Comparing hydrazine-derived reactive groups as

Journal of Enzyme Inhibition and Medicinal Chemistry

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Comparing hydrazine-derived reactive groups as inhibitors of quinone-dependent amine oxidases Ashley A. Burke, Elizabeth S. Severson, Shreya Mool, Maria J. Solares Bucaro, Frederick T. Greenaway & Charles E. Jakobsche To cite this article: Ashley A. Burke, Elizabeth S. Severson, Shreya Mool, Maria J. Solares Bucaro, Frederick T. Greenaway & Charles E. Jakobsche (2017) Comparing hydrazine-derived reactive groups as inhibitors of quinone-dependent amine oxidases, Journal of Enzyme Inhibition and Medicinal Chemistry, 32:1, 496-503, DOI: 10.1080/14756366.2016.1265518 To link to this article: http://dx.doi.org/10.1080/14756366.2016.1265518

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Published online: 23 Jan 2017.

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Date: 24 January 2017, At: 05:32

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY, 2017 VOL. 32, NO. 1, 496–503 http://dx.doi.org/10.1080/14756366.2016.1265518

ORIGINAL ARTICLE

Comparing hydrazine-derived reactive groups as inhibitors of quinone-dependent amine oxidases Ashley A. Burke, Elizabeth S. Severson, Shreya Mool, Maria J. Solares Bucaro, Frederick T. Greenaway and Charles E. Jakobsche Carlson School of Chemistry and Biochemistry, Clark University, Worcester, MA, USA

ABSTRACT

ARTICLE HISTORY

Lysyl oxidase has emerged as an important enzyme in cancer metastasis. Its activity has been reported to become upregulated in several types of cancer, and blocking its activity has been shown to limit the metastatic potential of various cancers. The small-molecules phenylhydrazine and b-aminopropionitrile are known to inhibit lysyl oxidase; however, issues of stability, toxicity, and poorly defined mechanisms limit their potential use in medical applications. The experiments presented herein evaluate three other families of hydrazine-derived compounds – hydrazides, alkyl hydrazines, and semicarbazides – as irreversible inhibitors of lysyl oxidase including determining the kinetic parameters and comparing the inhibition selectivities for lysyl oxidase against the topaquinone-containing diamine oxidase from lentil seedlings. The results suggest that the hydrazide group may be a useful core functionality that can be developed into potent and selective inhibitors of lysyl oxidase and eventually find application in cancer metastasis research.

Received 11 August 2016 Accepted 22 November 2016

Introduction Lysyl oxidase (LOX) is an enzyme whose activity is associated with multiple diseases including metastatic cancer, stiffening of connective tissue1, myocardial fibrosis1, chronic liver disease2, and hepatic fibrosis3. The correlation between high LOX activity and cancer metastasis is strong enough that upregulated LOX activity can be used as a diagnostic marker for the severity of cancer in patients. For example, higher LOX levels in human lung adenocarcinomas correlate with higher tumor invasiveness and lower 5-year patient survival rates4. Similarly, in human head and neck squamous cell carcinomas, higher levels of LOX correlate with later stage cancers, increased metastasis to the lymph node, and decreased overall patient survival5. In addition to LOX, there are four LOX-like enzymes (LOXL1–LOXL4) whose catalytic domains are highly conserved, but whose N-terminal domains enable unique biological functions6. LOXL2 also shows increased expression in a variety of cancers7. For many types of cancer, increased LOX activity promotes metastasis of cancer cells and progression of tumor growth. For example, El-Haibi et al. have shown that stimulating breast cancer cells to increase LOX synthesis activates those cells into a metastatic phenotype8. Cox et al. have shown that metastasis of cancer cells can be promoted by the secretion of enzymatically active LOX by neighboring fibroblast cells9. This effect is attributed to LOX's normal catalytic function, which promotes the crosslinking of collagen, modifies the extracellular matrix, and creates a microenvironment that is favorable for cell migration. Baker et al. have shown that treating colorectal cancer cells with LOX increases their propensity to metastasize and also to undergo angiogenesis CONTACT Charles E. Jakobsche [email protected] 01610, USA Supplemental data for this article can be accessed here.

KEYWORDS

Lysyl oxidase; hydrazine; enzyme kinetics; irreversible inhibition

after forming solid tumors10. The authors attribute these effects to upregulation of the angiogenesis-promoting VEGF pathway. Additional results indicate that LOX can increase cellular metastasis by activating focal adhesion kinase and Src kinase pathways and by increasing hydrogen peroxide levels11. By contrast, some gastric cancers suppress LOX activity12, which suggests that LOX's biology is quite complex. Blocking LOX's enzymatic function can reduce migration of cancer cells. Using siRNA to knock down LOX expression can significantly reduce the hypoxia-induced invasiveness of nonsmall-cell lung cancer cells13. Inhibiting LOX's catalytic activity in cervical cancer cells can reduce their invasion and migration and also block the epithelial–mesenchymal transition, which is associated with metastatic phenotypes14. Additionally, inhibiting LOX can decrease metastasis of human breast cancer-derived tumors in mice15. LOX performs its enzymatic function, converting primary amines into aldehydes, by using a quinone cofactor and a redoxactive copper ion. Specifically, the quinone cofactor is lysyl tyrosylquinone (LTQ) (Figure 1), which is structurally distinct from the topaquinone cofactor found in most other copper-containing amine oxidases. Our previous contributions to understanding the structural biology of LOX include identifying the histidine residues that serve as copper-binding ligands16 and identifying the cysteine pairs that form disulfide bridges to stabilize LOX's structure17. Although several crystal structures have been reported for various topaquinone-containing amine oxidases, some with covalentlybound hydrazine inhibitors18, very little is known about the structure of LOX and the nature of its active site. It has been hypothesized, however, that since LOX's natural substrates are

Carlson School of Chemistry & Biochemistry, Clark University, 950 Main Street, Worcester, MA

ß 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY

Figure 1. Overview of quinone-containing amine oxidase cofactors and inhibition by phenyl hydrazine. X ¼ OH for topaquinone; X ¼ lysine-eNH for lysyl tyrosylquinone.

proteins, the active site must be open and more like that of the Pichia pastoris amine oxidase19 rather than a narrow substrate channel like those typically found in topaquinone-containing amine oxidases. It has been well established that small-molecule aryl hydrazines, especially phenylhydrazine1, can act as irreversible inhibitors for LOX and most other quinone-containing amine oxidases20–23. Indeed, LOX's LTQ cofactor was originally identified by mass spectrometry and Edman degradation analysis of the adduct formed between LOX and 14C-phenylhydrazine24. The kinetics of inhibition of LOX by phenylhydrazine have been previously studied by Williamson et al., and these data show that the inhibition is competitive with substrate and irreversible25. Studies of a synthetic small-molecule model of LTQ have shown that the phenylhydrazine adduct preferentially tautomerizes into its azo form (Figure 1)26. Phenylhydrazine, however, is known to have low target specificity and to readily decompose under biological conditions, which limits its potential use for in vivo applications. Other types of hydrazine-containing organic molecules that are more stable than phenylhydrazine, such as alkyl hydrazines, hydrazides, and semicarbazides (Figure 2), have not been studied much as LOX inhibitors. Some of these structures have, however, been investigated as inhibitors of other copper-containing amine oxidases. The most established LOX inhibitor is b-aminopropionitrile (BAPN, 2, Figure 2). Although this molecule does covalently attach to the enzyme in a time-dependent manner, its kinetics do not follow those expected for direct irreversible inhibition27,28. Indeed, its mechanism of action, which is not yet fully understood, is thought to be by irreversible modification of an active-site residue by the aldehyde product28. BAPN treatment has also been reported to have some side effects, and it is not approved for clinical use29. We set out to evaluate the effectiveness and specificity of various organic hydrazine derivatives to help provide a basis for developing new selective irreversible inhibitors of LOX. These studies directly compare four families of organic hydrazine compounds as inhibitors of LOX and also of lentil seedling diamine oxidase (LSDAO), which was chosen as a representative topaquinonecontaining amine oxidase with a somewhat restrictive substrate-binding channel for comparison. Representative members of the

Figure 2. Inhibitor structures.

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alkyl hydrazine, hydrazide, and semicarbazide families (3–5) were synthesized and compared to phenylhydrazine, including analyses of their kinetic parameters for irreversible inhibition. These comparisons of inhibition parameters and selectivity provide a basis for deciding which of these “core” inhibitor structures are best suited as starting points for development of more complex molecules that could act as potent and selective inhibitors of LOX and also have favorable pharmacokinetic properties. Such inhibitors would be important not only as potential drug candidates, but also as chemical tools to study LOX-related biological mechanisms that are involved in cancer metathesis and other diseases.

Materials and methods LSDAO extraction The LSDAO extraction process was carried out at 4
C according to the method of Floris et al.30 with slight modifications. Eightday-old lentil seedlings (Lens esculenta) were blended and extracted with phosphate buffer (5 mM, pH 6.0, buffer A). Ammonium sulfate (230 g/L, 40% saturation) was used to precipitate contaminants, and then additional ammonium sulfate (125 g/ L, 60% saturation) was used to precipitate the LSDAO. The crude precipitate was redissolved, dialyzed against buffer A, applied to a DEAE column, and eluted with buffer A. Active fractions were adjusted to pH 6.5, applied to a CM resin column, and eluted with 5 mM phosphate buffer, pH 6.5. Active fractions were concentrated and the buffer was changed to 10 mM phosphate, pH 7.0 before the protein was applied to a Sephacryl S-300 column and eluted with the same buffer. The concentration of the LSDAO dimer was determined from its absorption at 278 nm in 0.1 M phosphate buffer31 using a molar extinction coefficient of 2.45  105 M1 cm1. The enzyme had very high activity (more than 1 lkat/mg protein). Analysis by a 7.5% SDS PAGE gel showed a single band. LOX extraction LOX was isolated from bovine aorta at 4
C using slight modifications of previously published procedures32. All steps were carried out at in 16 mM phosphate, pH 7.8 (buffer B). After blending the aorta in buffer B containing 400 mM NaCl and 1 mM EDTA to remove soluble contaminants, the enzyme was extracted with buffer B containing 4 M urea and 1 mM EDTA. The crude enzyme extract was filtered, diluted with an equal volume of buffer B to obtain a urea concentration of 2 M, and loaded onto a DEAE column. After washing with buffer B containing 400 mM NaCl, the enzyme was eluted with buffer B containing 400 mM NaCl and 6 M urea. The urea concentration was reduced to 4 M by adding buffer B, and the solution was added to a slurry of ceramic hydroxyapatite in buffer B containing 4 M urea. After stirring, the supernatant was removed by filtration and dialyzed overnight against buffer B. The solution was added to a slurry of ceramic hydroxyapatite in buffer B, washed with small portions of 1 M phosphate and then buffer B, and then eluted with buffer B containing 6 M urea and 500 mM NaCl. After concentration to about 20 mL, the protein was applied to a Sephacryl S-200 gel filtration column preequilibrated with buffer B containing 50 mM NaCl, 1 mM EDTA, and 6 M urea and eluted with the same buffer. Active fractions were concentrated to 1 mL. Total protein concentration for 6 M urea solutions33 was determined by its absorption at 280 nm using a molar extinction coefficient of 8.39  104 M1 cm 1. SDS-PAGE and mass spectrometric analysis indicated that the isolated LOX was mostly pure, but also included

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a small amount (5%) of a 22 kDa protein impurity that has been identified as tyrosine-rich acidic matrix protein, TRAMP, which is unreactive under the activity assay conditions34. The enzyme was stored as a concentrated solution at 4
C and was used immediately as it loses its activity very rapidly (complete loss within 10 days). Activity assay The activity assay is adopted from the method described by Palamakumbura et al.35. Enzyme and inhibitor were incubated at 37
C for the desired inhibition time, diluted into the assay mixture, and analyzed by fluorescence (Agilent Technologies Cary Eclipse Fluorescence Spectrometer, Cary Eclipse Software, 37
C, kex ¼ 568 and kem ¼ 581 nm). The assay was carried out in boric acid buffer (50 mM, pH 8.2) with 1.2 M urea for LOX or in phosphate buffer (0.1 M, pH ¼ 7.0) for LSDAO. The final reagent concentrations in the assay mixture were 10 mM cadaverine, 10 lM Amplex UltraRed (Life Technologies, Carlsbad, CA), and 1 U/mL horse radish peroxidase (Amresco, Solon, OH). The enzyme activity, which is proportional to the rate of increase in fluorescence, was measured for each experiment. Residual activity was calculated by dividing each rate by a maximum rate determined in the absence of inhibitor such that [residual activity] ¼ ([rate with inhibitor] – [baseline rate])/([maximum rate] – [baseline rate]). Baseline rates, which were typically