The rationale and future potential of angiogenesis inhibitors in neoplasia

[Targeted therapies in thoracic oncology]

INTRODUCTION

Better understanding of the alterations of cellular physiology during carcinogenesis has resulted in the development of new anticancer agents called biological targeted therapies. These therapies will probably complement the traditional treatments (surgery, radiotherapy and chemotherapy).

STATE OF THE ART

In thoracic oncology, targeted therapies may interfere with signal transduction by interaction with growth factors receptors. This is the case with monoclonal antibodies directed against the extracellular part of the receptors and with small molecules inhibiting the intracellular part of the receptors (for example, EGF-R).

PERSPECTIVES

Other strategies include the use of farnesyl transferase inhibitors or of antisense oligonucleotides; the new therapies may also inhibit angiogenesis by targeting either the VEGF receptor or the matrix metalloproteases. Inhibitors of metalloproteases were the first targeted agents tested. However, all published studies on metalloproteases inhibitors have been negative so far.

CONCLUSIONS

Currently, the agents most advanced in clinical development are the EGFR inhibitors (either monoclonal antibodies or small molecules inhibiting tyrosine-kinases) which, in those that have clinical activity, may produce a sustained response at a cost of a degree of toxicity.

Safety and Activity of the Combination of Pegylated Liposomal Doxorubicin and Weekly Docetaxel in Advanced Breast Cancer

BACKGROUND

The present study was designed with the aim of evaluating the tolerability and activity of pegylated liposomial doxorubicin (PLD) in combination with weekly docetaxel as first line treatment of advanced breast cancer.

PATIENTS AND METHODS

Fifty-seven patients entered the study. PLD was administered at escalating doses starting from 30 mg/m2, on day 1; docetaxel was administered at the fixed dose of 35 mg/m2 on days 2 and 9. A cycle of therapy consisted of 21 days.

RESULTS

The MTD was achieved at the dose of 40 mg/m2 of PLD, being febrile neutropenia and palmar-plantar-erythrodisesthesia (PPE) the dose-limiting toxicities (DLTs), so that the fixed dose of PLD for the Phase II study was 35 mg/m2. Forty-two consecutive patients received treatment at the established dose for a total of 194 cycles: among these, three patients were withdrawn for severe allergic reaction at the first administration of PLD. Hematological toxicity was moderate, the most common grade 1-3 non-hematological toxicities were stomatitis and PPE, occurring in 20 (47.5%) and 16 (38%) patients, respectively. No cardiac toxicity was recorded. According to the intent to treat analysis a major objective response was observed in 59.5% of patients (95% CI, 43.3-74.4%), with a median time to progression of 9 months and an estimated overall survival at 18 months of 62%.

CONCLUSION

The combination of PLD and weekly docetaxel is an effective first-line therapy for patients with advanced breast cancer. PPE and mucositis are the most relevant side effects of such a combination.

Parvovirus vectors for cancer gene therapy

Parvoviruses comprise a group of single-stranded DNA viruses with greater potential for gene therapy applications. Unique characteristics of paroviruses, such as non-pathogenicity, antioncogenicity and methods of efficient recombinant vector production, have drawn more attention towards utilising parvovirus-based vectors in cancer gene therapy. Although > 30 different parvoviruses have been identified so far, recombinant vectors derived from adeno-associated virus (AAV), minute virus of mice (MVM), LuIII and parvovirus H1 have been successfully tested in many preclinical models of human diseases, including cancer. The present article will focus on the potential of non-replicating and autonomously replicating parvoviral vectors in cancer gene therapy, including strategies that target tumour cells directly or indirectly.

Suppression of tumor growth by viral vector-mediated gene transfer of N-terminal truncated platelet factor 4

Platelet factor four (PF4), an inhibitor of endothelial cell proliferation in vitro, inhibits angiogenesis and tumor growth in vivo in experimental animals. The present study was designed to determine whether gene therapy-mediated expression of a form of PF4 lacking 16 amino acids of N-terminus from tumor cells could inhibit angiogenesis and tumor growth in vivo. Two replication-defective recombinant retroviral vectors were constructed. One encodes human PF4 (rRV-PF4) and the other encodes the N-truncated peptide (rRVp17-70). These vectors were then used to transduce KB cells, a human head and neck squamous carcinoma cell line. Expression of PF4 and p17-70 transgenes was confirmed by Western blot analysis. In vitro, both rRV-PF4 and rRVp17-70 were able to inhibit selectively the proliferation of human umbilical vascular endothelial cells (HUVEC) but not KB cells. In vivo activity was assessed by injecting 10(7) KB cells subcutaneously into nude mice and by monitoring subsequent tumor growth, xenograft vascular histochemistry, and animal survival. Viral vector-mediated cDNA transfer of PF4 and p17-70 resulted in inhibiting solid tumors through an anti-angiogenic action in vivo. Our data indicate that targeting tumor angiogenesis using viral-mediated gene transfer of full-length and N-terminal truncated PF4 represents a promising strategy for cancer gene therapy.

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.

Disparate effects of endostatin on tumor vascular perfusion and hypoxia in two murine mammary carcinomas

PURPOSE

Recent results in the literature have demonstrated that the antiangiogenic agent endostatin can enhance antitumor effects when administered before or during radiotherapy. To better understand the underlying pathophysiologic basis for this radiosensitization, the current study investigated whether short-term endostatin administration is linked to alterations in tumor vascular perfusion and oxygen delivery.

METHODS AND MATERIALS

Three daily doses of recombinant endostatin (20 mg/kg) were administered to two murine mammary carcinomas, the highly vascularized MCa-35 and the less vascularized MCa-4. Image analysis techniques were used to quantify (1) total and perfused vascular spacing, and (2) changes in tumor hypoxia as a function of distance from the nearest blood vessel.

RESULTS

In MCa-35 tumors, endostatin had no effect on vessel spacing, tumor hypoxia, or tumor growth. In MCa-4 tumors, total and perfused vessel spacings were also unchanged, but tumor growth was inhibited, and tumor hypoxia significantly decreased. These tumors demonstrated an increased vascular functionality suggestive of an increase in the number of intermittently perfused vessels, without corresponding alterations in tumor oxygen consumption rate.

CONCLUSIONS

Poorly vascularized, hypoxic mammary carcinomas were much more responsive to short-term endostatin treatment than well-vascularized, more homogeneously oxygenated tumors. Oxygen levels in the responsive tumors were transiently improved after treatment, which could have substantial implications with respect to the therapeutic effectiveness of combining antiangiogenic agents with conventional therapies.

Stimulation of extracellular signal-regulated kinase pathway by suramin with concomitant activation of DNA synthesis in cultured cells

Suramin is a well known antitrypanosomal drug and a novel experimental agent for the treatment of several cancers, yet the molecular mechanisms through which suramin exerts its effects on cell functions are not completely clear. In this study, we investigated the potential of suramin to activate the mitogen-activated protein kinase cascade in cultured Chinese hamster ovary (CHO) cells. The treatment of CHO cells with suramin increased the enzyme activity of extracellular signal-regulated kinases (ERK1/2) approximately 10-fold dose and time dependently. The EC(50) value was approximately 2.4 microM. This activation is inhibited by PD98059 and wortmannin/LY294002, indicating a crucial role for mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol 3-kinase (PI3K), respectively. Suramin-mediated stimulation of PI3K was confirmed by the observation that suramin stimulates the phosphorylation of protein kinase B (Akt) in a wortmannin-sensitive manner. Furthermore, cAMP response element-binding protein, a transcription factor, was also activated by suramin in a MEK-dependent manner. The suramin-induced phosphorylation of cGMP-dependent protein kinase was also suggested by a solid-phase kinase assay. The suramin effects on CHO cells were shown to have a concomitant increase in DNA synthesis, which was attenuated by PD98059. Similar activation of ERK1/2 activity by suramin was observed in other cell lines such as Chinese hamster lung or PC12 cells, but not in RBL2H3, ECV304, and OVK18 cells, indicating a cell-type specific mechanism for suramin. These results indicate that suramin induces mitogenic activity in several cell lines through the pathway from PI3K to MEK and ERK.

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In vitro and in vivo evaluations of THAM derived telomers bearing RGD and Ara-C for tumour neovasculature targeting

As an approach to the development of specific drug delivery systems, a new class of low macromolecular carriers called 'telomers' endowed with an antitumour agent, such as arabinofuranosylcytosine (Ara-C), RGDSK peptidic sequences, as tumour targeting moieties, and tyrosine groups labelled with 125I atoms allowing the in vivo scintigraphic follow up, were synthesized. Their tumour targeting ability was assessed in vivo in mice bearing a murine B16 melanoma. The biological results showed that the presence of RGDSK sequences onto the macromolecules leads to the selective targeting and the accumulation of telomers within the vascularized zone of the tumour. Moreover, such compounds exhibited in vitro a better IC(50) (0.015 muM) than pure Ara-C and in vivo an oncostatic index higher than 160%.

Anti-angiogenesis in cancer therapy

OBJECTIVE

To review tumor angiogenesis, identify potential targets for anti-angiogenic cancer therapy, and highlight certain anti-angiogenic agents in clinical trials.

DATA SOURCE

Research articles, abstracts, review articles, and book chapters.

CONCLUSION

Tumor angiogenesis is a complex, multistep process that provides a target for antineoplastic therapy whereby tumor neovasculature is interrupted at various steps in the angiogenic process. Clinical trials are investigating the application and efficacy of anti-angiogenic agents.

IMPLICATIONS FOR NURSING PRACTICE

Oncology nurses must continually increase their knowledge with the onset of newer, targeted agents. This will provide a background for educating and caring for the patient who is receiving anti-angiogenic therapy.

Expression of thymidine kinase driven by an endothelial-specific promoter inhibits tumor growth of Lewis lung carcinoma cells in transgenic mice

The possibility of inhibiting tumor growth by limiting angiogenesis has raised considerable interest. In this study, we examined the feasibility of inhibiting tumor growth by targeting a suicide gene in the endothelium. Toxicity must be directed solely to angiogenic cells. Therefore, we used the herpes simplex virus-thymidine kinase (TK) gene, in combination with the prodrug ganciclovir (GCV), which affects replicative cells. To test this strategy, we produced transgenic mice carrying the TK gene driven by the vascular endothelial (VE)-cadherin promoter. Lewis lung carcinoma cells were injected subcutaneously to establish tumors and to test the effect of GCV on tumor growth. In two independent transgenic lines, GCV treatment (75 mg/kg/day) resulted in a 66-71% reduction of tumor volume at day 20 postimplantation compared to wild-type mice (650 and 550 versus 1930 mm(3), P<0.02 and 0.01, respectively), whereas no significant difference was observed when vehicle alone was injected. Tumor growth inhibition was accompanied by a marked reduction in tumor vascular density (151 versus 276 vessels/mm(2), P<0.05) and an increase in tumor cell death, suggesting that tumor growth inhibition was caused by a reduction in tumor angiogenesis. Our data support the potential utility of endothelial targeting of suicide genes in cancer therapy.

Thalidomide for erythema nodosum leprosum and other applications

Thalidomide, administered as a sedative and antiemetic decades ago, was considered responsible for numerous devastating cases of birth defects and consequently was banned from markets worldwide. However, the drug remarkably has resurfaced with promise of immunomodulatory benefit in a wide array of immunologic disorders for which available treatments were limited. It is approved by the Food and Drug Administration for erythema nodosum leprosum (ENL). Although the relative paucity of leprosy and ENL worldwide may perceivably limit interest in and knowledge about thalidomide, increasing numbers of new and potential uses expand its applicability widely beyond ENL. Thalidomide, an inhibitor of tumor necrosis factor a, is the best known agent for short-term treatment of ENL skin manifestations, as well as postremission maintenance therapy to prevent recurrence. For this indication, it is effective as monotherapy and as part of combination therapy with corticosteroids. Studies of thalidomide in chronic graft-versus-host disease showed benefit in children and adults as treatment, but not as prophylaxis. The agent has been administered successfully for treatment of cachexia related to cancer, tuberculosis, and human immunodeficiency virus infection, although evidence of efficacy is inconclusive. Thalidomide monotherapy effectively induced objective response in trials in patients with both newly diagnosed and advanced or refractory multiple myeloma. Combination therapy with thalidomide and corticosteroids was also effective in these patients, as well as in treatment of aphthous and genital ulcers. Limited evidence supports the drug's benefit in treatment of Kaposi's sarcoma. Other thalidomide applications include Crohn's disease, rheumatoid arthritis, and multiple sclerosis. Somnolence, constipation, and rash were the most frequently cited adverse effects in studies, but thalidomide-induced neuropathy and idiopathic thromboembolism were critical causes for drug discontinuation. Thalidomide is still contraindicated in pregnant women, women of childbearing age, and sexually active men not using contraception. Clinicians should be conversant with thalidomide in ENL (its primary application) in the natural course of leprosy, as well as in the agent's other applications.

Effects of TNP-470 on proliferation and apoptosis in human colon cancer xenografts in nude mice

AIM: To study the effect of TNP-470 on cell growth, proliferation and apoptosis in human colon cancer xenografts in nude mice.

METHODS: Human colon cancer xenografts were transplanted into 20 nude mice. Mice were randomly divided into two groups. TNP-470 treated group received TNP-470 (30 mg/kg, s.c) every other day and the control group received a sham injection of same volume saline solution. They were sacrificed after 4 wk and their tumors were processed for histological examination. The expression of proliferating cell nuclear antigen (PCNA) in tumors was detected using immunohistochemical method with image analysis, and apoptosis in tumor cells was measured by TdT-mediated biotinyated-dUTP nick end labeling (TUNEL) staining.

RESULTS: Comparing with controls, tumor growth was significantly inhibited in TNP-470 treated group, the inhibitory rate being 54.4%. Expression of PCNA in tumors of TNP-470 treated group (PI 54.32 ± 11.47) was significantly lower than that of control group (PI 88.54 ± 12.36), P < 0.01. Apoptosis index (AI) of TNP-470 treated group (18.95 ± 1.71) was significantly higher than that of control group (7.26 ± 1.44), P < 0.001, typical morphological change of apoptosis in tumor cells was observed in TNP-470 treated group.

CONCLUSION: Besides the anti-angiogenic effects, TNP-470 can inhibit tumor growth by inhibiting the proliferation and inducing apoptosis of tumor cells.

Teratogenic effects of suramin on the chick embryo

Suramin, a polysulfonated naphthylamine, has been used for the chemotherapy of trypanosomiasis and onchocerciasis since about the 1920s. Currently, it is also being tested as an anticancer agent. It is hoped that suramin might stop the progression of some kinds of cancer since it has been found to inhibit the proliferation and migration of cells and the formation of new blood vessels. These processes are not only essential for the development and progression of cancer, but also for normal embryonic development. Suramin might, therefore, be a potent teratogen. In the literature, however, we have found only scant information on this subject. In the present study, we demonstrate the teratogenic effects of suramin on chick embryos. Suramin was injected into the coelomic cavity of chick embryos on incubation day (ID) 3. Following reincubation until ID 8, suramin-treated embryos ( n=50) were examined for congenital malformations and compared with a control group ( n=30). The survival rate of suramin-treated embryos was markedly reduced compared with controls (50% vs 90%). Among the 25 survivors the following malformations were recorded: caudal dysgenesia (100%), median facial clefts with hypertelorism (92%), malformations of the aortic arch arteries (88%), hypo-/aplasia of the allantoic vesicle (84%), microphthalmia (52%), abnormalities of the great arterial trunks (44%), unilateral or bilateral cleft lips (40%), heart defects with juxtaposition of the right atrial appendage (36%), persistence of the lens vesicle (32%), median clefts of the lower beak (8%), omphalocele (4%), and cloacal exstrophy (4%). These results show that suramin is a potent teratogen. The possible implications of our findings for human beings and the possible teratogenic mechanisms of suramin are discussed. Use of suramin in experimental teratology might help to clarify the morphogenesis of median facial clefts and of some congenital heart defects.

A novel strategy for the generation of angiostatic kringle regions from a precursor derived from plasminogen

In this study we have explored the feasibility of generating angiostatin by incorporating an endoproteolytic furin cleavage site into plasminogen to allow conversion of the precursor molecule into an angiostatic active K1-3 fragment. We show that secretable angiostatin can be successfully generated from cells infected with adenovirus carrying the furin-mutated plasminogen (AdmuthPlgK3). Supernatant from cells transduced with AdmuthPlagK3 inhibits tube formation and proliferation and migration of human umbilical vein endothelial cells with an efficiency similar to that of supernatant from cells infected with adenovirus expressing kringle 1-3 of plasminogen (AdK1-3). Administration of AdmuthPlgK3 and AdK1-3 in mice results in significantly decreased endothelial cell infiltration in VEGF-embedded Matrigel plugs. Treatment with AdmuthPlgK3 and AdK1-3 exerts strong antitumoral effect in models of hepatocellular carcinoma and Lewis lung cancer. This antitumor effect was associated with decreased microvessel density in the tumors. Taken together, our data demonstrate that angiostatin endowed with strong antiangiogenic and antitumor effects can be released from a furin-mutated plasminogen acting as a precursor. This strategy may have potential to develop angiostatic anti-cancer therapies.

Vascular endothelial growth factor monoclonal antibody inhibits growth of anaplastic thyroid cancer xenografts in nude mice

BACKGROUND

Anaplastic thyroid cancer (ATC) does not respond well to any treatment and is one of the most aggressive of all human cancers. Based on the importance of angiogenesis in solid tumor growth, we hypothesized that angiogenic blockade might reduce the growth of ATC.

METHODS

We tested the in vivo effect of vascular endothelial growth factor monoclonal antibody (VEGF-mAb) and thalidomide against ATC (ARO-81) xenografts in nude mice. Mice were injected subcutaneously with 1 x 10(6) ARO-81 cells, allowed to implant (1 week), and then given daily intraperitoneal injections of vehicle (control; n = 9), VEGF-mAb (200 microg/d; n = 9), or thalidomide (200 mg/kg per day; n = 9). Tumors were removed, sectioned, and stained for routine histology and immunohistochemistry.

RESULTS

At 6 weeks, VEGF-mAb-treated tumors were smaller (1603 +/- 296 mm(3)) than either the thalidomide-treated (6007 +/- 1498 mm(3); p = 0.008) or the control groups (4040 +/- 831 mm(3); p = 0.014) and the VEGF-mAb-treated animals maintained greater weight (30.4 +/- 0.84 g at week 6 versus thalidomide-treated, 26.0 +/- 0.94 g, p = 0.003; and control, 25.8 +/- 0.78 g, p = 0.001 animals). Central necrosis was observed in 3 of 9 VEGF-mAb-treated confidence interval (33%; 95% [CI] = 0.12-0.65) but in none of the control or thalidomide-treated tumors (0/18 total; 95% CI = 0.0-0.30; p = 0.029). VEGF staining intensity for VEGF-mAb- (2.0 +/- 0.24; p = 0.012) and thalidomide- (2.1 +/- 0.05; p = 0.052) treated tumors was greater than control (0.89 +/- 0.31) as was p53 staining grade (VEGF-mAb [1.3 +/- 0.37; p = 0.012]; thalidomide [1.0 +/- 0.41; p = 0.05]; and controls [0.11 +/- 0.11]).

CONCLUSION

We conclude that systemic VEGF-mAb significantly reduces growth of ATC xenografts and is associated with increased VEGF and p53 expression. Thalidomide has no effect on tumor growth, but is also associated with increased VEGF and p53 expression. These observations provide the first evidence that VEGF-mAb-induced angiogenesis blockade may be of use for the treatment of ATC.

Asymmetric total synthesis of (-)-azaspirene, a novel angiogenesis inhibitor

The asymmetric total synthesis of (-)-azaspirene, an angiogenesis inhibitor, has been accomplished, establishing its absolute stereochemistry. The key steps are a MgBr2.OEt2-mediated, diastereoselective Mukaiyama aldol reaction, a NaH-promoted, intramolecular cyclization of an alkynylamide, and the aldol reaction of a ketone containing functionalized gamma-lactam moiety without protection of tert-alcohol and amide functionalities.

Electrotransfer of gene encoding endostatin into normal and neoplastic mouse tissues: inhibition of primary tumor growth and metastatic spread

Electroporation-mediated gene transfer relies upon direct delivery of plasmids into cells permeabilized by electric fields, a method more efficient than transfer using nonviral vectors, although neither approaches the transfer efficiency of viral vectors. Here we studied electrotransfer of a gene encoding an angiogenesis inhibitor (endostatin) into primary tumors and muscle tissues, which would serve as a site of synthesis and secretion into the bloodstream of a therapeutic antimetastatic protein with systemic effects. Optimum electroporation conditions (voltage, number and duration of impulses, separation of caliper electrodes) were first established to maximize expression of a reporter gene transferred into murine Renca kidney carcinoma, B16(F10) melanoma, or skeletal muscle tissues. In neoplastic tissues, electrotransfer of plasmid DNA was far more efficient than electroporation with lipoplexes, but no differences between naked DNA and lipoplexes were found in case of electroporated muscles. We then studied the electrotransfer of plasmid DNA carrying the endostatin gene into pre-established experimental Renca tumors. A significant inhibition of tumor growth was observed in animals electroporated with this construct. Electrotransfer of the endostatin gene into muscle tissues resulted in reduced numbers of experimental B16(F10) metastases in the lungs. This study clearly shows that electroporation may be used to efficiently transfer antiangiogenic genes into both normal and neoplastic tissues.

A gene therapy for cancer based on the angiogenesis inhibitor, vasostatin

The growth and persistence of solid tumors and their metastasis are angiogenesis-dependent. Vasostatin, the N-terminal domain of calreticulin inclusive of amino acids 1-180, is a potent angiogenesis inhibitor. To investigate whether intramuscular administration of vasostatin gene has the antitumor activity in mouse tumor models, we constructed a plasmid DNA encoding vasostatin and a control vector. Production and secretion of vasostatin protein by COS cells transfected with the plasmid DNA encoding vasostatin (pSecTag2B-vaso) were confirmed by Western blot analysis and ELISA. Conditioned medium from vasostatin-transfected COS cells apparently inhibited human umbilical vein endothelial cell (HUVEC) and mouse endothelial cell (SVEC4-10) proliferation, compared with conditioned medium from the COS cells transfected with control vector or non-transfected cells. Treatment with pSecTag2B-vaso twice weekly for 4 weeks resulted in the inhibition of tumor growth and the prolongation of the survival of tumor-bearing mice. The sustained high level of vasostatin protein in serum could be identified in ELISA. Angiogenesis was apparently inhibited in tumor by immunohistochemical analysis. Angiogenesis was also inhibited in the chicken embryo CAM assay and mouse corneal micropocket assay. The increased apoptotic cells were found within the tumor tissues from the mice treated with plasmid DNA encoding vasostatin. Taken together, the data in the present study indicate that the cancer gene therapy by the intramuscular delivery of plasmid DNA encoding vasostatin, is effective in the inhibition of the systemic angiogenesis and tumor growth in murine models. The present findings also provide further evidence of the anti-tumor effects of the vasostatin, and may be of importance for the further exploration of the application of this molecule in the treatment of cancer.

Azaspirene: a novel angiogenesis inhibitor containing a 1-oxa-7-azaspiro[4.4]non-2-ene-4,6-dione skeleton produced by the fungus Neosartorya sp

[structure: see text] Azaspirene isolated from the fungus Neosartorya sp. is a novel angiogenesis inhibitor with a 1-oxa-7-azaspiro[4.4]non-2-ene-4,6-dione skeleton. Azaspirene inhibits the endothelial migration induced by vascular endothelial growth factor (ED100 = 27.1 microM).

Thalidomide in cancer treatment: a potential role in the elderly?

There is increased interest in the treatment of cancer with thalidomide because of its antiangiogenic, immunomodulating and sedative effects. In animal models, the antitumour activity of thalidomide is dependent on the species, route of administration and coadministration of other drugs. For example, thalidomide has shown antitumour effects as a single agent in rabbits, but not in mice. In addition, the antitumour effects of the conventional cytotoxic drug cyclophosphamide and the tumour necrosis factor inducer 5,6-dimethylxanthenone-4-acetic acid (DMXAA) were found to be potentiated by thalidomide in mice bearing colon 38 adenocarcinoma tumours. Further studies have revealed that thalidomide upregulates intratumoral production of tumour necrosis factor-alpha 10-fold over that induced by DMXAA alone. Coadministration of thalidomide also significantly reduced the plasma clearance of DMXAA and cyclophosphamide. All these effects of thalidomide may contribute to the enhanced antitumour activity. Recent clinical trials of thalidomide have indicated that it has minimal anticancer activity for most patients with solid tumours when used as a single agent, although it was well tolerated. However, improved responses have been reported in patients with multiple myeloma. Palliative effects of thalidomide on cancer-related symptoms have also been observed, especially for geriatric patients with prostate cancer. Thalidomide also eliminates the dose-limiting gastrointestinal toxic effects of irinotecan. There is preliminary evidence indicating that the clearance of thalidomide may be reduced in the elderly. The exact role of thalidomide in the treatment of cancer and cancer cachexia in the elderly remains to be elucidated. However, it may have some value as part of a multimodality anticancer therapy, rather than as a single agent.

Inhibition of tumor growth by systemic treatment with thrombospondin-1 peptide mimetics

Many normal human cells produce thrombospondin-1 (TSP-1), a potent antiangiogenic protein that promotes vascular quiescence. In various organ systems, including the brain, breast and bladder and in fibroblasts, TSP-1 secretion is reduced during tumorigenesis, thereby allowing induction of the vigorous neovascularization required for tumor growth and metastasis. Full-length and short TSP-1-derived peptides inhibit angiogenesis by inducing endothelial cell apoptosis and thus disrupting the vasculature of the growing tumor. CD36 expressed on the surface of endothelial cells functions as the primary antiangiogenic receptor for TSP-1. A D-isoleucyl enantiomer of a TSP-1 heptapeptide specifically inhibits the proliferation and migration of capillary endothelial cells. DI-TSP, an approximately 1 kDa capped version of this peptide, is also antiangiogenic in vitro, with a specific activity approaching that of the 450 kDa parental molecule. Here, we show that DI-TSP delivered systemically dose-dependently inhibits the growth of murine melanoma metastases in syngeneic animals and that its more soluble isomer, DI-TSPa, similarly blocks the progression of primary human bladder tumors in an orthotopic model in immune-deficient mice. Like intact TSP-1, these peptide mimetics had no effect on cancer cells growing in vitro but markedly suppressed the growth of endothelial cells by inducing receptor-dependent apoptosis. Antibodies raised against CD36 blocked the ability of peptides to induce apoptosis in endothelial cells but had no effect on tumor necrosis factor-alpha-induced apoptosis. In vivo, the peptide mimetics were associated with a significantly reduced microvessel density and increased apoptotic indices in both the endothelial and tumor cell compartments. Such short peptides targeted to a specific antiangiogenic receptor, potent and easy to synthesize, show great promise as lead compounds in clinical antiangiogenic strategies.

Assessment of antiangiogenic effect using 99mTc-EC-endostatin

PURPOSE

Tumor vascular density may provide a prognostic indicator of metastatic potential or survival. The purpose of this study was to develop 99mTc-ethylenedicysteine-endostatin (99mTc-EC-endostatin) for the evaluation of anti-angiogenesis therapy.

METHOD

99mTc-EC-endostatin was prepared by conjugating ethylenedicysteine (EC) to endostatin, followed by adding pertechnetate and tin chloride. Radiochemical purity was > 95%. In vitro cell viability, affinity and TUNEL assays were performed. Tissue distribution and planar imaging of radiolabeled endostatin were determined in tumor-bearing rats. To assess anti-angiogenic treatment response, rats were treated with endostatin, paclitaxel and saline, followed by imaging with 99mTc-EC-endostatin. Tumor response to endostatin therapy in tumor-bearing animal models was assessed by correlating tumor uptake dose with microvessel density, VEGF, bFGF and IL-8 expression during endostatin therapy.

RESULTS

In vitro cell viability and TUNEL assays indicated no marked difference between EC-endostatin and endostatin. Cellular uptake assay suggests that endostatin binds to endostatin receptor. Biodistribution of 99mTc-EC-endostatin in tumor-bearing rats showed increased tumor-to-tissue count density ratios as a function of time. Tumor uptake (%ID/g) of 99mTc-EC-endostatin was 0.2-0.5. Planar images confirmed that the tumors could be visualized clearly with 99mTc-EC-endostatin. The optimal time for imaging using radiolabeled endostatin was 2 hrs. 99mTc-EC-endostatin could assess treatment response. There was a correlation between tumor uptake and cellular targets expression.

CONCLUSION

The results indicate that it is feasible to use 99mTc-EC-endostatin to assess efficiency of anti-angiogenesis therapy.

Solid-phase synthesis of thalidomide and its analogues

A novel solid-phase synthesis of thalidomide and its metabolites and analogues is described. The synthetic strategy involves the coupling of hydroxymethyl polystyrene with phthalic anhydride to form the resin-linked acid. The acid is then reacted with primary amines followed by acid or base treatment to form thalidomide and its analogues with either open or closed phthalimide rings. Most of the analogues are synthesized with high yields (40.3-98.1% in three steps) and purities (92.3-98.9%).

The role of matrix metalloproteinases in wound healing

The structure, classification, function, and regulation of matrix metalloproteinases in normal and abnormal wound healing is discussed. Results from key studies suggest that neutrophil-derived matrix metalloproteinase 8 (MMP-8) is the predominant collagenase present in normal healing wounds, and that overexpression and activation of this collagenase may be involved in the pathogenesis of nonhealing chronic leg ulcers. Excessive collagenolytic activity in these chronic wounds is possible because of the reduced levels of tissue inhibitor metalloproteinase 1 (TIMP-1). However, until recently, there have been no studies evaluating levels of matrix metalloproteinase or tissue inhibitors of metalloproteinase activity in chronic diabetic foot wounds. Improving basic knowledge and pharmaceutical intervention in this area ultimately may help clinicians identify and proactively intervene in an effort to prevent normal wounds from becoming chronic. This may prevent the high prevalence of morbidity associated with this significant health problem.

Metronomic scheduling: the future of chemotherapy?

Tumour endothelium is a new target for anticancer treatments. Proliferating endothelial cells from the tumour, even if qualitatively different from those of blood vessels in the normal tissue of origin, remain putatively normal and genetically stable cells. The results of recent experimental studies have suggested that frequent administration of certain cytotoxic agents at low doses (a tenth to a third of the maximum tolerated dose), known as 'metronomic' chemotherapy, increases the antiangiogenic activity of the drugs. The effects of these metronomic schedules of cytotoxic agents may be further enhanced by concurrent administration of novel, selective, treatments that inhibit, at a molecular level, the processes of tumour formation and growth eg angiogenesis, growth factor pathways, and other signal transduction cascades. The need to treat patients for long periods also supports the use of metronomic scheduling for chemotherapy, to minimise toxicity and to target both proliferating tumour cells and endothelial cells. This review describes the experimental studies involving metronomic schedules of chemotherapy, alone and in combination with angiogenesis inhibitors, and suggests a new therapeutic anticancer paradigm for controlling cancer by long-term therapy, based on the development of combinations of metronomic cytotoxic agents with individually tailored compounds designed to target specific molecules.

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

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

Tumor angiogenesis as a therapeutic target

Angiogenesis - the formation of new blood vessels within a tumor (or many other tissue types) - has become a hotbed of pharmacological research as well as industrial drug discovery. This is the result of the efforts of a generation of scientists elucidating the complex (patho)physiological, biochemical and molecular events accompanying angiogenesis. It is estimated that >300 drug candidates are currently in various stages of testing, and it is, therefore, impossible to capture all of this in a brief review. Therefore, the emphasis here is on relatively advanced projects that are either in preclinical or clinical development, thus neglecting, to a large extent, the many exciting avenues being pursued in both academic and biotechnology laboratories. Although the potential of the approaches described cannot be overestimated, it is also important to note that there is still no drug on the market that achieves clinical benefit based on a selective modulation or inhibition of angiogenesis.

Intravascular HBO(2) saturations, perfusion and hypoxia in spontaneous and transplanted tumor models

Clinical trials utilizing strategies to manipulate tumor oxygenation, blood flow and angiogenesis are under way, although limited quantitative information exists regarding basic tumor pathophysiology. The current study utilized murine KHT fibrosarcomas, spontaneous mammary carcinomas and first-generation spontaneous transplants to examine heterogeneity in vascular structure and function, to relate these changes to the distribution of tumor hypoxia and to determine whether fundamental relationships among the different pathophysiological parameters exist. Three methods were included: (i) immunohistochemical staining of anatomical and perfused blood vessels, (ii) cryospectrophotometric measurement of intravascular oxyhemoglobin saturations and (iii) fluorescent detection of the EF5 hypoxic marker. While a distinct pattern of decreasing oxygenation with increasing distance from the tumor surface was observed for KHT tumors, striking intertumor variability was found in both spontaneous and first-generation transplants, with a reduced dependence on tumor volume. EF5 hypoxic marker uptake was also much more heterogeneous among individual spontaneous and first-generation tumors compared to KHT. Although mammary carcinomas demonstrated fewer anatomical blood vessels than fibrosarcomas, the proportion of perfused vessels was substantially reduced in KHT tumors, especially at larger tumor volumes. Vascular morphology, tissue histological appearance and pathophysiological parameters differed substantially between KHT tumors and both spontaneous and first-generation tumors. Such differences in vascular structure and function are also likely to correlate with altered response to therapies targeted to the vascular system. Finally, spontaneous differentiation status, tumor morphology, vascular configuration and function were well preserved in first-generation transplanted tumors, suggesting a close relationship between vascular development and function in early-generation transplants and spontaneous tumor models.

3D MR angiography of intratumoral vasculature using a novel macromolecular MR contrast agent

Noninvasive methods to visualize blood flow in the intratumoral vasculature have not previously been studied. In the present study, the use of a novel intravascular MR contrast agent with a generation-6 polyamidoamine dendrimer core (G6-(1B4M-Gd)192; MW: 175kD) was investigated, and the vasculature in experimental tumors was visualized using 3D MR angiography (MRA). Xenografted tumors in nude mice of two different histologies-KT005 (human osteogenic sarcoma) and LS180 (human colon carcinoma)-were used to obtain 3D MRA using G6-(1B4M-Gd)192 and Gd-DTPA. The contrast MR sectional images were correlated with the corresponding histological sections. The intratumoral vasculature in the KT005 tumor was clearly visualized by 3D MRA, which became more evident with the growth of the tumor xenograft. In contrast, the intratumoral vasculature in the LS180 tumor was sparser and much less developed than that in KT005 tumors. Blood vessels with a diameter as small as 100 microm based on histology were visualized using 0.033 mmol Gd/kg of G6-(1B4M-Gd)192. In conclusion, intratumoral vasculature with a 100-microm diameter was visualized better using 3D MRA with G6-(1B4M-Gd)192 than with Gd-DTPA.

Antiangiogenic agents and their promising potential in combined therapy

One of the most promising strategies for treating cancer is the addition of antiangiogenic therapy to therapeutic regimens. Angiogenesis, or the growth of new blood vessels from preexisting vessels, is essential both for the growth of a primary tumor and for successful metastasis. As a result of intense research in this field, a number of antiangiogenic agents have been identified and have demonstrated varying degrees of success in inhibiting the growth of solid tumors and metastases in preclinical and clinical studies. The real potential of antiangiogenic agents for cancer therapy resides in strategic combinations with each other, with chemotherapy, with radiation, and with tumor-targeting agents, such as radioimmunotherapy. Along with this new opportunity to develop synergistic therapy comes the challenging complexities of the physiologic systems regulating angiogenesis. These multifaceted systems could intimidate investigators seeking to take advantage of the potential synergy in combined cancer therapy. To aid in these efforts, this overview of key antiangiogenic agent mechanisms, combination strategies and initial studies of the potential synergy with chemotherapy, radiation and radioimmunotherapy is presented.

New agents for prostate cancer

Given the poor results with currently available therapies, it is imperative that new treatments be developed for patients with advanced prostate cancer. The next generation of therapies will include many novel biologic agents targeted at molecular defects in the cancer cell. Investigating the efficacy and safety of these compounds and evaluating their utility in combination with traditional therapies such as chemotherapy or radiotherapy are major goals of prostate cancer clinical research for the next decade.

Intra-tumoral administration of naked plasmid DNA encoding mouse endostatin inhibits renal carcinoma growth

Endostatin is a C-terminal fragment of collagen XVIII and has potent anti-angiogenic and anti-tumor activity. Mouse endostatin-coding sequences were obtained using PCR and linked to the signal sequence of influenzavirus hemagglutinin. The signal-sequence endostatin fragment was subcloned into plasmid vectors under the transcriptional control of cytomegalovirus promoter. Murine renal carcinoma (Renca) cells transfected with endostatin-coding plasmid are shown to secrete full-length endostatin. Endostatin-secreting Renca cells demonstrate slower growth in vivo compared to empty vector-transfected cells, but their in vitro growth is unaffected. Anti-angiogenic activity of secreted endostatin was confirmed in a Matrigel angiogenesis assay in vivo. We report growth inhibition of Renca tumors resulting from intra-tumoral delivery of plasmid vector encoding secretable endostatin. Elevated local concentrations of endostatin resulted from multiple intra-tumoral injections of endotoxin-purified plasmid DNA. Local endostatin levels were high enough to obtain growth arrest of Renca tumors.

Behaviour of metastasis in relation to vascular index in patients with node-positive breast cancer treated with adjuvant tamoxifen

Some experimental studies suggested that one possible oestrogen-receptor-unrelated mechanism of action of tamoxifen involves inhibition of angiogenesis. We evaluated the correlation of the degree of vascularisation of the primary tumour and we assessed it by using the panendothelial marker anti-CD31 and immunohistochemistry with microvessels count, performed at the vascular 'hot spot' of each single cancer, with the risk of recurrence in time. A cohort of 176 consecutive patients with node-positive invasive breast cancer treated with adjuvant tamoxifen (30 mg/daily for 3 years) and a median follow-up of 72 months was studied. Sixty-two patients developed metastasis (30 visceral, 18 skeletal and 14 in soft tissues) during the time of observation. The study of the hazard function for metastasis was performed by a generalized linear modelling approach with a binomial error according to Efron. The risk of first recurrence was strictly associated with vascular index, having the patients with the highest microvessel counts the highest risk of metastasis during all the period of observation. We did not find an interaction of vascularity with oestrogen receptor (ER) status. However, in the subgroup of patients with ER-positive tumours the hazard of metastasis was almost constant in time, while in that with ER-negative tumours it increased rapidly up to 20 months and, thereafter, decreased sharply. The results of our study are an indirect evidence that the patients with highly vascularized breast cancers may gain poor benefit of adjuvant tamoxifen and, therefore. that this antioestrogen is unlikely to retain a clinically relevant antiangiogenic activity in human breast cancer. Our data need confirmation by a prospective randomized clinical trial.

Pharmacological aspects of targeting cancer gene therapy to endothelial cells

Targeting cancer gene therapy to endothelial cells seems to be a rational approach, because (a) a clear correlation exists between proliferation of tumor vessels and tumor growth and malignancy, (b) differences of cell membrane structures between tumor endothelial cells and normal endothelial cells exist which could be used for targeting of vectors and (c) tumor endothelial cells are accessible to vector vehicles in spite of the peculiarities of the transvascular and interstitial blood flow in tumors. Based on the knowledge on the pharmacokinetics of macromolecules it can be concluded that vectors targeting tumor endothelial cells should own a long blood residence time after intravascular application. This precondition seems to be fulfilled best by vectors exhibiting a slight anionic charge. A long blood residence time would allow the formation of a high amount of complexes between tumor endothelial cells and vector particles. Such high amount of complexes should enable a high transfection rate of tumor endothelial cells. In view of their pharmacokinetic behavior nonviral vectors seem to be more suitable for in vivo targeting tumor endothelial cells than viral vectors. Specific binding of nonviral vectors to tumor endothelial cells should be enhanced by multifunctional ligands and the transduction efficiency should be improved by cationic carriers. Effector genes should encode proteins potent enough to induce reactions which eliminate the tumor tissue. To be effective to that degree such proteins should induce self-amplifying antitumor reactions. Examples for proteins which have the potential to induce such self-amplifying tumor reactions are proteins endowed with antiangiogenic and antiproliferative activity, enzymes which convert prodrugs into drugs and possibly also proteins which induce embolization of tumor vessels. The pharmacological data for such examples are discussed in detail.

3D-micro-MR angiography of mice using macromolecular MR contrast agents with polyamidoamine dendrimer core with reference to their pharmacokinetic properties

Four novel macromolecular MRI contrast agents, all of which had the same chemical composition but different molecular weights, were prepared using generation-3, -4, -5, and -6 polyamidoamine (PAMAM) dendrimers conjugated with a bifunctional diethylenetriaminepentaacetic acid derivative to change the blood retention, tissue perfusion, and excretion. Size-dependent changes in the pharmacokinetics were observed in the biodistribution study. (153)Gd-labeled generation-6 PAMAM-conjugates remained in the blood significantly longer than all of the other preparations (P < 0.001). The increase in blood-to-organ ratio of the preparations was found to correlate with increasing molecular size (P < 0.001). Additionally, 3D-micro MR images and angiography of mice of high quality and detail were obtained using PAMAM-(1B4M-Gd)x as a macro-molecular MRI contrast agent with a 1.5-T clinical MRI instrument. Numerous fine vessels of approximately 200 microm diameter were visualized on subtracted 3D-MR angiographms with G6D-(1B4M-Gd)(192). The quality of the images was sufficient to estimate the microvasculature of cancerous tissue for anti-angiogenesis therapy and to investigate knockout mice. Magn Reson Med 45:454-460, 2001.

Angiogenesis: regulators and clinical applications

Angiogenesis is a fundamental process in reproduction and wound healing. Under these conditions, neovascularization is tightly regulated. Unregulated angiogenesis may lead to several angiogenic diseases and is thought to be indispensable for solid tumor growth and metastasis. The construction of a vascular network requires different sequential steps including the release of proteases from "activated" endothelial cells with subsequent degradation of the basement membrane surrounding the existing vessel, migration of endothelial cells into the interstitial space, endothelial cell proliferation, and differentiation into mature blood vessels. These processes are mediated by a wide range of angiogenic inducers, including growth factors, chemokines, angiogenic enzymes, endothelial specific receptors, and adhesion molecules. Finally, when sufficient neovascularization has occurred, angiogenic factors are down-regulated or the local concentration of inhibitors increases. As a result, the endothelial cells become quiescent, and the vessels remain or regress if no longer needed. Thus, angiogenesis requires many interactions that must be tightly regulated in a spatial and temporal manner. Each of these processes presents possible targets for therapeutic intervention. Synthetic inhibitors of cell invasion (marimastat, Neovastat, AG-3340), adhesion (Vitaxin), or proliferation (TNP-470, thalidomide, Combretastatin A-4), or compounds that interfere with angiogenic growth factors (interferon-alpha, suramin, and analogues) or their receptors (SU6668, SU5416), as well as endogenous inhibitors of angiogenesis (endostatin, interleukin-12) are being evaluated in clinical trials against a variety of solid tumors. As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.