A bone-seeking clone exhibits different biological properties from the ACHN parental human renal cell carcinoma in vivo and in vitro

Extracellular vesicles secreted from bone metastatic renal cell carcinoma promote angiogenesis and endothelial gap formation in bone marrow in a time-dependent manner in a preclinical mouse model

Introduction

Bone is a major metastatic site of renal cell carcinoma (RCC). Recently, it is well recognized that bone metastatic tumor cells remodel bone marrow vasculature. However, the precise mechanism underlying cell-cell communication between bone metastatic RCC and the cells in bone marrow remains unknown. Extracellular vesicles (EVs) reportedly play crucial roles in intercellular communication between metastatic tumor cells and bone marrow. Therefore, we conducted the current study to clarify the histological alteration in vascular endothelium in bone marrow induced by EVs secreted from bone metastatic RCC cells as well as association between angiogenesis in bone marrow and bone metastasis formation.

Materials and methods

We established a bone metastatic RCC cell line (786-O BM) by in vivo selection and observed phenotypic changes in tissues when EVs were intravenously injected into immunodeficient mice. Proteomic analysis was performed to identify the protein cargo of EVs that could contribute to histological changes in bone. Tissue exudative EVs (Te-EVs) from cancer tissues of patients with bone metastatic RCC (BM-EV) and those with locally advanced disease (LA-EV) were compared for in vitro function and protein cargo.

Results

Treatment of mice with EVs from 786-O BM promoted angiogenesis in the bone marrow in a time-dependent manner and increased the gaps of capillary endothelium. 786-O BM EVs also promoted tube formation in vitro. Proteomic analysis of EVs identified aminopeptidase N (APN) as a candidate protein that enhances angiogenesis. APN knockdown in 786-O BM resulted in reduced angiogenesis in vitro and in vivo. When parental 786-O cells were intracardially injected 12 weeks after treatment with786-O BM EVs, more bone metastasis developed compared to those treated with EVs from parental 786-O cells. In patient samples, BM-EVs contained higher APN compared to LA-EV. In addition, BM-EVs promoted tube formation in vitro compared to LA-EVs.

Conclusion

EVs from bone metastatic RCC promote angiogenesis and gap formation in capillary endothelium in bone marrow in a time-dependent manner.

TGFβ instructs mTORC2 to activate PKCβII for increased TWIST1 expression in proximal tubular epithelial cell injury

The plasticity of proximal tubular epithelial cells in response to TGFβ contributes to the expression of TWIST1 to drive renal fibrosis. The mechanism of TWIST1 expression is not known. We show that both PI3 kinase and its target mTORC2 increase TGFβ-induced TWIST1 expression. TGFβ enhances phosphorylation on Ser-660 in the protein kinase C βII (PKCβII) hydrophobic motif site. Remarkably, phosphorylation-deficient PKCβIIS660A, kinase-dead PKCβII, and PKCβII knockdown blocked TWIST1 expression by TGFβ. Inhibition of TWIST1 arrested TGFβ-induced tubular cell hypertrophy and the expression of fibronectin, collagen I (α2), and α-smooth muscle actin. By contrast, TWIST1 overexpression induced these pathologies. Interestingly, the inhibition of PKCβII reduced these phenomena, which were countered by the expression of TWIST1. These results provide the first evidence for the involvement of the mTORC2-PKCβII axis in TWIST1 expression to promote tubular cell pathology.

Hypermethylation of mitochondrial DNA facilitates bone metastasis of renal cell carcinoma

Kidney cancers including clear cell carcinoma (RCC) are identified with very vulnerable mitochondria DNA (mtDNA) and frequent epigenetic aberrations. Bone metastasis from RCC is prevalent and destructive. Bone marrow contains a quite hypoxic microenvironment that usually insitigate 50% of hypermethylation events in conferring a selective advantage for tumor growth. We hypothesized that hypermethylation of mtDNA in RCC cells would significantly contribute to bone metastatic tumor progression. Methylation-specific polymerase chain reaction assay (MSP) was adopted to measure the methylation status of D-loop region of mtDNA in 15 pairs of bone metastatic and primary RCC as well as tumor adjescent normal kidney tissues. mtDNA copy number was examined by the real-time quantitative polymerase chain reaction (qPCR). Western blotting analysis was used to measure the accumulation of several DNA methyltransferases (DNMTs) in the mitochondria and nucleus fractions of bone metastatic RCC cells. mRNA expression of mitochondria encoded genes was examined by RT-PCR. Reactive oxygen species (ROS), mitochondrial membrane potential and ATP content were measured using in vitro cells treated with de-methylation drug 5-Azacytidine (5-Aza). Non-invasive bioluminescent imaging was performed to monitor tumor occurrence in skeleton in mice. Our results showed that the D-loop region in bone metastatic tumor cells was markedly hypermethylated than those in primary RCC tumor cells, that is associated with a decreased mtDNA copy number and accumulation of DNMT1 in the mitochondria. The bone-tropism tumor colonization and progression of RCC cells was significantly suppressed by demethylating the D-loop region of mtDNA and reducing the intracellular level of ROS and ATP by 5-Aza treatment. In conclusion, our study provided a direct association between hypermethylation of mtDNA in RCC with bone metastastic tumor growth.

Personal Medicine and Bone Metastases: Biomarkers, Micro-RNAs and Bone Metastases

Bone metastasis is a major cause of morbidity within solid tumours of the breast, prostate, lung and kidney. Metastasis to the skeleton is associated with a wide range of complications including bone fractures, spinal cord compression, hypercalcaemia and increased bone pain. Improved treatments for bone metastasis, such as the use of anti-bone resorptive bisphosphonate agents, within post-menopausal women have improved disease-free survival; however, these treatments are not without side effects. There is thus a need for biomarkers, which will predict the risk of developing the spread to bone within these cancers. The application of molecular profiling techniques, together with animal model systems and engineered cell-lines has enabled the identification of a series of potential bone-metastasis biomarker molecules predictive of bone metastasis risk. Some of these biomarker candidates have been validated within patient-derived samples providing a step towards clinical utility. Recent developments in multiplex biomarker quantification now enable the simultaneous measurement of up to 96 micro-RNA/protein molecules in a spatially defined manner with single-cell resolution, thus enabling the characterisation of the key molecules active at the sites of pre-metastatic niche formation as well as tumour-stroma signalling. These technologies have considerable potential to inform biomarker discovery. Additionally, a potential future extension of these discoveries could also be the identification of novel drug targets within cancer spread to bone. This chapter summarises recent findings in biomarker discovery within the key bone metastatic cancers (breast, prostate, lung and renal cell carcinoma). Tissue-based and circulating blood-based biomarkers are discussed from the fields of genomics, epigenetic regulation (micro-RNAs) and protein/cell-signalling together with a discussion of the potential future development of these markers towards clinical development.

Choosing The Right Animal Model for Renal Cancer Research

The increase in the life expectancy of patients with renal cell carcinoma (RCC) in the last decade is due to changes that have occurred in the area of preclinical studies. Understanding cancer pathophysiology and the emergence of new therapeutic options, including immunotherapy, would not be possible without proper research. Before new approaches to disease treatment are developed and introduced into clinical practice they must be preceded by preclinical tests, in which animal studies play a significant role. This review describes the progress in animal model development in kidney cancer research starting from the oldest syngeneic or chemically-induced models, through genetically modified mice, finally to xenograft, especially patient-derived, avatar and humanized mouse models. As there are a number of subtypes of RCC, our aim is to help to choose the right animal model for a particular kidney cancer subtype. The data on genetic backgrounds, biochemical parameters, histology, different stages of carcinogenesis and metastasis in various animal models of RCC as well as their translational relevance are summarized. Moreover, we shed some light on imaging methods, which can help define tumor microstructure, assist in the analysis of its metabolic changes and track metastasis development.

Autocrine and paracrine STIP1 signaling promote osteolytic bone metastasis in renal cell carcinoma

Bone metastases are responsible for some of the most devastating complications of renal cell carcinoma (RCC). However, pro-metastatic factors leading to the highly osteolytic characteristics of RCC bone metastasis have barely been explored. We previously developed novel bone-seeking RCC cell lines by the in vivo selection strategy and performed a comparative proteome analysis on their total cell lysate. Here, we focused on STIP1 (stress-induced phosphoprotein 1), the high up-regulated protein in the bone-seeking cells, and explored its clinical relevance and functions in RCC bone metastasis. We observed high levels of both intracellular and extracellular STIP1 protein in bone metastatic tissue samples. Elevated STIP1 mRNA in the primary RCC tumors remarkably correlated with worse clinical outcomes. Furthermore, both human recombinant STIP1 protein and anti-STIP1 neutralizing antibody were used in the functional studies. We found that 1) STIP1 protein on the extracellular surface of tumor cells promoted the proliferation and migration/invasion of RCC tumor cells through the autocrine STIP1-ALK2-SMAD1/5 pathway; and 2) STIP1 protein secreted into the extracellular tumor stromal area, promoted the differentiation of osteoclasts through the paracrine STIP1-PrPc-ERK1/2 pathway. Increased cathepsin K (CTSK), the key enzyme secreted by osteoclasts to degrade collagen and other matrix proteins during bone resorption was further detected in the differentiated osteoclasts. These results provide evidence of the great potential of STIP1 as a novel biomarker and therapeutic target in RCC bone metastasis.

Eight proteins play critical roles in RCC with bone metastasis via mitochondrial dysfunction

Most kidney cancers are renal cell carcinomas (RCC). RCC lacks early warning signs and 70 % of patients with RCC develop metastases. Among them, 50 % of patients having skeletal metastases developed a dismal survival of less than 10 % at 5 years. Therefore, exploring the key driving proteins and pathways involved in RCC bone metastasis could benefit patients’ therapy and prolong their survival. We examined the difference between the OS-RC-2 cells and the OS-RC-2-BM5 cells (subpopulation from OS-RC-2) of RCC with proteomics. Then we employed Western-blot, immunohistochemistry and the clinical database (oncomine) to screen and verify the key proteins and then we analyzed the functions and the related pathways of selected key proteins with system biology approaches. Our proteomic data revealed 26 significant changed spots (fold change <0.5 and >1.9, P < 0.05) between two cells. The Western blotting results validated for these identified spots were consistent with the proteomics’. From the public clinical database, 23 out of 26 proteins were connected with RCC metastases and 9 out of 23 with survival time directly (P < 0.05). Finally, only 8 out of 9 proteins had significantly positive results in tissues of RCC patients with bone metastasis compared with primary tumor (P < 0.05). System biology analyzing results showed these eight proteins mainly distributed in oxidative phosphorylation which indicates that mitochondria dysfunction played the critical role to regulate cells metastasis. Our article used a variety of experimental techniques to find eight proteins which abnormally regulated mitochondrial function to achieve a successful induction for RCC metastasis to bone.

Animal Models of Bone Metastasis

Bone is one of the most common sites of cancer metastasis in humans and is a significant source of morbidity and mortality. Bone metastases are considered incurable and result in pain, pathologic fracture, and decreased quality of life. Animal models of skeletal metastases are essential to improve the understanding of the molecular pathways of cancer metastasis and growth in bone and to develop new therapies to inhibit and prevent bone metastases. The ideal animal model should be clinically relevant, reproducible, and representative of human disease. Currently, an ideal model does not exist; however, understanding the strengths and weaknesses of the available models will lead to proper study design and successful cancer research. This review provides an overview of the current in vivo animal models used in the study of skeletal metastases or local tumor invasion into bone and focuses on mammary and prostate cancer, lymphoma, multiple myeloma, head and neck squamous cell carcinoma, and miscellaneous tumors that metastasize to bone.

Alterations in enhancer of zeste homolog 2, matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-2 expression are associated with ex vivo and in vitro bone metastasis in renal cell carcinoma

Renal cell carcinoma (RCC) has a high potential for bone metastasis; however, the molecular mechanisms underlying this metastasis have remained to be elucidated. The present study aimed to explore the expression levels of enhancer of zeste homolog 2 (EZH2), matrix metalloproteinase-2 (MMP2) and tissue inhibitor of metalloproteinase-2 (TIMP2) as determinants of RCC-associated bone metastasis. Their expression was evaluated in a newly generated RCC cell subline that has a high potential for bone metastasis, in tissue specimens from metastasized bone tissues from patients with RCC and in RCC tissues without metastasis. A total of 25 RCC tissue specimens without metastasis and 13 RCC tissue specimens with bone metastasis were acquired for immunohistochemical analysis of EZH2, MMP2 and TIMP2 protein expression. The expression levels of EZH2, MMP2 and TIMP2 mRNA and protein were analyzed in the ACHN and ACHN-BO5 cell lines using western blot and reverse transcription polymerase chain reaction (PCR) analyses. Methylation-specific PCR was also used to analyze TIMP2 promoter methylation. EZH2 and MMP2 proteins were found to be expressed at higher levels in tissues from patients where RCC had metastasized to the bone as compared with those in RCC patients without metastasis, whereas there was no significant difference in the expression of TIMP2 protein between the two tissues. Furthermore, the expression of EZH2 protein was correlated with MMP2 expression, but there was no significant correlation between the expression of EZH2 and TIMP2 proteins. The in vitro results using cell lines confirmed the ex vivo findings, indicating that the expression levels of EZH2 and MMP2 protein and mRNA were higher in ACHN-BO5 cells than those in ACHN cells. By contrast, TIMP2 protein and mRNA expression levels were lower in ACHN-BO5 cells than those in the parental ACHN cells. The TIMP2 promoter was highly methylated in ACHN-BO5 cells compared with that in ACHN cells. Upregulation of EZH2, MMP2 and TIMP2 expression was correlated with metastasis of RCC to bone tissues ex vivo and in vitro. Further studies are required in order to elucidate the mechanism underlying the altered expression of these genes.

Development of a realistic in vivo bone metastasis model of human renal cell carcinoma

About one-third of patients with advanced renal cell carcinoma (RCC) have bone metastases. The incidence of RCC is increasing and bone metastatic RCC merits greater focus. Realistic preclinical bone metastasis models of RCC are lacking, hampering the development of effective therapies. We developed a realistic in vivo bone metastasis model of human RCC by implanting precision-cut tissue slices under the renal capsule of immunodeficient mice. The presence of disseminated cells in bone marrow of tissue slice graft (TSG)-bearing mice was screened by human-specific polymerase chain reaction and confirmed by immunohistology using human-specific antibody. Disseminated tumor cells in bone marrow of TSG-bearing mice derived from three of seven RCC patients were detected as early as 1 month after tissue implantation at a high frequency with close resemblance to parent tumors (e.g., CAIX expression and high vascularity). The metastatic patterns of TSGs correlated with disease progression in patients. In addition, TSGs retained capacity to metastasize to bone at high frequency after serial passaging and cryopreservation. Moreover, bone metastases in mice responded to Temsirolimus treatment. Intratibial injections of single cells generated from TSGs showed 100 % engraftment and produced X-ray-visible tumors as early as 3 weeks after cancer cell inoculation. Micro-computed tomography (μCT) and histological analysis revealed osteolytic characteristics of these lesions. Our results demonstrated that orthotopic RCC TSGs have potential to develop bone metastases that respond to standard therapy. This first reported primary RCC bone metastasis model provides a realistic setting to test therapeutics to prevent or treat bone metastases in RCC.