The endothelial Tie1 receptor is ligand-less, but interacts with the Tie2 receptor for angiopoietins (Angpt). Angpt2 is expressed in tumor blood vessels, and its blockade inhibits tumor angiogenesis. Here we found that Tie1 deletion from the endothelium of adult mice inhibits tumor angiogenesis and growth by decreasing endothelial cell survival in tumor vessels, without affecting normal vasculature. Treatment with VEGF or VEGFR-2 blocking antibodies similarly reduced tumor angiogenesis and growth; however, no additive inhibition was obtained by targeting both Tie1 and VEGF/VEGFR-2. In contrast, treatment of Tie1-deficient mice with a soluble form of the extracellular domain of Tie2, which blocks Angpt activity, resulted in additive inhibition of tumor growth. Notably, Tie1 deletion decreased sprouting angiogenesis and increased Notch pathway activity in the postnatal retinal vasculature, while pharmacological Notch suppression in the absence of Tie1 promoted retinal hypervasularization. Moreover, substantial additive inhibition of the retinal vascular front migration was observed when Angpt2 blocking antibodies were administered to Tie1-deficient pups. Thus, Tie1 regulates tumor angiogenesis, postnatal sprouting angiogenesis, and endothelial cell survival, which are controlled by VEGF, Angpt, and Notch signals. Our results suggest that targeting Tie1 in combination with Angpt/Tie2 has the potential to improve antiangiogenic therapy.
The pharmacological inhibition of general transcriptional regulators has the potential to block growth through targeting multiple tumorigenic signaling pathways simultaneously. Here, using an innovative cell-based screen, we identify a structurally unique small molecule (named JIB-04) which specifically inhibits the activity of the Jumonji family of histone demethylases in vitro, in cancer cells, and in tumors in vivo. Unlike known inhibitors, JIB-04 is not a competitive inhibitor of α-ketoglutarate. In cancer but not in patient-matched normal cells, JIB-04 alters a subset of transcriptional pathways and blocks viability. In mice, JIB-04 reduces tumor burden and prolongs survival. Importantly, we find that patients with breast tumors that overexpress Jumonji demethylases have significantly lower survival. Thus JIB-04, a novel inhibitor of Jumonji demethylases in vitro and in vivo, constitutes a unique potential therapeutic and research tool against cancer, and validates the use of unbiased cellular screens to discover chemical modulators with disease relevance.
In lung cancer, platelet-derived growth factor receptor α (PDGFRα) is expressed frequently by tumor-associated stromal cells and by cancer cells in a subset of tumors. We sought to determine the effect of targeting stromal PDGFRα in preclinical lung tumor xenograft models (human tumor, mouse stroma). Effects of anti-human (IMC-3G3) and anti-mouse (1E10) PDGFRα mAbs on proliferation and PDGFRα signaling were evaluated in lung cancer cell lines and mouse fibroblasts. Therapy studies were performed using established PDGFRα-positive H1703 cells and PDGFRα-negative Calu-6, H1993, and A549 subcutaneous tumors in immunocompromised mice treated with vehicle, anti-PDGFRα mAbs, chemotherapy, or combination therapy. Tumors were analyzed for growth and levels of growth factors. IMC-3G3 inhibited PDGFRα activation and the growth of H1703 cells in vitro and tumor growth in vivo, but had no effect on PDGFRα-negative cell lines or mouse fibroblasts. 1E10 inhibited growth and PDGFRα activation of mouse fibroblasts, but had no effect on human cancer cell lines in vitro. In vivo, 1E10-targeted inhibition of murine PDGFRα reduced tumor growth as single-agent therapy in Calu-6 cells and enhanced the effect of chemotherapy in xenografts derived from A549 cells. We also identified that low expression cancer cell expression of VEGF-A and elevated expression of PDGF-AA were associated with response to stromal PDGFRα targeting. We conclude that stromal PDGFRα inhibition represents a means for enhancing control of lung cancer growth in some cases, independent of tumor cell PDGFRα expression.
Platelet-derived growth factor receptor; mouse model; lung cancer; stroma; microenvironment; fibroblast; xenograft
COX-2 is expressed highly in pancreatic cancer and implicated in tumor progression. COX-2 inhibition can reduce tumor growth and augment therapy. The precise function of COX-2 in tumors remains poorly understood, but it is implicated in tumor angiogenesis, evasion of apoptosis, and induction of epithelial-to-mesenchymal transition (EMT). Current therapeutic regimens for pancreatic cancer are minimally effective, highlighting the need for novel treatment strategies. Here, we report that apricoxib, a novel COX-2 inhibitor in phase II clinical trials, significantly enhances the efficacy of gemcitabine/ erlotinib in preclinical models of pancreatic cancer.
Human pancreatic cell lines were evaluated in vitro and in vivo for response to apricoxib ± standard-of-care therapy (gemcitabine + erlotinib). Tumor tissue underwent posttreatment analysis for cell proliferation, viability, and EMT phenotype. Vascular parameters were also determined.
COX-2 inhibition reduced the IC50 of gemcitabine ± erlotinib in six pancreatic cancer cell lines tested in vitro. Furthermore, apricoxib increased the antitumor efficacy of standard combination therapy in several orthotopic xenograft models. In vivo apricoxib combination therapy was only effective at reducing tumor growth and metastasis in tumors with elevated COX-2 activity. In each model examined, treatment with apricoxib resulted in vascular normalization without a decrease in microvessel density and promotion of an epithelial phenotype by tumor cells regardless of basal COX-2 expression.
Apricoxib robustly reverses EMT and augments standard therapy without reducing microvessel density and warrants further clinical evaluation in patients with pancreatic cancer.
The TGFβ pathway is under active consideration as a cancer drug target based on its capacity to promote cancer cell invasion and to create a pro-tumorigenic microenvironment. However, the clinical application of TGFβ inhibitors remains uncertain as genetic studies demonstrate a tumor suppressor function of TGFβ in pancreatic cancer and other epithelial malignancies. Here, we used genetically engineered mouse models to investigate the therapeutic impact of global TGFβ inhibition in pancreatic cancer in relation to tumor stage, genetic profile, and concurrent chemotherapy. We found that αvβ6 integrin acted as a key upstream activator of TGFβ in evolving pancreatic cancers. In addition, TGFβ or αvβ6 blockade increased tumor cell proliferation and accelerated both early and later disease stages. These effects were dependent on the presence of Smad4, a central mediator of TGFβ signaling. Therefore, our findings indicate that αvβ6 and TGFβ act in a common tumor suppressor pathway whose pharmacologic inactivation promotes pancreatic cancer progression.
pancreatic cancer; Transforming growth factor beta; Smad4; beta6 integrin; cancer therapeutics
Vascular endothelial growth factor receptor 2 (VEGFR2) is highly expressed by lymphatic endothelial cells and has been shown to stimulate lymphangiogenesis in adult mice. However, the role VEGFR2 serves in the development of the lymphatic vascular system has not been defined. Here we use the Cre-lox system to show that the proper development of the lymphatic vasculature requires VEGFR2 expression by lymphatic endothelium. We show that Lyve-1wt/Cre;Vegfr2flox/flox mice possess significantly fewer dermal lymphatic vessels than Vegfr2flox/flox mice. Although Lyve-1wt/Cre;Vegfr2flox/flox mice exhibit lymphatic hypoplasia, the lymphatic network is functional and contains all of the key features of a normal lymphatic network (initial lymphatic vessels and valved collecting vessels surrounded by smooth muscle cells (SMCs)). We also show that Lyve-1Cre mice display robust Cre activity in macrophages and in blood vessels in the yolk sac, liver and lung. This activity dramatically impairs the development of blood vessels in these tissues in Lyve-1wt/Cre;Vegfr2flox/flox embryos, most of which die after embryonic day14.5. Lastly, we show that inactivation of Vegfr2 in the myeloid lineage does not affect the development of the lymphatic vasculature. Therefore, the abnormal lymphatic phenotype of Lyve-1wt/Cre;Vegfr2flox/flox mice is due to the deletion of Vegfr2 in the lymphatic vasculature not macrophages. Together, this work demonstrates that VEGFR2 directly promotes the expansion of the lymphatic network and further defines the molecular mechanisms controlling the development of the lymphatic vascular system.
Although cyclooxygenase-2 (COX-2) inhibitors, such as the late stage development drug apricoxib, exhibit antitumor activity, their mechanisms of action have not been fully defined. In this study, we characterized the mechanisms of action of apricoxib in HT29 colorectal carcinoma. Apricoxib was weakly cytotoxic toward naive HT29 cells in vitro but inhibited tumor growth markedly in vivo. Pharmacokinetic analyses revealed that in vivo drug levels peaked at 2–4 µM and remained sufficient to completely inhibit prostaglandin E2 production, but failed to reach concentrations cytotoxic for HT29 cells in monolayer culture. Despite this, apricoxib significantly inhibited tumor cell proliferation and induced apoptosis without affecting blood vessel density, although it did promote vascular normalization. Strikingly, apricoxib treatment induced a dose-dependent reversal of epithelial–mesenchymal transition (EMT), as shown by robust upregulation of E-cadherin and the virtual disappearance of vimentin and ZEB1 protein expression. In vitro, either anchorage-independent growth conditions or forced EMT sensitized HT29 and non-small cell lung cancer cells to apricoxib by 50-fold, suggesting that the occurrence of EMT may actually increase the dependence of colon and lung carcinoma cells on COX-2. Taken together, these data suggest that acquisition of mesenchymal characteristics sensitizes carcinoma cells to apricoxib resulting in significant single-agent antitumor activity.
Secreted protein acidic and rich in cysteine (SPARC) influences the growth of several solid tumors. Our objectives were to determine the effect of SPARC on the growth and response to cisplatin therapy of platinum-resistant ovarian cancer.
SPARC expression was determined in 4 platinum-resistant ovarian cancer cell lines. The effect of increasing SPARC on cell proliferation was determined in vitro. The effect of host-derived SPARC on tumor growth and response to therapy was determined in vivo using the murine ovarian cancer cell line, OSEID8, which was injected into the peritoneum of wild-type (WT) and SPARC-null (SP−/−) mice.
Forced expression of SPARC decreased growth of platinum-resistant ovarian cancer cell lines in vitro. In vivo, tumor growth was more aggressive in the absence of host-derived SPARC resulting in decreased survival compared with WT mice (P = .005). Cisplatin did not improve survival of WT mice. In contrast, cisplatin therapy resulted in a significant survival advantage (P = .0048) and decreased tumor volume (P = .02) in SP−/− animals.
We conclude that SPARC is an important extracellular matrix protein that regulates the growth and chemosensitivity of ovarian cancer. In general, SPARC appears to control tumor cell growth but also impede the efficacy of cisplatin therapy. Therefore, selective inhibition of SPARC may provide an attractive strategy for increasing the efficacy of therapy in platinum-resistant ovarian tumors.
Chemosensitivity; extracellular matrix; murine; ovarian cancer; secreted protein acidic and rich in cysteine
Neovascularization (NV) in the cornea is a major cause of vision impairment and corneal blindness. Hemangiogenesis and lymphangiogenesis induced by inflammation underlie the pathogenesis of corneal NV. The current mainstay treatment, corticosteroid, treats the inflammation associated with corneal NV, but is not satisfactory due to such side effects as cataract and the increase in intraocular pressure. It is imperative to develop a novel therapy that specifically targets the hemangiogenesis, lymphangiogenesis and inflammation pathways underlying corneal NV. Histone deacetylase inhibitors (HDACi) have been in clinical trials for cancer and other diseases. In particular, HDACi suberoylanilide hydroxamic acid (SAHA, vorinostat, Zolinza) has been approved by the FDA for the treatment of cutaneous T-cell lymphoma. The functional mechanism of SAHA in cancer and especially in corneal NV remains unclear. Here, we show that topical application of SAHA inhibits neovascularization in an alkali-burn corneal injury model. Mechanistically, SAHA inhibits corneal NV by repressing hemangiogenesis, inflammation pathways and previously overlooked lymphangiogenesis. Topical SAHA is well tolerated on the ocular surface. In addition, the potency of SAHA in corneal NV appears to be comparable to the current steroid therapy. SAHA may possess promising therapeutic potential in alkali-burn corneal injury and other inflammatory neovascularization disorders.
corneal neovascularization; HDAC; HDAC inhibitor; hemangiogenesis; lymphangiogenesis; inflammation; alkali-burn injury
Perioperative blood transfusion has been linked to decreased survival in pancreatic cancer; however, the exact causal mechanism has not been elucidated. Allogeneic transfusions are known to expose patients to foreign cells and lipid mediators. We hypothesize that stored packed red cells (pRBCs) contain pro-cancer cytokines that augment tumor progression. We analyzed the plasma fraction of stored pRBCs for pro-cancer cytokines and evaluated the affect of both storage time and leukocyte reduction on these mediators.
Chemiarray™ analysis for pro-cancer cytokines was performed on the acellular plasma fraction of stored leukocyte-reduced (LR) and non-leukocyte-reduced (NLR) pRBCs at day 1 (D.1–fresh) and day 42 (D.42–outdate) of storage. Elevated expression of monocyte chemotactic protein-1 (MCP-1), regulated on activation, normal T cell expressed and secreted (RANTES), angiogenin, tumor necrosis factor-alpha (TNF-α), epidermal growth factor (EGF), and platelet-derived growth factor (PDGF) was found. Specific enzyme-linked immunosorbent assay was performed for each of these factors in LR and NLR blood at D.1, day 28, and D.42. Data were analyzed by ANOVA. A p value ≤0.05 was considered significant; N≥4 per group. Migration assays were performed using inhibitors of EGF (gefitinib) and PDGF (imatinib) on murine pancreatic adenocarcinoma cells (Pan02) exposed to D.1 and D.42 LR and NLR plasma. Proliferation assays were performed on Pan02 cells to test the inhibition of PDGF.
MCP-1 levels increased with storage time in LR blood, 86.3±6.3 pg/ml at D.1 vs. 121.2±6.1 pg/ml at D.42 (p=0.007), and NLR blood, 78.2±7.3 pg/ml at D.1 vs. 647.8±220.7 pg/ml at D.42 (p=0.02). RANTES levels are lower in LR compared to NLR stored blood, 3.0±1.9 vs. 15.8±0.7 pg/ml at D.42 (p<0.001), but similar in D.1 blood, 13.8±1.8 pg/ml in LR vs. 12.0±1.6 pg/ml in NLR. Angiogenin levels were different between LR and NLR blood, 0 pg/ml (undetectable) vs. 44.2±3.7 pg/ml (p<0.001). Storage time did not affect concentration. TNF-α levels were not different between LR and NLR blood, and there was no storage time effect on concentration. EGF and PDGF levels increased with storage time in NLR blood only, 216.4±3.8 pg/ml at D.1 vs. 1,436.4±238.6 pg/ml at D.42 for EGF (p=0.001), and 61.6±6.0 pg/ml at D.1 vs. 76.5±1.7 pg/ml at D.42 (p=0.003) for PDGF. Inhibition of EGF reduced migration in Pan02 cells treated with D.42 NLR blood, 245.9±11.2 vs. 164.6±10.6 cells/hpf (p<0.001). Inhibition of PDGF had no effect on Pan02 migration and reduced cell proliferation in cells treated with D.42 NLR, 181.1±1.5% over control vs. 157.5±2.1% (p<0.001).
Pro-cancer cytokines that can augment tumor progression were identified in pRBCs. Some of these factors are present in fresh blood. The soluble factors identified herein may represent possible therapeutic targets to offset negative effects of transfusion. These data stress the need for efforts in cancer patients to reduce transfusion requirements if needed.
Transfusion; Cancer; Storage lesion; Cytokines
Lung cancer is the leading cause of cancer-related mortality, and about 85% of the cases are non-small-cell lung cancer (NSCLC). Importantly, recent advance in cancer research suggests that altering cancer cell bioenergetics can provide an effective way to target such advanced cancer cells that have acquired mutations in multiple cellular regulators. This study aims to identify bioenergetic alterations in lung cancer cells by directly measuring and comparing key metabolic activities in a pair of cell lines representing normal and NSCLC cells developed from the same patient. We found that the rates of oxygen consumption and heme biosynthesis were intensified in NSCLC cells. Additionally, the NSCLC cells exhibited substantially increased levels in an array of proteins promoting heme synthesis, uptake and function. These proteins include the rate-limiting heme biosynthetic enzyme ALAS, transporter proteins HRG1 and HCP1 that are involved in heme uptake, and various types of oxygen-utilizing hemoproteins such as cytoglobin and cytochromes. Several types of human tumor xenografts also displayed increased levels of such proteins. Furthermore, we found that lowering heme biosynthesis and uptake, like lowering mitochondrial respiration, effectively reduced oxygen consumption, cancer cell proliferation, migration and colony formation. In contrast, lowering heme degradation does not have an effect on lung cancer cells. These results show that increased heme flux and function are a key feature of NSCLC cells. Further, increased generation and supply of heme and oxygen-utilizing hemoproteins in cancer cells will lead to intensified oxygen consumption and cellular energy production by mitochondrial respiration, which would fuel cancer cell proliferation and progression. The results show that inhibiting heme and respiratory function can effectively arrest the progression of lung cancer cells. Hence, understanding heme function can positively impact on research in lung cancer biology and therapeutics.
The molecular mechanisms that control the balance between antiangiogenic and proangiogenic factors and initiate the angiogenic switch in tumors remain poorly defined. By combining chemical genetics with multimodal imaging, we have identified an autocrine feed-forward loop in tumor cells in which tumor-derived VEGF stimulates VEGF production via VEGFR2-dependent activation of mTOR, substantially amplifying the initial proangiogenic signal. Disruption of this feed-forward loop by chemical perturbation or knockdown of VEGFR2 in tumor cells dramatically inhibited production of VEGF in vitro and in vivo. This disruption was sufficient to prevent tumor growth in vivo. In patients with lung cancer, we found that this VEGF:VEGFR2 feed-forward loop was active, as the level of VEGF/VEGFR2 binding in tumor cells was highly correlated to tumor angiogenesis. We further demonstrated that inhibition of tumor cell VEGFR2 induces feedback activation of the IRS/MAPK signaling cascade. Most strikingly, combined pharmacological inhibition of VEGFR2 (ZD6474) and MEK (PD0325901) in tumor cells resulted in dramatic tumor shrinkage, whereas monotherapy only modestly slowed tumor growth. Thus, a tumor cell-autonomous VEGF:VEGFR2 feed-forward loop provides signal amplification required for the establishment of fully angiogenic tumors in lung cancer. Interrupting this feed-forward loop switches tumor cells from an angiogenic to a proliferative phenotype that sensitizes tumor cells to MAPK inhibition.
Secreted protein acidic and rich in cysteine (SPARC) has been implicated in multiple
aspects of human cancer. However, its role in bladder carcinogenesis and metastasis
are unclear,with some studies suggesting it may be a promoter and others arguing the
opposite. Using a chemical carcinogenesis model in Sparc-deficient
mice and their wild-type littermates, we found that loss of SPARC accelerated the
development of urothelial preneoplasia (atypia and dysplasia), neoplasia, and
metastasis and was associated with decreased survival. SPARC reduced
carcinogen-induced inflammation and accumulation of reactive oxygen species as well
as urothelial cell proliferation. Loss of SPARC was associated with an inflammatory
phenotype of tumor-associated macrophages and fibroblasts, with concomitant increased
activation of urothelial and stromal NF-κB and AP1 in vivo and in vitro.
Syngeneic spontaneous and experimental metastasis models revealed that tumor- and
stroma-derived SPARC reduced tumor growth and metastasis through inhibition of
cancer-associated inflammation and lung colonization. In human bladder tumor tissues,
the frequency and intensity of SPARC expression were inversely correlated with
disease-specific survival. These results indicate that SPARC is produced by benign
and malignant compartments of bladder carcinomas where it functions to suppress
bladder carcinogenesis, progression, and metastasis.
Inhibitors of apoptosis proteins (IAPs) are key regulators of apoptosis and are inhibited by the second mitocondrial activator of caspases (SMAC). Previously, a small subset of TNFα-expressing non-small cell lung cancers (NSCLCs) was found to be sensitive to SMAC mimetics alone. In this study we determined if a SMAC mimetic (JP1201) could sensitize non-responsive NSCLC cell lines to standard chemotherapy. We found that JP1201 sensitized NSCLCs to doxorubicin, erlotinib, gemcitabine, paclitaxel, vinorelbine, and the combination of carboplatin with paclitaxel in a synergistic manner at clinically achievable drug concentrations. Sensitization did not occur with platinum alone. Furthermore, sensitization was specific for tumor compared to normal lung epithelial cells, increased in NSCLCs harvested after chemotherapy treatment, and did not induce TNFα secretion. Sensitization also was enhanced in vivo with increased tumor inhibition and increased survival of mice carrying xenografts. These effects were accompanied by caspase 3, 4, and 9 activation, indicating that both mitochondrial and ER stress-induced apoptotic pathways are activated by the combination of vinorelbine and JP1201. Chemotherapies that induce cell death through the mitochondrial pathway required only inhibition of XIAP for sensitization, while chemotherapies that induce cell death through multiple apoptotic pathways required inhibition of cIAP1, cIAP2, and XIAP. Therefore, the data suggest that IAP-targeted therapy using a SMAC mimetic provides a new therapeutic strategy for synergistic sensitization of NSCLCs to standard chemotherapy agents, which appears to occur independently of TNFα secretion.
non-small cell lung cancer; smac mimetic; vinorelbine; gemcitabine; IAPs
Lung cancer (LC) is a leading cause of death worldwide. Recent advances in chemotherapeutic agents have not yielded any significant improvement in the prognosis of patients with LC. The five-year survival rate for all combined disease stages remains about 15%. For this reason, new therapies such as those that inhibit tumor angiogenesis or block activity of growth factor receptors are of special interest in this group of patients. In this review we will summarize the most recent clinical data on biologic therapies that inhibit tumor angiogenesis in LC, focusing on those that are most clinically relevant.
lung cancer; angiogenesis; VEGF; antiangiogenesis
Perioperative blood transfusion in pancreatic cancer patients is linked to decreased survival; however, a causal mechanism has not been determined. During processing and storage of packed red blood cells (pRBCs) biologically active molecules accumulate in the acellular plasma fraction; therefore, we hypothesize that the plasma fraction of pRBCs promotes tumor progression.
Proliferation and migration of murine pancreas cancer and control cells were determined in vitro in response to the plasma fraction from leukocyte and non-leukocyte reduced, fresh versus stored pRBCs. Lastly, an immunocompetent murine model was used to assess the affect of the plasma fraction of pRBCs on pancreas cancer progression.
Incubation of pancreatic cancer cells with the plasma fraction of pRBCs increased proliferation and migration. Intravenous delivery of the acellular plasma fraction to mice with pancreatic cancer significantly increased the tumor weight in both leukocyte reduced and non-leukocyte reduced pRBCs groups (p<0.01) although tumor growth and morbidity was greatest in the non-leukocyte reduced group.
The plasma fraction of stored pRBCs promotes murine pancreatic cancer proliferation and migration in vitro and when administered intravenously significantly augments pancreatic cancer growth in immunocompetent mice.
transfusion; pancreas cancer; metastasis; proliferation; erythrocytes; immunomodulation
The innate immune signaling kinase, TBK1, couples pathogen surveillance to induction of host defense mechanisms. Pathological activation of TBK1 in cancer can overcome programmed cell death cues, enabling cells to survive oncogenic stress. The mechanistic basis of TBK1 prosurvival signaling, however, has been enigmatic. Here we show that TBK1 directly activates AKT by phosphorylation of the canonical activation loop and hydrophobic motif sites independently of PDK1 and mTORC2. Upon mitogen stimulation, triggering of the innate immune response, re-exposure to glucose, or oncogene activation, TBK1 is recruited to the exocyst, where it activates AKT. In cells lacking TBK1, insulin activates AKT normally, but AKT activation by exocyst-dependent mechanisms is impaired. Discovery and characterization of a 6-aminopyrazolopyrimidine derivative, as a selective low nanomolar TBK1 inhibitor, indicates this regulatory arm can be pharmacologically perturbed independently of canonical PI3K/PDK1 signaling. Thus, AKT is a direct TBK1 substrate that connects TBK1 to prosurvival signaling.
Pancreatic adenocarcinoma, a desmoplastic disease, is the fourth leading cause of cancer-related death in the Western world due, in large part, to locally invasive primary tumor growth and ensuing metastasis. SPARC is a matricellular protein that governs extracellular matrix (ECM) deposition and maturation during tissue remodeling, particularly, during wound healing and tumorigenesis. In the present study, we sought to determine the mechanism by which lack of host SPARC alters the tumor microenvironment and enhances invasion and metastasis of an orthotopic model of pancreatic cancer. We identified that levels of active TGFβ1 were increased significantly in tumors grown in SPARC-null mice. TGFβ1 contributes to many aspects of tumor development including metastasis, endothelial cell permeability, inflammation and fibrosis, all of which are altered in the absence of stromal-derived SPARC. Given these results, we performed a survival study to assess the contribution of increased TGFβ1 activity to tumor progression in SPARC-null mice using losartan, an angiotensin II type 1 receptor antagonist that diminishes TGFβ1 expression and activation in vivo. Tumors grown in SPARC-null mice progressed more quickly than those grown in wild-type littermates leading to a significant reduction in median survival. However, median survival of SPARC-null animals treated with losartan was extended to that of losartan-treated wild-type controls. In addition, losartan abrogated TGFβ induced gene expression, reduced local invasion and metastasis, decreased vascular permeability and altered the immune profile of tumors grown in SPARC-null mice. These data support the concept that aberrant TGFβ1-activation in the absence of host SPARC contributes significantly to tumor progression and suggests that SPARC, by controlling ECM deposition and maturation, can regulate TGFβ availability and activation.
SPARC prevents endoglin association with αV integrin, which blocks the activation of TGF-β signaling and promotes pericyte migration to nascent blood vessels.
Pericytes migrate to nascent vessels and promote vessel stability. Recently, we reported that secreted protein acidic and rich in cysteine (SPARC)–deficient mice exhibited decreased pericyte-associated vessels in an orthotopic model of pancreatic cancer, suggesting that SPARC influences pericyte behavior. In this paper, we report that SPARC promotes pericyte migration by regulating the function of endoglin, a TGF-β1 accessory receptor. Primary SPARC-deficient pericytes exhibited increased basal TGF-β1 activity and decreased cell migration, an effect blocked by inhibiting TGF-β1. Furthermore, TGF-β–mediated inhibition of pericyte migration was dependent on endoglin and αV integrin. SPARC interacted directly with endoglin and reduced endoglin interaction with αV integrin. SPARC deficiency resulted in endoglin-mediated blockade of pericyte migration, aberrant association of endoglin in focal complexes, an increase in αV integrins present in endoglin immunoprecipitates, and enhanced αV integrin–mediated activation of TGF-β. These results demonstrate that SPARC promotes pericyte migration by diminishing TGF-β activity and identify a novel function for endoglin in controlling pericyte behavior.
There is growing evidence that vascular endothelial growth factor-A (VEGF-A), a ligand of the receptor tyrosine kinases VEGFR1 and VEGFR2, promotes lymphangiogenesis. However, the underlying mechanisms by which VEGF-A induces the growth of lymphatic vessels remain poorly defined. Here we report that VEGFR2, not VEGFR1, is the primary receptor regulating VEGF-A-induced lymphangiogenesis. We show that specific inhibition of VEGF-A/VEGFR2 signaling with the fully human monoclonal antibody r84 significantly inhibits lymphangiogenesis in MDA-MB-231 tumors. In vitro experiments with primary human dermal lymphatic endothelial cells (LECs) demonstrate that blocking VEGF-A activation of VEGFR2, not VEGFR1, significantly inhibits VEGF-A-induced proliferation and migration of LECs. We show that VEGF-A stimulation of LECs leads to the phosphorylation of VEGFR2 (Tyr 951, 1054, 1059, 1175, and 1214) which subsequently triggers PKC dependent phosphorylation of ERK1/2 and PI3-K dependent phosphorylation of Akt. Additionally, we demonstrate that inhibitors that suppress the phosphorylation of ERK1/2 and Akt significantly block VEGF-A- induced proliferation and migration of LECs. Together, these results shed light on the mechanisms regulating VEGF-A-induced proliferation and migration of LECs, reveal that VEGFR2 is the primary signaling VEGF-A receptor on lymphatic endothelium, and suggest that therapeutic agents targeting the VEGF-A/VEGFR2 axis could be useful in blocking the pathological formation of lymphatic vessels.
Several studies demonstrate that hematopoietic tissues are a source of endothelial progenitor cells (EPCs), which contribute to newly formed blood vessels during tissue repair in adults. However, it is not clear which cell type in these hematopoietic tissues gives rise to EPCs.
To identity the origin of endothelial progenitors within the hematopoietic hierarchy, and assess their in vivo revascularization potential.
Methods and Results
Using a single cell sorting approach and in vitro multi-lineage differentiation assays, here we show that individual CD34+CD45+CD133+CD38+ cells from cord blood uniquely have the ability to differentiate into T and B lymphoid, myeloid, and endothelial cells. The latter were characterized by the expression of VE-cadherin, KDR, vWF, eNOs, the lack of CD45, CD133 and c-fms. Unexpectedly when transplanted into hind-limb ischemic NOD-scid IL2Rgammanull mice, freshly-isolated CD34+CD45+CD133+CD38+ cells maintained their hematopoietic identity and were rarely found to integrate into host blood vessels. Nevertheless, they significantly improve perfusion, most likely through a paracrine mechanism. On the other hand, endothelial cells derived in vitro from this fraction, are able to form vessels in vivo in both Matrigel plug and hind-limb ischemia transplantation assays.
These findings indicate that the CD34+CD45+CD133+CD38+ cell fraction contains a common progenitor for the hematopoietic and vascular lineages, and may represent a valuable cell source for therapeutic applications.
Cord blood; clonal analyses; endothelial progenitors; ischemia; engraftment
To investigate the frequency of xenotropic murine leukemia virus (MLV) presence in human cell lines established from mouse xenografts and to search for the evidence of horizontal viral spread to other cell lines.
Six of 23 (26%) mouse DNA free xenograft cultures were strongly positive for MLV and their sequences had greater than 99% homology to known MLV strains. Four of five available supernatant fluids from these viral positive cultures were strongly positive for RT activity. Three of these supernatant fluids were studied to confirm the infectivity of the released virions for other human culture cells. Of the 78 non-xenograft derived cell lines maintained in the xenograft culture-containing facilities, 13 (17%) were positive for MLV, including XMRV, a virus strain first identified in human tissues. By contrast, all 50 cultures maintained in a xenograft culture-free facility were negative for viral sequences.
We examined xenograft tumor cell lines from seven independent laboratories and 128 non-xenografted tumor cell lines. Cell line DNA was examined for mouse DNA contamination, and by 3 Taqman qPCR assays targeting the gag, env or pol regions of MLV. Sequencing was used for viral strain identification. Supernatant fluids were tested for reverse transcriptase (RT) activity.
Human cultures derived after mouse xenografting frequently contain and release highly infectious xenotropic MLV viruses. Laboratories working with xenograft-derived human cultures should be aware of the risk of contamination with potentially biohazardous human-tropic mouse viruses and their horizontal spread to other cultures.
xenograft cultures; xenotropic murine leukemia virus; retrovirus; XMRV virus; cell cultures; lung cancer; prostate cell line
The synthesis of a polylysine dendron containing eight GdDOTA units conjugated to peptoid dimer known to have a high affinity for the vascular endothelial growth factor receptor 2 (VEGFR2) is described. This simple low molecular weight system with a molecular r1 relaxivity of ~48 mM−1s−1 is shown to enhance MR images of tumors grown in mice in vivo.