Steps in prostate cancer progression that lead to bone metastasis

Prostate cancer is a complex disease in which metastasis to the bone is the main cause of death. Initial stages of metastasis are generally similar to those for most solid tumors; however, the mechanisms that underlie the homing of prostate tumor cells to the bone are not completely understood. Prostate cancer bone metastasis is also a microenvironment-driven disease, involving bidirectional interactions between the tumor and the bone microenvironment. In this review, we discuss the current understanding of the biologic processes and regulatory factors involved in the metastasis of prostate cancer cells, and their specific properties that promote growth in bone. Although many of these processes still need to be fully elucidated, a better understanding of the complex tumor/microenvironment interplay is slowly leading to more effective therapies for patients with prostate cancer bone metastases.     

前列腺癌骨骼转移的治疗策略

前列腺癌是骨转移肿瘤最常见的原发肿瘤。骨转移也是前列腺癌患者致死的主要原因之一，由于前列腺癌患者骨转移治疗后仍有较长的生存时间，合理选择治疗手段不仅可以改善患者生存质量，同时提高临床疗效。本文从骨转移发生的机理，可能性，治疗前临床评估，目前采用治疗手段的优劣等方面剖析了前列腺癌骨转移患者治疗策略的制定，对临床的治疗方法的选择有一定的参考价值。     

Human fucosyltransferase 6 enables prostate cancer metastasis to bone

Background:

The interaction between human prostate cancer (PCa) cells and bone marrow (BM) endothelium follows a rolling-and-adhesion cascade mediated by E-selectin ligand (ESL): E-selectin. This adhesion is enabled by elevated expression of α-1,3-fucosyltransferases (FTs), enzymes responsible for ESL-mediated bone metastasis in humans. In contrast, the incidence of bone metastasis in mice is rare.

Methods:

FT 3, 6 and 7 were overexpressed in mouse PCa cells. The rolling cell number, cell-rolling velocity and transendothelial migration were characterised in vitro. Fucosyltransferases-transduced mouse PCa cells expressing luciferase were inoculated into mice via left ventricle to compare the capability of bone metastasis. Mass spectrometry and immunoprecipitation were utilised for identification of ESLs.

Results:

Overexpression of FT3, FT6 or FT7 restored ESLs and enabled mouse PCa cells to roll and adhere in E-selectin-functionalised microtubes, similar to trafficking of circulating PCa cells in BM vessels. Following intracardiac inoculation, FT6-transduced cells induced robust bone metastasis in mice. Inhibition of FT6 by a fucose mimetic significantly reduced bone metastasis. Importantly, comparison of FT3, FT6 and FT7 gene expression in existing clinical samples showed significant upregulation of FT6 in PCa-distant metastases.

Conclusion:

FT6 is a key mediator of PCa cells trafficking to the BM. It may serve as a viable drug target in preclinical tests of therapeutics for reduction of PCa bone metastasis.     

Elevated serum periostin levels in patients with bone metastases from breast but not lung cancer

Periostin is a recently identified gene that is preferentially expressed in periosteum, indicating a potential role in bone formation and maintenance of structure. We independently identified and isolated periostin from cancer tissue, using the palindromic PCR-driven cDNA Differential Display technique. For the present work, we developed a novel sandwich chemiluminescence assay to detect serum periostin level using newly developed monoclonal and polyclonal antibodies. We investigated serum periostin levels in breast cancer and small cell lung cancer patients, especially in patients with bone metastasis. The study included 58 breast cancer and 44 small cell lung cancer patients. Serum periostin levels were elevated in breast cancer patients presenting with bone metastases (92.0 ± 28.6 ng/ml) compared to similar breast cancer patients without evidence of bone metastasis (55.0 ± 16.6 ng/ml, p = 0.04). No correlation was found between the serum periostin level and any other prognostic factors, such as clinical stage and lymph node metastasis in breast cancer. Serum periostin levels thus appear to serve as a marker of bone metastasis from breast cancer. In contrast, serum periostin levels were similar in samples from patients with small cell lung cancer who did or did not have bone metastasis. However, increasing T-stage and N-stage of patients with small cell lung cancer were correlated with higher periostin levels (T4, 126.5 ± 29.7 ng/ml v.s. T2, 64.9 ± 16.1 ng/ml, p = 0.03; and T4 v.s. T1, 36.3 ± 7.5 ng/ml, p = 0.01; N3, 108.7 ± 17.3 ng/ml v.s. N2, 49.7 ± 10.9 ng/ml, p = 0.01). Periostin has a substantial homology with the insect cell adhesion molecule, fasciclin I. Thus, expression of periostin may facilitate tumor cell adhesion to the bone surface. In fact, we found by in situ RNA hybridization, that the periostin gene was highly expressed in the stromal cells immediately surrounding the tumor, but not within the breast cancer cells themselves.     

Percentage of the positive area of bone metastasis is an independent predictor of disease death in advanced prostate cancer

We addressed in this study whether quantifying the extent of disease on bone scans can predict the disease death of patients with advanced prostate cancer using computer-assisted image analysis. Pretreatment radionuclide bone scans were reviewed in 56 patients with bone metastases from prostate cancer, and the percentage of the positive area on a bone scan (%PABS) was quantified automatically using a personal computer with the NIH Image program for estimation of the accurate extent of metastatic bone lesions on a bone scan. The significance of the %PABS as well as the other known prognostic factors was evaluated using univariate and multivariate Cox proportional hazards analysis. In univariate regression analysis, the %PABS (P=0.0155), serum alkaline phosphatase (P=0.0272), the tumour grade based on biopsy (P=0.044) and the number of bone lesions on bone scans (P=0.0388) were well associated with disease-specific survival. In multivariate analysis, the %PABS (P=0.0155, relative risk ratio 2.603), but not the other factors, was the independent predictor of the disease death. These results suggest that the %PABS is a novel parameter for predicting the prognosis of patients with advanced prostatic cancer.     

Targeted inhibition of cell-surface serine protease Hepsin blocks prostate cancer bone metastasis

The development of effective therapies inhibiting prostate cancer progression and metastasis may substantially impact prostate cancer mortality and potentially reduce the rates of invasive treatments by enhancing the safety of active surveillance strategies. Hepsin (HPN) is a cell surface serine protease amplified in a subset of human sarcomas (7.2%), as well as in ovarian (10%), lung adeno (5.4%), lung squamous cell (4.5%), adenoid cystic (5%), breast (2.6%), uterine (1.7%) and colon (1.4%) carcinomas. While HPN is not amplified in prostate cancer, it is one of the most prominently overexpressed genes in the majority of human prostate tumors and genetic experiments in mice indicate that Hepsin promotes prostate cancer metastasis, particularly metastasis to the bone marrow. We report here the development, analysis and animal trial of the small-molecule Hepsin inhibitor HepIn-13. Long-term exposure to HepIn-13 inhibited bone, liver and lung metastasis in a murine model of metastatic prostate cancer. These findings indicate that inhibition of Hepsin with small-molecule compounds could provide an effective tool for attenuation of prostate cancer progression and metastasis.     

Dasatinib inhibits the growth of prostate cancer in bone and provides additional protection from osteolysis

Background:

Dasatinib is a small molecule kinase inhibitor that has recently been shown to inhibit Src family kinases (SFK) and also has activity against CaP. Of importance to metastatic CaP, which frequently metastasises to bone, SFK are also vital to the regulation of bone remodelling. We sought to determine the ability of dasatinib to inhibit growth of CaP in bone.

Methods:

C4-2B CaP cells were injected into tibiae of SCID mice and treated with dasatinib, alone or in combination with docetaxel. Serum prostate-specific antigen levels, bone mineral density, radiographs and histology were analysed.

Results:

Treatment with dasatinib alone significantly lowered sacrifice serum prostate-specific antigen levels compared to control, 2.3±0.4 vs 9.2±2.1 (P=0.004). Combination therapy improved efficacy over dasatinib alone (P=0.010). Dasatinib increased bone mineral density in tumoured tibiae by 25% over control tumoured tibiae (P<0.001).

Conclusion:

Dasatinib inhibits growth of C4-2B cells in bone with improved efficacy when combined with docetaxel. Additionally, dasatinib inhibits osteolysis associated with CaP. These data support further study of dasatinib in clinical trials for men with CaP bone metastases.     

Significant addition to treatment options for bone metastasis in prostate cancer

Pathologic fractures, spinal compression, and pain take a great toll on the healthcare costs and well-being of men with prostate cancer metastatic to the bone. For almost 10 years, the only drug proven to prevent these skeletal-related adverse events was the bisphosphonate zoledronic acid. In a study published by Fizazi et al. in The Lancet, the monoclonal antibody to RANKL, denosumab, is shown to be superior to zoledronic acid in the prevention of these events. The only notable adverse event more frequent in either arm was increased hypocalcemia in the denosumab arm. There was a greater frequency of osteonecrosis of the jaw in the denosumab treatment group that did not reach statistical significance, but is of great concern. While further analysis is needed to determine the value of denosumab in preventing adverse events and improving quality of life, this new therapy is a significant addition to the treatment of men living with metastatic prostate cancer.     

Primary breast cancer stem-like cells metastasise to bone,switch phenotype and acquire a bone tropism signature

Background:

Bone metastases represent a common and severe complication in breast cancer, and the involvement of cancer stem cells (CSCs) in the promotion of bone metastasis is currently under discussion. Here, we used a human-in-mice model to study bone metastasis formation due to primary breast CSCs-like colonisation.

Methods:

Primary CD44⁺CD24⁻ breast CSCs-like were transduced by a luciferase-lentiviral vector and injected through subcutaneous and intracardiac (IC) routes in non-obese/severe-combined immunodeficient (NOD/SCID) mice carrying subcutaneous human bone implants. The CSCs-like localisation was monitored by in vivo luciferase imaging. Bone metastatic CSCs-like were analysed through immunohistochemistry and flow cytometry, and gene expression analyses were performed by microarray techniques.

Results:

Breast CSCs-like colonised the human-implanted bone, resulting in bone remodelling. Bone metastatic lesions were histologically apparent by tumour cell expression of epithelial markers and vimentin. The bone-isolated CSCs-like were CD44⁻CD24⁺ and showed tumorigenic abilities after injection in secondary mice. CD44⁻CD24⁺ CSCs-like displayed a distinct bone tropism signature that was enriched in genes that discriminate bone metastases of breast cancer from metastases at other organs.

Conclusion:

Breast CSCs-like promote bone metastasis and display a CSCs-like bone tropism signature. This signature has clinical prognostic relevance, because it efficiently discriminates osteotropic breast cancers from tumour metastases at other sites.     

前列腺癌骨转移的相关因素分析

目的：分析前列腺癌患者的临床资料,探讨前列腺癌骨转移的相关因素。方法以SPECT全身骨显像为诊断前列腺癌骨转移的金标准,回顾性分析235例前列腺癌患者的临床资料,采用单因素及多因素Logistic回归方法对前列腺癌骨转移的相关因素进行分析。结果单因素分析显示,两组在年龄、Gleason评分、TPSA值、FPSA值、F/T值及是否合并淋巴结转移的构成分布方面的差异具有统计学意义（P＜0.05）;多因素Logistic回归分析显示,合并淋巴结转移（OR=14.93）、年龄（OR=1.08）、Gleason评分（OR=2.90）、TPSA值（OR=1.05）与前列腺癌骨转移具有明显相关性,其中年龄≥70岁、Gleason评分≥8分、TPSA值≥20 ng/ml和F/T值≤0.16的前列腺癌患者发生骨转移的例数明显多于其他患者,差异均具有统计学意义（P＜0.05）。结论淋巴结转移、年龄、Gleason评分及TPSA值是前列腺癌骨转移的主要预测因素。对于年龄≥70岁、TPSA值≥20 ng/ml、Gleason评分≥8、F/T值≤0.16或者合并淋巴结转移的前列腺癌患者应该行SPECT全身骨显像检查,以便为患者临床早期发现及治疗提供帮助。     

Human prostate cancer bone metastases have an actionable immunosuppressive microenvironment

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PSA、ECT骨显像诊断前列腺癌骨转移的临床意义

目的:探讨前列腺特异抗原(PSA)、发射型计算机断层扫描(ECT)99Tc-MDP骨显像诊断前列腺癌骨转移的临床意义。方法:对80例(骨转移组31例,非骨转移组49例)前列腺癌病人的PSA、ECT与骨转移的关系进行回顾性分析。结果:骨转移组与非骨转移组的PSA值差异有显著性(139.36μg/Lvs37.58μg/L,P<0.01);PSA与骨转移的程度正相关,PSA<10μg/L,骨转移率为15.38%;PSA<20μg/L,骨转移率为19.35%;PSA>20μg/L,骨转移率为51.02%;PSA>100μg/L,骨转移率为78.95%。结论:ECT骨显像对前列腺癌骨转移有较高的敏感性,对未经治疗的前列腺癌病人,PSA<10μg/L,前列腺癌骨转移的可能性极小;PSA>100μg/L者,骨转移的可能性极大。PSA>20μg/L,建议行ECT骨扫描。     

PSA、ECT骨显像诊断前列腺癌骨转移的临床意义

目的：探讨前列腺特异抗原（PSA）、发射型计算机断层扫描（ECT）99Tc-MDP骨显像诊断前列腺癌骨转移的临床意义。方法：对80例（骨转移组31例,非骨转移组49例）前列腺癌病人的PSA、ECT与骨转移的关系进行回顾性分析。结果：骨转移组与非骨转移组的PSA值差异有显著性（139.36μg/Lvs37.58μg/L,P〈0.01）;PSA与骨转移的程度正相关,PSA〈10μg/L,骨转移率为15.38%;PSA〈20μg/L,骨转移率为19.35%;PSA〉20μg/L,骨转移率为51.02%;PSA〉100μg/L,骨转移率为78.95%。结论：ECT骨显像对前列腺癌骨转移有较高的敏感性,对未经治疗的前列腺癌病人,PSA〈10μg/L,前列腺癌骨转移的可能性极小;PSA〉100μg/L者,骨转移的可能性极大。PSA〉20μg/L,建议行ECT骨扫描。     

Honokiol, a natural plant product, inhibits the bone metastatic growth of human prostate cancer cells

BACKGROUND: Honokiol, a soluble nontoxic natural product derived from Magnolia spp., has been shown to induce apoptosis in malignant cells. The effect of honokiol and the combined therapy with docetaxel on prostate cancer (PCa) growth and bone metastasis was investigated in experimental models. METHODS: The in vitro proapoptotic effects of honokiol on human androgen-dependent and -independent PCa, bone marrow, bone marrow-derived endothelial, and prostate stroma cells were investigated. Honokiol-induced activation of caspases was evaluated by Western blot and FACS analysis. To confirm the cytotoxicity of honokiol, mice bone was inoculated in vivo with androgen-independent PCa, C4-2 cells and the effects of honokiol and/or docetaxel on PCa growth in bone were evaluated. Daily honokiol (100 mg/kg) and/or weekly docetaxel (5 mg/kg) were injected intraperitoneally for 6 weeks. PCa growth in mouse bone was evaluated by radiography, serum prostate-specific antigen (PSA) and tissue immunohistochemistry. RESULTS: Honokiol induced apoptosis in all cell lines tested. In PCa cells honokiol induced apoptosis via the activation of caspases 3, 8, and 9 and the cleavage of poly-adenosine diphosphate ribose polymerase in a dose- and time-dependent manner. Honokiol was shown to inhibit the growth and depress serum PSA in mice harboring C4-2 xenografts in the skeleton and the combination with docetaxel showed additive effects that inhibited further growth without evidence of systemic toxicity. Immunohistochemical staining confirmed honokiol exhibited growth-inhibitory, apoptotic, and antiangiogenic effects on PCa xenografts. CONCLUSIONS: The combination of honokiol and low-dose docetaxel may be used to improve patient outcome in androgen-independent prostate cancer with bone metastasis.     

FGF-8 is involved in bone metastasis of prostate cancer

Prostate cancer is the most common malignancy of men in Western countries. Patients with advanced prostate cancer suffer from incurable bone metastases. Recent data indicate that interactions between prostate cancer cells, osteoblasts, osteoclasts and the bone matrix are essential in the formation of bone metastases. FGF-8 is widely overexpressed in prostate cancer. Recently, FGF-8 has been found to affect both osteoblast and osteoclast differentiation. The aim of this study was to examine the role of FGF-8 in bone metastasis of prostate cancer. Immunohistochemistry was used to analyse FGF-8 expression in clinical samples of prostate cancer bone metastases. The functional significance of FGF-8 in growth of bone metastasis and formation of bone lesions was verified by using intratibial inoculations of FGF-8 or mock transfected PC-3 prostate cancer cells in nude mice. Intratibial tumors and bone lesions were analysed with X-ray, micro-CT and detailed histomorphometry using image analysis software and with immunostaining for osteocalcin and cathepsin K. Immunohistochemical analysis of tissue microarray of bone metastases of human prostate cancer showed that 76% of human bone metastasis samples (n = 25 from 11 patients) were positive for FGF-8. FGF-8 increased the growth of intratibial tumors and local formation of lytic and sclerotic lesions of bone. These results demonstrate that FGF-8 is expressed at a high frequency in bone metastases of human prostate cancer and that expression of FGF-8 in PC-3 prostate cancer cells increases their growth as intratibial tumors and modulates formation of bone lesions in an in vivo model of prostate cancer bone metastasis.     

Cathepsin L inactivation leads to multimodal inhibition of prostate cancer cell dissemination in a preclinical bone metastasis model

It is estimated that approximately 90% of patients with advanced prostate cancer develop bone metastases; an occurrence that results in a substantial reduction in the quality of life and a drastic worsening of prognosis. The development of novel therapeutic strategies that impair the metastatic process and associated skeletal adversities is therefore critical to improving prostate cancer patient survival. Recognition of the importance of Cathepsin L (CTSL) to metastatic dissemination of cancer cells has led to the development of several CTSL inhibition strategies. The present investigation employed intra‐cardiac injection of human PC‐3ML prostate cancer cells into nude mice to examine tumor cell dissemination in a preclinical bone metastasis model. CTSL knockdown confirmed the validity of targeting this protease and subsequent intervention studies with the small molecule CTSL inhibitor KGP94 resulted in a significant reduction in metastatic tumor burden in the bone and an improvement in overall survival. CTSL inhibition by KGP94 also led to a significant impairment of tumor initiated angiogenesis. Furthermore, KGP94 treatment decreased osteoclast formation and bone resorptive function, thus, perturbing the reciprocal interactions between tumor cells and osteoclasts within the bone microenvironment which typically result in bone loss and aggressive growth of metastases. These functional effects were accompanied by a significant downregulation of NFκB signaling activity and expression of osteoclastogenesis related NFκB target genes. Collectively, these data indicate that the CTSL inhibitor KGP94 has the potential to alleviate metastatic disease progression and associated skeletal morbidities and hence may have utility in the treatment of advanced prostate cancer patients.     

CD24 在前列腺癌组织中的表达及其临床意义

目的：探讨CD24 在前列腺癌组织中的表达及其与前列腺癌患者临床病理特征的关系。方法选取2016 年2 月至2019 年3 月福建医科大学附属泉州第一医院泌尿外科手术切除的40 例新鲜前列腺癌组织及相应的36 例癌旁组织,46 例前列腺增生组织标本取自TURP手术患者。通过流式细胞术检测40 例前列腺癌、36 例癌旁前列腺组织、46 例前列腺增生组织标本中CD24 的表达水平;运用单因素方差分析CD24 的表达量与前列腺癌患者的年龄、肿瘤分布情况、术前血清PSA含量、术后Gleason评分、临床分期和是否远处转移之间的关系。结果: 前列腺癌中CD24 的阳性表达率及平均荧光强度（MFI）值均明显高于癌旁前列腺组织和良性前列腺增生组织（均P<0.05）;术前血清PSA≥10 ng/ml、术后Gleason 评分≥8 分（低分化）、临床分期T4 期和远处转移的前列腺癌组织中CD24 的阳性细胞率及MFI值均明显高于对应组（均P<0.05）;且CD24 的表达随着术后Gleason 评分及临床分期的进展而逐渐增加（P<0.05）。结论：CD24 在前列腺癌组织中的表达增加,检测CD24 的表达水平可协助判断前列腺癌的发生、发展及侵袭转移等情况,具有潜在的临床应用价值。     

Effect of Paget's disease of bone (osteitis deformans) on the progression of prostate cancer bone metastasis

Background:Patients with prostate cancer tend to die from bone metastases. Until now, no evidence has shown that Paget's disease of bone (PDB) affects the progression of bone metastasis or overall survival of patients with prostate cancer.Methods:We searched our patient database for men who had presented with prostate cancer and PDB between June 1993 and March 2009, and identified best-matched control patients according to stage, grade, age, date of diagnosis, treatment, and race.Results:Among 1346 consecutive patients with prostate cancer diagnosed before 2008, 15 were confirmed to have comorbid PDB. Twenty-six more were identified from the institutional billing search. Including the 41 best-matched controls, our total study population was 82 patients. In the Kaplan-Meier analysis, we estimated median times from diagnosis of prostate cancer to bone metastasis to be 21.5 years for those with PDB and 9.4 years for those without PDB (P=0.044). Median overall survival times were 11.8 and 9.2 years for the two groups, respectively (P=0.008).Conclusion:For the first time, we have obtained evidence that patients with prostate cancer and PDB have delayed time to bone metastases and improved overall survival than do patients with prostate cancer alone.     

Integrating the immune microenvironment of prostate cancer induced bone disease

Prostate cancer (PCa) is the most frequently diagnosed cancer for men in the U.S. but does not impede patient survival until the disease is metastatic. Metastatic lesions most frequently occur in the bone, which exhibits a distinct microenvironment of immune and bone cell populations. Advances in the diagnosis and treatment of primary PCa allow for the use of tailored therapeutic approaches based on biomarkers, protein expression, and histopathology. Understanding the molecular and cellular characteristics of primary tumors has advanced therapeutic development and survival for patients with PCa. Personalized medicine has only recently emerged for the treatment of metastatic bone lesions. Tumor induced bone disease (TIBD) in patients with PCa can be classified into lytic, blastic, or mixed pathologies, with most patients exhibiting the blastic phenotype. Progress has been made in treating TIBD, but metastatic PCa has yet to be cured. Immune checkpoint inhibitors have exhibited limited responses in immunosuppressive PCa tumors, but have yet to be assessed in metastatic sites which may be susceptible to an increased inflammatory response. Recent discoveries have uncovered distinct tumor microenvironments (TMEs) of blastic and lytic bone metastases from patients with PCa, identifying actionable targets for therapeutic applications, including immune checkpoint inhibitors and targeted therapeutics. Enrichment for macrophages and T cells in patient samples suggests metastatic sites may be reappraised as immunologically targetable, despite their immunologically “cold” primary tumors. The practice of performing bone biopsies will help identify unique cellular and protein targets in the bone TME that can guide therapy decisions.     

Bone‐induced c‐kit expression in prostate cancer: A driver of intraosseous tumor growth

Loss of BRCA2 function stimulates prostate cancer (PCa) cell invasion and is associated with more aggressive and metastatic tumors in PCa patients. Concurrently, the receptor tyrosine kinase c‐kit is highly expressed in skeletal metastases of PCa patients and induced in PCa cells placed into the bone microenvironment in experimental models. However, the precise requirement of c‐kit for intraosseous growth of PCa and its relation to BRCA2 expression remain unexplored. Here, we show that c‐kit expression promotes migration and invasion of PCa cells. Alongside, we found that c‐kit expression in PCa cells parallels BRCA2 downregulation. Gene rescue experiments with human BRCA2 transgene in c‐kit‐transfected PCa cells resulted in reduction of c‐kit protein expression and migration and invasion, suggesting a functional significance of BRCA2 downregulation by c‐kit. The inverse association between c‐kit and BRCA2 gene expressions in PCa cells was confirmed using laser capture microdissection in experimental intraosseous tumors and bone metastases of PCa patients. Inhibition of bone‐induced c‐kit expression in PCa cells transduced with lentiviral short hairpin RNA reduced intraosseous tumor incidence and growth. Overall, our results provide evidence of a novel pathway that links bone‐induced c‐kit expression in PCa cells to BRCA2 downregulation and supports bone metastasis.