Cancer-associated osteoclast differentiation takes a good look in the miR(NA)ror

Tumor-bone cell interactions are critical for the development of metastasis-related osteolytic bone destruction. In this issue of Cancer Cell, Ell and colleagues show how a discrete miRNA network regulates osteoclastogenesis during breast cancer bone metastasis. A signature of upregulated miRNAs may have diagnostic and therapeutic implications for bone metastases

Skeletal muscle Ca2+ mishandling: another effect of bone-to-muscle signaling

Our appreciation of crosstalk between muscle and bone has recently expanded beyond mechanical force-driven events to encompass a variety of signaling factors originating in one tissue and communicating to the other. While the recent identification of new ‘myokines’ has shifted some focus to the role of muscle in this partnership, bone-derived factors and their effects on skeletal muscle should not be overlooked. This review summarizes some previously known mediators of bone-to-muscle signaling and also recent work identifying a new role for bone-derived TGF-β as a cause of skeletal muscle weakness in the setting of cancer-induced bone destruction. Oxidation of the ryanodine receptor/calcium release channel (RyR1) in skeletal muscle occurs via a TGF-β-Nox4-RyR1 axis and leads to calcium mishandling and decreased muscle function. Multiple points of potential therapeutic intervention were identified, from preventing the bone destruction to stabilizing the RYR1 calcium channel. This new data reinforces the concept that bone can be an important source of signaling factors in pathphysiological settings

The Role of TGFβ in Bone-Muscle Crosstalk

Purpose of Review The role of bone-derived factors in regulation of skeletal muscle function is an important emerging aspect of research into bone-muscle crosstalk. Implications for this area of research are far reaching and include understanding skeletal muscle weakness in cancer, osteoporosis, cachexia, rare diseases of bone, and aging. Recent Findings Recent research shows that bone-derived factors can lead to changes in the skeletal muscle. These changes can either be anabolic or catabolic, and we focus this review on the role of TGFβ in driving oxidative stress and skeletal muscle weakness in the setting of osteolytic cancer in the bone. Summary The bone is a preferred site for breast cancer metastasis and leads to pathological bone loss. Osteolytic cancer in the bone leads to release of TGFβ from the bone via osteoclast-mediated bone destruction. Our appreciation of crosstalk between the muscle and bone has recently expanded beyond mechanical force-driven events to encompass a variety of signaling factors originating in one tissue and communicating to the other. This review summarizes some previously known mediators of bone-to-muscle signaling and also recent work identifying a new role for bone-derived TGFβ as a cause of skeletal muscle weakness in the setting of osteolytic cancer in the bone. Multiple points of potential therapeutic intervention are discussed

Molecular mechanisms of bone metastasis and associated muscle weakness

Bone is a preferred site for breast cancer metastasis and leads to pathologic bone loss due to increased osteoclast-induced bone resorption. The homing of tumor cells to the bone depends on the support of the bone microenvironment in which the tumor cells prime the premetastatic niche. The colonization and growth of tumor cells then depend on adaptations in the invading tumor cells to take advantage of normal physiologic responses by mimicking bone marrow cells. This concerted effort by tumor cells leads to uncoupled bone remodeling in which the balance of osteoclast-driven bone resorption and osteoblast-driven bone deposition is lost. Breast cancer bone metastases often lead to osteolytic lesions due to hyperactive bone resorption. Release of growth factors from bone matrix during resorption then feeds a "vicious cycle" of bone destruction leading to many skeletal-related events. In addition to activity in bone, some of the factors released during bone resorption are also known to be involved in skeletal muscle regeneration and contraction. In this review, we discuss the mechanisms that lead to osteolytic breast cancer bone metastases and the potential for cancer-induced bone-muscle cross-talk leading to skeletal muscle weakness

MAPKs activation and mitochondrial depletion are associated with chemotherapy-related cachexia

poster abstractBackground. Cachexia, defined by increased fatigue and loss of muscle function, results from muscle and fat depletion and affects the majority of cancer patients with no effective treatments. Previous studies suggest that chemotherapy itself may contribute to cachexia, although the mechanisms responsible for these derangements are not clear. The purpose of this study was to investigate the mechanism(s) associated with chemotherapyrelated effects on body composition and muscle function. Methods. Chemotherapy regimens routinely used for the therapy of solid tumors were tested in normal CD2F1 mice, followed by assessment of body composition and muscle strength. Mitochondrial activity in muscle sections was evaluated, and TEM imaging in EDL muscle was performed. To determine whether chemotherapy modulates signaling pathways associated with the regulation of muscle mass, Western blotting, qRT-PCR and RNASequencing were utilized. Results. Administration of Folfox (5-FU, leucovorin, oxaliplatin), Folfiri (5-FU, leucovorin, irinotecan) or Gemcitabine/Paclitaxel for up to 5 weeks to normal mice caused marked decreases in adipose tissue and skeletal muscle content, coherent with reduced muscle strength. Notably, ERK1/2/MAPK and p38/MAPK signaling pathways, as well as myostatin expression were significantly up-regulated. TEM analysis unveiled a marked depletion in muscle mitochondrial content and alterations of the sarcomeric structure consistent with loss of muscle structural proteins in the mice receiving chemotherapy. Moreover, the RNA-Sequencing analysis identified several markers associated with mitochondrial homeostasis, lipid metabolism and acute phase response that were significantly affected by Folfiri administration. Conclusions. Our findings suggest that chemotherapy promotes the activation of MAPK- and myostatindependent muscle atrophy and causes mitochondrial depletion and alterations of the sarcomeric units, likely playing a causative role in the occurrence of muscle loss and weakness. Future investigations will clarify whether pharmacologically increasing muscle mass or inhibiting MAPK activation reduces chemotherapy-related cachexia, thereby providing potential pharmacological targets to improve efficacy and tolerance of anticancer drugs

Chemotherapy-related cachexia is associated with mitochondrial depletion and the activation of ERK1/2 and p38 MAPKs

Cachexia affects the majority of cancer patients, with currently no effective treatments. Cachexia is defined by increased fatigue and loss of muscle function resulting from muscle and fat depletion. Previous studies suggest that chemotherapy may contribute to cachexia, although the causes responsible for this association are not clear. The purpose of this study was to investigate the mechanism(s) associated with chemotherapy-related effects on body composition and muscle function. Normal mice were administered chemotherapy regimens used for the treatment of colorectal cancer, such as Folfox (5-FU, leucovorin, oxaliplatin) or Folfiri (5-FU, leucovorin, irinotecan) for 5 weeks. The animals that received chemotherapy exhibited concurrent loss of muscle mass and muscle weakness. Consistently with previous findings, muscle wasting was associated with up-regulation of ERK1/2 and p38 MAPKs. No changes in ubiquitin-dependent proteolysis or in the expression of TGFβ-family members were detected. Further, marked decreases in mitochondrial content, associated with abnormalities at the sarcomeric level and with increase in the number of glycolytic fibers were observed in the muscle of mice receiving chemotherapy. Finally, ACVR2B/Fc or PD98059 prevented Folfiri-associated ERK1/2 activation and myofiber atrophy in C2C12 cultures. Our findings demonstrate that chemotherapy promotes MAPK-dependent muscle atrophy as well as mitochondrial depletion and alterations of the sarcomeric units. Therefore, these findings suggest that chemotherapy potentially plays a causative role in the occurrence of muscle loss and weakness. Moreover, the present observations provide a strong rationale for testing ACVR2B/Fc or MEK1 inhibitors in combination with anticancer drugs as novel strategies aimed at preventing chemotherapy-associated muscle atrophy

Network Analysis of Skeletal Muscle During Spaceflight in Male Mice

Context: The unloading associated with spaceflight results in the rapid loss of bone and muscle tissue thereby affecting functionality. These are two of the most concerning physiologic changes that occur in space and could limit long-term occupation in space. Thus, a better understanding of the mechanisms of changes to bone and muscle could lead to development of improved therapies to counteract both spaceflight and terrestrial-based bone and muscle dysfunction.Methods: Here we used a non-biased, stringent, deep sequencing (96 million paired end reads targeting 100 bp read length) assay to examine genomic networks altered by spaceflight in the quadriceps (n=4/group). Specifically, 9 week old C57BL/6 male mice were housed on the International Space Station or at Kennedy Space Center for approximately four weeks (n=10/group). Results: 14,228 genes (70% of whole mouse genome) met the cut-off criteria and the data sets were mapped to an average of ~76% of the whole mouse genome. Of these, 840 genes met the t-test criteria, p\u3c0.05. Canonical networks linked to EIF2 signaling, calcium ion signaling, and oxidative stress response were significantly enriched by the differentially expressed genes. A comprehensive energy deprivation was indicated as functions related to protein synthesis and degradation, lipid synthesis and oxidation, and ATP hydrolysis were inhibited, and mitochondrial dysfunction was activated.Conclusions: This is the first time that skeletal muscle changes have been studied in male mice during spaceflight, and these data add important new findings to changes that occur to the musculoskeletal system in male mice during spaceflight. In orthopaedic trauma, many patients spend prolonged periods non-weight bearing and can experience significant muscle atrophy as a result. The networks analyzed in this work may prove to be targets for future therapies to counter this atrophy

Excess TGF-β mediates muscle weakness associated with bone metastases in mice

Cancer-associated muscle weakness is a poorly understood phenomenon, and there is no effective treatment. Here we find that seven different mouse models of human osteolytic bone metastases-representing breast, lung and prostate cancers, as well as multiple myeloma-exhibited impaired muscle function, implicating a role for the tumor-bone microenvironment in cancer-associated muscle weakness. We found that transforming growth factor (TGF)-β, released from the bone surface as a result of metastasis-induced bone destruction, upregulated NADPH oxidase 4 (Nox4), resulting in elevated oxidization of skeletal muscle proteins, including the ryanodine receptor and calcium (Ca(2+)) release channel (RyR1). The oxidized RyR1 channels leaked Ca(2+), resulting in lower intracellular signaling, which is required for proper muscle contraction. We found that inhibiting RyR1 leakage, TGF-β signaling, TGF-β release from bone or Nox4 activity improved muscle function in mice with MDA-MB-231 bone metastases. Humans with breast- or lung cancer-associated bone metastases also had oxidized skeletal muscle RyR1 that is not seen in normal muscle. Similarly, skeletal muscle weakness, increased Nox4 binding to RyR1 and oxidation of RyR1 were present in a mouse model of Camurati-Engelmann disease, a nonmalignant metabolic bone disorder associated with increased TGF-β activity. Thus, pathological TGF-β release from bone contributes to muscle weakness by decreasing Ca(2+)-induced muscle force production

Bone-Induced Expression of Integrin β3 Enables Targeted Nanotherapy of Breast Cancer Metastases

Bone metastases occur in approximately 70% of metastatic breast cancer patients, often leading to skeletal injuries. Current treatments are mainly palliative and underscore the unmet clinical need for improved therapies. In this study, we provide preclinical evidence for an antimetastatic therapy based on targeting integrin β3 (β3), which is selectively induced on breast cancer cells in bone by the local bone microenvironment. In a preclinical model of breast cancer, β3 was strongly expressed on bone metastatic cancer cells, but not primary mammary tumors or visceral metastases. In tumor tissue from breast cancer patients, β3 was significantly elevated on bone metastases relative to primary tumors from the same patient (n = 42). Mechanistic investigations revealed that TGFβ signaling through SMAD2/SMAD3 was necessary for breast cancer induction of β3 within the bone. Using a micelle-based nanoparticle therapy that recognizes integrin αvβ3 (αvβ3-MPs of ∼12.5 nm), we demonstrated specific localization to breast cancer bone metastases in mice. Using this system for targeted delivery of the chemotherapeutic docetaxel, we showed that bone tumor burden could be reduced significantly with less bone destruction and less hepatotoxicity compared with equimolar doses of free docetaxel. Furthermore, mice treated with αvβ3-MP-docetaxel exhibited a significant decrease in bone-residing tumor cell proliferation compared with free docetaxel. Taken together, our results offer preclinical proof of concept for a method to enhance delivery of chemotherapeutics to breast cancer cells within the bone by exploiting their selective expression of integrin αvβ3 at that metastatic site

Combination therapy in a xenograft model of glioblastoma: enhancement of the antitumor activity of temozolomide by an MDM2 antagonist

OBJECTIVE Improvement in treatment outcome for patients with glioblastoma multiforme (GBM) requires a multifaceted approach due to dysregulation of numerous signaling pathways. The murine double minute 2 (MDM2) protein may fulfill this requirement because it is involved in the regulation of growth, survival, and invasion. The objective of this study was to investigate the impact of modulating MDM2 function in combination with front-line temozolomide (TMZ) therapy in GBM. METHODS The combination of TMZ with the MDM2 protein-protein interaction inhibitor nutlin3a was evaluated for effects on cell growth, p53 pathway activation, expression of DNA repair proteins, and invasive properties. In vivo efficacy was assessed in xenograft models of human GBM. RESULTS In combination, TMZ/nutlin3a was additive to synergistic in decreasing growth of wild-type p53 GBM cells. Pharmacodynamic studies demonstrated that inhibition of cell growth following exposure to TMZ/nutlin3a correlated with: 1) activation of the p53 pathway, 2) downregulation of DNA repair proteins, 3) persistence of DNA damage, and 4) decreased invasion. Pharmacokinetic studies indicated that nutlin3a was detected in human intracranial tumor xenografts. To assess therapeutic potential, efficacy studies were conducted in a xenograft model of intracranial GBM by using GBM cells derived from a recurrent wild-type p53 GBM that is highly TMZ resistant (GBM10). Three 5-day cycles of TMZ/nutlin3a resulted in a significant increase in the survival of mice with GBM10 intracranial tumors compared with single-agent therapy. CONCLUSIONS Modulation of MDM2/p53-associated signaling pathways is a novel approach for decreasing TMZ resistance in GBM. To the authors' knowledge, this is the first study in a humanized intracranial patient-derived xenograft model to demonstrate the efficacy of combining front-line TMZ therapy and an inhibitor of MDM2 protein-protein interactions