Identification of osteopontin-dependent signaling pathways in a mouse model of human breast cancer

Osteopontin in cancer

Osteopontin (OPN) is a heavily post-translationally modified protein with a molecular weight of 44-70 kDa, depending on the degree of glycosylation. OPN is involved in various biological processes, including bone remodeling, immune response, cell adhesion, migration, and survival. It is essential for controlling osteoclast and osteoblast activity for maintaining bone mass and bone strength. Additionally, OPN has been linked to cardiovascular, inflammatory illnesses, as well as the onset and progression of cancer. OPN is a multifunctional protein that can interact with a variety of cell surface receptors, such as integrins, CD44, the urokinase-type plasminogen activator receptor (uPAR), as well as extracellular matrix (ECM) components (e.g. collagen and hydroxyapatite). These interactions contribute to its wide range of biological functions in general and has significant implications for bone biology, immunology and cancer, specifically. In this chapter, we summarize the structure of OPN with a focus on its molecular mechanisms of action in various cancers.

Mesenchymal Stromal Cells (MSCs): An Ally of B-Cell Acute Lymphoblastic Leukemia (B-ALL) Cells in Disease Maintenance and Progression within the Bone Marrow Hematopoietic Niche

Simple Summary

B-cell acute lymphoblastic leukemia (B-ALL) is the most common pediatric cancer. Even though the cure rate actually exceeds 85%, the prognosis of relapsed/refractory patients is dismal. Recent literature data indicate that the bone marrow (BM) microenvironment could play a crucial role in the onset, maintenance and progression of the disease. In particular, mesenchymal stromal cells (MSCs), which are key components of the BM niche, actively crosstalk with leukemic cells providing crucial signals for their survival and resistance to therapy. We hereby review the main mechanisms exploited by MSCs to nurture and protect B-ALL cells that could become appealing targets for innovative microenvironment remodeling therapies to be coupled with classical leukemia-directed strategies.

Abstract

Mesenchymal stromal cells (MSCs) are structural components of the bone marrow (BM) niche, where they functionally interact with hematopoietic stem cells and more differentiated progenitors, contributing to hematopoiesis regulation. A growing body of evidence is nowadays pointing to a further crucial contribution of MSCs to malignant hematopoiesis. In the context of B-cell acute lymphoblastic leukemia (B-ALL), MSCs can play a pivotal role in the definition of a leukemia-supportive microenvironment, impacting on disease pathogenesis at different steps including onset, maintenance and progression. B-ALL cells hijack the BM microenvironment, including MSCs residing in the BM niche, which in turn shelter leukemic cells and protect them from chemotherapeutic agents through different mechanisms. Evidence is now arising that altered MSCs can become precious allies to leukemic cells by providing nutrients, cytokines, pro-survivals signals and exchanging organelles, as hereafter reviewed. The study of the mechanisms exploited by MSCs to nurture and protect B-ALL blasts can be instrumental in finding new druggable candidates to target the leukemic BM microenvironment. Some of these microenvironment-targeting strategies are already in preclinical or clinical experimentation, and if coupled with leukemia-directed therapies, could represent a valuable option to improve the prognosis of relapsed/refractory patients, whose management represents an unmet medical need.

The antidiabetic drug metformin acts on the bone microenvironment to promote myeloma cell adhesion to preosteoblasts and increase myeloma tumour burden in vivo

Multiple myeloma is a haematological malignancy that is dependent upon interactions within the bone microenvironment to drive tumour growth and osteolytic bone disease. Metformin is an anti-diabetic drug that has attracted attention due to its direct antitumor effects, including anti-myeloma properties. However, the impact of the bone microenvironment on the response to metformin in myeloma is unknown. We have employed in vitro and in vivo models to dissect out the direct effects of metformin in bone and the subsequent indirect myeloma response. We demonstrate how metformin treatment of preosteoblasts increases myeloma cell attachment. Metformin-treated preosteoblasts increased osteopontin (OPN) expression that upon silencing, reduced subsequent myeloma cell adherence. Proliferation markers were reduced in myeloma cells cocultured with metformin-treated preosteoblasts. In vivo, mice were treated with metformin for 4 weeks prior to inoculation of 5TGM1 myeloma cells. Metformin-pretreated mice had an increase in tumour burden, associated with an increase in osteolytic bone lesions and elevated OPN expression in the bone marrow. Collectively, we show that metformin increases OPN expression in preosteoblasts, increasing myeloma cell adherence. In vivo, this translates to an unexpected indirect pro-tumourigenic effect of metformin, highlighting the importance of the interdependence between myeloma cells and cells of the bone microenvironment.

Electrochemical aptasensors for cancer diagnosis in biological fluids - A review

The tunability of SELEX procedure is an essential feature to supply bioaffinity receptors (aptamers) almost on demand for analytical and therapeutic purposes. This longstanding ambition is, however, not straightforward. Non-invasive cancer diagnosis, so called liquid biopsy, requires collection of body fluids with minimal or no sample pretreatment. In those raw matrices, aptamers must recognize minute amounts of biomarkers that are not unique entities but large sets of variants evolving with the disease stage. The susceptibility of aptasensors to assay conditions has driven the selection of aptamers to natural environments to ensure their optimum performance in clinical samples. We present herein a compilation of the SELEX procedures in natural milieus. By revising the electrochemical aptasensors applied to clinical samples for cancer diagnosis and tracing back to the original SELEX we analyze whether aptamers raised using these SELEX strategies are being incorporated to the diagnostic devices and how aptasensors are finding their way to a market dominated by antibody-based assays.

Myeloid zinc finger-1 regulates expression of cancer-associated fibroblast and cancer stemness profiles in breast cancer

BACKGROUND

Osteopontin acts thru myeloid zinc finger-1 and transforming growth factor-β to drive the adoption of a cancer-associated fibroblast phenotype by local mesenchymal stem cells. Cancer-associated fibroblasts increase cancer cell stemness.

METHODS

Mesenchymal stem cells were exposed to osteopontin or were cocultured with MB231 human breast cancer cells (high osteopontin producer) in the presence or absence of aptamer (inactivates extracellular osteopontin). Myeloid zinc finger-1 phosphorylation sites were identified, and phosphomutants of T134 (SCAN domain) and S453 (zinc finger DNA binding domain) were constructed. Transforming growth factor-β F and cancer-associated fibroblast markers (smooth muscle actin, vimentin, and tenascin-c) were measured in mesenchymal stem cells. In MB231, stemness markers Sox2, Nanog, and Oct4 were measured.

RESULTS

Mesenchymal stem cells plus osteopontin increased transforming growth factor-β and cancer-associated fibroblast markers (P < .05 vs mesenchymal stem cells alone); this was abolished by aptamer inactivation of osteopontin. In mesenchymal stem cells transfected with phosphoresistant myeloid zinc finger-1, osteopontin did not increase cancer-associated fibroblast markers or transforming growth factor-β. In contrast, phosphomimetic myeloid zinc finger-1 increased cancer-associated fibroblast markers and transforming growth factor-β (P < .05 vs mesenchymal stem cells alone). In mesenchymal stem cells plus MB231, MB231 stemness markers were increased (P < .05 vs MB231 alone). In MB231 plus mesenchymal stem cells expressing phosphoresistant myeloid zinc finger-1, MB231 stemness markers were not increased in comparison with MB231 plus mesenchymal stem cells.

CONCLUSION

Myeloid zinc finger-1 phosphorylation in mesenchymal stem cells drives the osteopontin-mediated cancer-associated fibroblast phenotype, which then increases the cancer cell stemness profile.

TNBC Challenge: Oligonucleotide Aptamers for New Imaging and Therapy Modalities

Compared to other breast cancers, triple-negative breast cancer (TNBC) usually affects younger patients, is larger in size, of higher grade and is biologically more aggressive. To date, conventional cytotoxic chemotherapy remains the only available treatment for TNBC because it lacks expression of the estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2), and no alternative targetable molecules have been identified so far. The high biological and clinical heterogeneity adds a further challenge to TNBC management and requires the identification of new biomarkers to improve detection by imaging, thus allowing the specific treatment of each individual TNBC subtype. The Systematic Evolution of Ligands by EXponential enrichment (SELEX) technique holds great promise to the search for novel targetable biomarkers, and aptamer-based molecular approaches have the potential to overcome obstacles of current imaging and therapy modalities. In this review, we highlight recent advances in oligonucleotide aptamers used as imaging and/or therapeutic agents in TNBC, discussing the potential options to discover, image and hit new actionable targets in TNBC.

Development of an electrochemical RNA-aptasensor to detect human osteopontin

Electrochemical aptasensors may be used to detect protein biomarkers related to tumor activity. Osteopontin (OPN), a protein present in several body fluids, has been suggested as a potential biomarker since its overexpression seems to be associated with breast cancer progression and metastasis. In this work, a simple and label-free voltammetric aptasensor for the detection of OPN, using an RNA aptamer previously reported to have affinity for human OPN as the molecular recognition element, and the ferro/ferricyanide solution as a redox probe, was developed. The RNA aptamer was synthetized and immobilized in a working microelectrode gold surface (diameter of 0.8mm) of a screen-printed strip with a silver pseudo-reference electrode and a gold counter electrode. The electrochemical behavior of the electrode surface after each preparation step of the aptasensor was studied using cyclic voltammetry and square wave voltammetry. The resulting voltammetric aptasensor was used to detect OPN in standard solutions. Cyclic voltammetry results showed that the aptasensor has reasonable detection and quantification limits (3.7 ± 0.6 nM and 11 ± 2 nM, respectively). Indeed, the detection limit falls within the osteopontin levels reported in the literature for patients with metastatic breast cancer. Moreover, the aptasensor is able to selectively detect the target protein in the presence of other interfering proteins, except for thrombin. Considering the overall results, a possible application of the aptasensor for cancer prognosis may be foreseen in a near future.

Interactions between osteopontin and vascular endothelial growth factor: Implications for cancer

For this comprehensive review, 257 publications with the keywords "osteopontin" or "OPN" and "vascular endothelial growth factor" or "VEGF" in PubMed were screened (time frame from year 1996 to year 2014). 37 articles were excluded because they were not focused on the interactions between these molecules, and papers relevant for transformation-related phenomena were selected. Osteopontin (OPN) and vascular endothelial growth factor (VEGF) are characterized by a convergence in function for regulating cell motility and angiogenesis, the response to hypoxia, and apoptosis. Often, they are co-expressed or one molecule induces the other, however, in some settings OPN-associated pathways and VEGF-associated pathways are distinct. Their relationships affect the pathogenesis in cancer, where they contribute to progression and angiogenesis and serve as markers for poor prognosis. The inhibition of OPN may reduce VEGF levels and suppress tumor progression. In vascular pathologies, these two cytokines mediate remodeling, but may also perpetuate inflammation and narrowing of the arteries. OPN and VEGF are elevated and contribute to vascularization in inflammatory diseases.

Role of osteopontin in the regulation of human bladder cancer proliferation and migration in T24 cells

Osteopontin (OPN), a secreted acid glycoprotein with a variety of functions, promotes tumor proliferation, differentiation, invasion and metastasis. The aim of the current study was to investigate whether OPN may serve as a potential therapeutic target for human bladder cancer. RNA interference (RNAi) was performed to downregulate the expression of the OPN gene in T24 human bladder cancer cells. The mRNA and protein expression levels of OPN following RNAi were determined using reverse transcription‑quantitative polymerase chain reaction and western blot analysis, respectively. In addition, the cell cycle progression, apoptosis and proliferation were investigated using by flow cytometric analysis and MTT assay. The cell invasion ability was measured using a Matrigel transwell assay. The mRNA and protein expression levels of OPN were found to be significantly downregulated following RNAi. The proliferation and invasion of T24 cells were significantly inhibited in vitro. In conclusion, RNAi‑targeting OPN may inhibit the proliferation, invasion and tumorigenicity of human bladder cancer cells. Therefore, OPN may serve as a potential therapeutic target for human bladder cancer.

Osteopontin mediates an MZF1-TGF-β1-dependent transformation of mesenchymal stem cells into cancer-associated fibroblasts in breast cancer

Interactions between tumor cells and cancer-associated fibroblasts (CAFs) in the tumor microenvironment (TMEN) significantly influence cancer growth and metastasis. Transforming growth factor-β (TGF-β) is known to be a critical mediator of the CAF phenotype, and osteopontin (OPN) expression in tumors is associated with more aggressive phenotypes and poor patient outcomes. The potential link between these two pathways has not been previously addressed. Utilizing in vitro studies using human mesenchymal stem cells (MSCs) and MDA-MB231 (OPN+) and MCF7 (OPN−) human breast cancer cell lines, we demonstrate that OPN induces integrin-dependent MSC expression of TGF-β1 to mediate adoption of the CAF phenotype. This OPN-TGF-β1 pathway requires the transcription factor, myeloid zinc finger 1 (MZF1). In vivo studies with xenotransplant models in NOD-scid mice showed that OPN expression increases cancer growth and metastasis by mediating MSC-to-CAF transformation in a process that is MZF1- and TGF-β1-dependent. We conclude that tumor-derived OPN engenders MSC-to-CAF transformation in the microenvironment to promote tumor growth and metastasis via the OPN-MZF1-TGF-β1 pathway.

Multifunctional ECM proteins in bone and teeth

The extracellular matrix (ECM) of all tissues and organs is a highly organized and complex structure unique to the specific organ type. The ECM contains structural and functional proteins that define cellular function, organization, behavior and ultimately organ characteristics and function. The ECM was initially thought to contain only a specific set of secretory proteins. However, our group and several other groups have shown that the ECM contains functional proteins that have been previously defined as solely intracellular. In the present review, we have focused on the ECM of mineralized tissues namely bone and dentin. We provide here, a brief review of some non-classical ECM proteins that have been shown to possess both intra and extracellular roles in the formation of these mineralized matrices.

Expression and localization of osteopontin, homing cell adhesion molecule/CD44, and integrin αvβ3 in mucoepidermoid carcinoma and acinic cell adenocarcinoma of salivary gland origin

OBJECTIVE

Osteopontin (OPN) plays a role in tumor progression. This study aimed to determine the expression of OPN, CD44, and integrin αvβ3 in pleomorphic adenoma (PA), acinic cell adenocarcinoma (ACA), and mucoepidermoid carcinoma (MEC).

STUDY DESIGN

Immunohistochemistry was used to semiquantify the levels of expression of OPN and its receptors in normal salivary glands (NSG) (n = 20), PA (n = 20), ACA (n = 11), and MEC (n = 29).

RESULTS

OPN expression was increased in ACA and MEC compared with PA and NSG (median scores, 6, 6, 4, and 4, respectively). CD44 expression was increased in ACA and reduced in MEC and PA compared with NSG (median scores, 8, 4, 3, and 5, respectively). Integrin αvβ3 median scores were 5 in ACA, 1 in MEC, and 0 in PA and NSG.

CONCLUSIONS

OPN is expressed in salivary gland tumors and is at higher levels in ACA and MEC.

Adhesion to osteopontin in the bone marrow niche regulates lymphoblastic leukemia cell dormancy

Malignant cells may evade death from cytotoxic agents if they are in a dormant state. The host microenvironment plays important roles in cancer progression, but how niches might control cancer cell dormancy is little understood. Here we show that osteopontin (OPN), an extracellular matrix molecule secreted by osteoblasts, can function to anchor leukemic blasts in anatomic locations supporting tumor dormancy. We demonstrate that acute lymphoblastic leukemia (ALL) cells specifically adhere to OPN in vitro and secrete OPN when localized to the endosteal niche in vivo. Using intravital microscopy to perform imaging studies of the calvarial bone marrow (BM) of xenografted mice, we show that OPN is highly expressed adjacent to dormant tumor cells within the marrow. Inhibition of the OPN-signaling axis significantly increases the leukemic cell Ki-67 proliferative index and leads to a twofold increase in tumor burden in treated mice. Moreover, using cell-cycle-dependent Ara-C chemotherapy to produce minimal residual disease (MRD) in leukemic mice, we show that OPN neutralization synergizes with Ara-C to reduce detectable BM MRD. Taken together, these data suggest that ALL interacts with extracellular OPN within the malignant BM, and that this interaction induces cell cycle exit in leukemic blasts, protecting them from cytotoxic chemotherapy.

The GM-CSF receptor family: mechanism of activation and implications for disease

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pluripotent cytokine produced by many cells in the body, which regulates normal and malignant hemopoiesis as well as innate and adaptive immunity. GM-CSF assembles and activates its heterodimeric receptor complex on the surface of myeloid cells, initiating multiple signaling pathways that control key functions such as cell survival, cell proliferation, and functional activation. Understanding the molecular composition of these pathways, the interaction of the various components as well as the kinetics and dose-dependent mechanics of receptor activation provides valuable insights into the function of GM-CSF as well as the related cytokines, interleukin-3 and interleukin-5. This knowledge provides opportunities for the development of new therapies to block the action of these cytokines in hematological malignancy and chronic inflammation.

Pharmacokinetic characterization of an RNA aptamer against osteopontin and demonstration of in vivo efficacy in reversing growth of human breast cancer cells

BACKGROUND

We report pharmacokinetic (PK) data, evaluation of modifications for increased stability, evaluation for cellular uptake, and mediation of regression of breast cancer for the aptamer OPN-R3.

METHODS

The OPN-R3 aptamer was assessed for PK data in vivo with additional comparison of IV and subcutaneous dosing. Five aptamer variants were generated by differential 2'-O-methylation for comparison with parent. OPN-R3-Cy3 was incubated with MDA-MB231 cells and cellular uptake evaluated under confocal microscopy. Mice were treated with OPN-R3, mutant, or saline 3 weeks after inoculation with MDA-MB231 cells and tumor size was evaluated.

RESULTS

OPN-R3 PK data were: t(1/2) 7.76 hours, T(max) 3 hours, C(max) 13.2 mmol/L, mean residence time 9 hours, AUC (0-t) 161.9 mmol/hr/L, and K(d) 57.2 nmol/L. The half-life was higher when given intravenously versus subcutaneously (E(1/2) 7.93 vs 0.74 hours). The 2' methylation of all available bases increased unmodified aptamer stability and affinity (t(1/2) 6.2 hours; K(d) 520 nmol/L), but this did not improve on parent aptamer (t(1/2) 7.78 hours, K(d) 18 nmol/L). The aptamer remained extracellular. OPN-R3 caused regression of tumor to levels seen at 1 week after tumor inoculation.

CONCLUSION

We show the efficacy of OPN-R3 for reversing growth of breast cancer cells with adequate PK stability for clinical application.

The role of osteopontin and osteopontin aptamer (OPN-R3) in fibroblast activity

BACKGROUND

Scarring is believed to be caused by both persistent inflammation and overexuberant fibroblast activation. Osteopontin (OPN) is a cytokine that promotes cell activation. The absence of OPN in vivo reduces dermal scarring. This suggests that OPN is involved in scar formation; however, how OPN exerts these pro-scarring effects is unknown. RNA aptamers are short RNA molecules that bind target proteins with high affinity. The aptamer OPN-R3 (R3) blocks OPN signaling. The role of R3 in preventing dermal fibrosis is unknown.

METHODS

Fibroblast migration was analyzed with the use of Boyden Chambers and HEMA-3 staining. Inverted confocal microscopy was used to assess fibroblast focal adhesion length. Adhesion was measured by incubating fluorescently stained fibroblasts on OPN coated 96-well plates. CellTiter 96 AQueous non-radioactive cell proliferation assay was utilized to investigate the proliferative activity of fibroblasts. Free floating collagen lattices were utilized to assess fibroblast contractility.

RESULTS

Human dermal fibroblasts migrated significantly in response to OPN. OPN did not induce a significant increase in focal adhesion length compared with controls. Adhesion studies demonstrated that OPN increased fibroblast adhesion. Proliferation assays indicate that OPN increased fibroblast growth. OPN increased fibroblast contractility of collagen lattices. The addition of R3 significantly inhibited OPN-induced activity.

CONCLUSION

OPN is associated with scar and exerts pro-scarring effects by increasing cellular migration, adhesion, proliferation, and contractility of human dermal fibroblasts. R3 prevents OPN mediated activity. OPN may be useful for promoting closure of non-healing wounds and the OPN specific aptamer, R3, may be useful for preventing fibrosis.

Osteopontin: a potentially important therapeutic target in cancer

INTRODUCTION

Cancer is an extremely complex disease and most cancer treatments are limited to chemotherapy, radiation and surgery. The progression of tumours towards malignancy requires the interaction of various cytokines, growth factors, transcription factors and effector molecules. Osteopontin is a cytokine-like, calcium-binding, extracelular-matrix- associated member of the small integrin-binding ligand, N-linked glycoprotein (SIBLING) family of proteins. It plays an important role in determining the oncogenic potential of various cancers. The role of osteopontin in various pathophysiological conditions suggests that the alteration in post-translational modification result in different functional forms that might change its normal physiological functions.

AREAS COVERED

Osteopontin -based anticancer therapy, which may provide a new insight for the effective management of cancer.

EXPERT OPINION

A better understanding of the signalling mechanism by which osteopontin promotes tumourigenesis may be useful in crafting novel osteopontin -based anticancer therapy. The role of osteopontin in promoting cancer progression is the subject of in depth investigation and thus targeting osteopontin might be a suitable therapeutic approach for the treatment of cancer.

Combined anti-angiogenic therapy against VEGF and integrin alphaVbeta3 in an orthotopic model of ovarian cancer

PURPOSE

We tested the efficacy of dual targeting of vascular endothelial growth factor (VEGF) and the alpha(V)beta(3) integrin in orthotopic mouse models of ovarian cancer.

RESULTS

In the SKOV3ip1 model, both single-agent bevacizumab and etaracizumab reduced tumor growth by 52-63% (p < 0.05), while combined therapy reduced growth by 63-74% compared to either agent alone (p < 0.05). Furthermore, bevacizumab/paclitaxel was superior to paclitaxel alone (weight reduction by 53%, p < 0.05), but etaracizumab/paclitaxel was not. Combining all three agents was more effective than either agent with paclitaxel (p < 0.05). Significantly, both bevacizumab and etaracizumab each sensitized the taxane-resistant SKOV3TRip2 cells to paclitaxel, reducing growth by 56-73% (p < 0.05). Both agents decreased proliferation and microvessel density, and increased apoptosis, alone and in combination with paclitaxel. In the HeyA8 model, there was significantly reduced growth with bevacizumab treatment, but not with etaracizumab, and combination therapy was not superior to bevacizumab alone.

EXPERIMENTAL DESIGN

In vivo therapy experiments were conducted in chemo-sensitive (SKOV3ip1, HeyA8) and -resistant (SKOV3TRip2) ovarian cancer models. VEGF was targeted with bevacizumab and alpha(V)beta(3) with etaracizumab. Mice were treated with each agent alone, together, or in combination with paclitaxel for assessment of tumor growth. Tumor specimens were tested for proliferative index, microvessel density and apoptosis.

CONCLUSIONS

Bevacizumab and etaracizumab are more effective in combination than individually in some ovarian cancer models, but not all. Both can sensitize taxane-resistant ovarian cancer cells to paclitaxel, though bevacizumab was superior to etaracizumab in this regard. Further study of this dual anti-angiogenic therapy is warranted.