Biology of Bone Metastases in Prostate Cancer

Engineering 3D approaches to model the dynamic microenvironments of cancer bone metastasis

Cancer metastasis to bone is a three-dimensional (3D), multistep, dynamic process that requires the sequential involvement of three microenvironments, namely, the primary tumour microenvironment, the circulation microenvironment and the bone microenvironment. Engineered 3D approaches allow for a vivid recapitulation of in vivo cancerous microenvironments in vitro, in which the biological behaviours of cancer cells can be assessed under different metastatic conditions. Therefore, modelling bone metastasis microenvironments with 3D cultures is imperative for advancing cancer research and anti-cancer treatment strategies. In this review, multicellular tumour spheroids and bioreactors, tissue engineering constructs and scaffolds, microfluidic systems and 3D bioprinting technology are discussed to explore the progression of the 3D engineering approaches used to model the three microenvironments of bone metastasis. We aim to provide new insights into cancer biology and advance the translation of new therapies for bone metastasis.

Endothelial Cells as Precursors for Osteoblasts in the Metastatic Prostate Cancer Bone

Prostate cancer cells metastasize to the bones, causing ectopic bone formation, which results in fractures and pain. The cellular mechanisms underlying new bone production are unknown. In a recent study, Lin and colleagues, by using state-of-the-art techniques, including prostate cancer mouse models in combination with sophisticated in vivo lineage-tracing technologies, revealed that endothelial cells form osteoblasts induced by prostate cancer metastasis in the bone. Strikingly, genetic deletion of osteorix protein from endothelial cells affected prostate cancer-induced osteogenesis in vivo. Deciphering the osteoblasts origin in the bone microenvironment may result in the development of promising new molecular targets for prostate cancer therapy.

CT-Guided Bone Biopsies in Metastatic Castration-Resistant Prostate Cancer: Factors Predictive of Maximum Tumor Yield

PURPOSE

To evaluate the success rate of CT-guided bone biopsies in metastatic castration-resistant prostate cancer (mCRPC) and to investigate associated technical, imaging, and clinical parameters affecting diagnostic yields.

MATERIALS AND METHODS

Eighty CT-guided bone biopsy specimens were obtained from 72 men (median age, 68 y; range, 49-89 y) enrolled in a multicenter trial to identify mechanisms of resistance in mCRPC. Successful biopsy was determined by histologic confirmation of tumor cells and successful isolation of RNA for molecular analysis.

RESULTS

The overall success rate of CT-guided bone biopsies was 69% (55/80) based on histology and 64% (35/55) based on isolation of molecular material for RNA sequencing. Biopsies performed in lesions with areas of radiolucency had significantly higher diagnostic yields compared with lesions of predominantly dense sclerosis (95% vs 33%; P = .002) and lesions of predominantly subtle sclerosis (95% vs 65%; P = .04). Success rates increased in lesions with density ≤ 475 HU (79% for ≤ 475 HU vs 33% for > 475 HU; P = .001) and in lesions with ill-defined margins (76% for ill-defined margins vs 36% for well-circumscribed margins; P = .005). Alkaline phosphatase was the only clinical parameter to correlate significantly with diagnostic yield (83% for > 110 U/L vs 50% for ≤ 110 U/L; P = .001).

CONCLUSIONS

Image-guided bone tumor biopsies can be successfully used to acquire cellular and molecular material for analyses in patients with osteoblastic prostate cancer metastases. Diagnostic yields are significantly increased in lesions with areas of radiolucency, density ≤ 475 HU, ill-defined margins, and interval growth and in patients with alkaline phosphatase > 110 U/L.

Disruption of collagen/apatite alignment impairs bone mechanical function in osteoblastic metastasis induced by prostate cancer

Prostate cancer (PCa) frequently metastasizes to the bone, generally inducing osteoblastic alterations that increase bone brittleness. Although there is growing interest in the management of the physical capability of patients with bone metastasis, the mechanism underlying the impairment of bone mechanical function remains unclear. The alignment of both collagen fibrils and biological apatite (BAp) c-axis, together with bone mineral density, is one of the strongest contributors to bone mechanical function. In this study, we analyzed the bone microstructure of the mouse femurs with and without PCa cell inoculation. Histological assessment revealed that the bone-forming pattern in the PCa-bearing bone was non-directional, resulting in a spongious structure, whereas that in the control bone was unidirectional and layer-by-layer, resulting in a compact lamellar structure. The degree of preferential alignment of collagen fibrils and BAp, which was evaluated by quantitative polarized microscopy and microbeam X-ray diffraction, respectively, were significantly lower in the PCa-bearing bone than in the control bone. Material parameters including Young's modulus and toughness, measured by the three-point bending test, were simultaneously decreased in the PCa-bearing bone. Specifically, there was a significant positive correlation between the degree of BAp c-axis orientation and Young's modulus. In conclusion, the impairment of mechanical function in the PCa-bearing bone is attributable to disruption of the anisotropic microstructure of bone in multiple phases. This is the first report demonstrating that cancer bone metastasis induces disruption of the collagen/BAp alignment in long bones, thereby impairing their mechanical function.

Rationale for Modernising Imaging in Advanced Prostate Cancer

CONTEXT

To effectively manage patients with advanced prostate cancer (APC), it is essential to have accurate, reproducible, and validated methods for detecting and quantifying the burden of bone and soft tissue metastases and for assessing their response to therapy. Current standard of care imaging with bone and computed tomography (CT) scans have significant limitations for the assessment of bone metastases in particular.

OBJECTIVE

We aimed to undertake a critical comparative review of imaging methods used for diagnosis and disease monitoring of metastatic APC from the perspective of their availability and ability to assess disease presence, extent, and response of bone and soft tissue disease.

EVIDENCE ACQUISITION

An expert panel of radiologists, nuclear medicine physicians, and medical physicists with the greatest experience of imaging in advanced prostate cancer prepared a review of the practicalities, performance, merits, and limitations of currently available imaging methods.

EVIDENCE SYNTHESIS

Meta-analyses showed that positron emission tomography (PET)/CT with different radiotracers and whole-body magnetic resonance imaging (WB-MRI) are more accurate for bone lesion detection than CT and bone scans (BSs). At a patient level, the pooled sensitivities for bone disease by using choline (CH)-PET/CT, WB-MRI, and BS were 91% (95% confidence interval [CI], 83-96%), 97% (95% CI, 91-99%), and 79% (95% CI, 73-83%), respectively. The pooled specificities for bone metastases detection using CH-PET/CT, WB-MRI, and BS were 99% (95% CI, 93-100%), 95% (95% CI, 90-97%), and 82% (95% CI, 78-85%), respectively. The ability of PET/CT and WB-MRI to assess therapeutic benefits is promising but has not been comprehensively evaluated. There is variability in the cost, availability, and quality of PET/CT and WB-MRI.

CONCLUSIONS

Standardisation of acquisition, interpretation, and reporting of WB-MRI and PET/CT scans is required to assess the performance of these techniques in clinical trials of treatment approaches in APC.

PATIENT SUMMARY

PET/CT and whole-body MRI scans have the potential to improve detection and to assess response to treatment of all states of advanced prostate cancer. Consensus recommendations on quality standards, interpretation, and reporting are needed but will require validation in clinical trials of established and new treatment approaches.

Thrombospondin-2 promotes prostate cancer bone metastasis by the up-regulation of matrix metalloproteinase-2 through down-regulating miR-376c expression

Background

Thrombospondin-2 (TSP-2) is a secreted matricellular glycoprotein that is found to mediate cell-to-extracellular matrix attachment and participates in many physiological and pathological processes. The expression profile of TSP-2 on tumors is controversial, and it up-regulates in some cancers, whereas it down-regulates in others, suggesting that the functional role of TSP-2 on tumors is still uncertain.

Methods

The expression of TSP-2 on prostate cancer progression was determined in the tissue array by the immunohistochemistry. The molecular mechanism of TSP-2 on prostate cancer (PCa) metastasis was investigated through pharmaceutical inhibitors, siRNAs, and miRNAs analyses. The role of TSP-2 on PCa metastasis in vivo was verified through xenograft in vivo imaging system.

Results

Based on the gene expression omnibus database and immunohistochemistry, we found that TSP-2 increased with the progression of PCa, especially in metastatic PCa and is correlated with the matrix metalloproteinase-2 (MMP-2) expression. Additionally, through binding to CD36 and integrin α_νβ₃, TSP-2 increased cell migration and MMP-2 expression. With inhibition of p38, ERK, and JNK, the TSP-2-induced cell migration and MMP-2 expression were abolished, indicating that the TSP-2’s effect on PCa is MAPK dependent. Moreover, the microRNA-376c (miR-376c) was significantly decreased by the TSP-2 treatment. Furthermore, the TSP-2-induced MMP-2 expression and the subsequent cell motility were suppressed upon miR-376c mimic stimulation. On the other hand, the animal studies revealed that the bone metastasis was abolished when TSP-2 was stably knocked down in PCa cells.

Conclusions

Taken together, our results indicate that TSP-2 enhances the migration of PCa cells by increasing MMP-2 expression through down-regulation of miR-376c expression. Therefore, TSP-2 may represent a promising new target for treating PCa.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0390-6) contains supplementary material, which is available to authorized users.

Tumor Cell-Derived Exosomes from the Prostate Cancer Cell Line TRAMP-C1 Impair Osteoclast Formation and Differentiation

Skeletal metastatic disease is a deleterious consequence of dissemination of tumor cells from numerous primary sites, such as prostate, lung and breast. Skeletal metastases are still incurable, resulting in development of clinical complications and decreased survival for cancer patients with metastatic disease. During the last decade, tumor cell-derived microvesicles have been identified and suggested to be involved in cancer disease progression. Whether cancer exosomes are involved in tumor and bone cell interactions in the metastatic site is still, however, a rather unexplored field. Here we show that exosomes isolated from the murine prostate cancer cell line TRAMP-C1 dramatically decrease fusion and differentiation of monocytic osteoclast precursors to mature, multinucleated osteoclasts. The presence of tumor cell-derived exosomes also clearly decreased the expression of established markers for osteoclast fusion and differentiation, including DC-STAMP, TRAP, cathepsin K, and MMP-9. In contrast, exosomes derived from murine fibroblastic cells did not affect osteoclast formation. Our findings suggest that exosomes released from tumor cells in the tumor-bone interface are involved in pathological regulation of bone cell formation in the metastatic site. This further strengthens the role of tumor cell-derived microvesicles in cancer progression and disease aggressiveness.

The role of microRNAs in bone metastasis

The skeleton represents a common site of metastases for osteotropic cancers such as prostate and breast tumors and novel therapeutic targets and new markers for the monitoring of bone lesions are urgently needed. The formation of bone metastases is a complex process that starts at the level of the confined tumor and that is characterized by a dynamic crosstalk between the primary cancer and the future metastatic site, the bone. Factors released by the primary tumor contribute to prepare a fertile “soil”, where a “pre-metastatic niche” is established prior to future colonization by cancer cells. When the primary cancer progress from the confined disease to its invasive phase, tumor cells will acquire an invasive phenotype, enter into the circulation and colonize the previously prepared site where they will establish a “metastatic niche”. Among the variety of molecules that participate in the metastatic cascade, microRNAs are a class of small non-coding RNA that play an important role in the development of metastatic bone lesions. Many studies have addressed the role of small non-coding RNAs (miRs) in metastasis in osteotropic cancers and have highlighted the role of miRs as oncogenes (oncomiRs) or tumor suppressor miRs.

In this review we present describe the role of miRs in the processing of the supportive bone microenvironment prior and after the bone colonization by cancer cells. Finally, future therapeutic strategies and perspectives are also discussed.