Overview Oncologic, Endocrine & Metabolic: Recent advances in angiogenesis inhibitors

Angiogenesis and Cancer Control: From Concept to Therapeutic Trial

Background

There is extraordinary interest in developing angiosuppressive agents for cancer treatment. Several new agents appear promising for the treatment of a variety of human cancers. Current concepts and new agents in clinical trials are the focus of this article. In particular, the introduction of a new treatment for human brain tumors is presented in detail, using an antiangiogenic agent, penicillamine, and depletion of an obligatory cofactor of angiogenesis, copper.

Methods

The explosive increase in literature on antiangiogenesis is reviewed using computerized search, findings presented at the recent national cancer and angiogenesis meetings. A specific protocol, NABTT 97-04, “Penicillamine and Copper Reduction for Newly Diagnosed Glioblastoma,” is presented as an example of angiotherapeutic drug discovery.

Results

A number of promising molecular approaches are being introduced to suppress tumor angiogenesis. Major categories of angiogenesis antagonists include protease inhibitors, direct inhibitors of endothelial cell proliferation and migration, suppression of angiogenic growth factors, inhibition of endothelial-specific integrin/survival signaling, chelators of copper, and inhibitors with specific other mechanisms. The preliminary results of early trials offer a glimpse into how antiangiogenesis therapy will be integrated into future care of the patient with cancer.

Conclusions

Thirty-five antiangiogenesis therapies are currently being evaluated in clinical trials. As we learn more about the fundamental mechanisms of angiogenesis, eg, the role of copper in growth factor activation, effective methods of cancer control will be implemented.

Antiangiogenic versus cytotoxic activity in analogues of aeroplysinin-1

A series of analogues of the potentially angiogenic inhibitor aeroplysinin-1 1 were synthesized and their in vitro antiangiogenic and cytotoxic activities evaluated. In the case of epoxy ketone 6 and azlactone 36 the relationship sprouting inhibition assay/cytotoxicity in BAE cells was enhanced by one order and two orders of magnitude, respectively, with respect to the reference. These results imply more specific antiangiogenic properties for the synthesized derivatives.

Caveolin expression in adult renal tumors

Histopathological criteria are usually sufficient for the accurate distinction of benign form malignant renal tumors. A minority of cases however, poses a vexing diagnostic dilemma. Recent studies suggest that caveolin, a scaffolding cell membrane protein may prove helpful in predicting the behavior of these neoplasms. We analyzed a series of 40 renal tumors of which 7 were clear cell and 6 granular Renal Cell Carcinomas (RCC), 10 cases of Papillary Carcinoma (PCC), 4 cases of Chromophobe Renal cell carcinomas (CRCR), 11 cases of Oncocytomas (OC) and 2 cases of Collecting Duct Carcinomas (CDC). The distribution of immunoreactivity was analyzed by quantifying caveolin cell membrane staining in each case. There was a statistically significant difference in the expression of caveolin-1 between oncocytoma with a mean labeling index of 91.7 and the cases of malignant renal tumors with a mean labeling index of 26.9 for RCC, 24 for CDC, 21 for CRCR, and 19.2 for PCC. The results suggest an association between loss of caveolin expression among malignant renal tumors that might be useful in distinguishing oncocytoma from malignant renal tumors and possibly implicates this peptide in their pathogenesis.

Nature of Interaction between basic fibroblast growth factor and the antiangiogenic drug 7,7-(carbonyl-bis[imino-N-methyl-4,2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino])-bis-(1,3-naphtalene disulfonate). II. Removal of polar interactions affects protein folding

Fibroblast growth factor-2 (basic FGF), a potent inducer of angiogenesis, and the naphthalene sulfonic distamycin A derivative, 7,7-(carbonyl-bis[imino-N-methyl-4,2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino])-bis-(1,3-naphtalene disulfonate) (PNU145156E), which exhibits in vivo antiangiogenic activity, form a tight reversible (1:1) complex. PNU145156E binds to the heparin and the selenate-binding sites on bFGF. The cis bFGF-heparin (2:1) complex, essential for the activation of the angiogenic process, is thus prevented. The nature of the forces involved in bFGF:PNU145156E complex, using the wild-type and the K128Q, K138Q, K134Q, and K128Q-K138Q point mutated bFGFs was sought. Based on thermodynamic analysis of the complexation constants, protein temperature stability profiles by ultraviolet absorption, circular dichroism measurements, fluorescence Förster energy-transfer, and anisotropy studies, in harmony with the published x-ray crystallographic structure, the following molecular interactions are proposed: reduced coulombic interactions, hence loosening of the complex by the removal of charged polar groups from the bFGF-heparin binding cleft resulted in decreased binding constants and in a change in the binding mode from polar to nonpolar. Concomitantly, upon mutation, the protein was rendered more compact, less flexible, and less aqueously exposed compared with the wild type. These were further pronounced with the double mutant: weaker dominantly nonpolar protein-drug interactions were accompanied by conspicuous folding. With heparin, however, wild-type bFGF forms a tighter complex with a more compact structure.

Expression of the caveolins in dermal vascular tumors

INTRODUCTION

Histopathologic criteria are usually sufficient for the accurate distinction of benign from malignant dermal vascular tumors. A minority of cases, however, pose a vexing diagnostic dilemma. Recent studies suggest that caveolin, a scaffolding cell membrane protein, may prove helpful in predicting the biologic behavior of endothelial-derived neoplasms.

METHODS

We analyzed a series of 30 dermal vascular tumors including 12 lobular capillary hemangiomas (LCH), 4 cases of targetoid hemosiderotic hemangiomas (TH), 4 cases of tufted angioma (TA), 12 cases of Kaposi's sarcoma (KS), 4 epithelioid (EH) and 1 spindle cell hemangioendothelioma (SH), and 4 cases of angiosarcoma (AS). The distribution of immunoreactivity was analyzed by quantifying cell membrane staining in each case.

RESULTS

There was a statistically significant difference in the expression of caveolin between LCH (mean labeling index=91.6), TH (mean labeling index=89.7), and TA (mean labeling index=87.2) and the cases of KS (mean labeling index=21.6, EH mean labeling index= 23.1), and the AS (mean labeling index=6.3).

CONCLUSIONS

These results indicate that antibodies to caveolin may be useful in separating benign and malignant dermal vascular tumors and possibly implicates this peptide in their pathogenesis.

Nature of interaction between basic fibroblast growth factor and the antiangiogenic drug 7,7-(Carbonyl-bis[imino-N-methyl-4, 2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino] )bis-(1, 3-naphthalene disulfonate)

PNU145156E (7,7-(carbonyl-bis[imino-N-methyl-4, 2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino]) -bis-(1, 3-naphthalene disulfonate)) is a naphthalene sulfonic distamycin A derivative that interacts with heparin-binding growth factors. Because PNU145156E inhibits tumor angiogenesis, it was selected for clinical development. Picosecond time-resolved fluorescence emission and anisotropy were used to characterize the binding of PNU145156E to the basic fibroblast growth factor (a protein associated with tumor angiogenesis). A decrease in PNU145156E fluorescence lifetime was observed as a function of human basic fibroblast growth factor (bFGF) concentration. Nonlinear least-squares fitting of the binding isotherm yielded Kd = 145 nM for a single class of binding sites. Time-resolved anisotropy gave Kd = 174 nM. Kd = 150 nM was independently verified by quantitative high-performance affinity chromatography. The displaced volume of the complex, calculated from its rotational correlation time, fitted a sphere of 1:1 stoichiometry. These results account for the formation of a tight yet reversible PNU145156E:bFGF complex. An evaluation of PNU145156E fluorescence lifetimes in various solvents has highlighted the forces involved in stabilizing the complex. These are mostly electrostatic-hydrophobic in nature, with a relatively low contribution from hydrogen bonding. Both polar and nonpolar groups are involved on the protein-binding site within a largely hydrophobic cleft. A potential binding trajectory, based on a combination of these results with site-directed chemical modification and known bFGF x-ray structure, is suggested.

Inhibition of angiogenesis by rhizoxin, a microbial metabolite containing two epoxide groups

Previous studies by our and other groups have shown that microbial products containing more than one epoxide group, including eponemycin, radicicol, depudecin and AGM-1470, exhibits anti-angio-genic activity in an in vivo assay system involving chorioallantoic membranes (CAMs) of growing chick embryos. Based on these findings, rhizoxin, a microbial metabolite that contains two epoxide groups and exhibits anti-tubulin activity, was tested for anti-angiogenic activity in a CAM assay system. Rhizoxin caused dose-dependent inhibition of embryonic angiogenesis, the ID50 value being 2 ng (3.2 pmol) per egg. In addition, this compound (2 mg/kg i.p.) significantly suppressed neovascularization induced by M5076 mouse tumor cells in a mouse dorsal air sac assay system, compared to the vehicle alone (P < 0.05). These results indicate that rhizoxin is a novel inhibitor of angiogenesis, and that is has potential as a new therapeutic agent for cancer.

Inhibition of tumor growth and metastasis by angiogenesis inhibitor TNP-470 on breast cancer cell lines in vitro and in vivo

Antitumor and antimetastatic activity of the angiogenesis inhibitor O-(chloroacetyl-carbamoyl) fumagillol (TNP-470), a semisynthetic analogue of fumagillin, was evaluated in breast cancer cell lines. In an in vitro MTT assay, after 72 hrs continuous exposure to TNP-470, growth inhibition was observed in all seven cell lines of murine (JYG-A, JYG-B, DD-762, and BALB/c-MC) or human (KPL-1, MDA-MB-231, and MKL-F) origin, in which the 50% inhibitory concentrations (IC50) at 72 hrs treatment were 4.6, 4.4, 4.6, 10.1, 35.0, 25.3, and 33.4 micrograms/ml, respectively. In an in vivo assay using JYG-A, JYG-B, KPL-1, and MDA-MB-231 cells by orthotopic (right thoracic mammary fat pad) transplantation in female nude mice, TNP-470 at 30 or 50 mg/kg body weight was injected s.c. every other day from the day of tumor cell inoculation until the end of the experiment. The inhibitory effect on primary tumor growth was obtained in all four cell lines in a dose-dependent manner. In the 50 mg/kg TNP-470-treated group, the reductions in tumor weight of the JYG-A, JYG-B, KPL-1, and MDA-MB-231 cells with respect to the controls were 50%, 30%, 4%, and 49%, respectively. Metastasis was seen in the JYG-A, JYG-B, and KPL-1 cells. The numbers of mice bearing pulmonary metastases of JYG-A and JYG-B cells and regional axillary lymph node metastases of KPL-1 cells were reduced, and TNP-470 at the 50 mg/kg dose to KPL-1 cells significantly reduced lymph node metastases compared with the control. Although the weight gain was retarded in the TNP-470-treated mice, weight loss was not seen. TNP-470 was highly effective in the treatment of breast cancer cells. These results suggest that the clinical use of TNP-470 may be a promising treatment for breast cancer patients.

Inhibitory Effect of the Angiogenesis Inhibitor O-(Chloroacetyl-carbamoyl)fumagillol(TNP-470) on Tumor Growth and Metastasis of Murine Mammary Tumor Cell Line (JYG-B)Inoculated in Female Nude Mice

The effect of the potent angiogenesis inhibitor O-(chloroacetyl-carbamoyl) fumagillol(TNP-470), a semisynthetic analogue of fumagillin on tumor growth and metastasis was studied using murine mammary tumor cells (JYG-B) inoculated into female nude mice. Injection of TNP-470 at 10 and 30 mg/kg doses, 3 times a week, until the end of the experiment (41 days)inhibited the s.c.inoculated primary tumor growth in a dose-dependent manner (45%and 65% in volume, respectively). TNP-470 at 30 and 60 mg/kg doses, 3 times a week, until the end of the experiment (35 days), reduced the weight of the i.p. inoculated total tumor mass of abdominal dissemination in a dose-dependent manner (54% and 76%, respectively). Pulmonary metastasis was found in all mice but TNP-470 significantly reduced the lung weight reflecting the total volume of the metastatic foci, and the numbers of metastatic foci in the liver and kidneys was reduced by TNP-470 treatment. These findings show that the angiogenesis inhibitor (TNP-470)has a strong inhibitory effect on tumor grwoth and metastasis in vivo.

Controlling the vasculature: angiogenesis, anti-angiogenesis and vascular targeting of gene therapy

Angiogenesis is the development of new blood vessels from an existing vascular bed. Normal vascular proliferation occurs only during embryonic development, the female reproductive cycle and wound repair. By contrast, many pathological conditions (for example, cancer, atherosclerosis and diabetic retinopathy), are characterized by persistent, unregulated angiogenesis. Conversely, inadequate angiogenesis can lead to failure of ulcers to heal and myocardial infarction. Control of vascular development could permit new therapeutic approaches to these disorders. For example, several anti-angiogenic drugs are currently undergoing clinical trials for the treatment of cancer, whereas enhancement of angiogenesis by exogenous growth factors can prevent or limit the damage in chronic wounds and duodenal ulcers. Here Tai-Ping Fan, Rhys Jaggar and Roy Bicknell highlight recent achievements and discuss the prospects of receptor antagonists, enzyme inhibitors, tumour suppressor genes and vascular targeted approaches, especially that of gene therapy, in the future development of angiotherapy.