Combination therapy with short interfering RNA vectors against VEGF-C and VEGF-A suppresses lymph node and lung metastasis in a mouse immunocompetent mammary cancer model

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

Lymphatic vessels in cancer

The lymphatic system, composed of initial and collecting lymphatic vessels as well as lymph nodes that are present in almost every tissue of the human body, acts as an essential transport system for fluids, biomolecules and cells between peripheral tissues and the central circulation. Consequently, it is required for normal body physiology but is also involved in the pathogenesis of various diseases, most notably cancer. The important role of tumor-associated lymphatic vessels and lymphangiogenesis in the formation of lymph node metastasis has been elucidated during the last two decades, whereas the underlying mechanisms and the relation between lymphatic and peripheral organ dissemination of cancer cells are incompletely understood. Lymphatic vessels are also important for tumor-host communication, relaying molecular information from a primary or metastatic tumor to regional lymph nodes and the circulatory system. Beyond antigen transport, lymphatic endothelial cells, particularly those residing in lymph node sinuses, have recently been recognized as direct regulators of tumor immunity and immunotherapy responsiveness, presenting tumor antigens and expressing several immune-modulatory signals including PD-L1. In this review, we summarize recent discoveries in this rapidly evolving field and highlight strategies and challenges of therapeutic targeting of lymphatic vessels or specific lymphatic functions in cancer patients.

Role of Transcriptional and Epigenetic Regulation in Lymphatic Endothelial Cell Development

The lymphatic system is critical for maintaining the homeostasis of lipids and interstitial fluid and regulating the immune cell development and functions. Developmental anomaly-induced lymphatic dysfunction is associated with various pathological conditions, including lymphedema, inflammation, and cancer. Most lymphatic endothelial cells (LECs) are derived from a subset of endothelial cells in the cardinal vein. However, recent studies have reported that the developmental origin of LECs is heterogeneous. Multiple regulatory mechanisms, including those mediated by signaling pathways, transcription factors, and epigenetic pathways, are involved in lymphatic development and functions. Recent studies have demonstrated that the epigenetic regulation of transcription is critical for embryonic LEC development and functions. In addition to the chromatin structures, epigenetic modifications may modulate transcriptional signatures during the development or differentiation of LECs. Therefore, the understanding of the epigenetic mechanisms involved in the development and function of the lymphatic system can aid in the management of various congenital or acquired lymphatic disorders. Future studies must determine the role of other epigenetic factors and changes in mammalian lymphatic development and function. Here, the recent findings on key factors involved in the development of the lymphatic system and their epigenetic regulation, LEC origins from different organs, and lymphatic diseases are reviewed.

Lymphatic Vasculature: An Emerging Therapeutic Target and Drug Delivery Route

The lymphatic system has received increasing scientific and clinical attention because a wide variety of diseases are linked to lymphatic pathologies and because the lymphatic system serves as an ideal conduit for drug delivery. Lymphatic vessels exert heterogeneous roles in different organs and vascular beds, and consequently, their dysfunction leads to distinct organ-specific outcomes. Although studies in animal model systems have led to the identification of crucial lymphatic genes with potential therapeutic benefit, effective lymphatic-targeted therapeutics are currently lacking for human lymphatic pathological conditions. Here, we focus on the therapeutic roles of lymphatic vessels in diseases and summarize the promising therapeutic targets for modulating lymphangiogenesis or lymphatic function in preclinical or clinical settings. We also discuss considerations for drug delivery or targeting of lymphatic vessels for treatment of lymphatic-related diseases. The lymphatic vasculature is rapidly emerging as a critical system for targeted modulation of its function and as a vehicle for innovative drug delivery.

Soluble Vegfr3 gene therapy suppresses multi-organ metastasis in a mouse mammary cancer model

Accumulating evidence on the association of VEGF-C with lymphangiogenesis and lymph node metastasis implicates lymphatic vessels as a potential target in anti-cancer therapy. To evaluate whether blocking VEGF-C and VEGFR-3 signaling can inhibit multi-organ metastases, a mouse metastatic mammary cancer model was subjected to gene therapy using a soluble VEGFR-3 expression vector (psVEGFR-3). We showed that psVEGFR-3 significantly diminished cell growth in vitro with or without added VEGF-C, and significantly reduced primary tumor growth and tumor metastases to wide-spectrum organs in vivo. Although apoptotic cell death and angiogenesis levels did not differ between the control and psVEGFR-3 groups, cell proliferation and lymphangiogenesis in the mammary tumors were significantly decreased in the psVEGFR-3 group. Furthermore, lymphatic vessel invasion was significantly inhibited in this group. Real-time RT-PCR analysis revealed significantly high expression of the Vegfr3 gene due to gene therapy, and the transcriptional levels of Pcna and Lyve1 tended to decrease in the psVEGFR-3 group. Immunofluorescence staining indicated that phospho-tyrosine expression was considerably lower in tumor cells of psVEGFR-3-treated mammary carcinomas than those of control tumors. Double immunofluorescence staining indicated that phospho-tyrosine⁺ /LYVE-1⁺ (a lymphatic vessel marker) tended to decrease in psVEGFR-3-treated mammary carcinomas compared with control mice, indicating a decline in the activity of the VEGF-C/VEGFR-3 axis. These findings showed that a blockade of VEGF-C/VEGFR-3 signaling caused by sVEGFR-3 sequestered VEGF-C and prevented the side-effects of anti-angiogenesis and suppressed overall metastases, suggesting their high clinical significance.

Plk1 promotes the migration of human lung adenocarcinoma epithelial cells via STAT3 signaling

Polo-like kinase (Plk)1 contributes to the development of human cancer via multiple mechanisms, such as promoting the migration of cancer cells. However, the mechanistic basis for the regulation of cell migration by Plk1 remains unknown. To address this question, the present study investigated the effect of Plk1 inhibition on the migration of human lung adenocarcinoma epithelial A549 cells and the molecular factors involved. A549 cells were treated with the Plk1 inhibitor, BI2536, and cell migration was evaluated with the wound-healing assay. The expression of matrix metallopeptidase (MMP)2, vascular endothelial growth factor (VEGF)A, total and phosphorylated signal transducer and activator of transcription (STAT)3 was assessed by western blotting and reverse transcription-polymerase chain reaction following Plk1 knockdown and/or STAT3 overexpression. The interaction between Plk1 and STAT3 was evaluated by co-immunoprecipitation. The levels of MMP2 and VEGFA were decreased by treatment with Plk1 inhibitor. The phosphorylation of STAT3, which acts upstream of MMP2 and VEGFA, was also decreased by Plk1 knockdown, an effect that was abrogated by STAT3 overexpression. In addition, Plk1 was detected to bind with STAT3 either directly or as part of a complex by co-immunoprecipitation experiments. These results indicated that Plk1 may promote the migration of A549 cells via regulation of STAT3 signaling.

TGF-β1 secreted by Tregs in lymph nodes promotes breast cancer malignancy via up-regulation of IL-17RB

Lymph node (LN) metastasis is commonly associated with systemic distant organ metastasis in human breast cancer and is an important prognostic predictor for survival of breast cancer patients. However, whether tumor‐draining LNs (TDLNs) play a significant role in modulating the malignancy of cancer cells for distant metastasis remains controversial. Using a syngeneic mouse mammary tumor model, we found that breast tumor cells derived from TDLN have higher malignancy and removal of TDLNs significantly reduced distant metastasis. Up‐regulation of oncogenic Il‐17rb in cancer cells derived from TDLNs contributes to their malignancy. TGF‐β1 secreted from regulatory T cells (Tregs) in the TDLNs mediated the up‐regulation of Il‐17rb through downstream Smad2/3/4 signaling. These phenotypes can be abolished by TGF‐β1 neutralization or depletion of Tregs. Consistently, clinical data showed that the up‐regulation of IL‐17RB in cancer cells from LN metastases correlated with the increased prevalence of Tregs as well as the aggressive growth of tumors in mouse xenograft assay. Together, these results indicate that Tregs in TDLNs play an important role in modulating the malignancy of breast cancer cells for distant metastasis. Blocking IL‐17RB expression could therefore be a potential approach to curb the process.

Synthetic α-mangostin dilaurate strongly suppresses wide-spectrum organ metastasis in a mouse model of mammary cancer

We previously reported that, in a mouse model of mammary cancer, α‐mangostin alone exhibits anti‐metastatic properties. To enhance this anti‐metastatic effect, we examined the efficacy of synthetic α‐mangostin dilaurate (MGD), prepared by adding lauric acid to α‐mangostin, in the same experimental system wherein mice bearing mammary tumors are exposed to dietary MGD at 0, 2000 and 4000 ppm. Lauric acid has a high propensity for lymphatic absorption, which is the most common pathway of initial dissemination of many solid malignancies. Both mammary tumor volumes and wide‐spectrum organ metastasis were markedly reduced at 2000 and 4000 ppm: furthermore, survival in the 4000‐ppm group was significantly greater than in control mice. Apoptosis in mammary carcinomas was also significantly increased in the 4000‐ppm group, whereas blood microvessel density and lymphatic vessel invasion were markedly reduced. In real‐time PCR analyses of tumor samples, increased p21 and decreased Pcna expression were observed with 4000 ppm but values were not statistically significant when compared to expression in control tumors. However, exposure to 4000 ppm significantly decreased expression of phospho‐Akt (Ser473/Thr308) as compared to the control, indicating a role in the anti‐tumorigenic effects of MGD. These findings suggest that MGD may be useful for adjuvant therapy and chemoprevention and that conjugated medium‐chain fatty acids may enhance the efficacy of certain chemotherapeutic agents.

Applications of Nanoparticles Probes for Prostate Cancer Imaging and Therapy

Prostate cancer (PCa) is the most common type of cancer in men with high morbidity and mortality. However, the current treatment with drugs often leads to chemotherapy resistance. It is known that the multi-disciplines research on molecular imaging is very helpful for early diagnosing, staging, restaging and precise treatment of PCa. In the past decades, the tumor-specific targeted drugs were developed for the clinic to treat prostate cancer. Among them, the emerging nanotechnology has brought about many exciting novel diagnosis and treatments systems for PCa. Nanotechnology can greatly enhance the treatment activity of PCa and provide novel theranostics platform by utilizing the unique physical/chemical properties, targeting strategy, or by loading with imaging/therapeutic agents. Herein, this chapter focuses on state-of-art advances in imaging and diagnosing PCa with nanomaterials and highlights the approaches used for functionalization of the targeted biomolecules, and in the treatment for various aspects of PCa with multifunctional nanoparticles, nanoplatforms and nanodelivery system.

Synaptonemal complex protein 3 is associated with lymphangiogenesis in non-small cell lung cancer patients with lymph node metastasis

Background

The interaction of vascular endothelial growth factor-C (VEGF-C)/VEGF-D/VEGF receptor-3 is considered to be a major driver of lymphangiogenesis, however the mechanism of this process remains unclear. We aimed to investigate the possible lymphangiogenic significance of synaptonemal complex protein 3 (SCP3) in non-small cell lung cancer (NSCLC).

Methods

The expression of SCP3, VEGF-C, and VEGF-D were measured and examined a correlation between SCP3 and VEGF-C or VEGF-D in various human lung cancer cell lines. Subsequently, we assessed SCP3, VEGF-A, VEGF-B, VEGF-C, and VEGF-D expression in archival tumor tissues from 89 NSCLC patients with lymph node (LN) metastasis by combined immunohistochemistry with quantitative digital image analysis.

Results

Positive correlations between SCP3 and VEGF-C expression (R² = 0.743) and VEGF-D expression (R² = 0.932) were detected in various human lung cancer cell lines. The high expression of SCP3, VEGF-A, VEGF-B, VEGF-C, and VEGF-D were detected in 24 (27.0%), 22 (24.7%), 27 (30.3%), 27 (30.3%), and 24 cases (27.0%), respectively. Notably, SCP3 positively correlated with VEGF-C and VEGF-D expression (for both, P < 0.001) and negatively correlated with VEGF-A and VEGF-B expression (P = 0.029 and P = 0.026, respectively). In multivariate analysis of patients with LN metastasis, SCP3 expression predicted worse overall survival (hazard ratio = 1.86, P = 0.008).

Conclusions

SCP3 is associated with lymphangiogenesis and provides insight into the SCP3-VEGF-C/VEGF-D axis based cancer therapy strategy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1241-5) contains supplementary material, which is available to authorized users.

Biomaterials for polynucleotide delivery to anchorage-independent cells

Comparison of various chemical vectors used for polynucleotide delivery to mammalian anchorage-independent cells.

Co-delivery of VEGF and Bcl-2 dual-targeted siRNA polymer using a single nanoparticle for synergistic anti-cancer effects in vivo

Cancer is a multifactorial disease which involves complex genetic mutation and dysregulation. Combinatorial RNAi technology and concurrent multiple gene silencing are expected to provide advanced strategies for effective cancer therapy, but a safe and effective carrier system is a prerequisite to successful siRNA delivery in vivo. We previously developed an effective tumor-targeting siRNA delivery system for in vivo application. In response to the success of this development, herein we present a dual-gene targeted siRNA and its delivery system, to achieve synergistic effects in cancer therapy. Two different sequences of siRNA were chemically modified to be randomly copolymerized in a single backbone of siRNA polymer (Dual-poly-siRNA), and the resulting Dual-poly-siRNA was incorporated into tumor-homing glycol chitosan nanoparticles. Based on the stability in serum and delivery in a tumor-targeted manner, intravenously administered Dual-poly-siRNA carrying glycol chitosan nanoparticles (Dual-NP) demonstrated successful dual-gene silencing in tumors. Notably, co-delivery of VEGF and Bcl-2 targeting siRNA led to more effective cancer therapy for convenient application.

Correlation between serum levels of vascular endothelial growth factor-C and sentinel lymph node status in early breast cancer

Axillary lymph nodes status is the most important prognosis factor in early breast cancer. This status is known by a selective sentinel lymph node biopsy (SLNB) and/or lymphadenectomy. Immunohistochemical studies of breast cancer tumour tissue have reported a relation between the increased expression of vascular endothelial growth factor-C (VEGF-C) and the risk of lymph node metastasis. We researched whether serum levels of VEGF-C could be a predictor factor of sentinel lymph node status in these patients. A prospective analysis was performed on serum from 174 patients with early breast cancer who underwent SLNB. The level of VEGF-C was determined by enzyme-linked immunosorbent assay. Clinical-pathologic variables were collected. Univariate analysis and multivariate logistic regression were conducted, taking SLNB positivity as the segmentation variable. The predictive value of VEGF-C was assessed using ROC curves. Of the sample group of 167 patients, 64 (38.3 %) had affected lymph node. Eighteen patients (28.1 %) presented micrometastasis; there were isolated tumour cells in 11 cases (17.2 %) and macrometastasis in 35 (54.6 %). The median value of VEGF-C was 6561.5 pg/ml. These values did not correlate with any clinical variables, and there was no association between the level of VEGF-C and SLNB status (p = 0.626). In the multivariate analysis, tumour size (p = 0.009) and the presence of vascular invasion (p < 0.001) were independently associated with sentinel lymph node affected. Serum levels of VEGF-C do not appear to predict sentinel lymph node status in patients with early breast cancer who undergo SLNB.

Gene Electrotransfer of Plasmid with Tissue Specific Promoter Encoding shRNA against Endoglin Exerts Antitumor Efficacy against Murine TS/A Tumors by Vascular Targeted Effects

Vascular targeted therapies, targeting specific endothelial cell markers, are promising approaches for the treatment of cancer. One of the targets is endoglin, transforming growth factor-β (TGF-β) co-receptor, which mediates proliferation, differentiation and migration of endothelial cells forming neovasculature. However, its specific, safe and long-lasting targeting remains the challenge. Therefore, in our study we evaluated the transfection efficacy, vascular targeted effects and therapeutic potential of the plasmid silencing endoglin with the tissue specific promoter, specific for endothelial cells marker endothelin-1 (ET) (TS plasmid), in comparison to the plasmid with constitutive promoter (CON plasmid), in vitro and in vivo. Tissue specificity of TS plasmid was demonstrated in vitro on several cell lines, and its antiangiogenic efficacy was demonstrated by reducing tube formation of 2H11 endothelial cells. In vivo, on a murine mammary TS/A tumor model, we demonstrated good antitumor effect of gene electrotransfer (GET) of either of both plasmids in treatment of smaller tumors still in avascular phase of growth, as well as on bigger tumors, already well vascularized. In support to the observations on predominantly vascular targeted effects of endoglin, histological analysis has demonstrated an increase in necrosis and a decrease in the number of blood vessels in therapeutic groups. A significant antitumor effect was observed in tumors in avascular and vascular phase of growth, possibly due to both, the antiangiogenic and the vascular disrupting effect. Furthermore, the study indicates on the potential use of TS plasmid in cancer gene therapy since the same efficacy as of CON plasmid was determined.

Inhibition of lymphangiogenesis and angiogenesis in breast tumor xenografts and lymph nodes by a peptide derived from transmembrane protein 45A

Angiogenesis, the formation of new blood vessels from preexisting blood vessels, is a process that supports tumor growth and metastatic dissemination. Lymphangiogenesis also facilitates metastasis by increasing dissemination through the lymphatic vessels (LVs). Even after treatment with antiangiogenic agents, breast cancer patients are vulnerable to LV-mediated metastasis. We report that a 14-amino acid peptide derived from transmembrane protein 45A shows multimodal inhibition of lymphangiogenesis and angiogenesis in breast cancer. The peptide blocks lymphangiogenic and angiogenic phenotypes of lymphatic and blood endothelial cells induced by tumor-conditioned media prepared from MDA-MB-231 breast cancer cells. The peptide delays growth of MDA-MB-231 tumor xenografts and normalizes tumor-conditioned lymph nodes (LNs). These studies demonstrate the antilymphangiogenic and antiangiogenic potential of the peptide against primary tumors and premetastatic, tumor-conditioned regional LNs. Mechanistically, the peptide blocks vascular endothelial growth factor receptors 2 and 3 (VEGFR2/3) and downstream proteins by binding to neuropilin 1/2 (NRP1/2) and inhibiting VEGFR2/3 and NRP1/2 complex formation in the presence of VEGFA/C.

siRNA and cancer immunotherapy

Immunotherapeutic approaches have been gaining attention in the field of cancer treatment because of their possible ability to eradicate cancer cells as well as metastases by recruiting the host immune system. On the other hand, RNA-based therapeutics with the ability to silence expression of specific targets are currently under clinical investigation for various disorders including cancer. As the mechanisms of tumor evasion from the host immune system are versatile, different molecules have the capacity to be targeted by RNAi technology in order to enhance the immune response against tumors. This technology has been used to silence specific targets in tumor cells, as well as immune cells in cancer cell lines, animal models and clinical trials. siRNAs can also stimulate innate immune responses through activation of Toll-like receptors. Although currently clinical trials of the application of siRNA in cancer immunotherapy are few, it is predicted that in future this technology will be used broadly in cancer treatment.

The role of the VEGF-C/VEGFRs axis in tumor progression and therapy

Vascular endothelial growth factor C (VEGF-C) has been identified as a multifaceted factor participating in the regulation of tumor angiogenesis and lymphangiogenesis. VEGF-C is not only expressed in endothelial cells, but also in tumor cells. VEGF-C signaling is important for progression of various cancer types through both VEGF receptor-2 (VEGFR-2) and VEGF receptor-3 (VEGFR-3). Likewise, both receptors are expressed mainly on endothelial cells, but also expressed in tumor cells. The dimeric VEGF-C undergoes a series of proteolytic cleavage steps that increase the protein binding affinity to VEGFR-3; however, only complete processing, removing both the N- and C-terminal propeptides, yields mature VEGF-C that can bind to VEGFR-2. The processed VEGF-C can bind and activate VEGFR-3 homodimers and VEGFR-2/VEGFR-3 heterodimers to elicit biological responses. High levels of VEGF-C expression and VEGF-C/VEGFRs signaling correlate significantly with poorer prognosis in a variety of malignancies. Therefore, the development of new drugs that selectively target the VEGF-C/VEGFRs axis seems to be an effective means to potentiate anti-tumor therapies in the future.

Mammary cancer gene therapy targeting lymphangiogenesis: VEGF-C siRNA and soluble VEGF receptor-2, a splicing variant

Metastasis contributes significantly to cancer mortality, and the most common pathway of initial dissemination is via the afferent ducts of the lymphatics. Overexpression of vascular endothelial growth factor (VEGF)-C has been associated with lymphangiogenesis and lymph node metastasis in a multitude of human neoplasms, including breast cancers. We recently reported that both VEGF-C siRNA and endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2, a new splicing variant) inhibit VEGF-C function and metastasis in a mouse model of metastatic mammary cancer. Here we briefly review our previous experimental work, specifically targeting tumor lymphangiogenesis, in which metastatic mouse mammary cancers received direct intratumoral injections of either expression vectors VEGF-C siRNA or esVEGFR-2, or the empty plasmid vector, once a week for 6 or 8 weeks, followed by in vivo gene electrotransfer of the injected tumors. Throughout our study, both tumor lymphangiogenesis and the multiplicity of lymph node metastasis were significantly inhibited, with an overall reduction in tumor growth, by both VEGF-C siRNA and esVEGFR-2; further, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed with both treatments. Thus, therapeutic strategies targeting lymphangiogenesis may have great clinical significance for the treatment of metastatic human breast cancer.

Macrophage-mediated lymphangiogenesis: the emerging role of macrophages as lymphatic endothelial progenitors

It is widely accepted that macrophages and other inflammatory cells support tumor progression and metastasis. During early stages of neoplastic development, tumor-infiltrating macrophages (TAMs) mount an immune response against transformed cells. Frequently, however, cancer cells escape the immune surveillance, an event that is accompanied by macrophage transition from an anti-tumor to a pro-tumorigenic type. The latter is characterized by high expression of factors that activate endothelial cells, suppress immune response, degrade extracellular matrix, and promote tumor growth. Cumulatively, these products of TAMs promote tumor expansion and growth of both blood and lymphatic vessels that facilitate metastatic spread. Breast cancers and other epithelial malignancies induce the formation of new lymphatic vessels (i.e., lymphangiogenesis) that leads to lymphatic and subsequently, to distant metastasis. Both experimental and clinical studies have shown that TAMs significantly promote tumor lymphangiogenesis through paracrine and cell autonomous modes. The paracrine effect consists of the expression of a variety of pro-lymphangiogenic factors that activate the preexisting lymphatic vessels. The evidence for cell-autonomous contribution is based on the observed tumor mobilization of macrophage-derived lymphatic endothelial cell progenitors (M-LECP) that integrate into lymphatic vessels prior to sprouting. This review will summarize the current knowledge of macrophage-dependent growth of new lymphatic vessels with specific emphasis on an emerging role of macrophages as lymphatic endothelial cell progenitors (M-LECP).

α-Mangostin extracted from the pericarp of the mangosteen (Garcinia mangostana Linn) reduces tumor growth and lymph node metastasis in an immunocompetent xenograft model of metastatic mammary cancer carrying a p53 mutation

BACKGROUND

The mangosteen fruit has a long history of medicinal use in Chinese and Ayurvedic medicine. Recently, the compound α-mangostin, which is isolated from the pericarp of the fruit, was shown to induce cell death in various types of cancer cells in in vitro studies. This led us to investigate the antitumor growth and antimetastatic activities of α-mangostin in an immunocompetent xenograft model of mouse metastatic mammary cancer having a p53 mutation that induces a metastatic spectrum similar to that seen in human breast cancers.

METHODS

Mammary tumors, induced by inoculation of BALB/c mice syngeneic with metastatic BJMC3879luc2 cells, were subsequently treated with α-mangostin at 0, 10 and 20 mg/kg/day using mini-osmotic pumps and histopathologically examined. To investigate the mechanisms of antitumor ability by α-mangostin, in vitro studies were also conducted.

RESULTS

Not only were in vivo survival rates significantly higher in the 20 mg/kg/day α-mangostin group versus controls, but both tumor volume and the multiplicity of lymph node metastases were significantly suppressed. Apoptotic levels were significantly increased in the mammary tumors of mice receiving 20 mg/kg/day and were associated with increased expression of active caspase-3 and -9. Other significant effects noted at this dose level were decreased microvessel density and lower numbers of dilated lymphatic vessels containing intraluminal tumor cells in mammary carcinoma tissues. In vitro, α-mangostin induced mitochondria-mediated apoptosis and G1-phase arrest and S-phase suppression in the cell cycle. Since activation by Akt phosphorylation plays a central role in a variety of oncogenic processes, including cell proliferation, anti-apoptotic cell death, angiogenesis and metastasis, we also investigated alterations in Akt phosphorylation induced by α-mangostin treatment both in vitro and in vivo. Quantitative analysis and immunohistochemistry showed that α-mangostin significantly decreased the levels of phospho-Akt-threonine 308 (Thr308), but not serine 473 (Ser473), in both mammary carcinoma cell cultures and mammary carcinoma tissues in vivo.

CONCLUSIONS

Since lymph node involvement is the most important prognostic factor in breast cancer patients, the antimetastatic activity of α-mangostin as detected in mammary cancers carrying a p53 mutation in the present study may have specific clinical applications. In addition, α-mangostin may have chemopreventive benefits and/or prove useful as an adjuvant therapy, or as a complementary alternative medicine in the treatment of breast cancer.

Notch restricts lymphatic vessel sprouting induced by vascular endothelial growth factor

Notch signaling plays a central role in cell-fate determination, and its role in lateral inhibition in angiogenic sprouting is well established. However, the role of Notch signaling in lymphangiogenesis, the growth of lymphatic vessels, is poorly understood. Here we demonstrate Notch pathway activity in lymphatic endothelial cells (LECs), as well as induction of delta-like ligand 4 (Dll4) and Notch target genes on stimulation with VEGF or VEGF-C. Suppression of Notch signaling by a soluble form of Dll4 (Dll4-Fc) synergized with VEGF in inducing LEC sprouting in 3-dimensional (3D) fibrin gel assays. Expression of Dll4-Fc in adult mouse ears promoted lymphangiogenesis, which was augmented by coexpressing VEGF. Lymphangiogenesis triggered by Notch inhibition was suppressed by a monoclonal VEGFR-2 Ab as well as soluble VEGF and VEGF-C/VEGF-D ligand traps. LECs transduced with Dll4 preferentially adopted the tip cell position over nontransduced cells in 3D sprouting assays, suggesting an analogous role for Dll4/Notch in lymphatic and blood vessel sprouting. These results indicate that the Notch pathway controls lymphatic endothelial quiescence, and explain why LECs are poorly responsive to VEGF compared with VEGF-C. Understanding the role of the Notch pathway in lymphangiogenesis provides further insight for the therapeutic manipulation of the lymphatic vessels.

Lymphangiogenesis and hemangiogenesis: potential targets for therapy

This review updates historical background from century-old observations on embryonic lymphatic system development through current understanding of the molecular basis of lymphvasculogenesis/lymphangiogenesis ("molecular lymphology"), highlighting similarities and differences with analogous blood vasculature processes. Topics covered include molecular mechanisms in lymphatic development, structural adaptations of the lymphatic vasculature to particulate and cellular transport and trafficking, lymphogenous route of clinical cancer spread, preservation of delineated lymphatic pathways during cancer operations, and anti-lymphangiogenesis in cancer therapy.

Effect of vegf gene knockdown on growth of the murine sarcoma cell line MS-K

The murine sarcoma cell line MS-K was previously established as a Ki-ras-positive cell line. Inoculation of this cell line under the flank of C3H/HeN mice results in the growth of large tumors with well-developed blood vessels within day 30 of transplantation without any metastasis because MS-K cells produce vascular endothelial growth factor (VEGF). To elucidate the role of VEGF in tumor formation in vivo, stable vegf-knockdown-MS-K clones were obtained using plasmid-based knockdown vectors. Interestingly, tumorigenesis was completely suppressed in a vegf-A-knockdown-MS-K clone [designated MS-K (A-KD)]. Proliferation and colony formation capacity of the MS-K (A-KD) cells in a semi-solid medium under low serum conditions was significantly lower than that of control MS-K (SCR) cells; however, the expression of vegf-receptor 1 (vegf-r-1) was not changed. Addition of the recombinant VEGF-A(165) partially restored the colony formation capacity of MS-K (A-KD) cells and caused the phosphorylation of VEGF-r-1 (Flt-1) in MS-K (Normal) cells. Furthermore, tumorigenicity of the vegf-r-1-knockdown-MS-K clone [designated MS-K (R1-KD)] had obviously delayed or strongly suppressed compared with the MS-K (Normal). These results indicate that Vascular endothelial growth factor-A, produced from MS-K, acts as a growth factor for MS-K cells itself and supports tumor formation in vivo by inducing the blood vessel formation.

VEGF and angiopoietin signaling in tumor angiogenesis and metastasis

Solid tumors require blood vessels for growth and dissemination, and lymphatic vessels as additional conduits for metastatic spread. The identification of growth factor receptor pathways regulating angiogenesis has led to the clinical approval of the first antiangiogenic molecules targeted against the vascular endothelial growth factor (VEGF)-VEGF receptor (VEGFR)-2 pathway. However, in many cases resistance to anti-VEGF-VEGFR therapy occurs, and thus far the clinical benefit has been limited to only modest improvements in overall survival. Therefore, novel treatment modalities are required. Here, we discuss the members of the VEGF-VEGFR family as well as the angiopoietin growth factors and their Tie receptors as potential novel targets for antiangiogenic and antilymphangiogenic therapies.

Down-regulation of transcobalamin receptor TCblR/CD320 by siRNA inhibits cobalamin uptake and proliferation of cells in culture

The clinical phenotype of cobalamin (Cbl) deficiency is dictated by the essential role of this vitamin in two key enzymatic reactions. Multiple proteins and receptors participate in the absorption, transport and delivery of this vitamin to tissue cells. Cellular uptake of Cbl is mediated by transcobalamin (TC), a plasma protein and a transmembrane receptor (TCblR) with high affinity for TC saturated with Cbl. Knockdown of TCblR with siRNA results in decreased TC-Cbl uptake. The ensuing Cbl deficiency leads to an increase in doubling time and decreased proliferation of these cells. The study confirms the seminal role of this receptor in the cellular uptake of Cbl and its down-regulation as a potential strategy to inhibit proliferation of cancer cells.

Inhibition of cervical cancer cell growth in vitro and in vivo with dual shRNAs

RNA interference (RNAi)-based gene silencing is widely used in laboratories for gene function studies and also holds a great promise for developing treatments for diseases. However, in vivo delivery of RNAi therapy remains a key issue. Lentiviral vectors have been employed for stable gene transfer and gene therapy and therefore are expected to deliver a stable and durable RNAi therapy. But this does not seem to be true in some disease models. Here, we showed that lentivirus delivered short-hairpin RNA (shRNA) against human papillomavirus (HPV) E6/E7 oncogenes were effective for only 2 weeks in a cervical cancer model. However, using this vector to carry two copies of the same shRNA or two shRNAs targeting at two different but closely related genes (HPV E6 and vascular endothelial growth factor) was more effective at silencing the gene targets and inhibiting cell or even tumor growth than their single shRNA counterparts. The cancer cells treated with dual shRNA were also more sensitive to chemotherapeutic drugs than single shRNA-treated cells. These results suggest that a multi-shRNA strategy may be a more attractive approach for developing an RNAi therapy for this cancer.

The endogenous soluble VEGF receptor-2 isoform suppresses lymph node metastasis in a mouse immunocompetent mammary cancer model

BACKGROUND

Cancer metastasis contributes significantly to cancer mortality and is facilitated by lymphangiogenesis and angiogenesis. A new splicing variant, endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2) that we recently identified is an endogenous selective inhibitor of lymphangiogenesis. To evaluate the antimetastatic potential of esVEGFR-2, gene therapy with vector expressing esVEGFR-2 (pesVEGFR-2) or endostatin (pEndo) as a positive control was conducted on murine metastatic mammary cancer.

METHODS

Syngeneic inoculated metastatic mammary cancers received direct intratumoral injection of pesVEGFR-2, pEndo or pVec as control, once a week for six weeks. In vivo gene electrotransfer was performed on the tumors after each injection.

RESULTS

Deaths from metastasis were much lower in the pesVEGFR-2 and pEndo groups than in those of the pVec. Tumor volume was significantly lower in the pesVEGFR-2 and the pEndo groups throughout the study. Multiplicity of lymph node and lung metastatic nodules was significantly suppressed in the pesVEGFR-2 and pEndo groups. Moreover, the total number of overall metastasis including the other organs was also decreased in these groups. However, pesVEGFR-2 was not able to decrease the number of lungs, ovaries, kidneys and adrenals with metastasis as counted by unilateral or bilateral metastasis. The number of CD34+/Lyve-1⁻ blood microvessels was significantly decreased in the pEndo group, while the number of CD34⁻/Lyve-1+ lymphatic vessels was significantly decreased in the pesVEGFR-2 and pEndo groups. In addition, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed in the pesVEGFR-2 and pEndo groups. Levels of apoptosis were significantly increased in the pEndo group, whereas the rates of cell proliferation were significantly decreased in the pesVEGFR-2 and pEndo groups.

CONCLUSIONS

Our data demonstrate that esVEGFR-2 can inhibit mainly lymph node metastasis. The antimetastatic activity of esVEGFR-2 may be of high clinical significance in the treatment of metastatic breast cancer because lymph node involvement is a most important prognostic factor in cancer patients.

Raloxifene inhibits tumor growth and lymph node metastasis in a xenograft model of metastatic mammary cancer

BACKGROUND

The effects of raloxifene, a novel selective estrogen receptor modulator, were studied in a mouse metastatic mammary cancer model expressing cytoplasmic ERα.

METHODS

Mammary tumors, induced by inoculation of syngeneic BALB/c mice with BJMC3879luc2 cells, were subsequently treated with raloxifene at 0, 18 and 27 mg/kg/day using mini-osmotic pumps.

RESULTS

In vitro study demonstrated that the ERα in BJMC3879luc2 cells was smaller (between 50 and 64 kDa) than the normal-sized ERα (66 kDa) and showed cytoplasmic localization. A statistically significant but weak estradiol response was observed in this cell line. When BJMC3879luc2 tumors were implanted into mice, the ERα mRNA levels were significantly higher in females than in males. In vitro studies showed that raloxifene induced mitochondria-mediated apoptosis and cell-cycle arrest in the G1-phase and a decrease in the cell population in the S-phase. In animal experiments, tumor volumes were significantly suppressed in the raloxifene-treated groups. The multiplicity of lymph node metastasis was significantly decreased in the 27 mg/kg group. Levels of apoptosis were significantly increased in the raloxifene-treated groups, whereas the levels of DNA synthesis were significantly decreased in these groups. No differences in microvessel density in tumors were observed between the control and raloxifene-treated groups. The numbers of dilated lymphatic vessels containing intraluminal tumor cells were significantly reduced in mammary tumors in the raloxifene-treated groups. The levels of ERα mRNA in mammary tumors tended to be decreased in the raloxifene-treated groups.

CONCLUSION

These results suggest that the antimetastatic activity of raloxifene in mammary cancer expressing cytoplasmic ERα may be a crucial finding with clinical applications and that raloxifene may be useful as an adjuvant therapy and for the chemoprevention of breast cancer development.

Current views on the function of the lymphatic vasculature in health and disease

The lymphatic vascular system is essential for lipid absorption, fluid homeostasis, and immune surveillance. Until recently, lymphatic vessel dysfunction had been associated with symptomatic pathologic conditions such as lymphedema. Work in the last few years had led to a better understanding of the functional roles of this vascular system in health and disease. Furthermore, recent work has also unraveled additional functional roles of the lymphatic vasculature in fat metabolism, obesity, inflammation, and the regulation of salt storage in hypertension. In this review, we summarize the functional roles of the lymphatic vasculature in health and disease.

The expression of EFEMP1 in cervical carcinoma and its relationship with prognosis

OBJECTIVE

The study was to explore the role of EFEMP1 protein in angiogenesis and its relationship with prognosis of cervical carcinoma.

METHODS

EFEMP1 expression was evaluated by immunohistochemistry. The microvascular density (MVD) was detected with CD34 staining, and VEGF mRNA expression was evaluated by hybridization in situ. The associations of EFEMP1 with clinicopathologic characteristics, MVD, VEGF mRNA and overall survival were studied.

RESULTS

EFEMP1 expression was positively correlated with MVD and VEGF mRNA, and its overexpression was found to be significantly associated with lymph node metastasis, vascular invasion and poor survival. Multivariate analysis showed that EFEMP1 overexpression was independently related to poor prognosis of cervical cancer.

CONCLUSIONS

EFEMP1 promotes angiogenesis and associates with lymph node metastasis, vascular invasion and poor prognosis of cervical carcinoma. The current study shows that EFEMP1 may be a useful prognostic factor for patients with cervical carcinoma.

Lymphangiogenesis: Molecular mechanisms and future promise

The growth of lymphatic vessels (lymphangiogenesis) is actively involved in a number of pathological processes including tissue inflammation and tumor dissemination but is insufficient in patients suffering from lymphedema, a debilitating condition characterized by chronic tissue edema and impaired immunity. The recent explosion of knowledge on the molecular mechanisms governing lymphangiogenesis provides new possibilities to treat these diseases.

Gonadotropin-regulated lymphangiogenesis in ovarian cancer is mediated by LEDGF-induced expression of VEGF-C

The risk and severity of ovarian carcinoma, the leading cause of gynecologic malignancy death, are significantly elevated in postmenopausal women. Ovarian failure at menopause, associated with a reduction in estrogen secretion, results in an increase of the gonadotropic luteinizing hormone (LH) and follicle-stimulating hormone (FSH), suggesting a role for these hormones in facilitating the progression of ovarian carcinoma. The current study examined the influence of hormonal stimulation on lymphangiogenesis in ovarian cancer cells. In vitro stimulation of ES2 ovarian carcinoma cells with LH and FSH induced expression of vascular endothelial growth factor (VEGF)-C. In vivo, ovariectomy of mice resulted in activation of the VEGF-C promoter in ovarian carcinoma xenografts, increased VEGF-C mRNA level, and enhanced tumor lymphangiogenesis and angiogenesis. Seeking the molecular mechanism, we examined the role of lens epithelium-derived growth factor (LEDGF/p75) and the possible contribution of its putative target, a conserved stress-response element identified in silico in the VEGF-C promoter. Using chromatin immunoprecipitation, we showed that LEDGF/p75 indeed binds the VEGF-C promoter, and binding is augmented by FSH. A corresponding hormonally regulated increase in the LEDGF/p75 mRNA and protein levels was observed. Suppression of LEDGF/p75 expression using small interfering RNA, suppression of LH and FSH production using the gonadotropin-releasing hormone antagonist cetrorelix, or mutation of the conserved stress-response element suppressed the hormonally induced expression of VEGF-C. Overall, our data suggest a possible role for elevated gonadotropins in augmenting ovarian tumor lymphangiogenesis in postmenopausal women.

Lymphangiogenesis and lymphatic metastasis in breast cancer

Lymphatic metastasis is the main prognostic factor for survival of patients with breast cancer and other epithelial malignancies. Mounting clinical and experimental data suggest that migration of tumor cells into the lymph nodes is greatly facilitated by lymphangiogenesis, a process that generates new lymphatic vessels from pre-existing lymphatics with the aid of circulating lymphatic endothelial progenitor cells. The key protein that induces lymphangiogenesis is vascular endothelial growth factor receptor-3 (VEGFR-3), which is activated by vascular endothelial growth factor-C and -D (VEGF-C and VEGF-D). These lymphangiogenic factors are commonly expressed in malignant, tumor-infiltrating and stromal cells, creating a favorable environment for generation of new lymphatic vessels. Clinical evidence demonstrates that increased lymphatic vessel density in and around tumors is associated with lymphatic metastasis and reduced patient survival. Recent evidence shows that breast cancers induce remodeling of the local lymphatic vessels and the regional lymphatic network in the sentinel and distal lymph nodes. These changes include an increase in number and diameter of tumor-draining lymphatic vessels. Consequently, lymph flow away from the tumor is increased, which significantly increases tumor cell metastasis to draining lymph nodes and may contribute to systemic spread. Collectively, recent advances in the biology of tumor-induced lymphangiogenesis suggest that chemical inhibitors of this process may be an attractive target for inhibiting tumor metastasis and cancer-related death. Nevertheless, this is a relatively new field of study and much remains to be established before the concept of tumor-induced lymphangiogenesis is accepted as a viable anti-metastatic target. This review summarizes the current concepts related to breast cancer lymphangiogenesis and lymphatic metastasis while highlighting controversies and unanswered questions.

Transcriptional regulation of vascular endothelial growth factor C by oxidative and thermal stress is mediated by lens epithelium-derived growth factor/p75

Vascular endothelial growth factor C (VEGF-C) plays a critical role in tumor lymphangiogenesis and lymph node metastasis. We report here that VEGF-C expression is regulated by microenvironmental stress including hyperthermia and oxidative stress. Furthermore, we show that this stress response is mediated by transcriptional activation mediated by lens epithelium-derived growth factor (LEDGF/p75). Ectopic expression of LEDGF/p75 in C6 rat glioma and in H1299 human non-small cell lung carcinoma induced VEGF-C expression in vitro, whereas in subcutaneous mouse tumor xenografts, LEDGF/p75 stimulated VEGF-C expression and augmented angiogenesis and lymphangiogenesis. Conversely, overexpression of a LEDGF/p75 native antisense or LEDGF/p75-targeted short interfering RNA downmodulated VEGF-C expression. LEDGF seemed to conferred this activity on binding to a conserved stress response element (STRE) located in the VEGF-C gene because mutating the STRE was sufficient for the suppression of basal and stress-induced activations of the VEGF-C promoter. Thus, the study reported here identified a role for LEDGF/p75 in stress-regulated transcriptional control of VEGF-C expression. These results provide a possible link for LEDGF/p75 in tumor lymphangiogenesis and cancer metastasis. Hence, our data suggest the LEDGF-VEGF-C axis as a putative biomarker for the detection of stress-induced lymphangiogenesis and LEDGF as a potential target for antimetastatic therapy.

Transfection of small RNAs globally perturbs gene regulation by endogenous microRNAs

Transfection of small RNAs (such as small interfering RNAs (siRNAs) and microRNAs (miRNAs)) into cells typically lowers expression of many genes. Unexpectedly, increased expression of genes also occurs. We investigated whether this upregulation results from a saturation effect--that is, competition among the transfected small RNAs and the endogenous pool of miRNAs for the intracellular machinery that processes small RNAs. To test this hypothesis, we analyzed genome-wide transcript responses from 151 published transfection experiments in seven different human cell types. We show that targets of endogenous miRNAs are expressed at significantly higher levels after transfection, consistent with impaired effectiveness of endogenous miRNA repression. This effect exhibited concentration and temporal dependence. Notably, the profile of endogenous miRNAs can be largely inferred by correlating miRNA sites with gene expression changes after transfections. The competition and saturation effects have practical implications for miRNA target prediction, the design of siRNA and short hairpin RNA (shRNA) genomic screens and siRNA therapeutics.

Transfection of small RNAs globally perturbs gene regulation by endogenous microRNAs

Transfection of small RNAs (such as small interfering RNAs (siRNAs) and microRNAs (miRNAs)) into cells typically lowers expression of many genes. Unexpectedly, increased expression of genes also occurs. We investigated whether this upregulation results from a saturation effect--that is, competition among the transfected small RNAs and the endogenous pool of miRNAs for the intracellular machinery that processes small RNAs. To test this hypothesis, we analyzed genome-wide transcript responses from 151 published transfection experiments in seven different human cell types. We show that targets of endogenous miRNAs are expressed at significantly higher levels after transfection, consistent with impaired effectiveness of endogenous miRNA repression. This effect exhibited concentration and temporal dependence. Notably, the profile of endogenous miRNAs can be largely inferred by correlating miRNA sites with gene expression changes after transfections. The competition and saturation effects have practical implications for miRNA target prediction, the design of siRNA and short hairpin RNA (shRNA) genomic screens and siRNA therapeutics.

From tumor lymphangiogenesis to lymphvascular niche

Metastasis in sentinel lymph nodes indicates the initial spread of tumors from a primary site. The recent discovery of tumor-associated growth of lymphatic vessels clarified that tumor lymphangiogenesis actively promotes enhanced draining/sentinel lymph node metastasis. Studies of experimental carcinogenesis have further established that tumors continue to induce lymphangiogenesis in metastatic foci such as draining lymph nodes. Lymphangiogenesis within draining lymph nodes probably contributes to enhanced distant lymph node and distant organ metastases. Lymph node lymphangiogenesis has recently been identified in several human malignancies, such as cutaneous malignant melanoma. Tumor-associated lymphangiogenesis thus has potential significance not only at the primary site, but also in lymph nodes. Primary tumors induce new lymphatic vessel growth in draining lymph nodes before metastasis. The remarkable enlargement of sinusoidal lymphatic endothelium might facilitate tumor cell transport to the lymph nodes, and potentially contribute to the migration, residence, and/or survival of metastatic tumor cancer stem cells by inducing a specific tumor microenvironment. Therefore, the novel concept of 'lymphvascular niche' is proposed herein to explain lymphatic network expansion. This concept might help to improve understanding of the molecular mechanism of lymph node metastasis, and change therapeutic approaches to treating cancer metastasis.

Tumor lymphatics

In this article we survey more than three centuries of observation and research into tumor-associated lymphatic vessels, and their role in the metastatic spread of cancer. This historical overview documents how questions regarding tumor lymphatics have been central to concepts about the process of metastasis, and how this has subsequently influenced the clinical treatment of cancer. In turn, we show how analysis of the efficacy of these treatments has challenged long-standing notions regarding the tumor lymphatics. Starting with the discovery of VEGFR-3 and its ligands VEGF-C and VEGF-D, we also review how the rapid developments over the last 15 years in the molecular analysis of the lymphatic system and in particular lymphangiogenesis have contributed to this debate. Finally we speculate on how apparently paradoxical bodies of evidence regarding the role of tumor lymphatics in determining patterns of metastatic spread might be reconciled.

Molecular targets and gene therapy of lung cancer

Lung cancer is of great interest in human pathology because its apparent aggressiveness cannot be stopped by applied treatment procedures. The lack of highly specific screening tests prevents an early diagnosis of the disease. Insidious beginning and diverse and unclear clinical picture are responsible for the fact that most cases are diagnosed at advanced stages. An increasing number of patients and a short length of survival are additional factors that make this disease an imperative in the clinical practice, while vague and mutually dependent etiological factors represent a challenge in laboratory studies of the pathogenesis. The objective of this review is to describe some of the potential molecular targets available for manipulation in lung cancer; vector currently used by thoracic investigators to deliver therapy, and illustrated the experience with clinical trials of gene therapy in lung cancer. While gene therapy offers new hopes for lung cancer treatment, it is the need to develop valid clinical protocols of randomized trials before safety using to various lung cancer patient populations.

Developmental and pathological lymphangiogenesis: from models to human disease

The lymphatic vascular system, the body's second vascular system present in vertebrates, has emerged in recent years as a crucial player in normal and pathological processes. It participates in the maintenance of normal tissue fluid balance, the immune functions of cellular and antigen trafficking and absorption of fatty acids and lipid-soluble vitamins in the gut. Recent scientific discoveries have highlighted the role of lymphatic system in a number of pathologic conditions, including lymphedema, inflammatory diseases, and tumor metastasis. Development of genetically modified animal models, identification of lymphatic endothelial specific markers and regulators coupled with technological advances such as high-resolution imaging and genome-wide approaches have been instrumental in understanding the major steps controlling growth and remodeling of lymphatic vessels. This review highlights the recent insights and developments in the field of lymphatic vascular biology.