Vascular endothelial growth factor and angiopoietin are required for prostate regeneration

BACKGROUND: The regulation of the prostate size by androgens may be partly the result of androgen effects on the prostatic vasculature. We examined the effect of changes in androgen levels on the expression of a variety of angiogenic factors in the mouse prostate and determined if vascular endothelial growth factor (VEGF)-A and the angiopoietins are involved in the vascular response to androgens. METHODS: Expression of angiogenic factors in prostate was quantitated using real-time PCR at different times after castration and after administration of testosterone to castrated mice. Angiopoietins were localized in prostate by immunohistochemistry and in situ hybridization. The roles of VEGF and the angiopoietins in regeneration of the prostate were examined in mice inoculated with cells expressing soluble VEGF receptor-2 or soluble Tie-2. RESULTS: Castration resulted in a decrease in VEGF-A, VEGF-B, VEGF-C, placenta growth factor, FGF-2, and FGF-8 expression after 1 day. In contrast, VEGF-D mRNA levels increased. No changes in angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), hepatocyte growth factor, VEGF receptor-1, VEGF receptor-2, or tie-2 mRNA levels were observed. Administration of testosterone to castrated mice had the opposite effect on expression of these angiogenic factors. Ang-2 was expressed predominantly in prostate epithelial cells whereas Ang-1 was expressed in epithelium and smooth muscle. Inoculation of mice with cells expressing soluble VEGF receptor-2 or Tie-2 blocked the increase in vascular density normally observed after administration of testosterone to castrated mice. The soluble receptors also blocked the increase in prostate weight and proliferation of prostatic epithelial cells. CONCLUSION: VEGF-A and angiopoietins are required for the vascular response to androgens and for the ability of the prostate to regenerate in response to androgens.     

Thrombospondin-1, vascular endothelial growth factor and fibroblast growth factor-2 are key functional regulators of angiogenesis in the prostate.

BACKGROUND: Prostate cells secrete many molecules capable of regulating angiogenesis; however, which of these actually function as essential regulators of neovascularization is not yet clear. METHODS: Functional angiogenic mediators secreted by normal and diseased prostate cells were identified using an in vitro angiogenesis assay. These factors were quantified by immunoblot or ELISA and localized in tissue by immunohistochemistry. RESULTS: Normal prostate epithelial cell secretions were anti-angiogenic due to inhibitory thrombospondin-1 (TSP-1) whereas this inhibitor was decreased in the pro-angiogenic secretions derived from benign prostatic hyperplasia (BPH) and cancer cells. This pro-angiogenic activity depended primarily on fibroblast growth factor-2 (FGF-2) and/or vascular endothelial growth factor (VEGF) whose secretion was increased. Immunolocalization studies confirmed that the changes detected in vitro also occurred in vivo. CONCLUSIONS: During disease progression in the prostate, production of TSP-1, the major inhibitor, is down-regulated while that of stimulatory FGF-2 and/or VEGF rise, leading to the induction of the new vessels necessary to support tumor growth.     

Testosterone induces vascular endothelial growth factor synthesis in the ventral prostate in castrated rats

PURPOSE: Recent studies suggest that the vasculature is important for the control of prostate growth. Castration induces an involution of the prostate gland and its vasculature. Replacement of testosterone stimulates endothelial cell proliferation and normalizes vascular volumes and blood flow several days before organ regrowth. Antiangiogenesis treatment inhibits the growth of prostate tumors. Understanding the regulation of the prostate vasculature may therefore provide important knowledge of the mechanisms responsible for the growth of non-malignant and malignant prostate tissue. Castration induced regression and testosterone stimulated regrowth of the prostatic vasculature have here been used to study the involvement of the angiogenic factor vascular endothelial growth factor (VEGF) and its receptors flt-1 and flk-1/KDR in the regulation of the prostatic vasculature. MATERIALS AND METHODS: VEGF, flt-1, and flk-1/KDR levels were quantified in the rat ventral prostate following castration and testosterone replacement. Methods used were competitive RT-PCR, Western blot and immunohistochemistry. RESULTS: VEGF mRNA and protein levels were significantly decreased by castration and testosterone treatment induced VEGF synthesis in the rat ventral prostate epithelium. Flt-1 and flk-1/KDR receptor levels were unaffected by castration and testosterone treatment. CONCLUSIONS: Castration down regulates VEGF and testosterone induces VEGF synthesis in epithelial cells in the rat ventral prostate.     

Differential expression of angiogenic cytokines by cell lines and primary cultures of human prostate cancer

Studies on angiogenic cytokines usually are initially based upon their expression by available established cell lines. Our hypothesis is that established epithelial prostate cancer (CaP) cell lines do not accurately reflect angiogenic cytokine expression as compared to epithelial and stromal components of primary cultures generated from clinical CaP specimens. Serum free and growth factor free conditioned medium (CM) was collected from PC3, LNCaP, and their orthotopic selected prostate cancer sublines. Surgically acquired and pathologically confirmed neoplastic prostate tissue was selectively grown for selection of epithelial or stromal components, and CM was also collected. CM was assayed for urokinase (u-PA), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and tumor necrosis factor alpha (TNF-alpha). u-PA was expressed only by androgen independent cell lines, but was detectable in the epithelial and stromal cultures of androgen sensitive primary cultures. bFGF was not secreted by cell lines nor epithelial primary cultures. VEGF was universally expressed, but TNF-alpha was not secreted by cells lines nor primary cultures. These data suggest that the expression of angiogenic cytokines by established epithelial CaP cell lines does not reflect epithelial and stromal primary cultures.Prostate Cancer and Prostatic Diseases (2001) 4, 106-111     

Androgens induce CD-9 in human prostate tissue

Based on microarray analyses of LNCaP and LNCaP-r prostatic cell-lines we tentatively identified CD-9 as an androgen sensitive protein. This prompted us to characterize the androgen sensitivity and the correlation to malignancy of CD-9 at the protein level. Using Western blot, RT-PCR and immunohistochemistry the expression of CD-9 was analysed in LNCaP cells stimulated during increasing time by the synthetic androgen R1881 and also in 88 specimens of human prostate cancer tissues. Expression of CD-9 was induced by R1881 in LNCaP. CD-9 was immunolocalized in human prostate tissue sections representing non-malignant tissue as well as tumour areas. In non-malignant glands CD-9 immunoreactivity was observed at the apical and lateral cell borders of luminal epithelial cells. Basal epithelial cells were largely unstained. In tumour areas CD-9 staining intensity was variable and apparently not related to primary Gleason grade. In prostate tissue from a patient under androgen ablation therapy no staining was observed in luminal epithelial cells or in the tumour areas, but some staining was observed in basal epithelial cells. CD-9 is regulated by androgens in LNCaP and present in human prostate specimens. The expression is variable and changes in expression levels. These and earlier studies using other tissues indicate that CD-9 and its cellular localization could have an important role in prostate cancer cell development.     

Vascular density is highest in the proximal region of the mouse prostate

BACKGROUND: The proximal region of the prostatic ducts harbor the prostatic epithelial stem cells. As stem cell niches in other organs are highly vascularized, we determined if the proximal region is more highly vascularized than the remaining regions of the prostate. The effect of androgen on vascular density in the different prostatic regions was also examined. METHODS: Sections from prostates were immunostained with antibodies to CD31, and the vascular density in proximal, intermediate, and distal regions was calculated by image analysis software. Vascular density was compared in prostates from castrated mice that received daily inoculations of testosterone or vehicle alone for 3 days. To examine the role of angiogenic factors in the response to androgen, some animals were also treated with soluble VEGF receptor-2-Fc or Tie-2--Fc fusion proteins, which inhibit the activities of VEGF and angiopoietins, respectively. The endothelial proliferative response to androgen was determined by double staining sections with antibodies to CD31 and Ki-67. RESULTS: In prostates from intact mice, vascular density was highest in the proximal region and lowest in the distal region. Administration of testosterone to castrated mice increased vascular density to the greatest extent in the distal and intermediate regions. The increase in vascular density required VEGF and the angiopoietins. Endothelial cell proliferation was less sensitive to androgen in the proximal region than the remainder of the prostate. CONCLUSIONS: Vascular density is highest in the proximal region of the prostate, but the proximal vessels are less responsive to testosterone.     

Thrombospondin-1, vascular endothelial growth factor expression and their relationship with p53 status in prostate cancer and benign prostatic hyperplasia

OBJECTIVE: To evaluate the expression of thrombospondin-1 (TSP-1, a potent inhibitor of angiogenesis) and vascular endothelial growth factor (VEGF, an important angiogenic factor in solid tumours) in prostate cancer, and their relationship with p53 status. PATIENTS AND METHODS: Using immunohistochemistry, the expression of VEGF, TSP-1 and p53 was assessed in 82 archival tissue specimens from 23 patients with benign prostatic hyperplasia (BPH), 22 with localized prostate cancer and 37 with metastatic prostate cancer. Seven of the last group had received androgen deprivation therapy. The relationship between the expression of VEGF, TSP-1 and p53 status was also evaluated with tumour grade and stage in patients with prostate cancer. RESULTS: The seven patients receiving hormonal treatment were excluded from the analysis because androgen deprivation significantly increased TSP-1 and decreased VEGF expression (both P < 0.01). Immunohistochemical analysis showed significantly higher VEGF and significantly lower TSP-1 expression (both P < 0.01) in prostate cancer than in BPH tissues. There was also significantly higher VEGF and significantly lower TSP-1 expression (both P < 0.05) in tissues from metastatic than localized prostate cancer. There was no significant correlation between VEGF or TSP-1 expression and Gleason score, but a significant inverse correlation between TSP-1 and VEGF expression. There was a significant association between VEGF expression and p53 status (P < 0.05), but TSP-1 expression was not associated with p53 status. CONCLUSIONS: Angiogenic factors, including VEGF and TSP-1, might be important in the development and progression of prostate cancer. These changes seem to be influenced by p53 status. Identifying the angiogenic factors involved in prostate cancer might lead to the development of diagnostic or therapeutic strategies based on anti-angiogenesis.     

Increased levels of plasma haemoxygenase-1 in prostate cancer

Angiogenesis, a key component of cancer, may be driven by angiogenic growth factors, such as vascular endothelial growth factor (VEGF) and angiopoietin-2. Haemoxygenase-1 (HO-1), a haem-degrading enzyme, may have alternative roles in angiogenesis. Levels of plasma HO-1 have not been reported in prostate cancer. We tested the hypothesis of abnormal HO-1 in 30 men with early prostate cancer, compared with 22 men with benign prostate disease (BPD) and 26 men free of prostate disease, and that HO-1 levels would correlate with VEGF, angiopoietin-2, von Willebrand factor (vWf, marking endothelial perturbation) and PSA. Plasma HO-1 was twofold higher in prostate cancer than in the two control groups, while vWf, VEGF and PSA were also raised (all P<0.02). In the subjects free of prostate disease and in the BPD groups, HO-1 correlated significantly with VEGF (r>0.5, P<0.02) but the correlation in prostate cancer was not significant (r=0.117, P=0.537). There were no correlations with PSA or the Gleason stage. We conclude that HO-1 is associated with VEGF in health and BPD, but in the presence of prostate cancer, raised levels of both HO-1 and VEGF fail to correlate. This observation may have implications for the pathogenesis of prostate cancer.     

Endothelial cells support the growth of prostate tissue in vivo

INTRODUCTION: The contribution of vascular endothelial cells to prostate growth has not been investigated. We examined whether endothelial cells support growth of prostate tissue when co-inoculated with prostate epithelial cells under the renal capsule. METHODS: Vascular endothelial cells were isolated from mice and co-inoculated under the renal capsule with a prostate luminal or basal epithelial cell line. After 60 days, kidneys were examined for growth of prostate tissue. Prostatic tissues were examined by immunohistochemistry for expression of cytokeratins 5 and 8, and vascular density was determined. To determine if increased expression of VEGF-A would increase prostatic growth, transfected endothelial cells overexpressing VEGF-A were co-inoculated with the prostate luminal or basal epithelial lines. RESULTS: Co-inoculation of endothelial cells and prostate luminal or basal epithelial cells resulted in significant growth of prostatic tissue, whereas inoculation of any of the cell lines alone resulted in little growth. The growths from co-inoculation of endothelial cells and luminal epithelial cells contained duct-like structures that stained with antibodies to cytokeratin 8, whereas those from co-inoculation of endothelial cells and basal epithelial cells contained cords of cells that stained with antibodies to cytokeratin 5. Overexpression of VEGF-A had no effect on growth of the prostatic tissues. CONCLUSION: Endothelial cells contribute to the growth of prostatic epithelial cells.     

Intermediate basal cells of the prostate: in vitro and in vivo characterization

BACKGROUND: Progenitor cells within the prostate basal layer may play important roles in differentiation and carcinogenesis; however, prostate stem cell populations remain uncharacterized. METHODS: Immunohistochemical and immunoblot analyses were used to characterize prostate epithelial cells (PrEC), a commercially available prostate basal cell isolate. RESULTS: Proliferating PrECs exhibited immunophenotypic characteristics most consistent with basal cells, but during senescence PrECs up-regulated androgen receptor (AR) mRNA, p27, and low-molecular-weight cytokeratin (LMWCK) expression, suggestive of partial differentiation. PrECs also stained strongly for involucrin, which marked a subset of intermediate prostate basal cells in vivo. Basal hyperplasia consisting of involucrin-positive cells was prevalent in prostate tissue from androgen-ablated patients, and formed epithelial clusters flanked by involucrin-negative basal and luminal monolayers. Cultivation of PrECs on matrigel together with androgen-treated stromal conditioned media resulted in dense aggregates, with a peripheral rim of basal-like cells expressing p63 and basal cytokeratins. CONCLUSIONS: PrEC represents an epithelial population whose basal characteristics are modified in response to matrigel, stromal factors, and senescence, consistent with a transient amplifying population. These cells may derive from a previously unrecognized, involucrin-positive subset present in vivo.     

Androgen Receptor Mediated Growth of Prostate (Cancer)

The understanding of the mode of action of androgens requires insight in the cell biological architecture of the prostate. In the prostate secretory acini, morphologically two cell layers can be discriminated; i.e. the basal and the luminal compartment. The stem cells are thought to be located in the basal compartment. The stem cells have the unique capacity of self-renewal, providing the full repertoire to develop the differentiated ductal system via transient proliferating/amplifying (TP/A) intermediate stem cells. These are in fact early and late progenitors for the exocrine/secretory and neuro-endocrine cells. Exocrine differentiation occurs in the majority of the luminal compartment and is identified by the expression of the androgen receptor (AR), keratin 18 (K18) and prostate specific antigen (PSA). Neuro-endocrine cells are dispersed in the prostate epithelium and express K5 and typical neuro-endocrine markers such as chromogranin A and/or bombesin. The exocrine lineage of differentiation is critically dependent on androgens and thus androgen deprivation therapy will result in declining numbers of secretory/exocrine cells, while the number of stem cells and TP/A intermediate stem cells remains stable. This implies that stem cells and TP/A intermediate stem cells are for their renewal androgen independent, although the TP/A intermediate stem cells are androgen sensitive for expanding the epithelial compartment.Recently, these TP/A intermediate stem cells gained attention because they are thought to play an important role in normal prostate growth as well as in neoplastic transformation. Current hypotheses suggest that from the TP/A cell population, the cancer stem cell develops. Hypothetically, the more committed the cancer stem cell is, the more sensitive the tumour might be for androgen ablation, which could explain why some patients are long-term hormone therapy responders, while others are intrinsically androgen independent. In conclusion, typing of the transformed TP/A intermediate stem cells could enable to discriminate long-term hormone responders from non-responders and could help individualisation of prostate cancer therapy in the future.     

Vascular endothelial growth factor expression and capillary architecture in high-grade PIN and prostate cancer in untreated and androgen-ablated patients

BACKGROUND: Recent studies have demonstrated that angiogenesis is a potent prognostic indicator for patients with prostate cancer (PCa) and have pointed out that the evaluation of vascular endothelial growth factor (VEGF) is useful in assessing the angiogenic phenotype in PCa. The aim of the study was to investigate immunohistochemically the expression of VEGF and its correlation with the pattern of capillary architecture in prostate cancer and high-grade prostatic intraepithelial neoplasia (PIN), in untreated and androgen-ablated patients. METHODS: Forty-five patients who underwent radical prostatectomy (RP) for localized prostate carcinoma were recruited for this study. The study population included two groups: 35 patients who did not receive chemo-, hormone, or radiation therapy before surgery, and 10 patients who were under complete androgen blockade (CAB) for 3 months at time of surgery. VEGF was examined by immunohistochemistry, and its tissue expression was compared with the pattern of capillary architecture evaluated by immunostaining the endothelial antigen CD34. The relationship of VEGF expression to chromogranin A-positive (e.g., neuroendocrine) cells was investigated. RESULTS: In normal tissue, the intensity of the VEGF immunoreactivity in the cytoplasm of secretory cells ranged from negative to low. Very few basal cells stained for VEGF. All prostate cancer specimens stained positively, the intensity of the immunoreaction ranging from low to strong and being correlated with the Gleason score. Strongly positive VEGF immunoreactivity was detected in vascular endothelial cells and in stromal cells surrounding blood vessels. Two discrete immunostaining patterns were observed in high-grade PIN. VEGF expression of low-to-moderate intensity was defined as pattern A. The other, characterized by a strong cytoplasmic immunoreaction similar to that of poorly differentiated tumors, was defined as pattern B. The capillary architecture in high-grade PIN with pattern A was similar to the orderly vascular network seen in normal prostates, whereas in the pattern B it had the characteristics of microvessels usually seen in PCa. The degree of vascularization in the stroma adjacent to intensely VEGF-stained cells (neuroendocrine phenotype) was higher than that noted in association with secretory cells. CAB before surgery downregulated the expression of VEGF and decreased the degree of vascularization, except in the cell areas with neuroendocrine (NE) features. CONCLUSIONS: Our immunohistochemical results indicate that significant levels of VEGF are present in prostate cancer and in a population of PIN lesions, expression being highest in association with NE cells. VEGF expression is downregulated by hormonal manipulation, except in the population of NE cells.     

Blood vessels are regulators of growth, diagnostic markers and therapeutic targets in prostate cancer

The vasculature plays an important role in the normal and malignant prostate. Under basal conditions both glandular epithelial and stromal prostate cells produce an abundance of blood flow and angiogenesis regulating substances and the expression of these is generally increased in prostate tumors. The proportion of proliferating endothelial cells is high in the normal prostate compared to other tissues in the body. After castration effects on the vasculature, such as decreased blood flow and vascular regression, precede effects on the glandular compartment. Correspondingly, hormone induced prostate growth is characterized by early effects on the vasculature such as increased blood flow and endothelial cell proliferation, thus indicating that the vasculature may be involved in the androgenic regulation of the prostate. Prostatic intraepithelial neoplasia (PIN) and prostate cancer are associated with increased vascular density and in experimental models prostate cancer growth is apparently angiogenesis-dependent since tumor growth and progression can be inhibited by antiangiogenic treatment. Moreover, vascular density has been related to prognosis in prostate cancer patients. A better understanding of the pathways regulating angiogenesis in the normal prostate and how these pathways change during malignant transformation can hopefully lead to better prognostic markers and therapies for the large group of patients with prostate cancer. The purpose of this review is therefore to summarize the current knowledge on the role and regulation of the vasculature in the prostate and its potential clinical applications.     

Stroma-epithelium crosstalk in prostate cancer

The critical role played by stroma-epithelium crosstalk in carcinogenesis and progression of prostate cancer has been increasingly recognized. These interactions are mediated by a variety of paracrine factors secreted by cancer cells and/or stromal cells. In human prostate cancer, reactive stroma is characterized by an increase in myofibroblasts and a corresponding amplification of extracellular matrix production and angiogenesis. Permanent genetic mutations have been reported in stromal cells as well as in tumour cells. Transforming growth factor-J3, vascular endothelial growth factor, platelet-derived growth factor and fibroblast growth factor signalling pathways are involved in the process of angiogenesis, whereas hepatocyte growth factor, insulin-like growth factor-l, epidermal growth factor, CXC12 and Interleukin-6 play active roles in the progression, androgen-independent conversion and distal metastasis of prostate cancer. Some soluble factors have reciprocal interactions with androgens and the androgen receptor （AR）, and can even activate AR in the absence of the androgen ligand. In this article, we review the complex interactions between cancer cells and the surrounding microenvironment, and discuss the potential therapeutic targets in the stromal compartment of prostate cancer.     

Effects of finasteride on vascular endothelial growth factor

OBJECTIVE: Finasteride has been shown to reduce prostate bleeding in patients with benign prostatic hyperplasia (BPH). The mechanisms behind this are not known, but it has been suggested that finasteride reduces bleeding by inhibiting angiogenesis in the prostate. Studies in animals have shown that castration rapidly induces involution of the prostate vasculature, and androgen-stimulated prostate growth may be angiogenesis dependent. The objective of this study was to explore the response to finasteride on the vasculature and the expression of vascular endothelial growth factor (VEGF), a potent regulatory factor of angiogenesis in human prostate tissue. MATERIAL AND METHODS: Patients with BPH were randomly assigned to 3 months of treatment either with finasteride (5 mg/day) or placebo before undergoing transurethral resection of the prostate (TURP). Prostate tissue VEGF expression was quantified by Western blot and the vascular density determined in Factor VIII immunostained tissue sections. Serum concentrations of VEGF were measured with ELISA technique. RESULTS: Patients treated with finasteride (n = 15) showed a decrease in prostate tissue VEGF(165) expression compared with placebo (n = 13) treated patients (p < 0.05), but the vascular density and the serum VEGF levels were unaffected. CONCLUSIONS: This study shows that finasteride treatment decreases VEGF expression in the human prostate.     

Differential expression of angiopoietin-2 and vascular endothelial growth factor in androgen-independent prostate cancer models

OBJECTIVE

To investigate the relationship between microvessel density (MVD), blood vessel morphology and the expression of angiopoietin (Ang)‐1, Ang‐2, tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Tie)‐2, and vascular endothelial growth factor (VEGF) in androgen‐dependent (AD) and androgen‐independent (AI) prostate cancer models, to gain insight into the regulation of angiogenesis at different stages of prostate cancer.

MATERIALS AND METHODS

MVD and blood vessel morphology were evaluated by CD34 immunohistochemical staining. The mRNA and protein secretion of the Angs, Tie‐2 and VEGF were measured by real‐time polymerase chain reaction and enzyme‐linked immunosorbent assays, respectively, in LNCaP (AD) and LNCaP‐19, C4‐2, C4–2B₄ and PC‐3 (AI) prostate cancer xenografts in mice.

RESULTS

LNCaP, C4‐2 and C4–2B₄ xenografts had high expression of Ang‐2 and VEGF, similar MVD and blood vessel morphology_. However, the most angiogenic cell line LNCaP‐19 expressed low levels of both factors and had different vessel morphology. PC‐3 xenografts had a similar MVD to LNCaP, C4‐2 and C4–2B₄, but the Ang‐2 and VEGF expression as well as the vessel morphology were similar to LNCaP‐19.

CONCLUSION

The differences in MVD, blood vessel morphology and the expression of Ang‐2 and VEGF show that prostate cancer cells display angiogenic heterogeneity, which indicates different roles of these factors in the regulation of angiogenesis in different stages of prostate cancer.     

Development of the VCaP androgen-independent model of prostate cancer

Prostate epithelial cell growth is dependent on the presence of androgens, and transition of prostate cancer to an androgen-independent phenotype results in a highly aggressive, currently incurable cancer. We have developed a new preclinical model of androgen-independent prostate cancer derived from the VCaP prostate cancer epithelial cell line. VCaP cells were subcutaneously implanted and serially passaged in castrated male severe combined immunodeficient mice. Androgen independence was confirmed by WST-1 (a tetrazolium salt) cell proliferation assay in the absence or presence of dihydrotesterone (1-100 nM). VCaP androgen-sensitive cells responded dose dependently to dihydrotesterone, whereas VCaP androgen-independent cells did not alter their proliferation in response to dihydrotesterone. Gene expression of androgen receptor, B-cell lymphoma-2, prostate cancer antigen 3, prostate acid phosphatase, 6 transmembrane epithelial antigen of the prostate, and survivin was determined by polymerase chain reaction amplification. B-cell lymphoma-2 expression was up regulated in the VCaP androgen-independent lines compared to the VCaP androgen-sensitive, suggesting a possible mechanism of androgen independence. Furthermore, tumor-associated angiogenesis was assessed by immunofluorescence confocal microscopy of CD31. VCaP androgen-independent tumors showed enhanced angiogenesis compared to VCaP androgen-sensitive tumors. These results illustrate the development of a novel model of prostate cancer androgen independence and provide a new system to study angiogenesis and the transition to androgen independence.     

Vascular endothelial growth factor content in metastasizing and nonmetastasizing Dunning prostatic adenocarcinoma

BACKGROUND: Tumor angiogenesis is important in progressive tumor growth and metastasis. In the normal rat prostate and in androgen-sensitive prostate tumors androgen ablation causes an involution of the vasculature and a decrease in the vascular endothelial growth factor (VEGF) levels before regression of the prostate gland. To examine whether angiogenesis and metastasis are regulated by VEGF in androgen-insensitive and metastasizing prostate tumors, five Dunning rat prostate cancer sublines were tested; the androgen-sensitive, nonmetastasizing R3327 PAP, and the androgen-insensitive, low metastasizing AT-1, and the three androgen-insensitive, metastasizing AT-2, AT-3, and MatLyLu Dunning prostatic adenocarcinomas. METHODS: VEGF levels were quantified in the rat dorsolateral prostate and in the five Dunning sublines using competitive RT-PCR, Western blot, and Elisa. Vascular density was determined by factor VIII staining. RESULTS: VEGF mRNA was increased in all tumors compared with normal prostates. The two metastatic sublines AT-3 and MatLyLu and the nonmetastatic subline AT-1 showed the highest VEGF mRNA expression. VEGF protein levels in the prostate gland showed increased expression in the metastatic sublines, AT-2, AT-3, and MatLyLu, compared with the nonmetastatic AT-1 subline and the ventral prostate. VEGF proteins in serum were highest in the metastatic AT-3 subline. The vessel density was highest in the two highly metastatic sublines AT-3 and MatLyLu. CONCLUSIONS: Our results suggest that VEGF levels are associated with microvessel density and the previously established metastatic pattern of these rat prostate tumor systems.     

Therapeutic angiogenesis for coronary artery disease

Therapeutic angiogenesis may be a realistic approach in treating ischemic heart disease. VEGF is a major angiogenic factor involved in physiological as well as pathological angiogenesis. The ability of VEGF to promote angiogenesis in animal and clinical studies has been studied extensively. However, it is becoming clear that VEGF alone may not be sufficient to effectively complete the angiogenesis process. The use of more than one growth factor may be more pertinent in creating a sustainable angiogenic effect with clinically significant outcome. The challenge is to find complementary partners in angiogenesis to better affect the outcome of the process. To this end, we have been studying the effects of other angiogenic factors such as angiopoietin-1 (Ang-1) in a chronic ischemic porcine model. Single intramyocardial introduction of adenovirus-mediated gene transfer of Ang-1 into the left ventricle free wall has been found to enhance angiogenesis by augmenting the formation of new capillaries that manifested in improved total blood flow in the myocardium. A combined therapeutic angiogenesis study involving VEGF and Ang-1 is currently underway. Due to their unique complementary properties, it is expected that the combination will not merely enhance angiogenesis but will also lead to healthy and mature vascular network in the ischemic myocardium.