metastasis. This could explain the observation that tumors that stimulate bone resorption have a greater propensity to metastasize to bone. Induction of bone resorption causes the release of bone-derived growth factors that enhance tumor-cell survival and proliferation, chemotaxis to bone, and adhesion to the bone marrow endothelium [8]. Factors in the bone matrix, such as TGF-b, IGF-I and -II, collagen Type I peptides, and osteonectin, are chemoattractants for prostate cancer cells in vitro [20,33]. Other factors such as stromal cell-derived factor 1 enhance the migration of prostate cancer cells across the human bone marrow endothelium, whereas TGF-b or bone morphogenetic protein (BMP)-4 increase the adhesion of PC-3 prostate cancer cells to the bone marrow endothelium [20,34]. These are just some of the complex interactions that promote colonization of the bone by human prostate cancer cells Activation of osteoblasts Prostate cancer cells also secrete a variety of factors that stimulate osteoblasts to form new bone, including TGF-b, BMPs, endothelin-1, prostate-specific antigen (PSA), and IGFs (Fig. 1) [29]. TGF-b and BMPs (a family of at least 15 bone-derived peptides that are members of the extended TGF-b superfamily) promote osteoblast differentiation and activation and stimulate new bone formation in vivo [5,35,36]. Studies have shown that human prostate cancer cells express TGF-b at levels greater than those in normal prostate tissue, and many rat and human prostate cancer cell lines, as well as normal and neoplastic human prostate tissue, express a variety of BMPs [37,38]. Another prostate-specific growth factor is endothelin-1. This peptide is a potent vasoconstrictor that also stimulates osteoblast proliferation and inhibits osteoclast-mediated bone resorption in culture [13,39]. Endothelin-1 is produced by the prostatic epithelium, and high-affinity endothelin receptors are present throughout the prostate gland [12]. In addition, endothelin-1 is expressed in nearly every prostate cancer cell line and is significantly elevated in the circulation of patients with bone metastases from prostate cancer [13]. Endothelin-1 is also secreted in breast cancer cell lines that cause osteoblastic metastases in a mouse model. Yin et al. reported a decreased number of metastases resulting from treatment with an endothelin-a receptor antagonist [40]. The endothelin- A receptor antagonist atrasentan has been studied in patients with prostate cancer and bone metastases. Nelson et al. found that atrasentan dose-dependently suppressed serum levels of bone-specific alkaline phosphatase (BAP), a biochemical marker of bone formation (reviewed by Dr. Yong-jiang Hei in this supplement) [14]. Additional factors secreted by prostate tumors, including PSA and IGFs, may also increase tumor growth and enhance bone formation [5,41]. PSA is a serine protease that is an important biological marker for the diagnosis and management of prostate cancer, and PSA levels significantly correlate with the presence of bone metastases [42]. Proteases produced by tumor cells, including PSA, are thought to be responsible for dissociating IGFs from their binding proteins, thus enhancing tumor proliferation and osteoblast function [5] Characterization of bone lesions The complex interactions between prostate tumor cells and the bone microenvironment typically result in the formation of osteoblastic lesions. These lesions are characterized by increased new bone formation and exhibit radiographic evidence of increased bone density. However, biochemical studies have shown that biochemical markers of both bone resorption and bone formation are dramatically increased in patients with osteoblastic lesions [43,44]. In a recent study, urinary levels of the bone resorption marker N-telopeptide and serum levels of the bone formation marker BAP were measured in 77 patients with bone metastases from a variety of cancers [44]. Results showed that patients with osteoblastic lesions had significantly higher levels of both bone resorption and bone formation markers compared with patients presenting with osteolytic or mixed lesions (Fig. 2) [44]. Furthermore, bone marker levels correlated significantly with the number of metastatic bone lesions [44]. In a similar study of 97 patients with bone metastases secondary to either prostate, breast, or gastrointestinal cancer, both N- telopeptide and BAP elevations were more than 3-fold higher in patients with prostate cancer compared with breast cancer (Fig. 3) [45]. Although this biochemical evidence demonstrates increased bone resorption and bone formation in patients with prostate cancer, new bone growth is uncoupled from bone resorption and does not contribute to maintaining bone strength or rebuilding the bone at sites of bone resorption. This is evident in histomorphometric studies of prostate cancer tissue showing that osteoblastic lesions typically have a sclerotic appearance with areas of eroded bone

5 P.-A. Abrahamsson / European Urology Supplements 3 (2004) Fig. 2. Bone marker levels in patients with bone metastases were significantly higher in osteoblastic disease than in either osteolytic or mixed disease. (A) Urinary levels of N-telopeptide, a marker of bone resorption, and (B) serum levels of bone-specific alkaline phosphatase, a marker of bone formation, in 77 patients with osteoblastic, osteolytic, or mixed bone lesions. BCE = bone collagen equivalents; Cr = creatinine. Adapted from Demers et al., [44]. Copyright # 2000 American Cancer Society. Reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc. Fig. 3. Bone marker levels in patients with bone metastases were higher in patients with prostate cancer than in patients with either breast cancer or gastrointestinal (GI) cancer. (A) Urinary levels of N-telopeptide, and (B) serum levels of bone-specific alkaline phosphatase, in 97 patients with breast, prostate, or GI cancer with bone metastases. BCE = bone collagen equivalents; Cr = creatinine. Adapted with permission from Demers LM, et al. [45]. surfaces combined with increased bone volume at sites of metastases [46]. Therefore, there is a net loss of bone, and patients are at risk for vertebral collapse and other pathologic fractures [30]. These lesions are also associated with severe and unrelenting bone pain that often requires strong opioid analgesics and palliative radiotherapy. These data provide a better understanding of the observed clinical benefits of zoledronic acid in patients with prostate cancer. By inhibiting bone resorption, zoledronic acid not only breaks the cycle that results in increased osteolysis and tumor growth progression within a bone lesion, but also inhibits the bone destruction and remodeling that causes such profound pain. These studies also suggest that zoledronic acid may inhibit the formation of bone metastases when given to patients with earlier disease stages. Ongoing studies will address this question (reviewed by Dr. Yong-jiang Hei in this supplement). 3. Conclusions Men with advanced prostate cancer are at high risk for the development of bone metastases and associated skeletal complications. Soluble factors released from tumor cells and the mineralized bone matrix participate in the metastasis of tumor cells to bone. Tumor cells produce stromal factors that affect cell adhesion, motility, and migration, facilitating tumor cell detachment from the primary tumor and migration to the bone matrix. Subsequently, tumor cells secrete a variety of factors that disrupt normal bone remodeling by stimulating both osteoclast-mediated bone resorption and osteoblast-

6 8 P.-A. Abrahamsson / European Urology Supplements 3 (2004) 3 9 mediated bone formation. In turn, increased bone resorption results in the release of many bone-derived growth factors from the bone matrix that provide a fertile microenvironment for tumor cell proliferation. In patients with bone metastases from prostate cancer, bone lesions are primarily osteoblastic, but are also associated with increased osteolytic activity, resulting in marked increases in bone turnover, significant local bone loss, and clinically significant skeletal morbidity. This association of increased osteolytic activity with osteoblastic lesions is the basis for the observed clinical benefit of zoledronic acid in patients with bone metastases from prostate cancer. Preclinical evidence has demonstrated that zoledronic acid also has antitumor effects and can disrupt the process of bone metastasis in animal models of prostate cancer. References [1] Coleman RE. Metastatic bone disease: clinical features, pathophysiology and treatment strategies. Cancer Treat Rev 2001;27: [2] Mundy GR. Mechanisms of bone metastasis. Cancer 1997;80(Suppl): [3] McMurtry CT, McMurtry JM. Metastatic prostate cancer: complications and treatment. J Am Geriatr Soc 2003;51: [4] Morris MJ, Scher HI. Clinical approaches to osseous metastases in prostate cancer. Oncologist 2003;8: [5] Guise TA, Mundy GR. Cancer and bone. Endocr Rev 1998;19: [6] Nomura S, Takano-Yamamoto T. Molecular events caused by mechanical stress in bone. Matrix Biol 2000;19:91 6. [7] Boyde A. The real response of bone to exercise. J Anat 2003;203: [8] Mundy GR. Metastasis to bone: causes, consequences and therapeutic opportunities. Nat Rev Cancer 2002;2: [9] Padalecki SS, Carreon M, Grubbs B, Cui Y, Guise TA. Androgen deprivation enhances bone loss and prostate cancer metastases to bone: prevention by zoledronic acid. Oncology 2003;17(Suppl):32. [10] Bakewell S, Dowland N, Weilbaecher K. Beta 3 integrin / mice are protected from osteolytic bone metastases. Oncology 2003;17(Suppl 3):16 7. [11] Berruti A, Sperone P, Fasolis G, Torta M, Fontana D, Dogliotti L, et al. Pamidronate administration improves the secondary hyperparathyroidism due to Bone Hunger Syndrome in a patient with osteoblastic metastases from prostate cancer. Prostate 1997;33: [12] Langenstroer P, Tang R, Shapiro E, Divish B, Opgenorth T, Lepor H. Endothelin-1 in the human prostate: tissue levels, source of production and isometric tension studies. J Urol 1993;150: [13] Nelson JB, Hedican SP, George DJ, Reddi AH, Piantadosi S, Eisenberger MA, et al. Identification of endothelin-1 in the pathophysiology of metastatic adenocarcinoma of the prostate. Nat Med 1995;1: [14] Nelson JB, Nabulsi AA, Vogelzang NJ, Breul J, Zonnenberg BA, Daliani DD, et al. Suppression of prostate cancer induced bone remodeling by the endothelin receptor A antagonist atrasentan. J Urol 2003;169: [15] Lipton A. Management of metastatic bone disease and hypercalcemia of malignancy. Am J Cancer 2003;2: [16] Saad F, Gleason DM, Murray R, Tchekmedyian S, Venner P, Lacombe L, et al. A randomized, placebo-controlled trial of zoledronic acid in patients with hormone-refractory metastatic prostate carcinoma. J Natl Cancer Inst 2002;94: [17] Saad F, Gleason DM, Murray R, Tchekmedyian S, Venner P, Lacombe L, et al., for the Zoledronic Acid Prostate Cancer Study Group. Longterm efficacy of zoledronic acid for the prevention of skeletal complications in patients with metastatic hormone-refractory prostate cancer. J Natl Cancer Inst 2004;96: [18] Saad F, Gleason D, Murray R, Venner P, Goas JA, Chen B-L, et al. Long-term reduction of bone pain with zoledronic acid in patients with advanced prostate cancer metastatic to bone [poster]. Presented at American Urological Association; April 26 May 1, 2003; Chicago, Illinois [Abstract 1473]. [19] Geldof AA. Models for cancer skeletal metastasis: a reappraisal of Batson s plexus. Anticancer Res 1997;17: [20] Cooper CR, Chay CH, Gendernalik JD, Lee HL, Bhatia J, Taichman RS, et al. Stromal factors involved in prostate carcinoma metastasis to bone. Cancer 2003;97(Suppl): [21] Walz DA, Fenton JW. The role of thrombin in tumor cell metastasis. Invasion Metastasis ;14: [22] Lafleur MA, Hollenberg MD, Atkinson SJ, Knauper V, Murphy G, Edwards DR. Activation of pro-(matrix metalloproteinase-2) (pro- MMP-2) by thrombin is membrane-type-mmp-dependent in human umbilical vein endothelial cells and generates a distinct 63 kda active species. Biochem J 2001;357: [23] Romanov VI, Goligorsky MS. RGD-recognizing integrins mediate interactions of human prostate carcinoma cells with endothelial cells in vitro. Prostate 1999;39: [24] Teitelbaum SL. Bone resorption by osteoclasts. Science 2000;289: [25] Pécheur I, Peyruchaud O, Serre CM, Guglielmi J, Voland C, Bourre F, et al. Integrin a(v)b3 expression confers on tumor cells a greater propensity to metastasize to bone. FASEB J 2002;16: [26] Bezzi M, Hasmim M, Bieler G, Dormond O, Rüegg C. Zoledronate sensitizes endothelial cells to tumor necrosis factor-induced programmed cell death. Evidence for the suppression of sustained activation of focal adhesion kinase and protein kinase B/Akt. J Biol Chem 2003;278: [27] Heikkila P, Teronen O, Moilanen M, Konttinen YT, Hanemaaijer R, Laitinen M, et al. Bisphosphonates inhibit stromelysin-1 (MMP-3), matrix metalloelastase (MMP-12), collagenase-3 (MMP-13) and enamelysin (MMP-20), but not urokinase-type plasminogen activator, and diminish invasion and migration of human malignant and endothelial cell lines. Anticancer Drugs 2002;13: [28] Corey E, Brown LG, Quinn JE, Poot M, Roudier MP, Higano CS, et al. Zoledronic acid exhibits inhibitory effects on osteoblastic and osteolytic metastases of prostate cancer. Clin Cancer Res 2003;9: Erratum in: Clin Cancer Res 2003;9: [29] Saad F, Schulman CC. Role of bisphosphonates in prostate cancer. Eur Urol 2004;45: [30] Berruti A, Dogliotti L, Tucci M, Tarabuzzi R, Fontana D, Angeli A. Metabolic bone disease induced by prostate cancer: rationale for the use of bisphosphonates. J Urol 2001;166: [31] Bryden AA, Hoyland JA, Freemont AJ, Clarke NW, George NJ. Parathyroid hormone related peptide and receptor expression in paired primary prostate cancer and bone metastases. Br J Cancer 2002;86: [32] Royuela M, Ricote M, Parsons MS, Garcia-Tunon I, Paniagua R, de Miguel MP. Immunohistochemical analysis of the IL-6 family of cytokines and their receptors in benign, hyperplasic, and malignant human prostate. J Pathol 2004;202:41 9. [33] Cooper CR, Pienta KJ. Cell adhesion and chemotaxis in prostate cancer metastasis to bone: a minireview. Prostate Cancer Prostatic Dis 2000;3:6 12.

7 P.-A. Abrahamsson / European Urology Supplements 3 (2004) [34] Taichman RS, Cooper C, Keller ET, Pienta KJ, Taichman NS, McCauley LK. Use of the stromal cell-derived factor-1/cxcr4 pathway in prostate cancer metastasis to bone. Cancer Res 2002;62: [35] Noda M, Camilliere JJ. In vivo stimulation of bone formation by transforming growth factor-beta. Endocrinology 1989;124: [36] Sampath TK, Maliakal JC, Hauschka PV, Jones WK, Sasak H, Tucker RF, et al. Recombinant human osteogenic protein-1 (hop-1) induces new bone formation in vivo with a specific activity comparable with natural bovine osteogenic protein and stimulates osteoblast proliferation and differentiation in vitro. J Biol Chem 1992;267: [37] Steiner MS, Zhou ZZ, Tonb DC, Barrack ER. Expression of transforming growth factor-beta 1 in prostate cancer. Endocrinology 1994;135: [38] Harris SE, Harris MA, Mahy P, Wozney J, Feng JQ, Mundy GR. Expression of bone morphogenetic protein messenger RNAs by normal rat and human prostate and prostate cancer cells. Prostate 1994;24: [39] Alam AS, Gallagher A, Shankar V, Ghatei MA, Datta HK, Huang CL, et al. Endothelin inhibits osteoclastic bone resorption by a direct effect on cell motility: implications for the vascular control of bone resorption. Endocrinology 1992;130: [40] Yin JJ, Mohammad KS, Kakonen SM, Harris S, Wu-Wong JR, Wessale JL, et al. A causal role for endothelin-1 in the pathogenesis of osteoblastic bone metastases. Proc Natl Acad Sci USA 2003;100: [41] Mayahara H, Ito T, Nagai H, Miyajima H, Tsukuda R, Taketomi S, et al. In vivo stimulation of endosteal bone formation by basic fibroblast growth factor in rats. Growth Factors 1993;9: [42] Oesterling JE. Prostate specific antigen: a critical assessment of the most useful tumor marker for adenocarcinoma of the prostate. J Urol 1991;145: [43] Garnero P, Buchs N, Zekri J, Rizzoll R, Coleman RE, Delmas PD. Markers of bone turnover for the management of patients with bone metastases from prostate cancer. Br J Cancer 2000;82: [44] Demers LM, Costa L, Lipton A. Biochemical markers and skeletal metastases. Cancer 2000;88(Suppl): [45] Demers LM, Costa L, Lipton A. Biochemical markers and skeletal metastases. Clin Orthop 2003;415(Special Issue):S [46] Clarke NW, McClure J, George NJ. Morphometric evidence for bone resorption and replacement in prostate cancer. Br J Urol 1991;68:74 80.