The camptothecin derivative CPT-11 inhibits angiogenesis in a dual-color imageable orthotopic metastatic nude mouse model of human colon cancer

Recent studies have shown the expression of a stem cell marker protein, nestin, in nascent blood vessels in nestin-driven green fluorescent protein (ND-GFP) transgenic nude mice. In the present study, we visualized tumor angiogenesis and evaluated the antiangiogenic efficacy of CPT-11 in ND-GFP nude mice using dual-color fluorescence imaging. We orthotopically implanted ND-GFP nude mice with the human cancer cell line HCT-116 expressing red fluorescent protein (RFP). The mice were treated with CPT-11 at 40 mg/kg on days 7, 10, 14. Tumor angiogenesis was imaged and visualized by dual-color fluorescence imaging on day 17, three days after the last CPT-11 treatment. Tumor volume and the mean nascent blood vessel density were determined and compared to the control mice. The growing tumor had high expressions of nestin in the nascent blood vessels. The nascent blood vessels showed co-localization of the endothelial-cell-specific marker CD-31 under immunohistochemical staining. The nascent blood vessels were highly visible and their density was determined. ND-GFP nude mice that were administered CPT-11 showed significant reduction in the mean nascent blood vessel density and tumor volume. The dual-color model of ND-GFP transgenic nude mice orthotopically implanted with HCT-116 expressing RFP proved to be effective in visualizing and quantitating tumor growth and tumor angiogenesis. The results showed that CPT-11 is an effective inhibitor of angiogenesis and provided strong implications for wider clinical application of CPT-11 for colon cancer.     

Hair follicle-derived blood vessels vascularize tumors in skin and are inhibited by Doxorubicin

We have recently shown that the neural-stem cell marker nestin is expressed in hair follicle stem cells and the blood vessel network interconnecting hair follicles in the skin of transgenic mice with nestin regulatory element-driven green fluorescent protein (ND-GFP). The hair follicles were shown to give rise to the nestin-expressing blood vessels in the skin. In the present study, we visualized tumor angiogenesis by dual-color fluorescence imaging in ND-GFP transgenic mice after transplantation of the murine melanoma cell line B16F10 expressing red fluorescent protein. ND-GFP was highly expressed in proliferating endothelial cells and nascent blood vessels in the growing tumor. Results of immunohistochemical staining showed that the blood vessel-specific antigen CD31 was expressed in ND-GFP-expressing nascent blood vessels. ND-GFP expression was diminished in the vessels with increased blood flow. Progressive angiogenesis during tumor growth was readily visualized during tumor growth by GFP expression. Doxorubicin inhibited the nascent tumor angiogenesis as well as tumor growth in the ND-GFP mice transplanted with B16F10-RFP. This model is useful for direct visualization of tumor angiogenesis and evaluation of angiogenic inhibitors.     

Tumor imaging with multicolor fluorescent protein expression

Imaging with fluorescent proteins has been revolutionary and has led to the new field of in vivo cell biology. Many new applications of this technology have been developed. Green fluorescent protein (GFP)-labeled or red fluorescent protein (RFP)-labeled HT-1080 human fibrosarcoma cells were used to determine clonality of metastasis by imaging of metastatic colonies after mixed implantation of the red and green fluorescent cells. Resulting pure red or pure green colonies were scored as clonal, whereas mixed yellow colonies were scored as nonclonal. Dual-color fluorescent cancer cells expressing GFP in the nucleus and RFP in the cytoplasm were engineered. The dual-color cancer cells enable real-time nuclear–cytoplasmic dynamics to be visualized in living cells in vivo, including mitosis and apoptosis. The nuclear and cytoplasmic behavior of dual-color cancer cells in real time in blood vessels was observed as they trafficked by various means or extravasated in an abdominal skin flap. Dual-color cancer cells were also visualized trafficking through lymphatic vessels where they were imaged via a skin flap. Seeding and arresting of single dual-color cancer cells in the lung, accumulation of cancer-cell emboli, cancer-cell viability, and metastatic colony formation were imaged in real time in an open-chest nude mouse model using assisted ventilation. Novel treatment was evaluated in these imageable models. UVC irradiation killed approximately 70% of the dual-color cancer cells in a nude mouse model. An RFP-expressing glioma was transplanted to the spinal cord of transgenic nude mice expressing nestin-driven green fluorescent protein (ND-GFP). In ND-GFP mice, GFP is expressed in nascent blood vessels and neural stem cells. ND-GFP cells staining positively for neuronal class III-β-tubulin or CD31 surrounded the tumor, suggesting that the tumor stimulated both neurogenesis and angiogenesis. The tumor caused paralysis and also metastasized to the brain. The Salmonella typhimurium A1-R tumor-targeting bacterial strain was administered in the orthotopic spinal cord glioma model. The treated animals had a significant increase in survival and decrease in paralysis. S. typhimurium A1-R was effective against primary bone tumor and lung metastasis expressing RFP in a nude mouse model. S. typhimurium A1-R was effective against both axillary lymph and popliteal lymph node metastases of human dual-color pancreatic cancer and fibrosarcoma cells, respectively, as well as lung metastasis of the fibrosarcoma in nude mice. Imaging with fluorescent proteins will reveal mechanisms of cancer progression and provide visual targets for novel therapeutics.     

Tumor-targeting Salmonella typhimurium A1-R arrests growth of breast-cancer brain metastasis

Brain metastasis is a morbid, treatment-resistant, end-stage frequent occurrence in breast cancer patients. The aim of this study was to evaluate the efficacy of tumor-targeting Salmonella typhimurium A1-R on breast cancer brain metastases. High brain-metastatic variants of murine 4T1 breast cancer cells expressing red fluorescent protein (RFP) were injected orthotopically in the mammary fat pad in non-transgenic nude mice or in the left ventricle of non-transgenic nude mice and transgenic nude mice expressing nestin-driven green fluorescent protein (ND-GFP). ND-GFP mice express GFP in nascent blood vessels. In the orthotopically-injected mice, the primary tumor was surgically-resected in order to allow brain metastasis to develop. At various time points, the tumors and vasculature in the brain were imaged by confocal and stereo fluorescence microscopy. Some of the breast cancer cells that reached the brain extravasated and grew perivascularly and some of the cells proliferated within the vasculature. S. typhimurium A1-R significantly inhibited brain metastasis in both metastatic models and increased survival of the orthotopically-transplanted, primary-tumor-resected mice (p<0.05). The results of the present study suggest the clinical potential of bacterial therapy of breast cancer brain metastasis.     

Identification of neovasculature using nestin in colorectal cancer

CD34 is commonly used as an endothelial cell marker of tumor vessels. However, this marker detects not only newly formed, but also pre-existing large blood vessels. Nestin, a class VI intermediate filament protein, has recently received attention as a marker for detecting newly formed endothelial cells. In this study, whether nestin is a novel angiogenesis marker in colorectal cancer was examined. HCT-15, a human colon cancer cell line, was subcutaneously implanted into the dorsum of nude mice. After the tumor grew, the mice were perfused with fluorescent beads (Fluospheres). Then, the tumor tissues were used for immunofluorescence staining using nestin and the CD34 antibody. Immunohistochemistry was performed with nestin and CD34 on 101 human colorectal cancer tissue samples. Proliferating endothelial cells were detected immunohistochemically by a proliferating cell nuclear antigen (PCNA) antibody. Clinicopathological factors and prognosis were compared between two groups: that with a microvessel density (MVD) higher than the median MVD and that with MVD lower than the median MVD, as detected by nestin and CD34 labellings. Nestin was localized in endothelial cells in small blood vessels (median, 9.06 microm), whereas CD34 was localized in large blood vessels (median, 9.67 microm) in nude mice. The diameter of nestin-positive vessels was smaller than that of CD34-positive vessels in human colorectal cancer. The number ratio of PCNA-positive cells to nestin-positive vascular endothelial cells was higher than that of PCNA-positive to CD34-positive cells (p=0.002). There were no correlations between nestin-positive blood vessels and clinicopathological factors, but the prognosis was worse in the highly nestin-positive MVD group (p=0.071). Nestin is considered a novel angiogenesis marker of proliferating endothelial cells in colorectal cancer tissue.     

Transgenic nude mouse with ubiquitous green fluorescent protein expression as a host for human tumors

We report here the development of the transgenic green fluorescent protein (GFP) nude mouse with ubiquitous GFP expression. The GFP nude mouse was obtained by crossing nontransgenic nude mice with the transgenic C57/B6 mouse in which the beta-actin promoter drives GFP expression in essentially all tissues. In crosses between nu/nu GFP male mice and nu/+ GFP female mice, the embryos fluoresced green. Approximately 50% of the offspring of these mice were GFP nude mice. Newborn mice and adult mice fluoresced very bright green and could be detected with a simple blue-light-emitting diode flashlight with a central peak of 470 nm and a bypass emission filter. In the adult mice, the organs all brightly expressed GFP, including the heart, lungs, spleen, pancreas, esophagus, stomach, and duodenum. The following systems were dissected out and shown to have brilliant GFP fluorescence: the entire digestive system from tongue to anus; the male and female reproductive systems; brain and spinal cord; and the circulatory system, including the heart and major arteries and veins. The skinned skeleton highly expressed GFP. Pancreatic islets showed GFP fluorescence. The spleen cells were also GFP positive. Red fluorescent protein (RFP)-expressing human cancer cell lines, including PC-3-RFP prostate cancer, HCT-116-RFP colon cancer, MDA-MB-435-RFP breast cancer, and HT1080-RFP fibrosarcoma were transplanted to the transgenic GFP nude mice. All of these human tumors grew extensively in the transgenic GFP nude mouse. Dual-color fluorescence imaging enabled visualization of human tumor-host interaction by whole-body imaging and at the cellular level in fresh and frozen tissues. The GFP mouse model should greatly expand our knowledge of human tumor-host interaction.     

人源化肿瘤血管移植瘤模型的建立及应用

背景与目的:目前在肿瘤内皮细胞基因功能和靶向血管治疗肿瘤的研究中仍缺乏适宜的动物模型。本研究拟建立一种新的小鼠人源化肿瘤血管移植瘤模型。方法:将人肝窦微血管内皮细胞系(humanliversinusoidendothelialcells,HLSEC)分别与人肝癌细胞系BEL7402、人结肠癌细胞系LS174T、人食管癌细胞系NEC按不同比例混合共接种NOD/SCID小鼠或BALB/c裸小鼠,以单独接种肿瘤细胞的小鼠作为对照组,观察小鼠人移植瘤生长的情况。采用绿色荧光蛋白基因(greenfluorescentprotein,GFP)转染HLSEC,结合荧光显微镜检方法观察HLSEC在共接种移植瘤中的存活及血管形成的情况。免疫组化法检测肿瘤内微血管密度(microvesseldensity,MVD)。用抗人肝癌内皮细胞单抗2B6处理人肝癌移植瘤共接种模型,观察2B6对肿瘤生长的影响。结果:HLSEC与BEL7402细胞共接种NOD/SCID小鼠时,共接种组肿瘤生长速度显著加快,平均瘤重可达肿瘤单独接种组的5.1倍。在GFP表达阳性的HLSEC与BEL7402共接种的移植瘤冰冻切片中可见HLSEC的存在,并已形成瘤内新生血管。免疫组化检测发现共接种组移植瘤中的总MVD较肿瘤细胞单独接种组增加85.7%,采用抗人vWF多抗检测结果显示共接种组人源微血管平均MVD可达10.28～29.28,约占总血管数量的41%～65%。进一步将HLSEC分别与NEC、BEL7402及LS174T细胞共接种于BALB/c裸小鼠时,共接种组的瘤重是单独接种组的3.3～6.0倍。2B6单抗能使共接种人肝癌移植瘤中人源肿瘤血管密度减少65.1%,抑制肿瘤瘤重达71.8%。结论:HLSEC与人肿瘤细胞共接种小鼠后,能在移植瘤中存活、增殖,形成大量人源化的肿瘤新生血管,并在促进肿瘤快速生长中起重要作用。该小鼠人源化肿瘤血管移植瘤模型可为肿瘤内皮细胞相关基因及靶向治疗剂的研究提供一个新的有价值的工具。     

Angiopoietin‐1 alters tumor growth by stabilizing blood vessels or by promoting angiogenesis

The maturation of blood vessels requires mural cell adhesion to endothelial cells. Angiopoietin‐1 (Ang1), a ligand for Tie2 receptor expressed on endothelial cells, plays a critical role in cell adhesion between mural cells and endothelial cells and in endothelial cell sprouting from preexisting vessels in the absence of mural cells. Much information has been amassed on the Tie2–Ang1 system in physiological blood vessel formation during embryogenesis; however, the role of Ang1 in the tumor environment and its interaction with mural cells has not been well documented. Here we studied how Ang1 regulates maturation of blood vessels using the human colon cancer cell line HT29 and the human prostate cancer cell line PC3, and studied how Ang1 affects tumor growth. In a xenograft tumor model using female nude mice, we found that Ang1 enhanced angiogenesis and resulted in tumor growth in the case of PC3 tumors but suppressed tumor growth in the case of HT29 tumors. In PC3 tumors, the number of mural cells adhering to endothelial cells was less than that in HT29 tumors. Ang1 induced sprouting angiogenesis in PC3 tumors although there was little maturation of blood vessels. On the other hand, there was abundant mural cell adhesion to endothelial cells in HT29 tumors and Ang1 did not induce angiogenesis. These results suggest that Ang1 alters tumor growth in a manner that is dependent on the adhesion of mural cells and their localization in the tumor environment. (Cancer Sci 2008; 99: 2373–2379)     

Functional in vivo optical imaging of tumor angiogenesis, growth, and metastasis prevented by administration of anti-human VEGF antibody in xenograft model of human fibrosarcoma HT1080 cells

Angiogenesis plays a crucial role in cancer progression and metastasis. Thus, blocking tumor angiogenesis is potentially a universal approach to prevent tumor establishment and metastasis. In this study, we used in vivo and ex vivo fluorescence imaging to show that an antihuman vascular endothelial growth factor (VEGF) antibody represses angiogenesis and the growth of primary tumors of human fibrosarcoma HT1080 cells in implanted nude mice. Interestingly, administering the antihuman VEGF antibody reduced the development of new blood vessels and normalized pre-existing tumor vasculature in HT1080 cell tumors. In addition, antihuman VEGF antibody treatment decreased lung metastasis from the primary tumor, whereas it failed to block lung metastasis in a lung colonization experiment in which tumor cells were injected into the tail vein. These results suggest that VEGF produced by primary HT1080 cell tumors has a crucial effect on lung metastasis. The present study indicates that the in vivo fluorescent microscopy system will be useful to investigate the biology of angiogenesis and test the effectiveness of angiogenesis inhibitors. ( Cancer Sci 2009)     

Non-invasive Fluorescent-protein Imaging of Orthotopic Pancreatic-cancer-patient Tumorgraft Progression in Nude Mice

In order to individualize and therefore have more effective treatment for pancreatic cancer, we have developed a multicolor, imageable, orthotopic mouse model for individual patients with pancreatic cancer by passaging their tumors through transgenic nude mice expressing green fluorescent protein (GFP) and red fluorescent protein (RFP). The tumors acquired brightly fluorescent stroma from the transgenic host mice, which was stably associated with the tumors through multiple passages. In the present study, pancreatic cancer patient tumor specimens were initially established in NOD.CB17-Prkdc(scid)/NcrCrl (NOD/SCID) mice. The tumors were then passaged orthotopically into transgenic nude mice ubiquitously expressing GFP and subsequently to nude mice ubiquitously expressing RFP. The tumors, with very bright GFP and RFP stroma, were then orthotopically passaged to non-transgenic nude mice. It was possible to image the brightly fluorescent tumors non-invasively longitudinally as they progressed in the non-transgenic nude mice. This non-invasive imageable tumorgraft model will be valuable to screen for effective treatment options for individual patients with pancreatic cancer, as well as for the discovery of improved agents for this treatment-resistant disease.     

VEGF receptor antisense therapy inhibits angiogenesis and peritoneal dissemination of human gastric cancer in nude mice

The efficacy of a phosphorothioate antisense oligonucleotide (ASO) for KDR/Flk-1 (KDR/Flk-1-ASO), an endothelial cell-specific vascular endothelial growth factor (VEGF) receptor, was investigated on the peritoneal dissemination and angiogenesis of a human gastric cancer cell line in nude mice. Green fluorescent protein (GFP)-transduced NUGC-4 (NUGC-4-GFP) human gastric cancer cells were implanted into the peritoneal cavity of nude mice. KDR/Flk-1-ASO, -SO, or phosphate-buffered saline was administrated from days 7 to 14, 200 microg/mouse, once a day. The mice were sacrificed on day 28. Disseminated peritoneal tumor nodules expressing GFP were visualized by fluorescence microscopy. KDR/Flk-1-ASO significantly decreased the extent of peritoneal dissemination of the tumors. The number of cells undergoing apoptosis was significantly increased in the KDR/Flk-1-ASO-treated tumors. Microvessel density was significantly reduced in the KDR/Flk-1-ASO-treated tumor nodules. The KDR/Flk-1 antisense strategy, therefore, decreases tumor dissemination apparently by inhibiting angiogenesis.     

Opposing roles of murine duffy antigen receptor for chemokine and murine CXC chemokine receptor-2 receptors in murine melanoma tumor growth

The Duffy antigen receptor for chemokines (DARC) has been classified as a "silent" receptor, as it can bind CXC and CC chemokines to undergo ligand-induced receptor internalization, but is not coupled to trimeric G proteins required for the classic G protein-coupled receptor-mediated signaling. CXC chemokine receptor-2 (CXCR2) has been shown to play a major role in tumor angiogenesis. To test the hypothesis that these two chemokine receptors might play opposing roles in the growth of melanoma tumors, we developed a transgenic mouse model, where the preproendothelin promoter/enhancer (PPEP) is used to drive expression of either murine DARC (mDARC) or murine CXCR2 (mCXCR2) in endothelial cells. We show herein that the growth of melanoma tumor xenografts, established from s.c. injection of immortalized murine melanocytes overexpressing macrophage inflammatory protein-2, was inhibited or enhanced in the PPEP-mDARC and PPEP-mCXCR2 transgenic mice, respectively, compared with control mice. The early tumors formed in mDARC transgenic mice exhibited a significantly higher number of infiltrating leukocytes compared with either the control or mCXCR2 transgenic mice, suggesting a potential role for DARC expressed on endothelial cells in leukocyte migration. In addition, the tumor-associated angiogenesis in mDARC transgenic mice was reduced when compared with the control. Conversely, tumor angiogenesis was significantly increased in mCXCR2 transgenic mice. Results indicate that endothelial cell overexpression of mDARC increased leukocyte trafficking to the tumor, reduced the growth of blood vessels into the tumor, and reduced the growth rate of the tumor, whereas endothelial cell overexpression of mCXCR2 had the reverse effect on tumor angiogenesis and growth.     

Placental growth factor-1 attenuates vascular endothelial growth factor-A-dependent tumor angiogenesis during beta cell carcinogenesis

Members of the vascular endothelial growth factor (VEGF) family are critical players in angiogenesis and lymphangiogenesis. Although VEGF-A has been shown to exert fundamental functions in physiologic and pathologic angiogenesis, the exact role of the VEGF family member placental growth factor (PlGF) in tumor angiogenesis has remained controversial. To gain insight into PlGF function during tumor angiogenesis, we have generated transgenic mouse lines expressing human PlGF-1 in the beta cells of the pancreatic islets of Langerhans (Rip1PlGF-1). In single-transgenic Rip1PlGF-1 mice, intra-insular blood vessels are found highly dilated, whereas islet physiology is unaffected. Upon crossing of these mice with the Rip1Tag2 transgenic mouse model of pancreatic beta cell carcinogenesis, tumors of double-transgenic Rip1Tag2;Rip1PlGF-1 mice display reduced growth due to attenuated tumor angiogenesis. The coexpression of transgenic PlGF-1 and endogenous VEGF-A in the beta tumor cells of double-transgenic animals causes the formation of low-angiogenic hPlGF-1/mVEGF-A heterodimers at the expense of highly angiogenic mVEGF-A homodimers resulting in diminished tumor angiogenesis and reduced tumor infiltration by neutrophils, known to contribute to the angiogenic switch in Rip1Tag2 mice. The results indicate that the ratio between the expression levels of two members of the VEGF family of angiogenic factors, PlGF-1 and VEGF-A, determines the overall angiogenic activity and, thus, the extent of tumor angiogenesis and tumor growth.     

Orthotopic Transplant Mouse Models with Green Fluorescent Protein-expressing Cancer Cells to Visualize Metastasis and Angiogenesis

There have been major efforts in metastasis research in recent years, especially on the role of angiogenesis in the metastatic process. Much of the information in this area has been obtained from model systems that are not representative of clinical cancer. The technique of surgical orthotopic implantation (SOI) has allowed the development of clinically relevant metastatic models of human cancer in immunodeficient rodents such as the nude and SCID mouse. In order to allow direct visualization of the metastatic process, we took advantage of the green fluorescent protein (GFP) of the jellyfish, Aequorea victoria. A series of cancer cell lines have been stably transfected with vectors containing humanized GFP cDNA. To utilize GFP expression for metastasis studies, fragments of subcutaneously growing tumor, which were comprised of GFP-expressing cells, were implanted by SOI in nude mice. Subsequent metastases were visualized in systemic organs by GFP fluorescence in the lung, liver, bones, brain and other organs down to the single-cell level. With this fluorescent tool, we detected and visualized for the first time tumor cells at the microscopic level in fresh viable tissue in their normal host organs even in the live animal. Angiogenesis is readily visualized in the transplanted GFP-expressing tumors in real time in situ in the live animal using simple laparotomy and fluorescent techniques. The results with the GFP-transfected tumor cells, combined with the use of SOI, demonstrate a fundamental advance to visualize and study cancer metastasis and the role of angiogenesis and other factors in the metastatic process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Contributions of stromal metalloproteinase-9 to angiogenesis and growth of human ovarian carcinoma in mice

BACKGROUND: The expression level of several matrix metalloproteinases (MMPs), including MMP-2 and MMP-9, in ovarian cancer cells is directly associated with their invasive and metastatic potentials. MMP-9 is also expressed in stromal cells adjacent to the tumor. To investigate the contribution of MMP-9 expression in stromal cells to ovarian tumor growth, we examined angiogenesis and progressive growth of human ovarian cancer cells implanted into mice with and without the MMP-9 gene. METHODS: Human ovarian cancer cells SKOV3.ip1 and HEY-A8 were implanted into the peritoneal cavities of nude mice that lacked the gene for MMP-9 (MMP-9(-/-)) or were wild type for MMP-9 (MMP-9(+/+)) (10 mice of each genotype per cell line). Tumor incidence, tumor size, and volume of ascites fluid were recorded for each mouse at 30 and 45 days after HEY-A8 and SKOV3.ip1 cell injections, respectively. Blood vessel density and macrophage infiltration into the lesions were analyzed in excised tumors by immunohistochemistry and double immunofluorescence. Tumor growth was also studied in MMP-9(-/-) nude mice that had been reconstituted with spleen cells collected from either MMP-9(+/+) or MMP-9(-/-) nude mice. All statistical tests were two-sided. RESULTS: HEY-A8 cells expressed high levels of MMP-9, and SKOV3.ip1 cells expressed low levels. Nevertheless, tumor incidence and growth were statistically significantly lower in MMP-9(-/-) mice than in MMP-9(+/+) mice injected with cells from either line (for tumor size, P =.006 and.042 for HEY-A8 and SKOV3.ip1 cells, respectively). Compared with MMP-9(+/+) mice injected with human ovarian cancer cells, MMP-9(-/-) mice injected with human ovarian cancer cells displayed decreased microvessel density and decreased macrophage infiltration into the lesions. Compared with MMP-9(-/-) mice that received spleen cells (a rich source of macrophages) from MMP-9(-/-) mice, those that received spleen cells from MMP-9(+/+) mice before cancer cell injections displayed increased angiogenesis and tumorigenicity of the cancer cells. The growing tumors contained MMP-9-expressing macrophages. CONCLUSION: Host-derived MMP-9 expression, most likely in tumor-infiltrating macrophages, appears to play a critical role in angiogenesis and progressive growth of human ovarian tumors in mice.     

Utilization of bone marrow-derived endothelial cell precursors in spontaneous prostate tumors varies with tumor grade

Id1 and Id3 genes are required for vascularization, growth, and metastasis of xenograft tumors. In Id-deficient mice, tumor transplantation and proangiogenic factors fail to mobilize and recruit circulating endothelial precursor cells (CEPs) and hematopoietic cells, leading to defective tumor angiogenesis in various models. To investigate the requirement of Id genes and bone marrow incorporation in spontaneous prostate tumors, we crossbred Id mutant mice with the transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. Id1-/- Id3+/- TRAMP mice display delayed tumor growth at 24 weeks compared with wild-type TRAMP mice. Id1 and Id3 were strongly expressed in the endothelial cells of poorly differentiated prostate adenocarcinoma but not in the vasculature of well-differentiated tumors, a finding that is corroborated in human prostate tumor samples. In Id-deficient TRAMP mice, the poorly differentiated tumors show extensive hemorrhage, whereas well-differentiated tumors exhibit none. Transplantation with Id wild-type bone marrow significantly reduced the hemorrhage in poorly differentiated prostate adenocarcinomas with bone marrow-derived endothelial cells contributing to 14% of the tumor blood vessels. However, in well-differentiated prostate adenocarcinomas, there was little evidence of bone marrow-derived endothelial cell incorporation. These differences in the expression of Id genes, the effects of Id loss, and the recruitment of bone marrow-derived endothelial precursor cells in tumor vasculature between well-differentiated and poorly differentiated prostate adenocarcinoma suggest that tumor angiogenesis varies depending on the tumor grade.     

Mouse models for studying angiogenesis and lymphangiogenesis in cancer

The formation of new blood vessels (angiogenesis) is required for the growth of most tumors. The tumor microenvironment also induces lymphangiogenic factors that promote metastatic spread. Anti-angiogenic therapy targets the mechanisms behind the growth of the tumor vasculature. During the past two decades, several strategies targeting blood and lymphatic vessels in tumors have been developed. The blocking of vascular endothelial growth factor (VEGF)/VEGF receptor-2 (VEGFR-2) signaling has proven effective for inhibition of tumor angiogenesis and growth, and inhibitors of VEGF-C/VEGFR-3 involved in lymphangiogenesis have recently entered clinical trials. However, thus far anti-angiogenic treatments have been less effective in humans than predicted on the basis of pre-clinical tests in mice. Intrinsic and induced resistance against anti-angiogenesis occurs in patients, and thus far the clinical benefit of the treatments has been limited to modest improvements in overall survival in selected tumor types. Our current knowledge of tumor angiogenesis is based mainly on experiments performed in tumor-transplanted mice, and it has become evident that these models are not representative of human cancer. For an improved understanding, angiogenesis research needs models that better recapitulate the multistep tumorigenesis of human cancers, from the initial genetic insults in single cells to malignant progression in a proper tissue environment. To improve anti-angiogenic therapies in cancer patients, it is necessary to identify additional molecular targets important for tumor angiogenesis, and to get mechanistic insight into their interactions for eventual combinatorial targeting. The recent development of techniques for manipulating the mammalian genome in a precise and predictable manner has opened up new possibilities for the generation of more reliable models of human cancer that are essential for the testing of new therapeutic strategies. In addition, new imaging modalities that permit visualization of the entire mouse tumor vasculature down to the resolution of single capillaries have been developed in pre-clinical models and will likely benefit clinical imaging.     

Stromal Metalloproteinase-9 Is Essential to Angiogenesis and Progressive Growth of Orthotopic Human Pancreatic Cancer in Parabiont Nude Mice

We determined whether host matrix metalloproteinase (MMP) 9 is essential to angiogenesis and to the growth of L3.6pl human pancreatic cancer cells implanted into the pancreas of wild-type (MMP-9^+/+) and knockout (MMP-9^-/-) nude mice. Four weeks after tumor cell injection, pancreatic tumors in MMP-9^+/+ mice were large, had many blood vessels, and contained many macrophages expressing MMP-9. In contrast, pancreatic tumors in MMP-9^-/- mice were significantly smaller, had few blood vessels, and had few macrophages. Next, we parabiosed MMP-9^+/+ mice with MMP-9^+/+ mice, MMP-9^-/- mice with MMP-9^-/- mice, and MMP-9^+/+ mice with MMP-9^-/- mice. Two weeks after parabiosis, we implanted L3.6pl cells into the pancreas of the recipient mouse in each pair. Four weeks later, the mice were necropsied. The parabiosis experiment revealed a direct correlation between intratumoral MMP-9^+/+ expressing macrophages, angiogenesis, and progressive tumor growth. Because the expression of MMP-9 by L3.6pl tumor cells was similar in all parabionts, the data clearly demonstrate a major role for host-derived MMP-9 in angiogenesis and in the growth of human pancreatic cancer in the pancreas of nude mice.