AMINOALKYLAZIRIDINES AS SUBSTRATES AND INHIBITORS OF LYSYL OXIDASE: SPECIFIC INACTIVATION OF THE ENZYME BY N-(5-AMINOPENTYL)AZIRIDINE

Narasimhan Nagan¹, Patrick S. Callery² and Herbert M. Kagan¹

1 Department of Biochemistry, Boston University School of Medicine, 80 East Concord Street, Boston, MA 02118, and the ² Department of Pharmaceutical Sciences, School of Pharmacy, West Virginia University, Morgantown, WV 26506

Received 4/2/98 Accepted4/6/98

2. INTRODUCTION

Lysyl oxidase is a copper-dependent amine oxidase which initiates the biosynthesis of lysine-derived crosslinkages by oxidizing peptidyl lysine residues to alpha-aminoadipic-delta-semialdehyde in elastin and collagen. This peptidyl aldehyde is the precursor of the variety of crosslinkages found in these proteins (1,2). In addition to copper, lysyl oxidase also contains a covalently bound carbonyl prosthetic group which is essential for catalytic function. This cofactor has recently been identified in rat lysyl oxidase as lysyl topaquinone (LTQ) deriving from tyrosine 349 and lysine 314 (3). The irreversible inactivation of this enzyme by 1,2-alkyldiamines (4) is consistent with the reactivity of this orthoquinone moiety.

The possibility that the increased accumulation of insoluble, crosslinked collagen in fibrotic disease states may be restricted by the specific suppression of lysyl oxidase activity has stimulated the search for selective and potent inhibitors of this enzyme. Thus, this catalyst is subject to mechanism-based inhibition by beta-aminopropionitrile (5) and beta-haloethylamines (6) and is significantly more sensitive to these agents than other mechanistically similar amine oxidases acting on non-peptidyl amine substrates (7).

Certain para-substituted benzylamines (8) and 1,2-alkyldiamines (4) have also been found to be active site-directed inhibitors of lysyl oxidase. Aminoalkylaziridines (figure 1) have been shown to be effective inhibitors of diamine oxidase (9), which, like lysyl oxidase, contains both a copper(II) and a tyrosine-derived quinone cofactor (10,11). N-(4-Aminobutyl)aziridine, a potent inhibitor of cellular polyamine uptake, irreversibly inactivates diamine oxidase (9). These compounds are potentially covalent inactivators in view of their ability to alkylate an enzyme nucleophile at the aziridinyl moiety and to form Schiff base adducts with the carbonyl cofactor at the primary amino group (12-15). Thus, a series of aminoalkylaziridines have been assessed as novel active site directed inhibitors of lysyl oxidase in the present report.

Figure 1. Generic structure of alkylaminoaziridines; "n" = 3 through 7.