Lysyl Oxidase-like Protein LOXL2 Promotes Lung Metastasis of Breast Cancer

Cuproptosis in lung cancer: therapeutic options and prognostic models

Lung cancer (LC) is a serious threat to mankind. The survival of LC patients is still poor despite the enormous efforts that have been made to develop novel treatments. A copper-dependent cell death termed cuproptosis is distinct from known programmed cell death (PCD). Cuproptosis is induced by the disruption of the binding of copper to lipoylated tricarboxylic acid (TCA) cycle proteins of mitochondrial respiratory chains. Potential approaches for treating LC are inducing cell cuproptosis and targeting cell copper death mechanisms. Thus, in this review, we summarize the systemic and cellular metabolic processes of copper. We highlight the possible therapeutic options of employing copper ionophores and chelators for inducing cuproptosis. Moreover, we summarize the prognostic models based on cuproptosis-related genes (CRGs) to identify promising biomarkers for tumor diagnosis and therapy. This review aims to provide a comprehensive summary of CRGs-based prognostic models and promising therapeutic options for cuproptosis induction in LC.

LOXL2-mediated chromatin compaction is required to maintain the oncogenic properties of triple-negative breast cancer cells

Oxidation of histone H3 at lysine 4 (H3K4ox) is catalyzed by lysyl oxidase homolog 2 (LOXL2). This histone modification is enriched in heterochromatin in triple-negative breast cancer (TNBC) cells and has been linked to the maintenance of compacted chromatin. However, the molecular mechanism underlying this maintenance is still unknown. Here, we show that LOXL2 interacts with RuvB-Like 1 (RUVBL1), RuvB-Like 2 (RUVBL2), Actin-like protein 6A (ACTL6A), and DNA methyltransferase 1associated protein 1 (DMAP1), a complex involved in the incorporation of the histone variant H2A.Z. Our experiments indicate that this interaction and the active form of RUVBL2 are required to maintain LOXL2-dependent chromatin compaction. Genome-wide experiments showed that H2A.Z, RUVBL2, and H3K4ox colocalize in heterochromatin regions. In the absence of LOXL2 or RUVBL2, global levels of the heterochromatin histone mark H3K9me3 were strongly reduced, and the ATAC-seq signal in the H3K9me3 regions was increased. Finally, we observed that the interplay between these series of events is required to maintain H3K4ox-enriched heterochromatin regions, which in turn is key for maintaining the oncogenic properties of the TNBC cell line tested (MDA-MB-231).

LOX, but not LOXL2, promotes bone metastasis formation and bone destruction in triple-negative breast cancer

The primary function of the lysyl oxidase (LOX) family, including LOX and its paralogue LOX-like (LOXL)-2, is to catalyze the covalent crosslinking of collagen and elastin in the extracellular matrix. LOX and LOXL2 are also facilitating breast cancer invasion and metastatic spread to visceral organs (lungs, liver) in vivo. Conversely, the contribution of LOX and LOXL2 to breast cancer bone metastasis remains scant. Here, using gene overexpression or silencing strategies, we investigated the role of LOX and LOXL2 on the formation of metastatic osteolytic lesions in animal models of triple negative breast cancer. In vivo, the extent of radiographic metastatic osteolytic lesions in animals injected with LOX-overexpressing [LOX(+)] tumor cells was 3-fold higher than that observed in animals bearing tumors silenced for LOX [LOX(-)]. By contrast, the extent of osteolytic lesions between LOXL2(+) and LOXL2(-) tumor-bearing animals did not differ, and was comparable to that observed with LOX(-) tumor-bearing animals. In situ, TRAP staining of bone tissue sections from the hind limbs of LOX(+) tumor-bearing animals was substantially increased compared to LOX(-), LOXL2(+) and LOXL2(-)-tumor-bearing animals, which was indicative of enhanced active-osteoclast resorption. In vitro, tumor-secreted LOX increased osteoclast differentiation induced by RANKL, whereas LOXL2 seemed to counteract LOX's pro-osteoclastic activity. Furthermore, LOX (but not LOXL2) overexpression in tumor cells induced a robust production of IL-6, the latter being a pro-osteoclastic cytokine. Based on these findings, we propose a model in which LOX and IL-6 secreted from tumor cells act in concert to enhance osteoclast-mediated bone resorption that, in turn, promotes metastatic bone destruction in vivo.

Cuproptosis: A novel therapeutic target for overcoming cancer drug resistance

Cuproptosis is a newly identified form of cell death driven by copper. Recently, the role of copper and copper triggered cell death in the pathogenesis of cancers have attracted attentions. Cuproptosis has garnered enormous interest in cancer research communities because of its great potential for cancer therapy. Copper-based treatment exerts an inhibiting role in tumor growth and may open the door for the treatment of chemotherapy-insensitive tumors. In this review, we provide a critical analysis on copper homeostasis and the role of copper dysregulation in the development and progression of cancers. Then the core molecular mechanisms of cuproptosis and its role in cancer is discussed, followed by summarizing the current understanding of copper-based agents (copper chelators, copper ionophores, and copper complexes-based dynamic therapy) for cancer treatment. Additionally, we summarize the emerging data on copper complexes-based agents and copper ionophores to subdue tumor chemotherapy resistance in different types of cancers. We also review the small-molecule compounds and nanoparticles (NPs) that may kill cancer cells by inducing cuproptosis, which will shed new light on the development of anticancer drugs through inducing cuproptosis in the future. Finally, the important concepts and pressing questions of cuproptosis in future research that should be focused on were discussed. This review article suggests that targeting cuproptosis could be a novel antitumor therapy and treatment strategy to overcome cancer drug resistance.

Interactions between BRD4S, LOXL2, and MED1 drive cell cycle transcription in triple-negative breast cancer

Triple-negative breast cancer (TNBC) often develops resistance to single-agent treatment, which can be circumvented using targeted combinatorial approaches. Here, we demonstrate that the simultaneous inhibition of LOXL2 and BRD4 synergistically limits TNBC proliferation in vitro and in vivo. Mechanistically, LOXL2 interacts in the nucleus with the short isoform of BRD4 (BRD4S), MED1, and the cell cycle transcriptional regulator B-MyB. These interactions sustain the formation of BRD4 and MED1 nuclear transcriptional foci and control cell cycle progression at the gene expression level. The pharmacological co-inhibition of LOXL2 and BRD4 reduces BRD4 nuclear foci, BRD4-MED1 colocalization, and the transcription of cell cycle genes, thus suppressing TNBC cell proliferation. Targeting the interaction between BRD4S and LOXL2 could be a starting point for the development of new anticancer strategies for the treatment of TNBC.

Urokinase-type plasminogen activator (uPA) regulates invasion and matrix remodelling in colorectal cancer

Background

Cancer cells remodel their local physical environment through processes of matrix reorganisation, deposition, stiffening and degradation. Urokinase-type plasminogen activator (uPA), which is encoded by the PLAU gene, is an extracellular proteolytic enzyme known to be involved in cancer progression and tumour microenvironment (TME) remodelling. Perturbing uPA therefore has a strong potential as a mechano-based cancer therapy. This work is a bioengineering investigation to validate whether 1) uPA is involved in matrix degradation and 2) preventing matrix degradation by targeting uPA can reduce cancer cell invasion and metastasis.

Methods

To this aim, we used an engineered 3D in vitro model, termed the tumouroid, that appropriately mimics the tumour's native biophysical environment (3 kPa). A CRISPR-Cas9 mediated uPA knockout was performed to introduce a loss of function mutation in the gene coding sequence. Subsequently, to validate the translational potential of blocking uPA action, we tested a pharmacological inhibitor, UK-371,801. The changes in matrix stiffness were measured by atomic force microscopy (AFM). Invasion was quantified using images of the tumouroid, obtained after 21 days of culture.

Results

We showed that uPA is highly expressed in invasive breast and colorectal cancers, and these invasive cancer cells locally degrade their TME. PLAU (uPA) gene knock-out (KO) completely stopped matrix remodelling and significantly reduced cancer invasion. Many invasive cancer gene markers were also downregulated in the PLAU KO tumouroids. Pharmacological inhibition of uPA showed similarly promising results, where matrix degradation was reduced and so was the cancer invasion.

Conclusion

This work supports the role of uPA in matrix degradation. It demonstrates that the invasion of cancer cells was significantly reduced when enzymatic breakdown of the TME matrix was prevented. Collectively, this provides strong evidence of the effectiveness of targeting uPA as a mechano-based cancer therapy.

LOXL2 in Cancer: A Two-Decade Perspective

Lysyl Oxidase Like 2 (LOXL2) belongs to the lysyl oxidase (LOX) family, which comprises five lysine tyrosylquinone (LTQ)-dependent copper amine oxidases in humans. In 2003, LOXL2 was first identified as a promoter of tumour progression and, over the course of two decades, numerous studies have firmly established its involvement in multiple cancers. Extensive research with large cohorts of human tumour samples has demonstrated that dysregulated LOXL2 expression is strongly associated with poor prognosis in patients. Moreover, investigations have revealed the association of LOXL2 with various targets affecting diverse aspects of tumour progression. Additionally, the discovery of a complex network of signalling factors acting at the transcriptional, post-transcriptional, and post-translational levels has provided insights into the mechanisms underlying the aberrant expression of LOXL2 in tumours. Furthermore, the development of genetically modified mouse models with silenced or overexpressed LOXL2 has enabled in-depth exploration of its in vivo role in various cancer models. Given the significant role of LOXL2 in numerous cancers, extensive efforts are underway to identify specific inhibitors that could potentially improve patient prognosis. In this review, we aim to provide a comprehensive overview of two decades of research on the role of LOXL2 in cancer.

Copper homeostasis and cuproptosis in tumor pathogenesis and therapeutic strategies

Copper is an indispensable micronutrient for the development and replication of all eukaryotes, and its redox properties are both harmful and beneficial to cells. An imbalance in copper homeostasis is thought to be involved in carcinogenesis. Importantly, cancer cell proliferation, angiogenesis, and metastasis cannot be separated from the effects of copper. Cuproposis is a copper-dependent form of cell death that differs from other existing modalities of regulatory cell death. The role of cuproptosis in the pathogenesis of the nervous and cardiovascular systems has been widely studied; however, its impact on malignant tumors is yet to be fully understood from a clinical perspective. Exploring signaling pathways related to cuproptosis will undoubtedly provide a new perspective for the development of anti-tumor drugs in the future. Here, we systematically review the systemic and cellular metabolic processes of copper and the regulatory mechanisms of cuproptosis in cancer. In addition, we discuss the possibility of targeting copper ion drugs to prolong the survival of cancer patients, with an emphasis on the most representative copper ionophores and chelators. We suggest that attention should be paid to the potential value of copper in the treatment of specific cancers.

Cross-talk between non-ionizing electromagnetic fields and metastasis; EMT and hybrid E/M may explain the anticancer role of EMFs

Recent studies have shown that non-ionizing electromagnetic fields (NIEMFs) in a specific frequency, intensity, and exposure time can have anti-cancer effects on various cancer cells; however, the underlying precise mechanism of action is not transparent. Most cancer deaths are due to metastasis. This important phenomenon plays an inevitable role in different steps of cancer including progression and development. It has different stages including invasion, intravasation, migration, extravasation, and homing. Epithelial-mesenchymal transition (EMT), as well as hybrid E/M state, are biological processes, that involve both natural embryogenesis and tissue regeneration, and abnormal conditions including organ fibrosis or metastasis. In this context, some evidence reveals possible footprints of the important EMT-related pathways which may be affected in different EMFs treatments. In this article, critical EMT molecules and/or pathways which can be potentially affected by EMFs (e.g., VEGFR, ROS, P53, PI3K/AKT, MAPK, Cyclin B1, and NF-кB) are discussed to shed light on the mechanism of EMFs anti-cancer effect.

Targeting copper death genotyping associated gene RARRES2 suppresses glioblastoma progression and macrophages infiltration

BACKGROUND

Copper homeostasis is associated with malignant biological behavior in various tumors. The excessive accumulation of copper can induce tumor death, which is named cuproptosis, and it is also closely related to tumor progression and the formation of the immune microenvironment. However, the associations of cuproptosis with glioblastoma (GBM) prognosis and microenvironment construction are poorly understood.

METHOD

First, TCGA and GEO (GSE83300, GSE74187) merged datasets were used to analyze the association of cuproptosis-related genes (CRGs) with GBM. Then, we performed cluster analysis of CRGs in GBM from the GEO (GSE83300, GSE74187) and TCGA merged datasets. Subsequently, the prognostic risk model was constructed by least absolute shrinkage and selection operator (LASSO) according to gene expression features in CRG clusters. Next, we performed a series of in-depth analyses, including tumor mutational burden (TMB) analysis, cluster analysis, and GBM IDH status prediction. Finally, RARRES2 was identified as a target gene for GBM treatment, especially IDH wild-type GBM. In addition, we further analyzed the correlation of CRG clusters and RARRES2 expression with the GBM immune microenvironment by ESTIMATE and CIBERSORT analyses. In vitro experiments were conducted to demonstrate that targeting RARRES2 inhibits glioblastoma progression and macrophage infiltration, particularly IDH wild-type GBM.

RESULTS

In the present study, we demonstrated that the CRG cluster was closely related to GBM prognosis and immune cell infiltration. Moreover, the prognostic risk model constructed with the three genes (MMP19, G0S2, RARRES2) associated with the CRG clusters could well evaluate the prognosis and immune cell infiltration in GBM. Subsequently, after further analyzing the tumor mutational burden (TMB) in GBM, we confirmed that RARRES2 in the prognostic risk model could be used as a crucial gene signature to predict the prognosis, immune cell infiltration and IDH status of GBM patients.

CONCLUSION

This study fully revealed the potential clinical impact of CRGs on GBM prognosis and the microenvironment, and determined the effect of the crucial gene (RARRES2) on the prognosis and tumor microenvironment construction of GBM, meanwhile, our study also revealed over-expressed RARRES2 is related to the IDH satus of GBM, which provides a novel strategy for the treatment of GBM, particularly IDH wild-type GBM.

LOXL2 serves as a prognostic biomarker for hepatocellular carcinoma by mediating immune infiltration and vasculogenic mimicry

BACKGROUND

The development of human hepatocellular carcinoma (HCC) is a multistep process that is accompanied by progressive changes in the liver microenvironment, including immune evasion and angiogenesis. Lysyl oxidase-like 2 (LOXL2) has been suggested to contribute to tumour progression and metastasis; however, the underlying mechanism remains unclear. The purpose of the present study was to explore the relationship between LOXL2 and immune infiltration and vasculogenic mimicry (VM) and to identify the role of LOXL2 in HCC diagnosis prognosis evaluation.

METHODS

The Cancer Genome Atlas (TCGA), UALCAN, GEPIA and Kaplan-Meier plotter databases were used to analyse LOXL2 expression and perform survival analysis. The Tumour Immune Estimation Resource (TIMER) was used to analyse immune cell infiltration, immune cell biomarkers and immune checkpoints. Immunohistochemistry (IHC) of 201 HCC samples was used to confirm the expression of LOXL2 and its relationship with VM. Coimmunoprecipitation (co-IP) and gain- and loss-of-function studies were performed to confirm the molecular mechanism of LOXL2 in VM.

RESULTS

The expression of LOXL2 in HCC was higher than that in normal tissues at both the mRNA and protein levels. High expression of LOXL2 was associated with a poorer prognosis of HCC. The genetic alteration rate of LOXL2 was 5%. LOXL2 was positively related to immune cell infiltration and immune checkpoints (PD-1 and CTLA-4) in HCC. Co-IP showed that LOXL2 can interact directly with IQGAP1. Both gain- and loss-of-function studies showed that LOXL2 significantly induced cell migration, invasion and VM formation when IQGAP1 was upregulated.

CONCLUSIONS

LOXL2 is involved in immune cell infiltration and promotes VM by upregulating IQGAP1. LOXL2 can be used as a novel biomarker for HCC diagnosis and prognosis prediction.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

Macrophages direct cancer cells through a LOXL2-mediated metastatic cascade in pancreatic ductal adenocarcinoma

OBJECTIVE

The lysyl oxidase-like protein 2 (LOXL2) contributes to tumour progression and metastasis in different tumour entities, but its role in pancreatic ductal adenocarcinoma (PDAC) has not been evaluated in immunocompetent in vivo PDAC models.

DESIGN

Towards this end, we used PDAC patient data sets, patient-derived xenograft in vivo and in vitro models, and four conditional genetically-engineered mouse models (GEMMS) to dissect the role of LOXL2 in PDAC. For GEMM-based studies, K-Ras +/LSL-G12D;Trp53 LSL-R172H;Pdx1-Cre mice (KPC) and the K-Ras +/LSL-G12D;Pdx1-Cre mice (KC) were crossed with Loxl2 allele floxed mice (Loxl2Exon2 fl/fl) or conditional Loxl2 overexpressing mice (R26Loxl2 KI/KI) to generate KPCL2KO or KCL2KO and KPCL2KI or KCL2KI mice, which were used to study overall survival; tumour incidence, burden and differentiation; metastases; epithelial to mesenchymal transition (EMT); stemness and extracellular collagen matrix (ECM) organisation.

RESULTS

Using these PDAC mouse models, we show that while Loxl2 ablation had little effect on primary tumour development and growth, its loss significantly decreased metastasis and increased overall survival. We attribute this effect to non-cell autonomous factors, primarily ECM remodelling. Loxl2 overexpression, on the other hand, promoted primary and metastatic tumour growth and decreased overall survival, which could be linked to increased EMT and stemness. We also identified tumour-associated macrophage-secreted oncostatin M (OSM) as an inducer of LOXL2 expression, and show that targeting macrophages in vivo affects Osm and Loxl2 expression and collagen fibre alignment.

CONCLUSION

Taken together, our findings establish novel pathophysiological roles and functions for LOXL2 in PDAC, which could be potentially exploited to treat metastatic disease.

Mitochondrial RNA methyltransferase TRMT61B is a new, potential biomarker and therapeutic target for highly aneuploid cancers

Despite being frequently observed in cancer cells, chromosomal instability (CIN) and its immediate consequence, aneuploidy, trigger adverse effects on cellular homeostasis that need to be overcome by anti-stress mechanisms. As such, these safeguard responses represent a tumor-specific Achilles heel, since CIN and aneuploidy are rarely observed in normal cells. Recent data have revealed that epitranscriptomic marks catalyzed by RNA-modifying enzymes change under various stress insults. However, whether aneuploidy is associated with such RNA modifying pathways remains to be determined. Through an in silico search for aneuploidy biomarkers in cancer cells, we found TRMT61B, a mitochondrial RNA methyltransferase enzyme, to be associated with high levels of aneuploidy. Accordingly, TRMT61B protein levels are increased in tumor cell lines with an imbalanced karyotype as well as in different tumor types when compared to control tissues. Interestingly, while TRMT61B depletion induces senescence in melanoma cell lines with low levels of aneuploidy, it leads to apoptosis in cells with high levels. The therapeutic potential of these results was further validated by targeting TRMT61B in transwell and xenografts assays. We show that TRM61B depletion reduces the expression of several mitochondrial encoded proteins and limits mitochondrial function. Taken together, these results identify a new biomarker of aneuploidy in cancer cells that could potentially be used to selectively target highly aneuploid tumors.

Extracellular Matrix Glycation and Crosslinking in Mammary Tumor Progression

Breast cancer progression is accompanied by profound extracellular matrix (ECM) remodeling. A greater abundance of aligned fibrillar collagen is characteristic of invasive and aggressive breast cancers and has been associated with elevated activity of collagen crosslinking enzymes, such as lysyl oxidase (LOX) and lysyl hydroxylases (LH) and the formation of more mature collagen matrix crosslinks. Aligned collagen fibers can facilitate metastatic dissemination of tumor cells, and LOX inhibitors have been used to inhibit tumor progression and metastasis in experimental models. Thus, a better understanding of how matrix crosslinking alters tumor cell phenotypes, and behaviors would improve our ability to effectively treat aggressive metastatic breast cancer. Herein described is an experimental approach to glycate and crosslink a collagen-I/basement membrane extract ECM to study the impact of ECM crosslinking on mammary tumor progression in vivo. Moreover, glycation of collagen by sugars to form advanced glycation end products naturally occurs during aging, extending the potential relevance of this approach to research on mechanisms of aging involved in disease progression.

Loss of LOXL2 Promotes Uterine Hypertrophy and Tumor Progression by Enhancing H3K36ac-Dependent Gene Expression

Lysyl oxidase-like 2 (LOXL2) is a member of the scavenger receptor cysteine-rich (SRCR) repeat carrying LOX family. Although LOXL2 is suspected to be involved in histone association and chromatin modification, the role of LOXL2 in epigenetic regulation during tumorigenesis and cancer progression remains unclear. Here, we report that nuclear LOXL2 associates with histone H3 and catalyzes H3K36ac deacetylation and deacetylimination. Both the N-terminal SRCR repeats and the C-terminal catalytic domain of LOXL2 carry redundant deacetylase catalytic activity. Overexpression of LOXL2 markedly reduced H3K36 acetylation and blocked H3K36ac-dependent transcription of genes, including c-MYC, CCND1, HIF1A, and CD44. Consequently, LOXL2 overexpression reduced cancer cell proliferation in vitro and inhibited xenograft tumor growth in vivo. In contrast, LOXL2 deficiency resulted in increased H3K36 acetylation and aberrant expression of H3K36ac-dependent genes involved in multiple oncogenic signaling pathways. Female LOXL2-deficient mice spontaneously developed uterine hypertrophy and uterine carcinoma. Moreover, silencing LOXL2 in cancer cells enhanced tumor progression and reduced the efficacy of cisplatin and anti-programmed cell death 1 (PD-1) combination therapy. Clinically, low nuclear LOXL2 expression and high H3K36ac levels corresponded to poor prognosis in uterine endometrial carcinoma patients. These results suggest that nuclear LOXL2 restricts cancer development in the female reproductive system via the regulation of H3K36ac deacetylation.

SIGNIFICANCE

LOXL2 loss reprograms the epigenetic landscape to promote uterine cancer initiation and progression and repress the efficacy of anti-PD-1 immunotherapy, indicating that LOXL2 is a tumor suppressor.

Role of the Hypoxic-Secretome in Seed and Soil Metastatic Preparation

During tumor growth, the delivery of oxygen to cells is impaired due to aberrant or absent vasculature. This causes an adaptative response that activates the expression of genes that control several essential processes, such as glycolysis, neovascularization, immune suppression, and the cancer stemness phenotype, leading to increased metastasis and resistance to therapy. Hypoxic tumor cells also respond to an altered hypoxic microenvironment by secreting vesicles, factors, cytokines and nucleic acids that modify not only the immediate microenvironment but also organs at distant sites, allowing or facilitating the attachment and growth of tumor cells and contributing to metastasis. Hypoxia induces the release of molecules of different biochemical natures, either secreted or inside extracellular vesicles, and both tumor cells and stromal cells are involved in this process. The mechanisms by which these signals that can modify the premetastatic niche are sent from the primary tumor site include changes in the extracellular matrix, recruitment and activation of different stromal cells and immune or nonimmune cells, metabolic reprogramming, and molecular signaling network rewiring. In this review, we will discuss how hypoxia might alter the premetastatic niche through different signaling molecules.

Targeting the tumor stroma for cancer therapy

Tumors are comprised of both cancer cells and surrounding stromal components. As an essential part of the tumor microenvironment, the tumor stroma is highly dynamic, heterogeneous and commonly tumor-type specific, and it mainly includes noncellular compositions such as the extracellular matrix and the unique cancer-associated vascular system as well as a wide variety of cellular components including activated cancer-associated fibroblasts, mesenchymal stromal cells, pericytes. All these elements operate with each other in a coordinated fashion and collectively promote cancer initiation, progression, metastasis and therapeutic resistance. Over the past few decades, numerous studies have been conducted to study the interaction and crosstalk between stromal components and neoplastic cells. Meanwhile, we have also witnessed an exponential increase in the investigation and recognition of the critical roles of tumor stroma in solid tumors. A series of clinical trials targeting the tumor stroma have been launched continually. In this review, we introduce and discuss current advances in the understanding of various stromal elements and their roles in cancers. We also elaborate on potential novel approaches for tumor-stroma-based therapeutic targeting, with the aim to promote the leap from bench to bedside.

A 3D-Predicted Structure of the Amine Oxidase Domain of Lysyl Oxidase-Like 2

Lysyl oxidase-like 2 (LOXL2) has been recognized as an attractive drug target for anti-fibrotic and anti-tumor therapies. However, the structure-based drug design of LOXL2 has been very challenging due to the lack of structural information of the catalytically-competent LOXL2. In this study; we generated a 3D-predicted structure of the C-terminal amine oxidase domain of LOXL2 containing the lysine tyrosylquinone (LTQ) cofactor from the 2.4Å crystal structure of the Zn²⁺-bound precursor (lacking LTQ; PDB:5ZE3); this was achieved by molecular modeling and molecular dynamics simulation based on our solution studies of a mature LOXL2 that is inhibited by 2-hydrazinopyridine. The overall structures of the 3D-modeled mature LOXL2 and the Zn²⁺-bound precursor are very similar (RMSD = 1.070Å), and disulfide bonds are conserved. The major difference of the mature and the precursor LOXL2 is the secondary structure of the pentapeptide (His652-Lys653-Ala654-Ser655-Phe656) containing Lys653 (the precursor residue of the LTQ cofactor). We anticipate that this peptide is flexible in solution to accommodate the conformation that enables the LTQ cofactor formation as opposed to the β-sheet observed in 5ZE3. We discuss the active site environment surrounding LTQ and Cu²⁺ of the 3D-predicted structure.

Lysyl Oxidases: Orchestrators of Cellular Behavior and ECM Remodeling and Homeostasis

Lysyl oxidases have long been considered key secreted extracellular matrix modifying enzymes. As such, their activity has been associated with the crosslinking of collagens and elastin, and as a result, they have been linked to multiple developmental and pathological processes. However, numerous lines of evidence also demonstrated that members of this enzyme family are localized and are active within the cytoplasm or cell nuclei, where they regulate and participate in distinct cellular events. In this review, we focus on a few of these events and highlight the intracellular role these enzymes play. Close examination of these events, suggest that the intracellular activities of lysyl oxidases is mostly observed in processes where concomitant changes in the extracellular matrix takes place. Here, we suggest that the LOX family members act in the relay between changes in the cells’ environment and the intracellular processes that promote them or that follow.

The cellular and molecular mediators of metastasis to the lung

Organ-specific metastasis to secondary organs is dependent on the formation of a supportive pre-metastatic niche. This tissue-specific microenvironmental response is thought to be mediated by mutational and epigenetic changes to primary tumour cells resulting in altered cross-talk between cell types. This response is augmented through the release of tumour and stromal signalling mediators including cytokines, chemokines, exosomes and growth factors. Although researchers have elucidated some of the cancer-promoting features that are bespoke to organotropic metastasis to the lungs, it remains unclear if these are organ-specific or generic between organs. Understanding the mechanisms that mediate the metastasis-promoting synergy between the host microenvironment, immunity, and pulmonary structures may elucidate predictive, prognostic and therapeutic markers that could be targeted to reduce the metastatic burden of disease. Herein, we give an updated summary of the known cellular and molecular mechanisms that contribute to the formation of the lung pre-metastatic niche and tissue-specific metastasis.

Lysyl Oxidase-Like Protein-2 Silencing Suppresses the Invasion and Proliferation of Esophageal Cancer Cells

This study explores the effect of silencing lysyl oxidase-like protein-2 (LOXL2) gene on TE-1 cells. TE-1 cells were transfected by LOXL2-siRNA. E-cadherin, LOXL2, and Snail were detected using Western blot and Real-time PCR. Transwell invasion and migration assay was performed. Flow cytometry detected apoptosis. Cell growth was analyzed with CCK-8 and colony formation. After48 h of transfection, compared with control groups, LOXL2 mRNA in the LOXL2-siRNA group (0.40±0.01) lowered significantly (P < 0.05). Consistently, LOXL2 protein in LOXL2-siRNA group was (0.48± 0.02), significantly lower than that in blank control (1.04± 0.03) and negative control (1.02± 0.02) (P < 0.05). After 72 h of cell culture, the absorbance of LOXL2-siRNA group was (0.43±0.04), which reduced significantly than blank control (0.81±0.05) and negative control (0.84±0.06) (P < 0.05). Similarly, cell clone number after LOXL2-siRNA transfection (72.3±4.2)increased significantly than the negative control (178.8±4.6) and blank control (167.3±3.5) (P < 0.05). However, LOXL2 silencing did not significantly affect cell apoptosis. Furthermore, LOXL2 silencing inhibited Snail while increased E-cadherin (P < 0.05). Conclusively, LOXL2 silencing may suppress the invasion and proliferation of esophageal cancer cells via down-regulating Snail, and up-regulating E-cadherin to inhibit EMT in esophageal cancer cells.

Identifying General Tumor and Specific Lung Cancer Biomarkers by Transcriptomic Analysis

The bioinformatic pipeline previously developed in our research laboratory is used to identify potential general and specific deregulated tumor genes and transcription factors related to the establishment and progression of tumoral diseases, now comparing lung cancer with other two types of cancer. Twenty microarray datasets were selected and analyzed separately to identify hub differentiated expressed genes and compared to identify all the deregulated genes and transcription factors in common between the three types of cancer and those unique to lung cancer. The winning DEGs analysis allowed to identify an important number of TFs deregulated in the majority of microarray datasets, which can become key biomarkers of general tumors and specific to lung cancer. A coexpression network was constructed for every dataset with all deregulated genes associated with lung cancer, according to DAVID’s tool enrichment analysis, and transcription factors capable of regulating them, according to oPOSSUM´s tool. Several genes and transcription factors are coexpressed in the networks, suggesting that they could be related to the establishment or progression of the tumoral pathology in any tissue and specifically in the lung. The comparison of the coexpression networks of lung cancer and other types of cancer allowed the identification of common connectivity patterns with deregulated genes and transcription factors correlated to important tumoral processes and signaling pathways that have not been studied yet to experimentally validate their role in lung cancer. The Kaplan–Meier estimator determined the association of thirteen deregulated top winning transcription factors with the survival of lung cancer patients. The coregulatory analysis identified two top winning transcription factors networks related to the regulatory control of gene expression in lung and breast cancer. Our transcriptomic analysis suggests that cancer has an important coregulatory network of transcription factors related to the acquisition of the hallmarks of cancer. Moreover, lung cancer has a group of genes and transcription factors unique to pulmonary tissue that are coexpressed during tumorigenesis and must be studied experimentally to fully understand their role in the pathogenesis within its very complex transcriptomic scenario. Therefore, the downstream bioinformatic analysis developed was able to identify a coregulatory metafirm of cancer in general and specific to lung cancer taking into account the great heterogeneity of the tumoral process at cellular and population levels.

Context Matters: Response Heterogeneity to Collagen-Targeting Approaches in Desmoplastic Cancers

Simple Summary

A common feature of tumor types such as breast cancer, prostate cancer, pancreatic cancer, and soft-tissue sarcoma is the deposition of collagen-rich tissue called desmoplasia. However, efforts to control tumor growth by disrupting desmoplasia, collectively known as “collagen-targeting approaches”, have had mixed and contradictory results, sometimes even within the same cancer type. We believe that this phenomenon may be due—at least partially—to the fact that “collagen” is not a single molecule, but rather a diverse molecular family composed of 28 unique collagen types. Therefore, in this review, we discuss the diversity of collagen molecules in normal and cancer tissue, and explore how collagen heterogeneity relates to the mixed efficacy of collagen-targeting approaches for cancer therapy.

Abstract

The deposition of collagen-rich desmoplastic tissue is a well-documented feature of the solid tumor microenvironment (TME). However, efforts to target the desmoplastic extracellular matrix (ECM) en masse, or collagen molecules more specifically, have been met with mixed and sometimes paradoxical results. In this review, we posit that these discrepancies are due—at least in part—to the incredible diversity of the collagen superfamily. Specifically, whereas studies of “collagen-targeting” approaches frequently refer to “collagen” as a single molecule or relatively homogeneous molecular family, 28 individual collagens have been identified in mammalian tissues, each with a unique structure, supramolecular assembly pattern, tissue distribution, and/or function. Moreover, some collagen species have been shown to exert both pro- and anti-neoplastic effects in the desmoplastic TME, even within the same cancer type. Therefore, herein, we describe the diversity of the collagen family in normal tissues and highlight the context-specific roles of individual collagen molecules in desmoplastic tumors. We further discuss how this heterogeneity relates to the variable efficacy of “collagen-targeting” strategies in this setting and provide guidance for future directions in the field.

Lysyl Oxidases Expression and Breast Cancer Progression: A Bioinformatic Analysis

LOX (Lysyl oxidase) and LOX like 1–4 (LOXL1–4) are amine oxidases that catalyse the cross-linking of elastin and collagen in the extracellular matrix (ECM). This activity can facilitate cell migration and the formation of metastases. Consequently, inhibition of these enzymes and, in particular of LOXL2, has been suggested as a therapeutic strategy to prevent breast cancer metastasis. Although medicinal chemistry studies have struggled to specifically inhibit LOXL2, the importance of selectivity in this context is not clear. To explore the role of each LOX in breast cancer and consequently their potential as biomarkers or therapeutic targets, a bioinformatic-based approach was followed. The expression profile of LOXs, the putative associations among mRNA expression from each LOX and clinical observations, the correlation between expression of LOX enzymes and other genes, and the association between expression of LOXs and the tumour infiltrates were assessed for breast cancer. Overall, the patient outcome and the characteristics of breast tumours with LOX, LOXL1 and LOXL2 upregulation is distinct from those with high expression of LOXL3 and LOXL4. Additionally, the expression correlation between LOXs and other genes involved in cellular processes relevant for cancer biology, also reveals a similar trend for LOX, LOXL1 and LOX2. This work further supports the relevance of LOXL2 as a breast cancer progression biomarker and therapeutic target. We speculate that while the impact of LOXL3 inhibition may vary with breast cancer subtype, the therapeutical inhibition of LOX, LOXL1 and LOXL2 but not of LOXL4 may be the most beneficial.

Breast Cancer Genomics: Primary and Most Common Metastases

Specific genomic alterations have been found in primary breast cancer involving driver mutations that result in tumorigenesis. Metastatic breast cancer, which is uncommon at the time of disease onset, variably impacts patients throughout the course of their disease. Both the molecular profiles and diverse genomic pathways vary in the development and progression of metastatic breast cancer. From the most common metastatic site (bone), to the rare sites such as orbital, gynecologic, or pancreatic metastases, different levels of gene expression indicate the potential involvement of numerous genes in the development and spread of breast cancer. Knowledge of these alterations can, not only help predict future disease, but also lead to advancement in breast cancer treatments. This review discusses the somatic landscape of breast primary and metastatic tumors.

Lysyl Oxidase Family Enzymes and Their Role in Tumor Progression

The five genes of the lysyl oxidase family encode enzymes that covalently cross-link components of the extracellular matrix, such as various types of collagen and elastin, and, thus, promote the stabilization of extracellular matrixes. Several of these genes, in particular lysyl oxidase (LOX) and lysyl oxidase like-2 (LOXL2) were identified as genes that are upregulated by hypoxia, and promote tumor cells invasion and metastasis. Here, we focus on the description of the diverse molecular mechanisms by which the various lysyl oxidases affect tumor progression. We also describe attempts that have been made, and are still on-going, that focus on the development of efficient lysyl oxidase inhibitors for the treatment of various forms of cancer, and of diseases associated with abnormal fibrosis.

Biophysics Role and Biomimetic Culture Systems of ECM Stiffness in Cancer EMT

Oncological diseases have become the second leading cause of death from noncommunicable diseases worldwide and a major threat to human health. With the continuous progress in cancer research, the mechanical cues from the tumor microenvironment environment (TME) have been found to play an irreplaceable role in the progression of many cancers. As the main extracellular mechanical signal carrier, extracellular matrix (ECM) stiffness may influence cancer progression through biomechanical transduction to modify downstream gene expression, promote epithelial-mesenchymal transition (EMT), and regulate the stemness of cancer cells. EMT is an important mechanism that induces cancer cell metastasis and is closely influenced by ECM stiffness, either independently or in conjunction with other molecules. In this review, the unique role of ECM stiffness in EMT in different kinds of cancers is first summarized. By continually examining the significance of ECM stiffness in cancer progression, a biomimetic culture system based on 3D manufacturing and novel material technologies is developed to mimic ECM stiffness. The authors then look back on the novel development of the ECM stiffness biomimetic culture systems and finally provide new insights into ECM stiffness in cancer progression which can broaden the fields' horizons with a view toward developing new cancer diagnosis methods and therapies.

Mass Spectrometry-Based Disulfide Mapping of Lysyl Oxidase-like 2

Lysyl oxidase-like 2 (LOXL2) catalyzes the oxidative deamination of peptidyl lysines and hydroxylysines to promote extracellular matrix remodeling. Aberrant activity of LOXL2 has been associated with organ fibrosis and tumor metastasis. The lysine tyrosylquinone (LTQ) cofactor is derived from Lys653 and Tyr689 in the amine oxidase domain via post-translational modification. Based on the similarity in hydrodynamic radius and radius of gyration, we recently proposed that the overall structures of the mature LOXL2 (containing LTQ) and the precursor LOXL2 (no LTQ) are very similar. In this study, we conducted a mass spectrometry-based disulfide mapping analysis of recombinant LOXL2 in three forms: a full-length LOXL2 (fl-LOXL2) containing a nearly stoichiometric amount of LTQ, Δ1-2SRCR-LOXL2 (SRCR1 and SRCR2 are truncated) in the precursor form, and Δ1-3SRCR-LOXL2 (SRCR1, SRCR2, SRCR3 are truncated) in a mixture of the precursor and the mature forms. We detected a set of five disulfide bonds that is conserved in both the precursor and the mature recombinant LOXL2s. In addition, we detected a set of four alternative disulfide bonds in low abundance that is not associated with the mature LOXL2. These results suggest that the major set of five disulfide bonds is retained post-LTQ formation.

ELK3 Controls Gastric Cancer Cell Migration and Invasion by Regulating ECM Remodeling-Related Genes

Current therapeutic strategies for gastric cancer, including surgery and chemotherapy improve patient survival; however, the survival rate of patients with metastatic gastric cancer is very low. The molecular mechanisms underlying the dissemination of gastric cancer cells to distant organs are currently unknown. Here, we demonstrate that the E26 transformation-specific (ETS) transcription factor ELK3 (ELK3) gene is required for the migration and invasion of gastric cancer cells. The ELK3 gene modulates the expression of extracellular matrix (ECM) remodeling-related genes, such as bone morphogenetic protein (BMP1), lysyl oxidase like 2 (LOXL2), Snail family transcriptional repressor 1 (SNAI1), serpin family F member 1 (SERPINF1), decorin (DCN), and nidogen 1 (NID1) to facilitate cancer cell dissemination. Our in silico analyses indicated that ELK3 expression was positively associated with these ECM remodeling-related genes in gastric cancer cells and patient samples. The high expressions of ELK3 and other ECM remodeling-related genes were also closely associated with a worse prognosis of patients with gastric cancer. Collectively, these findings suggest that ELK3 acts as an important regulator of gastric cancer cell dissemination by regulating ECM remodeling.

Loxl3 Promotes Melanoma Progression and Dissemination Influencing Cell Plasticity and Survival

Simple Summary

Malignant melanoma is the most lethal skin cancer due to its aggressive clinical behavior and therapeutic resistance. A comprehensive knowledge of the molecular mechanisms underlying melanoma progression is urgently needed to improve the survival of melanoma patients. Phenotypic plasticity of melanoma cells has emerged as a key process in melanomagenesis and therapy resistance. This phenotypic plasticity is sustained by an epithelial-to-mesenchymal (EMT)-like program that favors multiple intermediate states and allows adaptation to changing microenvironments along melanoma progression. Given the essential role of lysyl oxidase-like 3 (LOXL3) in human melanoma cell survival and its contribution to EMT, we generated mice with conditional melanocyte-specific targeting of Loxl3, concomitant to Braf activation and Pten deletion. Our results supported a key role of Loxl3 for melanoma progression, metastatic dissemination, and genomic stability, and supported its contribution to melanoma phenotypic plasticity by modulating the expression of several EMT transcription factors (EMT-TFs).

Abstract

Malignant melanoma is a highly aggressive tumor causing most skin cancer-related deaths. Understanding the fundamental mechanisms responsible for melanoma progression and therapeutic evasion is still an unmet need for melanoma patients. Progression of skin melanoma and its dissemination to local or distant organs relies on phenotypic plasticity of melanoma cells, orchestrated by EMT-TFs and microphthalmia-associated TF (MITF). Recently, melanoma phenotypic switching has been proposed to uphold context-dependent intermediate cell states benefitting malignancy. LOXL3 (lysyl oxidase-like 3) promotes EMT and has a key role in human melanoma cell survival and maintenance of genomic integrity. To further understand the role of Loxl3 in melanoma, we generated a conditional Loxl3-knockout (KO) melanoma mouse model in the context of BrafV600E-activating mutation and Pten loss. Melanocyte-Loxl3 deletion increased melanoma latency, decreased tumor growth, and reduced lymph node metastatic dissemination. Complementary in vitro and in vivo studies in mouse melanoma cells confirmed Loxl3’s contribution to melanoma progression and metastasis, in part by modulating phenotypic switching through Snail1 and Prrx1 EMT-TFs. Importantly, a novel LOXL3-SNAIL1-PRRX1 axis was identified in human melanoma, plausibly relevant to melanoma cellular plasticity. These data reinforced the value of LOXL3 as a therapeutic target in melanoma.

Fibrosis in Mesothelioma: Potential Role of Lysyl Oxidases

Immunotherapies (such as checkpoint inhibitors) and standard chemotherapies (such as cisplatin) have limitations in the successful treatment of malignant pleural mesothelioma (MPM). Fibrosis is the accumulation of collagen in the extracellular matrix (ECM) of tissues, making them denser than that of healthy tissues and thereby affecting drug delivery and immune cell infiltration. Moreover, fibrosis severely affects the patient's breathing and quality of life. The production of collagen and its assembly is highly regulated by various enzymes such as lysyl oxidases. Many solid tumors aberrantly express the family of lysyl oxidases (LOX/LOXL). This review examines how LOX/LOXLs were found to be dysregulated in noncancerous and cancerous settings, discusses their roles in solid tumor fibrosis and pathogenesis and explores the role of fibrosis in the development and poor clinical outcomes of patients with MPM. We examine the current preclinical status of drugs targeting LOX/LOXLs and how the incorporation of such drugs may have therapeutic benefits in the treatment and management of patients with MPM.

Systematic Analysis of Expression and Prognostic Values of Lysyl Oxidase Family in Gastric Cancer

Background: Gastric cancer (GC) remains the fifth most commonly diagnosed malignancy worldwide, with a poor prognosis. The lysyl oxidase (LOX) family, a type of secreted copper-dependent amine oxidases, is comprised of LOX and four LOX-like (LOXL) 1–4 isoforms and has been reported to be dysregulated in a number of different type cancers. However, the diverse expression patterns and prognostic values of LOX family in GC have yet to be systematically analyzed.

Methods: ONCOMINE, GEPIA, UALCAN, Kaplan–Meier Plotter, LOGpc, cBioPortal, GeneMANIA and Metascape databases were utilized in this study to analyze the expression, prognostic values, mutations and functional networks of LOX family in GC.

Results: The mRNA expression levels of LOX, LOXL1 and LOXL2 were significantly higher in GC, the expression level of LOXL3 was contrary in different databases, while the expression level of LOXL4 made no difference; the expression levels of LOX, LOXL1 and LOXL3 were higher in stages 2–4 than that of normal tissues and stage 1, while the mRNA level of LOXL2 in stage 1–4 was higher than normal tissues; patients with high expression of LOX and LOXL 2-4 had poor OS; the genes correlated with LOX and LOXL2 were enriched in extracellular matrix organization, vasculature development and skeletal system development.

Conclusion: Our results indicated that the LOX family, especially LOX and LOXL2, might play an important role in GC oncogenesis, and they may become biomarkers for predicting tumor prognosis and potential targets for tumor therapy.

Spatial collagen stiffening promotes collective breast cancer cell invasion by reinforcing extracellular matrix alignment

The tumor micro-environment often contains stiff and irregular-bundled collagen fibers that are used by tumor cells to disseminate. It is still unclear how and to what extent, extracellular matrix (ECM) stiffness versus ECM bundle size and alignment dictate cancer cell invasion. Here, we have uncoupled Collagen-I bundling from stiffness by introducing inter-collagen crosslinks, combined with temperature induced aggregation of collagen bundling. Using organotypic models from mouse invasive ductal and invasive lobular breast cancers, we show that increased collagen bundling in 3D induces a generic increase in breast cancer invasion that is independent of migration mode. However, systemic collagen stiffening using advanced glycation end product (AGE) crosslinking prevents collective invasion, while leaving single cell invasion unaffected. Collective invasion into collagen matrices by ductal breast cancer cells depends on Lysyl oxidase-like 3 (Loxl3), a factor produced by tumor cells that reinforces local collagen stiffness. Finally, we present clinical evidence that collectively invading cancer cells at the invasive front of ductal breast carcinoma upregulate LOXL3. By uncoupling the mechanical, chemical, and structural cues that control invasion of breast cancer in three dimensions, our data reveal that spatial control over stiffness and bundling underlie collective dissemination of ductal-type breast cancers.

The microenvironment of brain metastases from solid tumors

Brain metastasis (BrM) is an area of unmet medical need that poses unique therapeutic challenges and heralds a dismal prognosis. The intracranial tumor microenvironment (TME) presents several challenges, including the therapy-resistant blood-brain barrier, a unique immune milieu, distinct intercellular interactions, and specific metabolic conditions, that are responsible for treatment failures and poor clinical outcomes. There is a complex interplay between malignant cells that metastasize to the central nervous system (CNS) and the native TME. Cancer cells take advantage of vascular, neuronal, immune, and anatomical vulnerabilities to proliferate with mechanisms specific to the CNS. In this review, we discuss unique aspects of the TME in the context of brain metastases and pathways through which the TME may hold the key to the discovery of new and effective therapies for patients with BrM.

Reciprocal regulation of LOXL2 and HIF1α drives the Warburg effect to support pancreatic cancer aggressiveness

Hypoxic microenvironment is common in solid tumors, particularly in pancreatic ductal adenocarcinoma (PDAC). The Warburg effect is known to facilitate cancer aggressiveness and has long been linked to hypoxia, yet the underlying mechanism remains largely unknown. In this study, we identify that lysyl oxidase-like 2 (LOXL2) is a hypoxia-responsive gene and is essential for the Warburg effect in PDAC. LOXL2 stabilizes hypoxia-inducible factor 1α (HIF1α) from prolyl hydroxylase (PHD)-dependent hydroxylation via hydrogen peroxide generation, thereby facilitating the transcription of multiple glycolytic genes. Therefore, a positive feedback loop exists between LOXL2 and HIF1α that facilitates glycolytic metabolism under hypoxia. Moreover, LOXL2 couples the Warburg effect to tumor growth and metastasis in PDAC. Hijacking glycolysis largely compromises LOXL2-induced oncogenic activities. Collectively, our results identify a hitherto unknown hypoxia-LOXL2-HIF1α axis in regulating the Warburg effect and provide an intriguing drug target for PDAC therapy.

The Role of Tumor Microenvironment and Exosomes in Dormancy and Relapse

Recent advancements in the field of cancer have established that the process of metastasis is organ-specific with tumor cell dissemination occurring in the very early stages of disease. Pre-metastatic niches are actively remodeled and transformed by both primary tumor specific factors and by influences from the extracellular matrix.Although improvements in cancer therapies have significantly improved outcomes in patients with early stage disease, the risk of recurrence and relapse leading to mortality remains high. Recent studies have emerged highlighting the influence of dormant tumor cells and exosomes as key players in cancer relapse. In this review we discuss the critical mediators of tumor progression and their link to cancer dormancy, while also exploring possible therapeutics for targeting relapse.

Recent Advances in Repurposing Disulfiram and Disulfiram Derivatives as Copper-Dependent Anticancer Agents

Copper (Cu) plays a pivotal role in cancer progression by acting as a co-factor that regulates the activity of many enzymes and structural proteins in cancer cells. Therefore, Cu-based complexes have been investigated as novel anticancer metallodrugs and are considered as a complementary strategy for currently used platinum agents with undesirable general toxicity. Due to the high failure rate and increased cost of new drugs, there is a global drive towards the repositioning of known drugs for cancer treatment in recent years. Disulfiram (DSF) is a first-line antialcoholism drug used in clinics for more than 65 yr. In combination with Cu, it has shown great potential as an anticancer drug by targeting a wide range of cancers. The reaction between DSF and Cu ions forms a copper diethyldithiocarbamate complex (Cu(DDC)₂ also known as CuET) which is the active, potent anticancer ingredient through inhibition of NF-κB and ubiquitin-proteasome system as well as alteration of the intracellular reactive oxygen species (ROS). Importantly, DSF/Cu inhibits several molecular targets related to drug resistance, stemness, angiogenesis and metastasis and is thus considered as a novel strategy for overcoming tumour recurrence and relapse in patients. Despite its excellent anticancer efficacy, DSF has proven unsuccessful in several cancer clinical trials. This is likely due to the poor stability, rapid metabolism and/or short plasma half-life of the currently used oral version of DSF and the inability to form Cu(DDC)₂ at relevant concentrations in tumour tissues. Here, we summarize the scientific rationale, molecular targets, and mechanisms of action of DSF/Cu in cancer cells and the outcomes of oral DSF ± Cu in cancer clinical trials. We will focus on the novel insights on harnessing the immune system and hypoxic microenvironment using DSF/Cu complex and discuss the emerging delivery strategies that can overcome the shortcomings of DSF-based anticancer therapies and provide opportunities for translation of DSF/Cu or its Cu(DDC)₂ complex into cancer therapeutics.

Understanding the molecular mechanism associated with reversal of oral submucous fibrosis targeting hydroxylysine aldehyde-derived collagen cross-links

Fibrosis is a pathological state characterized by excessive deposition of the extracellular matrix components leading to impaired tissue function in the affected organ. It results in scarring of the affected tissue akin to an over-healing wound as a consequence of chronic inflammation and repair in response to injury. Persistent trauma of susceptible oral mucosa due to habitual chewing of betel quid resulting in zealous healing of the mucosal tissue is one plausible explanation for the onset of oral submucous fibrosis (OSF). The irreversibility and resistance of collagen to degradation and its high potential to undergo malignant change are a major reason for morbidity in OSF. Hence, early diagnosis and timely treatment are crucial to prevent the progression of OSF to malignancy. This review focuses on the mechanistic insight into the role of collagen cross-links in advancing fibrosis and possible therapeutic targets that bring about a reversal of fibrosis. These options may be beneficial if attempted as a specific therapeutic modality in OSF as is in organ fibrosis. The upregulation of lysyl oxidase and lysyl hydroxylase has been shown to exhibit the higher levels of the hydroxylysine aldehyde-derived cross-links in fibrosis and tumor stroma promoting the tumor cell survival, resistance, and invasion. The in silico analysis highlights the potential drugs that may target the genes regulating collagen crosslinking.

A glitch in the matrix: organ-specific matrisomes in metastatic niches

Modification of the extracellular matrix (ECM) is a critical aspect of developing a metastasis-supportive organ niche. Recent work investigating ECM changes that facilitate metastasis has revealed ways in which different metastatic organ niches are similar as well as the distinct characteristics that make them unique. In this review, we present recent findings regarding how ECM modifications support metastasis in four frequent metastatic sites: the lung, liver, bone, and brain. We discuss ways in which these modifications are shared between metastatic organs as well as features specific to each location. We also discuss areas of technical innovation that could be advantageous to future research and areas of inquiry that merit further investigation.

E2A Modulates Stemness, Metastasis, and Therapeutic Resistance of Breast Cancer

Cancer stem cells (CSC) are considered responsible for tumor initiation, therapeutic resistance, and metastasis. A comprehensive knowledge of the mechanisms governing the acquisition and maintenance of cancer stemness is crucial for the development of new therapeutic approaches in oncology. E2A basic helix-loop-helix (bHLH) transcription factors are associated with epithelial-mesenchymal transition (EMT) and tumor progression, but knowledge of their functional contributions to cancer biology is still limited. Using a combination of in vivo and in vitro analyses in a novel PyMT-E2A conditional knockout mouse model and derived primary tumor cell lines, we report here an essential role of E2A in stemness, metastasis, and therapeutic resistance in breast cancer. Targeted deletion of E2A in the mammary gland impaired tumor-initiating ability and dedifferentiation potential and severely compromised metastatic competence of PyMT-driven mammary tumors. Mechanistic studies in PyMT-derived cell lines indicated that E2A actions are mediated by the upregulation of Snai1 transcription. Importantly, high E2A and SNAIL1 expression occurred in aggressive human basal-like breast carcinomas, highlighting the relevance of the E2A-Snail1 axis in metastatic breast cancer. In addition, E2A factors contributed to the maintenance of genomic integrity and resistance to PARP inhibitors in PyMT and human triple-negative breast cancer cells. Collectively, these results support the potential for E2A transcription factors as novel targets worthy of translational consideration in breast cancer. SIGNIFICANCE: These findings identify key functions of E2A factors in breast cancer cell stemness, metastasis, and drug resistance, supporting a therapeutic vulnerability to targeting E2A proteins in breast cancer.

Stresses in the metastatic cascade: molecular mechanisms and therapeutic opportunities

In this review, Shen and Kang provide an overview of the tumor-intrinsic and microenvironment- and treatment-induced stresses that tumor cells encounter in the metastatic cascade and the molecular pathways they develop to relieve these stresses.

Metastasis is the ultimate “survival of the fittest” test for cancer cells, as only a small fraction of disseminated tumor cells can overcome the numerous hurdles they encounter during the transition from the site of origin to a distinctly different distant organ in the face of immune and therapeutic attacks and various other stresses. During cancer progression, tumor cells develop a variety of mechanisms to cope with the stresses they encounter, and acquire the ability to form metastases. Restraining these stress-releasing pathways could serve as potentially effective strategies to prevent or reduce metastasis and improve the survival of cancer patients. Here, we provide an overview of the tumor-intrinsic, microenvironment- and treatment-induced stresses that tumor cells encounter in the metastatic cascade and the molecular pathways they develop to relieve these stresses. We also summarize the preclinical and clinical studies that evaluate the potential therapeutic benefit of targeting these stress-relieving pathways.

Fibroblast-macrophage reciprocal interactions in health, fibrosis, and cancer

Fibroblasts and macrophages are present in all tissues, and mounting evidence supports that these cells engage in direct communication to influence the overall tissue microenvironment and affect disease outcomes. Here, we review the current understanding of the molecular mechanisms that underlie fibroblast-macrophage interactions in health, fibrosis, and cancer. We present an integrated view of fibroblast-macrophage interactions that is centered on the CSF1-CSF1R axis and discuss how additional molecular programs linking these cell types can underpin disease onset, progression, and resolution. These programs may be tissue and context dependent, affected also by macrophage and fibroblast origin and state, as seen most clearly in cancer. Continued efforts to understand these cells and the means by which they interact may provide therapeutic approaches for the treatment of fibrosis and cancer.

Tumour-associated macrophages drive stromal cell-dependent collagen crosslinking and stiffening to promote breast cancer aggression

Stromal stiffening accompanies malignancy, compromises treatment and promotes tumour aggression. Clarifying the molecular nature and the factors that regulate stromal stiffening in tumours should identify biomarkers to stratify patients for therapy and interventions to improve outcome. We profiled lysyl hydroxylase-mediated and lysyl oxidase-mediated collagen crosslinks and quantified the greatest abundance of total and complex collagen crosslinks in aggressive human breast cancer subtypes with the stiffest stroma. These tissues harbour the highest number of tumour-associated macrophages, whose therapeutic ablation in experimental models reduced metastasis, and decreased collagen crosslinks and stromal stiffening. Epithelial-targeted expression of the crosslinking enzyme, lysyl oxidase, had no impact on collagen crosslinking in PyMT mammary tumours, whereas stromal cell targeting did. Stromal cells in microdissected human tumours expressed the highest level of collagen crosslinking enzymes. Immunohistochemical analysis of biopsies from a cohort of patients with breast cancer revealed that stromal expression of lysyl hydroxylase 2, an enzyme that induces hydroxylysine aldehyde-derived collagen crosslinks and stromal stiffening, correlated significantly with disease specific mortality. The findings link tissue inflammation, stromal cell-mediated collagen crosslinking and stiffening to tumour aggression and identify lysyl hydroxylase 2 as a stromal biomarker.

A Theoretical Approach to Coupling the Epithelial-Mesenchymal Transition (EMT) to Extracellular Matrix (ECM) Stiffness via LOXL2

Simple Summary

Epithelial-mesenchymal transition (EMT) is a key process in cancer progression through which cells weaken their cell-cell adhesion and gain mobility and invasive traits. Besides chemical signaling, recent studies have established the connection of EMT to mechanical microenvironment, such as the stiffness of extracellular matrix (ECM). LOXL2 is representative of a family of enzymes that promotes fiber cross-linking in ECM. With increased cross-linking comes increased stiffness, which induces EMT that can, in turn, elevate LOXL2 levels. As such, a positive feedback loop among EMT, LOXL2, and ECM stiffness can be formed. We built a mathematical model on a core biochemical reaction network featuring this feedback loop, and showed how strongly it drives EMT. We also illustrated mechanistically how cross-linking connects with stiffness, using a mechanical model of collagen (a major component of ECM). Using this theoretical framework, we demonstrated the heterogeneity of LOXL2/stiffness and its implications on migrating cancer cells that could seed metastasis, the growth of secondary malignant tumors. This framework can inspire experimental studies of more fine-grained mechanotransduction and biomechanical heterogeneity in cancers.

Abstract

The epithelial-mesenchymal transition (EMT) plays a critical role in cancer progression, being responsible in many cases for the onset of the metastatic cascade and being integral in the ability of cells to resist drug treatment. Most studies of EMT focus on its induction via chemical signals such as TGF-β or Notch ligands, but it has become increasingly clear that biomechanical features of the microenvironment such as extracellular matrix (ECM) stiffness can be equally important. Here, we introduce a coupled feedback loop connecting stiffness to the EMT transcription factor ZEB1, which acts via increasing the secretion of LOXL2 that leads to increased cross-linking of collagen fibers in the ECM. This increased cross-linking can effectively increase ECM stiffness and increase ZEB1 levels, thus setting a positive feedback loop between ZEB1 and ECM stiffness. To investigate the impact of this non-cell-autonomous effect, we introduce a computational approach capable of connecting LOXL2 concentration to increased stiffness and thereby to higher ZEB1 levels. Our results indicate that this positive feedback loop, once activated, can effectively lock the cells in a mesenchymal state. The spatial-temporal heterogeneity of the LOXL2 concentration and thus the mechanical stiffness also has direct implications for migrating cells that attempt to escape the primary tumor.

3D bioprinting of engineered breast cancer constructs for personalized and targeted cancer therapy

The bioprinting technique with specialized tissue production allows the study of biological, physiological, and behavioral changes of cancerous and non-cancerous tissues in response to pharmacological compounds in personalized medicine. To this end, to evaluate the efficacy of anticancer drugs before entering the clinical setting, tissue engineered 3D scaffolds containing breast cancer and derived from the especially patient, similar to the original tissue architecture, can potentially be used. Despite recent advances in the manufacturing of 3D bioprinted breast cancer tissue (BCT), many studies still suffer from reproducibility primarily because of the uncertainty of the materials used in the scaffolds and lack of printing methods. In this review, we present an overview of the breast cancer environment to optimize personalized treatment by examining and identifying the physiological and biological factors that mimic BCT. We also surveyed the materials and techniques related to 3D bioprinting, i.e, 3D bioprinting systems, current strategies for fabrication of 3D bioprinting tissues, cell adhesion and migration in 3D bioprinted BCT, and 3D bioprinted breast cancer metastasis models. Finally, we emphasized on the prospective future applications of 3D bioprinted cancer models for rapid and accurate drug screening in breast cancer.

Salting the Soil: Targeting the Microenvironment of Brain Metastases

Paget's "seed and soil" hypothesis of metastatic spread has acted as a foundation of the field for over a century, with continued evolution as mechanisms of the process have been elucidated. The central nervous system (CNS) presents a unique soil through this lens, relatively isolated from peripheral circulation and immune surveillance with distinct cellular and structural composition. Research in primary and metastatic brain tumors has demonstrated that this tumor microenvironment (TME) plays an essential role in the growth of CNS tumors. In each case, the cancerous cells develop complex and bidirectional relationships that reorganize the local TME and reprogram the CNS cells, including endothelial cells, pericytes, astrocytes, microglia, infiltrating monocytes, and lymphocytes. These interactions create a structurally and immunologically permissive TME with malignant processes promoting positive feedback loops and systemic consequences. Strategies to interrupt interactions with the native CNS components, on "salting the soil," to create an inhospitable environment are promising in the preclinical setting. This review aims to examine the general and specific pathways thus far investigated in brain metastases and related work in glioma to identify targetable mechanisms that may have general application across the spectrum of intracranial tumors.

LOXL2 Inhibitors and Breast Cancer Progression

LOX (lysyl oxidase) and lysyl oxidase like-1–4 (LOXL 1–4) are amine oxidases, which catalyze cross-linking reactions of elastin and collagen in the connective tissue. These amine oxidases also allow the cross-link of collagen and elastin in the extracellular matrix of tumors, facilitating the process of cell migration and the formation of metastases. LOXL2 is of particular interest in cancer biology as it is highly expressed in some tumors. This protein also promotes oncogenic transformation and affects the proliferation of breast cancer cells. LOX and LOXL2 inhibition have thus been suggested as a promising strategy to prevent metastasis and invasion of breast cancer. BAPN (β-aminopropionitrile) was the first compound described as a LOX inhibitor and was obtained from a natural source. However, novel synthetic compounds that act as LOX/LOXL2 selective inhibitors or as dual LOX/LOX-L inhibitors have been recently developed. In this review, we describe LOX enzymes and their role in promoting cancer development and metastases, with a special focus on LOXL2 and breast cancer progression. Moreover, the recent advances in the development of LOXL2 inhibitors are also addressed. Overall, this work contextualizes and explores the importance of LOXL2 inhibition as a promising novel complementary and effective therapeutic approach for breast cancer treatment.