Mesenchymal Stromal Cells: Emerging Roles in Bone Metastasis

The inferior performance of [68Ga]Ga-FAPI-04 PET/CT as a diagnostic and theranostic biomarker in [177Lu]Lu-DOTATATE refractory well-differentiated neuroendocrine tumors

PURPOSE

We aimed to investigate the potential of [68Ga]Ga-FAPI-04 PET/CT as an alternative diagnostic and theranostic tool in well-differentiated NETs refractory to [177Lu]Lu-DOTATATE therapy.

METHODS

Patients who received at least two cycles of [177Lu]Lu-DOTATATE therapy for metastatic NETs and progressed under treatment were included. All patients had performed [68Ga]Ga-DOTATATE and [68Ga]Ga-FAPI-04 PET/CT within 3 weeks. The number of PET-positive lesions related to NETs and tumor sites was documented. Mann-Whitney U and chi-square tests were used to compare SUVmax levels of tracers and the number of detected metastases.

RESULTS

Twelve patients (7 male, 5 female) who met the eligibility criteria were included in the study. Ten patients had grade 1-2 NET of various origins, and two had paraganglioma and pheochromocytoma. One hundred ninety-eight of 230 lesions (86%) were SSTR positive with a median SUVmax of 16.6 (2.2-76.5), and 88 of 230 lesions (38.2%) were [68Ga]Ga-FAPI-04 positive with a median SUVmax of 5.1 (2.3-21). Median SUVmax level and detected number of tumors were significantly higher in [68Ga]Ga-DOTATATE PET/CT (p=<0.001). [68Ga]Ga-FAPI-04 PET/CT was completely (n:2) or almost completely (n:3) negative in 5 (42%) patients. Two (17%) patients had flip-flop SSTR/FAPI uptake in tumors. In four patients (33%), tumor uptake or the number of PET-positive lesions was inferior in [68Ga]Ga-FAPI-04 PET/CT. In only one patient (8%), tumor uptakes were higher in [68Ga]Ga-FAPI-04 PET/CT. Low-dose [177Lu]Lu-FAPI-46 dosimetry was performed on the FAPI-dominant patient; absorbed radiation doses per GBq were 1.26 Gy, 0.36 Gy, 0.32 Gy, and 0.2 Gy for kidneys, liver, spleen, and total body, respectively. The mean absorbed dose per GBq was 0.33 Gy for liver mass and 0.41 Gy for metastatic lymph nodes.

CONCLUSION

Our preliminary results demonstrated that [68Ga]Ga-FAPI-04 PET/CT mainly failed in well-differentiated NETs refractory to [177Lu]Lu-DOTATATE therapy and had a limited role as an alternative diagnostic or theranostic agent. Further investigations with a larger patient population are required to determine the impact of [68Ga]Ga-FAPI-04 PET/CT on NETs.

Total flavonoids of Litchi chinensis Sonn. seed inhibit prostate cancer growth in bone by regulating the bone microenvironment via inactivation of the HGFR/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Litchi chinensis Sonn. (Litchi) seed, a traditional Chinese medicine, is habitually used in the clinical treatment of prostate cancer (PCa)-induced bone pain. In our previous study, flavonoids have been identified as the active ingredient of litchi seed against PCa. However, its anti-tumor activities in bone and associated molecular mechanisms are still unclear.

AIM OF THE STUDY

To investigate the effects and underlying mechanisms of total flavonoids of litchi seed (TFLS) on the growth of PCa in bone.

MATERIALS AND METHODS

The effect of TFLS on the growth of PCa in bone was observed using a mouse model constructed with tibial injection of luciferase-expressing RM1-luc cells. Conditioned medium (CM) from bone marrow stromal cells OP9 and CM treated with TFLS (T-CM) was used to investigate the effect on the proliferation, colony formation, and apoptosis of PCa cells (LNCaP, PC3, RM1). An antibody microarray was performed to detect cytokine expression in the supernatant fraction of OP9 cell cultures treated with TFLS or left untreated. Western blot assay was employed to determine the expression and activity of HGFR and its key downstream proteins, Akt, mTOR, NF-κB, and Erk, in PCa cells. The potential target was further verified using immunofluorescence and immunohistochemistry assays.

RESULTS

Treatment with TFLS (80 mg/kg, 24 days) significantly suppressed the growth of RM1 cells in bone. CM from bone marrow stromal cells OP9 stimulated the proliferation and colony formation of the PCa cells as well as inhibited the apoptosis of PC3 cells, while T-CM reversed the effects mediated by OP9 cells in vitro. In an antibody array assay, TFLS regulated the majority of cytokines in OP9 cell culture supernatant, among which HGF, HGFR, IGF-1R, and PDGF-AA showed the greatest fold changes. Mechanistically, CM upregulated HGFR and promoted phosphorylation of NF-κB while T-CM induced reduction of HGFR and dephosphorylation of NF-κB in PC3 cells. Moreover, T-CM inhibited NF-κB entry into PC3 cell nuclei. Data from in vivo experiments further confirmed the inhibitory effects of TFLS on NF-κB.

CONCLUSION

TFLS suppresses the growth of PCa in bone through regulating bone microenvironment and the underlying mechanism potentially involves attenuation of the HGFR/NF-κB signaling axis.

MDA-9/Syntenin in the tumor and microenvironment defines prostate cancer bone metastasis

Bone metastasis is a frequent and incurable consequence of advanced prostate cancer (PC). An interplay between disseminated tumor cells and heterogeneous bone resident cells in the metastatic niche initiates this process. Melanoma differentiation associated gene-9 (mda-9/Syntenin/syndecan binding protein) is a prometastatic gene expressed in multiple organs, including bone marrow-derived mesenchymal stromal cells (BM-MSCs), under both physiological and pathological conditions. We demonstrate that PDGF-AA secreted by tumor cells induces CXCL5 expression in BM-MSCs by suppressing MDA-9-dependent YAP/MST signaling. CXCL5-derived tumor cell proliferation and immune suppression are consequences of the MDA-9/CXCL5 signaling axis, promoting PC disease progression. mda-9 knockout tumor cells express less PDGF-AA and do not develop bone metastases. Our data document a previously undefined role of MDA-9/Syntenin in the tumor and microenvironment in regulating PC bone metastasis. This study provides a framework for translational strategies to ameliorate health complications and morbidity associated with advanced PC.

Bone Health Management in the Continuum of Prostate Cancer Disease

Prostate cancer (PCa) is the second-leading cause of cancer-related deaths in men. PCa cells require androgen receptor (AR) signaling for their growth and survival. Androgen deprivation therapy (ADT) is the preferred treatment for patients with locally advanced and metastatic PCa disease. Despite their initial response to androgen blockade, most patients eventually will develop metastatic castration-resistant prostate cancer (mCRPC). Bone metastases are common in men with mCRPC, occurring in 30% of patients within 2 years of castration resistance and in >90% of patients over the course of the disease. Patients with mCRPC-induced bone metastasis develop lesions throughout their skeleton; the 5-year survival rate for these patients is 47%. Bone-metastasis-induced early changes in the bone that proceed the osteoblastic response in the bone matrix are monitored and detected via modern magnetic resonance and PET/CT imaging technologies. Various treatment options, such as targeting osteolytic metastasis with bisphosphonates, prednisone, dexamethasone, denosumab, immunotherapy, external beam radiation therapy, radiopharmaceuticals, surgery, and pain medications are employed to treat prostate-cancer-induced bone metastasis and manage bone health. However, these diagnostics and treatment options are not very accurate nor efficient enough to treat bone metastases and manage bone health. In this review, we present the pathogenesis of PCa-induced bone metastasis, its deleterious impacts on vital organs, the impact of metastatic PCa on bone health, treatment interventions for bone metastasis and management of bone- and skeletal-related events, and possible current and future therapeutic options for bone management in the continuum of prostate cancer disease.

Effects of iron modulation on mesenchymal stem cell-induced drug resistance in estrogen receptor-positive breast cancer

Patients with estrogen receptor-positive (ER+) breast cancer, the most common subtype, remain at risk for lethal metastatic disease years after diagnosis. Recurrence arises partly because tumor cells in bone marrow become resistant to estrogen-targeted therapy. Here, we utilized a co-culture model of bone marrow mesenchymal stem cells (MSCs) and ER+ breast cancer cells to recapitulate interactions of cancer cells in bone marrow niches. ER+ breast cancer cells in direct contact with MSCs acquire cancer stem-like (CSC) phenotypes with increased resistance to standard antiestrogenic drugs. We confirmed that co-culture with MSCs increased labile iron in breast cancer cells, a phenotype associated with CSCs and disease progression. Clinically approved iron chelators and in-house lysosomal iron-targeting compounds restored sensitivity to antiestrogenic therapy. These findings establish iron modulation as a mechanism to reverse MSC-induced drug resistance and suggest iron modulation in combination with estrogen-targeted therapy as a promising, translatable strategy to treat ER+ breast cancer.

Development and Validation of Prognostic Nomogram for Elderly Breast Cancer: A Large-Cohort Retrospective Study

Purpose

Our research aims to study the bone metastatic patterns and prognostic outcomes in elderly breast cancer (BC) and to develop elder-specific nomograms.

Methods

We downloaded the data of BC patients between 2010 and 2016 from the Surveillance, Epidemiology, and End Results database. The differences in clinical features and prognosis between young (age < 65) and elderly (age ≥ 65) BC patients were compared. The univariate and multivariate Cox analyses were used to determine the overall survival (OS)- and cancer-specific survival (CSS)-related variables and establish two nomograms of BC patients with bone metastasis (BCBM). The receiver operating characteristic (ROC) curve with area under the curve (AUC), calibration curve, decision curve analysis (DCA), and Kaplan–Meier survival curve were selected to evaluate nomograms.

Results

A total of 230,177 BC patients were enrolled in our research, including 142,025 young and 88,152 elderly patients. The prognosis of elderly BCBM patients was significantly worse than young patients. Age, race, breast subtype, tumor size, tumor grade, brain metastasis, liver metastasis, surgery, and chemotherapy were independent prognostic variables for elderly BCBM patients, including OS and CSS. The AUC values at 12, 18, and 24 months were 0.750, 0.751, and 0.739 for OS nomogram and 0.759, 0.762, and 0.752 for CSS nomogram in the training cohort, which were higher than the AUC values of all single independent prognostic variables. The survival curve showed a distinct prognosis between low-, median- and high-risk groups (p < 0.001). Finally, calibration curves and DCA indicated that both nomograms have favorable performance.

Conclusion

Elderly and young patients presented with different bone metastatic frequencies, clinical features, and prognostic outcomes. Two elder-specific nomograms incorporating nine clinical variables were established and validated to be a valuable predictor for elderly BCBM patients.

Immune Checkpoint Inhibitor Therapy for Bone Metastases: Specific Microenvironment and Current Situation

The treatment of bone metastases is a thorny issue. Immunotherapy may be one of the few hopes for patients with unresectable bone metastases. Immune checkpoint inhibitors are the most commonly used immunotherapy drugs currently. In this review, the characteristics and interaction of bone metastases and their immune microenvironment were systematically discussed, and the relevant research progress of the immunological mechanism of tumor bone metastasis was reviewed. On this basis, we expounded the clinical application of immune checkpoint inhibitors for bone metastasis of common tumors, including non-small-cell lung cancer, renal cell carcinoma, prostate cancer, melanoma, and breast cancer. Then, the deficiencies and limitations in current researches were summarized. In-depth basic research on bone metastases and optimization of clinical treatment is needed.

Influences of the 3D microenvironment on cancer cell behaviour and treatment responsiveness: A recent update on lung, breast and prostate cancer models

The majority of in vitro studies assessing cancer treatments are performed in two-dimensional (2D) monolayers and are subsequently validated in in vivo animal models. However, 2D models fail to accurately model the tumour microenvironment. Furthermore, animal models are not directly applicable to mimic the human scenario. Three-dimensional (3D) culture models may help to address the discrepancies of 2D and animal models. When cancer cells escape the primary tumour, they can invade at distant organs building secondary tumours, called metastasis. The development of metastasis leads to a dramatic decrease in the life expectancy of patients. Therefore, 3D systems to model the microenvironment of metastasis have also been developed. Several studies have demonstrated changes in cell behaviour and gene expression when cells are cultured in 3D compared to 2D and concluded a better comparability to cells in vivo. Of special importance is the effect seen in response to anti-cancer treatments as models are built primarily to serve as drug-testing platforms. This review highlights these changes between cancer cells grown in 2D and 3D models for some of the most common cancers including lung, breast and prostate tumours. In addition to models aiming to mimic the primary tumour site, the effects of 3D cell culturing in bone metastasis models are also described. STATEMENT OF SIGNIFICANCE: Most in vitro studies in cancer research are performed in 2D and are subsequently validated in in vivo animal models. However, both models possess numerous limitations: 2D models fail to accurately model the tumour microenvironment while animal models are expensive, time-consuming and can differ considerably from humans. It is accepted that the cancer microenvironment plays a critical role in the disease, thus, 3D models have been proposed as a potential solution to address the discrepancies of 2D and animal models. This review highlights changes in cell behaviour, including proliferation, gene expression and chemosensitivity, between cancer cells grown in 2D and 3D models for some of the most common cancers including lung, breast and prostate cancer as well as bone metastasis.

Heterogeneous microenvironmental stiffness regulates pro-metastatic functions of breast cancer cells

Besides molecular and phenotypic variations observed in cancer cells, intratumoral heterogeneity also occurs in the tumor microenvironment. Correlative stiffness maps of different intratumor locations in breast tumor biopsies show that stiffness increases from core to periphery. However, how different local ECM stiffness regulates key functions of cancer cells in tumor progression remains unclear. Although increased tissue stiffness is an established driver of breast cancer progression, conclusions from 2D cultures do not correspond with newer data from cancer cells in 3D environments. Many past studies of breast cancer in 3D culture fail to recapitulate the stiffness of a real breast tumor or the various local stiffnesses present in a tumor microenvironment. In this study, we developed a series of collagen/alginate hybrid hydrogels with adjustable stiffness to match the core, middle, and peripheral zones of a breast tumor. We used this hydrogel system to investigate effects of different local stiffness on morphology, proliferation, and migration of breast cancer cells. RNA sequencing of cells in hydrogels with different stiffness revealed changes in multiple cellular processes underlying cancer progression, including angiogenesis and metabolism. We discovered that tumor cells in a soft environment enriched YAP1 and AP1 signaling related genes, whereas tumor cells in a stiff environment became more pro-angiogenic by upregulating fibronectin 1 (FN1) and matrix metalloproteinase 9 (MMP9) expression. This systematic study defines how the range of environmental stiffnesses present in a breast tumor regulates cancer cells, providing new insights into tumorigenesis and disease progression at the tumor-stroma interface. STATEMENT OF SIGNIFICANCE: Applied a well-defined hybrid hydrogel system to mimic the tumor microenvironment with heterogeneous local stiffness. Breast cancer cells tended to proliferate in soft core environment while migrate in stiff peripheral environment. Breast cancer cells shift from glycolysis to OXPHOS and fatty acid metabolism responding to stiff matrix microenvironment. The transcriptomic profile of breast cancer cells altered due to microenvironmental stiffness changes.

3D Printing and Bioprinting to Model Bone Cancer: The Role of Materials and Nanoscale Cues in Directing Cell Behavior

Bone cancer, both primary and metastatic, is characterized by a low survival rate. Currently, available models lack in mimicking the complexity of bone, of cancer, and of their microenvironment, leading to poor predictivity. Three-dimensional technologies can help address this need, by developing predictive models that can recapitulate the conditions for cancer development and progression. Among the existing tools to obtain suitable 3D models of bone cancer, 3D printing and bioprinting appear very promising, as they enable combining cells, biomolecules, and biomaterials into organized and complex structures that can reproduce the main characteristic of bone. The challenge is to recapitulate a bone-like microenvironment for analysis of stromal-cancer cell interactions and biological mechanics leading to tumor progression. In this review, existing approaches to obtain in vitro 3D-printed and -bioprinted bone models are discussed, with a focus on the role of biomaterials selection in determining the behavior of the models and its degree of customization. To obtain a reliable 3D bone model, the evaluation of different polymeric matrices and the inclusion of ceramic fillers is of paramount importance, as they help reproduce the behavior of both normal and cancer cells in the bone microenvironment. Open challenges and future perspectives are discussed to solve existing shortcomings and to pave the way for potential development strategies.

A 3D printed in vitro bone model for the assessment of molecular and cellular cues in metastatic neuroblastoma

Metastasis is a complex and multifactorial process highly dependent on the interaction between disseminated tumor cells and the pre-metastatic niche. The metastatic sites detected in the bone of patients affected by neuroblastoma (NB), a malignancy of the developing sympathetic nervous system, are particularly aggressive. To improve our current knowledge of metastatic tumor cell biology and improve treatment success, appropriate in vitro and in vivo models that more closely resemble the native metastatic niche are needed. In this study, the impact of the geometry of synthetic β-tricalcium-phosphate (β-TCP) structures on the interaction of NB tumor cells with the stromal component has been examined. The tumor microenvironment is dynamically shaped by the stroma, which sustains the growth of NB cells inside the metastatic niche. The 3D growth conditions are a determining factor for the cell proliferation rate in β-TCP. With respect to planar counterparts, channeled 3D β-TCP structures stimulate more interleukin-6 and Fibronectin production and define Connexin 43 distribution inside the cells. Together, these results highlight how the biomechanical properties of the 3D microenvironment enable tumor cells to form spheroid-shaped arrangements. This, in turn, facilitates their pro-migratory and pro-invasive patterns and mimics the in vivo situation by translating realistic mechanobiological cues to the metastatic NB.

The Role of Inflammation in Breast and Prostate Cancer Metastasis to Bone

Tumor metastasis to bone is a common event in multiple forms of malignancy. Inflammation holds essential functions in homeostasis as a defense mechanism against infections and is a strategy to repair injured tissue and to adapt to stress conditions. However, exaggerated and/or persistent (chronic) inflammation may eventually become maladaptive and evoke diseases such as autoimmunity, diabetes, inflammatory tissue damage, fibrosis, and cancer. In fact, inflammation is now considered a hallmark of malignancy with prognostic relevance. Emerging studies have revealed a central involvement of inflammation in several steps of the metastatic cascade of bone-homing tumor cells through supporting their survival, migration, invasion, and growth. The mechanisms by which inflammation favors these steps involve activation of epithelial-to-mesenchymal transition (EMT), chemokine-mediated homing of tumor cells, local activation of osteoclastogenesis, and a positive feedback amplification of the protumorigenic inflammation loop between tumor and resident cells. In this review, we summarize established and evolving concepts of inflammation-driven tumorigenesis, with a special focus on bone metastasis.

High stroma-derived WNT5A is an indicator for low-risk prostate cancer

Prostate cancer (PCa) is a major cause of cancer‐related death in men. Tumor‐derived protein derived from Wnt5A gene (WNT5A) plays an important role in primary and metastatic PCa. Surrounding stroma cells also produce WNT5A, which may modulate the biology of PCa. Here, we assessed the role of stroma‐derived WNT5A (stWNT5A) in primary PCa. A tissue microarray of samples obtained from 400 patients who underwent radical prostatectomy and control samples from 41 patients with benign prostate hyperplasia (BPH) was immunohistochemically assessed for expression of stWNT5A. The cores were scored for staining intensity: 0 (no staining), 1 (weak), 2 (moderate), or 3 (strong) and the stained stromal surface area: 0 (0%), 1 (1–25%), 2 (26–50%), 3 (51–75%), or 4 (76–100%). Gleason Score (GS) and TNM‐stage were assessed by stratifying the cohort into high‐risk (≥ pT3, pN1, GS ≥ 8) and non‐high‐risk patients. Ki67 and TUNEL assays were performed to assess proliferation and apoptosis. Expression of stWNT5A in BPH and tumor‐free control samples was 1.2‐fold higher compared to tumor samples (P < 0.001). Non‐high‐risk patients had a higher stWNT5A score than high‐risk patients (P < 0.05). stWNT5A expression was not correlated with overall and cancer‐specific survival. Proliferation (r² = 0.038, P < 0.001) and apoptosis (r² = 0.277, P < 0.001) negatively correlated with stWNT5A expression. In summary, we show that expression of stWNT5A is higher in benign tissue and non‐high‐risk PCa. Stroma‐derived Wnt signaling and tumor‐derived Wnt may differentially impact on tumor behavior. Future studies are warranted to dissect the Wnt profile in tumor vs. surrounding stroma tissues.

Incidence, prevalence, and outcomes of systemic malignancy with bone metastases

PURPOSE

Evidence on the incidence, prevalence, and outcomes of bone metastases among patients with systemic malignancy is limited. This study aimed to evaluate it using the Surveillance, Epidemiology, and End Results (SEER) database.

METHODS

We collected patients diagnosed with solid malignant tumors deriving outside of the bone, hematologic malignancies, Kaposi sarcoma, lymphoma, and myeloma from the SEER database (from 2010 to 2013). The incidence, prevalence, and outcomes of these systemic malignancies with bone metastases were then analyzed.

RESULTS

A total of 67,605 patients with bone metastases at cancer diagnosis were included. The highest rate of bone metastases was observed in patients with small-cell lung cancer at the time of alternative primary site cancer diagnosis. Among 226,816 cases with metastatic disease, cases with breast cancer (65.58%), and prostate cancer (89.60%) had a high incidence proportion (>10%) of identified bone metastases. Patients with additional bone metastases resulting from prostate cancer, breast cancer, and testis cancer presented the best survival time.

CONCLUSIONS

Incidence and prognosis differ considerably among bone metastases with different primary malignancy sites. These results may encourage appropriate application of bone imaging.

Molecular insights into the interplay between adiposity, breast cancer and bone metastasis

Cancer is a complex disease, with various pre-existing health ailments enhancing its pathology. In cancer, the extracellular environment contains various intrinsic physiological factors whose levels are altered with aging and pre-existing conditions. In obesity, the tumor microenvironment and metastases are enriched with factors that are both derived locally, and from other physiological compartments. Similarly, in obesity, the cancer cell environment both at the site of origin and at the secondary site i.e., metastatic niche, contains significantly more phenotypically-altered adipocytes than that of un-obese cancer patients. Indeed, obesity has been linked with cancer progression, metastasis, and therapy resistance. Adipocytes not only interact with tumor cells, but also with adjacent stromal cells at primary and metastatic sites. This review emphasizes the importance of bidirectional interactions between adipocytes and breast tumor cells in breast cancer progression and its bone metastases. This paper not only chronicles the role of various adipocyte-derived factors in tumor growth, but also describes the significance of adipocyte-derived bone metastatic factors in the development of bone metastasis of breast cancer. It provides a molecular view of the interplay between the adipocytes and tumor cells involved in breast cancer bone metastasis. However, more research is needed to determine if targeting cancer-associated adipocytes holds promise as a potential therapeutic approach for breast cancer bone metastasis treatment. Interplay between adipocytes and breast cancer cells at primary cancer site and metastatic bone microenvironment. AMSC Adipose-derived mesenchymal stem cell, CAA Cancer associated adipocytes, CAF Cancer associated fibroblast, BMSC Bone marrow derived mesenchymal stem cell, BMA Bone marrow adipocyte.

Characteristics of pre-metastatic niche: the landscape of molecular and cellular pathways

Metastasis is a major contributor to cancer-associated deaths. It involves complex interactions between primary tumorigenic sites and future metastatic sites. Accumulation studies have revealed that tumour metastasis is not a disorderly spontaneous incident but the climax of a series of sequential and dynamic events including the development of a pre-metastatic niche (PMN) suitable for a subpopulation of tumour cells to colonize and develop into metastases. A deep understanding of the formation, characteristics and function of the PMN is required for developing new therapeutic strategies to treat tumour patients. It is rapidly becoming evident that therapies targeting PMN may be successful in averting tumour metastasis at an early stage. This review highlights the key components and main characteristics of the PMN and describes potential therapeutic strategies, providing a promising foundation for future studies.

Autogenous bone particles combined with platelet-rich plasma can stimulate bone regeneration in rabbits

Long-term bone defects are a key clinical problem. Autogenous bone graft remains the gold standard for the treatment of these defects; however, improving the osteogenic properties and reducing the amount of autogenous bone is challenging. Autologous platelet-rich plasma (PRP) has been widely considered for treatment, due to its potentially beneficial effect on bone regeneration and vascularization. The aim of the present study was to explore the effects of autogenous bone particles combined with PRP on repairing segmental bone defects in rabbits. Briefly, a critical-size diaphyseal radius defect was established in 45 New Zealand White rabbits. Animals were randomly divided into four groups, according to the different implants: Group A, empty bone defect; group B, PRP; group C, autogenous bone particles + bone mesenchymal stem cells (BMSCs) on the left radius; group D, autogenous bone particles + PRP + BMSCs on the right radius. Bone samples were collected and further analyzed using X-ray, histology and histomorphometry 4, 8 and 12 weeks post-surgery. In addition, the effect of PRP on cell proliferation was detected by Cell Counting Kit-8 and the concentrations of growth factors (GFs), transforming GF (TGF)-β1 and platelet-derived GF (PDGF), in PRP were verified by ELISA. X-ray, histology and histomorphometry data revealed that the fraction area of the newly formed bone was larger in group D. In addition, PRP could improve cell proliferation, osteogenic differentiation and the release of GFs, TGF-β1 and PDGF-AB. In conclusion, these findings indicated that an autogenous bone particle + PRP + BMSC scaffold may be used as a potential treatment strategy for segmental defects in humans.

Chemokines in bone-metastatic breast cancer: Therapeutic opportunities

Due to non-response to chemotherapy, incomplete surgical resection, and resistance to checkpoint inhibitors, breast cancer with bone metastasis is notoriously difficult to cure. Therefore, the development of novel, efficient strategies to tackle bone metastasis of breast cancer is urgently needed. Chemokines, which induce directed migration of immune cells and act as guide molecules between diverse cells and tissues, are small proteins indispensable in immunity. These complex chemokine networks play pro-tumor roles or anti-tumor roles when produced by breast cancer cells in the tumor microenvironment. Additionally, chemokines have diverse roles when secreted by various immune cells in the tumor microenvironment of breast cancer, which can be roughly divided into immunosuppressive effects and immunostimulatory effects. Recently, targeting chemokine networks has been shown to have potential for use in treatment of metastatic malignancies, including bone-metastatic breast cancer. In this review, we focus on the role of chemokines networks in the biology of breast cancer and metastasis to the bone. We also discuss the therapeutic opportunities and future prospects of targeting chemokine networks, in combination with other current standard therapies, for the treatment of bone-metastatic breast cancer.

The Endosteal Niche in Breast Cancer Bone Metastasis

The establishment of bone metastasis remains one of the most frequent complications of patients suffering from advanced breast cancer. Patients with bone metastases experience high morbidity and mortality caused by excessive, tumor-induced and osteoclast-mediated bone resorption. Anti-resorptive treatments, such as bisphosphonates, are available to ease skeletal related events including pain, increased fracture risk, and hypercalcemia. However, the disease remains incurable and 5-year survival rates for these patients are below 25%. Within the bone, disseminated breast cancer cells localize in “metastatic niches,” special microenvironments that are thought to regulate cancer cell colonization and dormancy as well as tumor progression and subsequent development into overt metastases. Precise location and composition of this “metastatic niche” remain poorly defined. However, it is thought to include an “endosteal niche” that is composed of key bone cells that are derived from both, hematopoietic stem cells (osteoclasts), and mesenchymal stromal cells (osteoblasts, fibroblasts, adipocytes). Our knowledge of how osteoclasts drive the late stage of the disease is well-established. In contrast, much less is known about the interaction between osteogenic cells and disseminated tumor cells prior to the initiation of the osteolytic phase. Recent studies suggest that mesenchymal-derived cells, including osteoblasts and fibroblasts, play a key role during the early stages of breast cancer bone metastasis such as tumor cell homing, bone marrow colonization, and tumor cell dormancy. Hence, elucidating the interactions between breast cancer cells and mesenchymal-derived cells that drive metastasis progression could provide novel therapeutic approaches and targets to treat breast cancer bone metastasis. In this review we discuss evidences reporting the interaction between tumor cells and endosteal niche cells during the early stages of breast cancer bone metastasis, with a particular focus on mesenchymal-derived osteoblasts and fibroblasts.

Gold clusters prevent breast cancer bone metastasis by suppressing tumor-induced osteoclastogenesis

Rationale: Bone is the most frequent site for breast cancer metastasis, which accounts for the leading cause of death in advanced breast cancer patients. Serious skeletal-related events (SREs) caused by bone metastasis have a decisive impact on the life expectancy of breast cancer patients, making breast cancer almost incurable. Metastatic breast cancer cell induced pathological osteoclastogenesis is a key driver of bone metastasis and osteolytic bone lesions. We previously reported that gold clusters can prevent inflammation induced osteoclastogenesis and osteolysis in vivo. In this study, we investigated the effects of a BSA-coated gold cluster on metastatic breast cancer-induced osteoclastogenesis in vitro and tumor-induced osteolysis in vivo, and elucidated its possible mechanism. Methods: Breast cancer cell line MDA-MB-231 was used to evaluate the regulatory effects of gold clusters on breast cancer metastasis and tumor induced osteoclastogenesis in vitro. Cell counting kit-8, transwell, wound-healing and colony formation assays were performed to evaluate the effect of gold clusters on proliferation and metastasis of MDA-MB-231 cells. Tartrate-resistant acid phosphatase (TRAP) staining and filamentous-actin rings analysis were used to detect the regulatory effects of gold clusters on MDA-MB-231 cell-conditioned medium (MDA-MB-231 CM) triggered and receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis in mouse bone marrow-derived mononuclear cells (BMMs). A mouse model of breast cancer bone metastasis was used to evaluate the in vivo activity of the gold cluster on the tumor induced osteolysis. Results: The gold clusters suppressed the migration, invasion and colony formation of MDA-MB-231 cells in a dose-dependent manner in vitro. The gold clusters strongly inhibited both MDA-MB-231 CM triggered and RANKL-induced osteoclast formation from BMMs in vitro. Cell studies indicated that the gold clusters suppressed the expression of osteolysis-related factors in MDA-MB-231 cells and inhibited the subsequent activation of NF-κB pathway in BMMs. Treatment with the clusters at a dose of 10 mg Au/kg.bw significantly reduces the breast cancer cell induced osteolysis in vivo. Conclusion: Therefore, the gold clusters may offer new therapeutic agents for preventing breast cancer bone metastasis and secondary osteolysis to improve patient outcomes.

Harnessing the versatile role of OPG in bone oncology: counterbalancing RANKL and TRAIL signaling and beyond

More than 2 decades ago, the discovery of osteoprotegerin (OPG) as inhibitor of the receptor of activator of nuclear factor Kb (RANK) ligand (RANKL) revolutionized our understanding of bone biology and oncology. Besides acting as decoy receptor for RANKL, OPG acts as decoy receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). OPG, RANKL, and TRAIL are ubiquitously expressed, stimulating per se pivotal signaling cascades implicated in cancer. In the context of cancer cell-bone cell interactions, cancer cells skew the OPG/RANKL/RANK (RANKL cognate receptor) balance towards bone destruction and tumor growth through favoring the RANKL/RANK interface, circumventing OPG. Numerous preclinical and clinical studies demonstrate the dual role of OPG in cancer: antitumor and tumor-promoting. OPG potentially conveys an antitumor signal through inhibiting the tumor-promoting RANKL signaling-both the osteoclast-dependent and the osteoclast-independent-and the tumor-promoting TRAIL signaling. On the other hand, the presumed tumor-promoting functions of OPG are: (i) abrogation of TRAIL-induced apoptosis of cancer cells; (ii) abrogation of RANKL-induced antitumor immunity; and (iii) stimulation of oncogenic and prometastatic signaling cascades downstream of the interaction of OPG with diverse proteins. The present review dissects the role of OPG in bone oncology. It presents the available preclinical and clinical data sustaining the dual role of OPG in cancer and focuses on the imbalanced RANKL/RANK/OPG interplay in the landmark "vicious cycle" of skeletal metastatic disease, osteosarcoma, and multiple myeloma. Finally, current challenges and future perspectives in exploiting OPG signaling in bone oncology therapeutics are discussed.

Interleukin-22 Mediates the Chemotactic Migration of Breast Cancer Cells and Macrophage Infiltration of the Bone Microenvironment by Potentiating S1P/SIPR Signaling

The interleukin-22 (IL-22) signaling pathway is well known to be involved in the progression of various cancer types but its role in bone metastatic breast cancer remains unclear. We demonstrate using human GEO profiling that bone metastatic breast cancer displays elevated interleukin-22 receptor 1 (IL-22R1) and sphingosine-1-phosphate receptor 1 (S1PR1) expression. Importantly, IL-22 stimuli promoted the expression of IL-22R1 and S1PR1 in aggressive MDA-MB-231 breast cancer cells. IL-22 treatment also increased sphingosine-1-phosphate production in mesenchymal stem cells (MSCs) and induced the sphingosine-1-phosphate (S1P)-mediated chemotactic migration of MDA-MB-231 cells. This effect was inhibited by an S1P antagonist. In addition to the S1PR1 axis, IL-22 stimulated the expression of matrix metalloproteinase-9 (MMP-9), thereby promoting breast cancer cell invasion. Moreover, IL-22 induced IL22R1 and S1PR1 expression in macrophages, myeloid cell, and MCP1 expression in MSCs to facilitate macrophage infiltration. Immunohistochemistry indicated that IL-22R1 and S1PR1 are overexpressed in invasive malignant breast cancers and that this correlates with the MMP-9 levels. Collectively, our present results indicate a potential role of IL-22 in driving the metastasis of breast cancers into the bone microenvironment through the IL22R1-S1PR1 axis.

TLR4 signaling drives mesenchymal stromal cells commitment to promote tumor microenvironment transformation in multiple myeloma

Inflammation represents a key feature and hallmark of tumor microenvironment playing a major role in the interaction with mesenchymal stromal cells (MSC) in cancer progression. The aim of the present study was to investigate the crosstalk between MSCs and myeloma cells (MM) in the pro-inflammatory microenvironment promoting immune evasion and tumor growth. MSC were collected from patients with diagnosis of MGUS (n = 10), smoldering myeloma (n = 7), multiple myeloma at diagnosis (n = 16), relapse (n = 5) or refractory (n = 3), and from age-matched healthy controls (HC, n = 10) and cultured with peripheral blood mononucleated cells (PBMC) from healthy volunteer donors. Similarly to MM, we showed that MSC from smoldering multiple myeloma (SMM) patients activated neutrophils and conferred an immunosuppressive and pro-angiogenic phenotype. Furthermore, co-cultures of plasma cells (PC) and HC-MSC suggested that such activation is driven by MM cells through the switching into a pro-inflammatory phenotype mediated by toll-like receptor 4 (TLR4). These results were further confirmed using a zebrafish as an immunocompetent in vivo model, showing the role of MM-MSC in supporting PCs engraftment and Th2 response. Such effect was abolished following inhibition of TLR4 signaling in MM-MSC before co-injection with PC. Moreover, the addition of a TLR4 inhibitor in the co-culture of HC-MSC with MM cells prevented the activation of the pro-tumor activity in PC-educated MSC. In conclusion, our study provides evidence that TLR4 signaling plays a key role in MSC transformation by inducing a pro-tumor phenotype associated with a permissive microenvironment allowing immune escape and tumor growth.

Magnetic calcium phosphates nanocomposites for the intracellular hyperthermia of cancers of bone and brain

Aim: Magnetic hyperthermia is limited by the low selective susceptibility of neoplastic cells interspersed within healthy tissues, which we aim to improve on. Materials & methods: Two superparamagnetic calcium phosphates nanocomposites, that is, iron-doped hydroxyapatite and iron oxide (Mag) nanoparticles coated with amorphous calcium phosphate (Mag@CaP), were synthesized and tested for selective activity against brain and bone cancers. Results: Nanoparticle uptake and intracellular localization were prerequisites for reduction of cancer viability in alternate magnetic fields of extremely low power. Sheer adsorption onto the outer membrane was not sufficient to produce this effect, which was extremely significant for Mag@CaP and iron-doped hydroxyapatite, but negligible for Mag, demonstrating benefits of combining magnetic iron with calcium phosphates. Conclusion: Such selective effects are important in the global effort to rejuvenate clinical prospects of magnetic hyperthermia.

The Hippo Pathway in Prostate Cancer

Despite recent efforts, prostate cancer (PCa) remains one of the most common cancers in men. Currently, there is no effective treatment for castration-resistant prostate cancer (CRPC). There is, therefore, an urgent need to identify new therapeutic targets. The Hippo pathway and its downstream effectors—the transcriptional co-activators, Yes-associated protein (YAP) and its paralog, transcriptional co-activator with PDZ-binding motif (TAZ)—are foremost regulators of stem cells and cancer biology. Defective Hippo pathway signaling and YAP/TAZ hyperactivation are common across various cancers. Here, we draw on insights learned from other types of cancers and review the latest advances linking the Hippo pathway and YAP/TAZ to PCa onset and progression. We examine the regulatory interaction between Hippo-YAP/TAZ and the androgen receptor (AR), as main regulators of PCa development, and how uncontrolled expression of YAP/TAZ drives castration resistance by inducing cellular stemness. Finally, we survey the potential therapeutic targeting of the Hippo pathway and YAP/TAZ to overcome PCa.

Seeking for Correlative Genes and Signaling Pathways With Bone Metastasis From Breast Cancer by Integrated Analysis

Background: Bone metastasis frequently occurs in advanced breast cancer patients, and it is one of major causes of breast cancer associated mortality. The aim of the current study is to identify potential genes and related signaling pathways in the pathophysiology of breast cancer bone metastasis.

Methods: Three mRNA expression datasets for breast cancer bone metastasis were obtained from Gene Expression Omnibus (GEO) dataset. The differentially expressed genes (DEGs) were obtained. Functional analyses, protein-protein interaction (PPI) network, and transcription factors (TFs)-target genes network was constructed. Real-time PCR using clinical specimens was conducted to justify the results from integrated analysis.

Results: A 749 DEGs were obtained. Osteoclast differentiation and rheumatoid arthritis were two significantly enriched signaling pathways for DEGs in the bone metastasis of breast cancer. SMAD7 (degree = 10), TGFBR2 (degree = 9), VIM (degree = 8), FOS (degree = 8), PDGFRB (degree = 7), COL5A1 (degree = 6), ARRB2 (degree = 6), and ITGAV (degree = 6) were high degree genes in the PPI network. ETS1 (degree = 12), SPI1 (degree = 12), FOS (degree = 10), FLI1 (degree = 5), KLF4 (degree = 4), JUNB (degree = 4), NR3C1 (degree = 4) were high degree genes in the TFs-target genes network. Validated by QRT-PCR, the expression levels of IBSP, MMP9, MMP13, TNFAIP6, CD200, DHRS3, ASS1, RIPK4, VIM, and PROM1 were roughly consistent with our integrated analysis. Except PROM1, the other genes had a diagnose value for breast cancer bone metastasis.

Conclusions: The identified DEGs and signaling pathways may make contribution for understanding the pathological mechanism of bone metastasis from breast cancer.

Bone as a Preferential Site for Metastasis

Bone marrow provides a unique microenvironment favoring the colonization and outgrowth of metastatic tumor cells. Despite the high incidence of bone metastasis in breast and prostate cancer patients, many of the molecular mechanisms controlling metastatic progression remain unclear. Several gene signatures associated with bone metastasis have been reported, but no metastasis-specific gene alterations have been identified. Therefore, there has been considerable interest in understanding how the bone microenvironment impacts the behavior of disseminated tumor cells (DTCs) prior to and following colonization of the bone. Substantial evidence indicates that disruption of normal bone homeostasis by tumor-derived factors establishes a premetastatic niche within the bone that favors DTC colonization. Following dissemination, bone resident cells and the surrounding stroma provide critical signals that support tumor cell colonization, survival, and eventual outgrowth. Clinical data suggest that patients can harbor DTCs for years to decades prior to developing overt bone metastases, suggesting a period of tumor dormancy occurs in the bone marrow. Several dormancy-promoting factors have been recently identified; however, critical questions surrounding the molecular triggers and timing of tumor cell emergence from dormancy remain. Here, we review how metastatic tumor cells co-opt the bone marrow microenvironment for metastatic progression and discuss emerging insights into how to more effectively target DTCs and prevent metastasis. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Autophagy induces G0/G1 arrest and apoptosis in menstrual blood-derived endometrial stem cells via GSK3-β/β-catenin pathway

BACKGROUND/AIMS

Menstrual blood-derived endometrial stem cells (MenSCs) emerge as an ideal source for cell-based treatment in regenerative medicine and immunotherapy. However, the major obstacle is the low survival rate in tissues and the limited expansion number. Autophagy is an intracellular metabolic self-degradative process which plays important roles in normal cellular division and survival, and the present study aimed to explore the related mechanisms between autophagy and survival of MenSCs in vitro and in vivo.

METHODS

The MenSCs were obtained from menstrual blood procured from healthy female donors. In vitro, MenSCs were exposed to rapamycin and Earle's balanced salts solution (EBSS). We evaluated the MenSCs immunophenotypic cell cycle distribution by propidium iodide (PI) staining and cell apoptosis by Annexin V/PI staining as well as their proliferative potential by the MTT assay. We also assessed the expression of genes associated with the cell cycle and Gsk3β signaling pathway by western blot analysis. We depressed Atg5 and Gsk3β expression by short hairpin RNA (shRNA) and undertook the experiments. Moreover, the labeled MenSCs were observed and counted with DiI after transplantation into the mice via the tail vein by microscopy in vivo.

RESULTS

In vitro, rapamycin and starvation induced autophagy of MenSCs. Hyperactive autophagy significantly induced G0/G1 arrest and slightly promoted apoptosis of MenSCs. Meanwhile, autophagy could stimulate p-GSK3β expression in MenSCs. Further, knockdown GSK3β can accelerate the proliferation of MenSCs by shRNA and CHIR99021. Moreover, the shGSK3β MenSCs showed strong proliferative activity in vitro and in vivo.

CONCLUSIONS

Our results indicate that autophagy induced G0/G1 arrest and apoptosis of MenSCs via GSK3β/β-catenin pathway. Inhibiting autophagy or reduced GSK3β levels may improve survival rate in vivo, thus playing roles in MenSCs therapy.

Targeted Nanomedicine to Treat Bone Metastasis

Bone metastases are common complications of solid tumors, particularly those of the prostate, breast, and lungs. Bone metastases can lead to painful and devastating skeletal-related events (SREs), such as pathological fractures and nerve compressions. Despite advances in treatment for cancers in general, options for bone metastases remain inadequate and generally palliative. Anticancer drugs (chemotherapy and radiopharmaceuticals) do not achieve therapeutic concentrations in the bone and are associated with dose-limiting side effects to healthy tissues. Nanomedicines, with their tunable characteristics, have the potential to improve drug targeting to bone metastases while decreasing side effects for their effective treatment. In this review, we present the current state of the art for nanomedicines to treat bone metastases. We also discuss new treatment modalities enhanced by nanomedicine and their effects on SREs and disease progression.

Interactions Between Disseminated Tumor Cells and Bone Marrow Stromal Cells Regulate Tumor Dormancy

PURPOSE OF REVIEW

To succinctly summarize recent findings concerning dormancy regulating interactions between bone marrow stromal cells and disseminated tumor cells.

RECENT FINDINGS

Recent studies have highlighted roles of the bone marrow microenviroment, including osteoblasts, mesenchymal stem cells (MSCs), and endothelial cells, in inducing or maintaining cancer cell dormancy. Key pathways of interest include: osteoblast-induced transforming growth factor (TGF)-β2 signaling, transfer of MSC-derived exosomes containing dormancy inducing microRNA, cancer cell cannibalism of MSCs, and endothelial cell secretion of thrombospondin 1 (TSP1). The bone marrow is a common site of metastatic disease recurrence following a period of cancer cell dormancy. Understanding why disseminated tumor cells enter into dormancy and later resume cell proliferation and growth is vital to developing effective therapeutics against these cells. The bone marrow stroma and the various pathways through which it participates in crosstalk with cancer cells are essential to furthering understanding of how dormancy is regulated.