Regression of Metastatic Breast Cancer in a Patient Treated with the Anti-Angiogenic Drug Tnp-470

Promotor methylation in ocular surface squamous neoplasia development: epigenetics implications in molecular diagnosis

INTRODUCTION

Cancer is heavily influenced by epigenetic mechanisms that include DNA methylation, histone modifications, and non-coding RNA. A considerable proportion of human malignancies are believed to be associated with global DNA hypomethylation, with localized hypermethylation at promoters of certain genes.

AREA COVERED

The present review aims to emphasize on recent investigations on the epigenetic landscape of ocular surface squamous neoplasia, that could be targeted/explored using novel approaches such as personalized medicine.

EXPERT OPINION

While the former is thought to contribute to genomic instability, promoter-specific hypermethylation might facilitate tumorigenesis by silencing tumor suppressor genes. Ocular surface squamous neoplasia, the most prevalent type of ocular surface malignancy, is suggested to be affected by epigenetic mechanisms, as well. Although the exact role of epigenetics in ocular surface squamous neoplasia has mostly been unexplored, recent findings have greatly contributed to our understanding regarding this pathology of the eye.

Contact-facilitated drug delivery with Sn2 lipase labile prodrugs optimize targeted lipid nanoparticle drug delivery

Sn2 lipase labile phospholipid prodrugs in conjunction with contact-facilitated drug delivery offer an important advancement in Nanomedicine. Many drugs incorporated into nanosystems, targeted or not, are substantially lost during circulation to the target. However, favorably altering the pharmacokinetics and volume of distribution of systemic drug delivery can offer greater efficacy with lower toxicity, leading to new prolonged-release nanoexcipients. However, the concept of achieving Paul Erhlich's inspired vision of a 'magic bullet' to treat disease has been largely unrealized due to unstable nanomedicines, nanosystems achieving low drug delivery to target cells, poor intracellular bioavailability of endocytosed nanoparticle payloads, and the substantial biological barriers of extravascular particle penetration into pathological sites. As shown here, Sn2 phospholipid prodrugs in conjunction with contact-facilitated drug delivery prevent premature drug diffusional loss during circulation and increase target cell bioavailability. The Sn2 phospholipid prodrug approach applies equally well for vascular constrained lipid-encapsulated particles and micelles the size of proteins that penetrate through naturally fenestrated endothelium in the bone marrow or thin-walled venules of an inflamed microcirculation. At one time Nanomedicine was considered a 'Grail Quest' by its loyal opposition and even many in the field adsorbing the pains of a long-learning curve about human biology and particles. However, Nanomedicine with innovations like Sn2 phospholipid prodrugs has finally made 'made the turn' toward meaningful translational success.

The relationship between the cyclic-RGDfK ligand and αvβ3 integrin receptor

Ever since the finding that αvβ3 integrin receptors are over expressed on the endothelial cell surfaces of tumor vasculatures relative to normal resting vasculatures was disclosed in 1994, αvβ3 integrin receptor selective systems are finding increasing applications both for targeting anti-cancer drugs/genes selectively to tumor vasculatures and for imaging growing tumors. Among the cyclic peptide based integrin antagonists identified through both phage display and structure-activity studies, mainly αvβ3 integrin selective cyclic peptide c(RGDfK-) has found most widespread exploitations for targeting chemotherapeutic drugs/genes to both tumor and tumor vasculatures in anti-angiogenic cancer therapy. Herein we show that a lipopeptide containing widely acclaimed αvβ3 integrin receptor selective cyclic RGDfK ligand in its head-group area can effectively deliver genes into both the endothelial and tumor cells via all the three widely used integrin receptors namely αvβ3, αvβ5 & α5β1 integrins. We demonstrate that intravenous administration of the electrostatic complex of the cationic liposomes of an amphiphiles with cyclic RGDfK head-group and the anti-cancer p53 gene leads to significant tumor growth inhibition in a syngeneic mouse tumor model presumably through inducing apoptosis of tumor neovasculatures. The findings delineated herein provide experimental evidence that cyclic-RGDfK-ligand may not be that highly selective for αvβ3 integrin receptor as is popularly believed.

Antiangiogenic nanotherapy with lipase-labile Sn-2 fumagillin prodrug

BACKGROUND

The chemical instability of antiangiogenic fumagillin, combined with its poor retention during intravascular transit, requires an innovative solution for clinical translation. We hypothesized that an Sn-2 lipase-labile fumagillin prodrug, in combination with a contact-facilitated drug delivery mechanism, could be used to address these problems.

METHODS

α(v)β(3)-targeted and nontargeted nanoparticles with and without fumagillin in the prodrug or native forms were evaluated in vitro and in vivo in the Matrigel™ (BD Biosciences, CA, USA) plug model of angiogenesis in mice.

RESULTS

In vitro experiments demonstrated that the new fumagillin prodrug decreased viability at least as efficacious as the parent compound, on an equimolar basis. In the Matrigel mouse angiogenesis model, α(v)β(3)-fumagillin prodrug decreased angiogenesis as measured by MRI (3T), while the neovasculature was unaffected with the control nanoparticles.

CONCLUSION

The present approach resolved the previously intractable problems of drug instability and premature release in transit to target sites.

Angiogenesis imaging with vascular-constrained particles: the why and how

Angiogenesis is a keystone in the treatment of cancer and potentially many other diseases. In cancer, first-generation antiangiogenic therapeutic approaches have demonstrated survival benefit in subsets of patients, but their high cost and notable adverse side effect risk have fueled alternative development efforts to personalize patient selection and reduce off-target effects. In parallel, rapid advances in cost-effective genomic profiling and sensitive early detection of high-risk biomarkers for cancer, atherosclerosis, and other angiogenesis-related pathologies will challenge the medical imaging community to identify, characterize, and risk stratify patients early in the natural history of these disease processes. Conventional diagnostic imaging techniques were not intended for such sensitive and specific detection, which has led to the emergence of novel noninvasive biomedical imaging approaches. The overall intent of molecular imaging is to achieve greater quantitative characterization of pathologies based on microanatomical, biochemical, or functional assessments; in many approaches, the capacity to deliver effective therapy, e.g., antiangiogenic therapy, can be combined. Agents with both diagnostic and therapy attributes have acquired the moniker "theranostics." This review will explore biomedical imaging options being pursued to better segment and treat patients with angiogenesis-influenced disease using vascular-constrained contrast platform technologies.

Theragnostics for tumor and plaque angiogenesis with perfluorocarbon nanoemulsions

Molecular imaging agents are extending the potential of noninvasive medical diagnosis from basic gross anatomical descriptions to complicated phenotypic characterizations based upon the recognition of unique cell-surface biochemical signatures. Although originally the purview of nuclear medicine, "molecular imaging" is now studied in conjunction with all clinically relevant imaging modalities. Of the myriad of particles that have emerged as prospective candidates for clinical translation, perfluorocarbon nanoparticles offer great potential for combining targeted imaging with drug delivery, much like the "magic bullet" envisioned by Paul Ehrlich 100 years ago. Perfluorocarbon nanoparticles, once studied in Phase III clinical trials as blood substitutes, have found new life for molecular imaging and drug delivery. The particles have been adapted for use with all clinically relevant modalities and for targeted drug delivery. In particular, their intravascular constraint due to particle size provides a distinct advantage for angiogenesis imaging and antiangiogenesis therapy. As perfluorocarbon nanoparticles have recently entered Phase I clinical study, this review provides a timely focus on the development of this platform technology and its application for angiogenesis-related pathologies.

Nanomedicine strategies for molecular targets with MRI and optical imaging

The science of 'theranostics' plays a crucial role in personalized medicine, which represents the future of patient management. Over the last decade an increasing research effort has focused on the development of nanoparticle-based molecular-imaging and drug-delivery approaches, emerging as a multidisciplinary field that shows promise in understanding the components, processes, dynamics and therapies of a disease at a molecular level. The potential of nanometer-sized agents for early detection, diagnosis and personalized treatment of diseases is extraordinary. They have found applications in almost all clinically relevant biomedical imaging modality. In this review, a number of these approaches will be presented with a particular emphasis on MRI and optical imaging-based techniques. We have discussed both established molecular-imaging approaches and recently developed innovative strategies, highlighting the seminal studies and a number of successful examples of theranostic nanomedicine, especially in the areas of cardiovascular and cancer therapy.

Alphavbeta3-targeted nanotherapy suppresses inflammatory arthritis in mice

The purpose of this study was to assess whether an alternative treatment approach that targets angiogenesis, delivered through ligand-targeted nanotherapy, would ameliorate inflammatory arthritis. Arthritis was induced using the K/BxN mouse model of inflammatory arthritis. After arthritis was clearly established, mice received three consecutive daily doses of alpha(v)beta(3)-targeted fumagillin nanoparticles. Control groups received no treatment or alpha(v)beta(3)-targeted nanoparticles without drugs. Disease score and paw thickness were measured daily. Mice that received alpha(v)beta(3)-targeted fumagillin nanoparticles showed a significantly lower disease activity score (mean score of 1.4+/-0.4; P<0.001) and change in ankle thickness (mean increase of 0.17+/-0.05 mm; P<0.001) 7 d after arthritis induction, whereas the group that received alpha(v)beta(3)-targeted nanoparticles without drugs exhibited a mean arthritic score of 9.0 +/- 0.3 and mean change in ankle thickness of 1.01 +/- 0.09 mm. Meanwhile, the group that received no treatment showed a mean arthritic score of 9.8 +/- 0.5 and mean change in ankle thickness of 1.05 +/- 0.10 mm. Synovial tissues from animals treated with targeted fumagillin nanoparticles also showed significant decrease in inflammation and angiogenesis and preserved proteoglycan integrity. Ligand-targeted nanotherapy to deliver antiangiogenic agents may represent an effective way to treat inflammatory arthritis.

Three-dimensional MR mapping of angiogenesis with alpha5beta1(alpha nu beta3)-targeted theranostic nanoparticles in the MDA-MB-435 xenograft mouse model

Our objectives were 1) to characterize angiogenesis in the MDA-MB-435 xenograft mouse model with three-dimensional (3D) MR molecular imaging using alpha(5)beta(1)(RGD)- or irrelevant RGS-targeted paramagnetic nanoparticles and 2) to use MR molecular imaging to assess the antiangiogenic effectiveness of alpha(5)beta(1)(alpha(nu)beta(3))- vs. alpha(nu)beta(3)-targeted fumagillin (50 mug/kg) nanoparticles. Tumor-bearing mice were imaged with MR before and after administration of either alpha(5)beta(1)(RGD) or irrelevant RGS-paramagnetic nanoparticles. In experiment 2, mice received saline or alpha(5)beta(1)(alpha(nu)beta(3))- or alpha(nu)beta(3)-targeted fumagillin nanoparticles on days 7, 11, 15, and 19 posttumor implant. On day 22, MRI was performed using alpha(5)beta(1)(alpha(nu)beta(3))-targeted paramagnetic nanoparticles to monitor the antiangiogenic response. 3D reconstructions of alpha(5)beta(1)(RGD)-signal enhancement revealed a sparse, asymmetrical pattern of angiogenesis along the tumor periphery, which occupied <2.0% tumor surface area. alpha(5)beta(1)-targeted rhodamine nanoparticles colocalized with FITC-lectin corroborated the peripheral neovascular signal. alpha(5)beta(1)(alpha(nu)beta(3))-fumagillin nanoparticles decreased neovasculature to negligible levels relative to control; alpha(nu)beta(3)-targeted fumagillin nanoparticles were less effective (P>0.05). Reduction of angiogenesis in MDA-MB-435 tumors from low to negligible levels did not decrease tumor volume. MR molecular imaging may be useful for characterizing tumors with sparse neovasculature that are unlikely to have a reduced growth response to targeted antiangiogenic therapy.

Minute dosages of alpha(nu)beta3-targeted fumagillin nanoparticles impair Vx-2 tumor angiogenesis and development in rabbits

Fumagillin suppresses angiogenesis in cancer models and clinical trials, but it is associated with neurotoxicity at systemic doses. In this study, alpha(nu)beta(3)-targeted fumagillin nanoparticles were used to suppress the neovasculature and inhibit Vx-2 adenocarcinoma development using minute drug doses. Tumor-bearing rabbits were treated on days 6, 9, and 12 postimplantation with alpha(nu)beta(3)-targeted fumagillin nanoparticles (30 microg/kg), alpha(nu)beta(3)-targeted nanoparticles without drug, nontargeted fumagillin nanoparticles (30 microg/kg) or saline. On day 16, MRI was performed with alpha(nu)beta(3)-targeted paramagnetic nanoparticles to quantify tumor size and assess neovascularity. Tumor volume was reduced among rabbits receiving alpha(nu)beta(3)-targeted fumagillin nanoparticles (470+/-120 mm(3)) compared with the three control groups: nontargeted fumagillin nanoparticles (1370+/-300 mm(3), P<0.05), alpha(nu)beta(3)-targeted nanoparticles without drug (1080+/-180 mm(3), P<0.05) and saline (980+/-80 mm(3), P<0.05). MR molecular imaging of control rabbits (no fumagillin) revealed a predominant peripheral distribution of neovascularity representing 7.2% of the tumor rim volume, which decreased to 2.8% (P<0.05) with alpha(nu)beta(3)-targeted fumagillin nanoparticle treatment. Microscopically, the tumor parenchyma tended to show T-cell infiltration after targeted fumagillin treatment, which was not appreciated in control animals. These results suggest that alpha(nu)beta(3)-targeted fumagillin nanoparticles could provide a safe and effective means to deliver MetAP2 inhibitors alone or in combination with cytotoxic or immunotherapy.

Anti-angiogenic therapy: Prospects for treatment of ocular tumors

The growth of new blood vessels (angiogenesis) within tumors is essential for tumor growth, maintenance, and metastasis. Angiogenesis research has identified a host of pro- and anti-angiogenic factors that regulate an "angiogenic switch," which when turned on, allows tumors to assume a more aggressive form. Angiogensis inhibitors that target this switch are in clinical trials for a wide array of tumor types. Although angiogenesis inhibitors are already widely used to treat ocular disease, only limited case reports are currently available for the use of angiogenesis inhibitors to treat ocular tumors. Evidence for angiogenesis in the growth and spread of uveal melanoma, retinoblastoma, and von Hippel Lindau (VHL) disease exists. The very limited trials of angiogenesis inhibitors in the treatment of uveal melanoma and VHL are promising, although more extensive controlled trials will be needed to confirm their efficacy.

Protein-reactive natural products

Researchers in the post-genome era are confronted with the daunting task of assigning structure and function to tens of thousands of encoded proteins. To realize this goal, new technologies are emerging for the analysis of protein function on a global scale, such as activity-based protein profiling (ABPP), which aims to develop active site-directed chemical probes for enzyme analysis in whole proteomes. For the pursuit of such chemical proteomic technologies, it is helpful to derive inspiration from protein-reactive natural products. Natural products use a remarkably diverse set of mechanisms to covalently modify enzymes from distinct mechanistic classes, thus providing a wellspring of chemical concepts that can be exploited for the design of active-site-directed proteomic probes. Herein, we highlight several examples of protein-reactive natural products and illustrate how their mechanisms of action have influenced and continue to shape the progression of chemical proteomic technologies like ABPP.

Angiogenesis: noninvasive quantitative assessment with contrast-enhanced functional US in murine model

PURPOSE

To evaluate quantitative functional ultrasonography (US) in a murine gel model by using microbubble destruction kinetics to determine whether parametric indices provided with US could help assess angiogenesis.

MATERIALS AND METHODS

Institutional Animal Subjects Committee approved experiments and procedures. In 36 normal mice, two 0.4-mL gel implants were placed subcutaneously on either side of spine. One implant contained 0.5, 1.0, or 1.5 microg human basic fibroblast growth factor (bFGF) per milliliter of gel. Functional US quantitative analysis of angiogenesis with microbubble contrast agent was performed on days 3, 6, 9, and 12; histologic data were collected. Time-intensity curve of implant was fitted to mathematic decay model to calculate fractional blood volume and fraction of blood replaced per unit of time. Microvascular density (MVD) and percentage of microvascular area (MVA) were measured after anti-CD31 staining. Spearman rank order correlation was used in analyses.

RESULTS

bFGF-containing implants induced MVD of eight, 35, 42, and 42 vessels per square millimeter on days 3, 6, 9, and 12, respectively; in controls, MVD was four vessels/mm2 (P<.05 on days 6, 9, and 12). bFGF-containing implants induced percentage MVA of 2%, 5%, 20%, and 27%, respectively; in controls, it was 0.5% (P<.05). Maximum enhancement was significantly increased in bFGF implants (23.3 gray level+/-14.1 [standard deviation]) compared with controls (11.0+/-5.5, P<.001). Implants containing bFGF showed poor correlations between fractional blood volume and MVD (r2=0.42) or percentage MVA (r2=0.51) at US. There was no correlation between microbubble velocity and MVD (r2<0.05) or percentage MVA (r2<0.13).

CONCLUSION

Functional US perfusion parameters do not correlate with current histologic indices for quantifying angiogenesis. MVD, as a histologic quantitative measurement of angiogenesis, may not be an appropriate standard for contrast-enhanced imaging that relies on perfused neovessels.

Methionine aminopeptidase 2 inhibition is an effective treatment strategy for neuroblastoma in preclinical models

Tumor vascularity is correlated with an aggressive disease phenotype in neuroblastoma, suggesting that angiogenesis inhibitors may be a useful addition to current therapeutic strategies. We previously showed that the antiangiogenic compound TNP-470, an irreversible methionine aminopeptidase 2 (MetAP2) inhibitor, suppressed local and disseminated human neuroblastoma growth rates in murine models but had significant associated toxicity at the effective dose. We have recently shown that a novel, reversible MetAP2 inhibitor, A-357300, significantly inhibits CHP-134-derived neuroblastoma s.c. xenograft growth rate with a treatment-to-control (T/C) ratio at day 24 of 0.19 (P < 0.001) without toxicity. We now show that the combination of A-357300 with cyclophosphamide at the maximal tolerated dose sustained tumor regression with a T/C at day 48 of 0.16 (P < 0.001) in the CHP-134 xenograft model. A-357300 also significantly inhibited establishment and growth rate of hematogenous metastatic deposits following tail vein inoculation of CHP-134 cells and increased overall survival (P = 0.021). Lastly, A-357300 caused regression of established tumors in a genetically engineered murine model with progression-free survival in five of eight mice (P < 0.0001). There was no evidence of toxicity. These data show that MetAP2 may be an important molecular target for high-risk human neuroblastomas. We speculate that the growth inhibition may be through both tumor cell intrinsic and extrinsic (antiangiogenic) mechanisms. The potential for a wide therapeutic index may allow for treatment strategies that integrate MetAP2 inhibition with conventional cytotoxic compounds.

Tumour angiogenesis: a novel therapeutic target in patients with malignant disease

Angiogenesis refers to the formation of new blood vessels from an existing vasculature and is recognised as a necessary requirement for most tumours to grow beyond 1-2 mm in diameter. Factors established as playing a role in angiogenesis may be divided into two principal groups: (a) those that stimulate endothelial cell proliferation and/or elongation, migration and vascular morphogenesis including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet derived endothelial cell growth factor (PD-ECGF) and the tie and tek receptors, and (b) proteases and their receptors involved in the breakdown of basement membranes and the extracellular matrix (ECM) including the matrix metalloproteinases (MMPs), cathepsins and those involved in the plasmin cascade. Angiogenesis has been identified as a potential target for development of anticancer agents. The discovery of a range of naturally-occurring factors which negatively regulate angiogenesis, including the thrombospondins, angiostatin and endostatin, and the tissue inhibitors of MMPs (TIMPs), has given added impetus to this approach. Synthetic anti-angiogenic compounds have been developed, including TNP-470, carboxyamidotriazole, VEGF-tyrosine kinase inhibitors and MMP inhibitors (MMPI) which, like the naturally-occurring anti-angiogenic factors, inhibit angiogenesis in vitro and in vivo, and tumour development, growth and metastasis in vivo. Anti-angiogenic agents also enhance the antitumour activity of many conventional cytotoxic chemotherapeutic agents. Such combinations may have a particular role as adjuvant therapies following surgical resection of primary tumours. Unlike tumour cells, tumour associated endothelial cells do not develop resistance to anti-angiogenic agents. Furthermore, anti-angiogenic agents are generally cytostatic rather than cytotoxic. As such, these agents are, in general, likely to be administered over long periods of time. Therefore, as well as having proven antitumour efficacy, an anti-angiogenic compound will need to be well-tolerated if it is to become established in the clinical management of patients with malignant disease.

Clinical and pharmacokinetic study of TNP-470, an angiogenesis inhibitor, in combination with paclitaxel and carboplatin in patients with solid tumors

PURPOSE

Preclinical studies have demonstrated a synergistic effect with the angiogenesis inhibitor TNP-470 and several cytotoxic agents. A recent clinical trial with the combination of paclitaxel and TNP-470 has shown promising effects. The present study was designed to determine the toxicity and pharmacokinetics of carboplatin in combination with TNP-470 in comparison with the doublet regimen of paclitaxel and carboplatin in patients with solid tumors.

EXPERIMENTAL DESIGN

Enrolled in the study were 17 patients with lung (11), head/neck (3), sarcoma (2) and thymoma (1). The patients received intravenous paclitaxel and carboplatin on day 1 followed by TNP-470 (60 mg/m(2) i.v. over 1 h administered thrice weekly on Monday, Wednesday, and Friday). Each cycle of therapy consisted of 3 weeks. The initial cohort of three patients received carboplatin at AUC 5 mg/ml x min. No dose-limiting toxic effects occurred, thus the subsequent cohort received carboplatin at AUC 6 mg/ml x min. In addition to toxicity, the pharmacokinetics of carboplatin were evaluated, and tumor response and patient survival rates were assessed.

RESULTS

The administered regimen of paclitaxel (225 mg/m(2) i.v. over 3 h) and carboplatin (AUC 6 mg/ml x min i.v. over 1 h) on day 1 followed by TNP-470 (60 mg/m(2) i.v. over 1 h administered thrice weekly on Monday, Wednesday, and Friday) was defined as both the maximum tolerated and optimal dose. Hematological toxic effects were similar to those expected with the chemotherapy doublet. All neurocognitive impairments were graded as mild to moderate and reversed after discontinuation of TNP-470 administration. No alterations in the pharmacokinetic disposition of carboplatin were noted. Overall, the median survival duration was 297 days. Four patients (24%) had a partial response, and eight (47%) had stable disease.

CONCLUSIONS

The combination of TNP-470, paclitaxel, and carboplatin is a reasonably well tolerated regimen. Further randomized studies of TNP-470 with this doublet regimen are now warranted for non-small-cell lung carcinoma and other solid tumors.

Concise stereocontrolled routes to fumagillol, fumagillin, and TNP-470

A concise, diastereoselective synthesis of (+/-)-fumagillol (3) and formal, enantioselective syntheses of the potent angiogenesis inhibitors fumagillin (1) and TNP-470 (2) are reported. The origin of asymmetry is a highly diastereoselective Diels-Alder reaction using a diene with a chiral oxazolidinone auxiliary. The stereochemical course of a key conjugate addition reaction is controlled by the cup-shaped architecture of a cis-fused bicyclic enal. Other key steps include a facile hetero-Claisen rearrangement and a site-selective Sharpless epoxidation.

TNP-470 combined with nicardipine suppresses in vivo growth of PC-3, a human prostate cancer cell line

We examined effects of TNP-470 with or without nicardipine on in vivo or in vitro growth of a hormone-independent human prostate carcinoma cell line, PC-3. TNP-470 (30 mg/kg, daily) or nicardipine (25 microg/kg, daily) alone had little effects on in vivo growth of PC-3 cells in nude mice, whereas simultaneous administration of both agents significantly inhibited the growth of the xenografts. In vitro proliferation of PC-3 was not affected by TNP-470 and/or nicardipine. Combination of TNP-470 and nicardipine seems beneficial in the treatment of hormone-refractory prostate cancer.

Tumor angiogenesis: past, present and the near future

The concept of treating solid tumors by inhibiting tumor angiogenesis was first articulated almost 30 years ago. For the next 10 years it attracted little scientific interest. This situation changed, relatively slowly, over the succeeding decade with the discovery of the first pro-angiogenic molecules such as basic fibroblast growth factor and vascular endothelial growth factor (VEGF), and the development of methods of successfully growing vascular endothelial cells in culture as well as in vivo assays of angiogenesis. However, the 1990s have witnessed a striking change in both attitude and interest in tumor angiogenesis and anti-angiogenic drug development, to the point where a remarkably diverse group of over 24 such drugs is currently undergoing evaluation in phase I, II or III clinical trials. In this review I will discuss the many reasons for this. These features, together with other recent discoveries have created intense interest in initiating and expanding anti-angiogenic drug discovery programs in both academia and industry, and the testing of such newly developed drugs, either alone, or in various combinations with conventional cytotoxic therapeutics. However, significant problems remain in the clinical application of angiogenesis inhibitors such as the need for surrogate markers to monitor the effects of such drugs when they do not cause tumor regressions, and the design of clinical trials. Also of concern is that the expected need to use anti-angiogenic drugs chronically will lead to delayed toxic side effects in humans, which do not appear in rodents, especially in short-term studies.

Endostatin inhibits microvessel formation in the ex vivo rat aortic ring angiogenesis assay

Endostatin has demonstrated potent antiangiogenic and antitumor activity in mouse models. We have investigated the ex vivo rat aortic ring assay and a human vein model to assess the biological activity of murine and human endostatin. Rat aortic rings were exposed to recombinant murine endostatin (Spodoptera frugipera; Calbiochem, San Diego, CA) or recombinant human endostatin (Pichia pastoris; EntreMed, Rockville, MD). After 5 days, murine endostatin (500 microgram/ml) demonstrated inhibition of microvessel outgrowth with dose-dependent effects (down to 16 microgram/ml). No significant inhibition was observed with human endostatin in the rat assay. Human endostatin at 250 and 500 microgram/ml inhibited outgrowths from human saphenous vein rings after a 14-day incubation. Electron microscopy assessed the formation of basal lamina, confirming that the microvessels were progenitors of patent vessels. Immunostaining for Factor VIII or CD34 demonstrated that the microvessel cells were endothelial. BrdU incorporation assays supported the presence of proliferating endothelial cells, correlating with neovascularization from the aortic wall. We conclude that the rat aortic ring assay confirms the antiangiogenic activity of murine but not human endostatin, suggesting that the model may have species specificity. However, the human form shows biological activity against human vascular tissue.