Src family kinase/abl inhibitor dasatinib suppresses proliferation and enhances differentiation of osteoblasts. Oncogene. 2010;29:3196-3207. [PMID: 20228840 DOI: 10.1038/onc.2010.73]

Radium-223 Treatment Produces Prolonged Suppression of Resident Osteoblasts and Decreased Bone Mineral Density in Trabecular Bone in Osteoblast Reporter Mice

Radium 223 (Ra-223) is an α-emitting bone-homing radiopharmaceutical that targets tumor-induced osteoblasts and is used to reduce bone pain and prolong overall survival in men with bone-metastatic, castrate-resistant prostate cancer. However, increased fracture risk in skeletal sites with no bone metastasis has been observed in patients treated with Ra-223. Both luciferase- or green fluorescence protein (GFP)-labeled osteoblast reporter mice were used to monitor the effect of Ra-223 on resident osteoblasts and normal bone structure. Upon Ra-223 treatment, 70% of resident osteoblasts were reduced within 2 days, and the osteoblast reduction lasted for at least 18 weeks without detectable recovery, as measured by in vivo bioluminescent imaging. In GFP-labeled osteoblast reporter mice, Ra-223 mainly reduced osteoblasts localized in the trabecular bone areas; the osteoblasts in the growth plates were less affected. Micro-computed tomography analyses showed that Ra-223 significantly reduced bone mineral density and bone microstructure in the trabecular area of femurs but not in the cortical bone. Tumor-induced bone was generated by inoculating osteogenic TRAMP-BMP4 prostate cancer cells into the mouse femurs; Ra-223 treatment significantly reduced tumor-induced osteoblasts. Our study shows that Ra-223 affects bone structures that are not involved in bone metastasis. Strategies that improve bone health may reduce fracture risk in patients receiving Ra-223.

Dasatinib regulates the proliferation and osteogenic differentiation of PDLSCs through Erk and EID3 signals

Periodontal ligament stem cells (PDLSCs) are important candidate seed cells for alveolar bone tissue engineering. Dasatinib is a tyrosine kinase inhibitor, and its influence on the osteogenic differentiation of mesenchymal stem cells is a controversial topic. The present study explored the effects of different concentrations of dasatinib on the proliferation and osteogenic differentiation of PDLSCs and tentatively revealed the related mechanism. The results of CCK8 showed that low concentrations of dasatinib (1 nM) did not affect proliferation, while high concentrations of dasatinib significantly inhibited the proliferative activity of PDLSCs. This could be related to the inhibiting effects of dasatinib on Erk signals. ALP staining, alizarin red staining, and western blot proved that low concentrations of dasatinib (1 nM) promoted the osteogenic differentiation of PDLSCs, while high concentrations of dasatinib inhibited it. The negative effects of dasatinib on osteogenic differentiation were reversed when EID3 was knocked down, suggesting that EID3 mediates the regulation of dasatinib on the osteo-differentiation of PDLSCs. Taken together, high concentrations of dasatinib inhibited the proliferation and osteogenic differentiation of PDLSCs through Erk and EID3 signals, while low concentrations of dasatinib could be a potential method to enhance the bone regeneration ability of PDLSCs.

Dasatinib enhances curcumin-induced cytotoxicity, apoptosis and protective autophagy in human schwannoma cells HEI-193: The role of Akt/mTOR/p70S6K signalling pathway

The present study was carried out in human schwannoma cells (HEI-193) to determine the combined anti-cancer effect of curcumin and dasatinib. Cells were treated with curcumin only, dasatinib only, or the combination of curcumin and dasatinib for 24 hours. Cellular toxicity, cell proliferation, and cell death were determined by LDH, MTT, and trypan blue dye assays, respectively. ELISA based kit was used to determine apoptotic cell death. Western blotting was used to determine the expression of apoptotic and autophagy-associated protein markers. Similarly, expression levels of Akt/mTOR/p70S6K signalling pathway-related proteins were studied using Western blotting. Cell death and apoptosis were significantly higher in HEI-193 cells treated with curcumin and dasatinib combination compared to individual controls. The combination of curcumin and dasatinib significantly enhances autophagy markers compared to individual controls. Furthermore, the combination of curcumin and dasatinib significantly activates Akt/mTOR/p70S6K signalling pathway compared to individual controls. In conclusion, our results suggest that the combination of curcumin and dasatinib significantly enhances cytotoxicity, apoptosis, and protective autophagy in HEI-193 cells through Akt/mTOR/p70S6K signalling pathway.

The nonreceptor protein tyrosine kinase Src participates in every step of cancer-induced bone pain

Cancer-induced bone pain (CIBP) is a refractory form of pain that has a high incidence in advanced tumors. Src protein tyrosine kinase is mainly composed of six domains, with two states of automatic inhibition and activation. The modular domain allows Src to conveniently regulate by and communicate with a variety of proteins, directly or indirectly participate in each step of the CIBP process. Src is beneficial to the growth and proliferation of tumor cells, and it can promote the metastases of primary tumors to bone. In the microenvironment of bone metastasis, it mainly mediates bone resorption, activates related peripheral receptors to participate in the formation of pain signals, and may promote the generation of pathological sensory nerve fibers. In the process of pain signal transmission, it mainly mediates NMDAR and central glial cells to regulate pain signal intensity and central sensitization, but it is not limited to these two aspects. Both basic experimentation and clinical research have shown encouraging potential, providing new ideas and inspiration for the prevention and treatment of CIBP.

Bone marrow niches in the regulation of bone metastasis

The bone marrow has been widely recognised to host a unique microenvironment that facilitates tumour colonisation. Bone metastasis frequently occurs in the late stages of malignant diseases such as breast, prostate and lung cancers. The biology of bone metastasis is determined by tumour-cell-intrinsic traits as well as their interaction with the microenvironment. The bone marrow is a dynamic organ in which various stages of haematopoiesis, osteogenesis, osteolysis and different kinds of immune response are precisely regulated. These different cellular components constitute specialised tissue microenvironments-niches-that play critical roles in controlling tumour cell colonisation, including initial seeding, dormancy and outgrowth. In this review, we will dissect the dynamic nature of the interactions between tumour cells and bone niches. By targeting certain steps of tumour progression and crosstalk with the bone niches, the development of potential therapeutic approaches for the clinical treatment of bone metastasis might be feasible.

Whole-Body [18F]-Fluoride PET SUV Imaging to Monitor Response to Dasatinib Therapy in Castration-Resistant Prostate Cancer Bone Metastases: Secondary Results from ACRIN 6687

ACRIN 6687, a multi-center clinical trial evaluating differential response of bone metastases to dasatinib in men with metastatic castration-resistant prostate cancer (mCRPC), used [¹⁸F]-fluoride (NaF) PET imaging. We extend previous ACRIN 6687 dynamic imaging results by examining NaF whole-body (WB) static SUV PET scans acquired after dynamic scanning. Eighteen patients underwent WB NaF imaging prior to and 12 weeks into dasatinib treatment. Regional VOI analysis of the most NaF avid bone metastases and an automated whole-body method using Quantitative Total Bone Imaging software (QTBI; AIQ Solutions, Inc., Madison, WI, USA) were used. We assessed differences in tumor and normal bone, between pre- and on-treatment dasatinib, and evaluated parameters in association with PFS and OS. Significant decrease in average SUV_max and average SUV_peak occurred in response to dasatinib. Univariate and multivariate analysis showed NaF uptake had significant association with PFS. Pharmacodynamic changes with dasatinib in tumor bone can be identified by WB NaF PET in men with mCRPC. WB PET has the benefit of examining the entire body and is less complicated than single FOV dynamic imaging.

The multi-kinase inhibitor dasatinib suppresses autoinflammation and increases bone density in a mouse model for chronic recurrent multifocal osteomyelitis

Chronic recurrent multifocal osteomyelitis (CRMO) is an autoinflammatory bone disease that presents with bone destruction and pain. Although genetic studies have identified signalling pathways involving CRMO, molecularly targeted drugs remain unavailable. We used an animal model of CRMO as an in vivo screening system for candidate therapeutic agents. A gain-of-function mutation in Fgr, a member of Src family kinases (SFKs), causes peripheral paw inflammation and reduced bone mineral density (BMD) in Ali18 mice. The SFK inhibitor dasatinib was selected for administration to Ali18 mice daily for 2 weeks. Local inflammation and BMD were assessed by clinical scoring and computed tomography, respectively. Pilot studies in a small number of animals showed that dasatinib administration effectively suppressed the early phase of autoinflammation in Ali18 mice. Serial oral gavage of dasatinib to a group of Ali18 mice confirmed significant suppression of paw swelling with no side effects. Histological analysis revealed that abnormal proliferative bone marrow cells and inflammatory infiltration into the skin in the affected area were clearly reduced in the animals with dasatinib administration. Further, trabecular BMD in Ali18 long bones was restored to levels similar to that found in wild type mice. Our results indicate that autoinflammation and related-bone phenotypes were completely suppressed by the dasatinib kinase inhibitor in CRMO model animals. Thus, it is strongly suggested that dasatinib can be used for clinical treatments of CRMO with the combination of molecular diagnosis of the FGR locus. SIGNIFICANCE OF THE STUDY: Autoinflammation and related-bone phenotypes were effectively suppressed by the kinase inhibitor dasatinib in CRMO model animals. In combination with molecular analysis of the FGR locus, dasatinib is a strong candidate for the clinical treatments of CRMO. We propose that the animal model employed in this study can be used to screen this and other potential drugs for CRMO.

Biallelic mutations in LAMA5 disrupts a skeletal noncanonical focal adhesion pathway and produces a distinct bent bone dysplasia

Background

Beyond its structural role in the skeleton, the extracellular matrix (ECM), particularly basement membrane proteins, facilitates communication with intracellular signaling pathways and cell to cell interactions to control differentiation, proliferation, migration and survival. Alterations in extracellular proteins cause a number of skeletal disorders, yet the consequences of an abnormal ECM on cellular communication remains less well understood

Methods

Clinical and radiographic examinations defined the phenotype in this unappreciated bent bone skeletal disorder. Exome analysis identified the genetic alteration, confirmed by Sanger sequencing. Quantitative PCR, western blot analyses, immunohistochemistry, luciferase assay for WNT signaling were employed to determine RNA, proteins levels and localization, and dissect out the underlying cell signaling abnormalities.  Migration and wound healing assays examined cell migration properties.

Findings

This bent bone dysplasia resulted from biallelic mutations in LAMA5, the gene encoding the alpha-5 laminin basement membrane protein. This finding uncovered a mechanism of disease driven by ECM-cell interactions between alpha-5-containing laminins, and integrin-mediated focal adhesion signaling, particularly in cartilage. Loss of LAMA5 altered β1 integrin signaling through the non-canonical kinase PYK2 and the skeletal enriched SRC kinase, FYN. Loss of LAMA5 negatively impacted the actin cytoskeleton, vinculin localization, and WNT signaling.

Interpretation

This newly described mechanism revealed a LAMA5-β1 Integrin-PYK2-FYN focal adhesion complex that regulates skeletogenesis, impacted WNT signaling and, when dysregulated, produced a distinct skeletal disorder.

Funding

Supported by NIH awards R01 AR066124, R01 DE019567, R01 HD070394, and U54HG006493, and Czech Republic grants INTER-ACTION LTAUSA19030, V18-08-00567 and GA19-20123S.

c-Src kinase inhibits osteogenic differentiation via enhancing STAT1 stability

The proto-oncogene Src is ubiquitously expressed and is involved in cellular differentiation. However, the role of Src in embryonic stem (ES) cell osteogenic differentiation is largely unknown. Using the small molecule inhibitor PP2, c-Src specific siRNAs, and tet-inducible lentiviral vectors overexpressing active c-Src, we delineated an inhibitory role of c-Src in osteogenic differentiation of mouse embryonic stem cells (mESCs) and mouse MC3T3-E1s preosteoblasts. Active c-Src was shown to restrict the nuclear residency of Runt-related transcription factor 2 (Runx2) and its transcriptional activity with no detectable effect on Runx2 expression level. Furthermore, we showed Signal Transducer and Activator of Transcription 1 (STAT1) was indispensable to the inhibitory role of c-Src on Runx2 nuclear localization. Specifically, higher levels of active c-Src increased STAT1 half-life by inhibiting its proteasomal degradation, thereby increasing the cytoplasmic abundance of STAT1. More abundant cytoplasmic STAT1 bound and anchored Runx2, which restricted its nucleocytoplasmic shuttling and ultimately reduced Runx2 transcriptional activity. Collectively, this study has defined a new mechanism by which c-Src inhibits the transcriptional regulation of osteogenesis from mESCs in vitro.

Exosomes from Placenta-Derived Mesenchymal Stem Cells Are Involved in Liver Regeneration in Hepatic Failure Induced by Bile Duct Ligation

Although the liver has a regenerative capacity, hepatic failure is a severe and irreversible chronic disease. Placenta-derived mesenchymal stem cells (PD-MSCs) have distinctive features, such as recycling of the placenta waste after birth, ease of accessibility, abundant cell numbers, and strong immunosuppressive properties. Previously, we reported that PD-MSCs can regenerate the liver in hepatic failure through antifibrotic and autophagic mechanisms. Many reports have investigated whether exosomes, which are formed by the budding of vesicular bodies and are emitted into the blood, from stem cells have therapeutic potential in various diseases. C-reactive protein (CRP) is produced in hepatocytes and secreted via vessels. Therefore, the objectives of this study were to compare the expression of CRP in exosomes of a hepatic failure rat model (bile duct ligation, BDL) and to evaluate the therapeutic effect by their correlation between CRP and angiogenesis depending on PD-MSC transplantation. The exosomes were analyzed in a BDL rat model with transplantation of PD-MSCs through LC-MS analysis and precipitation solution. The exosomes, CRP, and factors related to these molecules were evaluated and quantified in exosomes as well as investigated by real-time PCR, Western blot, and immunofluorescence (IF) in vivo and in vitro. CRP was present in exosomes from serum of a rat model and increased by PD-MSC transplantation. In the exosomes, CRP upregulated the factors related to the Wnt signaling pathway and angiogenesis in the BDL rat liver-transplanted PD-MSCs. Also, CRP regulated the Wnt pathway and vascularization in rat hepatocytes by interacting with endothelial cells. Therefore, our findings indicate that CRP in exosomes excreted by PD-MSCs functions in angiogenesis via the Wnt signaling pathway.

Calreticulin regulates Src kinase in osteogenic differentiation from embryonic stem cells

Calreticulin, the major Ca²⁺ buffer of the endoplasmic reticulum plays an important role in the choice of fate by embryonic stem cells. Using the embryoid body method of organogenesis, we showed impaired osteogenesis in crt^-/- cells vis-à-vis calreticulin-containing osteogenic WT cells. In the non-osteogenic crt^-/- cells, c-Src- a non-receptor tyrosine kinase- was activated and its inhibition rescued osteogenesis. Most importantly, we demonstrated that calreticulin-containing cells had lower c-Src kinase activity, and this was accomplished via the Ca²⁺-homeostatic function of calreticulin. Specifically, lowering cytosolic [Ca²⁺] in calreticulin-containing osteogenic WT cells with BAPTA-AM, activated c-Src and impaired osteogenic differentiation. Conversely, increasing cytosolic [Ca²⁺] in crt^-/- cells with ionomycin deactivated c-Src kinase and restored osteogenesis. The immediate effector of calreticulin, the Ser/Thr phosphatase calcineurin, was less active in crt^-/- cells, however, its activity was rescued upon inhibition of c-Src activity by small molecule inhibitors. Finally, we showed that higher activity of calcineurin correlated with increased level of nuclear Runx2, a transcription factor that is the master regulator of osteogenesis. Collectively, our work has identified a novel pathway involving calreticulin regulated Ca²⁺ signalling via c-Src in osteogenic differentiation of embryonic stem cells.

Dasatinib Promotes Chondrogenic Differentiation of Human Mesenchymal Stem Cells via the Src/Hippo-YAP Signaling Pathway

Mesenchymal stem cells (MSCs) are progenitors of chondrocytes and could be used as a potential therapy for cartilage defects in diarthrodial joints. However, promoting chondrogenic differentiation of MSCs remains a daunting challenge. As a small molecular drug, dasatinib can promote MSC differentiation, although the exact mechanisms of chondrogenic differentiation are unclear. In this study, the differentiation of MSCs into osteoblasts, adipocytes, and chondrocytes was assessed by the protein and mRNA levels of osteoblast- and chondrocyte-related proteins using western blotting and real-time polymerase chain reaction, respectively. MSCs were induced to differentiate into chondrocytes or osteoblasts with or without dasatinib in vitro. The effects of dasatinib on cartilage regeneration were also assessed in vivo in a rabbit model of full-thickness cartilage defects using methacrylate gelatin hydrogel as scaffolds. Dasatinib promoted chondrogenic differentiation and inhibited osteogenic differentiation of MSCs. Furthermore, dasatinib significantly inhibited the expression of YAP and TAZ and the phosphorylation of Src, but it enhanced serine phosphorylation of YAP during the chondrogenic differentiation of MSCs in vitro. Inhibition of the Hippo pathway using XMU-MP-1 dramatically suppressed the serine phosphorylation of YAP and chondrogenic differentiation of MSCs. Moreover, we confirmed that the sustained release of dasatinib from the hydrogel promoted rabbit cartilage repair. The results demonstrated that dasatinib might promote chondrogenic differentiation of MSCs via the Src/Hippo-YAP signaling pathway and that hydrogel sustained-release dasatinib had a certain effect on the repair of cartilage defects.

Bone-Fracture-Targeted Dasatinib-Oligoaspartic Acid Conjugate Potently Accelerates Fracture Repair

Approximately 6.3 million bone fractures occur annually in the United States, resulting in considerable morbidity, deterioration in quality of life, loss of productivity and wages, and sometimes death (e.g., hip fractures). Although anabolic and antiresorptive agents have been introduced for treatment of osteoporosis, no systemically administered drug has been developed to accelerate the fracture-healing process. To address this need, we have undertaken to target a bone anabolic agent selectively to fracture surfaces in order to concentrate the drug's healing power directly on the fracture site. We report here that conjugation of dasatinib to a bone fracture-homing oligopeptide via a releasable linker reduces fractured femur healing times in mice by ∼60% without causing overt off-target toxicity or remodeling of nontraumatized bones. Thus, achievement of healthy bone density, normal bone volume, and healthy bone mechanical properties at the fracture site is realized after only 3-4 weeks in dasatinib-targeted mice, but it requires ∼8 weeks in PBS-treated controls. We conclude that targeting of dasatinib to bone fracture surfaces can significantly accelerate the healing process at dasatinib concentrations that are known to be safe in oncological applications.

Cell-based RNAi screening and high-content analysis in primary calvarian osteoblasts applied to identification of osteoblast differentiation regulators

Osteoblasts are responsible for the maintenance of bone homeostasis. Deregulation of their differentiation is etiologically linked to several bone disorders, making this process an important target for therapeutic intervention. Systemic identification of osteoblast regulators has been hampered by the unavailability of physiologically relevant in vitro systems suitable for efficient RNAi and for differentiation read-outs compatible with fluorescent microscopy-based high-content analysis (HCA). Here, we report a new method for identification of osteoblast differentiation regulators by combining siRNA transfection in physiologically relevant cells with high-throughput screening (HTS). Primary mouse calvarial osteoblasts were seeded in 384-well format and reverse transfected with siRNAs and their cell number and differentiation was assayed by HCA. Automated image acquisition allowed high-throughput analyses and classification of single cell features. The physiological relevance, reproducibility, and sensitivity of the method were validated using known regulators of osteoblast differentiation. The application of HCA to siRNAs against expression of 320 genes led to the identification of five potential suppressors and 60 activators of early osteoblast differentiation. The described method and the associated analysis pipeline are not restricted to RNAi-based screening, but can be adapted to large-scale drug HTS or to small-scale targeted experiments, to identify new critical factors important for early osteoblastogenesis.

Selective inhibition of Src family kinases by SU6656 increases bone mass by uncoupling bone formation from resorption in mice

Mice deficient in the non-receptor tyrosine kinase Src exhibit high bone mass due to impaired bone resorption and increased bone formation. Although several Src family kinase inhibitors inhibit bone resorption in vivo, they display variable effects on bone formation. SU6656 is a selective Src family kinase inhibitor with weaker activity towards the non-receptor tyrosine kinase Abl and receptor tyrosine kinases which are required for appropriate osteoblast proliferation, differentiation and function. Therefore, we sought to determine whether SU6656 could increase bone mass by inhibiting bone resorption and by stimulating bone formation, and to explore its mechanisms of action. Four-month-old female C57Bl/6J mice received intraperitoneal injections of either 25 mg/kg SU6656 or its vehicle every other day for 12 weeks. SU6656-treated mice exhibited increased bone mineral density, cortical thickness, cancellous bone volume and trabecular thickness. SU6656 inhibited bone resorption in mice as shown by reduced osteoclast number, and diminished expressions of Oscar, Trap5b and CtsK. SU6656 did not affect Rankl or Opg expressions. However, it blocked c-fms signaling, osteoclastogenesis and matrix resorption, and induced osteoclast apoptosis in vitro. In addition, SU6656 stimulated bone formation rates at trabecular, endosteal and periosteal bone envelopes, and increased osteoblast number in trabecular bone. SU6656 did not affect expressions of clastokines favoring bone formation in mice. However, it stimulated osteoblast differentiation and matrix mineralization by specifically facilitating BMP-SMAD signaling pathway in vitro. Knockdown of Src and Yes mimicked the stimulatory effect of SU6656 on osteoblast differentiation. In conclusion, SU6656 uncouples bone formation from resorption by inhibiting osteoclast development, function and survival, and by enhancing BMP-mediated osteoblast differentiation.

The Osteoclast in Bone Metastasis: Player and Target

Bone metastases are frequently the final fate of breast and prostate cancer patients. According to the definition of metastasis as an incurable disease, to date there are no effective treatments for tumor-associated bone metastases and this represents a real challenge for the researchers in the field. The bone is a heterogeneous environment that represents a fertile soil for tumor cells, supporting their growth. Among the different cell types present in the bone, in this review we will focus our attention on the osteoclasts, which are crucial players in the so called “vicious cycle”, a phenomenon triggered by tumor cells eventually leading to both tumor proliferation as well as bone deregulation, thus fueling the development of bone metastasis. The complex network, linking tumor cells to the bone by activating osteoclasts, represents a fruitful target for the treatment of bone metastases. In this review we will describe how tumor cells perturb the bone microenvironment by actively influencing osteoclast formation and activity. Moreover, we will describe the current antiresorptive drugs employed in the treatment of bone metastases as well as new, targeted therapies able to affect both cancer cells and osteoclasts.

Bone-targeted agents in multiple myeloma

Osteolytic bone disease, characterized by bone pain, increased risk of pathologic fractures, tumor-induced hypercalcemia known as skeletal-related events (SREs), is a frequent complication of patients with multiple myeloma (MM) and persists even in the absence of active disease, resulting in a major cause of morbidity and mortality. The interaction between myeloma cells and their surrounding cells in the bone marrow (BM) microenvironment promotes both myeloma cell growth and bone destruction and forms the vicious cycle of MM bone disease. Therefore, therapeutic strategies targeting the interaction between myeloma cells and cellular components including osteoclasts (OCs), stromal cells and osteoblasts (OBs) in the BM is crucial not only to attain tumor regression but also to prevent or delay the incidence of SREs, which leads to improve survival and quality of life in affected patients. Recently, several novel targets which act on components of the cycle for treating MM-associated bone disease have been identified in addition to current treatments including nitrogen-containing bisphosphonates. This review focuses on the overview of pathophysiology in MM-associated bone disease and summarizes its current clinical management. Several novel bone-targeted agents in preclinical setting will be also discussed.

Bone-Targeted Therapies in Cancer-Induced Bone Disease

Cancer-induced bone disease is a major source of morbidity and mortality in cancer patients. Thus, effective bone-targeted therapies are essential to improve disease-free, overall survival and quality of life of cancer patients with bone metastases. Depending of the cancer-type, bone metastases mainly involve the modulation of osteoclast and/or osteoblast activity by tumour cells. To inhibit metastatic bone disease effectively, it is imperative to understand its underlying mechanisms and identify the target cells for therapy. If the aim is to prevent bone metastasis, it is essential to target not only bone metastatic features in the tumour cells, but also tumour-nurturing bone microenvironment properties. The currently available bone-targeted agents mainly affect osteoclasts, inhibiting bone resorption (e.g. bisphosphonates, denosumab). Some agents targeting osteoblasts begin to emerge which target osteoblasts (e.g. romosozumab), activating bone formation. Moreover, certain drugs initially thought to target only osteoclasts are now known to have a dual action (activating osteoblasts and inhibiting osteoclasts, e.g. proteasome inhibitors). This review will focus on the evolution of bone-targeted therapies for the treatment of cancer-induced bone disease, summarizing preclinical and clinical findings obtained with anti-resorptive and bone anabolic therapies.

SRC kinase inhibition with saracatinib limits the development of osteolytic bone disease in multiple myeloma

Multiple myeloma (MM)-associated osteolytic bone disease is a major cause of morbidity and mortality in MM patients and the development of new therapeutic strategies is of great interest. The proto-oncogene SRC is an attractive target for such a strategy. In the current study, we investigated the effect of treatment with the SRC inhibitor saracatinib (AZD0530) on osteoclast and osteoblast differentiation and function, and on the development of MM and its associated bone disease in the 5TGM.1 and 5T2MM murine MM models. In vitro data showed an inhibitory effect of saracatinib on osteoclast differentiation, polarization and resorptive function. In osteoblasts, collagen deposition and matrix mineralization were affected by saracatinib. MM cell proliferation and tumor burden remained unaltered following saracatinib treatment and we could not detect any synergistic effects with drugs that are part of standard care in MM. We observed a marked reduction of bone loss after treatment of MM-bearing mice with saracatinib as reflected by a restoration of trabecular bone parameters to levels observed in naive control mice. Histomorphometric analyses support that this occurs through an inhibition of bone resorption. In conclusion, these data further establish SRC inhibition as a promising therapeutic approach for the treatment of MM-associated osteolytic bone disease.

BIGH3 Promotes Osteolytic Lesions in Renal Cell Carcinoma Bone Metastasis by Inhibiting Osteoblast Differentiation

BACKGROUND: Bone metastasis is common in renal cell carcinoma (RCC), and the lesions are mainly osteolytic. The mechanism of bone destruction in RCC bone metastasis is unknown. METHODS: We used a direct intrafemur injection of mice with bone-derived 786-O RCC cells (Bo-786) as an in vivo model to study if inhibition of osteoblast differentiation is involved in osteolytic bone lesions in RCC bone metastasis. RESULTS: We showed that bone-derived Bo-786 cells induced osteolytic bone lesions in the femur of mice. We examined the effect of conditioned medium of Bo-786 cells (Bo-786 CM) on both primary mouse osteoblasts and MC3T3-E1 preosteoblasts and found that Bo-786 CM inhibited osteoblast differentiation. Secretome analysis of Bo-786 CM revealed that BIGH3 (Beta ig h3 protein), also known as TGFBI (transforming growth factor beta-induced protein), is highly expressed. We generated recombinant BIGH3 and found that BIGH3 inhibited osteoblast differentiation in vitro. In addition, CM from Bo-786 BIGH3 knockdown cells (786-BIGH3 KD) reduced the inhibition of osteoblast differentiation compared to CM from vector control. Intrafemural injection of mice with 786-BIGH3 KD cells showed a reduction in osteolytic bone lesions compared to vector control. Immunohistochemical staining of 18 bone metastasis specimens from human RCC showed strong BIGH3 expression in 11/18 (61%) and moderate BIGH3 expression in 7/18 (39%) of the specimens. CONCLUSIONS: These results suggest that suppression of osteoblast differentiation by BIGH3 is one of the mechanisms that enhance osteolytic lesions in RCC bone metastasis, and raise the possibilty that treatments that increase bone formation may improve therapy outcomes.

Multiparameter Analysis of Off-Target Effects of Dasatinib on Bone Homeostasis in Patients With Newly Diagnosed Chronic Myelogenous Leukemia

BACKGROUND

We assessed patients with chronic myelogenous leukemia (CML) for serum calcium (Ca), phosphate (PO4), bone alkaline phosphatase, N-telopeptide (NTx), osteoprotegerin (OPG) levels, and trabecular bone area (TBA) in bone marrow (BM) specimens before and after treatment with dasatinib. We identified a significant increase in percentage of TBA in postdasatinib BM (P = .022). This suggests that dasatinib therapy can increase TBA without significant changes in bone and mineral metabolism. Interferences with bone homeostasis and mineral metabolism have been described in patients receiving imatinib for CML or gastrointestinal stromal tumors. Dasatinib is a potent second-generation tyrosine kinase inhibitor designed to inhibit ABL and SRC kinases while also interfering with the c-Kit, platelet-derived growth factor receptor, and STAT5 pathways.

PATIENTS AND METHODS

We used a multiparameter approach to examine the off-target effects of dasatinib in 30 patients with CML treated between 2009 and 2012. We recorded serum Ca and PO4 levels, analyzed markers of bone formation (bone alkaline phosphatase/bone-specific alkaline phosphatase [BAP]) and bone resorption (NTx), measured OPG levels, and digitally analyzed changes in TBA in paired BM biopsy specimens before and after treatment. We correlated all findings with each other and with the results of conventional cytogenetic and molecular analyses.

RESULTS

We identified a significant increase in the percentage of TBA in postdasatinib BM biopsy specimens (P = .022) and noted a decrease in serum OPG levels in 75% of patients. Ca, PO4, BAP, and NTx levels remained steady, without significant changes. There was no correlation between biomarker levels, percentage of TBA, and/or cytogenetic or molecular response.

CONCLUSION

These findings suggest that dasatinib therapy (within the therapeutic range) can increase trabecular bone, without causing significant changes in bone and mineral metabolism. Nonetheless, monitoring of bone health and skeletal integrity should be included into the long-term management of patients treated with dasatinib to further enhance our understanding of its safety profile and its potential role as a treatment modality for other bone diseases.

Differentially activated Src kinase in chemo-naïve human primary osteosarcoma cells and effects of a Src kinase inhibitor

The therapeutic treatment of osteosarcoma (OS), a rare malignant teenage cancer of the skeletal system, still represents a great challenge as patient survival after conventional protocol chemotherapy treatment has not improved in the last four decades leaving poor patient prognoses. Therefore, many efforts have been done to find increasingly reliable OS cell models and to identify "druggable" targets in OS, in order to identify novel effective therapeutic approaches and treatment strategies. In this contest, the more successful use of patient-derived cell cultures in respect to human commercial lines and findings of Src kinase deregulation in cancer, prompted us to study for the first time the activation state of Src and the potential activity of our Src inhibitor SI-83 in a number of chemo-naïve patient-derived primary OS cells. We here demonstrate that Src is hyperactivated in OS cells in respect to the nonmalignant counterpart and that SI-83 is able to strongly decrease cell viability, proliferation, Src₄₁₆ phosphorylation, and cell migration. © 2017 BioFactors, 43(6):801-811, 2017.

Cabozantinib-induced osteoblast secretome promotes survival and migration of metastatic prostate cancer cells in bone

Therapies that target cancer cells may have unexpected effects on the tumor microenvironment that affects therapy outcomes or render therapy resistance. Prostate cancer (PCa) bone metastasis is uniquely associated with osteoblastic bone lesions and treatment with cabozantinib, a VEGFR-2 and MET inhibitor, leads to a reduction in number and/or intensity of lesions on bone scans. However, resistance to cabozantinib therapy inevitably occurs. We examined the effect of cabozantinib on osteoblast differentiation and secretion in the context of therapy resistance. We showed that primary mouse osteoblasts express VEGFR2 and MET and cabozantinib treatment decreased osteoblast proliferation but enhanced their differentiation. A genome-wide analysis of transcriptional responses of osteoblasts to cabozantinib identified a set of genes accounting for inhibition of proliferation and stimulation of differentiation, and a spectrum of secreted proteins induced by cabozantinib, including pappalysin, IGFBP2, WNT 16, and DKK1. We determined that these proteins were upregulated in the conditioned medium of cabozantinib-treated osteoblasts (CBZ-CM) compared to control CM. Treatment of C4-2B4 or PC3-mm2 PCa cells with CBZ-CM increased the anchorage-independent growth and migration of these PCa cells compared to cells treated with control CM. These results suggest that the effect of cabozantinib on the tumor microenvironment may increase tumor cell survival and cause therapy resistance.

The Src family kinase inhibitor dasatinib delays pain-related behaviour and conserves bone in a rat model of cancer-induced bone pain

Pain is a severe and debilitating complication of metastatic bone cancer. Current analgesics do not provide sufficient pain relief for all patients, creating a great need for new treatment options. The Src kinase, a non-receptor protein tyrosine kinase, is implicated in processes involved in cancer-induced bone pain, including cancer growth, osteoclastic bone degradation and nociceptive signalling. Here we investigate the role of dasatinib, an oral Src kinase family and Bcr-Abl tyrosine kinase inhibitor, in an animal model of cancer-induced bone pain. Daily administration of dasatinib (15 mg/kg, p.o.) from day 7 after inoculation of MRMT-1 mammary carcinoma cells significantly attenuated movement-evoked and non-evoked pain behaviour in cancer-bearing rats. Radiographic - and microcomputed tomographic analyses showed significantly higher relative bone density and considerably preserved bone micro-architecture in the dasatinib treated groups, suggesting a bone-preserving effect. This was supported by a significant reduction of serum TRACP 5b levels in cancer-bearing rats treated with 15 mg/kg dasatinib. Furthermore, immunoblotting of lumbar spinal segments showed an increased activation of Src but not the NMDA receptor subunit 2B. These findings support a role of dasatinib as a disease modifying drug in pain pathologies characterized by increased osteoclast activity, such as bone metastases.

Basic FGF and PDGF-BB synergistically stimulate hyaluronan and IL-6 production by orbital fibroblasts

Orbital fibroblast activation is a central pathologic feature of Graves' Ophthalmopathy (GO). Basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) have been proposed to contribute to GO, but their effects on orbital fibroblasts are largely unknown. We found that bFGF stimulated proliferation and hyaluronan production, but not IL-6 production by orbital fibroblasts, while VEGF hardly affected orbital fibroblast activity. Remarkably, co-stimulation of orbital fibroblasts with bFGF and PDGF-BB synergistically enhanced IL-6 and hyaluronan production and displayed an additive effect on proliferation compared to either bFGF or PDGF-BB stimulation. Nintedanib, a FGF- and PDGF-receptor targeting drug, more efficiently blocked bFGF + PDGF-BB-induced IL-6 and hyaluronan production than dasatinib that only targets PDGF-receptor. In conclusion, bFGF may contribute to orbital inflammation and tissue remodeling in GO, especially through synergistic interaction with PDGF-BB. Multi-target therapy directed at the bFGF and PDGF pathways may potentially be of interest for the treatment of GO.

Characterization of anti-leukemia components from Indigo naturalis using comprehensive two-dimensional K562/cell membrane chromatography and in silico target identification

Traditional Chinese Medicine (TCM) has been developed for thousands of years and has formed an integrated theoretical system based on a large amount of clinical practice. However, essential ingredients in TCM herbs have not been fully identified, and their precise mechanisms and targets are not elucidated. In this study, a new strategy combining comprehensive two-dimensional K562/cell membrane chromatographic system and in silico target identification was established to characterize active components from Indigo naturalis, a famous TCM herb that has been widely used for the treatment of leukemia in China, and their targets. Three active components, indirubin, tryptanthrin and isorhamnetin, were successfully characterized and their anti-leukemia effects were validated by cell viability and cell apoptosis assays. Isorhamnetin, with undefined cancer related targets, was selected for in silico target identification. Proto-oncogene tyrosine-protein kinase (Src) was identified as its membrane target and the dissociation constant (Kd) between Src and isorhamnetin was 3.81 μM. Furthermore, anti-leukemia effects of isorhamnetin were mediated by Src through inducing G2/M cell cycle arrest. The results demonstrated that the integrated strategy could efficiently characterize active components in TCM and their targets, which may bring a new light for a better understanding of the complex mechanism of herbal medicines.

Emerging drugs for the treatment of bone metastasis

INTRODUCTION

Bone metastases are virtually incurable resulting in significant disease morbidity, reduced quality of life and mortality. Bone provides a unique microenvironment whose local interactions with tumor cells offer novel targets for therapeutic interventions. Increased understanding of the pathogenesis of bone disease has led to the discovery and clinical utility of bone-targeted agents other than bisphosphonates and denosumab, currently, the standard of care in this setting.

AREAS COVERED

In this review, we present the recent advances in molecular targeted therapies focusing on therapies that inhibit bone resorption and/or stimulate bone formation and novel anti-tumoral agents that exerts significant effects on skeletal metastases, nowadays available in clinical practice or in phase of development.

EXPERT OPINION

New emergent bone target therapies radium-223, mTOR inhibitors, anti-androgens have demonstrated the ability to increase overall survival in bone metastatic patients, other compounds, such as ET-1 and SRC inhibitors, up to now failed to clearly confirm in clinical trials their promising preclinical data.

Src enhances osteogenic differentiation through phosphorylation of Osterix

Osterix, a zinc-finger transcription factor, is required for osteoblast differentiation and new bone formation during embryonic development. The c-Src of tyrosine kinase is involved in a variety of cellular signaling pathways, leading to the induction of DNA synthesis, cell proliferation, and cytoskeletal reorganization. Src activity is tightly regulated and its dysregulation leads to constitutive activation and cellular transformation. The function of Osterix can be also modulated by post-translational modification. But the precise molecular signaling mechanisms between Osterix and c-Src are not known. In this study we investigated the potential regulation of Osterix function by c-Src in osteoblast differentiation. We found that c-Src activation increases protein stability, osteogenic activity and transcriptional activity of Osterix. The siRNA-mediated knockdown of c-Src decreased the protein levels and transcriptional activity of Osterix. Conversely, Src specific inhibitor, SU6656, decreased the protein levels and transcriptional activity of Osterix. The c-Src interacts with and phosphorylates Osterix. These results suggest that c-Src signaling modulates osteoblast differentiation at least in part through Osterix.

Src signaling pathways in prostate cancer

Knowledge of the molecular events that contribute to prostate cancer progression has created opportunities to develop novel therapy strategies. It is now well established that c-Src, a non-receptor tyrosine kinase, regulates a complex signaling network that drives the development of castrate-resistance and bone metastases, events that signal the lethal phenotype of advanced disease. Preclinical studies have established a role for c-Src and Src Family Kinases (SFKs) in proliferation, angiogenesis, invasion and bone metabolism, thus implicating Src signaling in both epithelial and stromal mechanisms of disease progression. A number of small molecule inhibitors of SFK now exist, many of which have demonstrated efficacy in preclinical models and several that have been tested in patients with metastatic castrate-resistant prostate cancer. These agents have demonstrated provocative clinic activity, particularly in modulating the bone microenvironment in a therapeutically favorable manner. Here, we review the discovery and basic biology of c-Src and further discuss the role of SFK inhibitors in the treatment of advanced prostate cancer.

Castration-resistant prostate cancer bone metastasis response measured by 18F-fluoride PET after treatment with dasatinib and correlation with progression-free survival: results from American College of Radiology Imaging Network 6687

(18)F-fluoride PET quantitatively images bone metabolism and may serve as a pharmacodynamic assessment for systemic therapy such as dasatinib, a potent SRC kinase inhibitor, with activity in bone.

METHODS

This was an imaging companion trial (American College of Radiology Imaging Network [ACRIN] 6687) to a multicenter metastatic castration-resistant prostate cancer (CRPC) tissue biomarker-guided therapeutic trial (NCT00918385). Men with bone metastatic CRPC underwent (18)F-fluoride PET before and 12 weeks after initiation of dasatinib (100 mg daily). Dynamic imaging was performed over a 15-cm field of view for trial assessments. The primary endpoint was to determine whether changes in (18)F-fluoride incorporation in tumor and normal bone occurred in response to dasatinib. Other endpoints included differential effect of dasatinib between (18)F-fluoride incorporation in tumor and normal bone, (18)F-fluoride transport in bone metastases, correlation with progression-free survival (PFS), prostate-specific antigen, and markers of bone turnover.

RESULTS

Eighteen participants enrolled, and 17 underwent interpretable baseline (18)F-fluoride PET imaging before initiation of dasatinib. Twelve of 17 patients underwent on-treatment PET imaging. Statistically significant changes in response to dasatinib were identified by the SUVmaxavg (average of maximum standardized uptake value [SUVmax] for up to 5 tumors within the dynamic field of view) in bone metastases (P = 0.0002), with a significant differential (18)F-fluoride PET response between tumor and normal bone (P < 0.0001). Changes in (18)F-fluoride incorporation in bone metastases had borderline correlation with PFS by SUVmaxavg (hazard ratio, 0.91; 95% confidence interval, 0.82-1.00; P = 0.056). Changes by SUVmaxavg correlated with bone alkaline phosphatase (P = 0.0014) but not prostate-specific antigen (P = 0.47).

CONCLUSION

This trial provides evidence of the ability (18)F-fluoride PET to delineate treatment response of dasatinib in CRPC bone metastases with borderline correlation with PFS.

Secretome analysis of an osteogenic prostate tumor identifies complex signaling networks mediating cross-talk of cancer and stromal cells within the tumor microenvironment

A distinct feature of human prostate cancer (PCa) is the development of osteoblastic (bone-forming) bone metastases. Metastatic growth in the bone is supported by factors secreted by PCa cells that activate signaling networks in the tumor microenvironment that augment tumor growth. To better understand these signaling networks and identify potential targets for therapy of bone metastases, we characterized the secretome of a patient-derived xenograft, MDA-PCa-118b (PCa-118b), generated from osteoblastic bone lesion. PCa-118b induces osteoblastic tumors when implanted either in mouse femurs or subcutaneously. To study signaling molecules critical to these unique tumor/microenvironment-mediated events, we performed mass spectrometry on conditioned media of isolated PCa-118b tumor cells, and identified 26 secretory proteins, such as TGF-β2, GDF15, FGF3, FGF19, CXCL1, galectins, and β2-microglobulin, which represent both novel and previously published secreted proteins. RT-PCR using human versus mouse-specific primers showed that TGFβ2, GDF15, FGF3, FGF19, and CXCL1 were secreted from PCa-118b cells. TGFβ2, GDF15, FGF3, and FGF19 function as both autocrine and paracrine factors on tumor cells and stromal cells, that is, endothelial cells and osteoblasts. In contrast, CXCL1 functions as a paracrine factor through the CXCR2 receptor expressed on endothelial cells and osteoblasts. Thus, our study reveals a complex PCa bone metastasis secretome with paracrine and autocrine signaling functions that mediate cross-talk among multiple cell types within the tumor microenvironment.

c-Abl tyrosine kinase promotes adipocyte differentiation by targeting PPAR-gamma 2

Adipocyte differentiation, or adipogenesis, is a complex and highly regulated process. A recent proteomic analysis has predicted that the nonreceptor tyrosine kinase Abelson murine leukemia viral oncogene (c-Abl) is a putative key regulator of adipogenesis, but the underlying mechanism remained obscure. We found that c-Abl was activated during the early phase of mouse 3T3-L1 preadipocyte differentiation. Moreover, c-Abl activity was essential and its inhibition blocked differentiation to mature adipocytes. c-Abl directly controlled the expression and activity of the master adipogenic regulator peroxisome proliferator-activator receptor gamma 2 (PPARγ2). PPARγ2 physically associated with c-Abl and underwent phosphorylation on two tyrosine residues within its regulatory activation function 1 (AF1) domain. We demonstrated that this process positively regulates PPARγ2 stability and adipogenesis. Remarkably, c-Abl binding to PPARγ2 required the Pro12 residue that has a phenotypically well-studied common human genetic proline 12 alanine substitution (Pro12Ala) polymorphism. Our findings establish a critical role for c-Abl in adipocyte differentiation and explain the behavior of the known Pro12Ala polymorphism.

A randomized phase II study of cediranib alone versus cediranib in combination with dasatinib in docetaxel resistant, castration resistant prostate cancer patients

BACKGROUND

Activation of the vascular endothelial growth factor receptor (VEGFR) and the oncogenic Src pathway has been implicated in the development of castration-resistant prostate cancer (CRPC) in preclinical models. Cediranib and dasatinib are multi-kinase inhibitors targeting VEGFR and Src respectively. Phase II studies of cediranib and dasatinib in CRPC have shown single agent activity.

METHODS

Docetaxel-pretreated CRPC patients were randomized to arm A: cediranib alone (20 mg/day) versus arm B: cediranib (20 mg/day) plus dasatinib (100 mg/day) given orally on 4-week cycles. Primary endpoint was 12-week progression-free survival (PFS) as per the Prostate Cancer Clinical Trials Working Group (PCWG2). Patient reported outcomes were evaluated using Functional Assessment of Cancer Therapy-Prostate (FACT-P) and Present Pain Intensity (PPI) scales. Correlative studies of bone turnover markers (BTM), including bone alkaline phosphate (BAP) and serum beta-C telopeptide (B-CTx) were serially assayed. Results A total of 22 patients, 11 per arm, were enrolled. Baseline demographics were similar in both arms. Median number of cycles =4 in arm A (range 1-12) and 2 in arm B (range 1-9). Twelve-week PFS was 73 % in arm A versus 18 % in arm B (p = 0.03). Median PFS in months (arm A versus B) was: 5.2 versus 2.6 (95 % CI: 1.9-6.5 versus 1.4-not reached). Most common grade 3 toxicities were hypertension, anemia and thrombocytopenia in arm A and hypertension, diarrhea and fatigue in arm B. One treatment-related death (retroperitoneal hemorrhage) was seen in arm A. FACT-P and PPI scores did not significantly change in either arm. No correlation between BTM and PFS was seen in either arm.

CONCLUSIONS

Although limited by small numbers, this randomized study showed that the combination of VEGFR and Src targeted therapy did not result in improved efficacy and may be associated with a worse outcome than VEGFR targeted therapy alone in patients with CRPC. ClinicalTrials.gov number: NCT01260688.

Bone-targeting agents in prostate cancer

Bone metastases are present in the vast majority of men with advanced prostate cancer, representing the main cause for morbidity and mortality. Recurrent or metastatic disease is managed initially with androgen deprivation but the majority of the patients eventually will progress to castration-resistant prostate cancer, with patients developing bone metastases in most of the cases. Survival and growth of the metastatic prostate cancer cells is dependent on a complex microenvironment (onco-niche) that includes the osteoblasts, the osteoclasts, the endothelium, and the stroma. This review summarizes agents that target the pathways involved in this complex interaction between prostate cancer and bone microenvironment and aim to transform lethal metastatic prostate cancer into a chronic disease.

Autophagy as a modulator and target in prostate cancer

Autophagy, or 'self-eating', is an adaptive process that enables cells to cope with metabolic, toxic, and even infectious stressors. Although the adaptive capability of autophagy is generally considered beneficial, autophagy can also enhance nutrient utilization and improve growth characteristics of cancer cells. Moreover, autophagy can promote greater cellular robustness in the context of therapeutic intervention. In advanced prostate cancer, preclinical data provide evidence that autophagy facilitates both disease progression and therapeutic resistance. Notably, androgen deprivation therapy, taxane-based chemotherapy, targeted kinase inhibition, and nutrient restriction all induce significant cellular distress and, subsequently, autophagy. Understanding the context-dependent role of autophagy in cancer development and treatment resistance has the potential to improve current treatment of advanced prostate cancer. Indeed, preclinical studies have shown that the pharmacological inhibition of autophagy (with agents including chloroquine, hydroxychloroquine, metformin, and desmethylclomipramine) can enhance the cell-killing effect of cancer therapeutics, and a number of these agents are currently under investigation in clinical trials. However, many of these autophagy modulators are relatively nonspecific, and cytotoxicity in noncancerous tissues is still a concern. Moving forward, refinement of autophagy modulation is needed.

SRC: marker or actor in prostate cancer aggressiveness

A key question for urologic practitioners is whether an apparently organ-confined prostate cancer (PCa) is actually aggressive or not. The dilemma is to specifically identify among all prostate tumors the very aggressive high-grade cancers that will become life-threatening by developing extra-prostatic invasion and metastatic potential and the indolent cancers that will never modify a patient's life expectancy. A choice must be made between several therapeutic options to achieve the optimal personalized management of the disease that causes as little harm as possible to patients. Reliable clinical, biological, or pathological markers that would enable distinctions to be made between aggressive and indolent PCas in routine practice at the time of initial diagnosis are still lacking. The molecular mechanisms that explain why a PCa is aggressive or not are also poorly understood. Among the potential markers and/or actors in PCa aggressiveness, Src and other members of the Src kinase family, are valuable candidates. Activation of Src-dependent intracellular pathways is frequently observed in PCa. Indeed, Src is at the cross-roads of several pathways [including androgen receptor (AR), TGFbeta, Bcl-2, Akt/PTEN or MAPK, and ERK …], and is now known to influence some of the cellular and tissular events that accompany tumor progression: cell proliferation, cell motility, invasion, epithelial-to-mesenchymal transition, resistance to apoptosis, angiogenesis, neuroendocrine differentiation, and metastatic spread. Recent work even suggests that Src could also play a part in PCa initiation in coordination with the AR. The aim of this review is to gather data that explore the links between the Src kinase family and PCa progression and aggressiveness.

Src inhibition potentiates antitumoral effect of paclitaxel by blocking tumor-induced angiogenesis

The protein kinase Src is frequently over-activated in advanced cancers where it modulates the signaling transduction cascade of several growth factors. The feasibility of combination treatment of Src inhibitors with chemotherapy is currently under investigation. We evaluated the anti-tumoral effect of paclitaxel (PTX) in combination with S13, a tyrosine kinase inhibitor with a prevalent specificity for Src, in a hormone-insensible prostate cancer (PCa) cell model. In vivo, combination treatment with PTX and S13 reduced dramatically PCa tumor growth with a relevant difference in the density of new blood vessels with respect to control and single treatments. This reduction was determined by a concomitant impairment of endothelial cell migration and of VEGF release by cancer cells. In fact, S13, when used alone, was sufficient to reduce tubule formation in vivo, and to inhibit VEGFR2 activation and FAK expression in endothelial cells. In addition, the combination treatment determined a significant reduction in ROS production and HIF-1 stabilization in PCa cells respect to single treatments with S13 or PTX. In conclusion, Src-inhibition could be an effective therapeutic strategy aimed at supporting the anti-angiogenic action of PTX in aggressive PCa.

Multiple myeloma mesenchymal stromal cells: Contribution to myeloma bone disease and therapeutics

Multiple myeloma is a hematological malignancy in which clonal plasma cells proliferate and accumulate within the bone marrow. The presence of osteolytic lesions due to increased osteoclast (OC) activity and suppressed osteoblast (OB) function is characteristic of the disease. The bone marrow mesenchymal stromal cells (MSCs) play a critical role in multiple myeloma pathophysiology, greatly promoting the growth, survival, drug resistance and migration of myeloma cells. Here, we specifically discuss on the relative contribution of MSCs to the pathophysiology of osteolytic lesions in light of the current knowledge of the biology of myeloma bone disease (MBD), together with the reported genomic, functional and gene expression differences between MSCs derived from myeloma patients (pMSCs) and their healthy counterparts (dMSCs). Being MSCs the progenitors of OBs, pMSCs primarily contribute to the pathogenesis of MBD because of their reduced osteogenic potential consequence of multiple OB inhibitory factors and direct interactions with myeloma cells in the bone marrow. Importantly, pMSCs also readily contribute to MBD by promoting OC formation and activity at various levels (i.e., increasing RANKL to OPG expression, augmenting secretion of activin A, uncoupling ephrinB2-EphB4 signaling, and through augmented production of Wnt5a), thus further contributing to OB/OC uncoupling in osteolytic lesions. In this review, we also look over main signaling pathways involved in the osteogenic differentiation of MSCs and/or OB activity, highlighting amenable therapeutic targets; in parallel, the reported activity of bone-anabolic agents (at preclinical or clinical stage) targeting those signaling pathways is commented.

Human placenta-derived mesenchymal stem cells promote hepatic regeneration in CCl4 -injured rat liver model via increased autophagic mechanism

Mesenchymal stem cells (MSCs) have great potential for cell therapy in regenerative medicine, including liver disease. Even though ongoing research is dedicated to the goal of bringing MSCs to clinical applications, further understanding of the complex underlying mechanisms is required. Autophagy, a type II programmed cell death, controls cellular recycling through the lysosomal system in damaged cells or tissues. However, it is still unknown whether MSCs can trigger autophagy to enhance regeneration and/or to provide a therapeutic effect as cellular survival promoters. We therefore investigated autophagy's activation in carbon tetrachloride (CCl4 )-injured rat liver following transplantation with chorionic plate-derived MSCs (CP-MSCs) isolated from placenta. The expression markers for apoptosis, autophagy, cell survival, and liver regeneration were analyzed. Whereas caspase 3/7 activities were reduced (p < .05), the expression levels of hypoxia-inducible factor-1α (HIF-1α) and factors for autophagy, survival, and regeneration were significantly increased by CP-MSCs transplantation. Decreased necrotic cells (p < .05) and increased autophagic signals (p < .005) were observed in CCl4 -treated primary rat hepatocytes during in vitro coculture with CP-MSCs. Furthermore, the upregulation of HIF-1α promotes the regeneration of damaged hepatic cells through an autophagic mechanism marked by increased levels of light chain 3 II (LC 3II). These results suggest that the administration of CP-MSCs promotes repair by systemically concomitant mechanisms involving HIF-1α and autophagy. These findings provide further understanding of the mechanisms involved in these processes and will help develop new cell-based therapeutic strategies for regenerative medicine in liver disease.

Dasatinib accelerates valproic acid-induced acute myeloid leukemia cell death by regulation of differentiation capacity

Dasatinib is a compound developed for chronic myeloid leukemia as a multi-targeted kinase inhibitor against wild-type BCR-ABL and SRC family kinases. Valproic acid (VPA) is an anti-epileptic drug that also acts as a class I histone deacetylase inhibitor. The aim of this research was to determine the anti-leukemic effects of dasatinib and VPA in combination and to identify their mechanism of action in acute myeloid leukemia (AML) cells. Dasatinib was found to exert potent synergistic inhibitory effects on VPA-treated AML cells in association with G₁ phase cell cycle arrest and apoptosis induction involving the cleavage of poly (ADP-ribose) polymerase and caspase-3, -7 and -9. Dasatinib/VPA-induced cell death thus occurred via caspase-dependent apoptosis. Moreover, MEK/ERK and p38 MAPK inhibitors efficiently inhibited dasatinib/VPA-induced apoptosis. The combined effect of dasatinib and VPA on the differentiation capacity of AML cells was more powerful than the effect of each drug alone, being sufficiently strong to promote AML cell death through G₁ cell cycle arrest and caspase-dependent apoptosis. MEK/ERK and p38 MAPK were found to control dasatinib/VPA-induced apoptosis as upstream regulators, and co-treatment with dasatinib and VPA to contribute to AML cell death through the regulation of differentiation capacity. Taken together, these results indicate that combined dasatinib and VPA treatment has a potential role in anti-leukemic therapy.

MicroRNA-4723 inhibits prostate cancer growth through inactivation of the Abelson family of nonreceptor protein tyrosine kinases

The Abelson (c-Abl) proto-oncogene encodes a highly conserved nonreceptor protein tyrosine kinase that plays a role in cell proliferation, differentiation, apoptosis and cell adhesion. c-Abl represents a specific anti-cancer target in prostate cancer as aberrant activity of this kinase has been implicated in the stimulation of prostate cancer growth and progression. However, the mechanism of regulation of c-Abl is not known. Here we report that Abl kinases are regulated by a novel microRNA, miR-4723, in prostate cancer. Expression profiling of miR-4723 expression in a cohort of prostate cancer clinical specimens showed that miR-4723 expression is widely attenuated in prostate cancer. Low miR-4723 expression was significantly correlated with poor survival outcome and our analyses suggest that miR-4723 has significant potential as a disease biomarker for diagnosis and prognosis in prostate cancer. To evaluate the functional significance of decreased miR-4723 expression in prostate cancer, miR-4723 was overexpressed in prostate cancer cell lines followed by functional assays. miR-4723 overexpression led to significant decreases in cell growth, clonability, invasion and migration. Importantly, miR-4723 expression led to dramatic induction of apoptosis in prostate cancer cell lines suggesting that miR-4723 is a pro-apoptotic miRNA regulating prostate carcinogenesis. Analysis of putative miR-4723 targets showed that miR-4723 targets integrin alpha 3 and Methyl CpG binding protein in addition to Abl1 and Abl2 kinases. Further, we found that the expression of Abl kinase is inversely correlated with miR-4723 expression in prostate cancer clinical specimens. Also, Abl1 knockdown partially phenocopies miR-4723 reexpression in prostate cancer cells suggesting that Abl is a functionally relevant target of miR-4723 in prostate cancer. In conclusion, we have identified a novel microRNA that mediates regulation of Abl kinases in prostate cancer. This study suggests that miR-4723 may be an attractive target for therapeutic intervention in prostate cancer.

Dasatinib inhibits mammary tumour development in a genetically engineered mouse model

Src family kinase activity is elevated in a number of human cancers including breast cancer. This increased activity has been associated with aggressive disease and poor prognosis. Src inhibitors are currently in clinical development with a number of trials currently assessing their activity in breast cancer. However, the results to date have been disappointing and a further evaluation of the preclinical effects of Src inhibitors is required to help establish whether these agents will be useful in the treatment of breast cancer. In this study we investigate the effects of dasatinib, which is a potent inhibitor of Src family kinases, on the initiation and development of breast cancer in a genetically engineered model of the disease. The mouse model utilized is driven by expression of activated ErbB-2 under the transcriptional control of its endogenous promoter coupled with conditional loss of Pten under the control of Cre recombinase expressed by the BLG promoter. We show that daily oral administration of dasatinib delays tumour onset and increases overall survival but does not inhibit the proliferation of established tumours. The striking difference between the dasatinib-treated group of tumours and the vehicle controls was the prominent squamous metaplasia that was seen in six out of 11 dasatinib-treated tumours. This was accompanied by a dramatic up-regulation of both E-cadherin and β-catenin and down-regulation of ErbB-2 in the dasatinib-treated tumours. Dasatinib also inhibited both the migration and the invasion of tumour-derived cell lines in vitro. Together these data support the argument that benefits of Src inhibitors may predominate in early or even pre-invasive disease.

Increased serum insulin-like growth factor-1 levels are associated with prolonged response to dasatinib-based regimens in metastatic prostate cancer

BACKGROUND

Dasatinib, an inhibitor of Src-family kinases, combined with docetaxel in men with castrate-resistant prostate cancer (CRPC), affects bone turnover markers in a phase I/II clinical trial in metastatic CRPC. Only a subset of men benefit from this therapy, and predictive markers are lacking. We hypothesized a role for insulin-like growth factor-1 (IGF-1) as a predictive marker, since IGF-1 is important in both prostate cancer progression and bone development. Hence, we determined the association of IGF-1 expression to treatment response, and whether this expression resulted from tumor cells, the microenvironment, or their interactions.

METHODS

We measured serum IGF-1 levels in men with CRPC treated with dasatinib plus docetaxel. To investigate the source of IGF-1, we utilized two different mouse models harboring human prostate cancer cells, and used species-specific IGF-1 ELISA kits (mouse vs. human).

RESULTS

In men with CRPC, an increase in IGF-1 levels after one cycle of treatment with dasatinib and docetaxel is associated with a higher response rate and longer duration of treatment. Xenograft experiments with subcutaneous and intratibial injection of prostate cancer cells suggest that direct interaction of prostate cancer cells with bone microenvironment is necessary for IGF-1 induction, is entirely host-derived, and occurs only in mice that respond to dasatinib-based therapy.

CONCLUSION

Our results support a role for serum IGF-1 as a potential biomarker for benefit from dasatinib-based combination treatments in CRPC.

Denosumab in breast cancer treatment

The bone is the most common site to which breast cancer metastasises. Recently, denosumab, a fully human monoclonal antibody that binds to receptor activator of nuclear factor kappa-B ligand (RANKL) has been developed as a new targeted bone therapy. In a large randomized phase III study with a head-to-head comparison of denosumab to zoledronic acid in patients with bone metastases of breast cancer, denosumab significantly delayed the time to first skeletal related event. In the adjuvant setting denosumab significantly increased bone mineral density compared to placebo in a phase III study in patients treated with aromatase inhibitors. Preclinical data suggest an effect of denosumab on tumour growth and even on carcinogenesis. This review describes the current indications for denosumab in the various settings of breast cancer treatment, with special attention for efficacy, short and long term toxicity and other relevant issues for clinical practice. Furthermore possible and necessary future research questions are proposed.

Elevated TNFR1 and serotonin in bone metastasis are correlated with poor survival following bone metastasis diagnosis for both carcinoma and sarcoma primary tumors

PURPOSE

There is an urgent need for therapies that will reduce the mortality of patients with bone metastasis. In this study, we profiled the protein signal pathway networks of the human bone metastasis microenvironment. The goal was to identify sets of interacting proteins that correlate with survival time following the first diagnosis of bone metastasis.

EXPERIMENTAL DESIGN

Using Reverse Phase Protein Microarray technology, we measured the expression of 88 end points in the bone microenvironment of 159 bone metastasis tissue samples derived from patients with primary carcinomas and sarcomas.

RESULTS

Metastases originating from different primary tumors showed similar levels of cell signaling across tissue types for the majority of proteins analyzed, suggesting that the bone microenvironment strongly influences the metastatic tumor signaling profiles. In a training set (72 samples), TNF receptor 1, alone (P = 0.0013) or combined with serotonin (P = 0.0004), TNFα (P = 0.0214), and RANK (P = 0.0226), was associated with poor survival, regardless of the primary tumor of origin. Results were confirmed by (i) analysis of an independent validation set (71 samples) and (ii) independent bioinformatic analysis using a support vector machine learning model. Spearman rho analysis revealed a highly significant number of interactions intersecting with ERα S118, serotonin, TNFα, RANKL, and matrix metalloproteinase in the bone metastasis signaling network, regardless of the primary tumor. The interaction network pattern was significantly different in the short versus long survivors.

CONCLUSIONS

TNF receptor 1 and neuroendocrine-regulated protein signal pathways seem to play an important role in bone metastasis and may constitute a novel drug-targetable mechanism of seed-soil cross talk in bone metastasis.

Src family kinase inhibitor PP2 accelerates differentiation in human intestinal epithelial cells

The proto-oncogene Src is an important protein tyrosine kinase involved in signaling pathways that control cell adhesion, growth, migration and survival. Here, we investigated the involvement of Src family kinases (SFKs) in human intestinal cell differentiation. We first observed that Src activity peaked in early stages of Caco-2/15 cell differentiation. Inhibition of SFKs with PP2, a selective SFK inhibitor, accelerated the overall differentiation program. Interestingly, all polarization and terminal differentiation markers tested, including sucrase-isomaltase, lactase-phlorizin hydrolase and E and Li-cadherins were found to be significantly up-regulated after only 3 days of treatment in the newly differentiating cells. Further investigation of the effects of PP2 revealed a significant up-regulation of the two main intestinal epithelial cell-specific transcription factors Cdx2 and HNF1α and a reduction of polycomb PRC2-related epigenetic repressing activity as measured by a decrease in H3K27me3, two events closely related to the control of cell terminal differentiation in the intestine. Taken together, these data suggest that SFKs play a key role in the control of intestinal epithelial cell terminal differentiation.

Combined Inhibition of IGF-1R/IR and Src family kinases enhances antitumor effects in prostate cancer by decreasing activated survival pathways

Background

Treatment of metastatic prostate cancer (PCa) with single agents has shown only modest efficacy. We hypothesized dual inhibition of different pathways in PCa results in improved tumor inhibition. The Src family kinases (SFK) and insulin-like growth factor-1 (IGF-1) signaling axes are aberrantly activated in both primary PCa and bone metastases and regulate distinct and overlapping functions in PCa progression. We examined the antitumor effects of combined inhibition of these pathways.

Materials and Methods

Src andIGF-1 receptor (IGF-1R) inhibition was achieved in vitro by short hairpin (sh)RNA and in vitro and in vivo by small molecule inhibitors (dasatinib and BMS-754807, against SFK and IGF-1R/Insulin Receptor(IR), respectively).

Results

In vitro, inhibition of IGF-1 signaling affected cell survival and proliferation. SFK blockade alone had modest effects on proliferation, but significantly enhanced the IGF-1R blockade. These findings correlated with a robust inhibition of IGF-1-induced Akt1 phophorylation by dasatinib, whereas Akt2 phosphorylation was SFK independent and only inhibited by BMS-754807. Thus, complete inhibition of both Akt genes, not seen by either drug alone, is likely a major mechanism for the decreased survival of PCa cells. Furthermore, dasatinib and BMS-754807 inhibited in vivo growth of the primary human xenograft MDA PCa 133, with corresponding inhibition of Akt in tumors. Also, both orthotopic and intratibial tumor growth of PC-3 cells were more potently inhibited by dual SFK and IGF-1R/IR blockade compared to either pathway alone, with a corresponding decrease in bone turnover markers.

Conclusions

Dual IGF-1R/IR and SFK inhibition may be a rational therapeutic approach in PCa by blocking both independent and complementary processes critical to tumor growth.

Activation of abl family kinases in solid tumors

Although c-Abl and Arg non-receptor tyrosine kinases are well known for driving leukemia development, their role in solid tumors has not been appreciated until recently. Accumulating evidence now indicates that c-Abl and/or Arg are activated in some solid tumor cell lines via unique mechanisms that do not involve gene mutation/translocation, and c-Abl/Arg activation promotes matrix degradation, invasion, proliferation, tumorigenesis, and/or metastasis, depending on the tumor type. However, some data suggest that c-Abl also may suppress invasion, proliferation, and tumorigenesis in certain cell contexts. Thus, c-Abl/Arg may serve as molecular switches that suppress proliferation and invasion in response to some stimuli (e.g., ephrins) or when inactive/regulated, or as promote invasion and proliferation in response to other signals (e.g., activated growth factor receptors, loss of inhibitor expression), which induce sustained activation. Clearly, more data are required to determine the extent and prevalence of c-Abl/Arg activation in primary tumors and during progression, and additional animal studies are needed to substantiate in vitro findings. Furthermore, c-Abl/Arg inhibitors have been used in numerous solid tumor clinical trials; however, none of these trials were restricted to patients whose tumors expressed highly activated c-Abl/Arg (targeted trial). Targeted trials are critical for determining whether c-Abl/Arg inhibitors can be effective treatment options for patients whose tumors are driven by c-Abl/Arg.