The angiogenic switch, a rate-limiting step in tumor progression, has already occurred by the time most human tumors are detectable. However, despite significant study of the mechanisms controlling this switch, the kinetics and reversibility of the process have not been explored. The stability of the angiogenic phenotype was examined using an established human liposarcoma xenograft model. Nonangiogenic cells inoculated into immunocompromised mice formed microscopic tumors that remained dormant for approximately 125 days (vs. <40 days for angiogenic cells) whereupon the vast majority (>95%) initiated angiogenic growth with second-order kinetics. These original, clonally derived angiogenic tumor cells were passaged through four in vivo cycles. At each cycle, a new set of single-cell clones was established from the most angiogenic clone and characterized for in vivo for tumorigenic activity. A total of 132 single-cell clones were tested in the second, third, and fourth in vivo passage. Strikingly, at each passage, a portion of the single-cell clones formed microscopic, dormant tumors. Following dormancy, like the original cell line, these revertant tumors spontaneously switched to the angiogenic phenotype. Finally, revertant clones were transcriptionally profiled and their angiogenic output determined. Collectively, these data demonstrate that the angiogenic phenotype in tumors is malleable and can spontaneously revert to the nonangiogenic phenotype in a population of human tumor cells.
Diabetes mellitus is a disease with considerable morbidity and mortality worldwide. Breakdown of the blood-retinal barrier and leakage from the retinal vasculature leads to diabetic macular edema, an important cause of vision loss in patients with diabetes. Although epidemiologic studies and randomized clinical trials suggest that glycemic control plays a major role in the development of vascular complications of diabetes, insulin therapies for control of glucose metabolism cannot prevent long-term retinal complications. The phenomenon of temporary paradoxical worsening of diabetic macular edema after insulin treatment has been observed in a number of studies. In prospective studies on non-insulin-dependent (type 2) diabetes mellitus patients, a change in treatment from oral drugs to insulin was often associated with a significant increased risk of retinopathy progression and visual impairment. Although insulin therapies are critical for regulation of the metabolic disease, their role in the retina is controversial. In this study with diabetic mice, insulin treatment resulted in increased vascular leakage apparently mediated by betacellulin and signaling via the epidermal growth factor (EGF) receptor. In addition, treatment with EGF receptor inhibitors reduced retinal vascular leakage in diabetic mice on insulin. These findings provide unique insight into the role of insulin signaling in mediating retinal effects in diabetes and open new avenues for therapeutics to treat the retinal complications of diabetes mellitus.
We investigated the use of dietary omega-3 (?-3) polyunsaturated fatty acids (PUFAs) in the treatment of neuroblastoma both as a sole agent and in combination with sunitinib, a broad-spectrum tyrosine kinase receptor inhibitor.
Despite recent advances and better understanding of the etiology and the pathogenesis of gastrointestinal ulcer diseases, e.g., duodenal ulcer, the molecular events leading to ulcer development, delayed healing, and recurrence remain poorly elucidated.
An angiogenesis inhibitor named Beta-35 has been identified and purified from the conditioned medium of mouse pancreatic ? cells tumor cells. Beta-35 has a molecular weight of 35 kDa and inhibits DNA synthesis of bovine capillary endothelial cells at a half-maximal concentration of approximately 5 nM. It shows anti-angiogenic activity in the chick embryo chorioallantoic membrane at a dose of about 1 ?g/embryo. Amino acid microsequencing and mass spectrometric analysis of the purified protein demonstrate that Beta-35 contains the first 314 residues of the N-terminal sequence of bovine transferrin. We have cloned and expressed this protein in Escherichia coli using the corresponding gene segment of Beta-35 contained in the cDNA of human transferrin. The recombinant protein of Beta-35 shows significant anti-tumor activity at a dose of 5mg/kg/day against human pancreatic cancer or melanoma implanted subcutaneously in SCID mice.
Endometriosis is a debilitating disease characterized by the growth of ectopic endometrial tissue. It is widely accepted that angiogenesis plays an integral part in the establishment and growth of endometriotic lesions. Recent data from a variety of angiogenesis-dependent diseases suggest a critical role of bone marrow-derived endothelial progenitor cells (EPCs) in neovascularization. In this study we examined the blood levels of EPCs and mature circulating endothelial cells in a mouse model of surgically induced endometriosis. Fluorescence-activated cell sorting analysis revealed elevated levels of EPCs in the blood of mice with endometriosis compared with control subject that underwent a sham operation. EPC concentrations positively correlated with the amount of endometriotic tissue and peaked 1 to 4 days after induction of disease. In a green fluorescent protein bone marrow transplant experiment we found green fluorescent protein-positive endothelial cells incorporated into endometriotic lesions but not eutopic endometrium, as revealed by flow cytometry and immunohistochemistry. Finally, treatment of endometriosis-bearing mice with the angiogenesis inhibitor Lodamin, an oral nontoxic formulation of TNP-470, significantly decreased EPC levels while suppressing lesion growth. Taken together, our data indicate an important role for bone marrow-derived endothelial cells in the pathogenesis of endometriosis and support the potential clinical use of anti-angiogenic therapy as a novel treatment modality for this disease.
Tumors implanted near the scapulae have been shown to grow four times faster than the same tumors implanted at the iliac crest. Although there were marked differences in the vascularization of tumors from these two different sites, the mechanism controlling regional angiogenesis was not identified. Here, we show site-specific growth of intraperitoneal tumor implants in the mouse abdomen. Our data indicate that the angiogenic response of the host differs significantly between the upper and lower sites in the mouse abdomen and reveal that the expansion of tumor mass is restricted to sites with low angiogenic responses, such as the bowel mesentery in the lower abdomen. We show that, in this model, this suppression of angiogenesis is due to an expression gradient of thrombospondin-1 (TSP-1), a potent endogenous angiogenesis inhibitor. Mice with a targeted deletion of TSP-1 no longer show regional restriction of tumor growth. The physiologic relevance of these findings may be seen in patients with peritoneal carcinomatosis, whereby tumors spread within the peritoneal cavity and show differential growth in the upper and lower abdomen. We hypothesize that the difference in tumor growth in these patients may be due to a gradient of TSP-1 expression in stroma. Finally, our studies suggest that upregulation of TSP-1 in tumor cells is one method to suppress the growth of tumors in the upper abdomen.
Platelets sequester angiogenesis regulatory proteins early in tumor growth, which suggests a new avenue for monitoring disease. To date, there are no clinically relevant reference ranges for markers of early angiogenesis. We introduce a new ELISA-based method for accurate and reproducible measurement of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), platelet factor 4 (PF4), thrombospondin-1 (TSP-1), fibroblast growth factor, basic (bFGF), and endostatin in platelets. To facilitate clinical applicability, the platelet levels in isolated samples were determined utilizing a new actin ELISA method. Platelets from healthy donors at single and repetitive time points were used for the assessment of normal ranges of these proteins. The physiological levels in platelets were: VEGF (0.74 +/- 0.37 pg/10(6) platelets); PDGF (23 +/- 6 pg/10(6)); PF4 (12 +/- 5 ng/10(6)); TSP-1 (31 +/- 12 ng/10(6)); bFGF (0.44 +/- 0.15 pg/10(6)); and endostatin (5.6 +/- 3.0 pg/10(6)). There was an excellent correlation (R(2) = 0.7) between the platelet levels calculated with the actin ELISA and complete blood count. The levels of the platelets were higher than those in platelet-poor plasma by factors of: VEGF (215-fold); PDGF (914-fold); PF-4 (516-fold); TSP-1 (813-fold); and bFGF (17-fold). The endostatin levels were nearly equivalent. The biovariability of the platelet proteins in eight healthy subjects over a 5-week period was found to be minimal. We describe accurate and direct measurements of the concentrations of VEGF, bFGF, PDGF, TSP-1, endostatin, and PF4 in platelets of healthy human subjects. In contrast to the highly variable levels in plasma and serum, the platelet-derived measurements were accurate and reproducible with minimal biovariability.
The chemotherapeutic agent etoposide is a topoisomerase II inhibitor widely used for cancer therapy. Low-dose oral etoposide, administered at close regular intervals, has potent anti-tumor activity in patients who are refractory to intravenous etoposide; however, the mechanism remains unclear. Since endothelial cells may be more sensitive than tumor cells to chemotherapy agents, we determined the effects of etoposide alone and in combination with oral cyclooxygenase-2 inhibitors and peroxisome-proliferator activated receptor ? ligands on angiogenesis and tumor growth in xenograft tumor models. Optimal anti-angiogenic (metronomic) and anti-tumor doses of etoposide on angiogenesis, primary tumor growth and metastasis were established alone and in combination therapy. Etoposide inhibited endothelial and tumor cell proliferation, decreased vascular endothelial growth factor (VEGF) production by tumor cells and suppressed endothelial tube formation at non-cytotoxic concentrations. In our in vivo studies, oral etoposide inhibited fibroblast growth factor 2 and VEGF-induced corneal neovascularization, VEGF-induced vascular permeability and increased levels of the endogenous angiogenesis inhibitor endostatin in mice. In addition, etoposide inhibited Lewis lung carcinoma (LLC) and human glioblastoma (U87) primary tumor growth as well as spontaneous lung metastasis in a LLC resection model. Furthermore, etoposide had synergistic anti-tumor activity in combination with celecoxib and rosiglitazone, which are also oral anti-angiogenic and anti-tumor agents. Etoposide inhibits angiogenesis in vitro and in vivo by indirect and direct mechanisms of action. Combining etoposide with celecoxib and rosiglitazone increases its efficacy and merits further investigation in future clinical trials to determine the potential usefulness of etoposide in combinatory anti-angiogenic chemotherapy.
Diabetic maculopathy, the leading cause of vision loss in patients with type 2 diabetes, is characterized by hyper-permeability of retinal blood vessels with subsequent formation of macular edema and hard exudates. The degree of hyperglycemia and duration of diabetes have been suggested to be good predictors of retinal complications. Intervention studies have determined that while intensive treatment of diabetes reduced the development of proliferative diabetic retinopathy it was associated with a two to three-fold increased risk of severe hypoglycemia. Thus we hypothesized the need to identify downstream glycemic targets, which induce retinal vascular permeability that could be targeted therapeutically without the additional risks associated with intensive treatment of the hyperglycemia. Betacellulin is a 32 kD member of the epidermal growth factor family with mitogenic properties for the retinal pigment epithelial cells. This led us to hypothesize a role for betacellulin in the retinal vascular complications associated with diabetes.
Vascular endothelial growth factor VEGF(165) is a critical element for development of the vascular system in physiological and pathological angiogenesis. VEGF isoforms have different affinities for heparan sulphate proteoglycan (HSPG) as well as for VEGF receptors; HSPGs are important regulators in vascular development. Therefore, inhibition of interactions between VEGF and HSPGs may prevent angiogenesis. Here, we demonstrate that an HSPG-binding synthetic peptide, corresponding to exon 6a-encoded domain of VEGF gene, has anti-angiogenic property. This 20 amino acids synthetic peptide prevents VEGF(165) binding to several different cell types, mouse embryonic sections and inhibits endothelial cell migration, despite its absence in VEGF(165) sequence. Our in vivo anti-tumor studies show that the peptide inhibits tumor growth in both mouse Lewis-Lung Carcinoma and human Liposarcoma tumor-bearing animal models. This is the first evidence that a synthetic VEGF fragment corresponding to exon 6a has functional antagonism both in vitro and in vivo. We conclude that the above HPSG binding peptide (6a-P) is a potent inhibitor of angiogenesis-dependent diseases.
2-methoxyestradiol (2ME2) is a potent antiangiogenic molecule that inhibits the expression of hypoxia-inducible factor (HIF)-1alpha and, consequently, of VEGF and other HIF-1alpha target genes. Although 2ME2 is elevated during pregnancy in maternal serum, its presence in fetal fluids and its impact in neonatal health are unknown. In this study, we 1) described normal levels of 2ME2 in maternal blood, cord blood, breast milk, and amniotic fluid, and 2) compared a composite measure of perinatal outcome between infants born with high and low levels of 2ME2. We found that 2ME2 was significantly decreased in all fluids compared with prepartum maternal serum. After stratifying babies by 2ME2 exposure levels, we observed no differences in the vulnerability to impaired lung development or to complications involving aberrant angiogenesis or vascular leak, such as necrotizing enterocolitis (NEC), intraventricular hemorrhage (IVH), posthemorrhagic hydrocephalus (PHH), and retinopathy of prematurity (ROP). In summary, fetal 2ME2 concentrations do not appear to affect neonatal outcome.
The sequential events leading to tumor progression include a switch to the angiogenic phenotype, dependent on a shift in the balance between positive and negative angiogenic regulators produced by tumor and stromal cells. Although the biologic properties of many angiogenesis regulatory proteins have been studied in detail, the mechanisms of their transport and delivery in vivo during pathologic angiogenesis are not well understood. Here, we demonstrate that expression of one of the most potent angiogenesis inhibitors, thrombospondin-1, is up-regulated in the platelets of tumor-bearing mice. We establish that this up-regulation is a consequence of both increased levels of thrombospondin-1 mRNA in megakaryocytes, as well as increased numbers of megakaryocytes in the bone marrow of tumor-bearing mice. Through the use of mouse tumor models and bone marrow transplantations, we show that platelet-derived thrombospondin-1 is a critical negative regulator during the early stages of tumor angiogenesis. Collectively, our data suggest that the production and delivery of the endogenous angiogenesis inhibitor thrombospondin-1 by platelets may be a critical host response to suppress tumor growth through inhibiting tumor angiogenesis. Further, this work implicates the use of thrombospondin-1 levels in platelets as an indicator of tumor growth and regression.
Within three decades, anti-angiogenic therapy has rapidly evolved into an integral component of current standard anti-cancer treatment. Anti-angiogenic therapy has fulfilled a number of its earlier proposed promises. The universality of this approach is demonstrated by the broad spectrum of malignant and benign tumor entities, as well as non-neoplastic diseases, that are currently treated with anti-angiogenic agents. In contrast to tumor cell targeting therapies, the development of acquired drug resistance (e.g., via mutations in growth factor receptor signaling genes) has not been described yet for the principal target of anti-angiogenic therapy--the tumor endothelium. Moreover, the tumor endothelium has emerged as a critical target of conventional cancer therapies, such as chemotherapy and radiotherapy. The presumption that tumor growth and metastasis are angiogenesis-dependent implies that the number of potential targets of an anti-cancer therapy could be reduced to those that stimulate the angiogenesis process. Therefore, the set of endogenous angiogenesis stimulants might constitute an "Achilles heel" of cancer. Direct targeting of tumor endothelium via, e.g., endogenous angiogenesis inhibitors poses another promising but clinically less explored therapeutic strategy. Indeed, the majority of current anti-angiogenic approaches block the activity of a single or at most a few pro-angiogenic proteins secreted by tumor cells or the tumor stroma. Based on our systems biology work on the angiogenic switch, we predicted that the redundancy of angiogenic signals might limit the efficacy of anti-angiogenic monotherapies. In support of this hypothesis, emerging experimental evidence suggests that tumors may become refractory or even evade the inhibition of a single pro-angiogenic pathway via compensatory upregulation of alternative angiogenic factors. Here, we discuss current concepts and propose novel strategies to overcome tumor evasion of anti-angiogenic therapy. We believe that early detection of tumors, prediction of tumor evasive mechanisms and rational design of anti-angiogenic combinations will direct anti-angiogenic therapy towards its ultimate goal--the conversion of cancer to a dormant, chronic, manageable disease.
Patients with Alport syndrome progressively lose renal function as a result of defective type IV collagen in their glomerular basement membrane. In mice lacking the alpha3 chain of type IV collagen (Col4A3 knockout mice), a model for Alport syndrome, transplantation of wild-type bone marrow repairs the renal disease. It is unknown whether cell-based therapies that do not require transplantation have similar potential. Here, infusion of wild-type bone marrow-derived cells into unconditioned, nonirradiated Col4A3 knockout mice during the late stage of disease significantly improved renal histology and function. Furthermore, transfusion of unfractionated wild-type blood into unconditioned, nonirradiated Col4A3 knockout mice improved the renal phenotype and significantly improved survival. Injection of mouse and human embryonic stem cells into Col4A3 knockout mice produced similar results. Regardless of treatment modality, the improvement in the architecture of the glomerular basement membrane is associated with de novo expression of the alpha3(IV) chain. These data provide further support for testing cell-based therapies for Alport syndrome.
New blood vessel growth via angiogenesis is a fundamental process in both physiological and pathological conditions. Physiological angiogenesis is critical during embryogenesis and placental development, whereas pathological angiogenesis plays an important role in the progression of many diseases, most notably tumor growth. Tumor angiogenesis is well accepted to be regulated by a balance of proangiogenic and antiangiogenic factors produced both by tumor cells and surrounding stromal cells. For many years, investigation of antiangiogenic therapies for cancer has focused on the proangiogenic cytokine, vascular endothelial growth factor; its receptors; or downstream signaling pathways. However, more recently with the identification of endogenous angiogenesis inhibitors, studies have turned toward understanding the role of endogenous antiangiogenic proteins in preventing disease progression. Clinical clues have suggested that specific populations may have dysregulated angiogenesis due to differential expression of endogenous angiogenesis regulators. For example, individuals with Down syndrome may possess a systemic antiangiogenic state with a significantly decreased incidence of angiogenesis-dependent diseases. Our work suggests that endogenous angiogenesis inhibitors may be the master regulators controlling progression of angiogenesis-dependent diseases such as vascular anomalies and cancer. The molecular regulation of angiogenesis is not yet fully understood; however, the Down syndrome population may give us insights toward novel therapies for controlling angiogenesis in disease.
Angiostatin, a proteolytic fragment of plasminogen, is a potent endogenous antiangiogenic agent. The molecular mechanisms governing angiostatins antiangiogenic and antitumor effects are not well understood. Here, we report the identification of mitochondrial compartment as the ultimate target of angiostatin. After internalization of angiostatin into the cell, at least 2 proteins within the mitochondria bind this molecule: malate dehydrogenase, a member of Krebs cycle, and adenosine triphosphate synthase. In vitro and in vivo studies revealed differential regulation of key prosurvival and angiogenesis-related proteins in angiostatin-treated tumors and tumor-endothelium. Angiostatin induced apoptosis via down-regulation of mitochondrial BCL-2. Angiostatin treatment led to down-regulation of c-Myc and elevated levels of another key antiangiogenic protein, thrombospondin-1, reinforcing its antitumor and antiangiogenic effects. Further evidence is provided for reduced recruitment and infiltration of bone marrow-derived macrophages in angiostatin-treated tumors. The observed effects of angiostatin were restricted to the tumor site and were not observed in other major organs of the mice, indicating unique tumor specific bioavailability. Together, our data suggest mitochondria as a novel target for antiangiogenic therapy and provide mechanistic insights to the antiangiogenic and antitumor effects of angiostatin.
The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI) gefitinib and erlotinib benefit some non-small cell lung cancer (NSCLC) patients, but most do not respond (primary resistance) and those who initially respond eventually progress (acquired resistance). EGFR TKI resistance is not completely understood and has been associated with certain EGFR and K-RAS mutations and MET amplification.
Clinical trials with antiangiogenic agents have not been able to validate plasma or serum levels of angiogenesis regulators as reliable markers of cancer presence or therapeutic response. We recently reported that platelets contain numerous proteins that regulate angiogenesis. We now show that accumulation of angiogenesis regulators in platelets of animals bearing malignant tumors exceeds significantly their concentration in plasma or serum, as well as their levels in platelets from non-tumor-bearing animals. This process is selective, as platelets do not take up a proportional amount of other plasma proteins (eg, albumin), even though these may be present at higher concentrations. We also find that VEGF-enriched Matrigel pellets implanted subcutaneously into mice or the minute quantities of VEGF secreted by microscopic subcutaneous tumors (0.5-1 mm(3)) result in an elevation of VEGF levels in platelets, without any changes in its plasma levels. The profile of other angiogenesis regulatory proteins (eg, platelet-derived growth factor, basic fibroblast growth factor) sequestered by platelets also reflects the presence of tumors in vivo before they can be macroscopically evident. The ability of platelets to selectively take up angiogenesis regulators in cancer-bearing hosts may have implications for the diagnosis and management of many angiogenesis-related diseases and provide a guide for antiangiogenic therapies.
A young girl with an arteriovenous malformation involving the right upper extremity developed rapidly progressive bony destruction that did not respond to embolization. Treatment with marimastat, starting at 3 years of age, resulted in rapid resolution of pain and gradual healing of bony destruction, associated with regression of the intraosseous arteriovenous shunts. New arteriovenous shunts with bony destruction developed over the years and responded to an increase in the dose of marimastat. Interruption of therapy resulted in recurrence of pain and formation of new lesions. The patient has been treated in this way for 12 years with no adverse effects from the drug.
Tumor progression is dependent on a number of sequential steps, including initial recruitment of blood vessels (i.e., angiogenic switch). Failure of a microscopic tumor to complete one or more of these early steps may lead to delayed clinical manifestation of the cancer. In this review we summarize some of the clinical and experimental evidence suggesting that microscopic human cancers can remain in an asymptomatic, non-detectable, and occult state for the life of a person or animal. We present three clinical cases where tumors present shortly after an accidental trauma in otherwise healthy individuals. We also review current experimental human tumor dormancy models with special emphasis on the angiogenic switch which closely recapitulates clinically observed delay in tumor recurrence.
Tumor dormancy has important implications for early detection and treatment of cancer. Lack of experimental models and limited clinical accessibility constitute major obstacles to the molecular characterization of dormant tumors. We have developed models in which human tumors remain dormant for a prolonged period of time (>120 days) until they switch to rapid growth and become strongly angiogenic. These angiogenic tumors retain their ability to grow fast once injected in new mice. We hypothesized that dormant tumors undergo a stable genetic reprogramming during their switch to the fast-growing phenotype. Genome-wide transcriptional analysis was done to dissect the molecular mechanisms underlying the switch of dormant breast carcinoma, glioblastoma, osteosarcoma, and liposarcoma tumors. A consensus expression signature distinguishing all four dormant versus switched fast-growing tumors was generated. In alignment with our phenotypic observation, the angiogenesis process was the most significantly affected functional gene category. The switch of dormant tumors was associated with down-regulation of angiogenesis inhibitor thrombospondin and decreased sensitivity of angiogenic tumors to angiostatin. The conversion of dormant tumors to exponentially growing tumors was also correlated with regulation and activation of pathways not hitherto linked to tumor dormancy process, such as endothelial cell-specific molecule-1, 5-ecto-nucleotidase, tissue inhibitor of metalloproteinase-3, epidermal growth factor receptor, insulin-like growth factor receptor, and phosphatidylinositol 3-kinase signaling. Further, novel dormancy-specific biomarkers such as H2BK and Eph receptor A5 (EphA5) were discovered. EphA5 plasma levels in mice and mRNA levels in tumor specimens of glioma patients correlated with diseases stage. These data will be instrumental in identifying novel early cancer biomarkers and could provide a rationale for development of dormancy-promoting tumor therapy strategies.
The incidence of many cancer types is significantly reduced in individuals with Downs syndrome, and it is thought that this broad cancer protection is conferred by the increased expression of one or more of the 231 supernumerary genes on the extra copy of chromosome 21. One such gene is Downs syndrome candidate region-1 (DSCR1, also known as RCAN1), which encodes a protein that suppresses vascular endothelial growth factor (VEGF)-mediated angiogenic signalling by the calcineurin pathway. Here we show that DSCR1 is increased in Downs syndrome tissues and in a mouse model of Downs syndrome. Furthermore, we show that the modest increase in expression afforded by a single extra transgenic copy of Dscr1 is sufficient to confer significant suppression of tumour growth in mice, and that such resistance is a consequence of a deficit in tumour angiogenesis arising from suppression of the calcineurin pathway. We also provide evidence that attenuation of calcineurin activity by DSCR1, together with another chromosome 21 gene Dyrk1a, may be sufficient to markedly diminish angiogenesis. These data provide a mechanism for the reduced cancer incidence in Downs syndrome and identify the calcineurin signalling pathway, and its regulators DSCR1 and DYRK1A, as potential therapeutic targets in cancers arising in all individuals.
Tumor dormancy refers to a critical stage in cancer development in which tumor cells remain occult for a prolonged period of time until they eventually progress and become clinically apparent. We previously showed that the switch of dormant tumors to fast-growth is angiogenesis dependent and requires a stable transcriptional reprogramming in tumor cells. Considering microRNAs (miRs) as master regulators of transcriptome, we sought to investigate their role in the control of tumor dormancy. We report here the identification of a consensus set of 19 miRs that govern the phenotypic switch of human dormant breast carcinoma, glioblastoma, osteosarcoma, and liposarcoma tumors to fast-growth. Loss of expression of dormancy-associated miRs (DmiRs, 16/19) was the prevailing regulation pattern correlating with the switch of dormant tumors to fast-growth. The expression pattern of two DmiRs (miR-580 and 190) was confirmed to correlate with disease stage in human glioma specimens. Reconstitution of a single DmiR (miR-580, 588 or 190) led to phenotypic reversal of fast-growing angiogenic tumors towards prolonged tumor dormancy. Of note, 60% of angiogenic glioblastoma and 100% of angiogenic osteosarcoma over-expressing miR190 remained dormant during the entire observation period of ? 120 days. Next, the ability of DmiRs to regulate angiogenesis and dormancy-associated genes was evaluated. Transcriptional reprogramming of tumors via DmiR-580, 588 or 190 over-expression resulted in downregulation of pro-angiogenic factors such as TIMP-3, bFGF and TGFalpha. In addition, a G-CSF independent downregulation of Bv8 was found as a common target of all three DmiRs and correlated with decreased tumor recruitment of bone marrow-derived CD11b+ Gr-1+ myeloid cells. In contrast, antiangiogenic and dormancy promoting pathways such as EphA5 and Angiomotin were upregulated in DmiR over-expressing tumors. This work suggests novel means to reverse the malignant tumor phenotype into an asymptomatic dormant state and may provide promising targets for early detection or prevention of cancer.
Antiangiogenesis therapy has become a vital part of the armamentarium against cancer. Hypertension is a dose-limiting toxicity for VEGF inhibitors. Thus, there is a pressing need to address the associated adverse events so these agents can be better used. The hypertension may be mediated by reduced NO bioavailability resulting from VEGF inhibition. We proposed that the hypertension may be prevented by coadministration with endostatin (ES), an endogenous angiogenesis inhibitor with antitumor effects shown to increase endothelial NO production in vitro. We determined that Fc-conjugated ES promoted NO production in endothelial and smooth muscle cells. ES also lowered blood pressure in normotensive mice and prevented hypertension induced by anti-VEGF antibodies. This effect was associated with higher circulating nitrate levels and was absent in eNOS-knockout mice, implicating a NO-mediated mechanism. Retrospective study of patients treated with ES in a clinical trial revealed a small but significant reduction in blood pressure, suggesting that the findings may translate to the clinic. Coadministration of ES with VEGF inhibitors may offer a unique strategy to prevent drug-related hypertension and enhance antiangiogenic tumor suppression.
The mechanisms underlying tumor dormancy have been elusive and not well characterized. We recently published an experimental model for the study of human tumor dormancy and the role of angiogenesis, and reported that the angiogenic switch was preceded by a local increase in VEGF-A and basic fibroblast growth factor. In this breast cancer xenograft model (MDA-MB-436 cells), analysis of differentially expressed genes revealed that heat shock protein 27 (HSP27) was significantly up-regulated in angiogenic cells compared with nonangiogenic cells. The effect of HSP27 down-regulation was further evaluated in cell lines, mouse models, and clinical datasets of human patients with breast cancer and melanoma. Stable down-regulation of HSP27 in angiogenic tumor cells was followed by long-term tumor dormancy in vivo. Strikingly, only 4 of 30 HSP27 knockdown xenograft tumors initiated rapid growth after day 70, in correlation with a regain of HSP27 protein expression. Significantly, no tumors escaped from dormancy without HSP27 expression. Down-regulation of HSP27 was associated with reduced endothelial cell proliferation and decreased secretion of VEGF-A, VEGF-C, and basic fibroblast growth factor. Conversely, overexpression of HSP27 in nonangiogenic cells resulted in expansive tumor growth in vivo. By clinical validation, strong HSP27 protein expression was associated with markers of aggressive tumors and decreased survival in patients with breast cancer and melanoma. An HSP27-associated gene expression signature was related to molecular subgroups and survival in breast cancer. Our findings suggest a role for HSP27 in the balance between tumor dormancy and tumor progression, mediated by tumor-vascular interactions. Targeting HSP27 might offer a useful strategy in cancer treatment.
Platelets sequester angiogenesis regulatory proteins which suggests an avenue for developing biomarkers to monitor disease. We describe a comparison of angiogenesis regulatory proteins found in platelets of colorectal cancer patients and normal controls. Platelet and plasma content of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet derived growth factor (PDGF), platelet factor 4 (PF4), thrombospondin-1 (TSP-1) and endostatin in 35 patients with colon cancer were compared with 84 age-matched healthy controls using ELISAs. We standardized the platelet preparation procedure, introduced process controls and normalized the respective protein levels to platelet numbers using an actin ELISA. Statistically significant differences were found in the median levels of VEGF, PF4 and PDGF in platelets of patients with cancer compared to healthy individuals. Platelet concentrations in cancer patients versus controls were: VEGF 1.3 versus 0.6 pg/10(6), PF4 18.5 versus 9.4 ng/10(6), and PDGF 34.1 versus 21.0 pg/10(6). Multivariable logistic regression analysis indicated that PDGF, PF4 and VEGF were independent predictors of colorectal carcinoma and as a set provided statistically significant discrimination (area under the curve = 0.893, P < .0001). No significant differences were detected for bFGF, endostatin, or TSP-1. Reference Change Value analysis determined that the differences seen were not clinically significant. Plasma levels yielded no correlations.
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