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

Intercellular Adhesion Molecule-1 and Vascular Cell Adhesion Molecule Are Induced by Ionizing Radiation on Lymphatic Endothelium

PURPOSE/OBJECTIVES

The goal of this study was to assess the effects of ionizing radiation on the expression of the integrin ligands ICAM-1 and VCAM that control leucocyte transit by lymphatic endothelial cells.

MATERIALS/METHODS

Confluent monolayers of primary human lymphatic endothelial cells (LEC) were irradiated with single dose of 2, 5, 10 or 20 Gy, with 6 MeV-x-rays using a Linear-Accelerator. ICAM-1 and VCAM expression was determined by flow cytometry. Human tissue specimens received a single dose of 20 Gy with 15 MeV-x-rays. MC38, B16-OVA or B16-VEGF-C tumors grown in C57BL/6 mice were irradiated with single dose of 20Gy using a Linear-Accelerator fitted with a 10mm Radiosurgery collimator. Clinical samples were obtained from patients previous and 4 weeks after complete standard radiotherapy. ICAM-1 and VCAM expression was detected in all tissue specimens by confocal microscopy. To understand the role of TGFβ in this process anti-TGFβ blocking mAb were injected i.p. 30min before radiotherapy. Cell adhesion to irradiated LEC was analyzed in adhesion experiments performed in the presence or in the absence of anti- TGFβ and /or anti-ICAM1 blocking mAb.

RESULTS

We demonstrate that lymphatic endothelial cells in tumor samples experience induction of surface ICAM-1 and VCAM when exposed to ionizing radiation in a dose- and time-dependent manner. These effects can be recapitulated in cultured LEC, and are in part mediated by TGFβ. These data are consistent with increases in ICAM-1 and VCAM expression on LYVE-1+ endothelial cells in freshly explanted human tumor tissue and in mouse transplanted tumors after radiotherapy. Finally, ICAM-1 and VCAM expression accounts for enhanced adherence of human T lymphocytes to irradiated LEC.

CONCLUSION

Our results show induction of ICAM-1 and VCAM on LVs in irradiated lesions and offer a starting point for elucidating the biological and therapeutic implications of targeting leukocyte traffic in combination to immunotherapy.

Antagonist antibodies to vascular endothelial growth factor receptor 2 (VEGFR-2) as anti-angiogenic agents

Interaction of numerous signaling pathways in endothelial and mesangial cells results in exquisite control of the process of physiological angiogenesis, with a central role played by vascular endothelial growth factor receptor 2 (VEGFR-2) and its cognate ligands. However, deregulated angiogenesis participates in numerous pathological processes. Excessive activation of VEGFR-2 has been found to mediate tissue-damaging vascular changes as well as the induction of blood vessel expansion to support the growth of solid tumors. Consequently, therapeutic intervention aimed at inhibiting the VEGFR-2 pathway has become a mainstay of treatment in cancer and retinal diseases. In this review, we introduce the concepts of physiological and pathological angiogenesis, the crucial role played by the VEGFR-2 pathway in these processes, and the various inhibitors of its activity that have entered the clinical practice. We primarily focus on the development of ramucirumab, the antagonist monoclonal antibody (mAb) that inhibits VEGFR-2 and has recently been approved for use in patients with gastric, colorectal, and lung cancers. We examine in-depth the pre-clinical studies using DC101, the mAb to mouse VEGFR-2, which provided a conceptual foundation for the role of VEGFR-2 in physiological and pathological angiogenesis. Finally, we discuss further clinical development of ramucirumab and the future of targeting the VEGF pathway for the treatment of cancer.

Driving CAR T-cells forward

The engineered expression of chimeric antigen receptors (CARs) on the surface of T cells enables the redirection of T-cell specificity. Early clinical trials using CAR T cells for the treatment of patients with cancer showed modest results, but the impressive outcomes of several trials of CD19-targeted CAR T cells in the treatment of patients with B-cell malignancies have generated an increased enthusiasm for this approach. Important lessons have been derived from clinical trials of CD19-specific CAR T cells, and ongoing clinical trials are testing CAR designs directed at novel targets involved in haematological and solid malignancies. In this Review, we discuss these trials and present strategies that can increase the antitumour efficacy and safety of CAR T-cell therapy. Given the fast-moving nature of this field, we only discuss studies with direct translational application currently or soon-to-be tested in the clinical setting.

Opposing Roles of JNK and p38 in Lymphangiogenesis in Melanoma

In primary melanoma, the amount of vascular endothelial growth factor C (VEGF-C) expression and lymphangiogenesis predicts the probability of metastasis to sentinel nodes, but conditions boosting VEGF-C expression in melanoma are poorly characterized. By comparative mRNA expression analysis of a set of 22 human melanoma cell lines, we found a striking negative correlation between VEGF-C and microphthalmia-associated transcription factor (MITF) expression, which was confirmed by data mining in GEO databases of human melanoma Affymetrix arrays. Moreover, in human patients, high VEGF-C and low MITF levels in primary melanoma significantly correlated with the chance of metastasis. Pathway analysis disclosed the respective c-Jun N-terminal kinase and p38/mitogen-activated protein kinase activities as being responsible for the inverse regulation of VEGF-C and MITF. Predominant c-Jun N-terminal kinase signaling results in a VEGF-C(low)/MITF(high) phenotype; these melanoma cells are highly proliferative, show low mobility, and are poorly lymphangiogenic. Predominant p38 signaling results in a VEGF-C(high)/MITF(low) phenotype, corresponding to a slowly cycling, highly mobile, lymphangiogenic, and metastatic melanoma. In conclusion, the relative c-Jun N-terminal kinase and p38 activities determine the biological behavior of melanoma. VEGF-C and MITF levels serve as surrogate markers for the respective c-Jun N-terminal kinase and p38 activities and may be used to predict the risk of metastasis in primary melanoma.

Tumor-induced VEGF-C overexpression in retroperitoneal lymph nodes in VX2 carcinoma-bearing rabbits

Objective

To establish the retroperitoneal lymph node (RLN) metastasis model of cervical carcinoma in rabbits and evaluate the relationship of vascular endothelial growth factor-C (VEGF-C) expression and the lymph node status.

Methods

Forty-eight rabbits were injected with VX2 cells or RPMI solution at muscular mucosae of the myometrium 0.5 cm away from the cervix. Animals were treated with or without cis-diamminedichloroplatinum(II) (cisplatin: DDP) and sacrificed on days 15, 21, and 27 post-VX2 or RPMI injections. Tumor mass and RLNs were examined histopathologically. Quantitative real-time PCR was used to examine the changes in VEGF-C mRNA expression. Levels of VEGF-C protein expression in tissues were determined using immunohistochemistry staining.

Results

Development of VX2 cervical carcinoma and the RLNs metastasis was confirmed with pathological examination. Significantly increased tumor volume was observed on days 15, 21, and 27 postinjection (P<0.05). The enlargement of RLNs was found on day 21. Expression of VEGF-C was significantly upregulated in peripheral white blood cells, tumor mass, and RLNs in an association with cancer progression. DDP resulted in a suppression of VEGF-C expression, whereas the influences on tumor mass and lymphatic metastasis were insignificant.

Conclusion

Elevated VEGF-C expressions in peripheral white blood cells and RLNs are associated with tumor progression and lymphatic metastasis. DDP treatment inhibits VEGF-C expression and fails to protect against metastatic cervical cancer.

The relevance of cell type- and tumor zone-specific VEGFR-2 activation in locally advanced colon cancer

Background

For the successful therapeutic use of inhibitors of the vascular endothelial growth factor receptor (VEGFR) pathway detailed knowledge of the mechanisms leading to tumor progression is indispensable. The main goal of this study was to determine the relevance of the VEGFR-2 activating pathway for colon carcinoma (CC) metastasis. The initial event is ligand-induced receptor activation through tyrosine autophosphorylation.

Methods

VEGFR-2, its ligands VEGF-C and VEGF-D and the phosphorylated (activated) receptor forms pVEGFR-2^Tyr1175 and pVEGFR-2^Tyr1214 were investigated immunohistochemically in different tumor compartments (intratumoral (zone 1) - invasive front (zone 2) – extratumoral soft tissue (zone 3)) and various cell types (tumor cells, inflammatory cells, macro- and microvasculature) in 84 non-metastatic, lymphogenous-metastatic and haematogenous-metastatic CC.

Results

VEGF-D produced by tumor cells has an autocrine affinity for its receptor VEGFR-2. In tumor budding regions VEGF-D-induced receptor activation by autophosphorylation at Tyr1214 seems to be a possible initial event of the VEGFR-2-mediated signaling pathway, but without effect on metastatic behaviour. In inflammatory cells of almost all CC VEGFR-2 phosphorylation at Tyr 1175 and Tyr 1214 was detectable without accompanying receptor expression, suggesting receptor activation without cell surface expression. Peritumoral inflammatory cells also expressed paracrine acting VEGF-C. The autocrine VEGF-D/VEGFR-2 signaling axis and receptor autophosphorylation at Tyr1214 appear to be main events for capillaries in all three tumor zones and for small vessels in zone 1 and 2. Independent of the metastatic status a large number of cases with capillary immunopositivity in the angiogenically active invasive front was documented, especially for VEGF-D, VEGFR-2 and pVEGFR-2^Tyr1214. VEGFR-2 positive extratumoral capillaries were significantly more common in distant metastatic CC. In all tumor compartments the investigated biomolecules were also detected in different frequencies in the macrovasculature, which is responsible for sufficient tumor vascularization. In addition, vascular paracrine-acting VEGF-C production was widely detected, but without zone and vessel-type dependence.

Conclusions

The VEGFR-2 activating pathway is closely involved in tumor cell-associated, vessel-mediated and immuno-inflammatory processes in colon carcinoma and appears to contribute to tumor survival and growth as well as maintenance of the infiltrative phenotype rather than to promote metastasis.

Camptothecin suppresses expression of matrix metalloproteinase-9 and vascular endothelial growth factor in DU145 cells through PI3K/Akt-mediated inhibition of NF-κB activity and Nrf2-dependent induction of HO-1 expression

Though camptothecin (CPT) possesses potent anti-inflammatory, immunomodulatory, anticancerous, and antiproliferative effects, little is known about the mechanism by which CPT regulates the expression of matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF). Therefore, the current study aimed to investigate the effects of CPT on the expression of MMP-9 and VEGF, which are important factors for the invasion of tumors. In vitro application of CPT resulted in a slight inhibition of cell proliferation and a significant reduction in the matrigel invasion of DU145 cells. Treatment with CPT also downregulated phorbol-12-myristate-13-acetate (PMA)- and tumor necrosis factor-α (TNF-α)-induced MMP-9 and VEGF expression by inhibiting nuclear factor-κB (NF-κB) activity. Downregulation of phosphoinositide 3-kinase (PI3K)/Akt phosphorylation in response to CPT was revealed as an upstream pathway regulating the expression of MMP-9 and VEGF accompanying the inhibition of NF-κB activity. We further confirmed that CPT inhibits PMA-induced MMP-9 and VEGF expression by upregulating nuclear factor-erythroid related factor-2 (Nrf2)-mediated heme oxygenase-1 (HO-1) induction. Taken together, these data indicate that CPT inhibits the invasion of cancer cells accompanied by suppression of MMP-9 and VEGF production by suppressing the PI3K/Akt-mediated NF-κB pathway and enhancing the Nrf2-dependent HO-1 pathway, suggesting that CPT may be a good candidate to inhibit MMP-9 and VEGF expression.

The non-canonical role of vascular endothelial growth factor-C axis in cancer progression

It has been shown in many clinical studies that the level of vascular endothelial growth factor-C (VEGF-C) positively correlates with lymph node metastasis. Nevertheless, beyond the canonical role of VEGF-C in stimulating lymphangiogenesis and thus promoting lymph node/distant metastasis, emerging evidence indicates that expression of VEGF-C contributes to various aspects of carcinogenicity via autocrine regulation. The newly identified functions of VEGF-C include but are not limited to proliferation, migration, invasion, and chemo-resistance. Besides tumor cell autocrine regulation, VEGF-C can also modulate the immune system such that tumor cells more easily escape immune surveillance. Therefore, understanding the functional roles and regulatory mechanisms related to the VEGF-C axis may lead to alternative strategies for cancer treatment. This mini-review will focus on summarizing recent discoveries regarding the unconventional functions of VEGF-C in cancer progression.

HET0016, a selective inhibitor of 20-HETE synthesis, decreases pro-angiogenic factors and inhibits growth of triple negative breast cancer in mice

A selective inhibitor of 20-HETE synthesis, HET0016, has been reported to inhibit angiogenesis. 20-HETE has been known as a second mitogenic messenger of angiogenesis inducing growth factors. HET0016 effects were analyzed on MDA-MB-231 derived breast cancer in mouse and invitro cell line. MDA-MB-231 tumor cells were implanted in animals’ right flank and randomly assigned to early (1 and 2), starting treatments on day 0, or delayed groups (3 and 4) on day 8 after implantation of tumor. Animals received HET0016 (10 mg/kg) treatment via intraperitoneal injection for 5 days/week for either 3 or 4 weeks. Control group received vehicle treatment. Tumor sizes were measured on days 7, 14, 21, and 28 and the animals were euthanized on day 22 and 29. Proteins were extracted from the whole tumor and from cells treated with 10 µM HET0016 for 4 and 24 hrs. Protein array kits of 20 different cytokines/factors were used. ELISA was performed to observe the HIF-1α and MMP-2 protein expression. Other markers were confirmed by IHC. HET0016 significantly inhibited tumor growth in all treatment groups at all-time points compared to control (p<0.05). Tumor growth was completely inhibited on three of ten animals on early treatment group. Treatment groups showed significantly lower expression of pro-angiogenic factors compared to control at 21 days; however, there was no significant difference in HIF-1α expression after treatments. Similar results were found invitro at 24 hrs of HET0016 treatment. After 28 days, significant increase of angiogenin, angiopoietin-1/2, EGF-R and IGF-1 pro-angiogenic factors were found (p<0.05) compared to control, as well as an higher intensity of all factors were found when compared to that of 21 day’s data, suggesting a treatment resistance. HET0016 inhibited tumor growth by reducing expression of different set of pro-angiogenic factors; however, a resistance to treatment seemed to happen after 21 days.

Vascular Endothelial Growth Factor in Colonic Cancer, Ulcerative Colitis and Colonic Adenoma: An Immunohistochemical Study

BACKGROUND: Colon cancer is one of the most common malignancies worldwide. Colonic adenoma and ulcerative colitis (UC) are important precancerous lesions. Vascular Endothelial Growth Factor (VEGF) is a well-known pro-angiogenic factor plays important role in physiologic and pathologic conditions and in neovascularization in cancer and hence becomes a potential target for anti-angiogenic cancer therapy.AIM: This study investigated VEGF immunohistochemical expression in colon cancer and its precancerous lesions. MATERIAL AND METHODS:  Paraffin blocks from two hospitals were collected in a year: Colon cancer: 20 cases, colonic adenoma: 15 cases, UC: 15 cases and 5 controls from normal mucosa. VEGF was assessed immunohistochemically using a primary anti-VEGF antibody (VG1, Dako, Denemark).RESULTS: Median age was 49 years (range 31-52) in cancer, 40 years (range 31-52) in adenomas and 33 years (range 27-43) in UC. VEGF expression was negative in control, significantly strongly positive in 90% of colonic adenocarcinoma (p= 0.001), significantly positive in adenomas (p= 0.002) - the weak positivity significantly seen in mild dysplasia (p= 0.001) - and significantly positive in 73.3% of UC cases (p=0.022).CONCLUSION: The significant increase in positivity of VEGF in precancerous to cancerous lesions may point to its potential role in the pathogenesis and progression of colonic neoplasia.

Endothelial deficiency of L1 reduces tumor angiogenesis and promotes vessel normalization

While tumor blood vessels share many characteristics with normal vasculature, they also exhibit morphological and functional aberrancies. For example, the neural adhesion molecule L1, which mediates neurite outgrowth, fasciculation, and pathfinding, is expressed on tumor vasculature. Here, using an orthotopic mouse model of pancreatic carcinoma, we evaluated L1 functionality in cancer vessels. Tumor-bearing mice specifically lacking L1 in endothelial cells or treated with anti-L1 antibodies exhibited decreased angiogenesis and improved vascular stabilization, leading to reduced tumor growth and metastasis. In line with these dramatic effects of L1 on tumor vasculature, the ectopic expression of L1 in cultured endothelial cells (ECs) promoted phenotypical and functional alterations, including proliferation, migration, tubulogenesis, enhanced vascular permeability, and endothelial-to-mesenchymal transition. L1 induced global changes in the EC transcriptome, altering several regulatory networks that underlie endothelial pathophysiology, including JAK/STAT-mediated pathways. In particular, L1 induced IL-6-mediated STAT3 phosphorylation, and inhibition of the IL-6/JAK/STAT signaling axis prevented L1-induced EC proliferation and migration. Evaluation of patient samples revealed that, compared with that in noncancerous tissue, L1 expression is specifically enhanced in blood vessels of human pancreatic carcinomas and in vessels of other tumor types. Together, these data indicate that endothelial L1 orchestrates multiple cancer vessel functions and represents a potential target for tumor vascular-specific therapies.

Inhibition of BMP signaling suppresses metastasis in mammary cancer

Bone Morphogenetic Proteins (BMPs) are secreted cytokines/growth factors that play differing roles in cancer. BMPs are overexpressed in human breast cancers, but loss of BMP signaling in mammary carcinomas can accelerate metastasis. We show that human breast cancers display active BMP signaling, which is rarely downregulated or homozygously deleted. We hypothesized that systemic inhibition of BMP signaling in both the tumor and the surrounding microenvironment could prevent tumor progression and metastasis. To test this hypothesis, we used DMH1, a BMP antagonist, in MMTV.PyVmT expressing mice. Treatment with DMH1 reduced lung metastasis and the tumors were less proliferative and more apoptotic. In the surrounding tumor microenvironment, treatment with DMH1 altered fibroblasts, lymphatic vessels and macrophages to be less tumor promoting. These results indicate that inhibition of BMP signaling may successfully target both the tumor and the surrounding microenvironment to reduce tumor burden and metastasis.

Overexpression of both platelet-derived growth factor-BB and vascular endothelial growth factor-C and its association with lymphangiogenesis in primary human non-small cell lung cancer

BACKGROUND

Metastatic spread of tumor through lymphatic vasculature is an important adverse prognostic factor in a variety of human cancer and tumor lymphangiogenesis requires the interplay of several growth factors. Platelet-derived growth factor (PDGF)-BB and vascular endothelial growth factor (VEGF)-C are two important molecules involving in tumor metastasis and lymphangiogenesis. Therefore, the aim of this study was to investigate the coexpression of PDGF-BB and VEGF-C in primary human non-small cell lung cancer (NSCLC) and its association with lymphangiogenesis.

METHODS

Using immunohistochemical staining, PDGF-BB and VEGF-C expression were detected in 109 primary NSCLC tissues, while the lymphatic micro-vessel density (LMVD) was counted.

RESULTS

Of 109 cases, PDGF-BB and VEGF-C overexpression was 66.97% (73/109) and 65.14% (71/109), respectively. 52 (47.7%) had overexpression of both PDGF-BB and VEGF-C (P+V+), 21 (19.3%) overexpression of PDGF-BB but low expression of VEGF-C (P+V-), 19(17.4%) overexpression of VEGF-C but low expression of PDGF-BB (P-V+) and 17(15.6%) low expression of both PDGF-BB and VEGF-C (P-V-). PDGF-BB expression was positively related to that of VEGF-C (r=0.451, p=0.034). LMVD in cases with P+V+was much higher than those with P-V- (p=0.004). In addition, the patients with P+V+were younger and also had larger tumor size, more likely lymph node metastasis and worse histological differentiation than those with P-V-. Moreover, the overall survival (OS) of patients with P+V+was shorter than those with P-V- (p=0.015).

CONCLUSION

Coexpression of both PDGF-BB and VEGF-C was associated with lymphangiogenesis and poor prognosis in NSCLC, and might play a critical role in NSCLC progression.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2261801312571320.

Effects of siRNA targeting BMPR-II on the biological activities of human liver cancer cells and its mechanism

Background

Bone morphogenetic protein receptor II (BMPR-II) plays an important role in tumor’s invasion and proliferation. In this study, we observed the effects of small interfering RNA (siRNA) targeting bone morphogenetic protein receptor II (BMPR-II) on the biological activities of human liver cells and explore its mechanism.

Methods

The molecular sequences of three siRNA targeting BMPR-IIwere designed and synthesized. In this study, there were 6 groups including group I (normal control), group II (blank control), group III (negative control) and group IV-VI (BMPR-II-siRNA-a, siRNA-b and siRNA-c-transfected cells, respectively). The levels of mRNA and protein of BMPR-II were determined to select the best sequence for BMPR-II silence. After liver cancer cells were transfected with the best sequence, proliferation and invasion of transfected cells were assessed, and apoptosis and cell cycle were detected. The expressions of mitogen-activated protein kinases (MAPKs) signal pathway-related VEGF-C protein were observed after BMPR-II silence and BMPR-II silence combined with inhibiting MAPKs signal pathway, respectively.

Results

RT-PCR and Western blot indicated that BMPR-II expression was the highest in HepG2 among the three liver cancer lines (P < 0.01) and the lowest in group IV among the six groups (P < 0.01). MTT assay and transwell assay revealed that the numbers of cell growth and cell transmembrane were significantly lower in group IV than in control groups 48 h after cells were transfected (P < 0.05). Flow cytometer showed that apoptosis was the highest and cells were significantly blocked in S phase 48 h after cells were transfected in group IV (P < 0.01). Western blot indicated that the protein levels of p-P38 (P < 0.01) and vascular endothelial growth factor-C (VEGF-C) (P < 0.01) were significantly decreased after BMPR-II silence. The protein level of VEGF-C was significantly decreased in PD98059 + siRNA-BMPR-II-a and SB203580 + siRNA-BMPR-II-a groups (P < 0.01), especially in SB203580 + siRNA-BMPR-II-a group (P < 0.01).

Conclusions

siRNA targeting BMPR-IIcan markedly inhibit HepG2 proliferation and invasion, promote apoptosis and block HepG2 in S phase. Its mechanism may be that BMPR-II silence down-regulates VEGF-C expression through MAPK/P38 and MAPK/ERK1/2 pathways, especially MAPK/P38. This study provides a new targeted therapy for liver cancer.

18β-Glycyrrhetinic acid suppresses TNF-α induced matrix metalloproteinase-9 and vascular endothelial growth factor by suppressing the Akt-dependent NF-κB pathway

Little is known about the molecular mechanism through which 18β-glycyrrhetinic acid (GA) inhibits metastasis and invasion of cancer cells. Therefore, this study aimed to investigate the effects of GA on the expression of matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) in various types of cancer cells. We found that treatment with GA reduces tumor necrosis factor-α (TNF-α)-induced Matrigel invasion with few cytotoxic effects. Our findings also showed that MMP-9 and VEGF expression increases in response to TNF-α; however, GA reverses their expression. In addition, GA inhibited inhibitory factor kappa B degradation, sustained nuclear factor-kappa B (NF-κB) subunits, p65 and p50, in the cytosol compartments, and consequently suppressed the TNF-α-induced DNA-binding activity and luciferase activity of NF-κB. Specific NF-κB inhibitors, pyrrolidine dithiocarbamate, MG132, and PS-1145, also attenuated TNF-α-mediated MMP-9 and VEGF expression as well as activity by suppressing their regulatory genes. Furthermore, phosphorylation of TNF-α-induced phosphatidyl-inositol 3 kinase (PI3K)/Akt was significantly downregulated in the presence of GA accompanying with the inhibition of NF-κB activity, and as presumed, the specific PI3K/Akt inhibitor LY294002 significantly decreased MMP-9 and VEGF expression as well as activity. These results suggest that GA operates as a potential anti-invasive agent by downregulating MMP-9 and VEGF via inhibition of PI3K/Akt-dependent NF-κB activity. Taken together, GA might be an effective anti-invasive agent by suppressing PI3K/Akt-mediated NF-κB activity.

Tissue engineering and regeneration of lymphatic structures

Tissue engineering is the process by which biological structures are recreated using a combination of molecular signals, cellular components and scaffolds. Although the perceived potential of this approach to reconstruct damaged or missing tissues is seemingly limitless, application of these ideas in vivo has been more difficult than expected. However, despite these obstacles, important advancements have been reported for a number of organ systems, including recent reports on the lymphatic system. These advancements are important since the lymphatic system plays a central role in immune responses, regulation of inflammation, lipid absorption and interstitial fluid homeostasis. Insights obtained over the past two decades have advanced our understanding of the molecular and cellular mechanisms that govern lymphatic development and function. Utilizing this knowledge has led to important advancements in lymphatic tissue engineering, which is the topic of this review.

Compartment model predicts VEGF secretion and investigates the effects of VEGF trap in tumor-bearing mice

Angiogenesis, the formation of new blood vessels from existing vasculature, is important in tumor growth and metastasis. A key regulator of angiogenesis is vascular endothelial growth factor (VEGF), which has been targeted in numerous anti-angiogenic therapies aimed at inhibiting tumor angiogenesis. Systems biology approaches, including computational modeling, are useful for understanding this complex biological process and can aid in the development of novel and effective therapeutics that target the VEGF family of proteins and receptors. We have developed a computational model of VEGF transport and kinetics in the tumor-bearing mouse, which includes three-compartments: normal tissue, blood, and tumor. The model simulates human tumor xenografts and includes human (VEGF121 and VEGF165) and mouse (VEGF120 and VEGF164) isoforms. The model incorporates molecular interactions between these VEGF isoforms and receptors (VEGFR1 and VEGFR2), as well as co-receptors (NRP1 and NRP2). We also include important soluble factors: soluble VEGFR1 (sFlt-1) and α-2-macroglobulin. The model accounts for transport via macromolecular transendothelial permeability, lymphatic flow, and plasma clearance. We have fit the model to available in vivo experimental data on the plasma concentration of free VEGF Trap and VEGF Trap bound to mouse and human VEGF in order to estimate the rates at which parenchymal cells (myocytes and tumor cells) and endothelial cells secrete VEGF. Interestingly, the predicted tumor VEGF secretion rates are significantly lower (0.007-0.023 molecules/cell/s, depending on the tumor microenvironment) than most reported in vitro measurements (0.03-2.65 molecules/cell/s). The optimized model is used to investigate the interstitial and plasma VEGF concentrations and the effect of the VEGF-neutralizing agent, VEGF Trap (aflibercept). This work complements experimental studies performed in mice and provides a framework with which to examine the effects of anti-VEGF agents, aiding in the optimization of such anti-angiogenic therapeutics as well as analysis of clinical data. The model predictions also have implications for biomarker discovery with anti-angiogenic therapies.