[Show abstract][Hide abstract] ABSTRACT: Identification of cell types in tumor-associated stroma that are involved in the development of melanoma is hampered by their heterogeneity. The authors used flow cytometry and immunohistochemistry to demonstrate that anti-MART-1 antibodies can discriminate between melanoma and stroma cells. They investigated the cellular composition of the MART-1-, non-hematopoietic melanoma-associated stroma, finding it consisted mainly of Sca-1+ and CD146+ cells. These cell types were also observed in the skin and muscle adjacent to developing melanomas. The Sca-1+ cell population was observed distributed in the epidermis, hair follicle bulges, and tumor capsule. The CD146+ population was found distributed within the tumor, mainly associated with blood vessels in a perivascular location. In addition to a perivascular distribution, CD146+ cells expressed α-smooth muscle actin, lacked expression of endothelial markers CD31 and CD34, and were therefore identified as pericytes. Pericytes were found to be associated with CD31+ endothelial cells; however, some pericytes were also observed associated with CD31-, MART-1+ B16 melanoma cells that appeared to form blood vessel structures. Furthermore, the authors observed extensive nuclear expression of HIF-1α in melanoma and stroma cells, suggesting hypoxia is an important factor associated with the melanoma microenvironment and vascularization. The results suggest that pericytes and Sca-1+ stroma cells are important contributors to melanoma development.
Full-text · Article · Dec 2011 · Journal of Histochemistry and Cytochemistry
[Show abstract][Hide abstract] ABSTRACT: Tumor tissue is composed of both cancer cells and stromal cells recruited from normal tissue. These cells include fibroblastic cells, endothelial cells, and cells of hematopoietic origin. The host-derived stromal cells play a critical role in all aspects of cancer biology including transformation, progression, tumor growth, and drug resistance. The interactions between stromal cells and cancer cells are of intense interest, and their complex interactions are beginning to be identified. Therapies that target components of the tumor microenvironment are showing efficacy in the clinic, particularly when used in combination with other therapeutic agents. In general these agents have been well tolerated, and targeting the stromal components may be a strategy for circumventing the problem of drug resistance. In this review, we highlight major stromal components, their interactions with tumor cells, and therapeutic approaches that disrupt host-tumor cell interactions. Advances in understanding host stromal components with respect to origin, subsets, and their signaling networks will reveal novel targets. Synergistic approaches that disrupt multiple host-tumor cell signaling pathways will lead to more effective therapies for cancer.
No preview · Article · Aug 2010 · Current Opinion in Pharmacology
[Show abstract][Hide abstract] ABSTRACT: The hypothesis that bone marrow-derived, circulating endothelial cells incorporate into tumor blood vessels is unresolved. We have measured the numbers of bone marrow-derived versus resident endothelial cells in spontaneous prostate cancers during different stages of tumor progression and in age-matched normal prostates. Bone marrow-derived endothelial cells were rare in dysplasia and in well differentiated cancers representing between 0 and 0.04% of the total tumor mass. Instead, approximately 99% of all tumor-associated bone marrow-derived cells were CD45(+) hematopoietic cells, including GR-1(+), F4-80(+), and CD11b(+) myeloid cells. Similar to peripheral blood mononuclear cells, these tumor-associated myeloid cells expressed matrix metalloproteinases (MMPs), consistent with their proposed catalytic role during tumor angiogenesis. Furthermore, freshly isolated CD11b(+) cells stimulated tumor endothelial cell cord formation by 10-fold in an in vitro angiogenesis assay. The bone marrow is, therefore, a reservoir for cells that augment tumor angiogenesis, but the tumor endothelium is derived primarily from the local environment.
[Show abstract][Hide abstract] ABSTRACT: Many of the current in vivo methods to evaluate angiogenesis are poorly quantifiable. Recently, the Matrigel plug assay has become the method of choice in many studies involving in vivo testing for angiogenesis. When known angiogenic factors are mixed with Matrigel and injected subcutaneously into mice, endothelial cells migrate into the gel plug. These endothelial cells form vessel-like structures, a process that mimics the formation of capillary networks. Here, we present a modification of the traditional Matrigel assay with improved method to quantify the amount of endothelial cells that incorporate into the plug. The removed plugs were subjected to a mild protease treatment, yielding intact cells. The liberated cells were then stained using an endothelial cell-specific markers, and counted by flow cytometry. This novel combination of FACS analysis with the traditional Matrigel assay improves the ability to quantify in vivo angiogenesis, and for the first time enables to determine the number of migrating and proliferating endothelial cells which reflects the angiogenesis rate.
No preview · Article · Mar 2009 · Journal of immunological methods
[Show abstract][Hide abstract] ABSTRACT: Tumor dormancy is a phenomenon whereby cancer cells persist below the threshold of diagnostic detection for months to decades. This condition may arise due to either cell cycle arrest or a dynamic equilibrium state in which cell proliferation is in balance with cells undergoing apoptosis. Tumor dormancy is usually a reference to occult cancer cells that persist for an extended period of time after treatment, but primary cancers can also exhibit extended growth plateaus below the limits of detection. For example, autopsies of individuals who died of trauma reveal that most individuals harbor microscopic primary cancers. Mechanisms that operate independently or successively may restrict tumor expansion throughout tumor progression from incipiency to late-stage cancer. Proposed mechanisms include cell cycle withdrawal, immune surveillance, and blocked angiogenesis. The precise mechanisms underlying dormancy remain to be established, and relevant models will have an important impact on diagnostic and therapeutic strategies for treating cancer. This review summarizes the phenomenon of tumor dormancy, experimental models, and potential mechanisms.
[Show abstract][Hide abstract] ABSTRACT: Two classes of circulating endothelial cells (CECs) have been identified and are distinguished by the expression of the stem cell markers CD117 or CD133 together with endothelial-specific antigens. Stem cell marker-positive CECs originate from bone marrow and have been designated as circulating endothelial progenitors (CEPs). We have demonstrated that exogenous vascular endothelial growth factor (VEGF) effectively mobilizes CEP cells. Furthermore, it has been demonstrated that VEGF regulates liver regeneration after partial hepatectomy. Although local endothelial cells can regulate tissue mass during liver regeneration, the contribution of CEPs to this process is unknown. We discovered loss of CD117 and CD133 from murine CEP cells and that both markers underestimated the number of bone marrow-derived CEP cells. We therefore used wild type and green fluorescent protein (GFP)-bone marrow transplanted into wild-type mice and performed 70% hepatectomies. Furthermore, we found that treatment with exogenous VEGF accelerated liver regeneration after 70% hepatectomy, whereas immunohistochemical analysis showed a 7-fold increase in the incorporation of CEP cells into liver vasculature. These results suggest that CEP cells play a role in regulating liver regeneration and that VEGF treatment can mobilize CEP cells to accelerate this process.
No preview · Article · Aug 2007 · Journal of Pediatric Surgery
[Show abstract][Hide abstract] ABSTRACT: Radiation can potentially suppress neovascularization by inhibiting the incorporation of hematopoietic precursors as well as damaging mature endothelial cells. The purpose of these studies was to quantify the effect of radiation on angiogenesis and to examine the relationship between bone marrow reconstitution and neovascularization. Immune competent, severe combined immunodeficient, RAG1-deficient, and green fluorescence protein transgenic mice in the C57 genetic background, as well as the highly angiogenic 129S1/SvlmJ strain of mice, underwent whole-body or localized exposure to radiation. The hematopoietic systems in the irradiated recipients were restored by bone marrow transfer. Hematopoietic reconstitution was assessed by doing complete blood counts. Angiogenesis was induced in the mouse cornea using 80 ng of purified basic fibroblast growth factor, and the neovascular response was quantified using a slit lamp biomicroscope. Following whole-body exposure and bone marrow transplantation, the hematopoietic system was successfully reconstituted over time, but the corneal angiogenic response was permanently and significantly blunted up to 66%. Localized exposure of the eyes to radiation suppressed corneal angiogenesis comparably to whole-body exposure. Whole-body irradiation with ocular shielding induced bone marrow suppression but did not inhibit corneal neovascularization. In mice exposed to radiation before tumor implantation, the reduced local angiogenic response correlated with significantly reduced growth of tumor cells in vivo. These results indicate that bone marrow suppression does not suppress neovascularization in the mouse cornea and that although hematopoietic stem cells can readily reconstitute peripheral blood, they do not restore a local radiation-induced deficit in neovascular response.
[Show abstract][Hide abstract] ABSTRACT: The green fluorescence protein (GFP) from the UBI-GFP/BL6 transgenic line was bred into C57BL/6J-scid and C.B-17-scid mice for investigating host-tumor cell interactions. These mice express high levels of GFP under the control of the ubiquitin promoter in virtually all cells examined. In tumor tissue generated by implanting tumor cells in the GFP transgenic SCID mice, the tumor cells and tumor-associated murine host cells were clearly distinguished by GFP expression. A population of cells expressing the endothelial cell marker VEGFR-2/Flk-1, and the progenitor markers c-Kit and Sca-1, were incorporated into tumor tissue. The majority of the Flk-1-positive cells were hematopoietic-derived cells that coexpressed CD45. To investigate the contribution of bone marrow-derived cells to the formation of tumor vessels and stroma, tumor cells were implanted in nontransgenic SCID mice that received a bone marrow transplant from GFP-expressing SCID mice. Although GFP-positive cells were readily detected by histology in tumors taken from bone marrow transplanted animals, they were spatially isolated and lacked organization. In contrast, if tumors were implanted in nontransgenic SCID mice adjacent to a patch of transplanted GFP-expressing skin, these tumors recruited GFP-positive cells that organized into tumor vessels. The results demonstrate that hematopoietic-derived cells, including Flk-1+/CD45+ cells, readily colonized the tumor stroma but were minimally incorporated in the tumor vasculature. The majority of the tumor vessels were instead recruited from tissue adjacent to the tumor. The expression of Flk-1 on nonendothelial, tumor-associated host cells raises the possibility that VEGF antagonists, such as Avastin, could inhibit tumor growth by a mechanism involving hematopoietic-derived CD45+/Flk-1+ cells, in addition to direct suppression of endothelial cell function.
Full-text · Article · Feb 2006 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: Tumor susceptibility, angiogenesis, and immune response differ between mouse strains. We, therefore, examined the growth rates of tumor xenografts in three genetically isolated strains of severe combined immunodeficient mice (C.B-17, C57BL/6J, and C3H). Tumors grew at significantly reduced rates in the C57BL/6J-scid strain. Engrafting bone marrow from the C57BL/6J-scid strain onto C.B-17-scid mice did not transfer the slow-growing tumor phenotype to the recipient mice; this counters the supposition that the slow-growing tumor phenotype is caused by a greater immune response to the xenograft in the C57BL/6J-scid strain. To establish the inheritance pattern of the slow-growing tumor phenotype, we reciprocally crossed C.B-17-scid mice and C57BL/6J-scid mice. Tumor growth was suppressed in all of the F1 progeny except the male mice derived from the cross between C.B-17-scid female and C57BL/6J-scid male mice. The F1 male mice that received the X chromosome from the C.B-17 strain displayed a fast-growing tumor phenotype. These results confirm that there are significant strain differences in capacity to support the growth of tumor xenografts. In addition, these results reveal the existence of a dominant allele involved in host suppression of tumor growth on the X chromosome of C57BL/6J mice.
[Show abstract][Hide abstract] ABSTRACT: Treatment of vascular malformations with sclerotherapy is often complicated by reexpansion secondary to endothelial recanalization. This study examined the use of an autologous fibroblast construct to enhance intraluminal scar formation after sclerotherapy.
New Zealand rabbits (n = 15) underwent ethanol sclerotherapy of a segment of the facial vein. After intraluminal saline flush, animals were equally divided into 3 groups. In group I, no further manipulations were performed. In groups II and III, collagen hydrogel was injected into the sclerosed vein, respectively, without and seeded with autologous green fluorescent protein-labeled fibroblasts. One week postoperatively, the vein segments were examined for patency and resected for histology.
The sclerosed vein segments remained occluded in all animals. Histological examination of luminal thrombi demonstrated numerous viable fibroblasts in group III, whereas there were none in the control specimens from groups I and II. The presence of the injected autologous green fluorescent protein-labeled fibroblasts within thrombi of group III was confirmed by immunohistochemistry.
An injectable tissue-engineered construct enhances sclerotherapy of the jugular vein in a leporine model by reliably delivering fibroblasts that populate the resultant thrombus. Further analysis of this novel therapeutic concept as a means to augment permanent scar formation and reduce luminal recanalization is warranted.
No preview · Article · Mar 2005 · Journal of Pediatric Surgery
[Show abstract][Hide abstract] ABSTRACT: This study examined the effects of amniocyte-based engineered tendons on partial diaphragmatic replacement.
Ovine mesenchymal amniocytes were labeled with green fluorescent protein (GFP), expanded, and seeded into a collagen hydrogel. Composite grafts (20 to 25 cm2) based on acellular dermis (group I), or acellular small intestinal submucosa (group II) received either a cell-seeded or an acellular hydrogel within their layers. Newborn lambs (n = 20) underwent partial diaphragmatic replacement with either an acellular or a cellular autologous construct from either group. At 3 to 12 months' postoperatively, implants were subjected to multiple analyses.
Diaphragmatic hernia recurrence was significantly higher in animals with acellular grafts (5 of 5) then in animals with cellular ones (1 of 4) in group I (P <.05) but not in group II (3 of 6 and 4 of 5, respectively). Cellular grafts had higher modular (5.27 +/- 1.98 v. 1.27 +/- 0.38 MPa) and ultimate (1.94 +/- 0.70 v. 0.29 +/- 0.05 MPa) tensile strength than acellular implants in group I (P <.05), but not in group II. Quantitative analyses showed no differences in extracellular matrix components between cellular and acellular implants in either group. All cellular implants showed GFP-positive cells.
Diaphragmatic repair with an autologous tendon engineered from mesenchymal amniocytes leads to improved mechanical and functional outcomes when compared with an equivalent acellular bioprosthetic repair, depending on scaffold composition. The amniotic fluid may be a preferred cell source for engineered diaphragmatic reconstruction.
No preview · Article · Jun 2004 · Journal of Pediatric Surgery
[Show abstract][Hide abstract] ABSTRACT: Some human tumor lines do not form visible tumors when inoculated into immunosuppressed mice. The fate of these human tumor lines was followed by transfecting them with green fluorescence protein before inoculating them into mice. Although the tumor lines failed to grow progressively, they formed small dormant microscopic foci maintained at constant mass by balanced proliferation and apoptosis. Transfecting the cells with either VEGF165 or activated c-Ha-ras induced loss of dormancy, which correlated with a shift in the angiogenic balance toward increased vascularity with reduced tumor cell apoptosis. These results support a model in which loss of dormancy is controlled in part by a switch to an angiogenic phenotype. These tumor lines may serve as models for investigating the cellular mechanisms controlling dormancy and identifying those factors that promote the loss of balanced proliferation and apoptosis. Finally, these models may prove useful in the design and testing of therapies directed toward eradicating dormant tumors and preventing tumor recurrence.
[Show abstract][Hide abstract] ABSTRACT: Tumor cells are known to be heterogeneous with respect to their metastatic activity, proliferation rate, and activity of several enzymes. However, little is known about the heterogeneity of tumor angiogenic activity. We investigated whether heterogeneity of angiogenic activity could be responsible for the well-known observation of "no take" of human tumors transplanted into immunodeficient mice.
Severe combined immunodeficient (SCID) mice were xenotransplanted subcutaneously with tumor tissue (n = 55) or cell suspension of a human liposarcoma cell line (SW-872) or subclones (n = 28), with varying cell proliferation rates. Xenograft tumor growth was recorded for up to 6 months. Tumor tissues were then removed and analyzed for tumor cell apoptosis, microvessel density, and cell proliferation. All statistical tests were two-sided.
Pieces of tumor derived from the parental cell line or its clones gave rise to three kinds of tumors: 1) highly angiogenic and fast-growing (aggressive) tumors, 2) weakly angiogenic and slow-growing tumors, and 3) nonangiogenic and stable tumors. Most tumors retained the original phenotype of their parental tumor. Tumor volume correlated positively with microvessel density (Spearman correlation coefficient [r] =.89; P< or =.0001) and inversely with tumor cell apoptosis (Spearman r = -.68; P =.002). Tumor volume was less strongly but still positively correlated with tumor cell proliferation in vivo (Spearman r =.55; P =.02).
Human liposarcoma cells appear to be heterogeneous in their angiogenic activity. When tumor cells with little or no angiogenic activity are transplanted into SCID mice, a microscopic, dormant tumor results that may not grow further. Because such tiny tumors are neither grossly visible nor palpable, they have previously been called "no take." The finding that an angiogenic tumor can contain subpopulations of tumor cells with little or no angiogenic activity may provide a novel mechanism for dormant micrometastases, late recurrence, and changes in rate of tumor progression.
Preview · Article · Aug 2001 · JNCI Journal of the National Cancer Institute
[Show abstract][Hide abstract] ABSTRACT: Background: Tumors commonly outgrow their blood supply, thereby creating hypoxic conditions, which induce apoptosis and increase expression of angiogenic growth factors. The bcl-2 oncogene inhibits apoptosis induced by a variety of stimuli, including hypoxia. On the basis of bcl-2's role in regulating apoptosis in response to hypoxia, we hypothesized that this oncogene might affect other responses to hypoxia, such as the expression of angiogenic growth factors. Methods: Three prostate carcinoma cell lines, PC3, LNCaP, and DU-145, were stably transfected with a bcl-2 complementary DNA (cDNA), and transfectants were analyzed in vitro for the expression of angiogenic factors after exposure to either normoxic (19% O 2 ) or hypoxic (1% O 2 ) conditions. The in vivo angiogenic potential of the transfected cells was determined by analyzing vessel density in xenografts derived from them and by measuring the ability of these xenografts to induce neovascularization when implanted in mouse corneal micropockets. Statistical tests were two-sided. Results: When exposed to hypoxic conditions, prostate carcinoma cells overexpressing bcl-2 expressed statistically significantly higher levels of vascular endothelial growth factor (VEGF), an angiogenic factor, than control-transfected cells ( P = .001 for PC3, P = .04 for DU-145 after 48 hours). This effect of bcl-2 was independent of its antiapoptotic activity because increased expression of VEGF was detected in PC3 cells overexpressing bcl-2 even though PC3 cells are inherently resistant to hypoxia-induced apoptosis. In vivo , xenograft tumors derived from the bcl-2-overexpressing prostate carcinoma cell lines displayed increased angiogenic potential and grew more aggressively than tumors derived from the control cell lines ( P = .03 for PC3). Treatment of bcl-2-overexpressing and control tumors with the antiangiogenic drug TNP-470 neutralized the aggressive angiogenesis in bcl-2-overexpressing tumors ( P = .04 for PC3, P = .004 for DU-145) and the moderate angiogenesis in control tumors ( P = .01 for PC3, P = .05 for DU-145), resulting in similar growth rates for both tumors. Conclusions: bcl-2 may play a dual role in tumorigenesis by suppressing apoptosis and by stimulating angiogenesis.
Full-text · Article · Mar 2001 · JNCI Journal of the National Cancer Institute
[Show abstract][Hide abstract] ABSTRACT: Several previously identified inhibitors of angiogenesis have been epoxide-containing fungus-derived metabolites. We therefore hypothesized that novel epoxide-containing low molecular weight compounds structurally resembling known antiangiogenic agents may also exhibit antiangiogenic activity. Cytochalasin E was found to be a potent and selective inhibitor of bovine capillary endothelial (BCE) cell proliferation. Cytochalasin E differed from other cytochalasins by the presence of an epoxide. The epoxide was required for activity, because acid-catalyzed hydrolysis of the epoxide abrogated the specificity and potency of cytochalasin E. Phalloidin staining indicated that disruption of actin stress fibers by cytochalasin E occurred only at relatively high concentrations. Lower concentrations of cytochalasin E preferentially inhibited BCE cell proliferation without disrupting actin stress fibers. In vivo, cytochalasin E inhibited angiogenesis induced by basic fibroblast growth factor by 40% to 50% in the mouse cornea assay and inhibited the growth of Lewis lung tumors by approximately 72%. Cytochalasin E is a potent antiangiogenic agent that may hold promise for the treatment of cancer and other types of pathologic angiogenesis.
No preview · Article · Sep 2000 · Journal of Pharmacology and Experimental Therapeutics
[Show abstract][Hide abstract] ABSTRACT: Many diseases, including cancer, are dependent on the growth of new blood vessels, a process known as angiogenesis. Differences in an individual's ability to grow new blood vessels may influence the rate of progression of these diseases. Here we show that different strains of inbred mice have an approximately 10-fold range of response to growth factor-stimulated angiogenesis in the corneal micropocket assay. The in vitro migratory activity of endothelial cells from aortic rings of selected strains correlated with the in vivo responsiveness. Further, a differential sensitivity to angiogenesis inhibitors was seen between strains, with one strain demonstrating resistance to both TNP-470 and thalidomide. These results suggest the presence of genetic factors that control individual angiogenic potential.
[Show abstract][Hide abstract] ABSTRACT: Endothelial malignancies, such as angiosarcoma and hemangioendothelioma, are often resistant to chemotherapy and surgery, and may result in death. Improved means of therapy are needed for these disorders.
We wanted to determine whether angiosarcoma can be treated with angiogenesis inhibitors in mice.
Mice were inoculated with a cell line that gives rise to angiosarcoma and were treated with the angiogenesis inhibitors 2-methoxyestradiol and TNP-470. Response to therapy was monitored by measurement of tumors.
TNP-470 caused an 84% reduction in tumor size, and 2-methoxyestradiol caused a 68% reduction in tumor size.
Angiogenesis inhibitors are highly effective in treatment of angiosarcoma in mice. Clinical trials of these agents in humans with angiosarcoma and hemangioendothelioma are warranted.
No preview · Article · Jul 1999 · Journal of the American Academy of Dermatology