Integrin alpha2beta 1 (α2β1) promotes prostate cancer skeletal metastasis

Navigating the biophysical landscape: how physical cues steer the journey of bone metastatic tumor cells

Many tumors prefer to metastasize to bone, but the underlying mechanisms remain elusive. The human skeletal system has unique physical properties, that are distinct from other organs, which play a key role in directing the behavior of tumor cells within bone. Understanding the physical journey of tumor cells within bone is crucial. In this review we discuss bone metastasis in the context of how physical cues in the bone vasculature and bone marrow niche regulate the fate of tumor cells. Our objective is to inspire innovative diagnostic and therapeutic approaches for bone metastasis from a mechanobiological perspective.

Therapeutic implications of signaling pathways and tumor microenvironment interactions in esophageal cancer

Esophageal cancer (EC) is significantly influenced by the tumor microenvironment (TME) and altered signaling pathways. Downregulating these pathways in EC is essential for suppressing tumor development, preventing metastasis, and enhancing therapeutic outcomes. This approach can increase tumor sensitivity to treatments, enhance patient outcomes, and inhibit cancer cell proliferation and spread. The TME, comprising cellular and non-cellular elements surrounding the tumor, significantly influences EC's development, course, and treatment responsiveness. Understanding the complex relationships within the TME is crucial for developing successful EC treatments. Immunotherapy is a vital TME treatment for EC. However, the heterogeneity within the TME limits the application of anticancer drugs outside clinical settings. Therefore, identifying reliable microenvironmental biomarkers that can detect therapeutic responses before initiating therapy is crucial. Combining approaches focusing on EC signaling pathways with TME can enhance treatment outcomes. This integrated strategy aims to interfere with essential signaling pathways promoting cancer spread while disrupting factors encouraging tumor development. Unraveling aberrant signaling pathways and TME components can lead to more focused and efficient treatment approaches, identifying specific cellular targets for treatments. Targeting the TME and signaling pathways may reduce metastasis risk by interfering with mechanisms facilitating cancer cell invasion and dissemination. In conclusion, this integrative strategy has significant potential for improving patient outcomes and advancing EC research and therapy. This review discusses the altered signaling pathways and TME in EC, focusing on potential future therapeutics.

The Potential of Extracellular Matrix- and Integrin Adhesion Complex-Related Molecules for Prostate Cancer Biomarker Discovery

Prostate cancer is among the top five cancer types according to incidence and mortality. One of the main obstacles in prostate cancer management is the inability to foresee its course, which ranges from slow growth throughout years that requires minimum or no intervention to highly aggressive disease that spreads quickly and resists treatment. Therefore, it is not surprising that numerous studies have attempted to find biomarkers of prostate cancer occurrence, risk stratification, therapy response, and patient outcome. However, only a few prostate cancer biomarkers are used in clinics, which shows how difficult it is to find a novel biomarker. Cell adhesion to the extracellular matrix (ECM) through integrins is among the essential processes that govern its fate. Upon activation and ligation, integrins form multi-protein intracellular structures called integrin adhesion complexes (IACs). In this review article, the focus is put on the biomarker potential of the ECM- and IAC-related molecules stemming from both body fluids and prostate cancer tissue. The processes that they are involved in, such as tumor stiffening, bone turnover, and communication via exosomes, and their biomarker potential are also reviewed.

Integrin β1 regulates the perineural invasion and radioresistance of oral squamous carcinoma cells by modulating cancer cell stemness

Perineural invasion and radioresistance are the main determinants of treatment outcomes in oral squamous cell carcinoma (OSCC), but the exact mechanism is still unknown. We conducted an in vitro experiment to evaluate the role of integrin β1 (ITGB1) in the perineural invasion, radioresistance, and tumor aggressiveness of OSCC. Two OSCC cell lines (SCC25, SCC15) and radiation-induced radioresistant OSCC cell lines were used in this study. The expression of ITGB1 was compared between control radiosensitive and radioresistant OSCC cell lines. ITGB1 was inhibited by small hairpin RNA, and then the adhesion to neuronal cells, responsiveness to radiation, and aggressiveness of both OSCC cell lines were evaluated. Expression of ITGB1 and adhesion to neuronal cells were increased in radioresistant OSCC compared with control radiosensitive OSCC, and increased ITGB1 expression was more prominent in cancer stem cell-like cells. When the expression of ITGB1 was inhibited, the adhesion to neuronal cells, resistance to radiation, and invasion and migration of radioresistant OSCC were significantly reduced. Moreover, the expression of cancer stem cell markers and size of spheroid formations were also significantly attenuated by inhibiting ITGB1. These findings suggest that ITGB1 may be a significant contributor to perineural invasion and the maintenance of radioresistance in OSCC cells, and is associated with cancer stem cell-like cells. Furthermore, our results suggest a possible relationship between perineural invasion and radioresistance of OSCC. More detailed research is warranted to evaluate the role of ITGB1 as a novel emerging therapeutic target for radioresistant OSCC.

Oxidative stress induced by Pollonein-LAAO, a new L-amino acid oxidase from Bothrops moojeni venom, prompts prostate tumor spheroid cell death and impairs the cellular invasion process in vitro

Cancer cells produce abnormal levels of reactive oxygen species (ROS) that contribute to promote their malignant phenotype. In this framework, we hypothesized that the change in ROS concentration above threshold could impair key events of prostate cancer cells (PC-3) progression. Our results demonstrated that Pollonein-LAAO, a new L-amino acid oxidase obtained from Bothrops moojeni venom, was cytotoxic to PC-3 cells in two-dimensional and in tumor spheroid assays. Pollonein-LAAO was able to increase the intracellular ROS generation that culminates in cell death from apoptosis by both intrinsic and extrinsic pathways due to the up-regulation of TP53, BAX, BAD, TNFRSF10B and CASP8. Additionally, Pollonein-LAAO reduced mitochondrial membrane potential and caused G0/G1 phase to delay, due to the up-regulation of CDKN1A and the down-regulation of the expression of CDK2 and E2F. Interestingly, Pollonein-LAAO inhibited critical steps of the cellular invasion process (migration, invasion and adhesion), due to the down-regulation of SNAI1, VIM, MMP2, ITGA2, ITGAV and ITGB3. Furthermore, the Pollonein-LAAO effects were associated with the intracellular ROS production, since the presence of catalase restored the invasiveness of PC-3 cells. In this sense, this study contributes to the potential use of Pollonein-LAAO as ROS-based agent to enhance the current understanding of cancer treatment strategies.

Animal models of bone metastatic prostate cancer

Metastatic disease is a main cause of mortality in prostate cancer and remains to be incurable despite emerging new treatment agents. Development of novel treatment agents are confined within the boundaries of our knowledge of bone metastatic prostate cancer. Exploration into the underlying mechanism of metastatic tumorigenesis and treatment resistance will further expose novel targets for novel treatment agents. Up to date, many of these researches have been conducted with animal models which have served as classical tools that play a pivotal role in understanding the fundamental nature of cancer. The ability to reproduce the natural course of prostate cancer would be of profound value. However, currently available models do not reproduce the entire process of tumorigenesis to bone metastasis and are limited to reproducing small portions of the entire process. Therefore, knowledge of available models and understanding the strengths and weaknesses for each model is key to achieve research objectives. In this article, we take an overview of cell line injection animal models and patient derived xenograft models that have been applied to the research of human prostate cancer bone metastasis.

Prostate cancer bone metastases biology and clinical management (Review)

Prostate cancer (PCa) is one of the most prominent causes of cancer-related mortality in the male population. A highly impactful prognostic factor for patients diagnosed with PCa is the presence or absence of bone metastases. The formation of secondary tumours at the bone is the most commonly observed site for the establishment of PCa metastases and is associated with reduced survival of patients in addition to a cohort of life-debilitating symptoms, including mobility issues and chronic pain. Despite the prevalence of this disease presentation and the high medical relevance of bone metastases, the mechanisms underlying the formation of metastases to the bone and the understanding of what drives the osteotropism exhibited by prostate tumours remain to be fully elucidated. This lack of in-depth understanding manifests in limited effective treatment options for patients with advanced metastatic PCa and culminates in the low rate of survival observed for this sub-set of patients. The present review aims to summarise the most recent promising advances in the understanding of how and why prostate tumours metastasise to the bone, with the ultimate aim of highlighting novel treatment and prognostic targets, which may provide the opportunity to improve the diagnosis and treatment of patients with PCa with bone metastases.

Non-coding RNA regulation of integrins and their potential as therapeutic targets in cancer

BACKGROUND

Integrins are integral to cell signalling and management of the extracellular matrix, and exquisite regulation of their expression is essential for a variety of cell signalling pathways, whilst disordered regulation is a key driver of tumour progression and metastasis. Most recently non-coding RNAs in the form of micro-RNA (miRNA) and long non-coding RNA (lncRNA) have emerged as a key mechanism by which tissue dependent gene expression is controlled. Whilst historically these molecules have been poorly understood, advances in 'omic' technologies and a greater understanding of non-coding regions of the genome have revealed that non-coding RNAs make up a large proportion of the transcriptome.

CONCLUSIONS AND PERSPECTIVES

This review examines the regulation of integrin genes by ncRNAs, provides and overview of their mechanism of action and highlights how exploitation of these discoveries is informing the development of novel chemotherapeutic agents in the treatment of cancer. MiRNA molecules have been the most extensively characterised and negatively regulate most integrin genes, classically regulating genes through binding to recognition sequences in the mRNA 3'-untranslated regions of gene transcripts. LncRNA mechanisms of action are now being elucidated and appear to be more varied and complex, and may counter miRNA molecules, directly engage integrin mRNA transcripts, and guide or block both transcription factors and epigenetic machinery at integrin promoters or at other points in integrin regulation. Integrins as therapeutic targets are of enormous interest given their roles as oncogenes in a variety of tumours, and emerging therapeutics mimicking ncRNA mechanisms of action are already being trialled.

Genistein and coumestrol reduce MCF-7 breast cancer cell viability and inhibit markers of preferential metastasis, bone matrix attachment and tumor-induced osteoclastogenesis

The propensity of breast cancer to preferentially metastasize to the skeleton is well known. Once established in bone metastatic breast cancers have a poor prognosis due to their ability to promote extensive bone loss which augments tumor burden. Unfortunately, current anti-resorptive therapies for skeletal metastasis are typically prescribed after secondary tumors have formed and are palliative in nature. One group of compounds with the potential to reduce both tumor burden and osteolysis are phytoestrogens (PE), but the mechanisms mediating a beneficial effect are unclear. Therefore, the current study examined the effect of genistein and coumestrol alone or in combination on breast cancer cell number, expression of mediators of preferential skeletal metastasis, bone matrix attachment and tumor-induced osteoclast formation. Results showed that genistein and coumestrol significantly reduced viable cell number in an estrogen receptor dependent manner (p < 0.05), whereas combinations of PE had no effect. In addition, genistein and coumestrol significantly reduced expression of genes driving epithelial to mesenchymal transition (snail), bone attachment (CXCR4 and integrin αV) and osteolysis (PTHrP and TNF-α). In keeping with this genistein and coumestrol significantly suppressed attachment of breast cancer cells to bone matrix and inhibited tumor and RANKL-induced osteoclast formation. Our data suggests that phytoestrogens not only decrease breast cancer cell viability but also antagonize essential tumor bone interactions that establish and drive the progression of skeletal metastasis.

Bone Metastases and Health in Prostate Cancer: From Pathophysiology to Clinical Implications

Clinically relevant bone metastases are a major cause of morbidity and mortality for prostate cancer patients. Distinct phenotypes are described: osteoblastic, the more common osteolytic and mixed. A molecular classification has been also proposed. Bone metastases start with the tropism of cancer cells to the bone through different multi-step tumor-host interactions, as described by the "metastatic cascade" model. Understanding these mechanisms, although far from being fully elucidated, could offer several potential targets for prevention and therapy. Moreover, the prognosis of patients is markedly influenced by skeletal-related events. They can be correlated not only with bone metastases, but also with "bad" bone health. There is a close correlation between osteoporosis-a skeletal disorder with decreased bone mass and qualitative alterations-and prostate cancer, in particular when treated with androgen deprivation therapy, a milestone in its treatment. Systemic treatments for prostate cancer, especially with the newest options, have improved the survival and quality of life of patients with respect to skeletal-related events; however, all patients should be evaluated for "bone health" and osteoporotic risk, both in the presence and in the absence of bone metastases. Treatment with bone-targeted therapies should be evaluated even in the absence of bone metastases, as described in special guidelines and according to a multidisciplinary evaluation.

Integrin alpha 2 is associated with tumor progression and postoperative recurrence in non-small cell lung cancer

BACKGROUND

Integrins are transmembrane proteins that mediate cell adhesion to extracellular matrix. Whereas expression of integrin alpha 2 is associated with motility, invasiveness and cellular differentiation in various tumors, the role of integrin alpha 2 in lung cancer has not been studied in detail. The aim of this study was to determine whether and how aberrant integrin alpha 2 expression in non-small cell lung cancer leads to different outcomes.

METHODS

We measured expression of integrin alpha 2 by quantitative polymerase chain reaction in 100 samples collected from non-small cell lung cancer patients who had undergone surgical resection. We assigned patients to high and low expression groups and analyzed survival. Cellular morphology, adhesion, proliferation, migration and invasion were examined in human lung cancer cell lines.

RESULTS

Among 100 cases, 41 were female, with a median age of 71 years. High expression of integrin alpha 2 in non-small cell lung cancer was associated with lower recurrence-free survival (P = 0.004). Overexpression of integrin alpha 2 in cell lines had no effect on cell proliferation or invasion but resulted in increased cell size (1416 μm2 versus 470 μm2 in H522 cells, P < 0.001; 1822 μm2 versus 1029 μm2 in H661 cells, P = 0.02), adhesion (P < 0.001 in H522 and H661 cells) and migration (gap area filled was 71% versus 36% in H522 cells, P < 0.001; 57% versus 26% in H661 cells, P = 0.001). These changes were suppressed by E7820, an inhibitor of integrin alpha 2.

CONCLUSIONS

Integrin alpha 2 may play a significant role in lung cancer adhesion and migration, and may lead to a higher risk of recurrence.

The effects of inhibition and siRNA knockdown of collagen-binding integrins on human umbilical vein endothelial cell migration and tube formation

Blood vessels in the body are lined with endothelial cells which have vital roles in numerous physiological and pathological processes. Collagens are major constituents of the extracellular matrix, and many adherent cells express several collagen-binding adhesion receptors. Here, we study the endothelium-collagen interactions mediated by the collagen-binding integrins, α1β1, α2β1, α10β1 and α11β1 expressed in human umbilical vein endothelial cells (HUVECs). Using qPCR, we found expression of the α10 transcript of the chondrocyte integrin, α10β1, along with the more abundant α2, and low-level expression of α1. The α11 transcript was not detected. Inhibition or siRNA knockdown of the α2-subunit resulted in impaired HUVEC adhesion, spreading and migration on collagen-coated surfaces, whereas inhibition or siRNA knockdown of α1 had no effect on these processes. In tube formation assays, inhibition of either α1 or α2 subunits impaired the network complexity, whereas siRNA knockdown of these integrins had no such effect. Knockdown of α10 had no effect on cell spreading, migration or tube formation in these conditions. Overall, our results indicate that the collagen-binding integrins, α1β1 and α2β1 play a central role in endothelial cell motility and self-organisation.

Prostate cancer cells of increasing metastatic potential exhibit diverse contractile forces, cell stiffness, and motility in a microenvironment stiffness-dependent manner

During metastasis, all cancer types must migrate through crowded multicellular environments. Simultaneously, cancers appear to change their biophysical properties. Indeed, cell softening and increased contractility are emerging as seemingly ubiquitous biomarkers of metastatic progression which may facilitate metastasis. Cell stiffness and contractility are also influenced by the microenvironment. Stiffer matrices resembling the tumor microenvironment cause metastatic cells to contract more strongly, further promoting contractile tumorigenic phenotypes. Prostate cancer (PCa), however, appears to deviate from these common cancer biophysics trends; aggressive metastatic PCa cells appear stiffer, rather than softer, to their lowly metastatic PCa counterparts. Although metastatic PCa cells have been reported to be more contractile than healthy cells, how cell contractility changes with increasing PCa metastatic potential has remained unknown. Here, we characterize the biophysical changes of PCa cells of various metastatic potential as a function of microenvironment stiffness. Using a panel of progressively increasing metastatic potential cell lines (22RV1, LNCaP, DU145, and PC3), we quantified their contractility using traction force microscopy (TFM), and measured their cortical stiffness using optical magnetic twisting cytometry (OMTC) and their motility using time-lapse microscopy. We found that PCa contractility, cell stiffness, and motility do not universally scale with metastatic potential. Rather, PCa cells of various metastatic efficiencies exhibit unique biophysical responses that are differentially influenced by substrate stiffness. Despite this biophysical diversity, this work concludes that mechanical microenvironment is a key determinant in the biophysical response of PCa with variable metastatic potentials. The mechanics-oriented focus and methodology of the study is unique and complementary to conventional biochemical and genetic strategies typically used to understand this disease, and thus may usher in new perspectives and approaches.

Prostate Cancer Stem Cells: Clinical Aspects and Targeted Therapies

Despite decades of research and successful improvements in diagnosis and therapy, prostate cancer (PC) remains a major challenge. In recent years, it has become clear that PC stem cells (PCSCs) are the driving force in tumorigenesis, relapse, metastasis, and therapeutic resistance of PC. In this minireview, we discuss the impact of PCSCs in the clinical practice. Moreover, new therapeutic approaches to combat PCSCs are presented with the aim to achieve an improved outcome for patients with PC.

Development and preliminary evaluation of an integrin α2β1-targeted PET probe as a supplement and alternative of PSMA imaging for prostate cancer

An integrin α₂β₁-targeted PET probe (⁶⁸Ga-IABtP) was developed to serve as a supplement and alternative of PSMA imaging for prostate cancer. ⁶⁸Ga-IABtP was synthesized by labeling the precursor peptide with ⁶⁸Ga with 93% labeling yield and 4.14 MBq/μg specific radioactivity. ⁶⁸Ga-IABtP showed no specific uptake in LNCaP prostate cancer cell with low integrin α₂β₁ expression but significantly increased uptake in PC-3 prostate cancer cell with high integrin α₂β₁ expression, which could be specifically blocked by the integrin α₂β₁ monoclonal antibody. The efflux experiments demonstrated that ⁶⁸Ga-IABtP could rapidly penetrate into PC-3 cell after cell binding, thereby prolonging the residence time in the tumor and allow enough time for probe clearance from the circulation and non-specific organs. The biodistribution study indicated that ⁶⁸Ga-IABtP showed no specific accumulation in non-target organs and was quickly cleared from the kidney. The in vivo PET-CT imaging demonstrated that ⁶⁸Ga-IABtP showed no specific uptake in LNCaP tumor but could specifically accumulate in the PC-3 tumor, and was rapidly cleared from spleen, intestine, kidney and liver, resulting in excellent contrast effect with low background signal and high target to non-target ratios.

Integrins regulate stemness in solid tumor: an emerging therapeutic target

Integrins are the adhesion molecules and transmembrane receptors that consist of α and β subunits. After binding to extracellular matrix components, integrins trigger intracellular signaling and regulate a wide spectrum of cellular functions, including cell survival, proliferation, differentiation and migration. Since the pattern of integrins expression is a key determinant of cell behavior in response to microenvironmental cues, deregulation of integrins caused by various mechanisms has been causally linked to cancer development and progression in several solid tumor types. In this review, we discuss the integrin signalosome with a highlight of a few key pro-oncogenic pathways elicited by integrins, and uncover the mutational and transcriptomic landscape of integrin-encoding genes across human cancers. In addition, we focus on the integrin-mediated control of cancer stem cell and tumor stemness in general, such as tumor initiation, epithelial plasticity, organotropic metastasis and drug resistance. With insights into how integrins contribute to the stem-like functions, we now gain better understanding of the integrin signalosome, which will greatly assist novel therapeutic development and more precise clinical decisions.

Selectivity of the collagen-binding integrin inhibitors, TC-I-15 and obtustatin

Integrins are a family of 24 adhesion receptors which are both widely-expressed and important in many pathophysiological cellular processes, from embryonic development to cancer metastasis. Hence, integrin inhibitors are valuable research tools which may have promising therapeutic uses. Here, we focus on the four collagen-binding integrins α1β1, α2β1, α10β1 and α11β1. TC-I-15 is a small molecule inhibitor of α2β1 that inhibits platelet adhesion to collagen and thrombus deposition, and obtustatin is an α1β1-specific disintegrin that inhibits angiogenesis. Both inhibitors were applied in cellular adhesion studies, using synthetic collagen peptide coatings with selective affinity for the different collagen-binding integrins and testing the adhesion of C2C12 cells transfected with each. Obtustatin was found to be specific for α1β1, as described, whereas TC-I-15 is shown to be non-specific, since it inhibits both α1β1 and α11β1 as well as α2β1. TC-I-15 was 100-fold more potent against α2β1 binding to a lower-affinity collagen peptide, suggestive of a competitive mechanism. These results caution against the use of integrin inhibitors in a therapeutic or research setting without testing for cross-reactivity.

Insights into homeobox B9: a propeller for metastasis in dormant prostate cancer progenitor cells

BACKGROUND

Metastasis is the major cause of treatment failure and cancer-related deaths in prostate cancer (PCa) patients. Our previous study demonstrated that a CD44⁺ subpopulation isolated from PCa cells or tumours possesses both stem cell properties and metastatic potential, serving as metastatic prostate cancer stem cells (mPCSCs) in PCa metastasis. However, the underlying mechanisms remain unknown.

METHODS

In this study, we established PCa models via the orthotopic and subcutaneous implantation of different human PCa cancer cell lines, and compared the metastatic efficacy, after which process function analysis of target genes was pinpointed.

RESULTS

Several novel differentially expressed genes (DEGs) between orthotopic and ectopic tumours were identified. Among them, human homeobox B9 (HOXB9) transcription factor was found to be essential for PCa metastasis, as evidenced by the diminished number of lung metastatic foci derived from orthotopic implantation with HOXB9-deficient CWR22 cells, compared with the control. In addition, HOXB9 protein expression was upregulated in PCa tissues, compared with paracancer and benign prostate hyperplasia tissues. It was also positively correlated with Gleason scores. Gain- and loss-of-function assays showed that HOXB9 altered the expression of various tumour metastasis- and cancer stem cell (CSC) growth-related genes in a transforming growth factor beta (TGFβ)-dependent manner. Moreover, HOXB9 was overexpressed in an ALDH⁺CD44⁺CXCR4⁺CD24⁺ subpopulation of PCa cells that exhibited enhanced TGFβ-dependent tumorigenic and metastatic abilities, compared with other isogenic PCa cells. This suggests that HOXB9 may contribute to PCa tumorigenesis and metastasis via TGFβ signalling. Of note, ALDH⁺CD44⁺CXCR4⁺CD24⁺-PCa cells exhibited resistance to castration and antiandrogen therapy and were present in human PCa tissues.

CONCLUSION

Taken together, our study identified HOXB9 as a critical regulator of metastatic mPCSC behaviour. This occurs through altering the expression of a panel of CSC growth- and invasion/metastasis-related genes via TGFβ signalling. Thus, targeting HOXB9 is a potential novel therapeutic PCa treatment strategy.

Type I collagen promotes tumor progression of integrin β1 positive gastric cancer through a BCL9L/β-catenin signaling pathway

The mechanism of extracellular matrix induced tumor progression is poorly understood. Based on the TCGA database and clinical tumor tissues analysis, we observed abundant type I collagen expression in tumor tissues and poor overall survival in gastric patients with high integrin β1 (ITGB1) expression. In vitro, our study found that 3D collagen culture promoted the capability of colony formation and growth in ITGB1 positive gastric cancer, whereas limited colony growth was observed in ITGB1 negative gastric cancer, suggesting the role of ITGB1 in type I collagen associated tumor progression. Mechanistically, we demonstrated that type I collagen was capable of promoting the activation of BCL9L/β-catenin signaling pathway through ITGB1, thereby contributing to the gastric cancer development. Subsequently, β-catenin signals further up-regulated the expression anti-apoptosis protein BCL2, leading to the chemo-resistance in gastric cancer cells. Blockade of β-catenin signals efficiently improved the anticancer effects of chemotherapy, providing an innovative sight for clinical gastric cancer therapy.

The extracellular matrix proteins type I collagen, type III collagen, fibronectin, and laminin 421 stimulate migration of cancer cells

For metastasis formation, individual cells from a primary tumor must migrate toward other tissues. The aim of this study was to determine if mesenchymal stromal cells (MSCs) from human bone marrow are able to emit signals that induce this migratory activity in cancer cells. We separated the supernatant of MSCs derived from human bone marrow by size-exclusion and ion-exchange chromatography and have subsequently studied the migratory behavior of the prostate cancer cell line PC3 and the breast cancer cell line MDA-MB-231 toward the respective fractions in a transwell migration assay. We identified the extracellular matrix (ECM) proteins type I collagen, type III collagen, fibronectin, and laminin 421 as potential drivers of cancer cell migration. These results could be reproduced using the corresponding isolated or recombinant ECM proteins. Knockdown of the gene encoding beta 1 integrin, an important cell surface receptor for fibronectin, has led to inhibition of cancer cell migration. This supports the hypothesis that beta 1 integrin signaling represents an initial event that leads to metastasis, and that signaling is triggered by binding of integrin heterodimers to ECM molecules. Further characterization of signaling factors and their respective receptors will have implications for anticancer drug development.

Biphasic α2β1 Integrin Expression in Breast Cancer Metastasis to Bone

Integrins participate in the pathogenesis and progression of tumors at many stages during the metastatic cascade. However, current evidence for the role of integrins in breast cancer progression is contradictory and seems to be dependent on tumor stage, differentiation status, and microenvironmental influences. While some studies suggest that loss of α2β1 enhances cancer metastasis, other studies suggest that this integrin is pro-tumorigenic. However, few studies have looked at α2β1 in the context of bone metastasis. In this study, we aimed to understand the role of α2β1 integrin in breast cancer metastasis to bone. To address this, we utilized in vivo models of breast cancer metastasis to bone using MDA-MB-231 cells transfected with an α2 expression plasmid (MDA-OEα2). MDA cells overexpressing the α2 integrin subunit had increased primary tumor growth and dissemination to bone but had no change in tumor establishment and bone destruction. Further in vitro analysis revealed that tumors in the bone have decreased α2β1 expression and increased osteolytic signaling compared to primary tumors. Taken together, these data suggest an inverse correlation between α2β1 expression and bone-metastatic potential. Inhibiting α2β1 expression may be beneficial to limit the expansion of primary tumors but could be harmful once tumors have established in bone.

Long Noncoding RNA HOXA11-AS and Transcription Factor HOXB13 Modulate the Expression of Bone Metastasis-Related Genes in Prostate Cancer

Long noncoding RNAs (lncRNAs) are emerging as critical regulators of gene expression, which play fundamental roles in cancer development. In this study, we found that homeobox A11 antisense RNA (HOXA11-AS), a highly expressed lncRNA in cell lines derived from prostate cancer bone metastases, promoted the cell invasion and proliferation of PC3 prostate cancer cells. Transcription factor homeobox B13 (HOXB13) was identified as an upstream regulator of HOXA11-AS.HOXA11-AS regulated bone metastasis-associated C-C motif chemokine ligand 2 (CCL2)/C-C chemokine receptor type 2 (CCR2) signaling in both PC3 prostate cancer cells and SaOS2 osteoblastic cells. The HOXB13/HOXA11-AS axis also regulated integrin subunits (ITGAV and ITGB1) specific to prostate cancer bone metastasis. HOXB13, in combination with HOXA11-AS, directly regulated the integrin-binding sialoprotein (IBSP) promoter. Furthermore, conditioned medium containing HOXA11-AS secreted from PC3 cells could induce the expression of CCL2 and IBSP in SaOS2 osteoblastic cells. These results suggest that prostate cancer HOXA11-AS and HOXB13 promote metastasis by regulation of CCL2/CCR2 cytokine and integrin signaling in autocrine and paracrine manners.

Bone metastasis: mechanisms, therapies, and biomarkers

Skeletal metastases are frequent complications of many cancers, causing bone complications (fractures, bone pain, disability) that negatively affect the patient's quality of life. Here, we first discuss the burden of skeletal complications in cancer bone metastasis. We then describe the pathophysiology of bone metastasis. Bone metastasis is a multistage process: long before the development of clinically detectable metastases, circulating tumor cells settle and enter a dormant state in normal vascular and endosteal niches present in the bone marrow, which provide immediate attachment and shelter, and only become active years later as they proliferate and alter the functions of bone-resorbing (osteoclasts) and bone-forming (osteoblasts) cells, promoting skeletal destruction. The molecular mechanisms involved in mediating each of these steps are described, and we also explain how tumor cells interact with a myriad of interconnected cell populations in the bone marrow, including a rich vascular network, immune cells, adipocytes, and nerves. We discuss metabolic programs that tumor cells could engage with to specifically grow in bone. We also describe the progress and future directions of existing bone-targeted agents and report emerging therapies that have arisen from recent advances in our understanding of the pathophysiology of bone metastases. Finally, we discuss the value of bone turnover biomarkers in detection and monitoring of progression and therapeutic effects in patients with bone metastasis.

Integrin α2β1 inhibition attenuates prostate cancer cell proliferation by cell cycle arrest, promoting apoptosis and reducing epithelial-mesenchymal transition

Integrin α2β1 plays an important role in cellular migration and metastasis processes associated with prostate cancer. The aim of this study was to assess whether selective inhibition of integrin α2β1 is an effective strategy to target metastatic prostate cancer cells. In this regard, we examined the effects of the inhibitor BTT-3033, which selectively interferes with the connection between integrin a2b1 and its ligand, on migration, epithelial-mesenchymal transition (EMT), cell cycle arrest, apoptosis, and specific intracellular signaling pathways using LNcap-FGC and DU-145 prostate cancer cell lines. Western blot analysis and immunocytochemistry assays showed that inhibition of integrin a2b1 inhibits EMT, through the increased expression of E-cadherin and decreased expression of N-cadherin and vimentin. Scratch wound healing assays revealed a direct effect on integrin α2β1 in the migration capacity of cells. In addition, treatment with BTT-3033 induced a reduction in cell viability and proliferation, as assessed by MTT and BrdU assays. In addition, the results show that BTT-3033 inhibits cell proliferation by inducing G1 cell cycle arrest. Moreover, inhibition of integrin α2β1 induces apoptosis through the activation of ROS, Bax protein upregulation, caspase-3 activation, and depletion of ΔΨm.  Molecular signaling studies showed that integrin α2β1 was a positive regulator of MKK7 phosphorylation. In conclusion, our results reveal a critical role for integrin a2b1 in the proliferation of prostate cancer cells, as demonstrated by EMT inhibition, cell cycle arrest, and apoptosis induction in response to treatment with its specific inhibitor BT-3033.

Targeted Delivery of Therapeutics to Urological Cancer Stem Cells

Urological cancer refers to cancer in organs of the urinary system and the male reproductive system. It mainly includes prostate cancer, bladder cancer, renal cancer, etc., seriously threatening patients' survival. Although there are many advances in the treatment of urological cancer, approved targeted therapies often result in tumor recurrence and therapy failure. An increasing amount of evidence indicated that cancer stem cells (CSCs) with tumor-initiating ability were the source of treatment failure in urological cancer. The development of CSCstargeted strategy can provide a possibility for the complete elimination of urological cancer. This review is based on a search of PubMed, Google scholar and NIH database (http://ClinicalTrials.gov/) for English language articles containing the terms: "biomarkers", "cancer stem cells", "targeting/targeted therapy", "prostate cancer", bladder cancer" and "kidney cancer". We summarized the biomarkers and stem cell features of the prostate, bladder and renal CSCs, outlined the targeted strategies for urological CSCs from signaling pathways, cytokines, angiogenesis, surface markers, elimination therapy, differentiation therapy, immunotherapy, microRNA, nanomedicine, etc., and highlighted the prospects and future challenges in this research field.

Reciprocal Interplay Between Fibrillar Collagens and Collagen-Binding Integrins: Implications in Cancer Progression and Metastasis

Cancers are complex ecosystems composed of malignant cells embedded in an intricate microenvironment made of different non-transformed cell types and extracellular matrix (ECM) components. The tumor microenvironment is governed by constantly evolving cell-cell and cell-ECM interactions, which are now recognized as key actors in the genesis, progression and treatment of cancer lesions. The ECM is composed of a multitude of fibrous proteins, matricellular-associated proteins, and proteoglycans. This complex structure plays critical roles in cancer progression: it functions as the scaffold for tissues organization and provides biochemical and biomechanical signals that regulate key cancer hallmarks including cell growth, survival, migration, differentiation, angiogenesis, and immune response. Cells sense the biochemical and mechanical properties of the ECM through specialized transmembrane receptors that include integrins, discoidin domain receptors, and syndecans. Advanced stages of several carcinomas are characterized by a desmoplastic reaction characterized by an extensive deposition of fibrillar collagens in the microenvironment. This compact network of fibrillar collagens promotes cancer progression and metastasis, and is associated with low survival rates for cancer patients. In this review, we highlight how fibrillar collagens and their corresponding integrin receptors are modulated during cancer progression. We describe how the deposition and alignment of collagen fibers influence the tumor microenvironment and how fibrillar collagen-binding integrins expressed by cancer and stromal cells critically contribute in cancer hallmarks.

S100A9 promotes prostate cancer cell invasion by activating TLR4/NF-κB/integrin β1/FAK signaling

Background

S100A9, which is expressed in prostate cancer, has been reported in association with prostate cancer progression. However, the role of S100A9 in prostate cancer metastasis is largely unknown. The aim of this study was to investigate the effect of S100A9 on prostate cancer cell invasion and the involved mechanisms.

Materials and methods

Integrin β1 expression in PC-3 and DU-145 cells was determined by quantitative real-time polymerase chain reaction (PCR) (qRT-PCR) and Western blot. Cellular invasion was measured by transwell invasion assay. Western blot was used to determine protein expression. Concentrations of S100A9 and fibronectin were analyzed by enzyme-linked immunosorbent assay. The protein interaction was detected by immunoprecipitation. The NF-κB activity was measured by luciferase reporter assay. The DU-145 cells metastasis in vivo was determined in mice xenograft models after S100A9 overexpression.

Results

S100A9 promoted prostate cancer cells invasion, integrin β1 expression and fibronectin secretion. Further investigation evidenced that S100A9 interacted with Toll-like receptor 4 (TLR4) and activated NF-κB, which was responsible for tumor cell invasion, integrin β1 up-regulation and focal adhesion kinase (FAK) phosphorylation. Furthermore, integrin β1 inhibition led to decreased FAK phosphorylation and reduced tumor cell invasion. Overexpression of S100A9 increased xenograft tumor micro-metastases, integrin β1 expression and induced NF-κB and FAK activation in vivo.

Conclusion

Our study demonstrated that S100A9 promotes prostate cancer cell invasion, and one of the underlying molecular mechanisms is that S100A9 activates integrin β1/FAK through TLR4/NF-κB signaling leading to metastasis of prostate cancer cell.

Cytokines and Chemokines as Mediators of Prostate Cancer Metastasis

The consequences of prostate cancer metastasis remain severe, with huge impact on the mortality and overall quality of life of affected patients. Despite the convoluted interplay and cross talk between various cell types and secreted factors in the metastatic process, cytokine and chemokines, along with their receptors and signaling axis, constitute important factors that help drive the sequence of events that lead to metastasis of prostate cancer. These proteins are involved in extracellular matrix remodeling, epithelial-mesenchymal-transition, angiogenesis, tumor invasion, premetastatic niche creation, extravasation, re-establishment of tumor cells in secondary organs as well as the remodeling of the metastatic tumor microenvironment. This review presents an overview of the main cytokines/chemokines, including IL-6, CXCL12, TGFβ, CXCL8, VEGF, RANKL, CCL2, CX3CL1, IL-1, IL-7, CXCL1, and CXCL16, that exert modulatory roles in prostate cancer metastasis. We also provide extensive description of their aberrant expression patterns in both advanced disease states and metastatic sites, as well as their functional involvement in the various stages of the prostate cancer metastatic process.

Bufalin suppresses the migration and invasion of prostate cancer cells through HOTAIR, the sponge of miR-520b

Bufalin, the major active component of the traditional Chinese medicine ChanSu obtained from the skin and parotid venom glands of toads, has long been known as an anticancer agent. Recent studies show that microRNAs (miRs) are involved in the anticancer activities of bufalin, while long non-coding RNAs (lncRNAs) are known to interact with miRNAs to regulate various biological functions. In this paper, we investigated the possible network related to the antimetastatic effect of bufalin in prostate cancer (PCa) cells. We demonstrated that bufalin (0.05-10 µM) dose-dependently suppressed the proliferation of prostate cancer DU145 and PC3 cells with IC50 values of 0.89 and 1.28 µM, respectively. Furthermore, bufalin treatment significantly suppressed the cell migration and invasion. To explore the role of lncRNAs in the antimetastatic activity of bufalin, we used an lncRNA microarray and found that HOX transcript antisense RNA (HOTAIR) was the most markedly downregulated lncRNA in bufalin-treated PCa cells. Overexpression of HOTAIR counteracted the suppressing effects of bufalin on DU145 and PC3 cells. We then predicted and verified that HOTAIR upregulated FGFR1 expression by sponging miR-520b in PCa cells. In 40 patients with PCa bone metastasis, we used in situ hybridization or immunohistochemical assay to assess the HOTAIR and FGFR1 expression, which revealed that both HOTAIR and FGFR1 expression were significantly higher in bone metastasis tissues than in the primary PCa tissues. In addition, the level of serum HOTAIR was positively associated with the levels of serum bone metabolic markers (CTx, OST, B-ALP and PINP) and may serve as a reasonable biomarker for PCa bone metastasis. Taken together, this is the first study revealing that HOTAIR promotes PCa bone metastasis, and bufalin may be a promising candidate for the treatment of this disease.

ITGA2 as a potential nanotherapeutic target for glioblastoma

High grade gliomas, including glioblastoma (GBM), are the most common and deadly brain cancers in adults. Here, we performed a quantitative and unbiased screening of 70 cancer-related antigens using comparative flow cytometry and, for the first time, identified integrin alpha-2 (ITGA2) as a novel molecular target for GBM. In comparison to epidermal growth factor receptor (EGFR), a well-established GBM target, ITGA2 is significantly more expressed on human GBM cells and significantly less expressed on normal human glial cells. We also found that ITGA2 antibody blockade significantly impedes GBM cell migration but not GBM cell proliferation. To investigate the utility of ITGA2 as a therapeutic target in GBM, we designed and engineered an ITGA2 antibody-directed liposome that can selectively deliver doxorubicin, a standard-of-care chemotherapeutic agent, to GBM cells. This novel approach significantly improved antitumor efficacy. We also demonstrated that these ITGA2 antibody-directed liposomes can effectively breach the blood-brain tumor barrier (BBTB) in vitro via GBM-induced angiogenesis effects. These findings support further research into the use of ITGA2 as a novel nanotherapeutic target for GBM.

Tumor targeting with DGEA peptide ligands: a new aromatic peptide amphiphile for imaging cancers

A novel AIE-active self-assembled bioprobe TPE-FDGEA has been developed for selective cancer cell imaging.

Regulation and functions of integrin α2 in cell adhesion and disease

Integrins are cell adhesion molecules that are composed of an alpha (α) subunit and a beta (β) subunit with affinity for different extracellular membrane components. The integrin family includes 24 known members that actively regulate cellular growth, differentiation, and apoptosis. Each integrin heterodimer has a particular function in defined contexts as well as some partially overlapping features with other members in the family. As many reviews have covered the general integrin family in molecular and cellular studies in life science, this review will focus on the specific regulation, function, and signaling of integrin α2 subunit (CD49b, VLA-2; encoded by the gene ITGA2) in partnership with β1 (CD29) subunit in normal and cancer cells. Its roles in cell adhesion, cell motility, angiogenesis, stemness, and immune/blood cell regulations are discussed. The pivotal role of integrin α2 in many diseases such as cancer suggests its potential to be used as a novel therapeutic target.

Role of platelets and platelet receptors in cancer metastasis

The interaction of tumor cells with platelets is a prerequisite for successful hematogenous metastatic dissemination. Upon tumor cell arrival in the blood, tumor cells immediately activate platelets to form a permissive microenvironment. Platelets protect tumor cells from shear forces and assault of NK cells, recruit myeloid cells by secretion of chemokines, and mediate an arrest of the tumor cell platelet embolus at the vascular wall. Subsequently, platelet-derived growth factors confer a mesenchymal-like phenotype to tumor cells and open the capillary endothelium to expedite extravasation in distant organs. Finally, platelet-secreted growth factors stimulate tumor cell proliferation to micrometastatic foci. This review provides a synopsis on the current literature on platelet-mediated effects in cancer metastasis and particularly focuses on platelet adhesion receptors and their role in metastasis. Immunoreceptor tyrosine-based activation motif (ITAM) and hemi ITAM (hemITAM) comprising receptors, especially, glycoprotein VI (GPVI), FcγRIIa, and C-type lectin-like-2 receptor (CLEC-2) are turned in the spotlight since several new mechanisms and contributions to metastasis have been attributed to this family of platelet receptors in the last years.

Implication of Integrin α2β1 in Proliferation and Invasion of Human Breast Carcinoma and Melanoma Cells: Noncanonical Function of Akt Protein Kinase

Blocking the expression of integrin α2β1, which was accomplished by transduction of α2-specific shRNA, resulted in significant inhibition of proliferation and clonal activity in human MCF-7 breast carcinoma and SK-Mel-147 melanoma cells. Along with these changes, deprivation of α2β1 caused a sharp decrease in melanoma cell invasion in vitro. Analysis of integrin-mediating signal pathways that control cell behavior revealed a significant increase in activity of Akt protein kinase in response to depletion of α2β1. The increase in Akt activity that accompanies a suppressive effect on cell invasion contradicts well-known Akt function aimed at stimulation of tumor progression. This contradiction could be explained by the "reversed" (noncanonical) role played by Akt in some cells that consists in suppression rather than promotion of invasive phenotype. To test this suggestion, the effects of Akt inhibitors on invasive activity of SK-Mel-147 cells were investigated. If the above suggestion is true, then inhibition of Akt in cells depleted of α2β1 should result in the restoration of their invasive activity. It appeared that treatment with LY294002, which inhibits all Akt isoforms (Akt1, Akt2, Akt3), not only failed to restore the invasive phenotype of melanoma cells but further attenuated their invasive activity. However, treatment of the cells with an Akt1-specific inhibitor significantly increased their invasion. Thus, the stimulating effect of α2β1 integrin on invasion of melanoma cells is realized through a mechanism based on inhibition of one of the Akt isoforms, which in these cells exhibits a noncanonical function consisting in suppression of invasion.

HDAC Inhibition Counteracts Metastatic Re-Activation of Prostate Cancer Cells Induced by Chronic mTOR Suppression

This study was designed to investigate whether epigenetic modulation by histone deacetylase (HDAC) inhibition might circumvent resistance towards the mechanistic target of rapamycin (mTOR) inhibitor temsirolimus in a prostate cancer cell model. Parental (par) and temsirolimus-resistant (res) PC3 prostate cancer cells were exposed to the HDAC inhibitor valproic acid (VPA), and tumor cell adhesion, chemotaxis, migration, and invasion were evaluated. Temsirolimus resistance was characterized by reduced binding of PC3^res cells to endothelium, immobilized collagen, and fibronectin, but increased adhesion to laminin, as compared to the parental cells. Chemotaxis, migration, and invasion of PC3^res cells were enhanced following temsirolimus re-treatment. Integrin α and β receptors were significantly altered in PC3^res compared to PC3^par cells. VPA significantly counteracted temsirolimus resistance by down-regulating tumor cell–matrix interaction, chemotaxis, and migration. Evaluation of integrin expression in the presence of VPA revealed a significant down-regulation of integrin α5 in PC3^res cells. Blocking studies demonstrated a close association between α5 expression on PC3^res and chemotaxis. In this in vitro model, temsirolimus resistance drove prostate cancer cells to become highly motile, while HDAC inhibition reversed the metastatic activity. The VPA-induced inhibition of metastatic activity was accompanied by a lowered integrin α5 surface level on the tumor cells.

Upregulation of LGALS1 is associated with oral cancer metastasis

Background

Oral cancer metastasis is a devastating process that contributes to poor prognosis and high mortality, yet its detailed underlying mechanisms remain unclear. Here, we aimed to evaluate metastasis-specific markers in oral cancer and to provide comprehensive recognition concerning functional roles of the specific target in oral cancer metastasis.

Methods

Lectin, galactoside-binding, soluble, 1 (LGALS1) was identified by secretomic analysis. LGALS1 expression of patient samples with oral cancer on the tissue microarray were examined by immunochemical (IHC) staining. Small interfering RNA (siRNA)-mediated knockdown of LGALS1 revealed the role of LGALS1 in oral cancer metastasis in vitro and in vivo.

Results

LGALS1 was observed to be upregulated in highly invasive oral cancer cells, and elevated LGALS1 expression was correlated with cancer progression and lymph node metastasis in oral cancer tissue specimens. Functionally, silencing LGALS1 resulted in suppressed cell growth, wound healing, cell migration, and cell invasion in oral cancer cells in vitro. Knockdown of LGALS1 in highly invasive oral cancer cells dramatically inhibited lung metastasis in an in vivo mouse model. Mechanistic studies suggested p38 mitogen-activated protein kinase (MAPK) phosphorylation, upregulated MMP-9, and mesenchymal phenotypes of epithelial-mesenchymal transition (EMT) in highly invasive oral cancer cells, whereas siRNA against LGALS1 resulted in the inactivation of p38 MAPK pathway, downregulated MMP-9, and EMT inhibition.

Conclusions

These findings demonstrate that elevated LGALS1 is strongly correlated with oral cancer progression and metastasis, and that it could potentially serve as a prognostic biomarker and an innovative target for oral cancer therapy.

Integrin α2β1 decelerates proliferation, but promotes survival and invasion of prostate cancer cells

High expression level of integrin α2β1 is a hallmark of prostate cancer stem cell like cells. The role of this collagen receptor is controversial since it is down regulated in poorly differentiated carcinomas, but concomitantly proposed to promote metastasis. Here, we show that docetaxel resistant DU145 prostate cancer cells express high levels of α2β1 and that α2β1^High subpopulation of DU145 cells proliferates slower than the cells representing α2β1^Low subpopulation. To further study this initial observation we used Crispr/Cas9 technology to create an α2β1 negative DU145 cell line. Furthermore, we performed rescue experiment by transfecting α2 knockout cells with vector carrying α2 cDNA or with an empty vector for appropriate control. When these two cell lines were compared, α2β1 positive cells proliferated slower, were more resistant to docetaxel and also migrated more effectively on collagen and invaded faster through matrigel or collagen. Integrin α2β1 was demonstrated to be a positive regulator of p38 MAPK phosphorylation and a selective p38 inhibitor (SB203580) promoted proliferation and inhibited invasion. Effects of α2β1 integrin on the global gene expression pattern of DU145 cells in spheroid cultures were studied by RNA sequencing. Integrin α2β1 was shown to regulate several cancer progression related genes, most notably matrix metalloproteinase-1 (MMP-1), a recognized invasion promoting protein. To conclude, the fact that α2β1 decelerates cell proliferation may explain the dominance of α2β1 negative/low cells in primary sites of poorly differentiated carcinomas, while the critical role of α2β1 integrin in invasion stresses the importance of this adhesion receptor in cancer dissemination.

Chronic low dose ethanol induces an aggressive metastatic phenotype in TRAMP mice, which is counteracted by parthenolide

Despite advances in prostate cancer therapy, dissemination and growth of metastases results in shortened survival. Here we examined the potential anti-cancer effect of the NF-κB inhibitor parthenolide (PTL) and its water soluble analogue dimethylaminoparthenolide (DMAPT) on tumour progression and metastasis in the TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model of prostate cancer. Six-week-old male TRAMP mice received PTL (40 mg/kg in 10% ethanol/saline), DMAPT (100 mg/kg in sterile water), or vehicle controls by oral gavage thrice weekly until palpable tumour formation. DMAPT treatment slowed normal tumour development in TRAMP mice, extending the time-to-palpable prostate tumour by 20%. PTL did not slow overall tumour development, while the ethanol/saline vehicle used to administer PTL unexpectedly induced an aggressive metastatic tumour phenotype. Chronic ethanol/saline vehicle upregulated expression of NF-κB, MMP2, integrin β1, collagen IV, and laminin, and induced vascular basement membrane degradation in primary prostate tumours, as well as increased metastatic spread to the lung and liver. All of these changes were largely prevented by co-administration with PTL. DMAPT (in water) reduced metastasis to below that of water-control. These data suggest that DMAPT has the potential to be used as a cancer preventive and anti-metastatic therapy for prostate cancer. Although low levels of ethanol consumption have not been shown to strongly correlate with prostate cancer epidemiology, these results would support a potential effect of chronic low dose ethanol on metastasis and the TRAMP model provides a useful system in which to further explore the mechanisms involved.

The composition of prostate core matrisome in vivo and in vitro unveiled by mass spectrometric analysis

BACKGROUND

The composition and organization of extracellular matrix (ECM) are important regulators of cell behavior. In particular in the prostate, this central role of the ECM is further stressed by the fact that several potential markers of prostate stem cells are matrix receptors.

METHODS

We established 12 fibroblastic cell lines from cancerous and non-cancerous areas of six prostates and allowed the cells to produce ECM under cell culture conditions. We also performed a proteome wide analysis of the ECM components by mass spectrometry. To study the in vitro activation of fibroblastic cells we compared the differences between the ECM produced in cell culture by six non-cancerous-tissue-derived fibroblasts and the in vivo matrisome from the corresponding non-cancerous tissue of prostate.

RESULTS

Our results suggest that at tissue level the ECM is mainly produced by fibroblastic cells and that it contains standard collagen I fibrils and fibril-associated proteins. Beaded-filament forming collagen VI is also abundant and basement membranes potentially contain five laminin subtypes and collagens XV and XVIII. As the main finding, we also detected differences when in vivo and in vitro matrisomes were compared. Only 65 out of 206 proteins were found to be common for both in vivo and in vitro samples. Majority of the 55 proteins, which were solely detected in in vivo samples, were considered to be plasma derived. Eighty-six proteins were solely found from in vitro fibroblast-derived ECM, and most of them were related to matrix remodeling or growth factor action, proposing that the activation of fibroblasts in cell culture may remarkably modify their gene expression profile. Finally, in comparison to traditional 2D in vitro cell culture, the ECM composition of 3D spheroid culture was analyzed. The matrisome in spheroid culture did not resemble the in vivo ECM more closely than in monolayer culture.

CONCLUSIONS

Artificial activation of ECM remodeling seems to be a distinctive feature in in vitro models. In conclusion the constitution of ECM produced by prostate derived fibroblasts in vitro is similar, but not identical to the prostate ECM in vivo as shown here by mass spectrometric analysis.

RGD cadherins and α2β1 integrin in cancer metastasis: A dangerous liaison

We propose a new cadherin family classification comprising epithelial cadherins (cadherin 17 [CDH17], cadherin 16, VE-cadherin, cadherin 6 and cadherin 20) containing RGD motifs within their sequences. Expression of some RGD cadherins is associated with aggressive forms of cancer during the late stages of metastasis, and CDH17 and VE-cadherin have emerged as critical actors in cancer metastasis. After binding to α2β1 integrin, these cadherins promote integrin β1 activation, and thereby cell adhesion, invasion and proliferation, in liver and lung metastasis. Activation of α2β1 integrin provokes an affinity increase for type IV collagen, a major component of the basement membrane and a critical partner for cell anchoring in liver and other metastatic organs. Activation of α2β1 integrin by RGD motifs breaks an old paradigm of integrin classification and supports an important role of this integrin in cancer metastasis. Recently, synthetic peptides containing the RGD motif of CDH17 elicited highly specific and selective antibodies that block the ability of CDH17 RGD to activate α2β1 integrin. These monoclonal antibodies inhibit metastatic colonization in orthotopic mouse models of liver and lung metastasis for colorectal cancer and melanoma, respectively. Hopefully, blocking the cadherin RGD ligand capacity will give us control over the integrin activity in solid tumors metastasis, paving the way for development of new agents of cancer treatment.

ST6Gal-I overexpression facilitates prostate cancer progression via the PI3K/Akt/GSK-3β/β-catenin signaling pathway

ST6Gal-I sialyltransferase adds α2,6-linked sialic acids to the terminal ends of glycan chains of glycoproteins and glycolipids. ST6Gal-I is reportedly upregulated in many cancers, including hepatocellular carcinoma, ovarian cancer and breast cancer. However, the expression and function of ST6Gal-I in prostate cancer (PCa) and the mechanism underlying this function remain largely unknown. In this study, we observed that ST6Gal-I expression was upregulated in human PCa tissues compared to non-malignant prostate tissues. High ST6Gal-I expression was positively correlated with Gleason scores, seminal vesicle involvement and poor survival in patients with PCa. ST6Gal-I knockdown in aggressive prostate cancer PC-3 and DU145 cells significantly inhibited the proliferation, growth, migration and invasion capabilities of these cells. ST6Gal-I knockdown decreased the levels of several PI3K/Akt/GSK-3β/ β-catenin pathway components, such as p-PI3K, (Ser473)p-Akt, (Ser9)p-GSK-3β and β-catenin. Furthermore, targeting this pathway with a PI3K inhibitor or Akt RNA interference decreased p-Akt, p-GSK-3β and β-catenin expression, resulting in decreased PC-3 and DU145 proliferation, migration and invasion. Taken together, these results indicate that ST6Gal-I plays a critical role in cell proliferation and invasion via the PI3K/Akt/GSK-3β/β-catenin signaling pathway during PCa progression and that it might be a promising target for PCa prognosis determination and therapy.

The Use of PET Imaging for Prognostic Integrin α2β1 Phenotyping to Detect Non-Small Cell Lung Cancer and Monitor Drug Resistance Responses

PURPOSE: Growing evidence has demonstrated that aberrant expression of integrin α2β1 might contribute to the invasion, metastasis and drug resistance of non-small cell lung cancer (NSCLC). Thus, the integrin α2β1 targeting ⁶⁸Ga-DOTA-A2B1 tracer was validated in NSCLC in contrast to accumulation of the clinically used ¹⁸F-FDG PET tracer to see if ⁶⁸Ga-DOTA-A2B1-PET imaging can offer a valuable and critical diagnostic imaging criterion for the identification of phenotypes of aggressive lung cancer.

METHODS: To verify the prognostic value of integrin α2β1, several quantitative and functional in vitro assays were validated in different NSCLC cell lines (CL1-0, CL1-5, A549 and selected A549⁺⁺ cells). Positron emission tomography (PET) imaging studies using both standard ¹⁸F-FDG and a newly developed ⁶⁸Ga-labeled integrin α2β1 (⁶⁸Ga-DOTA-A2B1) tracer were sequentially performed on mice with lung tumor xenografts in different anatomic locations (subcutaneous, orthotopic and osseous) to validate the targeting capability of the ⁶⁸Ga-DOTA-A2B1 tracers. Treatment responses were monitored by injecting animals with metastatic bone tumors with 5 mg/kg doxorubicin. All in vivo treatment responses in each treatment subgroup were monitored with a PET imaging system to evaluate the up-regulation of integrin expression at the earliest stage of treatment (6 h).

RESULTS: The PET and computed tomography (CT) images from NSCLC xenograft animals unambiguously demonstrated accumulation of the integrin tracer ⁶⁸Ga-DOTA-A2B1 in the tumor lesions at all locations. The average tumor uptake and tumor-to-normal (T/N) ratio were 2.51 ± 0.56 %ID/g and T/N = 2.82, 3.40 ± 0.42 %ID/g and T/N = 1.52, and 1.58 ± 0.108 %ID/g and T/N = 2.31 in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). The xenograft tumors were all clearly visible. In contrast, the accumulation of ¹⁸F-FDG reached 3.6 ± 0.76 %ID/g, 1.39 ± 0.075 %ID/g and 3.78 ± 0.73 %ID/g in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). However, due to the high background uptake by normal tissue, the T/N values were less than or close to 1, making the tumors almost indistinguishable in the PET imaging analysis. Furthermore, ⁶⁸Ga-DOTA-A2B1-PET imaging of the treated osseous tumor model demonstrated more than 19% tracer uptake in A549 lesions (1.72 ± 0.95 %ID/g vs. pretreatment 1.44 ± 0.12 %ID/g,p = 0. 015) 6 h post-treatment with doxorubicin. The elevated intensity of tracer uptake was in accordance with the results of in vitroWestern blot and ex vivo integrin staining, demonstrating elevated integrin α2β1 expression.

CONCLUSION: In this study, integrin α2β1 was identified as a biomarker of aggressive malignant NSCLC. Thus, efforts should be devoted to validating integrin α2β1 as a potential target for non-invasive diagnosis and as a predictive marker for monitoring treatment responses using a preclinical PET imaging system.

Monoclonal Antibodies Directed against Cadherin RGD Exhibit Therapeutic Activity against Melanoma and Colorectal Cancer Metastasis

Purpose: New targets are required for the control of advanced metastatic disease. We investigated the use of cadherin RGD motifs, which activate the α2β1integrin pathway, as targets for the development of therapeutic monoclonal antibodies (mAb).Experimental Design: Cadherin 17 (CDH17) fragments and peptides were prepared and used for immunization and antibody development. Antibodies were tested for inhibition of β1 integrin and cell adhesion, proliferation, and invasion assays using cell lines from different cancer types (colorectal, pancreatic, melanoma, and breast cancer). Effects of the mAbs on cell signaling were determined by Western blot analysis. Nude mice were used for survival analysis after treatment with RGD-specific mAbs and metastasis development.Results: Antibodies against full-length CDH17 failed to block the binding to α2β1 integrin. However, CDH17 RGD peptides generated highly selective RGD mAbs that blocked CDH17 and vascular-endothelial (VE)-cadherin-mediated β1 integrin activation in melanoma and breast, pancreatic, and colorectal cancer cells. Antibodies provoked a significant reduction in cell adhesion and proliferation of metastatic cancer cells. Treatment with mAbs impaired the integrin signaling pathway activation of FAK in colorectal cancer, of JNK and ERK kinases in colorectal and pancreatic cancers, and of JNK, ERK, Src, and AKT in melanoma and breast cancer. In vivo, RGD-specific mAbs increased mouse survival after inoculation of melanoma and colorectal cancer cell lines to cause lung and liver metastasis, respectively.Conclusions: Blocking the interaction between RGD cadherins and α2β1 integrin with highly selective mAbs constitutes a promising therapy against advanced metastatic disease in colon cancer, melanoma, and, potentially, other cancers. Clin Cancer Res; 24(2); 433-44. ©2017 AACRSee related commentary by Marshall, p. 253.

Identification of LRP-1 as an endocytosis and recycling receptor for β1-integrin in thyroid cancer cells

LRP-1 is a large endocytic receptor mediating the clearance of various molecules from the extracellular matrix. LRP-1 was reported to control focal adhesion turnover to optimize the adhesion-deadhesion balance to support invasion. To better understand how LRP-1 coordinates cell-extracellular matrix interface, we explored its ability to regulate cell surface integrins in thyroid carcinomas. Using an antibody approach, we demonstrated that β1-integrin levels were increased at the plasma membrane under LRP1 silencing or upon RAP treatment, used as LRP-1 antagonist. Our data revealed that LRP-1 binds with both inactive and active β1-integrin conformations and identified the extracellular ligand-binding domains II or IV of LRP-1 as sufficient to bind β1-integrin. Using a recombinant β1-integrin, we demonstrated that LRP-1 acts as a regulator of β1-integrin intracellular traffic. Moreover, RAP or LRP-1 blocking antibodies decreased up to 36% the number of β1-integrin-containing endosomes. LRP-1 blockade did not significantly affect the levels of β1-integrin-containing lysosomes while decreasing localization of β1-integrin within Rab-11 positive vesicles. Overall, we identified an original molecular process in which LRP-1 acts as a main regulator of β1-integrin internalization and recycling in thyroid cancer cells.

The extracellular matrix and focal adhesion kinase signaling regulate cancer stem cell function in pancreatic ductal adenocarcinoma

Cancer stem cells (CSCs) play an important role in the clonogenic growth and metastasis of pancreatic ductal adenocarcinoma (PDAC). A hallmark of PDAC is the desmoplastic reaction, but the impact of the tumor microenvironment (TME) on CSCs is unknown. In order to better understand the mechanisms, we examined the impact of extracellular matrix (ECM) proteins on PDAC CSCs. We quantified the effect of ECM proteins, β1-integrin, and focal adhesion kinase (FAK) on clonogenic PDAC growth and migration in vitro and tumor initiation, growth, and metastasis in vivo in nude mice using shRNA and overexpression constructs as well as small molecule FAK inhibitors. Type I collagen increased PDAC tumor initiating potential, self-renewal, and the frequency of CSCs through the activation of FAK. FAK overexpression increased tumor initiation, whereas a dominant negative FAK mutant or FAK kinase inhibitors reduced clonogenic PDAC growth in vitro and in vivo. Moreover, the FAK inhibitor VS-4718 extended the anti-tumor response to gemcitabine and nab-paclitaxel in patient-derived PDAC xenografts, and the loss of FAK expression limited metastatic dissemination of orthotopic xenografts. Type I collagen enhances PDAC CSCs, and both kinase-dependent and independent activities of FAK impact PDAC tumor initiation, self-renewal, and metastasis. The anti-tumor impact of FAK inhibitors in combination with standard chemotherapy support the clinical testing of this combination.