Angiogenesis inhibitors and their delivery systems

Differential regulation of angiogenesis using degradable VEGF-binding microspheres

Vascular endothelial growth factor (VEGF) spatial and temporal activity must be tightly controlled during angiogenesis to form perfusable vasculature in a healing wound. The native extracellular matrix (ECM) regulates growth factor activity locally via sequestering, and researchers have used ECM-mimicking approaches to regulate the activity of VEGF in cell culture and in vivo. However, the impact of dynamic, affinity-mediated growth factor sequestering has not been explored in detail with biomaterials. Here, we sought to modulate VEGF activity dynamically over time using poly(ethylene glycol) microspheres containing VEGF-binding peptides (VBPs) and exhibiting varying degradation rates. The degradation rate of VBP microspheres conferred a differential ability to up- or down-regulate VEGF activity in culture with primary human endothelial cells. VBP microspheres with fast-degrading crosslinks reduced VEGF activity and signaling, while VBP microspheres with no inherent degradability sequestered and promoted VEGF activity in culture with endothelial cells. VBP microspheres with degradable crosslinks significantly reduced neovascularization in vivo, but neither non-degradable VBP microspheres nor bolus delivery of soluble VBP reduced neovascularization. The covalent incorporation of VBP to degradable microspheres was required to reduce neovascularization in a mouse model of choroidal neovascularization in vivo, which demonstrates a potential clinical application of degradable VBP microspheres to reduce pathological angiogenesis. The results herein highlight the ability to modulate the activity of a sequestered growth factor by changing the crosslinker identity within PEG hydrogel microspheres. The insights gained here may instruct the design and translation of affinity-based growth factor sequestering biomaterials for regenerative medicine applications.

Controlled release of polypeptides and other macromolecules

The use of polymeric matrices for the controlled release of polypeptides and other macromolecular drugs is reviewed. Three principal mechanisms of release include diffusion of the polypeptide through the polymer, erosion of the polymer matrix, and the application of magnetic fields to force more drug out of the matrix. The diffusion controlled systems generally utilize ethylene-vinyl acetate copolymer. The advantage of these systems is facile manipulation of the pore structure to obtain desired release kinetics. Release of many different polypeptides from these systems for periods of months has been demonstrated. Bioerosion provides the advantage that the polymer system does not need to be retrieved. Magnetism provides a mechanism whereby desired increases and decreases in polypeptide release rates can be achieved on demand.

Low molecular weight fraction of shark cartilage can modulate immune responses and abolish angiogenesis

Shark cartilage has proven to have inhibitory effects on angiogenesis. In this research, we studied the effects of shark cartilage on the immune system. Firstly, we isolated and purified a shark cartilage protein fraction with the most immunostimulatory effects. Our fraction was composed of two proteins with molecular weights of about 14 and 15 kDa. This fraction highly augments delayed-type hypersensitivity response against sRBC in mice, and decreases the cytotoxic activity of Natural Killer cells. Furthermore, intraperitoneal injection of this fraction to tumor-bearing mice could increase T-cell infiltration into the tumor, and decrease the tumor lesion size. Also, this fraction has strong inhibitory effect on HBMEC proliferation and migration in fibrin matrix. According to these results, we suppose that this fraction is a good candidate for further studies in cancer therapy.

Angiogenesis with biomaterial-based drug- and cell-delivery systems

Angiogenesis, the formation of new blood vessels from existing ones, is an important event in several biological processes, including wound healing. It plays a key role in determining the final functionality and integration of any implanted medical device. In addition, angiogenesis is a required event for organ development and has been accepted as a rate-limiting step in engineering tissue replacements. Besides these regenerative processes, uncontrolled angiogenesis is also involved in a number of pathologies, including tumor growth and metastases. Like angiogenesis, biomaterials also play a role in wound healing after medical device implantation and in tissue engineering. Interactions between the device biomaterials and host tissue will factor into the final device integration. Additionally, tissue-engineering strategies utilize biomaterials to a great extent because the paradigm of tissue engineering involves the use of cells, growth factors and scaffolding matrices in order to regenerate or replace tissue. Since almost all tissues are three-dimensional, the biomaterial scaffold plays an integral role in the paradigm. This review will emphasize the influence of biomaterials on angiogenesis as it applies to medical device implantation, tissue engineering and therapies for pathological angiogenesis.

Local anti-angiogenic brain tumor therapies

The critical role of angiogenesis in the growth of solid tumors, including neoplasms of the central nervous system, has provided the impetus for research leading to the discovery of inhibitors of tumor neovascularization. The therapeutic potential of systemically administered antiangiogenic drugs for brain tumors, however, is limited by a variety of anatomic and physiologic barriers to drug delivery. Implantable controlled-release polymers for local drug administration directly into the tumor parenchyma have therefore been developed to achieve therapeutic concentrations of these drugs within the brain while minimizing systemic toxicity. With use of these polymers, successful antiangiogenic therapy for treatment of experimental intracranial malignancies has been achieved. This has been demonstrated with a variety of otherwise unrelated drugs -- including the angiostatic steroids, tetracycline derivatives, and amiloride -- which modulate collagenase activity, and thus, basement membrane and interstitial matrix metabolism. Controlled-release polymers provide a clinically practicable method of achieving sustained antiangiogenic therapy which can be readily used in combination with other treatment modalities such as cytoreductive surgery, radiation, and cytotoxic chemotherapy.

The role of growth factors in vascular cell development and differentiation

The control of vascular growth and differentiation is a complex system of activity and interaction between positive and negative modulators of these processes. A number of important stimulators and inhibitors of both smooth muscle cells and endothelial cells have now been purified and biochemically characterized. Imbalances in the activity of these factors can result in serious pathologies. In this chapter, we briefly discuss the biology of blood vessel development and growth, review the current literature which describes these stimulators and inhibitors, and discuss current therapeutic strategies designed around these growth modulators.

Temporomandibular joint disc replacement made by tissue-engineered growth of cartilage

OBJECTIVE

To test the effectiveness of the new technique of tissue-engineered growth of cartilage, temporomandibular joint (TMJ) disc replacements were created by seeding dissociated chondrocytes on synthetic, three-dimensional, bioresorbable polymer constructs of a predetermined anatomic shape, incubating the cell-polymer constructs in vitro, and transplanting them into test animals.

MATERIALS AND METHODS

Twelve highly porous and bioresorbable cell-transplantation devices in the shape of TMJ discs were created using biodegradable polylactid and polyglycolic acid fibers. Bovine articular cartilage was dissociated into chondrocytes and the cells were allowed to attach to the three-dimensional polymer scaffolds and multiply in vitro. After 1 week, the cell-polymer constructs were implanted subcutaneously into nude mice. The neocartilage was assessed by magnetic resonance imaging (MRI) techniques, gross inspection, histology, and biomechanical and biochemical analysis after 12 weeks.

RESULTS

All implants seeded with chondrocytes showed gross evidence of histologically organized hyaline cartilage. The scaffolds maintained their specific shape. They not only showed appropriate intrinsic stability during neomorphogenesis of cartilage in vitro and in vivo, but also seemed to guide the growth of cartilage. The presence of sulfated glycosaminoglycans was shown by aldehyde fuchsin alcian blue staining of the specimens. Type II collagen, considered to be indicative of cartilage formation, was found in the specimens tested. MRI showed signal characteristics similar to those of hyaline cartilage. Analysis of neocartilage force/displacement curves and aqueous phase compliance using a closed compression chamber suggested that the ability of the constructs to resist deformation was similar to that of native donor cartilage.

CONCLUSION

The technology of tissue-engineered growth of cartilage on individually designed scaffolds may have many applications not only in reconstructive surgery of the TMJ, but also in craniomaxillofacial, plastic, and orthopedic surgery.

Inhibition of tumor angiogenesis

The exponential growth of solid tumors depends upon induction of new vessel growth, a process mediated by diffusable angiogenic factors produced by tumor cells. By inhibiting angiogenesis, it is now possible to modulate tumor growth and metastasis in laboratory animals. The first described inhibitor of angiogenesis was a protein derived from cartilage. Other important classes of antiangiogenic agents include angiostatic steroids combined with heparin or heparin derivatives, and the synthetic derivatives of fumigallin. As the mechanisms of action of these and other angiostatic agents are being elucidated, it is becoming apparent that many modulators of collagen metabolism inhibit angiogenesis and may offer clinically useful anticancer treatments. Minocycline and other tetracycline derivatives with anticollagenase properties have been shown to be potent inhibitors of angiogenesis. These agents, when administered with other standard cancer therapies, help prolong survival in laboratory animals with solid tumors. Further studies of these biologic response modifiers of tumor progression are under way in the hope that they will offer effective new treatments for cancer in humans.

Angiogenesis inhibition: a review

In this review we discuss the concept of anti-angiogenesis, which is the inhibition of neovascularization. Anti-angiogenic agents are viewed from the standpoint of their effect on various elements of the angiogenic process, including induction of vascular discontinuity, endothelial cell movement, endothelial cell proliferation, and three-dimensional restructuring of patent vessels. An effort is made to place the many different approaches to anti-angiogenesis research into a comprehensible structure, in order to identify problems of evaluation and interpretation, thereby providing a clearer basis for determining promising and needed directions for further investigation.

Design of nasoseptal cartilage replacements synthesized from biodegradable polymers and chondrocytes

Reconstructive and aesthetic surgery of the nose is a challenging problem in facial plastic surgery. In this study, biodegradable polymers composed of polyglycolic acid (PGA) and poly-L-lactic acid (PLLA) and their co-polymers were used to produce templates to transplant cells and promote regeneration of structural cartilage. A highly porous anatomically shaped three-dimensional non-woven PGA fibre network was sprayed with a coating polymer solution. Reinforcement of the outer circumference of the 12 nasoseptal constructs using high molecular weight PLLA further stabilized the constructs during the process of neomorphogenesis of cartilage, both during in vitro incubation and in vivo implantation. These cell transplantation devices also proved to be adhesive substrates for dissociated bovine chondrocytes. When implanted subcutaneously into nude mice, the polymer templates guided the reorganization after 8 wk of the bovine chondrocytes into neocartilage in the precisely designed size and shape of the original size and shape of the polymer delivery device. All implants loaded with chondrocytes showed evidence of formation of histologically organized hyaline cartilage. The implantation of nasal scaffolds without cells did not show cartilage formation. The technique of tissue engineered growth of cartilage has potential applications in orthopaedic, plastic and reconstructive, and craniomaxillofacial surgery.

Joint resurfacing with cartilage grown in situ from cell-polymer structures

We tested the potential of a new technology developed in our laboratory to create new hyaline cartilage for resurfacing distal femoral joint surfaces of New Zealand White rabbits that had been surgically denuded of articular cartilage. We removed hyaline cartilage from the patellar groove of the distal femurs in 24 rabbits. Chondrocytes isolated from the excised cartilage of 12 of these rabbits (experimentals) were seeded onto synthetic biocompatible, biodegradable polymers composed of polyglycolic acid. The cells were labeled in vitro with a thymidine analog, BrdU (5-bromo-2'-deoxyuridine). After 1 week in vitro, the cell-polymer structures were implanted onto the denuded surfaces of 12 defects made in the hyaline cartilage of the contralateral knees of the experimental animals. Twelve control animals received either no implants or implants not containing cells on similar surgical defects. After 7 weeks, we found evidence of new cartilage growth in 11 of the 12 experimental animals and virtually no new cartilage formation in any of the animals in either control group. Immunohistochemical analysis demonstrated the presence of BrdU-labeled chondrocytes in representative specimens.

Tissue-engineered growth of cartilage: the effect of varying the concentration of chondrocytes seeded onto synthetic polymer matrices

Ninety-six synthetic bioresorbable cell-delivery devices (10 x 10 x 0.5 mm) were seeded, varying the concentrations of living chondrocytes (2, 10, 20, 100 million cells/cc) isolated from shoulders of freshly killed calves and implanted subcutaneously on the dorsum of nude mice after 1 week of in vitro culture. This resulted in the formation of new cartilage in 95.6% of the implants. Twenty-four control implants (0 cells seeded) did not show cartilage formation. During 12 weeks of in vivo implantation, the wet weight and the thickness of the specimens (10, 20, 100 million cells/cc) increased significantly. Histologic analysis revealed cells appearing in their own lacunar structures surrounded by basophilic matrix. The increase in sulfated glycosaminoglycan content indicated the maturation of the extracellular matrix. The ability to manipulate the growth of new cartilage on biocompatible polymer scaffolds by varying the cell density before in vivo implantation will allow engineering to optimize the utilization of chondrocytes in relation to the desired shape, thickness, and quality of the new cartilage.

Isolation and characterization of an inhibitor of neovascularization from scapular chondrocytes

An inhibitor of neovascularization from the conditioned media of scapular chondrocytes established and maintained in serum-free culture has been isolated and characterized. To determine whether this chondrocyte-derived inhibitor (ChDI) was capable of inhibiting neovascularization in vivo, this protein was assayed in the chick chorioallantoic membrane assay. ChDI was a potent inhibitor of angiogenesis in vivo (4 micrograms = 87% avascular zones). This inhibitor is also an inhibitor of fibroblast growth factor-stimulated capillary endothelial cell (EC) proliferation and migration, as well as being an inhibitor of mammalian collagenase. ChDI significantly suppressed capillary EC proliferation in a dose-dependent, reversible manner with an IC50 (the inhibitory concentration at which 50% inhibition is achieved) of 2.025 micrograms/ml. Inhibition by ChDI of growth factor-stimulated capillary EC migration was also observed using a modified Boyden chamber assay (IC50 = 255 ng/ml). SDS-PAGE analysis followed by silver staining of ChDI purified to apparent homogeneity revealed a single band having an M(r) of 35,550. Gel elution experiments demonstrated that only protein eluting at this molecular weight was anti-angiogenic. These studies are the first demonstration that chondrocytes in culture can produce a highly enriched, potent inhibitor of neovascularization which also inhibits collagenase.

Inhibitors of Angiogenesis

Angiogenesis, the formation of new capillaries, is essential to a number of important physiological events, both normal and pathological. Recently, increased attention has focused on the purification and characterization of inhibitors of this process, because of the potential therapeutic value of angiogenesis inhibitors in controlling such "angiogenic diseases" as proliferative retinopathy, solid tumors, rheumatoid arthritis, and neovascular glaucoma. We review the process of neovascularization and the assays that have been developed to study its inhibition in vivo and in vitro. We also discuss the properties of different angiogenesis inhibitors and examine the mechanisms by which such inhibitors could potentially intervene in the process of neovascularization.

Establishment from mouse growth cartilage of clonal cell lines with responsiveness to parathyroid hormone, alkaline phosphatase activity, and ability to produce an endothelial cell growth inhibitor

Three clonal cell lines with differences in responsiveness to parathyroid hormone (PTH), alkaline phosphatase activity, and ability to produce an endothelial cell growth inhibitor(s) during more than 3 years, more than 58 passages, in culture were established from growth cartilage (GC) of mouse ribs. In sparse cultures the three clonal cell lines, MGC/T1.4, MGC/T1.17, and MGC/T1.18, all showed fibroblast-like morphology. However, as they became confluent, MGC/T1.4 cells became polygonal and then multilayered. MGC/T1.18 cells also became polygonal, but showed contact inhibition. MGC/T1.17 cells remained fibroblastic in confluent cultures and formed nodules when cultured for more than 7 days after they became confluent. These nodules calcified in the presence of beta-glycerophosphate. Glycosaminoglycan (GAG) synthesis in the parent uncloned line, MGC/T1 cells, at early passages was about 50-75% of that of primary cultures of mouse GC cells. The GAG syntheses in the three clonal lines were much lower than that of primary cultures of GC cells. Moreover, the sizes of proteoglycan monomers synthesized by these cells were not the same as that of cartilage-specific proteoglycan. The three clonal lines mainly synthesized type I collagen. PTH increased the intracellular cyclic AMP level in MGC/T1, MGC/T1.4, T1.17, and T1.18 cells: their maximal levels, observed after 2 minutes, were, respectively, about 160, 150, 70, and 200 times that of controls. The activity of alkaline phosphatase in MGC/T1.17 cells was higher than that in primary cultures of mouse GC cells, whereas those in MGC/T1 and T1.4 cells were comparable with that of GC cells, and that in MGC/T1.18 was lower. The three clonal lines, and especially MGC/T1.4, secreted a heat-stable, nondializable growth inhibitor(s) of endothelial cells into the culture medium. Because of their different properties, these cell lines should be useful for studies on endochondral ossification, the actions of PTH on skeletal cells, and anti-angiogenesis factors.

Inhibition of vascular endothelial cell growth and trypsin activity by vitreous

Vitreous from bovine, human and chick embryo has been found to contain a trypsin inhibitory activity. Chymotrypsin-inhibitory activity was also identified in bovine and chick embryo vitreous. Following either ultrafiltration or Bio Gel P-10 chromatography, these activities appear in fractions having a molecular weight greater than 10000 MW (ultrafiltration) or greater than 13000 MW (P-10 void volume), and are separable from low molecular weight aortic endothelial cell growth inhibitory activity present either in the ultrafiltrate or P-10 retarded volume. Treatment of the trypsin inhibitory fraction with hyaluronidase had no effect on trypsin inhibition, nor did addition of hyaluronic acid inhibit trypsin. Chick embryo vitreous and hyalocyte-conditioned medium were found to contain aortic endothelial cell growth inhibitory activity in both the void volume and retarded volume fractions following Bio Gel P-10 chromatography. Both the 6200 MW bovine vitreous endothelial cell growth inhibitor and the high molecular weight chick embryo vitreous endothelial cell growth inhibitor (greater than 13000 MW) were similar, in that most of the activity did not bind to heparin linked to Sepharose CL-6B.

A study of angiogenesis factors from five different sources using a radioimmunoassay

The use of a radioimmunoassay (RIA) demonstrated that angiogenic factors from human and animal tumours, normal bovine retinas, myocardial infarcts, synovial fluid from patients with joint diseases and wound fluid shared common antigenic determinants. Values for angiogenesis factors expressed as microgram Walker tumour TAF/mg protein varied from 0.8 (wound fluid) to 207 (myocardial infarct). Activated macrophages produced an angiogenic factor which did not cross-react. Normal tissue extracts which were non-angiogenic by the chicken chorioallantoic membrane assay also failed to cross-react in the RIA. The antigenic similarity of angiogenic factors from such a wide variety of sources suggests that, in order to minimize therapeutic side effects, it would be best to use angiogenic agonists and antagonists locally.

Cancer metastasis: experimental approaches, theoretical concepts, and impacts for treatment strategies

It has been the purpose of this article to describe recent advances in cancer metastasis research. Clinical realities and experimental approaches to the study of underlying basic mechanisms of metastasis formation were discussed. Wherever possible, results were reported which led to the development of theoretical concepts. Such results and concepts were finally evaluated in light of their possible impact for the design of new treatment strategies. Experimental findings from many diverse research fields were summarized with the help of tables, figures, and references. It was concluded that the process of metastasis is a dynamic event that can be described as a sequence of interrelated steps. Experimental results indicated that malignant cells that migrate and disseminate from the primary organ to distant sites and there eventually develop into metastases have to survive a series of potentially lethal interactions. Intimate tumor-host interactions were reported to take place all along the metastatic process. They were elucidated at the steps of angiogenesis, invasion, organ interaction, dormancy, tumor rejection, and tumor immune escape. The outcome of such tumor-host interactions seemed to depend on intrinsic properties of the tumor cells themselves as well as on the responsiveness of the host. Metastasis does not appear as a merely random process. Both clinical and experimental studies revealed that the whole process can be described more appropriately in terms of stochastic, sequential, and selective events, each of which is controlled and influenced by a number of mechanisms. With regard to therapeutic intervention, a selective event offers more possibilities than a random one because it is governed by rules that can be exploited experimentally. Various impacts from experimental studies for the design of antimetastatic cancer treatment strategies were discussed. Sequential steps of the metastatic cascade could become new therapy targets. Conventional empirically derived treatment modalities should become flanked by methods aimed more specifically at critical steps of cancer spread in order to prevent progression of the disease. This is where basic research on mechanisms could make significant contributions to therapy planning in the future. Furthermore, possible negative effects of surgery, radiotherapy, and adjuvant chemotherapy or immunotherapy that could result in enhancement of metastatic progression need to be critically evaluated to limit them as much as possible.(ABSTRACT TRUNCATED AT 400 WORDS)

Shark cartilage contains inhibitors of tumor angiogenesis

Shark cartilage contains a substance that strongly inhibits the growth of new blood vessels toward solid tumors, thereby restricting tumor growth. The abundance of this factor in shark cartilage, in contrast to cartilage from mammalian sources, may make sharks an ideal source of the inhibitor and may help to explain the rarity of neoplasms in these animals.