Dormant tumor cells expressing LOXL2 acquire a stem-like phenotype mediating their transition to proliferative growth

Lysyl Oxidase (LOX) Family Proteins: Key Players in Breast Cancer Occurrence and Progression

The lysyl oxidase (LOX) family proteins are secreted copper-dependent amine oxidases, comprised of five paralogues: LOX and LOX-like 1-4 (LOXL1-4), which are characterized by catalytic activity contributing to the remodeling of the cross-linking of the structural extracellular matrix (ECM). ECM remodeling plays a key role in the angiogenesis surrounding tumours, whereby a corrupt tumour microenvironment (TME) takes shape. Additionally, dysregulation and aberrant expression of LOX family proteins have been implicated in the occurrence and progression of various types of human cancers, including lung cancer, hepatocellular carcinoma, gastric cancer, renal cell carcinoma, and colorectal cancer. Breast cancer is the most prevalent malignant tumour in women worldwide, and its incidence rate is increasing annually. In recent years, a growing body of evidence has revealed significant upregulation of LOX family proteins in breast cancer, which contributes to cancer cell proliferation, invasion, and metastasis. Furthermore, elevated expression of LOX family proteins is closely associated with poor prognosis in breast cancer patients. We herein review the structure, regulation, function, and mechanisms of LOX family proteins in the occurrence and progression of breast cancer. In addition, we highlight recent insights into their mechanisms and their potential involvement in the clinical value and novel biological roles of LOX family members in tumour progression and the TME of breast cancer. This review will provide a theoretical basis and reference for clinical diagnosis and treatment of breast cancer, as well as for the screening of effective LOX-specific inhibitors.

The ubiquitin-proteasome system in the regulation of tumor dormancy and recurrence

Tumor recurrence is a mechanism triggered in sparse populations of cancer cells that usually remain in a quiescent state after strict stress and/or therapeutic factors, which is affected by a variety of autocrine and microenvironmental cues. Despite thorough investigations, the biology of dormant and/or cancer stem cells is still not fully elucidated, as for the mechanisms of their reawakening, while only the major molecular patterns driving the relapse process have been identified to date. These molecular patterns profoundly interfere with the elements of cellular proteostasis systems that support the efficiency of the recurrence process. As a major proteostasis machinery, we review the role of the ubiquitin-proteasome system (UPS) in tumor cell dormancy and reawakening, devoting particular attention to the functions of its components, E3 ligases, deubiquitinating enzymes and proteasomes in cancer recurrence. We demonstrate how UPS components functionally or mechanistically interact with the pivotal proteins implicated in the recurrence program and reveal that modulators of the UPS hold promise to become an efficient adjuvant therapy for eradicating refractory tumor cells to impede tumor relapse.

In Vitro and In Vivo Systems to Study Tumor Dormancy and the Transition to Overt Metastases Induced by the Fibrotic Milieu

Metastatic breast cancer is a major cause of mortality among breast cancer patients (Sauer et al. Front Oncol: 11:659963, 2021). It may emerge years or even decades after the initial treatment of the primary tumor. This latency in the manifestation of the disease is attributed to the presence of early disseminated tumor cells (DTCs) that lay quiescent (dormant) for years until they emerge as clinically overt metastases. Given that to date we have no treatment to cure metastatic disease, it is vital to investigate ways to eradicate dormant DTCs and/or prevent their emergence to overt metastases. Here, we present a modified 3-dimensional in vitro system to model the in vivo growth characteristics of several tumor cell lines that exhibit either dormant behavior (D2.0R, MCF7) or transient dormant metastatic behavior (D2A1) at a metastatic secondary site. Additionally, we present an in vitro and complementary in vivo system to study the switch from dormancy to metastatic growth driven by a fibrotic-like milieu enriched with the deposition of type I collagen.

How circulating tumor cluster biology contributes to the metastatic cascade: from invasion to dissemination and dormancy

Circulating tumor cells (CTCs) are known to be prognostic for metastatic relapse and are detected in patients as solitary cells or cell clusters. Circulating tumor cell clusters (CTC clusters) have been observed clinically for decades and are of significantly higher metastatic potential compared to solitary CTCs. Recent studies suggest distinct differences in CTC cluster biology regarding invasion and survival in circulation. However, differences regarding dissemination, dormancy, and reawakening require more investigations compared to solitary CTCs. Here, we review the current state of CTC cluster research and consider their clinical significance. In addition, we discuss the concept of collective invasion by CTC clusters and molecular evidence as to how cluster survival in circulation compares to that of solitary CTCs. Molecular differences between solitary and clustered CTCs during dormancy and reawakening programs will also be discussed. We also highlight future directions to advance our current understanding of CTC cluster biology.

Dormancy in Breast Cancer

The pattern of delayed recurrence in a subset of breast cancer patients has long been explained by a model that incorporates a variable period of cellular or tumor mass dormancy prior to disease relapse. In this review, we critically evaluate existing data to develop a framework for inferring the existence of dormancy in clinical contexts of breast cancer. We integrate these clinical data with rapidly evolving mechanistic insights into breast cancer dormancy derived from a broad array of genetically engineered mouse models as well as experimental models of metastasis. Finally, we propose actionable interventions and discuss ongoing clinical trials that translate the wealth of knowledge gained in the laboratory to the long-term clinical management of patients at a high risk of developing recurrence.

Lysyl oxidase-like 2 promotes stemness and enhances antitumor effects of gefitinib in head and neck cancer via IFIT1 and IFIT3

Lysyl oxidase-like 2 (LOXL2) is a matrix-remodeling enzyme that has recently been identified as an important regulator of tumor progression and metastasis. This study discovered that LOXL2 expression in oral squamous cell carcinoma (OSCC) tissues was significantly associated with tumor clinical stage, lymph node metastasis and patients' overall survival time. LOXL2-overexpressing human buccal SCC TW2.6 (TW2.6/LOXL2) and hypopharyngeal SCC FaDu (FaDu/LOXL2) cells exhibited enhanced migration, invasion, epithelial-mesenchymal transition (EMT), and cancer stem cell (CSC) phenotypes, independently of its enzymatic activity. Moreover, TW2.6/LOXL2 significantly increased tumor-initiating frequency in SCID mice. We further demonstrated that LOXL2 increased the levels of interferon-induced protein with tetratricopeptide repeats 1 (IFIT1) and IFIT3 in TW2.6/LOXL2 and FaDu/LOXL2 cells. We also identified IFIT1 and IFIT3 as key downstream components of LOXL2 action in migration, invasion, EMT, and CSC phenotypes in TW2.6 and FaDu cells. Furthermore, a significant positive correlation between LOXL2 expression and IFIT1 and IFIT3 overexpression in human OSCC tissues was observed. In addition, TW2.6/LOXL2 and FaDu/LOXL2 cells were 3.3- to 3.6-fold more susceptible to the epidermal growth factor receptor (EGFR) inhibitor gefitinib than were their respective control cells. The antitumor effect of gefitinib on orthotopic TW2.6/LOXL2 xenograft tumor was fourfold higher than that on controls. Our results indicate that LOXL2 expression is a strong prognostic factor for OSCC and may be used as a marker to identify patients most likely to respond to EGFR-targeted therapy.

Awakening of Dormant Breast Cancer Cells in the Bone Marrow

Up to 40% of patients with breast cancer (BC) have metastatic cells in the bone marrow (BM) at the initial diagnosis of localized disease. Despite definitive systemic adjuvant therapy, these cells survive in the BM microenvironment, enter a dormant state and recur stochastically for more than 20 years. Once they begin to proliferate, recurrent macrometastases are not curable, and patients generally succumb to their disease. Many potential mechanisms for initiating recurrence have been proposed, but no definitive predictive data have been generated. This manuscript reviews the proposed mechanisms that maintain BC cell dormancy in the BM microenvironment and discusses the data supporting specific mechanisms for recurrence. It addresses the well-described mechanisms of secretory senescence, inflammation, aging, adipogenic BM conversion, autophagy, systemic effects of trauma and surgery, sympathetic signaling, transient angiogenic bursts, hypercoagulable states, osteoclast activation, and epigenetic modifications of dormant cells. This review addresses proposed approaches for either eliminating micrometastases or maintaining a dormant state.

Reciprocal Regulation of Cancer-Associated Fibroblasts and Tumor Microenvironment in Gastrointestinal Cancer: Implications for Cancer Dormancy

Gastrointestinal (GI) cancers remain a major cause of cancer-related deaths worldwide. Despite the progress made in current treatments, patients with GI cancers still have high recurrence rates after initial treatment. Cancer dormancy, which involves the entry and escape of cancer cells from dormancy, is linked to treatment resistance, metastasis, and disease relapse. Recently, the role of the tumor microenvironment (TME) in disease progression and treatment has received increasing attention. The crosstalk between cancer-associated fibroblasts (CAF)-secreted cytokines/chemokines and other TME components, for example, extracellular matrix remodeling and immunomodulatory functions, play crucial roles in tumorigenesis. While there is limited direct evidence of a relationship between CAFs and cancer cell dormancy, this review explores the potential of CAF-secreted cytokines/chemokines to either promote cancer cell dormancy or awaken dormant cancer cells under different conditions, and the therapeutic strategies that may be applicable. By understanding the interactions between cytokines/chemokines released by CAFs and the TME, and their impact on the entry/escape of cancer dormancy, researchers may develop new strategies to reduce the risk of therapeutic relapse in patients with GI cancers.

The genomic regulation of metastatic dormancy

The genomics and pathways governing metastatic dormancy are critically important drivers of long-term patient survival given the considerable portion of cancers that recur aggressively months to years after initial treatments. Our understanding of dormancy has expanded greatly in the last two decades, with studies elucidating that the dormant state is regulated by multiple genes, microenvironmental (ME) interactions, and immune components. These forces are exerted through mechanisms that are intrinsic to the tumor cell, manifested through cross-talk between tumor and ME cells including those from the immune system, and regulated by angiogenic processes in the nascent micrometastatic niche. The development of new in vivo and 3D ME models, as well as enhancements to decades-old tumor cell pedigree models that span the development of metastatic dormancy to aggressive growth, has helped fuel what arguably is one of the least understood areas of cancer biology that nonetheless contributes immensely to patient mortality. The current review focuses on the genes and molecular pathways that regulate dormancy via tumor-intrinsic and ME cells, and how groups have envisioned harnessing these therapeutically to benefit patient survival.

C4orf47 contributes to the dormancy of pancreatic cancer under hypoxic conditions

In our comprehensive analysis of pancreatic cancer pathology, we found that the C4orf47 molecule was upregulated in hypoxic environments. C4orf47 is reported to be a centrosome-associated protein, but its biological significance in cancer is completely unknown; therefore, we assessed its role in pancreatic cancer. We found that C4orf47 was a direct target of HIF-1α and is upregulated in hypoxic conditions, in which it suppressed the cell cycle and inhibits cell proliferation through up-regulation of the cell cycle repressors Fbxw-7, P27, and p57; and the down-regulation of the cell cycle promoters c-myc, cyclinD1, and cyclinC. Furthermore, C4orf47 induced epithelial-mesenchymal transition and enhanced their cell plasticity and invasiveness. In addition, the p-Erk/p-p38 ratio was significantly enhanced and down-regulated CD44 expression by C4orf47 suppression, suggesting that C4orf47 is involved in pancreatic cancer dormancy under hypoxic conditions. Furthermore, the potential of C4orf47 expression was a good prognostic biomarker for pancreatic cancer. These results contribute to the elucidation of the pathology of refractory pancreatic cancer and the development of novel therapeutic strategies.

Regulation of Metastatic Tumor Dormancy and Emerging Opportunities for Therapeutic Intervention

Cancer recurrence and metastasis, following successful treatment, constitutes a critical threat in clinical oncology and are the leading causes of death amongst cancer patients. This phenomenon is largely attributed to metastatic tumor dormancy, a rate-limiting stage during cancer progression, in which disseminated cancer cells remain in a viable, yet not proliferating state for a prolonged period. Dormant cancer cells are characterized by their entry into cell cycle arrest and survival in a quiescence state to adapt to their new microenvironment through the acquisition of mutations and epigenetic modifications, rendering them resistant to anti-cancer treatment and immune surveillance. Under favorable conditions, disseminated dormant tumor cells 're-awake', resume their proliferation and thus colonize distant sites. Due to their rarity, detection of dormant cells using current diagnostic tools is challenging and, thus, therapeutic targets are hard to be identified. Therefore, unraveling the underlying mechanisms required for keeping disseminating tumor cells dormant, along with signals that stimulate their "re-awakening" are crucial for the discovery of novel pharmacological treatments. In this review, we shed light into the main mechanisms that control dormancy induction and escape as well as emerging therapeutic strategies for the eradication of metastatic dormant cells, including dormancy maintenance, direct targeting of dormant cells and re-awakening dormant cells. Studies on the ability of the metastatic cancer cells to cease proliferation and survive in a quiescent state before re-initiating proliferation and colonization years after successful treatment, will pave the way toward developing innovative therapeutic strategies against dormancy-mediated metastatic outgrowth.

Lysyl Oxidase Family Proteins: Prospective Therapeutic Targets in Cancer

The lysyl oxidase (LOX) family, consisting of LOX and LOX-like proteins 1–4 (LOXL1–4), is responsible for the covalent crosslinking of collagen and elastin, thus maintaining the stability of the extracellular matrix (ECM) and functioning in maintaining connective tissue function, embryonic development, and wound healing. Recent studies have found the aberrant expression or activity of the LOX family occurs in various types of cancer. It has been proved that the LOX family mainly performs tumor microenvironment (TME) remodeling function and is extensively involved in tumor invasion and metastasis, immunomodulation, proliferation, apoptosis, etc. With relevant translational research in progress, the LOX family is expected to be an effective target for tumor therapy. Here, we review the research progress of the LOX family in tumor progression and therapy to provide novel insights for future exploration of relevant tumor mechanism and new therapeutic targets.

Connexin32 regulates expansion of liver cancer stem cells via the PI3K/Akt signaling pathway

Liver cancer stem cells (LCSCs) are responsible for liver cancer recurrence, metastasis, and drug resistance. Previous studies by the authors demonstrated that upregulated expression of connexin 32 (Cx32) reversed doxorubicin resistance and reduced invasion and metastasis of liver cancer cells. However, the role of Cx32 in expansion of LCSCs remains unclear. A total of 85 patients were enrolled in the present study and followed-up for 5 years. The expression of Cx32 in hepatocellular carcinoma (HCC) tissues and corresponding paracancerous tissues were detected by immunohistochemistry (IHC). Cx32 was silenced in HepG2 cells and overexpressed in HCCLM3 cells and the stemness of liver cells was examined by detecting the expression of LCSC markers (EpCAM, CD133, Nanog, Oct4, Sox9, c-Myc), sphere formation, and xenograft tumorigenesis. Finally, the effect of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway on Cx32-regulated LCSC expansion was investigated. Cx32 was downregulated in LCSCs and HCC tissues, and predicted poor prognosis in patients with HCC. Overexpression of Cx32 in HCCLM3 cells significantly inhibited LCSC expansion, tumorigenesis, and phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway activity. By contrast, silencing of Cx32 in HepG2 cells upregulated expansion of LCSCs and PI3K/Akt pathway activity. Modulating the activity of the PI3K/Akt pathway by SC-79 and LY294002 in HepG2 and HCCLM3 cells, respectively, confirmed that Cx32 could affect the expansion of LCSCs through PI3K/Akt signaling. In conclusion, the present study demonstrated that Cx32 regulated the expansion of LCSCs, and increased expression of Cx32 significantly inhibited the expansion of LCSCs, suggesting that Cx32 may be an optimal target for intervention of HCC.

Novel estrogen-responsive genes (ERGs) for the evaluation of estrogenic activity

Estrogen action is mediated by various genes, including estrogen-responsive genes (ERGs). ERGs have been used as reporter-genes and markers for gene expression. Gene expression profiling using a set of ERGs has been used to examine statistically reliable transcriptomic assays such as DNA microarray assays and RNA sequencing (RNA-seq). However, the quality of ERGs has not been extensively examined. Here, we obtained a set of 300 ERGs that were newly identified by six sets of RNA-seq data from estrogen-treated and control human breast cancer MCF-7 cells. The ERGs exhibited statistical stability, which was based on the coefficient of variation (CV) analysis, correlation analysis, and examination of the functional association with estrogen action using database searches. A set of the top 30 genes based on CV ranking were further evaluated quantitatively by RT-PCR and qualitatively by a functional analysis using the GO and KEGG databases and by a mechanistic analysis to classify ERα/β-dependent or ER-independent types of transcriptional regulation. The 30 ERGs were characterized according to (1) the enzymes, such as metabolic enzymes, proteases, and protein kinases, (2) the genes with specific cell functions, such as cell-signaling mediators, tumor-suppressors, and the roles in breast cancer, (3) the association with transcriptional regulation, and (4) estrogen-responsiveness. Therefore, the ERGs identified here represent various cell functions and cell signaling pathways, including estrogen signaling, and thus, may be useful to evaluate estrogenic activity.

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.

Dormancy: There and Back Again

Many cells are capable of maintaining viability in a non-dividing state with minimal metabolism under unfavorable conditions. These are germ cells, adult stem cells, and microorganisms. Unfortunately, a resting state, or dormancy, is possible for tuberculosis bacilli in a latent form of the disease and cancer cells, which may later form secondary tumors (metastases) in different parts of the body. These cells are resistant to therapy that can destroy intensely dividing cells and to the host immune system. A cascade of reactions that allows cells to enter and exit dormancy is triggered by regulatory factors from the microenvironment in niches that harbor the cells. A ratio of forbidding and permitting signals dictates whether the cells become dormant or start proliferation. The only difference between the cell dormancy regulation in normal and pathological conditions is that pathogens, mycobacteria, and cancer cells can influence their own fate by changing their microenvironment. Certain mechanisms of these processes are considered in the review.

Thorny ground, rocky soil: Tissue-specific mechanisms of tumor dormancy and relapse

Disseminated tumor cells (DTCs) spread systemically yet distinct patterns of metastasis indicate a range of tissue susceptibility to metastatic colonization. Distinctions between permissive and suppressive tissues are still being elucidated at cellular and molecular levels. Although there is a growing appreciation for the role of the microenvironment in regulating metastatic success, we have a limited understanding of how diverse tissues regulate DTC dormancy, the state of reversible quiescence and subsequent awakening thought to contribute to delayed relapse. Several themes of microenvironmental regulation of dormancy are beginning to emerge, including vascular association, co-option of pre-existing niches, metabolic adaptation, and immune evasion, with tissue-specific nuances. Conversely, DTC awakening is often associated with injury or inflammation-induced activation of the stroma, promoting a proliferative environment with DTCs following suit. We review what is known about tissue-specific regulation of tumor dormancy on a tissue-by-tissue basis, profiling major metastatic organs including the bone, lung, brain, liver, and lymph node. An aerial view of the barriers to metastatic growth may reveal common targets and dependencies to inform the therapeutic prevention of relapse.

Exosomes Derived from Radioresistant Breast Cancer Cells Promote Therapeutic Resistance in Naïve Recipient Cells

Radiation resistance is a significant challenge in the treatment of breast cancer in humans. Human breast cancer is commonly treated with surgery and adjuvant chemotherapy/radiotherapy, but recurrence and metastasis upon the development of therapy resistance results in treatment failure. Exosomes are extracellular vesicles secreted by most cell types and contain biologically active cargo that, when transferred to recipient cells, can influence the cells’ genome and proteome. We propose that exosomes secreted by radioresistant (RR) cells may be able to disseminate the RR phenotype throughout the tumour. Here, we isolated exosomes from the human breast cancer cell line, MDA-MB-231, and the canine mammary carcinoma cell line, REM134, and their RR counterparts to investigate the effects of exosomes derived from RR cells on non-RR recipient cells. Canine mammary cancer cells lines have previously been shown to be excellent translational models of human breast cancer. This is consistent with our current data showing that exosomes derived from RR cells can increase cell viability and colony formation in naïve recipient cells and increase chemotherapy and radiotherapy resistance, in both species. These results are consistent in cancer stem cell and non-cancer stem cell populations. Significantly, exosomes derived from RR cells increased the tumoursphere-forming ability of recipient cells compared to exosomes derived from non-RR cells. Our results show that exosomes are potential mediators of radiation resistance that could be therapeutically targeted.

Remodeling the ECM: Implications for Metastasis and Tumor Dormancy

While most primary tumors can be effectively treated, therapeutics fail to efficiently eliminate metastases. Metastases arise from cancer cells that leave the primary tumor and seed distant sites. Recent studies have shown that cancer cells disseminate early during tumor progression and can remain dormant for years before they resume growth. In these metastatic organs, cancer cells reside in microenvironments where they interact with other cells, but also with the extracellular matrix (ECM). The ECM was long considered to be an inert, non-cellular component of tissues, providing their architecture. However, in recent years, a growing body of evidence has shown that the ECM is a key driver of cancer progression, and it can exert effects on tumor cells, regulating their metastatic fate. ECM remodeling and degradation is required for the early steps of the metastatic cascade: invasion, tumor intravasation, and extravasation. Similarly, ECM molecules have been shown to be important for metastatic outgrowth. However, the role of ECM molecules on tumor dormancy and their contribution to the dormancy-supportive niches is not well understood. In this perspective article, we will summarize the current knowledge of ECM and its role in tumor metastasis and dormancy. We will discuss how a better understanding of the individual components of the ECM niche and their roles mediating the dormant state of disseminated tumor cells (DTCs) will advance the development of new therapies to target dormant cells and prevent metastasis outgrowth.

Novel mechanism for OSM-promoted extracellular matrix remodeling in breast cancer: LOXL2 upregulation and subsequent ECM alignment

BACKGROUND

Invasive ductal carcinoma (IDC) is a serious problem for patients as it metastasizes, decreasing 5-year patient survival from > 95 to ~ 27%. The breast tumor microenvironment (TME) is often saturated with proinflammatory cytokines, such as oncostatin M (OSM), which promote epithelial-to-mesenchymal transitions (EMT) in IDC and increased metastasis. The extracellular matrix (ECM) also plays an important role in promoting invasive and metastatic potential of IDC. Specifically, the reorganization and alignment of collagen fibers in stromal ECM leads to directed tumor cell motility, which promotes metastasis. Lysyl oxidase like-2 (LOXL2) catalyzes ECM remodeling by crosslinking of collagen I in the ECM. We propose a novel mechanism whereby OSM induces LOXL2 expression, mediating stromal ECM remodeling of the breast TME.

METHODS

Bioinformatics was utilized to determine survival and gene correlation in patients. IDC cell lines were treated with OSM (also IL-6, LIF, and IL-1β) and analyzed for LOXL2 expression by qRT-PCR and immunolabelling techniques. Collagen I contraction assays, 3D invasion assays, and confocal microscopy were performed with and without LOXL2 inhibition to determine the impact of OSM-induced LOXL2 on the ECM.

RESULTS

Our studies demonstrate that IDC patients with high LOXL2 and OSM co-expression had worse rates of metastasis-free survival than those with high levels of either, individually, and LOXL2 expression is positively correlated to OSM/OSM receptor (OSMR) expression in IDC patients. Furthermore, human IDC cells treated with OSM resulted in a significant increase in LOXL2 mRNA, which led to upregulated protein expression of secreted, glycosylated, and enzymatically active LOXL2. The expression of LOXL2 in IDC cells did not affect OSM-promoted EMT, and LOXL2 was localized to the cytoplasm and/or secreted. OSM-induced LOXL2 promoted an increase in ECM collagen I fiber crosslinking, which led to significant fiber alignment between cells and increased IDC cell invasion.

CONCLUSIONS

Aligned collagen fibers in the ECM provide pathways for tumor cells to migrate more easily through the stroma to nearby vasculature and tissue. These results provide a new paradigm through which proinflammatory cytokine OSM promotes tumor progression. Understanding the nuances in IDC metastasis will lead to better potential therapeutics to combat against the possibility.

Inhibition of DEC2 is necessary for exiting cell dormancy in salivary adenoid cystic carcinoma

Background

Patients were prone to have poor prognosis once dormant tumor cells being reactivated. However, the molecular mechanism of tumor cell dormancy remains poorly understood. This study aimed to investigate the function of DEC2 in the dormancy of salivary adenoid cystic carcinoma (SACC) in vitro and vivo.

Methods

The function of DEC2 in tumor dormancy of SACC was investigated in nude mice by establishing primary and lung metastasis model. Meanwhile, the interaction between hypoxia and SACC dormancy and the role of DEC2 were demonstrated through CoCl₂ induced hypoxia–mimicking microenvironments. Furthermore, the expression of DEC2 was detected by immunohistochemical staining in primary SACC samples with and without recurrence.

Results

In the primary SACC, DEC2 overexpression inhibited cell proliferation, increased cell population arrested in G0/G1 phase, and participated in dormancy regulation, which limited tumor growth. Intriguingly, in the model of lung metastasis, the level of DEC2 was reduced significantly and resulted in dormancy exit and growth resumption of SACC cells. Then, we found that DEC2 may associate with hypoxia in contributing to tumor dormancy, which might provide a possible cue to explain the different roles of DEC2 in primary and metastasis lesions. And overexpression of DEC2 induced dormancy and promoted migration and invasion through activating EMT program. Finally, DEC2 positive expression was shown to be significantly correlated with recurrence and dormancy of SACC patients.

Conclusions

These findings provide a novel insight into the role of DEC2 gene in tumor dormancy and metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01956-0.

Innovative Approaches in the Battle Against Cancer Recurrence: Novel Strategies to Combat Dormant Disseminated Tumor Cells

Cancer recurrence remains a great fear for many cancer survivors following their initial, apparently successful, therapy. Despite significant improvement in the overall survival of many types of cancer, metastasis accounts for ~90% of all cancer mortality. There is a growing understanding that future therapeutic practices must accommodate this unmet medical need in preventing metastatic recurrence. Accumulating evidence supports dormant disseminated tumor cells (DTCs) as a source of cancer recurrence and recognizes the need for novel strategies to target these tumor cells. This review presents strategies to target dormant quiescent DTCs that reside at secondary sites. These strategies aim to prevent recurrence by maintaining dormant DTCs at bay, or eradicating them. Various approaches are presented, including: reinforcing the niche where dormant DTCs reside in order to keep dormant DTCs at bay; promoting cell intrinsic mechanisms to induce dormancy; preventing the engagement of dormant DTCs with their supportive niche in order to prevent their reactivation; targeting cell-intrinsic mechanisms mediating long-term survival of dormant DTCs; sensitizing dormant DTCs to chemotherapy treatments; and, inhibiting the immune evasion of dormant DTCs, leading to their demise. Various therapeutic approaches, some of which utilize drugs that are already approved, or have been tested in clinical trials and may be considered for repurposing, will be discussed. In addition, clinical evidence for the presence of dormant DTCs will be reviewed, along with potential prognostic biomarkers to enable the identification and stratification of patients who are at high risk of recurrence, and who could benefit from novel dormant DTCs targeting therapies. Finally, we will address the shortcomings of current trial designs for determining activity against dormant DTCs and provide novel approaches.

Autophagy and Cancer Dormancy

Metastasis and relapse account for the great majority of cancer-related deaths. Most metastatic lesions are micro metastases that have the capacity to remain in a non-dividing state called “dormancy” for months or even years. Commonly used anticancer drugs generally target actively dividing cancer cells. Therefore, cancer cells that remain in a dormant state evade conventional therapies and contribute to cancer recurrence. Cellular and molecular mechanisms of cancer dormancy are not fully understood. Recent studies indicate that a major cellular stress response mechanism, autophagy, plays an important role in the adaptation, survival and reactivation of dormant cells. In this review article, we will summarize accumulating knowledge about cellular and molecular mechanisms of cancer dormancy, and discuss the role and importance of autophagy in this context.

Towards a Framework for Better Understanding of Quiescent Cancer Cells

Quiescent cancer cells (QCCs) are cancer cells that are reversibly suspended in G₀ phase with the ability to re-enter the cell cycle and initiate tumor growth, and, ultimately, cancer recurrence and metastasis. QCCs are also therapeutically challenging due to their resistance to most conventional cancer treatments that selectively act on proliferating cells. Considering the significant impact of QCCs on cancer progression and treatment, better understanding of appropriate experimental models, and the evaluation of QCCs are key questions in the field that have direct influence on potential pharmacological interventions. Here, this review focuses on existing and emerging preclinical models and detection methods for QCCs and discusses their respective features and scope for application. By providing a framework for selecting appropriate experimental models and investigative methods, the identification of the key players that regulate the survival and activation of QCCs and the development of more effective QCC-targeting therapeutic agents may mitigate the consequences of QCCs.

LOXL2 in cancer: regulation, downstream effectors and novel roles

Lysyl oxidase-like 2 (LOXL2) is a copper and lysine tyrosyl-quinone (LTQ)-dependent amine oxidase belonging to the lysyl oxidase (LOX) family, the canonical function of which is to catalyze the crosslinking of elastin and collagen in the extracellular matrix (ECM). Many studies have revealed that the aberrant expression of LOXL2 in multiple cancers is associated with epithelial-mesenchymal transition (EMT), metastasis, poor prognosis, chemoradiotherapy resistance, and tumor progression. LOXL2 is regulated in many ways, such as transcriptional regulation, alternative splicing, microRNA regulation, posttranslational modification, and cleavage. Beyond affecting the extracellular environment, various intracellular roles, such as oxidation and deacetylation activities in the nucleus, have been reported for LOXL2. Additionally, LOXL2 contributes to tumor cell invasion by promoting cytoskeletal reorganization. Targeting LOXL2 has become a potential therapeutic strategy to combat many types of cancers. Here, we provide an overview of the regulation and downstream effectors of LOXL2 and discuss the intracellular role of LOXL2 in cancer.

Tuning Cancer Fate: Tumor Microenvironment's Role in Cancer Stem Cell Quiescence and Reawakening

Cancer cell dormancy is a common feature of human tumors and represents a major clinical barrier to the long-term efficacy of anticancer therapies. Dormant cancer cells, either in primary tumors or disseminated in secondary organs, may reawaken and relapse into a more aggressive disease. The mechanisms underpinning dormancy entry and exit strongly resemble those governing cancer cell stemness and include intrinsic and contextual cues. Cellular and molecular components of the tumor microenvironment persistently interact with cancer cells. This dialog is highly dynamic, as it evolves over time and space, strongly cooperates with intrinsic cell nets, and governs cancer cell features (like quiescence and stemness) and fate (survival and outgrowth). Therefore, there is a need for deeper insight into the biology of dormant cancer (stem) cells and the mechanisms regulating the equilibrium quiescence-versus-proliferation are vital in our pursuit of new therapeutic opportunities to prevent cancer from recurring. Here, we review and discuss microenvironmental regulations of cancer dormancy and its parallels with cancer stemness, and offer insights into the therapeutic strategies adopted to prevent a lethal recurrence, by either eradicating resident dormant cancer (stem) cells or maintaining them in a dormant state.

The Role of the ECM in Lung Cancer Dormancy and Outgrowth

The dissemination of tumor cells to local and distant sites presents a significant challenge in the clinical management of many solid tumors. These cells may remain dormant for months or years before overt metastases are re-awakened. The components of the extracellular matrix, their posttranslational modifications and their associated factors provide mechanical, physical and chemical cues to these disseminated tumor cells. These cues regulate the proliferative and survival capacity of these cells and lay the foundation for their engraftment and colonization. Crosstalk between tumor cells, stromal and immune cells within primary and secondary sites is fundamental to extracellular matrix remodeling that feeds back to regulate tumor cell dormancy and outgrowth. This review will examine the role of the extracellular matrix and its associated factors in establishing a fertile soil from which individual tumor cells and micrometastases establish primary and secondary tumors. We will focus on the role of the lung extracellular matrix in providing the architectural support for local metastases in lung cancer, and distant metastases in many solid tumors. This review will define how the matrix and matrix associated components are collectively regulated by lung epithelial cells, fibroblasts and resident immune cells to orchestrate tumor dormancy and outgrowth in the lung. Recent advances in targeting these lung-resident tumor cell subpopulations to prevent metastatic disease will be discussed. The development of novel matrix-targeted strategies have the potential to significantly reduce the burden of metastatic disease in lung and other solid tumors and significantly improve patient outcome in these diseases.

Evolving roles of lysyl oxidase family in tumorigenesis and cancer therapy

The lysyl oxidase (LOX) family is comprised of LOX and four LOX-like proteins (LOXL1, LOXL2, LOXL3, and LOXL4), and mainly functions in the remodeling of extracellular matrix (ECM) and the cross-linking of collagen and elastic fibers. Recently, a growing body of research has demonstrated that LOX family is critically involved in the regulation of cancer cell proliferation, migration, invasion and metastasis. In this review, we discuss the roles of LOX family members in the development and progression of different types of human cancers. Furthermore, we also describe the potential inhibitors of LOX family proteins and highlight that LOX family might be an important therapeutic target for cancer therapy.

Mechano-therapeutics: Targeting Mechanical Signaling in Fibrosis and Tumor Stroma

Pathological remodeling of the extracellular matrix (ECM) by activated myofibroblasts is a hallmark of fibrotic diseases and desmoplastic tumors. Activation of myofibroblasts occurs in response to fibrogenic tissue injury as well as in tumor-associated fibrotic reactions. The molecular determinants of myofibroblast activation in fibrosis and tumor stroma have traditionally been viewed to include biochemical agents, such as dysregulated growth factor and cytokine signaling, which profoundly alter the biology of fibroblasts, ultimately leading to overexuberant matrix deposition and fibrosis. More recently, compelling evidence has shown that altered mechanical properties of the ECM such as matrix stiffness are major drivers of tissue fibrogenesis by promoting mechano-activation of fibroblasts. In this Review, we discuss new insights into the role of the biophysical microenvironment in the amplified activation of fibrogenic myofibroblasts during the development and progression of fibrotic diseases and desmoplastic tumors. We also summarize novel therapeutic targets for anti-fibrotic therapy based on the mechanobiology of tissue fibrosis and tumor stroma, a class of drugs known as "mechano-therapeutics".

Epithelial-Mesenchymal Transition in Cancer: A Historical Overview

Epithelial-mesenchymal transitions (EMTs), the acquisition of mesenchymal features from epithelial cells, occur during some biological processes and are classified into three types: the first type occurs during embryonic development, the second type is associated with adult tissue regeneration, and the third type occurs in cancer progression. EMT occurring during embryonic development in gastrulation, renal development, and the origin and fate of the neural crest is a highly regulated process, while EMT occurring during tumor progression is highly deregulated. EMT allows the solid tumors to become more malignant, increasing their invasiveness and metastatic activity. Secondary tumors frequently maintain the typical histologic characteristics of the primary tumor. These histologic features connecting the secondary metastatic tumors to the primary is due to a process called mesenchymal-epithelial transition (MET). MET has been demonstrated in different mesenchymal tumors and is the expression of the reversibility of EMT. EMT modulation could constitute an approach to avoid metastasis. Some of the targeted small molecules utilized as antiproliferative agents have revealed to inhibit EMT initiation or maintenance because EMT is regulated through signaling pathways for which these molecules have been designed.

Interplay of EMT and CSC in Cancer and the Potential Therapeutic Strategies

The mechanism of epithelial-mesenchymal transition (EMT) consists of the cellular phenotypic transition from epithelial to mesenchymal status. The cells exhibiting EMT exist in cancer stem cell (CSC) population, which is involved in drug resistance. CSCs demonstrating EMT feature remain after cancer treatment, which leads to drug resistance, recurrence, metastasis and malignancy of cancer. In this context, the recent advance of nanotechnology in the medical application has ascended the possibility to target CSCs using nanomedicines. In this review article, we focused on the mechanism of CSCs and EMT, especially into the signaling pathways in EMT, regulation of EMT and CSCs by microRNAs and nanomedicine-based approaches to target CSCs.

Mechanisms of Metastatic Tumor Dormancy and Implications for Cancer Therapy

Metastasis, a multistep process during which tumor cells disseminate to secondary organs, represents the main cause of death for cancer patients. Metastatic dormancy is a late stage during cancer progression, following extravasation of cells at a secondary site, where the metastatic cells stop proliferating but survive in a quiescent state. When the microenvironmental conditions are favorable, they re-initiate proliferation and colonize, sometimes years after treatment of the primary tumor. This phenomenon represents a major clinical obstacle in cancer patient care. In this review, we describe the current knowledge regarding the genetic or epigenetic mechanisms that are activated by cancer cells that either sustain tumor dormancy or promote escape from this inactive state. In addition, we focus on the role of the microenvironment with emphasis on the effects of extracellular matrix proteins and in factors implicated in regulating dormancy during colonization to the lungs, brain, and bone. Finally, we describe the opportunities and efforts being made for the development of novel therapeutic strategies to combat metastatic cancer, by targeting the dormancy stage.

Dormant disseminated tumor cells and cancer stem/progenitor-like cells: Similarities and opportunities

Distant recurrences occurring years after removal of the primary tumor arise from disseminated tumor cells (DTCs) that lie dormant (quiescent/asymptomatic) until they emerge to overt metastases. These quiescent DTCs are resistant to conventional treatments. Hence, to date there is no available treatment which targets dormant DTCs before they form overt metastases. Therefore, understanding the biology of dormant DTCs and the mechanisms of their reactivation is vital in our pursuit to develop therapies to prevent cancer from ever recurring. This review will address the striking similarities between the biology of DTCs and the biology of cancer stem cells (CSCs) or CSC-like cells including cancer progenitor-like cells. These similarities are related to intrinsic mechanisms of survival and quiescence, and their cross-talk with mediators, produced in their surrounding niches that may support either dormancy or outgrowth. Unraveling these similarities may provide us with exciting opportunities to either mitigate the survival of residing dormant DTCs/CSCs or maintain them in a dormant state. Whether the stemness properties of CSCs/cancer progenitor-like cells already comprising the recurring tumor can be exploited in order to differentiate them, and thus promote their dormancy, will be explored as well. Overall, these emerging concepts may provide us with new opportunities to prevent lethal recurrences.

Cell-intrinsic survival signals. The role of autophagy in metastatic dissemination and tumor cell dormancy

Metastasis is the main cause of cancer-related deaths. Disseminated tumor cells (DTCs), which seed metastasis, can remain undetected in a dormant state for decades after treatment of the primary tumor and their persistence is the main cause of late relapse and death in a substantial proportion of cancer patients. Understanding the mechanisms underlying the survival of dormant DTCs is of utmost importance to develop new therapies that effectively kill DTCs while in a quiescent state, therefore preventing metastatic disease and minimizing the chance of future relapses. Besides key interactions with the local microenvironment, dormant DTCs must integrate survival mechanisms to remain viable for long periods of time. Here, the pro-survival role of autophagy in tumor cell dissemination and dormant DTC maintenance are discussed, as well as the implications of the current knowledge for future research efforts.

Cancer stem cells in breast and prostate: Fact or fiction?

Since the introduction of the cancer stem cell (CSC) hypothesis, accumulating evidence shows that most cancers present stem-like niches. However, therapies aimed at targeting this niche have not been as successful as expected. New evidence regarding CSCs hierarchy, similarities with normal tissue stem cells and cell plasticity might be key in understanding their role in cancer biology and how to efficiently eliminate them. In this Chapter, we discuss what is known in breast and prostate CSCs from their initial discoveries to the current therapeutic efforts in the field. Future challenges towards better CSC identification and isolation strategies will be key to shed light into how CSCs could accurately be targeted in combination to traditional therapies to ultimately prolong patient survival.

Prognostic and clinicopathological significance of LOXL2 in cancers: A systematic review and meta-analysis

BACKGROUND

Lysyl oxidase-like 2 (LOXL2) is an extracellular matrix (ECM)-modifying enzyme which can regulate the tensile strength of connective tissues by crosslink of collagen and elastin. Numerous studies have claimed correlations between LOXL2 expression and prognosis or clinicopathological characteristics in various cancers. However, the validities of these claims are still in question. To address these experimental results, a meta-analysis was done to assess the prognostic and clinicopathological significance of LOXL2 expression in various cancers.

METHODS

The keywords were used for searching systematically in PubMed, Web of Science, Embase, Wanfang database, and CNKI. Stata SE15.0 was used for meta-analysis. The hazard ratio (HR) and odds ratios (ORs) were pooled to assess the relationship between LOXL2 expression and overall survival (OS), disease-free survival (DFS), and clinicopathological parameters.

RESULTS

Seventeen studies with 3,881 patients were considered as valid studies. The results indicated that the patients who had a positive LOXL2 expression had a shorter OS (HR 1.60, 95% CI 1.26-1.94, p < 0.001) or DFS (HR 1.46, 95% CI 1.14-1.78, p < 0.001). For clinicopathological parameters, statistical significances were presented in age (OR 1.34, 95% CI 1.13-1.58, p = 0.001), lymph node metastasis (OR 2.20, 95% CI 1.37-3.53, p < 0.001), tumor size (OR 1.46, 95% CI 1.15-1.85, p = 0.002), and vascular invasion (OR 1.82, 95% CI 1.33-2.48, p < 0.001).

CONCLUSIONS

The results demonstrate that positive LOXL2 expression presents poorer OS and worse clinicopathological parameters. LOXL2 may be an effective biomarker to evaluate the prognosis in different type of cancers.

Lysyl Oxidase-Like Protein 2 Promotes Tumor Lymphangiogenesis and Lymph Node Metastasis in Breast Cancer

Tumor lymphangiogenesis has been previously documented to predict regional lymph node metastasis and promote the spread to distant organs. However, the underlying mechanism initiating tumor lymphangiogenesis remains unclear. Here we described a novel role of tumor cell-derived Lysyl Oxidase-like protein 2 (LOXL2) in promoting lymphangiogenesis and lymph node metastasis in breast cancer. Immunohistochemistry (IHC) analysis of samples from breast cancer patients showed that the expression of LOXL2 was positively correlated with lymphatic vessel density and breast cancer malignancy. In animal studies, LOXL2-overexpressing breast cancer cells significantly increased lymphangiogenesis and lymph node metastasis, whereas knockdown of LOXL2 suppressed both processes. In order to study the mechanisms of lymphangiogenesis progression, we performed further in vitro investigations and the data revealed that LOXL2 significantly enhanced lymphatic endothelial cells (LECs) invasion and tube formation through directly activation of the Akt-Snail and Erk pathways. Moreover, LOXL2 also stimulated fibroblasts to secrete high level of pro- lymphangiogenic factors VEGF-C and SDF-1α. Taken together, our study elucidates a novel function of tumor cell secreted LOXL2 in lymphangiogenesis and lymph node metastasis, demonstrating that LOXL2 serves as a promising target for anti-lymphangiogenesis and anti-metastasis therapies for breast cancer.

Engineered In Vitro Models of Tumor Dormancy and Reactivation

Metastatic recurrence is a major hurdle to overcome for successful control of cancer-associated death. Residual tumor cells in the primary site, or disseminated tumor cells in secondary sites, can lie in a dormant state for long time periods, years to decades, before being reactivated into a proliferative growth state. The microenvironmental signals and biological mechanisms that mediate the fate of disseminated cancer cells with respect to cell death, single cell dormancy, tumor mass dormancy and metastatic growth, as well as the factors that induce reactivation, are discussed in this review. Emphasis is placed on engineered, in vitro, biomaterial-based approaches to model tumor dormancy and subsequent reactivation, with a focus on the roles of extracellular matrix, secondary cell types, biochemical signaling and drug treatment. A brief perspective of molecular targets and treatment approaches for dormant tumors is also presented. Advances in tissue-engineered platforms to induce, model, and monitor tumor dormancy and reactivation may provide much needed insight into the regulation of these processes and serve as drug discovery and testing platforms.

Hyaluronan arrests human breast cancer cell growth by prolonging the G0/G1 phase of the cell cycle

In clinical breast cancer patients, quiescent disseminated tumor cells (DTCs) can persist for a long time in the bone marrow (BM) under the influence of microenvironmental cues. As a high molecular weight polysaccharide, hyaluronan (HA) not only has been shown to regulate cancer processes including cell invasion, metastasis, migration, and proliferation, but also is a major component of the BM extracellular matrix. Here, we tested whether HA promotes breast cancer cell quiescence through detecting cell proliferation, cell cycle phase distribution, and the expression of cell cycle-related regulator proteins. In our results, HA slowed the growth and prolonged the G0/G1 phase of the highly metastatic, bone-seeking human breast cancer MDA-MB-231BO cell line, which is consistent with results that HA activated p38α/β, inhibited phospho-ERK1/2 levels and reduced the ERK/p38 signaling ratio. Additionally, we examined the crucial cell cycle factors p21cip1 and Cyclin D1, both of which influence the transition from G1 to S phase. The results revealed that p21cip1 expression was up-regulated by HA, which was consequently accompanied by a decrease in Cyclin D1 level. Further research with a 3D culture model indicated that HA maintained low Ki-67 and high p21cip1 expression levels in MDA-MB-231BO cells. In summary, our work revealed that HA might contribute to DTC quiescence.

Cellular Phenotype Plasticity in Cancer Dormancy and Metastasis

Cancer dormancy is a period of cancer progression in which residual tumor cells exist, but clinically remain asymptomatic for a long time, as well as resistant to conventional chemo- and radiotherapies. Cellular phenotype plasticity represents that cellular phenotype could convert between epithelial cells and cells with mesenchymal traits. Recently, this process has been shown to closely associate with tumor cell proliferation, cancer dormancy and metastasis. In this review, we have described different scenarios of how the transition from epithelial to mesenchymal morphology (EMT) and backwards (MET) are connected with the initiation of dormancy and reactivation of proliferation. These processes are fundamental for cancer cells to invade tissues and metastasize. Recognizing the mechanisms underlying the cellular phenotype plasticity as well as dormancy and targeting them is likely to increase the efficiency of traditional tumor treatment inhibiting tumor metastasis.

EMT and Stemness in Tumor Dormancy and Outgrowth: Are They Intertwined Processes?

Metastases are the major cause of cancer patients' mortality and can occur years and even decades following apparently successful treatment of the primary tumor. Early dissemination of cancer cells, followed by a protracted period of dormancy at distant sites, has been recently recognized as the clinical explanation for this very-long latency. The mechanisms that govern tumor dormancy at distant sites and their reactivation to proliferating metastases are just beginning to be unraveled. Tumor cells, that survive the immune surveillance and hemodynamic forces along their journey in the circulation and successfully colonize and adopt to the new and "hostile" microenvironment and survive in a quiescent dormant state for years before emerging to proliferative state, must display high plasticity. Here we will discuss whether the plasticity of dormant tumor cells is required for their long-term survival and outgrowth. Specifically, we will focus on whether epithelial mesenchymal transition and acquisition of stem-like properties can dictate their quiescent and or their proliferative fate. Deeper understanding of these intertwining processes may facilitate in the future the development of novel therapies.

Reawakening of dormant estrogen-dependent human breast cancer cells by bone marrow stroma secretory senescence

Background

Dormant estrogen receptor positive (ER+) breast cancer micrometastases in the bone marrow survive adjuvant chemotherapy and recur stochastically for more than 20 years. We hypothesized that inflammatory cytokines produced by stromal injury can re-awaken dormant breast cancer cells.

Methods

We used an established in vitro dormancy model of Michigan Cancer Foundation-7 (MCF-7) breast cancer cells incubated at clonogenic density on fibronectin-coated plates to determine the effects of inflammatory cytokines on reactivation of dormant ER+ breast cancer cells. We measured induction of a mesenchymal phenotype, motility and the capacity to re-enter dormancy. We induced secretory senescence in murine stromal monolayers by oxidation, hypoxia and estrogen deprivation with hydrogen peroxide (H₂O₂), carbonyl-cyanide m-chlorophenylhydrazzone (CCCP) and Fulvestrant (ICI 182780), respectively, and determined the effects on growth of co-cultivated breast cancer cells.

Results

Exogenous recombinant human (rh) interleukin (IL)-6, IL-8 or transforming growth factor β1 (TGFβ1) induced regrowth of dormant MCF-7 cells on fibronectin-coated plates. Dormant cells had decreased expression of E-cadherin and estrogen receptor α (ERα) and increased expression of N-cadherin and SNAI2 (SLUG). Cytokine or TGFβ1 treatment of dormant clones induced formation of growing clones, a mesenchymal appearance, increased motility and an impaired capacity to re-enter dormancy. Stromal injury induced secretion of IL-6, IL-8, upregulated tumor necrosis factor alpha (TNFα), activated TGFβ and stimulated the growth of co-cultivated MCF-7 cells. MCF-7 cells induced secretion of IL-6 and IL-8 by stroma in co-culture.

Conclusions

Dormant ER+ breast cancer cells have activated epithelial mesenchymal transition (EMT) gene expression programs and downregulated ERα but maintain a dormant epithelial phenotype. Stromal inflammation reactivates these cells, induces growth and a mesenchymal phenotype. Reactivated, growing cells have an impaired ability to re-enter dormancy. In turn, breast cancer cells co-cultured with stroma induce secretion of IL-6 and IL-8 by the stroma, creating a positive feedback loop.

[Mechanisms and implications of cancer cell dormancy in head and neck carcinoma]

Disease metastasis and relapse in many cancer patients several years (even decades) after surgical remission have been recently acknowledged as cases of cancer dormancy. Although cases of minimal residual disease are well documented, knowledge on its biological mechanisms and clinical implications remains limited. To date, numerous reviews have summarized the three potential models that may explain this phenomenon, including the angiogenic, immunologic, and cellular dormancy. In this study, we discuss newly uncovered mechanisms governing tumor cell dormancy in head and neck cancer, emphasizing on the crosstalk between dormant tumor cells and their microenvironments. Additionally, we explore the mechanisms on the reactivation of dormant residual tumor cells in anatomical sites, including the lymph nodes and bone marrow.

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

The lysyl oxidase-like protein LOXL2 has been suggested to contribute to tumor progression and metastasis, but in vivo evidence has been lacking. Here we provide functional evidence that LOXL2 is a key driver of breast cancer metastasis in two conditional transgenic mouse models of PyMT-induced breast cancer. LOXL2 ablation in mammary tumor cells dramatically decreased lung metastasis, whereas LOXL2 overexpression promoted metastatic tumor growth. LOXL2 depletion or overexpression in tumor cells does not affect extracellular matrix stiffness or organization in primary and metastatic tumors, implying a function for LOXL2 independent of its conventional role in extracellular matrix remodeling. In support of this likelihood, cellular and molecular analyses revealed an association of LOXL2 action with elevated levels of the EMT regulatory transcription factor Snail1 and expression of several cytokines that promote premetastatic niche formation. Taken together, our findings established a pathophysiologic role and new function for LOXL2 in breast cancer metastasis. Cancer Res; 77(21); 5846-59. ©2017 AACR.

Cancer cell dormancy: mechanisms and implications of cancer recurrence and metastasis

More recently, disease metastasis and relapse in many cancer patients several years (even some decades) after surgical remission are regarded as tumor dormancy. However, the knowledge of this phenomenon is cripplingly limited. Substantial quantities of reviews have summarized three main potential models that can be put forth to explain such process, including angiogenic dormancy, immunologic dormancy, and cellular dormancy. In this review, newly uncovered mechanisms governing cancer cell dormancy are discussed, with an emphasis on the cross talk between dormant cancer cells and their microenvironments. In addition, potential mechanisms of reactivation of these dormant cells in certain anatomic sites including lymph nodes and bone marrow are discussed. Molecular mechanism of cellular dormancy in head and neck cancer is also involved.

Exploration of Serum Proteomic Profiling and Diagnostic Model That Differentiate Crohn's Disease and Intestinal Tuberculosis

AIM

To explore the diagnostic models of Crohn's disease (CD), Intestinal tuberculosis (ITB) and the differential diagnostic model between CD and ITB by analyzing serum proteome profiles.

METHODS

Serum proteome profiles from 30 CD patients, 21 ITB patients and 30 healthy controls (HCs) were analyzed by using weak cationic magnetic beads combined with MALDI-TOF-MS technique to detect the differentially expressed proteins of serum samples. Three groups were made and compared accordingly: group of CD patients and HCs, group of ITB patients and HCs, group of CD patients and ITB patients. Wilcoxon rank sum test was used to screen the ten most differentiated protein peaks (P < 0.05). Genetic algorithm combining with support vector machine (SVM) was utilized to establish the optimal diagnostic models for CD, ITB and the optimal differential diagnostic model between CD and ITB. The predictive effects of these models were evaluated by Leave one out (LOO) cross validation method.

RESULTS

There were 236 protein peaks differently expressed between group of CD patients and HCs, 305 protein peaks differently expressed between group of ITB patients and HCs, 332 protein peaks differently expressed between group of CD patients and ITB patients. Ten most differentially expressed peaks were screened out between three groups respectively (P < 0.05) to establish diagnostic models and differential diagnostic model. A diagnostic model comprising of four protein peaks (M/Z 4964, 3029, 2833, 2900) can well distinguish CD patients and HCs, with a specificity and sensitivity of 96.7% and 96.7% respectively. A diagnostic model comprising four protein peaks (M/Z 3030, 2105, 2545, 4210) can well distinguish ITB patients and HCs, with a specificity and sensitivity of 93.3% and 95.2% respectively. A differential diagnostic model comprising three potential biomarkers protein peaks (M/Z 4267, 4223, 1541) can well distinguish CD patients and ITB patients, with a specificity and sensitivity of 76.2% and 80.0% respectively. Among the eleven protein peaks from the diagnostic models and differential diagnostic model, two have been successfully purified and identified, Those two peaks were M/Z 2900 from the diagnostic model between CD and HCs and M/Z 1541 from the differential diagnostic model between CD and ITB. M/Z 2900 was identified as appetite peptide, M/Z 1541 was identified as Lysyl oxidase-like 2 (LOXL-2).

CONCLUSION

The differently expressed protein peaks analyzed by serum proteome with weak cationic magnetic beads combined MALDI-TOF-MS technique can effectively distinguish CD patients and HCs, ITB patients and HCs, CD patients and ITB patients. The diagnostic model between CD patients and HCs consisting of four protein peaks (M/Z 4964, 3029, 2833, 2900), the diagnostic model between ITB patients and HCs comprising four protein peaks (M/Z 3030, 2105, 2545, 4210) and the differential diagnostic model between CD patients and ITB patients comprising three protein peaks (M/Z 4267, 4223, 1541) had high specificity and sensitivity and can contribute to diagnoses of CD, ITB and the differential diagnosis between CD and ITB. Two proteins from the diagnostic model of CD and the differential diagnostic model between CD and ITB were identified. Further experiments are required using a larger cohort of samples.