Escaping Antiangiogenic Therapy: Strategies Employed by Cancer Cells

Deciphering the Molecular Mechanisms behind Drug Resistance in Ovarian Cancer to Unlock Efficient Treatment Options

Ovarian cancer is a highly lethal form of gynecological cancer. This disease often goes undetected until advanced stages, resulting in high morbidity and mortality rates. Unfortunately, many patients experience relapse and succumb to the disease due to the emergence of drug resistance that significantly limits the effectiveness of currently available oncological treatments. Here, we discuss the molecular mechanisms responsible for resistance to carboplatin, paclitaxel, polyadenosine diphosphate ribose polymerase inhibitors, and bevacizumab in ovarian cancer. We present a detailed analysis of the most extensively investigated resistance mechanisms, including drug inactivation, drug target alterations, enhanced drug efflux pumps, increased DNA damage repair capacity, and reduced drug absorption/accumulation. The in-depth understanding of the molecular mechanisms associated with drug resistance is crucial to unveil new biomarkers capable of predicting and monitoring the kinetics during disease progression and discovering new therapeutic targets.

Advance in vasculogenic mimicry in ovarian cancer (Review)

Ovarian cancer (OC) is a common and highly prevalent malignant tumor in women, associated with a high mortality rate, easy recurrence and easy metastasis, which is predominantly at an advanced stage when detected in patients. This renders the cancer more difficult to treat, and consequently it is also associated with a low survival rate, being the malignancy with the highest mortality rate among the various gynecological tumors. As an important factor affecting the development and metastasis of OC, understanding the underlying mechanism(s) through which it is formed and developed is crucial in terms of its treatment. At present, the therapeutic methods of angiogenic mimicry for OC remain in the preliminary stages of exploration and have not been applied in actual clinical practice. In the present review, various signaling pathways and factors affecting angiogenic mimicry in OC were described, and the chemical synthetic drugs, natural compound extracts, small-molecule protein antibodies and their associated targets, and so on, that target angiogenic mimicry in the treatment of OC, were discussed. The purpose of this review was to provide new research ideas and potential theoretical support for the discovery of novel therapeutic targets for OC that may be applied in the clinic, with the aim of effectively reducing its metastasis and recurrence rates.

The role of TOP2A in immunotherapy and vasculogenic mimicry in non-small cell lung cancer and its potential mechanism

Type IIA topoisomerase (TOP2A) is significantly associated with malignant tumor development, invasion, treatment and its prognosis, and has been shown to be a therapeutic target against cancer. In contrast, the role of TOP2A in the immunotherapy of non-small cell lung cancer as well as in Vasculogenic mimicry (VM) formation and its potential mechanisms are unclear. The aim of this study was to investigate the role of TOP2A in proliferation, skeleton regulation, motility and VM production in non-small cell lung cancer and its mechanisms by using bioinformatics tools and molecular biology experiments. Subgroup analysis showed that the low-risk group had a better prognosis, while the high-risk group was positively correlated with high tumor mutational load, M1-type macrophage infiltration, immune checkpoint molecule expression, and immunotherapy efficacy. As confirmed by further clinical specimens, the presence of TOP2A and VM was significantly and positively correlated with poor prognosis. Our study established a model based on significant co-expression of TOP2A genes, which significantly correlated with mutational load and immunotherapy outcomes in patients with non-small cell lung cancer. Further mechanistic exploration suggests that TOP2A plays an important role in immunotherapy and VM formation in NSCLC through upregulation of Wnt3a and PD-L1 expression.

CVM-1118 (foslinanib), a 2-phenyl-4-quinolone derivative, promotes apoptosis and inhibits vasculogenic mimicry via targeting TRAP1

CVM-1118 (foslinanib) is a phosphoric ester compound selected from 2-phenyl-4-quinolone derivatives. The NCI 60 cancer panel screening showed CVM-1125, the major active metabolite of CVM-1118, to exhibit growth inhibitory and cytotoxic effects at nanomolar range. CVM-1118 possesses multiple bioactivities, including inducing cellular apoptosis, cell cycle arrest at G₂/M, as well as inhibiting vasculogenic mimicry (VM) formation. The TNF receptor associated protein 1 (TRAP1) was identified as the binding target of CVM-1125 using nematic protein organization technique (NPOT) interactome analysis. Further studies demonstrated CVM-1125 reduced the protein level of TRAP1 and impeded its downstream signaling by reduction of cellular succinate levels and destabilization of HIF-1α. The pharmacogenomic biomarkers associated with CVM-1118 were also examined by Whole Genome CRISPR Knock-Out Screening. Two hits (STK11 and NF2) were confirmed with higher sensitivity to the drug in cell knock-down experiments. Biological assays indicate that the mechanism of action of CVM-1118 is via targeting TRAP1 to induce mitochondrial apoptosis, suppress tumor cell growth, and inhibit vasculogenic mimicry formation. Most importantly, the loss-of-function mutations of STK11 and NF2 are potential biomarkers of CVM-1118 which can be applied in the selection of cancer patients for CVM-1118 treatment. CVM-1118 is currently in its Phase 2a clinical development.

Vascular Progenitor Cells: From Cancer to Tissue Repair

Vascular progenitor cells are activated to repair and form a neointima following vascular damage such as hypertension, atherosclerosis, diabetes, trauma, hypoxia, primary cancerous lesions and metastases as well as catheter interventions. They play a key role not only in the resolution of the vascular lesion but also in the adult neovascularization and angiogenesis sprouting (i.e., the growth of new capillaries from pre-existing ones), often associated with carcinogenesis, favoring the formation of metastases, survival and progression of tumors. In this review, we discuss the biology, cellular plasticity and pathophysiology of different vascular progenitor cells, including their origins (sources), stimuli and activated pathways that induce differentiation, isolation and characterization. We focus on their role in tumor-induced vascular injury and discuss their implications in promoting tumor angiogenesis during cancer proliferation and migration.

Promising Nanomedicines of Shikonin for Cancer Therapy

Malignant tumor, the leading cause of death worldwide, poses a serious threat to human health. For decades, natural product has been proven to be an essential source for novel anticancer drug discovery. Shikonin (SHK), a natural molecule separated from the root of Lithospermum erythrorhizon, shows great potential in anticancer therapy. However, its further clinical application is significantly restricted by poor bioavailability, adverse effects, and non-selective toxicity. With the development of nanotechnology, nano drug delivery systems have emerged as promising strategies to improve bioavailability and enhance the therapeutic efficacy of drugs. To overcome the shortcoming of SHK, various nano drug delivery systems such as liposomes, polymeric micelles, nanoparticles, nanogels, and nanoemulsions, were developed to achieve efficient delivery for enhanced antitumor effects. Herein, this review summarizes the anticancer pharmacological activities and pharmacokinetics of SHK. Additionally, the latest progress of SHK nanomedicines in cancer therapy is outlined, focusing on long circulation, tumor targeting ability, tumor microenvironment responsive drug release, and nanosystem-mediated combination therapy. Finally, the challenges and prospects of SHK nanomedicines in the future clinical application are spotlighted.

Tumor-on-a-chip: Perfusable vascular incorporation brings new approach to tumor metastasis research and drug development

The extracellular matrix interacts with cancer cells and is a key factor in the development of cancer. Traditional two-dimensional models cannot mimic the natural in situ environment of cancer tissues, whereas three-dimensional (3D) models such as spherical culture, bioprinting, and microfluidic approaches can achieve in vitro reproduction of certain structures and components of the tumor microenvironment, including simulation of the hypoxic environment of tumor tissue. However, the lack of a perfusable vascular network is a limitation of most 3D models. Solid tumor growth and metastasis require angiogenesis, and tumor models with microvascular networks have been developed to better understand underlying mechanisms. Tumor-on-a-chip technology combines the advantages of microfluidics and 3D cell culture technology for the simulation of tumor tissue complexity and characteristics. In this review, we summarize progress in constructing tumor-on-a-chip models with efficiently perfused vascular networks. We also discuss the applications of tumor-on-a-chip technology to studying the tumor microenvironment and drug development. Finally, we describe the creation of several common tumor models based on this technology to provide a deeper understanding and new insights into the design of vascularized cancer models. We believe that the tumor-on-a-chip approach is an important development that will provide further contributions to the field.

Interference in melanoma CD248 function reduces vascular mimicry and metastasis

Background

Tumor vascular mimicry is an emerging issue that affects patient survival while having no treatment at the current moment. Despite several factors implicated in vascular mimicry, little is known about stromal factors that modulate tumor microenvironment and shape malignant transformation. CD248, a type-I transmembrane protein dominantly expressed in stromal cells, mediates the interaction between cells and extracellular matrix proteins. CD248 protein expression is associated with the metastatic melanoma phenotype and promotes tumor progression in the stromal cells. This study aimed to explore the cell-autonomous effects of CD248 in melanoma vascular mimicry to aid cancer therapy development.

Methods

Loss-of-function approaches in B16F10 melanoma cells were used to study the cell-autonomous effects of CD248 on cell adhesion, migration, proliferation, and vascular mimicry. A solid-phase binding assay was performed to identify the interaction between CD248 and fibronectin. Horizontal and vertical cell migration assays were performed to analyze cell migration activity, and cell-patterned network formation on Matrigel was used to evaluate vascular mimicry activity. Recombinant CD248 (rCD248) proteins were generated, and whether rCD248 interfered with melanoma CD248 functions was evaluated in vitro. An experimental lung metastasis mouse model was used to investigate the effect of rCD248 treatment in vivo.

Results

CD248 protein expression in melanoma cells was increased by a fibroblast-conditioned medium. Knockdown of CD248 expression significantly decreased cell adhesion to fibronectin, cell migration, and vascular mimicry in melanoma cells. The lectin domain of CD248 was directly involved in the interaction between CD248 and fibronectin. Furthermore, rCD248 proteins containing its lectin domain inhibited cell adhesion to fibronectin and slowed down cell migration and vascular mimicry. Treatment with rCD248 protein could reduce pulmonary tumor burden, accompanied by a reduction in vascular mimicry in mice with melanoma lung metastasis.

Conclusion

CD248 expression in melanoma cells promotes malignant transformation by increasing the activity of cell adhesion, migration, and vascular mimicry, whereas rCD248 protein functions as a molecular decoy interfering with tumor-promoting effects of CD248 in melanoma cells.

Mechanisms of chemotherapy resistance in ovarian cancer

Ovarian cancer is one of the most lethal gynecologic cancers. The standard therapy for ovarian cancer has been the same for the past two decades, a combination treatment of platinum with paclitaxel. Recently, the FDA approved three new therapeutic drugs, two poly (ADP-ribose) polymerase inhibitors (olaparib and niraparib) and one vascular endothelial growth factor inhibitor (bevacizumab) as maintenance therapies for ovarian cancer. In this review, we summarize the resistance mechanisms for conventional platinum-based chemotherapy and for the newly FDA-approved drugs.

Runt related transcription factor-1 plays a central role in vessel co-option of colorectal cancer liver metastases

Colorectal cancer liver metastasis (CRCLM) has two major histopathological growth patterns: angiogenic desmoplastic and non-angiogenic replacement. The replacement lesions obtain their blood supply through vessel co-option, wherein the cancer cells hijack pre-existing blood vessels of the surrounding liver tissue. Consequentially, anti-angiogenic therapies are less efficacious in CRCLM patients with replacement lesions. However, the mechanisms which drive vessel co-option in the replacement lesions are unknown. Here, we show that Runt Related Transcription Factor-1 (RUNX1) overexpression in the cancer cells of the replacement lesions drives cancer cell motility via ARP2/3 to achieve vessel co-option. Furthermore, overexpression of RUNX1 in the cancer cells is mediated by Transforming Growth Factor Beta-1 (TGFβ1) and thrombospondin 1 (TSP1). Importantly, RUNX1 knockdown impaired the metastatic capability of colorectal cancer cells in vivo and induced the development of angiogenic lesions in liver. Our results confirm that RUNX1 may be a potential target to overcome vessel co-option in CRCLM.

Evidence-Based Second-Line Treatment in RAS Wild-Type/Mutated Metastatic Colorectal Cancer in the Precision Medicine Era

Target-oriented agents improve metastatic colorectal cancer (mCRC) survival in combination with chemotherapy. However, the majority of patients experience disease progression after first-line treatment and are eligible for second-line approaches. In such a context, antiangiogenic and anti-Epidermal Growth Factor Receptor (EGFR) agents as well as immune checkpoint inhibitors have been approved as second-line options, and RAS and BRAF mutations and microsatellite status represent the molecular drivers that guide therapeutic choices. Patients harboring K- and N-RAS mutations are not eligible for anti-EGFR treatments, and bevacizumab is the only antiangiogenic agent that improves survival in combination with chemotherapy in first-line, regardless of RAS mutational status. Thus, the choice of an appropriate therapy after the progression to a bevacizumab or an EGFR-based first-line treatment should be evaluated according to the patient and disease characteristics and treatment aims. The continuation of bevacizumab beyond progression or its substitution with another anti-angiogenic agents has been shown to increase survival, whereas anti-EGFR monoclonals represent an option in RAS wild-type patients. In addition, specific molecular subgroups, such as BRAF-mutated and Microsatellite Instability-High (MSI-H) mCRCs represent aggressive malignancies that are poorly responsive to standard therapies and deserve targeted approaches. This review provides a critical overview about the state of the art in mCRC second-line treatment and discusses sequential strategies according to key molecular biomarkers.

Foxq1 promotes metastasis of nasopharyngeal carcinoma by inducing vasculogenic mimicry via the EGFR signaling pathway

In nasopharyngeal carcinoma (NPC), the treatment of tumor metastasis and recurrence is challenging and is associated with poor clinical efficacy. Vasculogenic mimicry (VM) is a new blood-supply model of malignant tumor that is closely related to tumors’ distant metastasis. Our previous study demonstrated that miR-124 could target Foxq1 to inhibit NPC metastasis. Whether Foxq1 affects metastasis through vasculogenic mimicry is worth consideration. In this study, we show that VM formation positively correlates with the expression of Foxq1, and EGFR, and the TNM stage in 114 NPC patient samples. Meanwhile, we show that VM-positive NPC patients have a poor prognosis. Furthermore, using in vitro and vivo approaches, we confirm that Foxq1 has a significant effect on NPC metastasis through promoting VM formation, which could be effectively inhibited by EGFR inhibitors (Nimotuzumab or Erlotinib). Also a synergistic efficacy of anti-EGFR and anti-VEGF drugs has been found in NPC inhibition. Mechanistically, the luciferase reporter gene and CHIP assays show that Foxq1 directly binds to the EGFR promoter region and regulates EGFR transcription. In conclusion, our results show that Foxq1 is regulated by miR-124 and that it promotes NPC metastasis by inducing VM via the EGFR signaling pathway. Overall, these results provide a new theoretical support and a novel target selection for anti-VM therapy in the treatment of nasopharyngeal carcinoma.

The complexity of tumour angiogenesis based on recently described molecules

Tumour angiogenesis is a crucial factor associated with tumour growth, progression, and metastasis. The whole process is the result of an interaction between a wide range of different molecules, influencing each other. Herein we summarize novel discoveries related to the less known angiogenic molecules such as galectins, pentraxin-3, Ral-interacting protein of 76 kDa (RLIP76), long non-coding RNAs (lncRNAs), B7-H3, and delta-like ligand-4 (DLL-4) and their role in the process of tumour angiogenesis. These molecules influence the most important molecular pathways involved in the formation of blood vessels in cancer, including the vascular endothelial growth factor (VEGF)-vascular endothelial growth factor receptor interaction (VEGFR), HIF1-a activation, or PI3K/Akt/mTOR and JAK-STAT signalling pathways. Increased expression of galectins, RLIP76, and B7H3 has been proven in several malignancies. Pentraxin-3, which appears to inhibit tumour angiogenesis, shows reduced expression in tumour tissues. Anti-angiogenic treatment based mainly on VEGF inhibition has proved to be of limited effectiveness, leading to the development of drug resistance. The newly discovered molecules are of great interest as a potential source of new anti-cancer therapies. Their role as targets for new drugs and as prognostic markers in neoplasms is discussed in this review.

From Conventional to Precision Therapy in Canine Mammary Cancer: A Comprehensive Review

Canine mammary tumors (CMTs) are the most common neoplasm in intact female dogs. Canine mammary cancer (CMC) represents 50% of CMTs, and besides surgery, which is the elective treatment, additional targeted and non-targeted therapies could offer benefits in terms of survival to these patients. Also, CMC is considered a good spontaneous intermediate animal model for the research of human breast cancer (HBC), and therefore, the study of new treatments for CMC is a promising field in comparative oncology. Dogs with CMC have a comparable disease, an intact immune system, and a much shorter life span, which allows the achievement of results in a relatively short time. Besides conventional chemotherapy, innovative therapies have a large niche of opportunities. In this article, a comprehensive review of the current research in adjuvant therapies for CMC is conducted to gather available information and evaluate the perspectives. Firstly, updates are provided on the clinical-pathological approach and the use of conventional therapies, to delve later into precision therapies against therapeutic targets such as hormone receptors, tyrosine kinase receptors, p53 tumor suppressor gene, cyclooxygenases, the signaling pathways involved in epithelial-mesenchymal transition, and immunotherapy in different approaches. A comparison of the different investigations on targeted therapies in HBC is also carried out. In the last years, the increasing number of basic research studies of new promising therapeutic agents on CMC cell lines and CMC mouse xenografts is outstanding. As the main conclusion of this review, the lack of effort to bring the in vitro studies into the field of applied clinical research emerges. There is a great need for well-planned large prospective randomized clinical trials in dogs with CMC to obtain valid results for both species, humans and dogs, on the use of new therapies. Following the One Health concept, human and veterinary oncology will have to join forces to take advantage of both the economic and technological resources that are invested in HBC research, together with the innumerable advantages of dogs with CMC as a spontaneous animal model.

The Role of Anti-angiogenesis in the Treatment Landscape of Non-small Cell Lung Cancer - New Combinational Approaches and Strategies of Neovessel Inhibition

Tumor progression depends primarily on vascular supply, which is facilitated by angiogenic activity within the malignant tissue. Non-small cell lung cancer (NSCLC) is a highly vascularized tumor, and inhibition of angiogenesis was projected to be a promising therapeutic approach. Over a decade ago, the first anti-angiogenic agents were approved for advanced stage NSCLC patients, however, they only produced a marginal clinical benefit. Explanations why anti-angiogenic therapies only show modest effects include the highly adaptive tumor microenvironment (TME) as well as the less understood characteristics of the tumor vasculature. Today, advanced methods of in-depth characterization of the NSCLC TME by single cell RNA sequencing (scRNA-Seq) and preclinical observations enable a detailed characterization of individual cancer landscapes, allowing new aspects for a more individualized inhibition of angiogenesis to be identified. Furthermore, the tumor vasculature itself is composed of several cellular subtypes, which closely interact with other cellular components of the TME, and show distinct biological functions such as immune regulation, proliferation, and organization of the extracellular matrix. With these new insights, combinational approaches including chemotherapy, anti- angiogenic and immunotherapy can be developed to yield a more target-oriented anti-tumor treatment in NSCLC. Recently, anti-angiogenic agents were also shown to induce the formation of high endothelial venules (HEVs), which are essential for the formation of tertiary lymphoid structures, and key components in triggering anti-tumor immunity. In this review, we will summarize the current knowledge of tumor-angiogenesis and corresponding anti-angiogenic therapies, as well as new aspects concerning characterization of tumor-associated vessels and the resulting new strategies for anti-angiogenic therapies and vessel inhibition in NSCLC. We will further discuss why anti-angiogenic therapies form an interesting backbone strategy for combinational therapies and how anti-angiogenic approaches could be further developed in a more personalized tumor-oriented fashion with focus on NSCLC.

Allogenic mouse cell vaccine inhibits lung cancer progression by inhibiting angiogenesis

Aim: This research investigated the therapeutic effect of an allogeneic mouse brain microvascular endothelial cell vaccine on lung cancer and further elucidated its potential anti-angiogenic mechanism. Materials & methods: The immune effect of the allogeneic bEnd.3 vaccine and DC vaccine loaded with bEnd.3 antigen on the subcutaneous transplantation of Lewis lung cancer (LLC) was assessed by ELISA, the CCK test and the CTL killing test. The mechanism was preliminarily revealed by immunohistochemistry and immunoblot analysis. Results: This study revealed that tumor volume was decreased (p < .01) and the survival was prolonged significantly (p < .05) by the bEnd.3 vaccine in subcutaneous LLC transplantation in the vaccine prevention group. In contrast, both tumor volume in the serum therapeutic group and survival of bEnd.3 vaccine were not significantly different from those of the control group (p > .05). Importantly, tumor volume and survival of the T lymphocyte therapeutic group were decreased and prolonged (p < .05). In addition, both tumor volume and survival of DC vaccine loaded with bEnd.3 in the vaccine prevention group were decreased and prolonged significantly (p < .01). Furthermore, bEnd.3 vaccine and DC vaccine loaded with bEnd.3 both produced the activity of killing bEnd.3 target cells in vitro.The reason may induce the immune mice to produce anti-VEGFR-II, anti-endoglin and anti-integrin αν antibodies to have an anti-angiogenesis function. Conclusion: The allogeneic mouse bEnd.3 cell vaccine can block angiogenesis and prevent the development of lung cancer transplantation tumors.

Extracellular Vesicles Are Key Regulators of Tumor Neovasculature

Tumor progression involves a series of biologically important steps in which the crosstalk between cancer cells and the surrounding environment is an important issue. Angiogenesis is a key tumorigenic phenomenon for cancer progression. Tumor-related extracellular vesicles (EVs) modulate the tumor microenvironment (TME) through cell-to-cell communication. Tumor cells in a hypoxic TME release more EVs than cells in a normoxic environment due to uncontrollable tumor proliferation. Tumor-derived EVs in the TME influence endothelial cells (ECs), which then play multiple roles, contributing to tumor angiogenesis, loss of the endothelial vascular barrier by binding to ECs, and subsequent endothelial-to-mesenchymal transition. In contrast, they also indirectly induce tumor angiogenesis through the phenotype switching of various cells into cancer-associated fibroblasts, the activation of tumor-associated ECs and platelets, and remodeling of the extracellular matrix. Here, we review current knowledge regarding the involvement of EVs in tumor vascular-related cancer progression.

Resistance to Anti-angiogenic Therapies: A Mechanism Depending on the Time of Exposure to the Drugs

Angiogenesis, the formation of new blood vessels from preexisting one, represents a critical process for oxygen and nutrient supply to proliferating cells, therefore promoting tumor growth and metastasis. The Vascular Endothelial Growth Factor (VEGF) pathway is one of the key mediators of angiogenesis in cancer. Therefore, several therapies including monoclonal antibodies or tyrosine kinase inhibitors target this axis. Although preclinical studies demonstrated strong antitumor activity, clinical studies were disappointing. Antiangiogenic drugs, used to treat metastatic patients suffering of different types of cancers, prolonged survival to different extents but are not curative. In this review, we focused on different mechanisms involved in resistance to antiangiogenic therapies from early stage resistance involving mainly tumor cells to late stages related to the adaptation of the microenvironment.

Overcoming Compensatory Mechanisms toward Chronic Drug Administration to Ensure Long-Term, Sustainable Beneficial Effects

Chronic administration of drugs leads to the activation of compensatory mechanisms that may inhibit some of their activity and induce unwanted toxicity. These mechanisms are an obstacle for maintaining a sustainable effect for many chronic medications. Pathways that adapt to the burden induced by chronic drugs, whether or not related to the underlying disease, can lead to a partial or complete loss of effect. Variability characterizes many biological systems and manifests itself as large intra- and inter-individual differences in the response to drugs. Circadian rhythm-based chronotherapy is further associated with variability in responses noted among patients. This paper reviews current knowledge regarding the loss of effect of chronic medications and the range of variabilities that have been described in responses and loss of responses. Establishment of a personalized platform for overcoming these prohibitive mechanisms is presented as a model for ensuring long-term sustained medication effects. This novel platform implements personalized variability signatures and individualized circadian rhythms for preventing and opposing the prohibitive effect of the compensatory mechanisms induced by chronic drug administration.

Anti-VEGF Drugs in the Treatment of Multiple Myeloma Patients

The interaction between the bone marrow microenvironment and plasma cells plays an essential role in multiple myeloma progression and drug resistance. The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway in vascular endothelial cells activates and promotes angiogenesis. Moreover, VEGF activates and promotes vasculogenesis and vasculogenic mimicry when it interacts with VEGF receptors expressed in precursor cells and inflammatory cells, respectively. In myeloma bone marrow, VEGF and VEGF receptor expression are upregulated and hyperactive in the stromal and tumor cells. It has been demonstrated that several antiangiogenic agents can effectively target VEGF-related pathways in the preclinical phase. However, they are not successful in treating multiple myeloma, probably due to the vicarious action of other cytokines and signaling pathways. Thus, the simultaneous blocking of multiple cytokine pathways, including the VEGF/VEGFR pathway, may represent a valid strategy to treat multiple myeloma. This review aims to summarize recent advances in understanding the role of the VEGF/VEGFR pathway in multiple myeloma, and mainly focuses on the transcription pathway and on strategies that target this pathway.

Resveratrol Promotes Tumor Microvessel Growth via Endoglin and Extracellular Signal-Regulated Kinase Signaling Pathway and Enhances the Anticancer Efficacy of Gemcitabine against Lung Cancer

The synergistic anticancer effect of gemcitabine (GEM) and resveratrol (RSVL) has been noted in certain cancer types. However, whether the same phenomenon would occur in lung cancer is unclear. Here, we uncovered the molecular mechanism by which RSVL enhances the anticancer effect of GEM against lung cancer cells both in vitro and in vivo. We established human lung adenocarcinoma HCC827 xenografts in nude mice and treated them with GEM and RSVL to detect their synergistic effect in vivo. Tumor tissue sections from nude mice were subjected to hematoxylin and eosin staining for blood vessel morphological observation, and immunohistochemistry was conducted to detect CD31-positive staining blood vessels. We also established the HCC827-human umbilical vein endothelial cell (HUVEC) co-culture model to observe the tubule network formation. Human angiogenesis antibody array was used to screen the angiogenesis-related proteins in RSVL-treated HCC827. RSVL suppressed the expression of endoglin (ENG) and increased tumor microvessel growth and blood perfusion into tumor. Co-treatment of RSVL and GEM led to more tumor growth suppression than treatment of GEM alone. Mechanistically, using the HCC827-HUVEC co-culture model, we showed that RSVL-suppressed ENG expression was accompanied with augmented levels of phosphorylated extracellular signal-regulated kinase (ERK) 1/2 and increased tubule network formation, which may explain why RSVL promoted tumor microvessel growth in vivo. RSVL promoted tumor microvessel growth via ENG and ERK and enhanced the anticancer efficacy of GEM. Our results suggest that intake of RSVL may be beneficial during lung cancer chemotherapy.

Three-Dimensional Histologic, Immunohistochemical, and Multiplex Immunofluorescence Analyses of Dynamic Vessel Co-Option of Spread Through Air Spaces in Lung Adenocarcinoma

INTRODUCTION

Spread through air spaces (STAS) is a method of invasion in lung adenocarcinoma and is associated with tumor recurrence and poor survival. The spatial orientation of STAS cells in the lung alveolar parenchyma is not known. The aim of this study was to use high-resolution and high-quality three-dimensional (3D) reconstruction of images from immunohistochemical (IHC) and multiplex immunofluorescence (IF) experiments to understand the spatial architecture of tumor cell clusters by STAS in the lung parenchyma.

METHODS

Four lung adenocarcinomas, three micropapillary-predominant and one solid predominant adenocarcinoma subtypes, were investigated. A 3D reconstruction image was created from formalin-fixed, paraffin-embedded blocks. A total of 350 serial sections were obtained and subjected to hematoxylin and eosin (100 slides), IHC (200 slides), and multiplex IF staining (50 slides) with the following antibodies: cluster of differentiation 31, collagen type IV, thyroid transcription factor-1, and E-cadherin. Whole slide images were reconstructed into 3D images for evaluation.

RESULTS

Serial 3D image analysis by hematoxylin and eosin, IHC, and IF staining revealed that the micropapillary clusters and solid nests of STAS are focally attached to the alveolar walls, away from the main tumor.

CONCLUSIONS

Our 3D reconstructions found that STAS tumor cells can attach to the alveolar walls rather than appearing free floating, as seen on the two-dimensional sections. This suggests that the tumor cells detach from the main tumor, migrate through air spaces, and reattach to the alveolar walls through vessel co-option, allowing them to survive and grow. This may explain the higher recurrence rate and worse survival of patients with STAS-positive tumors who undergo limited resection than those who undergo lobectomy.

Resistance Mechanisms to Anti-angiogenic Therapies in Cancer

Tumor growth and metastasis rely on tumor vascular network for the adequate supply of oxygen and nutrients. Tumor angiogenesis relies on a highly complex program of growth factor signaling, endothelial cell (EC) proliferation, extracellular matrix (ECM) remodeling, and stromal cell interactions. Numerous pro-angiogenic drivers have been identified, the most important of which is the vascular endothelial growth factor (VEGF). The importance of pro-angiogenic inducers in tumor growth, invasion and extravasation make them an excellent therapeutic target in several types of cancers. Hence, the number of anti-angiogenic agents developed for cancer treatment has risen over the past decade, with at least eighty drugs being investigated in preclinical studies and phase I-III clinical trials. To date, the most common approaches to the inhibition of the VEGF axis include the blockade of VEGF receptors (VEGFRs) or ligands by neutralizing antibodies, as well as the inhibition of receptor tyrosine kinase (RTK) enzymes. Despite promising preclinical results, anti-angiogenic monotherapies led only to mild clinical benefits. The minimal benefits could be secondary to primary or acquired resistance, through the activation of alternative mechanisms that sustain tumor vascularization and growth. Mechanisms of resistance are categorized into VEGF-dependent alterations, non-VEGF pathways and stromal cell interactions. Thus, complementary approaches such as the combination of these inhibitors with agents targeting alternative mechanisms of blood vessel formation are urgently needed. This review provides an updated overview on the pathophysiology of angiogenesis during tumor growth. It also sheds light on the different pro-angiogenic and anti-angiogenic agents that have been developed to date. Finally, it highlights the preclinical evidence for mechanisms of angiogenic resistance and suggests novel therapeutic approaches that might be exploited with the ultimate aim of overcoming resistance and improving clinical outcomes for patients with cancer.

Expression of fibroblast growth factor receptor 4 and clinical response to lenvatinib in patients with anaplastic thyroid carcinoma: a pilot study

PURPOSE

Fibroblast growth factor receptor 4 (FGFR4) expression has association with tumor malignancy. In thyroid cancers, FGFR4 has been reported to be characteristically expressed in aggressive thyroid tumors, such as anaplastic thyroid carcinoma (ATC).

METHODS

We investigated FGFR4 expression in patients with ATC and analyzed their clinical responses to lenvatinib. Primary tumor samples were obtained from 12 patients with ATC who underwent surgery or core needle biopsy. FGFR4 protein expression in all ATC samples was analyzed via immunohistochemistry, and the treatment efficacy of lenvatinib was evaluated.

RESULTS

The proportion of FGFR4-positive cells in the samples ranged from 0 to 50%. Four patients had partial responses, and three patients had stable diseases as a best clinical response to lenvatinib. The median PFS durations of patients with none, weak, and moderate intensity were 0.5, 3.2 (95% CI 1.1-not estimable [NE]), and 4.6 (95% CI 1.1-NE) months, respectively (p = 0.003).

CONCLUSIONS

Because FGFR4 was expressed in ATC tissues, the FGFR4 expression might be associated with the treatment efficacy of lenvatinib in a part of ATC patients. To clarify whether FGFR4 can serve as a prognostic or predictive factor for lenvatinib therapy, more cases must be accumulated.

Potential Therapeutic Strategies for Lung and Breast Cancers through Understanding the Anti-Angiogenesis Resistance Mechanisms

Breast and lung cancers are among the top cancer types in terms of incidence and mortality burden worldwide. One of the challenges in the treatment of breast and lung cancers is their resistance to administered drugs, as observed with angiogenesis inhibitors. Based on clinical and pre-clinical findings, these two types of cancers have gained the ability to resist angiogenesis inhibitors through several mechanisms that rely on cellular and extracellular factors. This resistance is mediated through angiogenesis-independent vascularization, and it is related to cancer cells and their microenvironment. The mechanisms that cancer cells utilize include metabolic symbiosis and invasion, and they also take advantage of neighboring cells like macrophages, endothelial cells, myeloid and adipose cells. Overcoming resistance is of great interest, and researchers are investigating possible strategies to enhance sensitivity towards angiogenesis inhibitors. These strategies involved targeting multiple players in angiogenesis, epigenetics, hypoxia, cellular metabolism and the immune system. This review aims to discuss the mechanisms of resistance to angiogenesis inhibitors and to highlight recently developed approaches to overcome this resistance.

Inhibition of Dimethylarginine Dimethylaminohydrolase (DDAH) Enzymes as an Emerging Therapeutic Strategy to Target Angiogenesis and Vasculogenic Mimicry in Cancer

The small free radical gas nitric oxide (NO) plays a key role in various physiological and pathological processes through enhancement of endothelial cell survival and proliferation. In particular, NO has emerged as a molecule of interest in carcinogenesis and tumor progression due to its crucial role in various cancer-related events including cell invasion, metastasis, and angiogenesis. The dimethylarginine dimethylaminohydrolase (DDAH) family of enzymes metabolize the endogenous nitric oxide synthase (NOS) inhibitors, asymmetric dimethylarginine (ADMA) and monomethyl arginine (L-NMMA), and are thus key for maintaining homeostatic control of NO. Dysregulation of the DDAH/ADMA/NO pathway resulting in increased local NO availability often promotes tumor growth, angiogenesis, and vasculogenic mimicry. Recent literature has demonstrated increased DDAH expression in tumors of different origins and has also suggested a potential ADMA-independent role for DDAH enzymes in addition to their well-studied ADMA-mediated influence on NO. Inhibition of DDAH expression and/or activity in cell culture models and in vivo studies has indicated the potential therapeutic benefit of this pathway through inhibition of both angiogenesis and vasculogenic mimicry, and strategies for manipulating DDAH function in cancer are currently being actively pursued by several research groups. This review will thus provide a timely discussion on the expression, regulation, and function of DDAH enzymes in regard to angiogenesis and vasculogenic mimicry, and will offer insight into the therapeutic potential of DDAH inhibition in cancer based on preclinical studies.

Necrosis in the Tumor Microenvironment and Its Role in Cancer Recurrence

Cancer recurrence is one of the most imminent problems in the current world of medicine, and it is responsible for most of the cancer-related death rates worldwide. Long-term administration of anticancer cytotoxic drugs may act as a double-edged sword, as necrosis may lead to renewed cancer progression and treatment resistance. The lack of nutrients, coupled with the induced hypoxia, triggers cell death and secretion of signals that affect the tumor niche. Many efforts have been made to better understand the contribution of hypoxia and metabolic stress to cancer progression and resistance, but mostly with respect to inflammation. Here we provide an overview of the direct anticancer effects of necrotic signals, which are not necessarily mediated by inflammation and the role of DAMPs (damage-associated molecular patterns) on the formation of a pro-cancerous environment.

Angiopoietin1 Deficiency in Hepatocytes Affects the Growth of Colorectal Cancer Liver Metastases (CRCLM)

Colorectal cancer liver metastases (CRCLM) that receive their blood supply via vessel co-option are associated with a poor response to anti-angiogenic therapy. Angiopoietins (Ang1 and Ang2) with their Tyrosine-protein kinase receptor (Tie2) have been shown to support vessel co-option. We demonstrate significantly higher expression of Ang1 in hepatocytes adjacent to the tumor region of human chemonaïve and treated co-opting (replacement histopathological growth patterns: RHGP) tumors. To investigate the role of the host Ang1 expression, Ang1 knockout (KO) mice were injected intra-splenically with metastatic MC-38 colon cancer cells that develop co-opting liver metastases. We observed a reduction in the number of liver metastases and interestingly, for the first time, the development of angiogenic driven desmoplastic (DHGP) liver metastases. In addition, in-vitro, knockout of Ang1 in primary hepatocytes inhibited viability, migration and invasion ability of MC-38 cells. We also demonstrate that Ang 1 alone promotes the migration and growth of both human and mouse colon cancer cell lines These results provide evidence that high expression of Ang1 in the host liver is important to support vessel co-option (RHGP lesions) and when inhibited, favours the formation of angiogenic driven liver metastases (DHGP lesions).

Fact or Fiction, It Is Time for a Verdict on Vasculogenic Mimicry?

The term vasculogenic mimicry (VM) refers to the capacity of certain cancer cells to form fluid-conducting structures within a tumor in an endothelial cell (EC)-free manner. Ever since its first report by Maniotis in 1999, the existence of VM has been an extremely contentious issue. The overwhelming consensus of the literature suggests that VM is frequently observed in highly aggressive tumors and correlates to lower patient survival. While the presence of VM in vivo in animal and patient tumors are claimed upon the strong positive staining for glycoproteins (Periodic Acid Schiff, PAS), it is by no means universally accepted. More controversial still is the existence of an in vitro model of VM that principally divides the scientific community. Original reports demonstrated that channels or tubes occur in cancer cell monolayers in vitro when cultured in matrigel and that these structures may support fluid movement. However, several years later many papers emerged stating that connections formed between cancer cells grown on matrigel represented VM. We speculate that this became accepted by the cancer research community and now the vast majority of the scientific literature reports both presence and mechanisms of VM based on intercellular connections, not the presence of fluid conducting tubes. In this opinion paper, we call upon evidence from an exhaustive review of the literature and original data to argue that the majority of in vitro studies presented as VM do not correspond to this phenomenon. Furthermore, we raise doubts on the validity of concluding the presence of VM in patient samples and animal models based solely on the presence of PAS+ staining. We outline the requirement for new biomarkers of VM and present criteria by which VM should be defined in vitro and in vivo.

Vasculogenic mimicry-associated ultrastructural findings in human and canine inflammatory breast cancer cell lines

Background

Human inflammatory breast cancer (IBC) and canine inflammatory mammary cancer (IMC) are the most lethal mammary cancers. An exacerbated angiogenesis and the existence of vasculogenic mimicry (VM) are hallmarks of these tumors. The information regarding VM and ultrastructural characteristics of mammary cell lines is scant.

Methods

In this study, IBC cell line SUM149 and IMC cell line IPC-366 in adherent (2D) and non-adherent (3D) (mammospheres, cancer stem cells) conditions were analyzed by transmission and scanning electron microscopy (TEM and SEM, respectively).

Results

The TEM revealed round to oval shape cells with microvilli on the surface, high numbers of peroxisomes in close apposition to lipid droplets and some extracellular derived vesicles. The TEM and the SEM mammospheres revealed group of cells clumping together with a central lumen (resembling a mammary acini). The cells joint are tight junctions and zonula adherens. By SEM two cell morphologies were observed: spherical and flattened cells. There was evidence endothelial-like cells (ELCs), which is characteristic for this disease, showing several or unique cytoplasmic empty space. ELCs were more frequent in 3D than in 2D culture conditions and contained Weibel-Palade cytoplasmic bodies, which are exclusive structures of endothelial cells.

Conclusions

Both cell lines, IPC-366 and SUM-149, shared ultrastructural characteristics, further supporting canine IMC as a model for the human disease. To the best of our knowledge, this is the first study that demonstrate the morphological differentiation of cultured cancer stem cells from cancer epithelial cell lines into endothelial-like cells, confirming the vasculogenic mimicry phenomenon from an ultrastructural point of view.

Role of EphA2-PI3K signaling in vasculogenic mimicry induced by cancer-associated fibroblasts in gastric cancer cells

Although erythropoietin-producing human hepatocellular receptor A2 (EphA2) signaling serves an important role in the tumor microenvironment, its contribution to vasculogenic mimicry (VM) formation in gastric cancer cells remains unclear. The aim of the present study was to investigate the role of EphA2 in VM formation induced by cancer-associated fibroblasts (CAFs). The conditioned medium of CAFs (CAF-CM) was prepared from 12 patients with gastric adenocarcinoma. VM was evaluated by the number of tubules and intersections in gastric cancer cells following CAF-CM treatment. The role of EphA2-phosphoinositide 3-kinase (PI3K) in VM was investigated using EphA2-targeted small interfering (si)RNAs (siEphA2), EphA2 inhibitors and PI3K-inhibitors. CAF-CM-induced VM formation was significantly associated with high protein expression levels of EphA2. EphA2 inhibitor and siEphA2 manipulation significantly decreased VM formation by CAF-CM. In siEphA2 cells, decreased expression levels of VM-associated proteins were observed. CAF-CM-induced VM formation was blocked by the PI3K-inhibitor. In conclusion, CAFs facilitate VM formation via EphA2-PI3K signaling in gastric cancer cells. Thus, EphA2-PI3K signaling may be required for CAF-promoted VM formation during gastric tumorigenesis.

HypoxamiRs Profiling Identify miR-765 as a Regulator of the Early Stages of Vasculogenic Mimicry in SKOV3 Ovarian Cancer Cells

Vasculogenic mimicry (VM) is a novel cancer hallmark in which malignant cells develop matrix-associated 3D tubular networks with a lumen under hypoxia to supply nutrients needed for tumor growth. Recent studies showed that microRNAs (miRNAs) may have a role in VM regulation. In this study, we examined the relevance of hypoxia-regulated miRNAs (hypoxamiRs) in the early stages of VM formation. Data showed that after 48 h hypoxia and 12 h incubation on matrigel SKOV3 ovarian cancer cells undergo the formation of matrix-associated intercellular connections referred hereafter as 3D channels-like structures, which arose previous to the apparition of canonical tubular structures representative of VM. Comprehensive profiling of 754 mature miRNAs at the onset of hypoxia-induced 3D channels-like structures showed that 11 hypoxamiRs were modulated (FC>1.5; p < 0.05) in SKOV3 cells (9 downregulated and 2 upregulated). Bioinformatic analysis of the set of regulated miRNAs showed that they might impact cellular pathways related with tumorigenesis. Moreover, overall survival analysis in a cohort of ovarian cancer patients (n = 485) indicated that low miR-765, miR-193b, miR-148a and high miR-138 levels were associated with worst patients outcome. In particular, miR-765 was severely downregulated after hypoxia (FC < 32.02; p < 0.05), and predicted to target a number of protein-encoding genes involved in angiogenesis and VM. Functional assays showed that ectopic restoration of miR-765 in SKOV3 cells resulted in a significant inhibition of hypoxia-induced 3D channels-like formation that was associated with a reduced number of branch points and patterned tubular-like structures. Mechanistic studies confirmed that miR-765 decreased the levels of VEGFA, AKT1 and SRC-α transducers and exerted a negative regulation of VEGFA by specific binding to its 3‘UTR. Finally, overall survival analysis of a cohort of ovarian cancer patients (n = 1435) indicates that high levels of VEGFA, AKT1 and SRC-α and low miR-765 expression were associated with worst patients outcome. In conclusion, here we reported a novel hypoxamiRs signature which constitutes a molecular guide for further clinical and functional studies on the early stages of VM. Our data also suggested that miR-765 coordinates the formation of 3D channels-like structures through modulation of VEGFA/AKT1/SRC-α axis in SKOV3 ovarian cancer cells.

Class I histone deacetylase inhibitor suppresses vasculogenic mimicry by enhancing the expression of tumor suppressor and anti-angiogenesis genes in aggressive human TNBC cells

Triple-negative breast cancer (TNBC) cells form angiogenesis-independent vessel-like structures to survive, known as vasculogenic mimicry (VM), contributing to a poor prognosis for cancer patients. Nuclear localized class I histone deacetylases (HDACs) enzymes, particularly HDACs 1, 2, 3 deacetylate chromatin histones, are overexpressed in cancers and epigenetically regulate the expression of genes involved in cancer initiation and progression. The specific HDAC inhibitor, entinostat, has been shown to attenuate tumor progression and metastasis in TNBC. In this study, we hypothesized that entinostat would enhance the expression of anti-angiogenic and tumor suppressor genes and would thus suppress VM structures in TNBC cells in a 3D Matrigel cell culture preclinical model. Our data indicated that invasive triple-negative MDA-MB-231, LM2-4 and BT-549 breast cancer cells, but not poorly invasive luminal MCF-7 cells, efficiently underwent matrix-associated VM formation. Approximately 80% of TNBC cells with the stem cell phenotype potential formed vessel-like structures when mixed with Matrigel and cultured in the low attachment tissue culture plate. The molecular mechanisms of VM formation are rather complex, while angiogenesis inhibitor genes are downregulated and pro-angiogenesis genes are upregulated in VM-forming cells. Our data revealed that treatment of the TNBC VM phenotype cells with entinostat epigenetically led to the re-expression of the anti-angiogenic genes, serpin family F member 1 (SERPINF1) and thrombospondin 2 (THBS2), and to that of the tumor suppressor genes, phosphatase and tensin homolog (PTEN) and p21, and reduced VM structures. We also found that treatment of the TNBC VM phenotype cells with entinostat downregulated the expression of vascular endothelial growth factor A (VEGF-A), and that of the epithelial-mesenchymal transition (EMT)-related genes, Vimentin and β-catenin. METABIRC and TCGA breast cancer cohort mRNA expression data analysis revealed that a high expression of the anti-angiogenesis-associated genes, THBS2, SERPINF1 and serpin family B member 5 (SERPINB5), and of the tumor suppressor gene, PTEN, was associated with a better overall survival (OS) of breast cancer patients. Taken together, the findings of this study demonstrate that HDACs 1, 2, 3 partly contribute to VM formation in TNBC cells; thus, HDACs may be an important therapeutic target for TNBC.

The role of sema4D in vasculogenic mimicry formation in non-small cell lung cancer and the underlying mechanisms

Vasculogenic mimicry (VM) is a special vascular pattern in malignant tumors, which is composed of highly aggressive tumor cells. This tumor cell-mediated blood supply pattern is closely associated with a poor prognosis in cancer patients. The interaction of axon guidance factor Sema4D and its high affinity receptor plexinB1 could activate small GTPase RhoA and its downstream ROCKs; this process has an active role in the migration of endothelial cells and tumor angiogenesis. Here, we have begun to uncover the role of this pathway in VM formation in non-small cell lung cancer (NSCLC). First, we confirmed this special form of vasculature in NSCLC tissues and found the existence of VM channels in tumor tissues was correlated with Sema4D expression. Further, we found that inhibition of Sema4D in the human NSCLC cells H1299 and HCC827 reduces VM formation both in vitro and in vivo. Moreover, we demonstrated that downregulating the expression of plexinB1 by siRNA expressing vectors and inhibiting the RhoA/ROCK signaling pathway using fasudil can reduce VM formation of H1299 and HCC827 cells. Finally, we found that suppression of Sema4D leads to less stress fibers and depleted the motility of H1299 and HCC827 cells. Collectively, our study implicates Sema4D plays an important role in the process of VM formation in NSCLC through activating the RhoA/ROCK pathway and regulating tumor cell plasticity and migration. Modulation of the Sema4D/plexinB1 and downstream RhoA/ROCK pathway may prevent the tumor blood supply through the VM pattern, which may eventually halt growth and metastasis of NSCLC.

Expression of vascular endothelial growth factor receptor 2 and clinical response to lenvatinib in patients with anaplastic thyroid cancer

PURPOSE

Angiogenesis plays a crucial role in the development, growth, and metastasis of carcinomas, and studies have reported conflicting evidence regarding the VEGFR expression in anaplastic thyroid cancer. We investigated the expression of VEGFR2 in patients with anaplastic thyroid cancer (ATC) and analyzed the clinical response to the VEGFR inhibitor lenvatinib.

METHODS

This cross-sectional study included primary tumor samples obtained from 12 patients with ATC, including 5 males and 7 females (age range 63-89 years) who underwent surgery or core needle biopsy for a thyroid tumor in the Department of Breast and Endocrine Surgery at Kanagawa Cancer Center in Kanagawa, Japan. VEGFR2 protein expression in the ATC samples was analyzed by immunohistochemistry in all patients, and the therapeutic effect of lenvatinib was evaluated in seven patients who underwent tissue biopsy and lesion evaluation.

RESULTS

VEGFR expression was not detected in any of the samples from the 12 patients. Four of the 12 patients treated with lenvatinib had partial response, the three patients achieved stable disease, and the five patients were not examined.

CONCLUSIONS

There was no correlation between the expression of VEGFR2 in tumor tissue and the clinical response to lenvatinib among patients with ATC. Further studies are necessary to elucidate the mechanism underlying the response to lenvatinib.

The role of tumor microenvironment in resistance to anti-angiogenic therapy

Anti-angiogenic therapy has been demonstrated to increase progression-free survival in patients with many different solid cancers. Unfortunately, the benefit in overall survival is modest and the rapid emergence of drug resistance is a significant clinical problem. Over the last decade, several mechanisms have been identified to decipher the emergence of resistance. There is a multitude of changes within the tumor microenvironment (TME) in response to anti-angiogenic therapy that offers new therapeutic opportunities. In this review, we compile results from contemporary studies related to adaptive changes in the TME in the development of resistance to anti-angiogenic therapy. These include preclinical models of emerging resistance, dynamic changes in hypoxia signaling and stromal cells during treatment, and novel strategies to overcome resistance by targeting the TME.

Collateral Damage Intended-Cancer-Associated Fibroblasts and Vasculature Are Potential Targets in Cancer Therapy

After oncogenic transformation, tumor cells rewire their metabolism to obtain sufficient energy and biochemical building blocks for cell proliferation, even under hypoxic conditions. Glucose and glutamine become their major limiting nutritional demands. Instead of being autonomous, tumor cells change their immediate environment not only by their metabolites but also by mediators, such as juxtacrine cell contacts, chemokines and other cytokines. Thus, the tumor cells shape their microenvironment as well as induce resident cells, such as fibroblasts and endothelial cells (ECs), to support them. Fibroblasts differentiate into cancer-associated fibroblasts (CAFs), which produce a qualitatively and quantitatively different extracellular matrix (ECM). By their contractile power, they exert tensile forces onto this ECM, leading to increased intratumoral pressure. Moreover, along with enhanced cross-linkage of the ECM components, CAFs thus stiffen the ECM. Attracted by tumor cell- and CAF-secreted vascular endothelial growth factor (VEGF), ECs sprout from pre-existing blood vessels during tumor-induced angiogenesis. Tumor vessels are distinct from EC-lined vessels, because tumor cells integrate into the endothelium or even mimic and replace it in vasculogenic mimicry (VM) vessels. Not only the VM vessels but also the characteristically malformed EC-lined tumor vessels are typical for tumor tissue and may represent promising targets in cancer therapy.

Acquired tumor resistance to antiangiogenic therapy: Mechanisms at a glance

Angiogenesis is critical for oxygen and nutrient delivery to proliferating tumor cells. Therefore, as angiogenesis is required and vital for the tumor growth and metastasis. Antiangiogenic therapy is considered to be beneficial for tumor growth prevention due to starvation of tumor of oxygen and nutrients, but in some cases, the benefits are not permanent. Tyrosine kinase inhibitors and many other agents often target angiogenesis through inhibition of the vascular endothelial growth factor (VEGF) pathway. Although preclinical studies showed satisfactory outcomes in tumor growth inhibition, antiangiogenic therapy in the clinical setting may not be effective. The resistance observed in several tumor types through alternative angiogenic “escape” pathways contributes to restoration of tumor growth and may induce progression, enhancement of invasion, and metastasis. Therefore, activation of major compensatory angiogenic pathways, sustaining tumor angiogenesis during VEGF blockade contributing to the recurrence of tumor growth overcome antiangiogenic strategies. In this review, we summarize the novel mechanisms involved in evasive resistance to antiangiogenic therapies and represent different cancer types which have the ability to adapt to VEGF inhibition achieving resistance to antiangiogenic therapy through these adaptive mechanisms.

Off-tumor targets compromise antiangiogenic drug sensitivity by inducing kidney erythropoietin production

Anti-VEGF drugs are commonly used for treatment of a variety of cancers in human patients, and they often develop resistance. The mechanisms underlying anti-VEGF resistance in human cancer patients are largely unknown. Here, we show that in mouse tumor models and in human cancer patients, the anti-VEGF drug-induced kidney hypoxia augments circulating levels of erythropoietin (EPO). Gain-of-function studies show that EPO protects tumor vessels from anti-VEGF treatment and compromises its antitumor effects. Loss of function by blocking EPO function using a pharmacological approach markedly increases antitumor activity of anti-VEGF drugs through inhibition of tumor angiogenesis. Similarly, genetic loss-of-function data shows that deletion of EpoR in nonerythroid cells significantly increases antiangiogenic and antitumor effects of anti-VEGF therapy. Finally, in a relatively large cohort study, we show that treatment of human colorectal cancer patients with bevacizumab augments circulating EPO levels. These findings uncover a mechanism of desensitizing antiangiogenic and anticancer effects by kidney-produced EPO. Our work presents conceptual advances of our understanding of mechanisms underlying antiangiogenic drug resistance.

Vascularized Tissue-Engineered Model for Studying Drug Resistance in Neuroblastoma

Neuroblastoma is a vascularized pediatric tumor derived from neural crest stem cells that displays vasculogenic mimicry and can express a number of stemness markers, such as SOX2 and NANOG. Tumor relapse is the major cause of succumbing to this disease, and properties attributed to cancer stem-like cells (CSLC), such as drug-resistance and cell plasticity, seem to be the key mechanisms. However, the lack of controllable models that recapitulate the features of human neuroblastoma limits our understanding of the process and impedes the development of new therapies. In response to these limitations, we engineered a perfusable, vascularized in vitro model of three-dimensional human neuroblastoma to study the effects of retinoid therapy on tumor vasculature and drug-resistance.

METHODS

The in vitro model of neuroblastoma was generated using cell-sheet engineering and cultured in a perfusion bioreactor. Firstly, we stacked three cell sheets containing SKNBE(2) neuroblastoma cells and HUVEC. Then, a vascular bed made of fibrin, collagen I and HUVEC cells was placed onto a collagen-gel base with 8 microchannels. After gelling, the stacked cell sheets were placed on the vascular bed and cultured in the perfusion bioreactor (perfusion rate: 0.5 mL/min) for 4 days. Neuroblastoma models were treated with 10μM isotretionin in single daily doses for 5 days.

RESULTS

The bioengineered model recapitulated vasculogenic mimicry (vessel-like structure formation and tumor-derived endothelial cells-TECs), and contained CSLC expressing SOX2 and NANOG. Treatment with Isotretinoin destabilized vascular networks but failed to target vasculogenic mimicry and augmented populations of CSLCs expressing high levels of SOX2. Our results suggest that CSLCs can transdifferentiate into drug resistant CD31⁺-TECs, and reveal the presence of an intermediate state STEC (stem tumor-derived endothelial cell) expressing both SOX2 and CD31.

CONCLUSION

Our results reveal some roles of SOX2 in drug resistance and tumor relapse, and suggest that SOX2 could be a therapeutic target in neuroblastoma.

Integrin Activation Contributes to Lower Cisplatin Sensitivity in MV3 Melanoma Cells by Inducing the Wnt Signalling Pathway

Background: integrins have been associated with the development of chemotherapy resistant tumour cells, mostly those of hematopoietic origin, by mediating the binding to the extracellular matrix. The relevance for solid tumour cells and the underlying mechanisms remain elusive. Methods: using MTT assays, we detected the loss in cisplatin sensitivity of human MV3 melanoma cells upon integrin activation. Underlying cellular pathways were evaluated by flow cytometry. A crosstalk between integrin activation and the canonical wnt signalling pathway was tested by measuring β-catenin activity. Results: MV3 cells display a higher resistance against cisplatin cytotoxicity when cellular integrins were activated by manganese or collagen. Proteome profiler array showed a deregulation of the integrin expression pattern by cisplatin. Integrin activation by manganese induces the phosphorylation of PI3K/AKT. The inhibition of PI3K using BEZ235 strongly increases cell sensitivity to cisplatin, blocking manganese and collagen effects. PI3K/AKT activates wnt signalling by blocking Gsk3-β, which was confirmed by β-catenin up-regulation and nuclear localization. Integrins did not affect E-cadherin expression levels, thus endothelial to mesenchymal transition (EMT) can be excluded. Conclusion: This is the first report on an integrin/wnt signalling activation axis addressing the consequences for chemotherapy sensitiveness of melanoma cells, which thus offers novel therapeutic targets for approaches to interfere with chemoresistance.

Angiogenesis inhibitors in early development for gastric cancer

INTRODUCTION

Angiogenesis, or the generation of new blood vessels from pre-existent ones is a critical process for tumor growth and progression. Hence, the development of angiogenesis inhibitors with therapeutic potential has been a central focus for researchers. Most angiogenesis inhibitors target the Vascular Endothelial Growth Factor (VEGF) pathway, however a number of tyrosine kinase inhibitors (TKIs), immunomodulatory drugs (IMiDs) and inhibitors of the mammalian Target-Of-Rapamycin (mTOR) pathway also display antiangiogenic activity. Areas covered: Here we review the effectiveness of a variety of compounds with antiangiogenic properties in preclinical and clinical settings in gastric cancer (GC). Expert opinion: In coming years angiogenesis will remain as a therapeutic target in GC. To date, ramucirumab a monoclonal antibody that targets VEGFR2 is the most successful antiangiogenic tested in clinical studies, and it is now well established as a second-line therapy in GC. The arrival of precision medicine and the success of immune checkpoint inhibitors will increase the number of clinical trials using targeted agents like ramucirumab in combination with immune checkpoint inhibitors. A hypothetical working model that combines ramucirumab with immunotherapy is presented. Also, the impact of nanotechnology and a molecular subtype classification of GC are discussed.

Modeling tumor cell adaptations to hypoxia in multicellular tumor spheroids

Under hypoxic conditions, tumor cells undergo a series of adaptations that promote evolution of a more aggressive tumor phenotype including the activation of DNA damage repair proteins, altered metabolism, and decreased proliferation. Together these changes mitigate the negative impact of oxygen deprivation and allow preservation of genomic integrity and proliferative capacity, thus contributing to tumor growth and metastasis. As a result the presence of a hypoxic microenvironment is considered a negative clinical feature of many solid tumors. Hypoxic niches in tumors also represent a therapeutically privileged environment in which chemo- and radiation therapy is less effective. Although the negative impact of tumor hypoxia has been well established, the precise effect of oxygen deprivation on tumor cell behavior, and the molecular signals that allow a tumor cell to survive in vivo are poorly understood. Multicellular tumor spheroids (MCTS) have been used as an in vitro model for the avascular tumor niche, capable of more accurately recreating tumor genomic profiles and predicting therapeutic response. However, relatively few studies have used MCTS to study the molecular mechanisms driving tumor cell adaptations within the hypoxic tumor environment. Here we will review what is known about cell proliferation, DNA damage repair, and metabolic pathways as modeled in MCTS in comparison to observations made in solid tumors. A more precise definition of the cell populations present within 3D tumor models in vitro could better inform our understanding of the heterogeneity within tumors as well as provide a more representative platform for the testing of therapeutic strategies.

Structural and functional identification of vasculogenic mimicry in vitro

Vasculogenic mimicry (VM) describes a process by which cancer cells establish an alternative perfusion pathway in an endothelial cell-free manner. Despite its strong correlation with reduced patient survival, controversy still surrounds the existence of an in vitro model of VM. Furthermore, many studies that claim to demonstrate VM fail to provide solid evidence of true hollow channels, raising concerns as to whether actual VM is actually being examined. Herein, we provide a standardized in vitro assay that recreates the formation of functional hollow channels using ovarian cancer cell lines, cancer spheres and primary cultures derived from ovarian cancer ascites. X-ray microtomography 3D-reconstruction, fluorescence confocal microscopy and dye microinjection conclusively confirm the existence of functional glycoprotein-rich lined tubular structures in vitro and demonstrate that many of structures reported in the literature may not represent VM. This assay may be useful to design and test future VM-blocking anticancer therapies.

Ovarian cancer: Novel molecular aspects for clinical assessment

Ovarian cancer is a very heterogeneous tumor which has been traditionally characterized according to the different histological subtypes and differentiation degree. In recent years, innovative molecular screening biotechnologies have allowed to identify further subtypes of this cancer based on gene expression profiles, mutational features, and epigenetic factors. These novel classification systems emphasizing the molecular signatures within the broad spectrum of ovarian cancer have not only allowed a more precise prognostic prediction, but also proper therapeutic strategies for specific subgroups of patients. The bulk of available scientific data and the high refinement of molecular classifications of ovarian cancers can today address the research towards innovative drugs with the adoption of targeted therapies tailored for single molecular profiles leading to a better prediction of therapeutic response. Here, we summarize the current state of knowledge on the molecular bases of ovarian cancer, from the description of its molecular subtypes derived from wide high-throughput analyses to the latest discoveries of the ovarian cancer stem cells. The latest personalized treatment options are also presented with recent advances in using PARP inhibitors, anti-angiogenic, anti-folate receptor and anti-cancer stem cells treatment approaches.

Targeted brain delivery nanoparticles for malignant gliomas

Brain tumors display the highest mortality rates of all childhood cancers, and over the last decade its prevalence has steadily increased in elderly. To date, effective treatments for brain tumors and particularly for malignant gliomas remain a challenge mainly due to the low permeability and high selectivity of the blood-brain barrier (BBB) to conventional anticancer drugs. In recent years, the elucidation of the cellular mechanisms involved in the transport of substances into the brain has boosted the development of therapeutic-targeted nanoparticles (NPs) with the ability to cross the BBB. Here, we present a comprehensive overview of the available therapeutic strategies developed against malignant gliomas based on 'actively targeted' NPs, the challenges of crossing the BBB and blood-brain tumor barrier as well as its mechanisms and a critical assessment of clinical studies that have used targeted NPs for the treatment of malignant gliomas. Finally, we discuss the potential of actively targeted NP-based strategies in clinical settings, its possible side effects and future directions for therapeutic applications. First draft submitted: 4 October 2016; Accepted for publication: 14 October 2016; Published online: 23 November 2016.