In vivo gene transfer of pigment epithelium-derived factor inhibits tumor growth in syngeneic murine models of thoracic malignancies

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

Association of pigment epithelium derived factor expression with cancer progression and prognosis: a meta-analysis study

BACKGROUND

Pigment epithelium derived factor (PEDF) is a secreted protein that strongly suppresses angiogenesis and directly inhibits cancer cells proliferation. The differential expression of PEDF has been observed in multiple types of human tumors. However, it is unclear as to how PEDF expression is associated with cancer progression and if PEDF could serve as a prognostic marker for cancer patients.

METHODS

We performed a comprehensive search for the studies on PEDF expression in 14 top-ranked types of solid tumor cancer with the highest incidence. A systemic approach was used to screen for qualified studies and to extract data. Meta-analysis was performed to investigate if PEDF expression is associated with the TNM staging, tumor size, lymph node invasion, distal metastasis and pathological grade of tumor in a pan-cancer manner. A Kaplan-Meier curve was plotted with the digitally-reconstituted patient survival data to study the effect of PEDF expression on the prognosis of cancer patients.

RESULTS

A total of nine studies were selected, reviewed and analyzed. Meta-analysis suggested that decreased PEDF protein expression was associated with higher TNM staging (OR = 2.13, 95% CI: 1.61-2.81), larger tumor size (OR = 1.42, 95% CI: 1.1-1.84), larger possibility of lymph node invasion (OR = 1.68, 95% CI: 1.26-2.22) and higher pathological grade (OR = 1.6, 95% CI: 1.2-2.13). No correlation was found between PEDF expression and tumor distal metastasis, gender or age. In addition, low PEDF protein level in tumor tissue is correlated with shorter overall survival (P < 0.05).

CONCLUSIONS

Low PEDF protein expression in cancer is significantly associated with more advanced cancer progression and significantly poorer survival. The differential clinical outcome among patients with various PEDF expression suggests its prognostic value.

The increasing role of pigment epithelium-derived factor in metastasis: from biological importance to a promising target

Pigment epithelium-derived factor (PEDF) is a non-inhibitory member of the serpin (serine protease inhibitor) family and is a well-known potent anti-tumor factor in a variety of cancers. It has been ascertained that PEDF regulates multiple metastatic processes through various plausible mechanisms, including inhibiting angiogenesis, inducing apoptosis, stimulating extracellular matrix (ECM) degradation, and suppressing the epithelial-to-mesenchymal transition (EMT) process. Although PEDF has been recognized as an anti-metastatic marker in most studies, its role remains controversial with conflicting reports of PEDF as a metastatic marker. The emerging insights into the mechanism(s) of PEDF in tumor progression and its therapeutic effects are discussed systematically in this review, aiming to improve our understanding in the context of metastasis and drug development.

Therapeutic Potential of Pigment Epithelium-derived Factor in Cancer

Pigment epithelium-derived factor (PEDF) is one of the serine protease inhibitors with multifunctional properties, which is produced by various types of organs and tissues. There is an accumulating body of evidence that PEDF plays an important role in the maintenance of tissue homeostasis. Indeed, PEDF not only works as an endogenous inhibitor of angiogenesis, but also suppresses oxidative stress, inflammatory and thrombotic reactions in cell culture systems, animal models, and humans. Furthermore, we, along with others, have found that PEDF inhibits proliferation of, and induces apoptotic cell death in, numerous kinds of tumors. In addition, circulating as well as tumor expression levels of PEDF have been inversely associated with tumor growth and metastasis. These observations suggest that supplementation of PEDF proteins and/or enhancement of endogenous PEDF expression could be a novel therapeutic strategy for the treatment of cancer. Therefore, in this paper, we review the effects of PEDF on diverse types of cancer, and discuss its therapeutic perspectives.

Chitosan sulfate inhibits angiogenesis via blocking the VEGF/VEGFR2 pathway and suppresses tumor growth in vivo

SCTS inhibits neovascularization by blocking the VEGF/VEGFR2 signal pathway and exerts anti-tumor effects.

A dock derived compound against laminin receptor (37 LR) exhibits anti-cancer properties in a prostate cancer cell line model

Laminin receptor (67 LR) is a 67 kDa protein derived from a 37 kDa precursor (37 LR). 37/67 LR is a strong clinical correlate for progression, aggression, and chemotherapeutic relapse of several cancers including breast, prostate, and colon. The ability of 37/67 LR to promote cancer cell aggressiveness is further increased by its ability to transduce physiochemical and mechanosensing signals in endothelial cells and modulate angiogenesis. Recently, it was demonstrated that 37/67 LR modulates the anti-angiogenic potential of the secreted glycoprotein pigment epithelium-derived factor (PEDF). Restoration of PEDF balance is a desirable therapeutic outcome, and we sought to identify a small molecule that could recapitulate known signaling properties of PEDF but without the additional complications of peptide formulation or gene delivery safety validation. We used an in silico drug discovery approach to target the interaction interface between PEDF and 37 LR. Following cell based counter screening and binding validation, we characterized a hit compound's anti-viability, activation of PEDF signaling-related genes, anti-wound healing, and anti-cancer signaling properties. This hit compound has potential for future development as a lead compound for treating tumor growth and inhibiting angiogenesis.

Genetic Modification of the Lung Directed Toward Treatment of Human Disease

Genetic modification therapy is a promising therapeutic strategy for many diseases of the lung intractable to other treatments. Lung gene therapy has been the subject of numerous preclinical animal experiments and human clinical trials, for targets including genetic diseases such as cystic fibrosis and α1-antitrypsin deficiency, complex disorders such as asthma, allergy, and lung cancer, infections such as respiratory syncytial virus (RSV) and Pseudomonas, as well as pulmonary arterial hypertension, transplant rejection, and lung injury. A variety of viral and non-viral vectors have been employed to overcome the many physical barriers to gene transfer imposed by lung anatomy and natural defenses. Beyond the treatment of lung diseases, the lung has the potential to be used as a metabolic factory for generating proteins for delivery to the circulation for treatment of systemic diseases. Although much has been learned through a myriad of experiments about the development of genetic modification of the lung, more work is still needed to improve the delivery vehicles and to overcome challenges such as entry barriers, persistent expression, specific cell targeting, and circumventing host anti-vector responses.

Effects of silencing endothelin-1 on invasion and vascular formation in lung cancer

Endothelin-1 (ET-1), which exists not only in the vascular endothelium but is also widely present in various tissues and cells, is an important cardiovascular regulatory factor that serves an important role in maintaining the basal vascular tone and homeostasis in the cardiovascular system. In the present study, the ET-1 gene was silenced by RNA interference, and the effects on lung cancer cell proliferation and tumor cell invasion were then detected by Cell Counting kit-8 and Transwell assays. In addition, the expression of apoptosis, growth and invasion-associated proteins, including RhoA/C, vascular endothelial growth factor, pigment epithelium-derived factor, AKT, E-cadherin and cyclooxygenase-2 was evaluated by western blotting upon silencing ET-1. In the present study, Endostar, a recombinant human endostatin injectable drug, was also used, and it was assessed whether the sensitivity of tumor cells to this drug could be increased by silencing ET-1. Both in vivo and in vivo tests were carried out in the present study. The experimental data indicated that ET-1 silencing can inhibit tumor cell proliferation and invasion, particularly in the presence of Endostar.

Pigment Epithelium-Derived Factor (PEDF) Improves Ischemic Cardiac Functional Reserve Through Decreasing Hypoxic Cardiomyocyte Contractility Through PEDF Receptor (PEDF-R)

BACKGROUND

Pigment epithelium-derived factor (PEDF), which belongs to the noninhibitory serpin family, has shown the ability to stimulate several physiological processes, such as antiangiogenesis, anti-inflammation, and antioxidation. In the present study, the effects of PEDF on contractility and calcium handling of rat ventricular myocytes were investigated.

METHODS AND RESULTS

Adult Sprague-Dawley rat models of acute myocardial infarction (AMI) were surgically established. PEDF-lentivirus was delivered into the myocardium along and away from the infarction border to overexpress PEDF. Video edge detection was used to measure myocyte shortening in vitro. Intracellular Ca(2+) was measured in cells loaded with the Ca(2+) sensitive fluorescent indicator, Fura-2-acetoxymethyl ester. PEDF local overexpression enhanced cardiac functional reserve in AMI rats and reduced myocardial contracture bordering the infracted area. Exogenous PEDF treatment (10 nmol/L) caused a significant decrease in amplitudes of isoproterenol-stimulated myocyte shortening, Ca(2+) transients, and caffeine-evoked Ca(2+) transients in vitro. We then tested a potential role for PEDF receptor-mediated effects on upregulation of protein kinase C (PKC) and found evidence of signaling through the diacylglycerol/PKCα pathway. We also confirmed that pretreatment of cardiomyocytes with PEDF exhibited dephosphorylation of phospholamban at Ser(16), which could be attenuated with PKC inhibition.

CONCLUSIONS

The results suggest that PEDF depresses myocyte contractility by suppressing phosphorylation of phospholamban and Ca(2+) transients in a PKCα-dependent manner through its receptor, PEDF receptor, therefore improving cardiac functional reserve during AMI.

Pigment epithelial-derived factor gene loaded novel COOH-PEG-PLGA-COOH nanoparticles promoted tumor suppression by systemic administration

Anti-angiogenesis has been proposed as an effective therapeutic strategy for cancer treatment. Pigment epithelium-derived factor (PEDF) is one of the most powerful endogenous anti-angiogenic reagents discovered to date and PEDF gene therapy has been recognized as a promising treatment option for various tumors. There is an urgent need to develop a safe and valid vector for its systemic delivery. Herein, a novel gene delivery system based on the newly synthesized copolymer COOH-PEG-PLGA-COOH (CPPC) was developed in this study, which was probably capable of overcoming the disadvantages of viral vectors and cationic lipids/polymers-based nonviral carriers. PEDF gene loaded CPPC nanoparticles (D-NPs) were fabricated by a modified double-emulsion water-in-oil-in-water (W/O/W) solvent evaporation method. D-NPs with uniform spherical shape had relatively high drug loading (~1.6%), probably because the introduced carboxyl group in poly (D,L-lactide-co-glycolide) terminal enhanced the interaction of copolymer with the PEDF gene complexes. An excellent in vitro antitumor effect was found in both C26 and A549 cells treated by D-NPs, in which PEDF levels were dramatically elevated due to the successful transfection of PEDF gene. D-NPs also showed a strong inhibitory effect on proliferation of human umbilical vein endothelial cells in vitro and inhibited the tumor-induced angiogenesis in vivo by an alginate-encapsulated tumor cell assay. Further in vivo antitumor investigation, carried out in a C26 subcutaneous tumor model by intravenous injection, demonstrated that D-NPs could achieve a significant antitumor activity with sharply reduced microvessel density and significantly promoted tumor cell apoptosis. Additionally, the in vitro hemolysis analysis and in vivo serological and biochemical analysis revealed that D-NPs had no obvious toxicity. All the data indicated that the novel CPPC nanoparticles were ideal vectors for the systemic delivery of PEDF gene and might be widely used as systemic gene vectors.

Anti-tumor effects of pigment epithelium-derived factor (PEDF): implication for cancer therapy. A mini-review

Pigment epithelium-derived factor (PEDF) is a secreted glycoprotein and a non-inhibitory member of the serine protease inhibitor (serpin) family. It is widely expressed in human fetal and adult tissues but its expression decreases with age and in malignant tissues. The main anti-cancer activities of PEDF derive from its dual effects, either indirectly on the tumor microenvironment (indirect antitumor action) or directly on the tumor itself (direct antitumor influence). The indirect antitumor activities of PEDF were uncovered from the early findings that it stimulates retinoblastoma cell differentiation and that additionally it possesses anti-angiogenic, anti-tumorigenic and anti-metastatic properties. The mechanisms of its direct antitumor effect, however, have not been fully elucidated. This review highlights recent progress in our understanding of the multifunctional activities of PEDF and, in particular, its anti-cancer signaling mechanisms. Additionally, we discuss the possibility of using novel phosphaplatin compounds that can upregulate PEDF expression as a chemotherapy for cancer treatment.

Trophic factors in the pathogenesis and therapy for retinal degenerative diseases

Trophic factors are endogenously secreted proteins that act in an autocrine and/or paracrine fashion to affect vital cellular processes such as proliferation, differentiation, and regeneration, thereby maintaining overall cell homeostasis. In the eye, the major contributors of these molecules are the retinal pigment epithelial (RPE) and Müller cells. The primary paracrine targets of these secreted proteins include the photoreceptors and choriocapillaris. Retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa are characterized by aberrant function and/or eventual death of RPE cells, photoreceptors, choriocapillaris, and other retinal cells. We discuss results of in vitro and in vivo animal studies in which candidate trophic factors, either singly or in combination, were used in an attempt to ameliorate photoreceptor and/or retinal degeneration. We also examine current trophic factor therapies as they relate to the treatment of retinal degenerative diseases in clinical studies.

The effects of PEDF on cancer biology: mechanisms of action and therapeutic potential

The potent actions of pigment epithelium-derived factor (PEDF) on tumour-associated cells, and its extracellular localization and secretion, stimulated research on this multifunctional serpin. Such studies have identified several PEDF receptors and downstream signalling pathways. Known cellular PEDF responses have expanded from the initial discovery that PEDF induces retinoblastoma cell differentiation to its anti-angiogenic, antitumorigenic and antimetastatic properties. Although the diversity of PEDF activities seems to be complex, they are consistent with the varied mechanisms that regulate this multimodal factor. If PEDF is to be used for cancer management, a deeper appreciation of its many functions and mechanisms of action is needed.

AAV-mediated human PEDF inhibits tumor growth and metastasis in murine colorectal peritoneal carcinomatosis model

Background

Angiogenesis plays an important role in tumor growth and metastasis, therefore antiangiogenic therapy was widely investigated as a promising approach for cancer therapy. Recently, pigment epithelium-derived factor (PEDF) has been shown to be the most potent inhibitor of angiogenesis. Adeno-associated virus (AAV) vectors have been intensively studied due to their wide tropisms, nonpathogenicity, and long-term transgene expression in vivo. The objective of this work was to evaluate the ability of AAV-mediated human PEDF (hPEDF) as a potent tumor suppressor and a potential candidate for cancer gene therapy.

Methods

Recombinant AAV₂ encoding hPEDF (rAAV₂-hPEDF) was constructed and produced, and then was assigned for in vitro and in vivo experiments. Conditioned medium from cells infected with rAAV₂-hPEDF was used for cell proliferation and tube formation tests of human umbilical vein endothelial cells (HUVECs). Subsequently, colorectal peritoneal carcinomatosis (CRPC) mouse model was established and treated with rAAV₂-hPEDF. Therapeutic efficacy of rAAV₂-hPEDF were investigated, including tumor growth and metastasis, survival time, microvessel density (MVD) and apoptosis index of tumor tissues, and hPEDF levels in serum and ascites.

Results

rAAV₂-hPEDF was successfully constructed, and transmission electron microscope (TEM) showed that rAAV₂-hPEDF particles were non-enveloped icosahedral shape with a diameter of approximately 20 nm. rAAV₂-hPEDF-infected cells expressed hPEDF protein, and the conditioned medium from infected cells inhibited proliferation and tube-formation of HUVECs in vitro. Furthermore, in CRPC mouse model, rAAV₂-hPEDF significantly suppressed tumor growth and metastasis, and prolonged survival time of treated mice. Immunofluorescence studies indicated that rAAV₂-hPEDF could inhibit angiogenesis and induce apoptosis in tumor tissues. Besides, hPEDF levels in serum and ascites of rAAV₂-hPEDF-treated mice were significant higher than those in rAAV₂-null or normal saline (NS) groups.

Conclusions

Thus, our results suggest that rAAV₂-hPEDF may be a potential candidate as an antiangiogenic therapy agent.

AAV-mediated gene transfer of human pigment epithelium-derived factor inhibits Lewis lung carcinoma growth in mice

Pigment epithelium-derived factor (PEDF) is the most potent inhibitor of angiogenesis in the mammalian eye, and mechanisms through which PEDF exerts its antitumour activity have recently been defined. The aim of our research was to evaluate the ability of adeno-associated virus (AAV) vector-mediated transfer of human PEDF to inhibit Lewis lung carcinoma (LCC) cell growth. Intratumoural injection of AAV-PEDF caused significant reduction of the tumour volume and prolonged the survival time of mice bearing LLC cells, which were associated with decreased microvessel density and increased apoptosis in the tumours. AAV vectors represent a very promising tool for cancer gene therapy. No noticeable toxicity concerning AAV was detected as inferred from monitoring changes in animal body weight as well as basic organ structure and histological morphology, and by analyzing mouse liver and kidney function. Our findings indicate that AAV-mediated PEDF gene expression may offer an active approach to inhibit LLC growth and that treatment with AAV-PEDF may provide a promising therapeutic strategy in lung cancer treatment.

Codon preference optimization increases heterologous PEDF expression

Pigment epithelium-derived factor (PEDF) is widely known for its neurotrophic and antiangiogenic functions. Efficacy studies of PEDF in animal models are limited because of poor heterologous protein yields. Here, we redesigned the human PEDF gene to preferentially match codon frequencies of E coli without altering the amino acid sequence. Following de novo synthesis, codon optimized PEDF (coPEDF) and the wtPEDF genes were cloned into pET32a containing a 5′ thioredoxin sequence (Trx) and the recombinant Trx-coPEDF or Trx-wtPEDF fusion constructs expressed in native and two tRNA augmented E coli hosts - BL21-CodonPlus(DE3)-RIL and BL21-CodonPlus(DE3)-RP, carrying extra copies of tRNA^arg,ile,leu and tRNA^arg,pro genes , respectively. Trx-PEDF fusion proteins were isolated using Ni-NTA metal affinity chromatography and PEDF purified after cleavage with factor Xα. Protein purity and identity were confirmed by western blot, MALDI-TOF, and UV/CD spectral analyses. Expression of the synthetic gene was ∼3.4 fold greater (212.7 mg/g; 62.1 mg/g wet cells) and purified yields ∼4 fold greater (41.1 mg/g; 11.3 mg/g wet cell) than wtPEDF in the native host. A small increase in expression of both genes was observed in hosts supplemented with rare tRNA genes compared to the native host but expression of coPEDF was ∼3 fold greater than wtPEDF in both native and codon-bias-adjusted E coli strains. ΔGs at −3 to +50 of the Trx site of both fusion genes were −3.9 kcal/mol. Functionally, coPEDF was equally as effective as wtPEDF in reducing oxidative stress, promoting neurite outgrowth, and blocking endothelial tube formation. These findings suggest that while rare tRNA augmentation and mRNA folding energies can significantly contribute to increased protein expression, preferred codon usage, in this case, is advantageous to translational efficiency of biologically active PEDF in E coli. This strategy will undoubtedly fast forward studies to validate therapeutic utility of PEDF in vivo.

Pigment epithelium-derived factor stimulates tumor macrophage recruitment and is downregulated by the prostate tumor microenvironment

Pigment epithelium-derived factor (PEDF) is a potent inhibitor of angiogenesis but whether it has additional effects on the tumor microenvironment is largely unexplored. We show that overexpression of PEDF in orthotopic MatLyLu rat prostate tumors increased tumor macrophage recruitment. The fraction of macrophages expressing inducible nitric oxide synthase, a marker of cytotoxic M1 macrophages, was increased, suggesting that PEDF could enhance antitumor immunity. In addition, PEDF overexpression reduced vascular growth both in the tumor and in the surrounding normal tissue, slowed tumor growth, and decreased lymph node metastasis. Contrary, extratumoral lymphangiogenesis was increased. PEDF expression is, for reasons unknown, often decreased or lost during prostate tumor progression. When AT-1 rat prostate tumor cells, expressing high levels of PEDF messenger RNA (mRNA) and protein, were injected into the prostate, PEDF is markedly downregulated, suggesting that factors in the microenvironment suppressed its expression. One such factor could be macrophage-derived tumor necrosis factor alpha (TNFalpha). A fraction of the accumulating macrophages expressed TNFalpha, and TNFalpha treatment downregulated the expression of PEDF protein and mRNA in prostate AT-1 tumor cells in vitro and in the rat ventral prostate in vivo. PEDF apparently has multiple effects in prostate tumors: it suppresses angiogenesis and metastasis, but it also causes macrophage accumulation. Accumulating macrophages may inhibit tumor growth, but they may also suppress PEDF and enhance lymph angiogenesis and, in this way, eventually enhance tumor growth.

Accurate molecular classification of cancer using simple rules

BACKGROUND

One intractable problem with using microarray data analysis for cancer classification is how to reduce the extremely high-dimensionality gene feature data to remove the effects of noise. Feature selection is often used to address this problem by selecting informative genes from among thousands or tens of thousands of genes. However, most of the existing methods of microarray-based cancer classification utilize too many genes to achieve accurate classification, which often hampers the interpretability of the models. For a better understanding of the classification results, it is desirable to develop simpler rule-based models with as few marker genes as possible.

METHODS

We screened a small number of informative single genes and gene pairs on the basis of their depended degrees proposed in rough sets. Applying the decision rules induced by the selected genes or gene pairs, we constructed cancer classifiers. We tested the efficacy of the classifiers by leave-one-out cross-validation (LOOCV) of training sets and classification of independent test sets.

RESULTS

We applied our methods to five cancerous gene expression datasets: leukemia (acute lymphoblastic leukemia [ALL] vs. acute myeloid leukemia [AML]), lung cancer, prostate cancer, breast cancer, and leukemia (ALL vs. mixed-lineage leukemia [MLL] vs. AML). Accurate classification outcomes were obtained by utilizing just one or two genes. Some genes that correlated closely with the pathogenesis of relevant cancers were identified. In terms of both classification performance and algorithm simplicity, our approach outperformed or at least matched existing methods.

CONCLUSION

In cancerous gene expression datasets, a small number of genes, even one or two if selected correctly, is capable of achieving an ideal cancer classification effect. This finding also means that very simple rules may perform well for cancerous class prediction.

cDNA microarray analysis of pigment epithelium-derived factor-regulated gene expression profile in prostate carcinoma cells

OBJECTIVES

To clarify molecular mechanisms involved in the action of pigment epithelium-derived factor (PEDF) in hormone insensitive prostate cancer cells.

METHODS

Total ribonucleic acid from untreated and PEDF-treated cells was subjected to microarray analysis using BioStar 8464 microarray. Real-time polymerase chain reaction analysis was conducted to confirm the microarray data.

RESULTS

Twenty-seven out of 8464 genes were found altered in both cell lines. Common gene responses altered by PEDF were identified and included genes known to alter cell signaling as well as genes involved in catalytic activity, cell proliferation, angiogenesis and apoptosis. Real-time reverse transcription polymerase chain reaction, in accordance with the microarray analysis, indicated that PEDF treatment caused an upregulation in the mRNA expression level of stanniocalcin 2, brain-specific angiogenesis inhibitor 2 and growth arrest, DNA-damage-inducible, alpha, and downregulation in the messenger ribonucleic acid level of fibroblast growth factor 3, teratocarcinoma-derived growth factor, neuropilin1, and endothelial Per/ARNT/Sim domain protein1, respectively.

CONCLUSIONS

These findings demonstrate that PEDF administration causes significant changes in the gene expression of the prostate, providing insights into the potential role of PEDF in the treatment of prostate cancer.

Anti-angiogenic therapy for osteosarcoma

Even in tumor centers using established protocols, the survival rate of patients with osteosarcoma has not improved significantly in recent years. Novel therapies are urgently needed as an adjunct to conventional treatment modalities, to reduce the dose and subsequent toxicity associated with current chemotherapy, improve local disease control, prevent development of metastases, and offer an alternative treatment for those tumors that are poorly responsive to chemotherapy. Anti-angiogenic therapy currently holds great potential in conjunction with conventional treatment modalities for osteosarcoma. Specifically, anti-angiogenic factors derived from cartilage, a natural barrier to osteosarcoma invasion, may have important therapeutic applications in osteosarcoma.

Pigment epithelium-derived factor as a multifunctional antitumor factor

The design of new therapeutic strategies for cancer treatment is based on the combination of drugs directed against different tumor compartments, including the tumor cells themselves and components of the stroma, such as the tumor vasculature. Indeed, several antiangiogenic compounds have entered clinical trials for use alone or in combination with conventional cytotoxic drugs. Pigment epithelium-derived factor (PEDF) is a multifunctional natural peptide with complex neurotrophic, neuroprotective, antiangiogenic, and proapoptotic biological activities, any of which could potentially be exploited for therapeutic purposes. This review summarizes recent studies that reveal the antitumor potential of PEDF based on its antiangiogenic properties and its newly discovered direct antitumor effects, which involve the induction of differentiation or apoptosis in tumor cells. We also discuss possible therapeutic applications of PEDF, based on these mechanistic insights and on the identification of functional domains that retain specific biological activities.

Gene transfer of pigment epithelium-derived factor suppresses tumor growth and angiogenesis in a hepatoblastoma xenograft model

Normal hepatocytes express pigment epithelium-derived factor (PEDF), an endogenous antiangiogenic factor. We hypothesized that decreased PEDF expression may be one mechanism driving hepatoblastoma growth, and in vivo gene transfer of PEDF could suppress neovascularization and limit tumor growth. PEDF functional activity was determined in vitro using endothelial cell migration assays and in vivo using a subcutaneous tumor model. HUH-6 human hepatoblastoma tumors were treated with hybrid adenoviral/adeno-associated viral expression vectors for PEDF (Hyb-PEDF, n = 4) or beta-galactosidase (Hyb-betagal, n = 4) daily for 4 d. Mitotic figures, microvascular density (MVD), PEDF, and VEGF expression were assessed. Hyb-PEDF treatment inhibited in vivo tumor growth (p < 0.008) and decreased MVD (p < 0.001), the number of mitotic figures (p < 0.001), and VEGF expression when compared with Hyb-betagal-treated tumors. HUH-6 expression of PEDF was dramatically reduced when cultured under hypoxic conditions and also when grown in vivo, and the addition of neutralizing anti-PEDF antibody increased the already high baseline angiogenic activity of the HUH-6 cell secretions in vitro (p < 0.04). PEDF is an important endogenous regulator of the liver vasculature. Augmenting intra-tumoral PEDF levels inhibits tumor growth by reducing angiogenesis and VEGF expression. Potent inhibitors of angiogenesis, such as PEDF, may be an effective alternative treatment for children with hepatoblastoma.

Pigment epithelium-derived factor: a multimodal tumor inhibitor

Pigment epithelium-derived factor (PEDF), a noninhibitory member of the serine protease inhibitor (serpin) family, is a well-known potent endogenous inhibitor of angiogenesis. It has been known for years to be aberrantly expressed in ocular disorders, but in recent years, down-regulation has been shown to be prevalent in a range of cancers as well. This review describes the trimodal anticancer activities of this interesting protein: antiangiogenesis, apoptosis-mediated tumor suppression, and tumor cell differentiation. The key to successful antitumor therapy with this protein is the ability to synthesize the recombinant form of the protein (or its active shortened forms) and deliver at therapeutic doses or alternatively to use gene transfer technology to prolong the effect in vivo. Although there is a substantial amount of work carried out at the preclinical stage with this protein, more groundwork has to be done before PEDF is tested against cancer in clinical trials.

Pigment epithelium-derived factor as a new diagnostic marker for melanocytic tumors

Pigment epithelium-derived factor (PEDF), a potent antiangiogenetic factor, has been lately known to correlate well with angiogenic and metastatic potentials of tumor cells. We investigated the expression of PEDF protein in various types of human tumor cells by an immunohistochemical technique using a monoclonal antibody. Consequently, we found the significantly frequent and intense expression of PEDF in human melanocytic tumor cells including malignant melanoma as compared to non-melanocytic ones. We evaluated the diagnostic usefulness of anti-PEDF antibody in melanocytic tumors by comparing its immunoreactive sensitivity with that of other conventional melanocytic markers such as S-100 protein, HMB-45 and Melan-A, and found that PEDF possess the equal ability to others on its sensitivity. We finally concluded that PEDF is a useful diagnostic marker for melanocytic tumors, especially malignant melanomas, by its use in combination with other markers.

In silico comparison of gene expression levels in ten human tumor types reveals candidate genes associated with carcinogenesis

Most human cancers are characterized by genomic instability. Changes associated with such may result in altered expression of numerous genes. The sequence information available in the public databases can be used to identify transcripts differentially expressed in cancers. Determining cancer-related genes that are commonly deregulated in different tumor types may facilitate identification of targets for cancer diagnoses and therapeutic treatments. Using a data-mining tool named Digital Differential Display (DDD) from the UniGene database at the NCBI web site, gene expression levels of ten different tumor types and their counterpart normal tissues were analyzed. Unigenes which showed transcriptional regulation in more than five tumor types with > or =2-fold differences from normal tissues were identified. The expression data of selected Unigenes were subjected to clustering analysis. 127 commonly up-regulated genes and 92 commonly down-regulated genes were identified. Clustering analysis using these genes showed that most tumor types can be clustered into a separate branch from most normal tissues. Nineteen genes that have been shown to be involved in carcinogenesis by experimental evidence were also identified. Present computational analyses revealed 219 candidate cancer-related genes that are commonly deregulated in ten human tumor types which may contribute to the progress of carcinogenesis.

Pigment epithelium-derived factor gene therapy inhibits human pancreatic cancer in mice

PURPOSE

Pigment epithelium-derived factor (PEDF), which has recently been shown to be the most potent inhibitor of angiogenesis in the mammalian eye, is also expressed in the pancreas. Previously, we have screened the expression of PEDF by immunohistochemical analysis and showed that low expression of PEDF is associated with increased risk of hepatic metastasis and short survival. The purpose of this study was to investigate whether PEDF gene is a potent tumor suppressor and a potential candidate for cancer gene therapy.

EXPERIMENTAL DESIGN

We investigated both in vitro and in vivo growth characteristics of human pancreatic adenocarcinoma cell lines that were stably transfected to overexpress human PEDF and therapeutic effects of lentivirus-based vectors expressing PEDF on tumor growth in murine s.c. tumor model.

RESULTS

We discovered that cells secreted PEDF protein in the media and this exhibited strong inhibitory effects on proliferation and migration of human umbilical vein endothelial cells. The size of PEDF-overexpressing pancreatic adenocarcinoma tumors was significantly smaller than that of control tumors in s.c. tumor models. Moreover, the growth of PEDF-overexpressing pancreatic adenocarcinoma cells was significantly suppressed in comparison with control cells in peritoneal metastasis models. In gene transfer models, intratumoral injection of a lentivirus vector encoding PEDF (LV-PEDF) caused significant inhibition of tumor growth. The antitumor effect observed after treatment with LV-PEDF was associated with decreased microvessel density in tumors.

CONCLUSION

Our data suggest that PEDF may exert a biological effect on tumor angiogenesis and PEDF gene therapy may provide a new approach for treatment of pancreatic adenocarcinoma.

Endogenous inhibitors of angiogenesis

Angiogenesis, the formation of new blood vessels, is required for many pathologic processes, including invasive tumor growth as well as physiologic organ/tissue maintenance. Angiogenesis during development and adulthood is likely regulated by a balance between endogenous proangiogenic and antiangiogenic factors. It is speculated that tumor growth requires disruption of such balance; thus, the angiogenic switch must be turned "on" for cancer progression. If the angiogenic switch needs to be turned on to facilitate the tumor growth, the question remains as to what the physiologic status of this switch is in the adult human body; is it "off," with inhibitors outweighing the stimulators, or maintained at a fine "balance," keeping the proangiogenic properties of many factors at a delicate "activity" balance with endogenous inhibitors of angiogenesis. The physiologic status of this balance is important to understand as it might determine an individual's predisposition to turn the switch on during pathologic events dependent on angiogenesis. Conceivably, if the physiologic angiogenesis balance in human population exists somewhere between off and even balance, an individual's capacity and rate to turn the switch on might reflect their normal physiologic angiogenic status. In this regard, although extensive knowledge has been gained in our understanding of endogenous growth factors that stimulate angiogenesis, the activities associated with endogenous inhibitors are poorly understood. In this review, we will present an overview of the knowledge gained in studies related to the identification and characterization of 27 different endogenous inhibitors of angiogenesis.

Two Functional Epitopes of Pigment Epithelial–Derived Factor Block Angiogenesis and Induce Differentiation in Prostate Cancer

Pigment epithelial-derived factor (PEDF), an angiogenesis inhibitor with neurotrophic properties, balances angiogenesis in the eye and blocks tumor progression. Its neurotrophic function and the ability to block vascular leakage is replicated by the PEDF 44-mer peptide (residues 58-101). We analyzed PEDFs' three-dimensional structure and identified a potential receptor-binding surface. Seeking PEDF-based antiangiogenic agents we generated and tested peptides representing the middle and lower regions of this surface. We identified previously unknown antiangiogenic epitopes consisting of the 34-mer (residues 24-57) and a shorter proximal peptide (TGA, residues 16-26) with the critical stretch L19VEEED24 and a fragment within the 44-mer (ERT, residues 78-94), which retained neurotrophic activity. The 34-mer and TGA, but not the 44-mer reproduced PEDF angioinhibitory signals hinged on c-jun-NH2-kinase-dependent nuclear factor of activated T cell deactivation and caused apoptosis. Conversely, the ERT, but not the 34-mer/TGA induced neuronal differentiation. For the 44-mer/ERT, we showed a novel ability to cause neuroendocrine differentiation in prostate cancer cells. PEDF and the peptides bound endothelial and PC-3 prostate cancer cells. Bound peptides were displaced by PEDF, but not by each other, suggesting multiple receptors. PEDF and its active fragments blocked tumor formation when conditionally expressed by PC-3 cells. The 34- and 44-mer used distinct mechanisms: the 34-mer acted on endothelial cells, blocked angiogenesis, and induced apoptosis whereas 44-mer prompted neuroendocrine differentiation in cancer cells. Our results map active regions for the two PEDF functions, signaling via distinct receptors, identify candidate peptides, and provide their mechanism of action for future development of PEDF-based tumor therapies.

The regulation of pro-inflammatory gene expression induced by pigment epithelium-derived factor in rat cultured microglial cells

Pigment epithelium-derived factor (PEDF) is a potent and broadly acting neurotrophic factor that protects various cultured neurons against apoptotic stimuli. To investigate whether PEDF acts not only on neurons, but also glial cells, we analyzed the effects of recombinant human PEDF (rhPEDF) on cytokine mRNA levels, transcription factors, and signal transduction pathways in cultured microglial cells. RT-PCR analysis revealed that pro-inflammatory genes such as IL-1beta, IL-6, and TNFalpha were induced in rhPEDF-treated cultured microglial cells. Furthermore, rapid phosphorylation of CREB protein had occurred in rhPEDF-treated neonatal astrocytes. Up-regulation of pro-inflammatory genes by rhPEDF was blocked by overexpression of dominant negative CREB or a mutated form of IkappaBalpha. These results suggest that the induction of pro-inflammatory genes by rhPEDF is mediated via activation of NF-kappaB or CREB in microglial cells. Taken together, these results demonstrate that PEDF is a multipotent factor, capable of affecting not only neurons, but also microglial cells, and suggests that it may act as a neuro-immune modulator in the rodent brain.

Pigment epithelium-derived factor induces the production of chemokines by rat microglia

Many studies have shown that pigment epithelium-derived factor (PEDF) has neurotrophic effects on retinal cells and hippocampal, spinal cord, and cerebellar granule cell neurons, but much less work has examined the effects of PEDF on glia. In this study, we show that PEDF changes microglial morphology within 1 h of exposure, to a more deactivated form, while having no effect on the expression of such activation markers as OX-42 and ED-1. In contrast, urea activates acid phosphatase, and PEDF blocks that activation. PEDF also activates NFkappaB, accompanied by the induction of mRNAs and proteins for the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha, MIP-2, and MIP-3alpha. All the chemokines stimulate acid phosphatase activity, and high doses of MIP-2 and MIP-3alpha), alter the morphology of the microglia at 1 h after treatment. These results suggest that the use of PEDF for clinical treatments, such as for retinal neovascularization, brain injury, or ischemia, should be undertaken with caution because of the possibility of induction of inflammation caused by microglial or other immune cell migration in response to the chemokines induced by PEDF.

Pigment epithelium-derived factor induces pro-inflammatory genes in neonatal astrocytes through activation of NF-?B and CREB

Pigment epithelium-derived factor (PEDF) is a potent and broadly acting neurotrophic factor that protects neurons in various types of cultured neurons against glutamate excitotoxicity and induced-apoptosis. Some of the effects of PEDF reflect specific changes in gene expression, mediated via activation of the transcription factor NF-kappa B in neurons. To investigate whether PEDF also modulates gene expression in astrocytes, we employed the use of RT-PCR to analyze the gene expression of certain pro-inflammatory genes and found that genes such as IL-1 beta, IL-6, TNF-alpha, MIP1 alpha, and MIP3 alpha were induced in PEDF-treated cultured neonatal astrocytes, but not in adult astrocytes. Electrophoresis mobility shift assay (EMSA) revealed that a time- and dose-dependent increase of NF-kappa B- and AP-1-DNA binding activity was observed in PEDF-treated neonatal astrocytes. Furthermore, rapid phosphorylation of CREB protein had occurred in PEDF-treated neonatal astrocytes. Upregulation of pro-inflammatory and AP-1-related genes by PEDF was blocked by overexpression of dominant negative CREB or a mutated form of I kappa B alpha. These results suggest that the induction of pro-inflammatory genes is mediated via activation of NF-kappa B, AP-1, and CREB in neonatal astrocytes. Taken together, these results demonstrate that PEDF is a multipotent factor, capable of affecting not only neurons, but also neonatal astrocytes, and suggests that it may act as a neuroimmune modulator in the developmental brain.

Effect of inhibition of multiple steps of angiogenesis in syngeneic murine pleural mesothelioma

BACKGROUND

Angiogenesis is a multistep process in which the endothelial cell plays a pivotal role. We hypothesized that the combination of two antiangiogenic agents with distinct mechanisms of action would more effectively inhibit tumor growth than either agent alone in a murine mesothelioma model.

METHODS

A syngeneic murine mesothelioma flank tumor model (AB-12) was established in BALB/c mice. Separate adenovirus vectors expressing the cDNAs for human pigment epithelium-derived factor (AdPEDF) and a soluble form of the human vascular endothelial growth factor receptor-1 (Adsflt-1) were administered intratumorally. End points measured included tumor size, animal survival, and microvessel density using CD31 immunohistochemistry. An orthotopic model of mesothelioma was established by implanting AB-12 cells into the murine pleural cavity. Simultaneously, AdPEDF and Adsflt-1 were instilled intrapleurally and tumor burden and survival were recorded. The development of pulmonary emphysema was also assessed by calculating the mean linear intercept (a measure of interalveolar septal distance) in histologic lung sections from tumor-free mice after vector administration.

RESULTS

In the flank tumor model, the combination of AdPEDF and Adsflt-1 inhibited tumor growth, prolonged survival, and decreased microvessel density more profoundly compared with either AdPEDF or Adsflt-1 alone. In the orthotopic model, the combination was also more effective in prolonging survival. Intrapleural AdPEDF or Adsflt-1 did not increase the mean linear intercept compared with controls in tumor-free mice.

CONCLUSIONS

In this murine model, inhibiting multiple mechanisms of angiogenesis using two agents is a more effective antineoplastic strategy than using either agent alone. In addition, instillation of antiangiogenic gene transfer vectors into the pleural space does not result in histologic evidence of pulmonary emphysema.

Inhibition of Xenografted Human Melanoma Growth and Prevention of Metastasis Development by Dual Antiangiogenic/Antitumor Activities of Pigment Epithelium-Derived Factor

Human melanoma mortality is associated with the growth of metastasis in selected organs including the lungs, liver, and brain. In this study, we examined the consequences of overexpression of pigment epithelium-derived factor (PEDF), a neurotrophic factor and potent angiogenesis inhibitor, on both melanoma primary tumor growth and metastasis development. PEDF overexpression by melanoma cells greatly inhibited subcutaneous tumor formation and completely prevented lung and liver metastasis in immunocompromised mice after tail vein injection of metastatic human melanoma cell lines. Whereas the effects of PEDF on primary tumor xenografts appear mostly associated with inhibition of the angiogenic tumor response, abrogation of melanoma metastasis appears to depend on direct PEDF effects on both migration and survival of melanoma cells. PEDF-mediated inhibition of melanoma metastases could thus have a major impact on existing therapies for melanoma.

Antiangiogenic property of pigment epithelium-derived factor in hepatocellular carcinoma

Pigment epithelium-derived factor (PEDF) is one of the most powerful endogenous antiangiogenic reagents discovered to date. Its antiangiogenic potential in neoplastic disease remains unclear. In this study, we investigated antiangiogenic property of PEDF in hepatocellular carcinoma (HCC), a typical hypervascular tumor. In HCC cell lines, constitutive messenger RNA and protein expression of PEDF varied. Genomic DNA encoding the PEDF gene was the same in the cell lines examined by Southern blotting. In chemically induced hypoxic conditions, secreted PEDF protein was suppressed in contrast to elevation of vascular endothelial growth factor protein. When PEDF was overexpressed by gene transfer, proliferation and migration of endothelial cells were inhibited in conditioned media derived from all HCC cell lines. However, the serum concentration of PEDF, as measured by enzyme-linked immunosorbent assay, was decreased in patients with cirrhosis or HCC complicated by cirrhosis compared to healthy volunteers and patients with chronic hepatitis. According to the endothelial cell proliferation assay, the serum PEDF of patients with HCC had antiangiogenic activity. Moreover, intratumoral injection of a PEDF-expressing plasmid in athymic mouse models caused significant inhibition of preestablished tumor growth. In conclusion, PEDF plays a role in the angiogenic properties of HCC. Reduction of serum PEDF concentration associated with the development of chronic liver diseases may contribute to the progression of HCC. In addition, gene therapy using PEDF may provide an efficient treatment for HCC.

Expression of Pigment Epithelium-Derived Factor Decreases Liver Metastasis and Correlates with Favorable Prognosis for Patients with Ductal Pancreatic Adenocarcinoma

Pigment epithelium-derived factor (PEDF) is expressed in several normal organs and identified as an inhibitor of neovascularization. In the present study, we screened the expression of PEDF immunohistochemically and investigated its correlation with clinicopathological features in patients who underwent surgery for ductal pancreatic adenocarcinoma. Of the 80 patients, 22 cases (27.5%) were positive for PEDF. A significant association was found between the PEDF expression and low microvessel density (P = 0.0003). No correlation was found between PEDF expression and age, gender, depth of invasion, tumor diameter, lymphatic invasion, venous, invasion or histopathological grading. The patients in pathological stage II had a significantly higher incidence of PEDF-positive expression than those in pathological stage III or IVA (P = 0.0418). PEDF immunoreactivity was inversely associated with liver metastasis (P = 0.0422). The survival of patients that were PEDF positive was significantly longer than that of those with negative expression (P = 0.0026). Multivariate analysis using the Cox regression model indicated that PEDF-positive expression was an independent favorable prognostic factor (risk ratio, 0.394; P = 0.0016). We conclude that PEDF expression suggests a more favorable prognosis than in patients whose carcinomas lack PEDF expression.