Tetrathiomolybdate (choline salt; ATN-224), a specific, high-affinity copper binder, is currently being evaluated in several phase II cancer trials. ATN-224 inhibits CuZn superoxide dismutase 1 (SOD1) leading to antiangiogenic and antitumour effects. The pharmacodynamics of tetrathiomolybdate has been followed by tracking ceruloplasmin (Cp), a biomarker for systemic copper. However, at least in mice, the inhibition of angiogenesis occurs before a measurable decrease in systemic copper is observed. Thus, the identification and characterisation of other biomarkers to follow the activity of ATN-224 in the clinic is of great interest. Here, we present the preclinical evaluation of two potential biomarkers for the activity of ATN-224: (i) SOD activity measurements in blood cells in mice and (ii) levels of endothelial progenitor cells (EPCs) in bonnet macaques treated with ATN-224. The superoxide dismutase activity in blood cells in mice is rapidly inhibited by ATN-224 treatment at doses at which angiogenesis is maximally inhibited. Furthermore, ATN-224 dosing in bonnet macaques causes a profound and reversible decrease in EPCs without significant toxicity. Thus, both SOD activity measurements and levels of EPCs may be useful biomarkers of the antiangiogenic activity of ATN-224 to be used in its clinical development.

Superoxide dismutase 1 (SOD1) is an abundant copper/zinc enzyme found in the cytoplasm that converts superoxide into hydrogen peroxide and molecular oxygen. Tetrathiomolybdate (ATN-224) has been recently identified as an inhibitor of SOD1 that attenuates FGF-2- and VEGF-mediated phosphorylation of ERK1/2 in endothelial cells. However, the mechanism for this inhibition was not elucidated. Growth factor (GF) signaling elicits an increase in reactive oxygen species (ROS), which inactivates protein tyrosine phosphatases (PTP) by oxidizing an essential cysteine residue in the active site. ATN-224-mediated inhibition of SOD1 in tumor and endothelial cells prevents the formation of sufficiently high levels of H 2 O 2 , resulting in the protection of PTPs from H 2 O 2 -mediated oxidation. This, in turn, leads to the inhibition of EGF-, IGF-1-, and FGF-2-mediated phosphorylation of ERK1/2. Pretreatment with exogenous H 2 O 2 or with the phosphatase inhibitor vanadate abrogates the inhibition of ERK1/2 phosphorylation induced by ATN-224 or SOD1 siRNA treatments. Furthermore, ATN-224-mediated SOD1 inhibition causes the down-regulation of the PDGF receptor. SOD1 inhibition also increases the steady-state levels of superoxide, which induces protein oxidation in A431 cells but, surprisingly, does not oxidize phosphatases. Thus, SOD1 inhibition in A431 tumor cells results in both prooxidant effects caused by the increase in the levels of superoxide and antioxidant effects caused by lowering the levels of H 2 O 2 . These results identify SOD1 as a master regulator of GF signaling and as a therapeutic target for the inhibition of angiogenesis and tumor growth.

Background: Identifying biomarkers that monitor clinical response to cancer therapies is crucial. Tetrathiomolybdate (TM) is a highly specific, high-affinity, orally available copper-binding compound that inhibits CuZn SOD1, leading to robust anti-angiogenic and anti-tumor effects. TM is currently being evaluated in Phase II cancer trials including for relapsed and refractory multiple myeloma (MM). TM's inhibition of angiogenesis has been attributed to depletion of systemic Cu, which is known to affect multiple key angiogenesis regulators; however, in mice, inhibition of angiogenesis by TM occurred before a measurable decrease in systemic Cu. We have recently shown that in MM, circulating endothelial progenitor cell (EPC) levels serve as a reliable biomarker of disease severity which covaries with tumor load and disease progression. Furthermore, recent evidence from our laboratory and by others indicates that EPCs display evidence of clonality and are genetically related to MM cells. In the present study, the relationship between anti-angiogenic and anti-SOD1 activities of TM were compared by determining its effects on:

PURPOSE:A second-generation tetrathiomolybdate analogue (ATN-224; choline tetrathiomolybdate), which selectively binds copper with high affinity, is currently completing two phase I clinical trials in patients with advanced solid and advanced hematologic malignancies. However, there is very little information about the mechanism of action of ATN-224 at the molecular level.EXPERIMENTAL DESIGN:The effects of ATN-224 on endothelial and tumor cell growth were evaluated in cell culture experiments in vitro. The antiangiogenic activity of ATN-224 was investigated using the Matrigel plug model of angiogenesis.RESULTS:ATN-224 inhibits superoxide dismutase 1 (SOD1) in tumor and endothelial cells. The inhibition of SOD1 leads to inhibition of endothelial cell proliferation in vitro and attenuation of angiogenesis in vivo. The inhibition of SOD1 activity in endothelial cells is dose and time dependent and leads to an increase in the steady-state levels of superoxide anions, resulting in the inhibition of extracellular signal-regulated kinase phosphorylation without apparent induction of apoptosis. In contrast, the inhibition of SOD1 in tumor cells leads to the induction of apoptosis. The effects of ATN-224 on endothelial and tumor cells could be substantially reversed using Mn(III)tetrakis(4-benzoic acid)porphyrin chloride, a catalytic small-molecule SOD mimetic.CONCLUSIONS:These data provide a distinct molecular target for the activity of ATN-224 and provide validation for SOD1 as a target for the inhibition of angiogenesis and tumor growth.

Proc Amer Assoc Cancer Res, Volume 47, 2006 4687 Tetrathiomolybdate (TM) is a copper binding drug that has demonstrated anti-tumor and anti-angiogenic activity in a number of preclinical studies as well as preliminary evidence of anti-tumor activity in cancer patients. However, very little is understood about the mechanism of action of TM at the molecular level. ATN-224 is a second generation analogue of TM that is currently entering several Phase II cancer trials. ATN-224 inhibits CuZn superoxide dismutase (SOD1), which catalyzes the dismutation of superoxide anion (O2-) into H2O2 and O2. In endothelial cells, SOD1 inhibition results in reduced phosphorylation of ERK1/2 mediated by FGF-2 and VEGF. This leads to suppression of proliferation in vitro and the inhibition of angiogenesis in vivo . In the present study, we demonstrate that ATN-224 inhibition of SOD1 also leads to the inhibition of EGF, IGF-1 and PDGF mediated ERK phosphorylation in a variety of tumor cell lines (A431, HT-29 and U87). This inhibition appears to occur at the level of the growth factor receptor, since (i) ATN-224 mediated SOD1 inhibition in A431 cells decreases EGF mediated phosphorylation of EGFR; and, (ii) ATN-224 treatment of U87 glioma cells stimulated with PDGF decreases levels of the PDGF receptor. In contrast to endothelial cells, where ATN-224 inhibits proliferation but does not cause cell death, the induction of apoptosis is observed in tumor cells treated with ATN-224. Further, EGF, PDGF and IGF-1 have been reported to elicit an increase in H2O2 by activating superoxide producing enzymes when bound to their receptors. Superoxide produced in this way is then converted into H2O2, which inactivates phosphatases by oxidizing an essential cysteine residue in the active site. SOD1 inhibition mediated by ATN-224 in A431 cells impedes the H2O2 mediated inactivation of PTEN and other phosphatases, suggesting that the preservation of phosphatase activity contributes to ATN-224 inhibition of growth factor mediated signaling. These results support the inhibition of SOD1 by ATN-224 as a novel therapeutic strategy for the inhibition of multiple signaling pathways implicated in tumor growth and angiogenesis.

A series of novel, multisubstrate, bicyclic pyrimidine nucleoside inhibitors of human thymidine phosphorylase (TP) is described. Thymidine phosphorylase has been implicated in angiogenesis and plays a significant role in tumor progression and metastasis. The presence and orientation of the phosphonate moiety (acting as a phosphate mimic) in these derivatives were critical for inhibitory activity. The most active compounds possessed a phosphonate group in an endo orientation. This was consistent with molecular modeling results that showed the endo isomer protein-ligand complex to be lower in energy than the exo complex.

The anti-angiogenic properties of the histidine-proline-rich (H/P) domain of HPRG have recently been described (Juarez JC, et al. Cancer Research 2002; 62: 5344-50). However, the binding site that mediates these properties is unknown. HPRG is evolutionarily, functionally and structurally related to cleaved high molecular weight kininogen (HKa), an anti-angiogenic polypeptide that stimulates apoptosis of proliferating endothelial cells through binding to cell-surface tropomyosin (Zhang J-C, et al. Proc Natl Acad Sci USA 2002; 99: 12224-9). In this study, we demonstrate that HPRG binds with high affinity to FGF-2-stimulated human umbilical vein endothelial cells (HUVEC) and immobilized tropomyosin in a Zn2+ or pH-dependent manner, and that this interaction is mediated by the H/P domain of HPRG. At least two binding sites for HPRG, tropomyosin and heparan sulfate proteoglycans (HSPs), were identified on the surface of FGF-2-activated endothelial cells. Translocation of tropomyosin to the surface of HUVEC occurred in response to FGF-2, and the anti-angiogenic activity of HPRG in a Matrigel plug model was partially inhibited by soluble tropomyosin. These results suggest that HPRG binds to endothelial cell surface tropomyosin which at least partially mediates the antiangiogenic effects of HPRG.

The antiangiogenic activity of the multidomain plasma protein histidine-proline-rich glycoprotein (HPRG) is localized to its histidine-proline-rich (H/P) domain and has recently been shown to be mediated, at least partially, through binding to cell-surface tropomyosin in fibroblast growth factor-2-activated endothelial cells (X. Guan et al., Thromb Haemost, in press). HPRG and its H/P domain, but not the other domains of HPRG, bind specifically and with high affinity to tropomyosin. In this study, we characterize the interaction of the H/P domain with tropomyosin and delineate the region within the H/P domain responsible for that interaction. The H/P domain of HPRG consists mostly of repetitions of the consensus sequence [H/P][H/P]PHG. Applying an in vitro tropomyosin binding assay, we demonstrate that the synthetic peptide HHPHG binds to tropomyosin in vitro and inhibits angiogenesis and tumor growth in vivo. The affinity for tropomyosin increases exponentially upon multimerization of the HHPHG sequence, with a concurrent increase in antiangiogenic activity. Specifically, the tetramer (HHPHG)4 has significant antiangiogenic activity in the Matrigel plug model (IC50 approximately 600 nm) and antitumor effects in two syngeneic mouse tumor models. Thus, we show that a 16-mer peptide analogue mimics the antiangiogenic activity of intact HPRG and is also able to inhibit tumor growth, suggesting that cell surface tropomyosin may represent a novel antiangiogenic target for the treatment of cancer.

A novel class of thymidine phosphorylase (TP) inhibitors has been designed based on analogy to the enzyme substrate as well as known inhibitors. Flexible docking studies, using a homology model of human TP, of the designed N-(2,4-dioxo-1,2,3,4-tetrahydro-thieno[3,2-d]pyrimidin-7-yl)-guanidines as well as their synthetic precursors provide insight into the observed experimental trends in binding affinity.

We recently reported that the two-chain form of human high molecular weight kininogen (HKa) inhibits angiogenesis by inducing endothelial cell apoptosis (Zhang et al. 2000). This property appears to be primarily conferred by HKa domain 5 (HKa D5). In this manuscript, we further characterize the activity of these polypeptides toward proliferating endothelial cells, as well as their in vivo anti-angiogenic activity in the chick chorioallantoic membrane (CAM). We also demonstrate that short peptides derived from endothelial cell binding regions in HKa domains 3 and 5 inhibit endothelial cell proliferation and induce endothelial cell apoptosis. Like HKa and HKa D5, peptides derived from the latter domain induce endothelial cell apoptosis in a Zn(2+)-dependent manner, while those derived from domain 3 function independently of Zn2+. The implications of these findings to the regulation of angiogenesis and development of anti-angiogenic therapeutics are discussed.

Conformationally altered proteins and protein fragments derived from the extracellular matrix and hemostatic system may function as naturally occurring angiogenesis inhibitors. One example of such a protein is cleaved high molecular weight kininogen (HKa). HKa inhibits angiogenesis by inducing apoptosis of proliferating endothelial cells, effects mediated largely by HKa domain 5. However, the mechanisms underlying the antiangiogenic activity of HKa have not been characterized, and its binding site on proliferating endothelial cells has not been defined. Here, we report that the induction of endothelial cell apoptosis by HKa, as well as the antiangiogenic activity of HKa in the chick chorioallantoic membrane, was inhibited completely by antitropomyosin monoclonal antibody TM-311. TM-311 also blocked the high-affinity Zn2+-dependent binding of HKa to both purified tropomyosin and proliferating endothelial cells. Confocal microscopic analysis of endothelial cells stained with monoclonal antibody TM-311, as well as biotin labeling of cell surface proteins on intact endothelial cells, revealed that tropomyosin exposure was enhanced on the surface of proliferating cells. These studies demonstrate that the antiangiogenic effects of HKa depend on high-affinity binding to endothelial cell tropomyosin.

Intrapleural loculation can increase morbidity in hemothoraces or parapneumonic effusions. Intrapleural fibrin precedes visceral-parietal pleural adhesions. We speculated that single-chain urokinase plasminogen activator alone or bound to its receptor could prevent these adhesions by their relative resistance to local inhibition by plasminogen activator inhibitors. We found that recombinant human single-chain urokinase-bound rabbit pleural mesothelial cells or lung fibroblasts with kinetics similar to that reported for human cells (kD of approximately 5 nM). The receptor-bound fibrinolysin maintained in vitro fibrinolytic activity in the presence of pleural fluids from rabbits with tetracycline-induced pleural injury over 24 hours. In rabbits given intrapleural single-chain urokinase 24 and 48 hours after intrapleural tetracycline (n = 10 animals), adhesions were prevented, whereas the receptor-complexed form (n = 12) attenuated adhesions versus vehicle/tetracycline-treated rabbits (n = 22, p <or= 0.005 in both cases). There were more adhesions in the complex than the single-chain urokinase group (p = 0.02). Residual antigenic but not functional evidence of the interventional agents remained in pleural fluids at 72 hours after tetracycline. No local or systemic bleeding occurred because of either interventional agent. The data demonstrate that single-chain urokinase inhibits, whereas lysin-receptor complexes attenuate, adhesion formation in tetracycline-induced pleural injury in rabbits.

Histidine-proline-rich glycoprotein (HPRG) is an abundant multidomain plasma protein evolutionarily related to high-molecular-weight kininogen. The cleaved form of high-molecular-weight kininogen has recently been demonstrated to exhibit antiangiogenic activities in vitro (J. C. Zhang et al., FASEB J., 14: 2589-2600, 2000), mediated primarily through domain 5. HPRG contains a histidine-proline-rich (H/P) domain with sequence and functional similarities to HKa-D5. We hypothesized that HPRG may also have antiangiogenic properties, localized within its H/P domain. The H/P domain is highly conserved among species, and because rabbit H/P domain is more resistant to internal proteolytic cleavage than the human domain, the rabbit HPRG (rbHPRG) was primarily used to assess the antiangiogenic activity of HPRG. Rabbit HPRG inhibited human umbilical vein endothelial cell (HUVEC) tube formation stimulated by fibroblast growth factor-2 (FGF-2) or vascular endothelial growth factor on a Matrigel surface as well as cell proliferation of FGF-2 stimulated HUVECs. The antiangiogenic activity of rbHPRG was localized to the H/P domain by use of proteolytic fragments of rbHPRG and was further confirmed and characterized in two in vivo models of angiogenesis: the chorioallantoic membrane of the chick assay and the mouse Matrigel plug assay. Caspase-3 activation was observed in HUVECs stimulated with FGF-2 in the presence of rbHPRG, suggesting that apoptosis of activated endothelial cells may be one of the mechanisms underlying its antiangiogenic activity. Finally, the H/P domain of rbHPRG reduced tumor cell number when tumor cells were co-inoculated in the Matrigel plug assay. In conclusion, the H/P domain within HPRG induces the apoptosis of activated endothelial cells leading to potent antiangiogenic effects.

u‐PA contributes to CaP progression, especially in the metastatic androgen‐insensitive state. In vitro, u‐PA is expressed by androgen‐insensitive, but not androgen‐sensitive, CaP cell lines. We hypothesized that in androgen‐sensitive CaP an activated ARE represses u‐PA expression but in androgen‐insensitive CaP this repression is lost and u‐PA is upregulated through MAP kinase signaling pathways. To determine whether binding of the DHT–AR complex to AREs in the u‐PA promoter region represses u‐PA transcription in androgen‐sensitive CaP, we studied 2 PC3 androgen‐insensitive human CaP cell lines stably transfected with AR [PC3(AR)2 and PC3(AR)13] and 1 mock‐transfected cell line [PC3(M)]. In the presence of the synthetic androgen mibolerone, both PC3(AR)2 and PC3(AR)13, but not PC3(M), cells showed decreased u‐PA expression as assayed by Western and Northern blotting. The AR inhibitor flutamide abrogated mibolerone's effect. Androgen regulation of a second gene, PSA, was also demonstrated in the PC3(AR)2 cell line. To explore the pathway stimulating u‐PA expression in CaP, we performed transient transfections in PC3(AR)2 cells using u‐PA promoter‐regulated CAT reporter constructs. Compared to full‐length u‐PA promoter–CAT constructs, either deletion or mutation of the 5′ AP‐1 or PEA3 site reduced CAT expression. The location of androgen responsiveness in the u‐PA promoter was not identified through the combination of promoter search and transient transfection assays, indicating that a more complicated mechanism is involved in the AR‐mediated downmodulation of u‐PA expression. © 2001 Wiley‐Liss, Inc.

The urokinase-type plasminogen activator receptor (u-PAR) has been implicated in tumor progression, and previous studies have shown that the expression of this gene is strongly up-regulated by PMA. Although the signaling mechanism by which PMA modulates u-PAR expression is not known, the effect of this phorbol ester on the expression of other genes has been ascribed to activation of the c-Raf-1-ERK signaling pathway. However, in the current study we examined an alternate possibility that the inductive effect of PMA on u-PAR expression also required a JNK1-dependent signaling cascade usually associated with stress-inducing stimuli. PMA treatment of the u-PAR-deficient OVCAR-3 ovarian cancer cells, which contain low JNK activities, resulted in a rapid (5 min) increase in JNK activity. Maximal JNK activity (12-fold induction) occurred after 30 min; this preceding the earliest detected rise in u-PAR protein (2 h). Dose-response studies with PMA also indicated that the increased JNK activity was tightly correlated with elevated u-PAR protein levels. The stimulation of u-PAR promoter activity by PMA required an intact upstream AP-1 motif (-184) and in PMA-treated cells this motif was bound with c-Jun as indicated from mobility shift assays. PMA up-regulated the c-Jun trans acting activity as indicated by the higher activity of a GAL4-regulated luciferase reporter in phorbol-ester-treated cells co-transfected with an expression vector encoding the c-Jun transactivation domain fused to the GAL4 DNA-binding domain. The ability of PMA to stimulate u-PAR promoter activity was effectively titrated out by the co-expression of either a kinase-defective JNK1 or a dominant negative MEKK1 the latter being an upstream activator of JNK1. Conversely, u-PAR promoter activity was stimulated by the co-expression of a constitutively active MEKK1 and this induction was antagonized by the inclusion of the kinase-defective JNK1 plasmid. We also determined the biological significance of the JNK1-dependent signaling cascade in regulating u-PAR promoter activity by c-Ha-ras since this oncogene is activated and/or overexpressed in a variety of tumors including ovarian cancer. Transfection of an activated c-Ha-ras into OVCAR-3 cells stimulated u-PAR promoter activity over 20-fold and this could be countered by the individual expression of dominant negative expression constructs to Rac-1, MEKK1 or JNK1. Taken together, these data suggest that the PMA- or c-Ha-Ras-dependent stimulation of u-PAR gene expression requires a JNK1-dependent signaling module and that, at least for PMA, the concurrent stimulation of a JNK1-independent signaling module is also required. Thus, caution should be exercised in invoking linear signaling modules to account for the regulation of inducible gene expression.