Apelin as a marker for monitoring the tumor vessel normalization window during antiangiogenic therapy

Exploring exercise-driven exerkines: unraveling the regulation of metabolism and inflammation

Exercise has many beneficial effects that provide health and metabolic benefits. Signaling molecules are released from organs and tissues in response to exercise stimuli and are widely termed exerkines, which exert influence on a multitude of intricate multi-tissue processes, such as muscle, adipose tissue, pancreas, liver, cardiovascular tissue, kidney, and bone. For the metabolic effect, exerkines regulate the metabolic homeostasis of organisms by increasing glucose uptake and improving fat synthesis. For the anti-inflammatory effect, exerkines positively influence various chronic inflammation-related diseases, such as type 2 diabetes and atherosclerosis. This review highlights the prospective contribution of exerkines in regulating metabolism, augmenting the anti-inflammatory effects, and providing additional advantages associated with exercise. Moreover, a comprehensive overview and analysis of recent advancements are provided in this review, in addition to predicting future applications used as a potential biomarker or therapeutic target to benefit patients with chronic diseases.

Localized apelin-17 analogue-bicelle interactions as a facilitator of membrane-catalyzed receptor recognition and binding

The apelinergic system encompasses two peptide ligand families, apelin and apela, along with the apelin receptor (AR or APJ), a class A G-protein-coupled receptor. This system has diverse physiological effects, including modulating heart contraction, vasodilation/constriction, glucose regulation, and vascular development, with involvement in a variety of pathological conditions. Apelin peptides have been previously shown to interact with and become structured upon binding to anionic micelles, consistent with a membrane-catalyzed mechanism of ligand-receptor binding. To overcome the challenges of observing nuclear magnetic resonance (NMR) spectroscopy signals of a dilute peptide in biological environments, 19F NMR spectroscopy, including diffusion ordered spectroscopy (DOSY) and saturation transfer difference (STD) experiments, was used herein to explore the membrane-interactive behaviour of apelin. NMR-optimized apelin-17 analogues with 4-trifluoromethyl-phenylalanine at various positions were designed and tested for bioactivity through ERK activation in stably-AR transfected HEK 293 T cells. Far-UV circular dichroism (CD) spectropolarimetry and 19F NMR spectroscopy were used to compare the membrane interactions of these analogues with unlabelled apelin-17 in both zwitterionic/neutral and net-negative bicelle conditions. Each analogue binds to bicelles with relatively weak affinity (i.e., in fast exchange on the NMR timescale), with preferential interactions observed at the cationic residue-rich N-terminal and mid-length regions of the peptide leaving the C-terminal end unencumbered for receptor recognition, enabling a membrane-anchored fly-casting mechanism of peptide search for the receptor. In all, this study provides further insight into the membrane-interactive behaviour of an important bioactive peptide, demonstrating interactions and biophysical behaviour that cannot be neglected in therapeutic design.

Immunological characterization of stroke-heart syndrome and identification of inflammatory therapeutic targets

Acute cardiac dysfunction caused by stroke-heart syndrome (SHS) is the second leading cause of stroke-related death. The inflammatory response plays a significant role in the pathophysiological process of cardiac damage. However, the mechanisms underlying the brain-heart interaction are poorly understood. Therefore, we aimed to analysis the immunological characterization and identify inflammation therapeutic targets of SHS. We analyzed gene expression data of heart tissue 24 hours after induction of ischemia stoke by MCAO or sham surgery in a publicly available dataset (GSE102558) from Gene Expression Omnibus (GEO). Bioinformatics analysis revealed 138 differentially expressed genes (DEGs) in myocardium of MCAO-treated compared with sham-treated mice, among which, immune and inflammatory pathways were enriched. Analysis of the immune cells infiltration showed that the natural killer cell populations were significantly different between the two groups. We identified five DIREGs, Aplnr, Ccrl2, Cdkn1a, Irak2, and Serpine1 and found that their expression correlated with specific populations of infiltrating immune cells in the cardiac tissue. RT-qPCR and Western blot methods confirmed significant changes in the expression levels of Aplnr, Cdkn1a, Irak2, and Serpine1 after MCAO, which may serve as therapeutic targets to prevent cardiovascular complications after stroke.

Design and preclinical evaluation of a novel apelin-based PET radiotracer targeting APJ receptor for molecular imaging of angiogenesis

APJ has been extensively described in the pathophysiology of angiogenesis and cell proliferation. The prognostic value of APJ overexpression in many diseases is now established. This study aimed to design a PET radiotracer that specifically binds to APJ. Apelin-F13A-NODAGA (AP747) was synthesized and radiolabeled with gallium-68 ([68Ga]Ga-AP747). Radiolabeling purity was excellent (> 95%) and stable up to 2 h. Affinity constant of [67Ga]Ga-AP747 was measured on APJ-overexpressing colon adenocarcinoma cells and was in nanomolar range. Specificity of [68Ga]Ga-AP747 for APJ was evaluated in vitro by autoradiography and in vivo by small animal PET/CT in both colon adenocarcinoma mouse model and Matrigel plug mouse model. Dynamic of [68Ga]Ga-AP747 PET/CT biodistributions was realized on healthy mice and pigs for two hours, and quantification of signal in organs showed a suitable pharmacokinetic profile for PET imaging, largely excreted by urinary route. Matrigel mice and hindlimb ischemic mice were submitted to a 21-day longitudinal follow-up with [68Ga]Ga-AP747 and [68Ga]Ga-RGD2 small animal PET/CT. [68Ga]Ga-AP747 PET signal in Matrigel was significantly more intense than that of [68Ga]Ga-RGD2. Revascularization of the ischemic hind limb was followed by LASER Doppler. In the hindlimb, [68Ga]Ga-AP747 PET signal was more than twice higher than that of [68Ga]Ga-RGD2 on day 7, and significantly superior over the 21-day follow-up. A significant, positive correlation was found between the [68Ga]Ga-AP747 PET signal on day 7 and late hindlimb perfusion on day 21. We developed a new PET radiotracer that specifically binds to APJ, [68Ga]Ga-AP747 that showed more efficient imaging properties than the most clinically advanced tracer of angiogenesis, [68Ga]Ga-RGD2.

Beyond starving cancer: anti-angiogenic therapy

Tumor blood vessels contribute to cancer progression by supplying nutrients and oxygen to the tumor, removing waste products, and providing a pathway to distant organs. Current angiogenesis inhibitors primarily target molecules in the vascular endothelial growth factor (VEGF) signaling pathway, inhibiting cancer growth and metastasis by preventing the formation of blood vessels that feed cancer. They also normalize vascular structural abnormalities caused by excess VEGF and improve reflux, resulting in increased drug delivery to cancer tissue and immune cell mobilization. As a result, by normalizing blood vessels, angiogenesis inhibitors have been shown to enhance the effects of chemotherapy and immunotherapy. We present findings on the characteristics of tumor vascular endothelial cells that angiogenesis inhibitors target.

Angiogenic inhibitor pre-administration improves the therapeutic effects of immunotherapy

In lung cancer, immune checkpoint inhibitors (ICIs) are often inadequate for tumor growth inhibition. Angiogenic inhibitors (AIs) are required to normalize tumor vasculature for improved immune cell infiltration. However, in clinical practice, ICIs and cytotoxic antineoplastic agents are simultaneously administered with an AI when tumor vessels are abnormal. Therefore, we examined the effects of pre-administering an AI for lung cancer immunotherapy in a mouse lung cancer model. Using DC101, an anti-vascular endothelial growth factor receptor 2 (VEGFR2) monoclonal antibody, a murine subcutaneous Lewis lung cancer (LLC) model was used to determine the timing of vascular normalization. Microvessel density (MVD), pericyte coverage, tissue hypoxia, and CD8-positive cell infiltration were analyzed. The effects of an ICI and paclitaxel after DC101 pre-administration were investigated. On Day 3, increased pericyte coverage and alleviated tumor hypoxia represented the highest vascular normalization. CD8+ T-cell infiltration was also highest on Day 3. When combined with an ICI, DC101 pre-administration significantly reduced PD-L1 expression. When combined with an ICI and paclitaxel, only DC101 pre-administration significantly inhibited tumor growth, but simultaneous administration did not. AI pre-administration, and not simultaneous administration, may increase the therapeutic effects of ICIs due to improved immune cell infiltration.

Cancer apelin receptor suppresses vascular mimicry in malignant melanoma

Several reports indicate that apelin is often over-expressed in tumors, and therefore it has been suggested that the apelin-apelin receptor (APJ) system may induce tumor progression. In contrast, our previous research revealed high expression of the apelin-APJ system in tumor blood vessels, suggesting its involvement in the regulation of tumor vessel formation and normalization, resulting in the suppression of tumor growth by promoting the infiltration of T cells. Thus, the effect of the apelin-APJ system on tumors remains controversial. In this report, to clarify the effect of apelin in tumor cells, we analyzed the function of APJ in tumor cells using APJ knock out (KO) mice. In APJ-KO mice, Apelin overexpression in B16/BL6 (B16) melanoma cells induced greater tumor growth than controls. In an APJ-KO melanoma inoculation model, although angiogenesis is suppressed compared to wild type, no difference is evident in tumor growth. We found that APJ deficiency promoted vascular mimicry in tumors. In vitro, cultured APJ-KO B16 cells demonstrated a spindle-like shape. This phenotypic change was thought to be induced by epithelial-mesenchymal transition (EMT) based on evidence that APJ-KO B16 cells show persistently high levels of the mesenchymal maker, Zeb1; however, we found that EMT did not correlate with the transforming growth factor-β/smad signaling pathway in our model. We propose that apelin-APJ system in cancer cells induces tumor growth but negatively regulates EMT and tumor malignancy.

Apelin promotes osteosarcoma metastasis by upregulating PLOD2 expression via the Hippo signaling pathway and hsa_circ_0000004/miR-1303 axis

Osteosarcoma is a highly mortal bone tumor, with a high metastatic potential, promoted in part by the enzyme procollagen-lysine 2-oxoglutarate 5-dioxygenase 2 (PLOD2). Increasing level of PLOD2 in osteosarcoma tissue correlates with lymphatic and distant metastasis. The adipokine apelin (APLN) is also found in different cancers and APLN upregulation promotes angiogenesis and metastasis, but its effects on osteosarcoma metastasis are uncertain. We explored APLN functioning in metastatic osteosarcoma. An analysis of records from the Gene Expression Omnibus (GEO) database showed higher levels of APLN expression in osteosarcoma tissue than in normal tissue. Similarly, levels of APLN and PLOD2 mRNA synthesis were upregulated in osteosarcoma tissue. Levels of APLN and PLOD2 protein correlated positively with osteosarcoma clinical stages. APLN increased PLOD2 expression in human osteosarcoma cell lines and cell migration via the mammalian Sterile 20-like kinase 1 (MST1), monopolar spindle-one-binder protein (MOB)1, and YAP cascades, and through hsa_circ_0000004 functioning as a sponge of miR-1303. We also found that knockdown of APLN antagonized lung metastasis in mice with osteosarcoma. APLN may be a therapeutic target in osteosarcoma metastasis.

The Apelin/APLNR system modulates tumor immune response by reshaping the tumor microenvironment

Apelin is an endogenous ligand of the Apelin receptor (APLNR), a seven-transmembrane G protein-coupled receptor, which is widely distributed in human tissue. The Apelin/APLNR system is involved in regulating several physiological and pathological processes. The Apelin expression is increased in a variety of cancer and the Apelin/APLNR system could regulate the development of tumors through mediating autophagy, apoptosis, pyroptosis, and other biological processes to regulate tumor cell proliferation, migration, and invasion. The Apelin/APLNR system also participates in immune response and immune regulation through PI3K-Akt, ERK-MAPK, and other signal pathways. The latest research points out that there is a negative regulatory relationship between APLNR and immune checkpoint PD-L1. In this review, we outline the significance of the Apelin/APLNR signaling pathway in tumorigenesis and its immune regulation. These endeavors provide new insights into the translational application of Apelin/APLNR in cancer and may contribute to the promotion of more effective treatments for cancers.

Apelin-driven endothelial cell migration sustains intestinal progenitor cells and tumor growth

Stem and progenitor cells residing in the intestinal crypts drive the majority of colorectal cancers (CRCs), yet vascular contribution to this niche remains largely unexplored. VEGFA is a key driver of physiological and tumor angiogenesis. Accordingly, current anti-angiogenic cancer therapies target the VEGFA pathway. Here we report that in CRC expansion of the stem/progenitor pool in intestinal crypts requires VEGFA-independent growth and remodeling of blood vessels. Epithelial transformation induced expression of the endothelial peptide apelin, directs migration of distant venous endothelial cells towards progenitor niche vessels ensuring optimal perfusion. In the absence of apelin, loss of injury-inducible PROX1+ epithelial progenitors inhibited both incipient and advanced intestinal tumor growth. Our results establish fundamental principles for the reciprocal communication between vasculature and the intestinal progenitor niche and provide a mechanism for resistance to VEGFA-targeting drugs in CRCs.

Value of Immunohistochemical Expression of Apelin, Succinate Dehydrogenase B, Chromogranin B, Human Epidermal Growth Factor Receptor-2, Contactin 4, and Succinyl-CoA Synthetase Subunit Beta in Differentiating Metastatic From Non-Metastatic Pheochromocytoma and Paraganglioma

OBJECTIVE

We aimed to retrospectively collect pathologically identified pheochromocytoma and paraganglioma (PPGL) tumor tissues from our center and investigate the expression of apelin and succinyl-CoA synthetase subunit beta (SUCLG2), human epidermal growth factor receptor-2 (HER2 or ERBB-2), contactin 4 (CNTN4), chromogranin B (CHGB), and succinate dehydrogenase B (SDHB) in metastatic and non-metastatic PPGLs, for exploring their roles in the diagnosis of metastatic PPGLs.

METHODS

A total of 369 patients with pathologically and surgically confirmed PPGLs at Xiangya Hospital, Central South University, between June 2010 and June 2020 were retrospectively included. Sixty patients-12 patients with metastatic PPGLs and 48 patients with non-metastatic PPGLs-were selected through propensity score matching (1:4) to reduce the effect of PPGL type, sex, and age. We observed and quantified the expression of apelin, SDHB, CHGB, ERBB-2, CNTN4, and SUCLG2 in paraffin-embedded samples using immunohistochemical staining.

RESULTS

No significant differences were observed between the metastatic group and non-metastatic group with respect to the expression of CNTN4 and SUCLG2. The expression of apelin, SDHB, CHGB, and ERBB-2 was significantly different between the two groups. The expression of apelin, SDHB, and CHGB was significantly lower in the metastatic group than that in the non-metastatic group (P < 0.001). ERBB-2 expression was significantly higher in the metastatic group than in the non-metastatic group (P = 0.042). Kaplan-Meier analysis revealed that patients with negative expression of apelin, SDHB, and CHGB showed significantly lower metastasis-free survival than those with positive expression. Multivariate Cox analysis revealed that SDHB and CHGB levels were independently associated with metastasis-free survival.

CONCLUSION

The expression levels of apelin, CHGB, SDHB, and ERBB-2 may be predictive biomarkers for the diagnosis of metastatic PPGLs. Patients with negative expression of apelin, CHGB, and SDHB should be subjected to frequent postoperative follow-up procedures.

APELIN IN HEART FAILURE

Apelin is a biologically active protein encoded by the APLN gene. It was first isolated in 1998 as a ligand for the APJ receptor. It exists in several isoforms differing in polypeptide chain length and biological activity. It is secreted by white adipose tissue, and its expression has been identified in many body tissues, including the cardiovascular system, kidneys, lungs, CNS (especially the hypothalamus, suprachiasmatic and ventricular nuclei), skeletal muscle, mammary glands, adrenal glands, ovaries, stomach, liver cells, placenta, and breast milk. However, the highest concentrations were observed in the endocardium and endothelium of vascular smooth muscle cells. In myocardial tissue, apelin has a positive inotropic effect and exerts an opposing effect to the RAA (renin-angiotensin-aldosterone) system, lowering blood pressure. Therefore, its positive role in early stages of heart failure, in patients with hypertension and ischemic heart disease is emphasized. The synthesis and secretion of apelin by adipocytes makes it possible to classify this peptide as an adipokine. Therefore, its production in adipose tissue is enhanced in obesity. Furthermore, apelin has been shown to increase cellular sensitivity to insulin and improve glucose tolerance in the onset of type 2 diabetes, and therefore appears to play a significant role in the pathogenesis of metabolic disease. An accurate assessment of the importance of apelin in cardiovascular disease requires further studies, which may contribute to the use of apelin in the treatment of heart failure.

A modular ROS-responsive platform co-delivered by 10-hydroxycamptothecin and dexamethasone for cancer treatment

Traditional and single treatment strategies are difficult to achieve good results due to tumor resistance and complex mechanisms. Combination therapy through co-delivery systems is one of the methods to improve the effectiveness of cancer treatment. The polyprodrug platform has inherent advantages such as high drug loading and strong stability. Herein, a new reactive oxygen species (ROS)-responsive micelle composed of poly 10-hydroxycamptothecin (pHCPT) and PEG is reported, which loaded dexamethasone (DEX) as synergistic drugs. The micelles collapse in the complex microenvironment of tumor cells to release DEX. The first released DEX can increase the ROS level of tumor cells, thereby facilitating the cleavage of thioketal bonds to release intact HCPT molecules. Meanwhile, DEX can normalize tumor blood vessels, reduce adverse reactions, and further improve the efficacy of HCPT. This co-delivery system shows an ideal tumor suppressive effect in vivo and in vitro. Designing drugs into a modular multi-drug platform and selecting appropriate synergistic drugs according to the treatment plan provides a convenient strategy for future clinical treatment.

Vascular Normalization: A New Window Opened for Cancer Therapies

Preclinical and clinical antiangiogenic approaches, with multiple side effects such as resistance, have not been proved to be very successful in treating tumor blood vessels which are important targets for tumor therapy. Meanwhile, restoring aberrant tumor blood vessels, known as tumor vascular normalization, has been shown not only capable of reducing tumor invasion and metastasis but also of enhancing the effectiveness of chemotherapy, radiation therapy, and immunotherapy. In addition to the introduction of such methods of promoting tumor vascular normalization such as maintaining the balance between proangiogenic and antiangiogenic factors and targeting endothelial cell metabolism, microRNAs, and the extracellular matrix, the latest molecular mechanisms and the potential connections between them were primarily explored. In particular, the immunotherapy-induced normalization of blood vessels further promotes infiltration of immune effector cells, which in turn improves immunotherapy, thus forming an enhanced loop. Thus, immunotherapy in combination with antiangiogenic agents is recommended. Finally, we introduce the imaging technologies and serum markers, which can be used to determine the window for tumor vascular normalization.

Vascular normalisation as the stepping stone into tumour microenvironment transformation

A functional vascular system is indispensable for drug delivery and fundamental for responsiveness of the tumour microenvironment to such medication. At the same time, the progression of a tumour is defined by the interactions of the cancer cells with their surrounding environment, including neovessels, and the vascular network continues to be the major route for the dissemination of tumour cells in cancer, facilitating metastasis. So how can this apparent conflict be reconciled? Vessel normalisation-in which redundant structures are pruned and the abnormal vasculature is stabilised and remodelled-is generally considered to be beneficial in the course of anti-cancer treatments. A causality between normalised vasculature and improved response to medication and treatment is observed. For this reason, it is important to discern the consequence of vessel normalisation on the tumour microenvironment and to modulate the vasculature advantageously. This article will highlight the challenges of controlled neovascular remodelling and outline how vascular normalisation can shape disease management.

Critical APJ receptor residues in extracellular domains that influence effector selectivity

Human APJ receptor/apelin receptor (APJR), activated by apelin peptide isoforms, regulates a wide range of physiological processes. The role of extracellular loop (ECL) domain residues of APJR in ligand binding and receptor activation has not been established yet. Based on multiple sequence alignment of APJ receptor from various organisms, we identified conserved residues in the extracellular domains. Alanine substitutions of specific residues were characterized to evaluate their ligand binding efficiency and G_q -, G_i -, and β-arrestin-mediated signaling. Mutation-dependent variation in ligand binding and signaling was observed. W¹⁹⁷ A in ECL2 and L²⁷⁶ L²⁷⁷ W²⁷⁹ -AAA in ECL3 were deficient in G_i and β-arrestin signaling pathways with relatively preserved G_q -mediated signaling. T¹⁶⁹ T¹⁷⁰ -AA, Y¹⁸² A, and T¹⁹⁰ A mutants in ECL2 showed impaired β-arrestin-dependent cell signaling while maintaining G protein_- mediated signaling. Structural comparison with angiotensin II type I receptor revealed the importance of ECL2 and ECL3 residues in APJR ligand binding and signaling. Our results unequivocally confirm the specific role of these ECL residues in ligand binding and in orchestrating receptor conformations that are involved in preferential/biased signaling functions.

Study Progression of Apelin/APJ Signaling and Apela in Different Types of Cancer

Apelin is an endogenous ligand that binds to the G protein-coupled receptor angiotensin-like-receptor 1 (APJ). Apelin and APJ are widely distributed in organs and tissues and are involved in multiple physiological and pathological processes including cardiovascular regulation, neuroendocrine stress response, energy metabolism, etc. Additionally, apelin/APJ axis was found to play an important role in cancer development and progression. Apela is a newly identified endogenous ligand for APJ. Several studies have revealed the potential role of Apela in cancers. In this article, we review the current studies focusing on the role of apelin/APJ signaling and Apela in different cancers. Potential mechanisms by which apelin/APJ and Apela mediate the regulation of cancer development and progression were also mentioned. The Apelin/APJ signaling and Apela may serve as potential therapeutic candidates for treatment of cancer.

Characterization and evaluation of the tissue distribution of CRH, apelin, and GnRH2 reveal responses to feeding states in Schizothorax davidi

Schizothorax davidi is a rare fish in Southwest China and is considered a promising species for aquaculture. Compared with other teleosts, little is known about the endocrine regulation of feeding in this species. In this study, we identified the CRH, apelin, and GnRH2 genes in S. davidi and assessed the effects of different energy statuses on CRH, apelin, and GnRH2 expression. Our results showed that the full-length cDNA sequences of CRH, apelin, and GnRH2 of S. davidi were 995, 905, and 669 bp long, respectively. Furthermore, CRH was mainly expressed in the hypothalamus, telencephalon, and myelencephalon; apelin was highly expressed in the spleen and heart; and GnRH2 mRNA was widely distributed in all examined tissues, with the highest level in the hypothalamus. Notably, the levels of CRH and GnRH2 increased in the hypothalamus at 1 h and 3 h post-feeding, while hypothalamic apelin levels decreased. Conversely, CRH and GnRH2 expression in the hypothalamus significantly decreased after fasting for 7 days and returned to the control levels after re-feeding for 3 or 5 days. In contrast, fasting increased apelin levels in the hypothalamus. Overall, this study suggests that CRH, apelin, and GnRH2 play critical roles in appetite regulation in S. davidi. These results provide an essential groundwork to elucidate the appetite regulatory systems in S. davidi as well as in other teleosts.

Efficacy of Combination Chemotherapy Using a Novel Oral Chemotherapeutic Agent, FTD/TPI, with Ramucirumab Murine Version DC101 in a Mouse Syngeneic Cancer Transplantation Model

Trifluridine/tipiracil (FTD/TPI) (a.k.a. TAS-102) is a combination drug for metastatic colorectal cancer (CRC) and severely pretreated metastatic gastric/gastroesophageal junction (GEJ) cancers, comprising FTD, a thymidine-based antineoplastic nucleoside analog, and TPI, which enhances FTD bioavailability. Herein, in KRAS mutant murine colorectal cancer CT26 syngeneic models, we investigate whether combination therapy with DC101 (a surrogate ramucirumab antibody, rat antimouse vascular endothelial growth factor receptor (VEGFR)-2 monoclonal antibody (mAb)) improves FTD/TPI efficacy. Tumor growth inhibition (TGI) on day 15 was 38.0% and 30.6% upon DC101 monotherapy and FTD/TPI monotherapy respectively, and 60.3% upon combination therapy. Tumor volume was significantly lower (p < 0.001) upon combination treatment than upon FTD/TPI or DC101 monotherapy, indicating the additive effects of FTD/TPI and DC101. DNA-incorporated FTD levels on Day 8 were significantly higher in combination therapy with FTD/TPI (for 5 consecutive days) and DC101 (on alternate days for 7days) than in FTD/TPI monotherapy. Furthermore, vascular endothelial cell-specific marker CD31 was downregulated in DC101-treated tumors on day 8. These results indicate that combination therapy with FTD/TPI and DC101 is a promising treatment alternative regardless of KRAS mutations.

An Overview of In Vitro, In Vivo, and Computational Techniques for Cancer-Associated Angiogenesis Studies

Angiogenesis is a crucial area in scientific research because it involves many important physiological and pathological processes. Indeed, angiogenesis is critical for normal physiological processes, including wound healing and embryonic development, as well as being a component of many disorders, such as rheumatoid arthritis, obesity, and diabetic retinopathies. Investigations of angiogenic mechanisms require assays that can activate the critical steps of angiogenesis as well as provide a tool for assessing the efficacy of therapeutic agents. Thus, angiogenesis assays are key tools for studying the mechanisms of angiogenesis and identifying the potential therapeutic strategies to modulate neovascularization. However, the regulation of angiogenesis is highly complex and not fully understood. Difficulties in assessing the regulators of angiogenic response have necessitated the development of an alternative approach. In this paper, we review the standard models for the study of tumor angiogenesis on the macroscopic scale that include in vitro, in vivo, and computational models. We also highlight the differences in several modeling approaches and describe key advances in understanding the computational models that contributed to the knowledge base of the field.

Exercise-Induced Myokines can Explain the Importance of Physical Activity in the Elderly: An Overview

Physical activity has been found to aid the maintenance of health in the elderly. Exercise-induced skeletal muscle contractions lead to the production and secretion of many small proteins and proteoglycan peptides called myokines. Thus, studies on myokines are necessary for ensuring the maintenance of skeletal muscle health in the elderly. This review summarizes 13 myokines regulated by physical activity that are affected by aging and aims to understand their potential roles in metabolic diseases. We categorized myokines into two groups based on regulation by aerobic and anaerobic exercise. With aging, the secretion of apelin, β-aminoisobutyric acid (BAIBA), bone morphogenetic protein 7 (BMP-7), decorin, insulin-like growth factor 1 (IGF-1), interleukin-15 (IL-15), irisin, stromal cell-derived factor 1 (SDF-1), sestrin, secreted protein acidic rich in cysteine (SPARC), and vascular endothelial growth factor A (VEGF-A) decreased, while that of IL-6 and myostatin increased. Aerobic exercise upregulates apelin, BAIBA, IL-15, IL-6, irisin, SDF-1, sestrin, SPARC, and VEGF-A expression, while anaerobic exercise upregulates BMP-7, decorin, IGF-1, IL-15, IL-6, irisin, and VEGF-A expression. Myostatin is downregulated by both aerobic and anaerobic exercise. This review provides a rationale for developing exercise programs or interventions that maintain a balance between aerobic and anaerobic exercise in the elderly.

Effects of Jinlongshe granules on gastric precancerous lesions in rats and its mechanism

OBJECTIVE

To investigate the anti-gastric precancerous lesions effect and mechanism of Traditional Chinese Medicine Jinlongshe (JLS) granules in ethanol extractive of A. manshuriensis (EEA)-induced gastric precancerous lesions rats.

METHODS

A rat model with the part typical proliferation of the gastric epithelium mucosa was established by EEA. These rats received different doses of JLS granules treatment for four weeks. Bodyweight, histological and ultrastructural changes of gastric precancerous lesions were evaluated. The expression of Apelin and CD34 mRNA and proteins of the gastric tissue were analyzed by quantitative Realtime PCR, western blot and immunohistochemical staining.

RESULTS

We found that the treatment of JLS granules prevented the bodyweight loss and improved behavioral abnormalities of rats that received EEA. The histological and ultrastructural analysis also showed that JLS granules ameliorated EEA induced gastric precancerous lesions in a dose-dependent manner. The expression levels of two critical proteins involved in the angiogenesis of gastric carcinoma, Apelin, and CD34, were significantly reduced by the treatment of JLS granules.

CONCLUSION

Our results indicated that JLS could inhibit the expression of the Apelin and CD34 genes in rat gastric mucosa, which reversed gastric precancerous lesions.

Integrated Analysis of miRNA-mRNA Network Reveals Different Regulatory Patterns in the Endometrium of Meishan and Duroc Sows during Mid-Late Gestation

Simple Summary

Meishan pigs have a lower fetal loss rate during mid-late gestation compared to Duroc pigs. Differentially expressed mRNAs and miRNAs detected in endometrial tissue from Meishan and Duroc sows at mid-late gestation are involved in regulating hormone and oxygen levels, blood vessel development, and developmental processes affecting reproduction. In addition, ssc-miR-503 and ssc-miR-671-5p were shown to target the EGF and ESR1 genes, respectively. These findings provided an important resource for studying embryonic mortality during mid-late gestation in pigs.

Abstract

Embryo loss is a major factor affecting profitability in the pig industry. Embryonic mortality occurs during peri-implantation and mid-late gestation in pigs. Previous investigations have shown that the embryo loss rate in Meishan pigs is significantly lower than in commercial breeds. Most studies have focused on embryonic mortality during early gestation, but little is known about losses during mid-late gestation. In this study, we performed a transcriptome analysis of endometrial tissue in mid-late gestation sows (gestation days 49 and 72) sampled from two breeds (Meishan (MS) and Duroc (DU)) that have different embryo loss rates. We identified 411, 1113, 697, and 327 differentially expressed genes, and 14, 36, 57, and 43 differentially expressed miRNAs in four comparisons (DU49 vs. DU72, DU49 vs. MS49, DU72 vs. MS72, and MS49 vs. MS72), respectively. Subsequently; seven differentially expressed mRNAs and miRNAs were validated using qPCR. Functional analysis suggested the differentially expressed genes and miRNAs target genes mainly involved in regulation of hormone levels, blood vessel development, developmental process involved in reproduction, embryonic placenta development, and the immune system. A network analysis of potential miRNA-gene interactions revealed that differentially expressed miRNAs in Meishan pigs are involved in the response to estradiol and oxygen levels, and affect angiogenesis and blood vessel development. The binding site on ssc-miR-503 for epidermal growth factor (EGF) and the binding site on ssc-miR-671-5p for estrogen receptor α (ESR1) were identified using a dual luciferase assay. The results of this study will enable further exploration of miRNA-mRNA interactions important in pig pregnancy and will help to uncover molecular mechanisms affecting embryonic mortality in pigs during mid-late gestation.

Bevacizumab has bidirectional regulatory effects on the secretion of basic fibroblast growth factor in glioma cells

Previous studies suggest that upregulated basic fibroblast growth factor (bFGF) plays a key role in the resistance to anti-vascular endothelial growth factor (VEGF) therapy in glioma. This study reported that anti-VEGF treatment regulated bFGF secretion in a double-edged manner. That is, moderate VEGF neutralization reduced bFGF production, whereas VEGF overblocking enhanced bFGF secretion in glioma cells. Our data provide a new perspective on the treatment of glioma with anti-VEGF, and the underlying mechanism is worthy of further study.

Chronic treatment with apelin, losartan and their combination reduces myocardial infarct size and improves cardiac mechanical function

The renin-angiotensin system (RAS) has a deleterious and apelin/APJ system has protective effect on the ischaemic heart. The collaboration between these systems in the pathophysiology of myocardial infarction is not clear. We determined the effect of chronic pretreatment with apelin, losartan and their combination on ischaemia-reperfusion (IR) injury in the isolated perfused rat heart and on the expression of apelin-13 receptor (APJ) and angiotensin type 1 receptor (AT1R) in the myocardium. During 5 days before the induction of IR, saline (vehicle), apelin-13 (Apl), F13A (apelin antagonist), losartan (Los, AT1R antagonist) and the combination of Apl and Los were administered intraperitoneally in rats. Ischaemia was induced by left anterior descending (LAD) artery occlusion for 30 minutes followed by reperfusion for 55 minutes in the Langendorff isolated heart perfusion system. Pretreatment with Apl, Los and the combination of Apl + Los significantly reduced infarct size by about 30, 33 and 48 percent respectively; and significantly improved the left ventricular function indices such as left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP) and rate pressure product (RPP). IR increased AT1R protein level but it did not change APJ significantly. AT1R expression was reduced in groups treated with Apl, Los and Apl + Los. Findings showed that chronic pretreatment with apelin along with AT1R antagonist had more protective effects against IR injury. Combination therapy may diminish the risk of IR-induced heart damage, by reducing AT1R expression, in the heart of patients with coronary artery disease that are at the risk of MI and reperfusion injury.

International Union of Basic and Clinical Pharmacology. CVII. Structure and Pharmacology of the Apelin Receptor with a Recommendation that Elabela/Toddler Is a Second Endogenous Peptide Ligand

The predicted protein encoded by the APJ gene discovered in 1993 was originally classified as a class A G protein-coupled orphan receptor but was subsequently paired with a novel peptide ligand, apelin-36 in 1998. Substantial research identified a family of shorter peptides activating the apelin receptor, including apelin-17, apelin-13, and [Pyr1]apelin-13, with the latter peptide predominating in human plasma and cardiovascular system. A range of pharmacological tools have been developed, including radiolabeled ligands, analogs with improved plasma stability, peptides, and small molecules including biased agonists and antagonists, leading to the recommendation that the APJ gene be renamed APLNR and encode the apelin receptor protein. Recently, a second endogenous ligand has been identified and called Elabela/Toddler, a 54-amino acid peptide originally identified in the genomes of fish and humans but misclassified as noncoding. This precursor is also able to be cleaved to shorter sequences (32, 21, and 11 amino acids), and all are able to activate the apelin receptor and are blocked by apelin receptor antagonists. This review summarizes the pharmacology of these ligands and the apelin receptor, highlights the emerging physiologic and pathophysiological roles in a number of diseases, and recommends that Elabela/Toddler is a second endogenous peptide ligand of the apelin receptor protein.

The association between apelin polymorphisms and hypertension in China: A meta-analysis

INTRODUCTION:

Apelin plays an important part in regulating blood pressure, metabolism, and the development of cancer. Recent studies have investigated the association of apelin polymorphisms and hypertension risk, but no meta-analysis has been conducted.

MATERIALS AND METHODS:

Five studies were included in this meta-analysis in total. The pooled odds ratio and its corresponding 95% confidence interval were calculated by the random-effect model.

RESULTS:

The overall pooled odds ratio of the distribution of rs3761581 G allelic frequency was 0.90 (95% confidence interval: 0.82-1.00). In female participants, the pooled odds ratio of the frequency of G allele was 1.01 (95% confidence interval: 0.89-1.14). For males, the pooled odds ratio of the frequency of G allele was 0.69 (95% confidence interval: 0.46-1.03). As for rs56204867, the overall pooled odds ratio of the frequency of G allele was 1.09 (95% confidence interval: 0.86-1.37). In females, the pooled odds ratio of the frequencies of the G allele was 1.05 (95% confidence interval: 0.86-1.29). In male participants, the frequency of G allele did not show significant correlation with hypertension (pooled odds ratio=1.21 95% confidence interval: 0.81-1.79).

CONCLUSION:

This meta-analysis revealed that there was no correlation between apelin polymorphisms, rs3761581 and rs56204867, and the prevalence of hypertension.

Apatinib, a selective VEGFR2 inhibitor, improves the delivery of chemotherapeutic agents to tumors by normalizing tumor vessels in LoVo colon cancer xenograft mice

Tumor vascular normalization has been proposed as a therapeutic strategy for malignant neoplasms, which can also interpret the synergistic effect of anti-angiogenesis agents combined with chemotherapy. Apatinib (Apa), a highly selective VEGFR2 inhibitor, attracts much attentions due to its encouraging anticancer activity, especially in the clinical trials of combined treatment. In this study, we investigated whether Apa could promote vascular normalization in tumor in a certain time window. Mice bearing LoVo colon cancer xenograft were orally administrated Apa (150 mg kg^-1 per day) for 5, 7, 10, or 12 days. Apa significantly inhibited tumor growth and decreased the microvessel density. Using multi-photon microscopy and electron microscopy, we found that Apa improved tumor vessel morphology by pruning distorted vessel branches and decreased the gap between endothelial cells after a 7-day treatment. Furthermore, Apa decreased vessel leakage and increased pericyte coverage on vascular endothelial cells, suggesting that tumor vessels were more mature and integrated. The intratumoral distribution of adriamycin (ADR) in Apa group was improved from day 7 to 10 without change in plasma drug concentration. Tumor blood perfusion was also increased in this window, and the expression of hypoxia induced factor 1α was downregulated, suggesting the effect of Apa on alleviating tumor hypoxic micro-environment. In conclusion, Apa may improve the effective perfusion of tumor vessels and increase the intratumoral distribution of ADR in a certain time window via normalizing tumor vessels. This normalization window (7 to 10 days of treatment) may contribute to develop a regimen of combined medication in clinic use of Apa.

Multifunctional APJ Pathway Promotes Ovarian Cancer Progression and Metastasis

High mortality rates in ovarian cancer are due to late-stage diagnosis when extensive metastases are present, coupled with the eventual development of resistance to standard chemotherapy. There is, thus, an urgent need to identify targetable pathways to curtail this deadly disease. In this study, we show that the apelin receptor, APJ, is a viable target that promotes tumor progression of high-grade serous ovarian cancer (HGSOC). APJ is specifically overexpressed in tumor tissue, and is elevated in metastatic tissues compared with primary tumors. Importantly, increased APJ expression significantly correlates with decreased median overall survival (OS) by 14.7 months in patients with HGSOC. Using various ovarian cancer model systems, we demonstrate that APJ expression in cancer cells is both necessary and sufficient to increase prometastatic phenotypes in vitro, including proliferation, cell adhesion to various molecules of the extracellular matrix (ECM), anoikis resistance, migration, and invasion; and these phenotypes are efficiently inhibited by the APJ inhibitor, ML221. Overexpression of APJ also increases metastasis of ovarian cancer cells in vivo. Mechanistically, the prometastatic STAT3 pathway is activated downstream of APJ, and in addition to the ERK and AKT pathways, contributes to its aggressive phenotypes. Our findings suggest that the APJ pathway is a novel and viable target, with potential to curb ovarian cancer progression and metastasis. IMPLICATIONS: The APJ pathway is a viable target in HGSOC.

Targeting APLN/APLNR Improves Antiangiogenic Efficiency and Blunts Proinvasive Side Effects of VEGFA/VEGFR2 Blockade in Glioblastoma

Antiangiogenic therapy of glioblastoma (GBM) with bevacizumab, a VEGFA-blocking antibody, may accelerate tumor cell invasion and induce alternative angiogenic pathways. Here we investigate the roles of the proangiogenic apelin receptor APLNR and its cognate ligand apelin in VEGFA/VEGFR2 antiangiogenic therapy against distinct subtypes of GBM. In proneural GBM, apelin levels were downregulated by VEGFA or VEGFR2 blockade. A central role for apelin/APLNR in controlling GBM vascularization was corroborated in a serial implantation model of the angiogenic switch that occurs in human GBM. Apelin and APLNR are broadly expressed in human GBM, and knockdown or knockout of APLN in orthotopic models of proneural or classical GBM subtypes significantly reduced GBM vascularization compared with controls. However, reduction in apelin expression led to accelerated GBM cell invasion. Analysis of stereotactic GBM biopsies from patients as well as from in vitro and in vivo experiments revealed increased dissemination of APLNR-positive tumor cells when apelin levels were reduced. Application of apelin-F13A, a mutant APLNR ligand, blocked tumor angiogenesis and GBM cell invasion. Furthermore, cotargeting VEGFR2 and APLNR synergistically improved survival of mice bearing proneural GBM. In summary, we show that apelin/APLNR signaling controls GBM angiogenesis and invasion and that both pathologic features are blunted by apelin-F13A. We suggest that apelin-F13A can improve the efficiency and reduce the side effects of established antiangiogenic treatments for distinct GBM subtypes. SIGNIFICANCE: Pharmacologic targeting of the APLNR acts synergistically with established antiangiogenic treatments in glioblastoma and blunts therapy resistance to current strategies for antiangiogenesis.See related commentary by Amoozgar et al., p. 2104.

Monitoring of tumor vascular normalization: the key points from basic research to clinical application

Tumor vascular normalization alleviates hypoxia in the tumor microenvironment, reduces the degree of malignancy, and increases the efficacy of traditional therapy. However, the time window for vascular normalization is narrow; therefore, how to determine the initial and final points of the time window accurately is a key factor in combination therapy. At present, the gold standard for detecting the normalization of tumor blood vessels is histological staining, including tumor perfusion, microvessel density (MVD), vascular morphology, and permeability. However, this detection method is almost unrepeatable in the same individual and does not dynamically monitor the trend of the time window; therefore, finding a relatively simple and specific monitoring index has important clinical significance. Imaging has long been used to assess changes in tumor blood vessels and tumor changes caused by the oxygen environment in clinical practice; some preclinical and clinical research studies demonstrate the feasibility to assess vascular changes, and some new methods were in preclinical research. In this review, we update the most recent insights of evaluating tumor vascular normalization.

The Role of Apelin in Cardiovascular Diseases, Obesity and Cancer

Apelin is an endogenous peptide identified as a ligand of the G protein-coupled receptor APJ. Apelin belongs to the family of adipokines, which are bioactive mediators released by adipose tissue. Extensive tissue distribution of apelin and its receptor suggests, that it could be involved in many physiological processes including regulation of blood pressure, body fluid homeostasis, endocrine stress response, cardiac contractility, angiogenesis, and energy metabolism. Additionally, this peptide participates in pathological processes, such as heart failure, obesity, diabetes, and cancer. In this article, we review current knowledge about the role of apelin in organ and tissue pathologies. We also summarize the mechanisms by which apelin and its receptor mediate the regulation of physiological and pathological processes. Moreover, we put forward an indication of apelin as a biomarker predicting cardiac diseases and various types of cancer. A better understanding of the function of apelin and its receptor in pathologies might lead to the development of new medical compounds.

Contribution of Tumor Endothelial Cells in Cancer Progression

Tumor progression depends on the process of angiogenesis, which is the formation of new blood vessels. These newly formed blood vessels supply oxygen and nutrients to the tumor, supporting its progression and providing a gateway for tumor metastasis. Tumor angiogenesis is regulated by the balance between angiogenic activators and inhibitors within the tumor microenvironment. Because the newly formed tumor blood vessels originate from preexisting normal vessels, tumor blood vessels, and tumor endothelial cells (TECs) have historically been considered to be the same as normal blood vessels and endothelial cells; however, evidence of TECs’ distinctive abnormal phenotypes has increased. In addition, it has been revealed that TECs constitute a heterogeneous population. Thus, TECs that line tumor blood vessels are important targets in cancer therapy. We have previously reported that TECs induce cancer metastasis. In this review, we describe recent studies on TEC abnormalities related to cancer progression to provide insight into new anticancer therapies.

Apelin: A putative novel predictive biomarker for bevacizumab response in colorectal cancer

Bevacizumab (bvz) is currently employed as an anti-angiogenic therapy across several cancer indications. Bvz response heterogeneity has been well documented, with only 10-15% of colorectal cancer (CRC) patients benefitting in general. For other patients, clinical efficacy is limited and side effects are significant. This reinforces the need for a robust predictive biomarker of response. To identify such a biomarker, we performed a DNA microarray-based transcriptional profiling screen with primary endothelial cells (ECs) isolated from normal and tumour colon tissues. Thirteen separate populations of tumour-associated ECs and 10 of normal ECs were isolated using fluorescence-activated cell sorting. We hypothesised that VEGF-induced genes were overexpressed in tumour ECs; these genes could relate to bvz response and serve as potential predictive biomarkers. Transcriptional profiling revealed a total of 2,610 differentially expressed genes when tumour and normal ECs were compared. To explore their relation to bvz response, the mRNA expression levels of top-ranked genes were examined using quantitative PCR in 30 independent tumour tissues from CRC patients that received bvz in the adjuvant setting. These analyses revealed that the expression of MMP12 and APLN mRNA was significantly higher in bvz non-responders compared to responders. At the protein level, high APLN expression was correlated with poor progression-free survival in bvz-treated patients. Thus, high APLN expression may represent a novel predictive biomarker for bvz unresponsiveness.

MR imaging biomarkers evaluating vascular normalization window after anti-vessel treatment

The beginning and the end of the vascular normalization window are not clear in response to anti-angiogenic therapies. We used dynamic contrast-enhanced MRI (DCE-MRI) and intravoxel incoherent motion MRI (IVIM-MRI) to noninvasively evaluate the vascular normalization window. MRI was performed five times: before treatment and on the second, fourth, sixth and eighth days of treatment. Quantitative perfusion parameters were calculated at each time point, including the volume transfer coefficient (Ktrans), reverse transfer constant (Kep), pseudodiffusion coefficient (D^*) and perfusion fraction (f). Tumors were evaluated for changes by immunohistochemistry. An increase in Ktrans and Kep was observed after bevacizumab treatment on days 2 and 4. Similar trends were observed for D^* and f on days 2 and 4. However, the parameters of Ktrans, Kep, D^* and f were decreased on days 6 and 8. A significant increase of the vessel maturity index between the treatment and control groups was measured on days 2 and 4, but this increase abated by days 6 and 8. IVIM and DCE-MRI are helpful when quantifying the tumor perfusion and evaluating the vascular normalization window after anti-vessel therapy. IVIM and DCE-MRI can outline the important period after anti-vessel treatment.

Pharmacological targeting of apelin impairs glioblastoma growth

Glioblastoma are highly aggressive brain tumours that are associated with an extremely poor prognosis. Within these tumours exists a subpopulation of highly plastic self-renewing cancer cells that retain the ability to expand ex vivo as tumourspheres, induce tumour growth in mice, and have been implicated in radio- and chemo-resistance. Although their identity and fate are regulated by external cues emanating from endothelial cells, the nature of such signals remains unknown. Here, we used a mass spectrometry proteomic approach to characterize the factors released by brain endothelial cells. We report the identification of the vasoactive peptide apelin as a central regulator for endothelial-mediated maintenance of glioblastoma patient-derived cells with stem-like properties. Genetic and pharmacological targeting of apelin cognate receptor abrogates apelin- and endothelial-mediated expansion of glioblastoma patient-derived cells with stem-like properties in vitro and suppresses tumour growth in vivo. Functionally, selective competitive antagonists of apelin receptor were shown to be safe and effective in reducing tumour expansion and lengthening the survival of intracranially xenografted mice. Therefore, the apelin/apelin receptor signalling nexus may operate as a paracrine signal that sustains tumour cell expansion and progression, suggesting that apelin is a druggable factor in glioblastoma.

Apelin (APLN) regulates progesterone secretion and oocyte maturation in bovine ovarian cells

APLN and its G-protein coupled receptor APLNR are expressed in the bovine ovary. However their role in granulosa cells and oocytes is unknown. Here, we studied their expression in bovine ovarian cells and investigated their regulation in cultured luteinizing granulosa cells in response to IGF1 and FSH. We determined the effect and the molecular mechanism of APLN (isoforms 17 and 13) on bovine granulosa cell progesterone secretion and on oocyte maturation. By RT-qPCR and immunoblot, we showed that the expression of both APLN and APLNR in granulosa and oocytes significantly increased with ovarian follicles size whereas it was similar in theca interstitial cells. In vitro, in unstimulated luteinizing bovine granulosa cells and in response to IGF1 (10^-8 M) but not to FSH (10^-8 M), we observed that APLN (-17 and -13) (10^-9 M) increased progesterone production; this was abolished in response to the APLNR antagonist ML221. These latter effects were dependent on the MAPK ERK1/2 kinase. Furthermore, we showed that APLN (-17 and -13) (10^-9 M) increased cell proliferation through AKT signaling. Conversely, the addition of APLN-13 and APLN-17 to in vitro maturation medium containing IGF1 (10^-8 M) but not FSH (10^-8 M) arrested most oocytes at the germinal vesicle stage, which was associated with a decrease in progesterone secretion, an inhibition in MAPK ERK1/2 phosphorylation and an increase in PRKA phosphorylation in oocytes. Thus, APLN can increase progesterone secretion and cell proliferation in bovine luteinizing granulosa cells in vitro, while it blocks meiotic progression at the germinal vesicle stage during bovine oocyte in vitro maturation.

Tumor apelin, not serum apelin, is associated with the clinical features and prognosis of gastric cancer

BACKGROUND

To study the association between Apelin expression and the clinical features and postoperative prognosis in patients with gastric cancer (Int J Cancer 136:2388-2401, 2015).

METHODS

Tumor samples and matched adjacent normal tissues were collected from 270 patients with GC receiving surgical resection. The tumor and serum Apelin levels were determined by immunohistochemistry and ELISA methods, respectively. GC cell lines were cultured for migration and invasive assays.

RESULTS

Our data showed that tumor Apelin expression status, instead of serum Apelin level, was closely associated with more advance clinical features including tumor differentiation, lymph node and distant metastases. Moreover, patients with high tumor Apelin level had a significantly shorter overall survival period compared to those with low Apelin expression and those with or negative Apelin staining. Our in vitro study revealed that the Apelin regulated the migration and invasion abilities of GC cell lines, accompanied by up-regulations of a variety of cytokines associated with tumor invasiveness.

CONCLUSION

Our data suggest that tumor Apelin can be used as a marker to evaluate clinical characteristics and predict prognosis in GC patients.

Antiangiogenic cancer treatment: The great discovery and greater complexity (Review)

The discovery of tumor angiogenesis opened a new path in fighting cancer. The approval of different antiangiogenic agents, most targeting vascular endothelial growth factor (VEGF) signaling, has either increased the effectiveness of standard chemotherapy or even replaced it by offering better patient outcomes. However, an increasing number of preclinical and clinical observations have shown that the process of angiogenesis is far from clearly understood. Apart from targeting the VEGF pathway, novel strategies aim to influence other molecular factors that are involved in tumor angiogenesis. In addition, naturally occurring compounds seem to offer additional agents for influencing angiogenesis. The first concept of antiangiogenic therapy aimed to destroy tumor vessels, while it turned out that, paradoxically, antiangiogenic drugs normalized vasculature and as a result offered an improvement in chemotherapeutic delivery. In order to design an effective treatment schedule, methods for detecting the time window of normalization and biomarkers predicting patient response are needed. The initial idea that antiangiogenic therapy would be resistance-free failed to materialize and currently we still face the obstacle of resistance to antiangiogenic therapy.

Apelin/APJ system and cancer

Apelin is an endogenous ligand of the apelin receptor (APJ), a seven-transmembrane G protein-coupled receptor. Apelin/APJ system has a wide tissue distribution in the brain as well as in peripheral organs including heart, lung, vessels, and adipose tissue. Apelin/APJ was involved in regulating cardiac and vascular function, heart development, and vascular smooth muscle cell proliferation. In this article, we summarize the role of apelin/APJ system on lung cancer, gastroesophageal and colonic cancer, hepatocellular carcinoma, prostate cancer, endometrial cancer, oral squamous cell carcinoma, brain cancer, and tumor neoangiogenesis. Apelin/APJ may be a potential anticancer therapeutic target.

Tumor angiogenesis--characteristics of tumor endothelial cells. Int J Clin Oncol. 2016;21:206-212. [PMID: 26879652 DOI: 10.1007/s10147-016-0957-1]

Tumor blood vessels provide nutrition and oxygen to the tumor, resulting in tumor progression. They also act as gatekeepers, inducing tumor metastasis. Thus, targeting tumor blood vessels is an important strategy in cancer therapy. Tumor endothelial cells (TECs), which line the inner layer of blood vessels of the tumor stromal tissue, are the main targets of anti-angiogenic therapy. Because new tumor blood vessels generally sprout from pre-existing vasculature, they have been considered to be the same as normal blood vessels. However, tumor blood vessels demonstrate a markedly abnormal phenotype that includes several important morphological changes. The degree of angiogenesis is determined by the balance between the angiogenic stimulators and inhibitors released by the tumor and host cells. Recent studies have revealed that TECs also exhibit altered characteristics which depend on the tumor microenvironment. Here, we review recent studies on TEC abnormalities and heterogeneity with respect to tumor progression and consider their therapeutic implications.

Apelin as a marker for monitoring the tumor vessel normalization window during antiangiogenic therapy

Antiangiogenic agents transiently normalize tumor vessel structure and improve vessel function, thereby providing a window of opportunity for enhancing the efficacy of chemotherapy or radiotherapy. Currently, there are no reliable predictors or markers reflecting this vessel normalization window during antiangiogenic therapy. Apelin, the expression of which is regulated by hypoxia, and which has well‐described roles in tumor progression, is an easily measured secreted protein. Here, we show that apelin can be used as a marker for the vessel normalization window during antiangiogenic therapy. Mice bearing s.c. tumors resulting from inoculation of the colon adenocarcinoma cell line HT29 were treated with a single injection of bevacizumab, a mAb neutralizing vascular endothelial growth factor. Tumor growth, vessel density, pericyte coverage, tumor hypoxia, and small molecule delivery were determined at four different times after treatment with bevacizumab (days 1, 3, 5, and 8). Tumor growth and vessel density were significantly reduced after bevacizumab treatment, which also significantly increased tumor vessel maturity, and improved tumor hypoxia and small molecule delivery between days 3 and 5. These effects abated by day 8, suggesting that a time window for vessel normalization was opened between days 3 and 5 during bevacizumab treatment in this model. Apelin mRNA expression and plasma apelin levels decreased transiently at day 5 post‐treatment, coinciding with vessel normalization. Thus, apelin is a potential indicator of the vessel normalization window during antiangiogenic therapy.