Methionine aminopeptidase (type 2) is the common target for angiogenesis inhibitors AGM-1470 and ovalicin

Phylogenetic relationships of methionine aminopeptidase 2 among Encephalitozoon species and genotypes of microsporidia

This report describes the characterization and phylogenetic analysis of the deduced amino acid sequences of methionine aminopeptidase 2 (MetAP-2) enzymes from microsporidian species and genotypes of the genus Encephalitozoon. Fragments of DNA encoding 318 to 335 amino acid residues of the MetAP-2 genes were isolated from genomic DNA prepared from cultured spores of Encephalitozoon hellem, Encephalitozoon intestinalis, and Encephalitozoon cuniculi genotypes I-III. Sequence comparisons of the deduced amino acid residues indicated that the microsporidian sequences are MetAP-2-like rather than MetAP-1-like. Alignments demonstrated that the new Encephalitozoon sequences included sequences and structures conserved in eukaryotic MetAP-2s, including the five conserved, active site residues, Asp, Asp, His, Glu, and His, considered to be critical for catalysis and for coordinating the cation (e.g., cobalt) co-factor, and included residues known to interact with the antibiotic, fumagillin. The primary structure of the Encephalitozoon MetAP-2s, however, showed some dissimilarity with human and yeast MetAP-2s, including the absence of the NH2-terminal polylysine tract. Phylogenetic comparison of these Encephalitozoon MetAP-2s with orthologues from related species and from other informative taxa confirmed that the MetAP-2s of these Encephalitozoon species and strains are closely related to each other and cluster with MetAP-2s.

EPR and X-ray crystallographic characterization of the product-bound form of the MnII-loaded methionyl aminopeptidase from Pyrococcus furiosus

Methionine aminopeptidases (MetAPs) are ubiquitous metallohydrolases that remove the N-terminal methionine from nascent polypeptide chains. Although various crystal structures of MetAP in the presence of inhibitors have been solved, the structural aspects of the product-bound step has received little attention. Both perpendicular- and parallel-mode electron paramagnetic resonance (EPR) spectra were recorded for the Mn(II)-loaded forms of the type-I (Escherichia coli) and type-II (Pyrococcus furiosus) MetAPs in the presence of the reaction product l-methionine (L-Met). In general, similar EPR features were observed for both [MnMn(EcMetAP-I)]-L-Met and [MnMn(PfMetAP-II)]-L-Met. The observed perpendicular-mode EPR spectra consisted of a six-line hyperfine pattern at g = 2.03 (A = 8.8 mT) with less intense signals with eleven-line splitting at g = 2.4 and 1.7 (A = 4.4 mT). The former feature results from mononuclear, magnetically isolated Mn(II) ions and this signal are 3-fold more intense in the [MnMn(PfMetAP-II)]-L-Met EPR spectrum than in the [MnMn(EcMetAP-I)]-L-Met spectrum. Inspection of the EPR spectra of both [MnMn(EcMetAP-I)]-L-Met and [MnMn(PfMetAP-II)]-L-Met at 40 K in the parallel mode reveals that the [Mn(EcMetAP-I)]-L-Met spectrum exhibits a well-resolved hyperfine split pattern at g = 7.6 with a hyperfine splitting constant of A = 4.4 mT. These data suggest the presence of a magnetically coupled dinuclear Mn(II) center. On the other hand, a similar feature was not observed for the [MnMn(PfMetAP-II)]-L-Met complex. Therefore, the EPR data suggest that L-Met binds to [MnMn(EcMetAP-I)] differently than [MnMn(PfMetAP-II)]. To confirm these data, the X-ray crystal structure of [MnMn(PfMetAP-II)]-L-Met was solved to 2.3 A resolution. Both Mn1 and Mn2 reside in a distorted trigonal bipyramidal geometry, but the bridging water molecule, observed in the [CoCo(PfMetAP-II)] structure, is absent. Therefore, L-Met binding displaces this water molecule, but the carboxylate oxygen atom of L-Met does not bridge between the two Mn(II) ions. Instead, a single carboxylate oxygen atom of L-Met interacts with only Mn1, while the N-terminal amine nitrogen atom binds to M2. This L-Met binding mode is different from that observed for L-Met binding [CoCo(EcMetAP-I)]. Therefore, the catalytic mechanisms of type-I MetAPs may differ somewhat from type-II enzymes when a dinuclear metalloactive site is present.

Amphidinolide h, a potent cytotoxic macrolide, covalently binds on actin subdomain 4 and stabilizes actin filament

The actin-targeting toxins have not only proven to be invaluable tools in studies of actin cytoskeleton structure and function but they also served as a foundation for a new class of anticancer drugs. Here, we describe that amphidinolide H (AmpH) targets actin cytoskeleton. AmpH induced multinucleated cells by disrupting actin organization in the cells, and the hyperpolymerization of purified actin into filaments of apparently normal morphology in vitro. AmpH covalently binds on actin, and the AmpH binding site is determined as Tyr200 of actin subdomain 4 by mass spectrometry and halo assay using the yeast harboring site-directed mutagenized actins. Time-lapse analyses showed that AmpH stimulated the formation of small actin-patches, followed by F-actin rearrangement into aggregates via the retraction of actin fibers. These results indicate that AmpH is a novel actin inhibitor that covalently binds on actin.

Inhibition of vessel permeability by TNP-470 and its polymer conjugate, caplostatin

Angiogenesis inhibitors, such as TNP-470 and the nontoxic HPMA copolymer-TNP-470 (caplostatin), are emerging as a class of anticancer drugs. We report that TNP-470 and caplostatin inhibit vascular hyperpermeability of tumor blood vessels as well as that induced in mouse skin by different mediators. Treatment with TNP-470 or angiostatin for 3 days was sufficient to reduce permeability of tumor blood vessels, delayed-type hypersensitivity, and pulmonary edema induced by IL-2. TNP-470 also inhibited VPF/VEGF-induced phosphorylation of VEGFR-2, calcium influx, and RhoA activation in endothelial cells. These results identify an activity of TNP-470, that of inhibiting vessel hyperpermeability. This activity likely contributes to TNP-470's antiangiogenic effect and suggests that caplostatin can be used in the treatment of cancer and inflammation.

Novel inhibitors targeted to methionine aminopeptidase 2 (MetAP2) strongly inhibit the growth of cancers in xenografted nude model

Inhibition of angiogenesis is emerging as a promising strategy for the treatment of cancer. In our study reported here, the effects of 4 highly potent methionine aminopeptidase 2 (MetAP2) inhibitors, IDR-803, IDR-804, IDR-805 and CKD-732 (designed by structure-based molecular modeling), on angiogenesis and tumor growth were assessed. Concentrations of these inhibitors as low as 2.5 nM were able to inhibit the growth of human umbilical vein endothelial cells (HUVEC) by as much as 50%, arresting growth in the G1 stage of mitosis. An intracellular accumulation of p21(WAF1/Cip1) protein was also observed. Furthermore, at higher concentrations (25 nM) of these 4 MetAP2 inhibitors, a significant induction of apoptosis was apparent in the same HUVEC cultures. As a result of these findings, the possible anticancer effects of these inhibitors were examined, utilizing the SNU-398 hepatoma cell line. Interestingly, pretreatment with these inhibitors led to an increased number of apoptotic cells of up to 60% or more, compared to untreated controls. Moreover, utilizing an in vivo xenografted murine model, these inhibitors suppressed the growth of engrafted tumor. In conclusion, these 4 inhibitory compounds potently exert an antiangiogenic effect to inhibit the growth of cancers in vivo and could potentially be useful for the treatment of a variety of cancers.

Yeast as a model system for anticancer drug discovery

Saccharomyces cerevisiae has been used extensively as a model for higher eukaryotes in the study of basic cellular processes. The high degree of conservation in terms of sequence similarity and function has made this organism useful in elucidating biological pathways, both yeast and human. Among these are pathways responsible for DNA damage repair and cell cycle control. This review presents an overview of opportunities for using yeast as a model system for anticancer drug discovery. It covers screens directed against specific cancer-related targets as well as contexts created by cancer-related alterations. The methodologies covered include pharmacological and genetic screens, as well as genome-wide approaches to drug target identification.

Peptide deformylase: a target for novel antibiotics?

Peptide deformylase (PDF) catalyses the hydrolytic removal of the N-terminal formyl group from nascent ribosome-synthesised polypeptides. Its activity is essential and it is present in all eubacteria. It is also present in the organelles of some eukaryotes. PDF represents a novel class of mononuclear iron protein, utilising an Fe(2+) ion to catalyse the hydrolysis of an amide bond. Due to its extreme lability, isolation and characterisation of PDF was not possible until very recently. This review will discuss the recent progress in the elucidation of the the structure and function of PDF, evaluating its suitability as a target for antibiotic design and summarising the current approaches to designing drugs that target PDF.

Anti-angiogenic therapies in cancer clinical trials

Strategies involving vasculature have widely been acknowledged to have therapeutic potential in the management of cancer and other diseases. Based on a large body of evidence from preclinical studies and early clinical trials there is considerable optimism that anti-angiogenesis and vascular targeting will be a major clinical therapy. This review considers some 30 anti-angiogenic and vascular targeting agents that are currently in cancer clinical trials and highlights specific problems relating to the assessment of the activity of these agents in patients, trial design, potential toxicities and resistance mechanisms.

Enantioselective Approaches to Potential MetAP-2 Reversible Inhibitors

[reaction: see text] Enantioselective deprotonation of 4-substituted cyclohexanones and highly stereoselective conjugate addition of higher order mixed cuprates were the key steps in a concise synthesis of fumagalone-related molecules. The origin of the (low) biological activity of the new compounds as compared to fumagalone is briefly discussed.

A stereoselective asymmetric synthesis of antibiotic (-)-Fumagillol using claisen rearrangement and intramolecular ester enolate alkylation as key steps

(-)-Fumagillol (1), a hydrolysis product of fumagillin, has been synthesized by several group from commercially available 1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose in a highly stereoselective manner. Chiral centers on C5 and C6 came from D-allofuranose and the asymmetric center on C4 was accomplished by 1,3-chirality transfer using the Claisen rearrangement on a chiral allyl alcohol. Chirality, which is necessary on an epoxide consisting of the spiro-ring system, was diastereoselectively constructed by the well-known reaction, intramolecular ester enolate alkylation (IEEA), which showed that this reaction can be applied to the alpha-alkoxy ester system. The epoxide on the side chain was regioselectively introduced by the difference between the number of substituents on the vinyl groups. This accomplishment proved that IEEA can be a useful tool for the synthesis of complex molecules.

Functional and developmental impact of cytosolic protein N-terminal methionine excision in Arabidopsis

Protein N-terminal methionine (Met) excision (NME) is carried out by two types of Met aminopeptidases (MAPs), MAP1 and MAP2, in eukaryotes. Three enzymes, MAP1A, MAP2A, and MAP2B, have been identified in the cytoplasm of Arabidopsis (Arabidopsis thaliana). MAP transcript quantification revealed a predominance of MAP2B and developmental and organ-specific regulation of both MAP1A and MAP2s. By combining reverse genetics and reverse chemogenomics in transgenic plant lines, we have devised specific and reversible switches for the investigation of the role of cytoplasmic NME in Arabidopsis and of the respective contributions of the two types of cytoplasmic MAPs throughout development. dsRNA interference and knockout (KO) plant lines targeting either MAP1A alone or both MAP2s simultaneously were constructed and shown to display wild-type phenotypes. In the MAP1A KO context, modulating MAP2 activity by treatment with various concentrations of the specific drug fumagillin impaired plant development, with particularly strong effects on the root system. Reciprocally, complete MAP2 inhibition in various MAP1A knocked-down genetic backgrounds also generated a gradient of developmentally abnormal plants, but the effects on the root system were milder than in the KO context. In the absence of MAP2 activity, the severity of the phenotype in the MAP1A knocked-down lines was correlated to the extent of MAP1A mRNA accumulation. Complete cytoplasmic NME inactivation blocked development after plant germination. Thus, in plants, (1) cytoplasmic NME is essential; (2) MAP1A and MAP2s are functionally interchangeable, which is not the case in fungi and animals, as a complete block of either MAP-type activity does not cause any visible molecular or phenotypic effect; and (3) a minimal level of cytoplasmic MAP is required for normal development.

Methionine aminopeptidases type I and type II are essential to control cell proliferation

The dependence of cell growth on methionine aminopeptidase (MetAP) function in bacteria and yeast is firmly established. Here we report experimental evidence that the control of cell proliferation in mammalian cells is directly linked and strictly dependent on the activity of both MetAP-1 and MetAP-2. The targeted downregulation of either methionine aminopeptidase MetAP-1 or MetAP-2 protein expression by small interfering RNA (siRNA) significantly inhibited the proliferation of human umbilical vein endothelial cells (HUVEC) (70%-80%), while A549 human lung carcinoma cell proliferation was less inhibited (20%-30%). The cellular levels of MetAP-2 enzyme were measured after MetAP-2 siRNA treatment and found to decrease over time from 4 to 96 h, while rapid and complete depletion of MetAP-2 enzyme activity was observed after 4 h treatment with two pharmacological inhibitors of MetAP-2, PPI-2458 and fumagillin. When HUVEC and A549 cells were treated simultaneously with MetAP-2 siRNA and PPI-2458, or fumagillin, which irreversibly inhibit MetAP-2 enzyme activity, no additive effect on maximum growth inhibition was observed. This strongly suggests that MetAP-2 is the single critical cellular enzyme affected by either MetAP-2 targeting approach. Most strikingly, despite their significantly different sensitivity to growth inhibition after targeting of either MetAP-1 or MetAP-2, HUVEC, and A549 cells, which were made functionally deficient in both MetAP-1 and MetAP-2 were completely or almost completely inhibited in their growth, respectively. This closely resembled the observed growth inhibition in genetically double-deficient map1map2 yeast strains. These results suggest that MetAP-1 and MetAP-2 have essential functions in the control of mammalian cell proliferation and that MetAP-dependent growth control is evolutionarily highly conserved.

Chimeric molecules to target proteins for ubiquitination and degradation

Protein degradation is one of the tactics used by the cell for irreversibly inactivating proteins. In eukaryotes, ATP-dependent protein degradation in the cytoplasm and nucleus is carried out by the 26S proteasome. Most proteins are targeted to the 26S proteasome by covalent attachment of a multiubiquitin chain. A key component of the enzyme cascade that results in attachment of the multiubiquitin chain to the target or labile protein is the ubiquitin ligase that controls the specificity of the ubiquitination reaction. Defects in ubiquitin-dependent proteolysis have been shown to result in a variety of human diseases, including cancer, neurodegenerative diseases, and metabolic disorders. The SCF (Skp1-Cullin-F-box-Hrt1) complex is a heteromeric ubiquitin ligase that multiubiquitinates proteins important for signal transduction and cell cycle progression. A technology was developed known as Protac (Proteolysis Targeting Chimeric Molecule) that acts as a bridge, bringing together the SCF ubiquitin ligase with a protein target, resulting in its ubiquitination and degradation. The Protac contains an SCF-binding peptide moiety at one end that is recognized by SCF that is chemically linked to the binding partner or ligand of the target protein. The first demonstration of the efficacy of Protac technology was the successful recruitment, ubiquitination, and degradation of the protein methionine aminopeptidase-2 (MetAP-2) through a covalent interaction between MetAP-2 and Protac. Subsequently, we demonstrated that Protacs could effectively ubiquitinate and degrade cancer-promoting proteins (estrogen and androgen receptors) through noncovalent interactions in vitro and in cells. Finally, cell-permeable Protacs can also promote the degradation of proteins in cells. This chapter includes experiments to test the ability of Protacs to target proteins in vitro and in cells.

Synthesis and biological evaluation of novel fumagillin and ovalicin analogues

A promising approach among the numerous efforts to cure cancer is the interruption of the tumour-induced formation of new blood vessels (angiogenesis). By suppressing angiogenesis with drugs, the tumour can neither grow to a life threatening size, nor metastasize. The natural product fumagillin 1 and the structurally related ovalicin 2 are two of the most potent anti-angiogenic compounds. Here, we report the design and synthesis of novel fumagillin and ovalicin analogues lacking reactive epoxy functionalities, which were thought to be responsible for the severe toxic side-effects observed. We also report a new synthetic approach and the determination of the anti-angiogenic properties of these compounds in endothelial cells.

Metalloform-selective inhibitors of escherichia coli methionine aminopeptidase and X-ray structure of a Mn(II)-form enzyme complexed with an inhibitor

Methionine aminopeptidase (MetAP) enzymes require a divalent metal ion such as Mn(II), Fe(II), Co(II), Ni(II), or Zn(II) for its removal of the N-terminal methionine from newly synthesized proteins, but it is not certain which of these ions is most important in vivo. Metalloform-selective MetAP inhibitors could be valuable for defining which metals are physiologically relevant for MetAP activation and could serve as leads for development of new therapeutic agents. We have screened a library of 43 736 small drug-like molecules against Escherichia coli MetAP and identified two groups of potent and highly metalloform-selective inhibitors of the Co(II)-form, and of the Mn(II)-form, of this enzyme. Compound 1 is 790-fold more selective for the Co(II)-form, while compound 4 is over 640-fold more potent toward the Mn(II)-form. The X-ray structure of a di-Mn(II) form of E. coli MetAP complexed with the Mn(II)-form-selective compound 4 was obtained, and it shows that the inhibitor interacts with both Mn(II) ions through the two oxygen atoms of its free carboxylate group. The preferential coordination of the hard (oxygen) donors to Mn(II) may contribute to its superb selectivity toward the Mn(II)-form.

High expression of methionine aminopeptidase 2 in human colorectal adenocarcinomas

PURPOSE

Several viral and eukaryotic proteins required for signal transduction and regulatory functions undergo lipophilic modification by the enzyme N-myristoyltransferase. Previously we reported that N-myristoyltransferase activity is higher in colon and gallbladder carcinoma than in the corresponding normal tissues. Methionine aminopeptidase 2 (MetAP2) is a bifunctional protein that plays a critical role in the regulation of post-translational processing and protein synthesis. To investigate whether MetAP2 contributes to the pathogenesis of colon carcinoma, we investigated the expression of MetAP2 in both normal and invasive tumor components of human samples.

EXPERIMENTAL DESIGN

We evaluated 50 cases of colon carcinoma for this study. In this report we analyzed 15 cases for MetAP2 activity and 13 cases for the expression of MetAP2 by Western blot in both the normal and in invasive tumor components of human samples. In addition, immunohistochemistry analysis was also carried out on samples from all patients.

RESULTS

MetAP activity was elevated in all cancerous tissues compared with normal tissues. Western blot analysis also showed the higher expression of MetAP2 in all cases of cancerous tissues. In addition, immunohistochemistry analysis revealed that all cases of colorectal adenocarcinoma showed moderate to strong cytoplasmic positivity for MetAP2 with increased intensity in the invasive component.

CONCLUSIONS

Elevated MetAP protein expression is associated with metastatic tumor progression and appears to be a strong molecular marker for clinical prognosis. MetAP2 inhibition may represent a potential target for therapeutic intervention in colorectal carcinoma.

Characterization of the active site and insight into the binding mode of the anti-angiogenesis agent fumagillin to the manganese(II)-loaded methionyl aminopeptidase from Escherichia coli

EPR spectra were recorded for methionine aminopeptidase from Escherichia coli (EcMetAP-I) samples (approximately 2.5 mM) to which one and two equivalents of Mn(II) were added (the latter is referred to as [MnMn(EcMetAP-I)]). The spectra for each sample were indistinguishable except that the spectrum of [MnMn(EcMetAP-I)] was twice as intense. The EPR spectrum of [MnMn(EcMetAP-I)] exhibited the characteristic six-line g approximately 2 EPR signal of mononuclear Mn(II) with A(av)((55)Mn)=9.3 mT (93 G) and exhibited Curie-law temperature dependence. This signal is typical of Mn(II) in a ligand sphere comprising oxygen and/or nitrogen atoms. Other features in the spectrum were observed only as the temperature was raised from that of liquid helium. The temperature dependences of these features are consistent with their assignment to excited state transitions in the S=1, 2 ... 5 non-Kramer's doublets, due to two antiferromagnetically coupled Mn(II) ions with an S=0 ground state. This assignment is supported by the observation of a characteristic 4.5 mT hyperfine pattern, and by the presence of signals in the parallel mode consistent with a non-Kramers' spin ladder. Upon the addition of the anti-angiogenesis agent fumagillin to [MnMn(EcMetAP-I)], very small changes were observed in the EPR spectrum. MALDI-TOF mass spectrometry indicated that fumagillin was, however, covalently coordinated to EcMetAP-I. Therefore, the inhibitory action of this anti-angiogenesis agent on EcMetAP-I appears to involve covalent binding to a polypeptide component at or near the active site rather than direct binding to the metal ions.

The C. elegans methionine aminopeptidase 2 analog map-2 is required for germ cell proliferation

We have investigated the physiological function of type 2 methionine aminopeptidases (MetAP2) using Caenorhabditis elegans as a model system. A homolog of human MetAP2 was found in the C. elegans genome, which we termed MAP-2. MAP-2 protein displayed methionine aminopeptidase activity and was sensitive to inhibition by fumagillin. Downregulation of map-2 expression by RNAi led to sterility, resulting from a defect in germ cell proliferation. These observations suggest that MAP-2 is essential for germ cell development in C. elegans and that this ubiquitous enzyme may play important roles in a tissue specific manner.

3-Amino-2-hydroxyamides and related compounds as inhibitors of methionine aminopeptidase-2

Substituted 3-amino-2-hydroxyamides and related hydroxyamides and acylhydrazines were identified as inhibitors of human methionine aminopeptidase-2 (MetAP2). Examination of substituents through parallel synthesis and iterative structure-based design allowed the identification of potent inhibitors with good selectivity against MetAP1. Diacylhydrazine 3t (A-357300) was identified as an analogue displaying inhibition of methionine processing and cellular proliferation in human microvascular endothelial cells (HMVEC).

Early genetic mechanisms underlying the inhibitory effects of endostatin and fumagillin on human endothelial cells

A tumor needs to initiate angiogenesis in order to develop its own blood supply, to grow, to invade, and to spread. Angiogenesis, under normal conditions, is a tightly regulated balance between endogenous pro- and antiangiogenic factors. In this study, we investigated, by microarray analysis, the effects of two known antiangiogenic agents (endostatin and fumagillin) on the gene expression profiles of human umbilical vein endothelial cells (HUVEC) in order to elucidate pathways common to the effects of these agents. We observed a majority of gene expression changes within 1 and 2 h of treatment. The genes demonstrating these early expression changes are involved in cell proliferation, gene transcription, and a number have unknown functions. We selected four genes (DOC1, KLF4, TC-1, ID1) from the microarray profile that showed a similar pattern of expression for both of the antiangiogenic agents we tested. We then used small interfering RNAs (siRNA) in an attempt to better understand the role of these selected genes in the inhibitory activity of these agents. Because the gene expression changes occurred within 1 and 2 h of treatment, these genes might be involved in the initial pathways of angiogenesis inhibition.

Degradation of target protein in living cells by small-molecule proteolysis inducer

Ubiquitin-dependent proteolysis of cellular proteins is one of the major pathways to regulate protein function posttranslationally. Here we demonstrate a potentially general method of degrading any targeted proteins by the ubiquitin-dependent proteolysis in living cells, using small-molecule proteolysis inducer (SMPI).

Magnetic Circular Dichroism and Cobalt(II) Binding Equilibrium Studies of Escherichia coli Methionyl Aminopeptidase

Equilibrium dialysis of methionyl aminopeptidase from Escherichia coli (EcMetAP) monitored by atomic absorption spectrometry and magnetic circular dichroism (MCD) shows that the enzyme binds up to 1.1 +/- 0.1 equiv of Co(2+) in the metal concentration range likely to be found in vivo. The dissociation constant, K(d), is estimated to be between 2.5 and 4.0 microM. Analysis of the temperature and magnetization behavior of the two major peaks in the MCD spectrum at 495 and 567 nm suggests that these transitions arise from Co(2+) with different ground states. Ligand field calculations using AOMX are used to assign the 495 nm peak to Co(2+) in the 6-coordinate binding site and the 567 nm peak to Co(2+) in the 5-coordinate site. This is further supported by the fact that the binding affinity of the Co(2+) associated with the 567 nm peak is enhanced when the pH is increased from 7.5 to 9.0, consistent with having an imidazole ligand from a histidine amino acid residue. On the basis of the MCD intensities, it is estimated that, when the 5-coordinate site is fully occupied, 0.1 equiv of cobalt is in the 6-coordinate site. Even when the cobalt concentration is very low, there is a small fraction of binuclear sites in EcMetAP formed through cooperative binding between the 5- and 6-coordinate Co(2+) ions. The magnetization behavior of the 6-coordinate Co(2+) MCD peak is consistent with an isolated pseudo-Kramer doublet ground state, suggesting that the cobalt ions in the binuclear sites are not magnetically coupled.

Expression of methionine aminopeptidase 2, N-myristoyltransferase, and N-myristoyltransferase inhibitor protein 71 in HT29

Protein myristoylation is a co-translational process, catalyzed by N-myristoyltransferase (NMT) that occurs after the initiating methionine is removed by methionine aminopeptidase (MetAP). The enzymes NMT and MetAP play a major role in the process of myristoylation of oncoproteins including the c-src family. In this study, we examined the levels of expression of MetAP2, NMT, and NMT inhibitor protein 71 (NIP71) in human colon cancer cell lines (HCCLs). We examined the influence of cell density on the expression of the above proteins in HT29 cells. Western blot analysis of MetAP2 and NMT demonstrated higher levels of protein expression in low density of HT29 while low expression in high density was observed. In addition, we observed that NIP71 and pp60(c-src) expressions were dependent on the cell density of HT29. This is the first study demonstrating the expression of MetAP2, NMT, pp60(c-src), and NIP71 in HCCLs.

Angiogenesis inhibitor TX-1898: syntheses of the enantiomers of sterically diverse haloacetylcarbamoyl-2-nitroimidazole hypoxic cell radiosensitizers

(R)- and (S)-Epichlorohydrins were used to prepare the enantiomers of sterically diverse haloacetylcarbamoyl-2-nitroimidazoles that function as hypoxic cell radiosensitizers. The synthetic design allowed for introduction of a side chain of varying bulk that permitted an examination of the steric effects on enantio-discrimination in biological assay systems. The single stereocenter also connected the two pharmacophores--a 2-nitroimidazole moiety critical to hypoxic cell radiosensitization, and a haloacetylcarbamoyl group to function as an anti-angiogenesis pharmacophore. In the chick embryo chorioallantoic membrane (CAM) assay, the R-enantiomers possessing the bulky p-tert-butylphenyl group showed higher anti-angiogenic activity than the corresponding S-enantiomers, while there were no differences in the activity between the enantiomers containing the less bulky methyl and tert-butyl groups. Among the compounds we report, R-p-tert-butylphenyl-bromoacetylcarbamoyl-2-nitroimidazole, TX-1898, was found to be the most promising candidate for further development of as anti-angiogenic hypoxic cell radiosensitizer.

Design, synthesis and evaluation of a series of novel fumagillin analogues

A series of fumagillin analogues targeted at understanding tolerability of MetAP2 toward substitution at C4 and C6 were synthesized. Initially, the C6 side chain was maintained as cinnamoyl ester and C4 was modified. It was concluded that replacing the natural C4 of fumagillin with a benzyl oxime at C4 resulted in moderate loss of activity toward binding to MetAP2. Placement of a primary or secondary carbamate at C6 did not improve the potency of compounds toward inhibition of MetAP2. However, the inhibitory activity against MetAP2 was gained back by placing polar groups such as piperazinyl carbamate at C6. Small alkyl substituents on the amine of piperazinyl carbamate were well tolerated.

A methionine aminopeptidase-2 inhibitor, PPI-2458, for the treatment of rheumatoid arthritis

The hallmark of rheumatoid arthritis (RA) is the progressive destruction of articular joints, characterized by invasive synovial hyperplasia and pathological neovascularization. Here we report that PPI-2458, a member of the fumagillin class of irreversible methionine aminopeptidase-2 (MetAP-2) inhibitors, potently inhibits the proliferation of human fibroblast-like synoviocytes (HFLS-RA), derived from RA patients, with a growth inhibitory concentration 50 (GI(50)) of 0.04 nM and a maximum inhibition of >95% at 1 nM. Human umbilical vein endothelial cells (HUVEC) are similarly inhibited in proliferation by PPI-2458 (GI(50), 0.2 nM). We developed a method to measure the level of MetAP-2 enzyme inhibition after exposure to PPI-2458 and demonstrate that growth inhibition of PPI-2458-sensitive HFLS-RA and HUVEC is linked to MetAP-2 enzyme inhibition, in a dose-dependent fashion. The secretion of several inflammatory mediators such as IL-6 and vascular endothelial growth factor from activated HFLS-RA was not inhibited by PPI-2458. The CNS toxicity profile of PPI-2458, determined by the incidence of seizures, is significantly improved over that of the parental compound TNP-470. In the rat model of peptidoglycan-polysaccharide-induced arthritis, PPI-2458 significantly attenuated paw swelling when therapeutically administered after the onset of chronic disease. We suggest that the mechanism of PPI-2458 action, highly selective and potent anti-proliferative activity on HFLS-RA and HUVEC in vitro, a significantly improved CNS toxicity profile, and marked attenuation of chronic disease in the rat peptidoglycan-polysaccharide arthritis model in vivo, positions this compound as a drug for the treatment of RA.

Eukaryotic initiation factor 2-associated glycoprotein, p67, shows differential effects on the activity of certain kinases during serum-starved conditions

Phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 is the major regulatory step in the initiation of protein synthesis in mammals. P67, a cellular glycoprotein, protects phosphorylation of eIF2alpha from kinases. P67 has five conserved amino acid residues at the D251, D262, H331, E364, and E459 positions. To determine the roles of these conserved amino acid residues in eIF2alpha phosphorylation during serum-starved conditions, we constitutively expressed D251A, D262A, H331A, E364A, and E459A mutants in rat tumor hepatoma cells. We find that the point mutants D251A, H331A, and E364A lower the levels of eIF2alpha phosphorylation. These low levels of phosphorylation decrease when serum-starved cells are grown in medium containing serum. To understand the mechanism of action of the p67 mutants in eIF2alpha phosphorylation during serum-starvation, we performed detailed biochemical analyses with the D251A mutant. We find that neither the O-GlcNAc modification on the D251A mutant nor the binding of D251A mutant with eIF2gamma has significant effects on eIF2alpha phosphorylation during serum-starved conditions. However, the D251A mutant inhibits p67's activity to suppress the activity of ERK1/2. Our data suggest that both p67 and the D251A mutant bind to ERK1, thus strengthening the idea that p67 regulates the activity of ERK1. During serum-starvation conditions, both PKR and PERK are phosphorylated and the D251A mutant shows increased stability of PERK as well as a slight decrease in its activity. Altogether, our data provide evidence to suggest that p67 modulates the expression and activity of certain eIF2alpha-specific kinases.

Depletion of methionine aminopeptidase 2 does not alter cell response to fumagillin or bengamides

Inhibition of endothelial cell growth by fumagillin has been assumed to be mediated by inhibition of the molecular target methionine aminopeptidase 2 (MetAp2). New data show that depletion of MetAp2 by siRNA does not inhibit endothelial cell growth. Moreover, MetAp2-depleted endothelial cells remain responsive to inhibition by either fumagillin or a newly identified MetAp2 enzyme inhibitor. These data suggest that MetAp2 function is not required for endothelial cell proliferation.

Intractable wounds and infections: the role of impaired vascularity and advanced surgical methods for treatment

Fracture nonunion, delayed union, and osteomyelitis remain serious problems with substantial morbidity and mortality rates. Healing promoters, including bone morphogenic proteins, fibroblast growth factors, and transforming growth factor-beta, regulate bone growth in experimental models, such as those employing a "critical gap" to establish nonunion, but have not been effective in clinical situations. This paradox may relate to the fact that such agents target cells, yet in the setting of a clinical nonunion or osteomyelitis, the affected area is frequently hypovascular and therefore deficient in target precursor cells. Wound healing is dependent on local tissue vascularity. Surgical procedures, such as local and remote tissue transfer, which are designed to modify this cell-deficient, poorly vascularized environment, have proved very successful but are often complex and costly. No simple pharmacologic means of upregulating such angiogenesis currently exists.

Design and synthesis of chromogenic thiopeptolide substrates as MetAPs active site probes

Twenty one chromogenic thiopeptolide substrates were designed and synthesized as the active site probes and analyzed with each S1 site of mutant residues and enzymes of wild-type MetAP1s. The preliminary enzymatic experiments indicate that cysteine 70 or 202, at either Escherichia coli or human MetAP1, played a crucial role in the methionine hydrolysis.

Study of puupehenone and related compounds as inhibitors of angiogenesis

Puupehenone, a sesquiterpene produced by certain sponges, was selected in the course of a blind screening for new potential inhibitors of angiogenesis. In our study, we compare the potential anti-angiogenic activities of puupehenone and another 11 related compounds that were either natural products from marine origin or their synthetic derivatives. The effects of these compounds were determined with cell growth and differentiation assays on bovine aorta endothelial cells. Our results show that these compounds are weak inhibitors to cell growth and are not selective for endothelial cells. However, contrary to cell growth, the differentiation of endothelial cells into tubular structures was completely inhibited by 7 of these compounds at concentrations equal or lower than 3 microM. Three of these compounds, isozonarol, 8-epipuupehedione and 8 epi-9,11-dihydropuupehedione, completely inhibited the in vivo angiogenesis in the CAM assay at doses equal or lower than 30 nmol/egg. Further characterisation showed that these 3 terpenes also inhibited endothelial cell production of urokinase and invasion. One compound (8-epipuupehedione) inhibited endothelial cell migration in a dose-dependent manner. The anti-angiogenic properties of the selected compounds, the simplicity of their structures and the feasibility of their synthesis make them attractive drugs for further evaluation in the treatment of angiogenesis-related pathologies.

Psammaplin A, a marine natural product, inhibits aminopeptidase N and suppresses angiogenesis in vitro

Psammaplin A (PsA) is a phenolic natural product isolated from a marine sponge, which showed a potent cytotoxicity against several cancer cell lines. In present study, PsA was found to inhibit mammalian aminopeptidase N (APN) that plays a key role in tumor cell invasion and angiogenesis. PsA inhibited the APN activity with an IC50 of 18 microM in a non-competitive manner. Moreover, PsA potently inhibited the proliferation of several cancer and endothelial cells. Interestingly, the anti-proliferative effect of PsA was dependent on the cellular amount of APN expression. Finally, PsA suppressed the invasion and tube formation of endothelial cells stimulated by basic fibroblast growth factor. These data demonstrate that PsA is a new inhibitor of APN and can be developed as a novel anti-angiogenic agent.

TNP-470 promotes initial vascular sprouting in xenograft tumors

TNP-470 (AGM-1470), an analogue of fumagillin, was one of the first molecules proposed to have antiangiogenic properties. This concept was based on its ability to inhibit both endothelial proliferation in vitro and tumor growth in vivo in a number of xenograft models. Yet, subsequent investigations indicated that the biochemical activities associated with TNP-470 are not selective for endothelial cells. Moreover, recent evidence suggests that this agent inhibits tumor growth in vivo, but without a corresponding decrease in angiogenesis. Therefore, we performed a detailed comparison of TNP-470 to a validated antiangiogenic agent, a VEGF inhibitor termed VEGF-Trap, using a xenograft model of Wilms tumor. Treatment with TNP-470 for 5 weeks significantly suppressed xenograft growth (83%). Surprisingly, this inhibition was not associated with a decrease in angiogenesis, but instead with an increase in tiny neovessels. To determine whether this was a direct effect of TNP-470 on tumor vessels, we examined its effect in a short-term assay using large tumors with established vasculature. In contrast to treatment with VEGF-Trap, which led to rapid vessel regression and tumor hypoxia, tumors exposed to TNP-470 for 1 day displayed increased capillary sprouting, with significantly increased microvessel density, vessel length, and branch points. TNP-470 did not induce tumor hypoxia as demonstrated by minimal pimonidazole staining and VEGF expression. TNP-470 did, however, cause a marked increase in apoptosis of tumor cells. Our results indicate that the antitumor effects of TNP-470 cannot be attributed to prevention of neoangiogenesis, but instead to its direct action on tumor cells.

Targeting angiogenesis with a conjugate of HPMA copolymer and TNP-470

Angiogenesis is crucial for tumor growth. Angiogenesis inhibitors, such as O-(chloracetyl-carbamoyl) fumagillol (TNP-470), are thus emerging as a new class of anticancer drugs. In clinical trials, TNP-470 slowed tumor growth in patients with metastatic cancer. However, at higher doses necessary for tumor regression, many patients experienced neurotoxicity. We therefore synthesized and characterized a water-soluble conjugate of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer, Gly-Phe-Leu-Gly linker and TNP-470. This conjugate accumulated selectively in tumor vessels because of the enhanced permeability and retention (EPR) effect. HPMA copolymer-TNP-470 substantially enhanced and prolonged the activity of TNP-470 in vivo in tumor and hepatectomy models. Polymer conjugation prevented TNP-470 from crossing the blood-brain barrier (BBB) and decreased its accumulation in normal organs, thereby avoiding drug-related toxicities. Treatment with TNP-470 caused weight loss and neurotoxic effects in mice, whereas treatment with the conjugate did not. This new approach for targeting angiogenesis inhibitors specifically to the tumor vasculature may provide a new strategy for the rational design of cancer therapies.

A novel technique for quantifying changes in vascular density, endothelial cell proliferation and protein expression in response to modulators of angiogenesis using the chick chorioallantoic membrane (CAM) assay

Reliable quantitative evaluation of molecular pathways is critical for both drug discovery and treatment monitoring. We have modified the CAM assay to quantitatively measure vascular density, endothelial proliferation, and changes in protein expression in response to anti-angiogenic and pro-angiogenic agents. This improved CAM assay can correlate changes in vascular density with changes seen on a molecular level. We expect that these described modifications will result in a single in vivo assay system, which will improve the ability to investigate molecular mechanisms underlying the angiogenic response.

Role of Aminopeptidase in Angiogenesis

Microvessels are composed of endothelial cells and surrounding pericytes. Angiogenesis, a neo-vessel formation from pre-existing microvessels, is a complex phenomenon, which requires following sequential steps: detachment of pre-existing pericytes for vascular destabilization, extracellular matrix turnover, migration, proliferation, tube formation by endothelial cells (ECs), and reattachment of pericytes for vascular stabilization. Aminopeptidases regulate the N-terminal modification of proteins and peptides for maturation, activation or degradation, and thereby relate to a variety of biological processes. Recently, three aminopeptidases have been reported to be involved in angiogenesis. They include type 2 methionine aminopeptidase, aminopeptidase N, and adipocyte-derived leucine aminopeptidase/puromycin insensitive leucyl-specific aminopeptidase. This review will focus on the possible role of these aminopeptidases in angiogenesis.

Peptidyl hydroxamic acids as methionine aminopeptidase inhibitors

A new class of methionine aminopeptidase (MetAP) inhibitors, which contain an internal hydroxamate (N-acyl-N-alkylhydroxylamine) core as the metal-chelating group, has been designed, synthesized, and tested. The compounds exhibited reversible, competitive inhibition against Escherichia coli MetAP as well as human MetAP-1 and MetAP-2. The most potent inhibitor had a K(i) value of 2.5 microM and >20-fold selectivity toward E. coli MAP.

Investigation of novel fumagillin analogues as angiogenesis inhibitors

Modification of fumagillin was conducted to develop MetAP-2 inhibitors with desirable pharmacological properties. Replacement of the C4 side chain by benzyloxime preserves the inhibitory activity against MetAP-2 enzyme. Fumagillin analogues containing the C4 benzyloxime moiety were found to be very sensitive to the nature of the C6 substituent on the inhibition activity of HUVEC proliferation. This lack of correlation between MetAP-2 and HUVEC activities might be due to the cellular metabolism of the compounds by epoxide hydrolase, which is present in the cell. Compound (E)-3d, containing ethylpiperazinyl carbamate at C6 position, exhibited antiangiogenic effects similar to TNP-470 on matrigel plug assay and rat corneal micropocket assay.

A single amino acid residue defines the difference in ovalicin sensitivity between type I and II methionine aminopeptidases

TNP-470, the first anti-angiogenic small molecule to enter clinical trials, targets methionine aminopeptidase-2 (MetAP-2), a metalloprotease that cleaves the N-terminal methionine of proteins. Previously, biochemical binding, in vivo yeast studies, and structural studies of human methionine aminopeptidase-2 bound to TNP-470 and its analogs fumagillin and ovalicin revealed that these compounds exhibit specificity for MetAP-2 over its family member MetAP-1. To further elucidate the nature of this specificity, we developed a yeast-based screen for human MetAP-2 mutations that confer ovalicin resistance. Of the three resistant alleles, A362T appeared in the majority of clones and was found to be the most resistant to the ovalicin class of inhibitors. Alignment of human MetAP-2 with human MetAP-1, which is naturally ovalicin-resistant, revealed that the analogous residue in MetAP-1 is also a threonine. Mutation of this residue to alanine resulted in an ovalicin-sensitive MetAP-1 allele, demonstrating that an alanine at this position is critical for inhibition by ovalicin. These results provide a molecular explanation for the specificity exhibited by this class of anti-angiogenic agents for MetAP-2 over MetAP-1 and may prove useful in the development of additional MetAP-2-specific therapeutic agents.

Proteomics-based Target Identification

LAF389 is a synthetic analogue of bengamides, a class of marine natural products that produce inhibitory effects on tumor growth in vitro and in vivo. A proteomics-based approach has been used to identify signaling pathways affected by bengamides. LAF389 treatment of cells resulted in altered mobility of a subset of proteins on two-dimensional gel electrophoresis. Detailed analysis of one of the proteins, 14-3-3gamma, showed that bengamide treatment resulted in retention of the amino-terminal methionine, suggesting that bengamides directly or indirectly inhibited methionine aminopeptidases (MetAps). Both known MetAps are inhibited by LAF389. Short interfering RNA suppression of MetAp2 also altered amino-terminal processing of 14-3-3gamma. A high resolution structure of human MetAp2 co-crystallized with a bengamide shows that the compound binds in a manner that mimics peptide substrates. Additionally, the structure reveals that three key hydroxyl groups on the inhibitor coordinate the di-cobalt center in the enzyme active site.

Protonation States of Methionine Aminopeptidase and Their Relevance for Inhibitor Binding and Catalytic Activity

We have performed a computational study of different protomeric states of the methionine aminopeptidase active site using a combined quantum-mechanical/molecular mechanical simulation approach. The aim of this study was to clarify the native protonation state of the enzyme, which is needed for the development of novel irreversible inhibitors that can possibly be used as antiangiogenic and antibiotic drugs by virtual screening and other drug design methods. The results of the simulations indicated that two protonation states are possible without disturbing the overall geometry of the active site. We then verified experimentally the presence of the two protonation states by studying the substrate hydrolysis and inhibitor binding reactions at different pH values and come to the conclusion that one of the protomeric states is relevant for inhibitor binding, whereas the other is relevant for substrate hydrolysis. This result has implications for the development of other inhibitors of this class of enzymes and adds a new perspective to the pharmacological properties of the antiangiogenic drug fumagillin, which is an irreversible inhibitor of the human methionine aminopeptidase type II.

The 1.15A crystal structure of the Staphylococcus aureus methionyl-aminopeptidase and complexes with triazole based inhibitors

Methionyl aminopeptidases (MetAPs) represent a unique class of protease that are responsible for removing the N-terminal methionine residue from proteins and peptides. There are two major classes of MetAPs (type I and type II) described and each class can be subdivided into two subclasses. Eukaryotes contain both the type I and type II MetAPs, whereas prokaryotes possess only the type I enzyme. Due to the physiological importance of these enzymes there is considerable interest in inhibitors to be used as antiangiogenic and antimicrobial agents. Here, we describe the 1.15A crystal structure of the Staphylococcus aureus MetAP-I as an apo-enzyme and its complexes with various 1,2,4-triazole-based derivatives at high-resolution. The protein has a typical "pita-bread" fold as observed for the other MetAP structures. The inhibitors bind in the active site with the N1 and N2 atoms of the triazole moiety complexing two divalent ions. The 1,2,4-triazols represent a novel class of potent non-peptidic inhibitors for the MetAP-Is.