Inhibition of Galactosyltransferases by a Novel Class of Donor Analogues Karine Descroix, †,⊥ Thomas Pesnot, †,⊥ Yayoi Yoshimura, ‡ Sebastian S. Gehrke, †,∥ Warren Wakarchuk, § Monica M. Palcic, ‡ and Gerd K. Wagner* ,†,∥ † School of Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K. ‡ Carlsberg Laboratory, Gamle Carlsberg Vej 10, 1799 Copenhagen V, Denmark § National Research Council Canada, Institute for Biological Science, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada * S Supporting Information ABSTRACT: Galactosyltransferases (GalT) are important molecular targets in a range of therapeutic areas, including infection, inflammation, and cancer. GalT inhibitors are therefore sought after as potential lead compounds for drug discovery. We have recently discovered a new class of GalT inhibitors with a novel mode of action. In this publication, we describe a series of analogues which provide insights, for the first time, into SAR for this new mode of GalT inhibition. We also report that a new C- glycoside, designed as a chemically stable analogue of the most potent inhibitor in this series, retains inhibitory activity against a panel of GalTs. Initial results from cellular studies suggest that despite their polarity, these sugar-nucleotides are taken up by HL- 60 cells. Results from molecular modeling studies with a representative bacterial GalT provide a rationale for the differences in bioactivity observed in this series. These findings may provide a blueprint for the rational development of new GalT inhibitors with improved potency. ■ INTRODUCTION Galactosyltransferases (GalTs) are a family of carbohydrate- active enzymes which transfer a D-galactose (D-Gal) residue from the donor UDP-α-D-galactose (UDP-Gal, Figure 1) to a specific acceptor substrate. 1 D-Galactose is an essential component of many biologically and therapeutically important glycan structures, including the human blood group B antigen, 2 the cancer epitopes of the Lewis family (e.g., sialyl Lewis X, sLe x ), 3 and the lipooligosaccharide (LOS) antigen of certain Gram-negative bacteria. 4 GalTs involved in the biosynthesis of these glycan structures have therefore been identified as promising targets for anticancer and anti-infective drug discovery. 5−7 The human galactosyltransferase (GalT) β-1,4- GalT1, for example, catalyzes the galactosylation of GlcNAc- or Glc-based acceptors during sLe x biosynthesis. Expression levels of β-1,4-GalT1 are elevated in highly metastatic lung cancer, 8 and decoy substrates of β-1,4-GalT1 reduce selectin-mediated tumor metastasis in Lewis lung carcinoma cells. 9 β-1,4-GalT1 therefore represents a promising target for blocking sLe x formation, and β-1,4-GalT inhibitors are sought after as chemical tools to study these enzymes and processes and as potential anticancer agents. 10−12 GalTs have also attracted interest as novel targets for antibacterial drug discovery, in particular approaches directed at targeting virulence factors. 13 Gram-negative LOS structures containing a Gal-Gal terminal epitope are important virulence factors for a range of human pathogens including Neisseria meningitidis and Haemophilus influenzae. 14,15 The terminal oligosaccharides of the bacterial LOS structures mimic human glycolipids and allow the pathogen to evade recognition by the host immune system. 14 A key step in the biosynthesis of LOS structures in some Gram-negative bacteria is the addition of D- Gal onto a terminal lactose, which is catalyzed by the α-1,4- GalT LgtC. 14 The expression of LgtC has been associated with the high-level serum resistance of the nontypeable Haemophilus influenzae (NTHI) strain R2866. 15 The primary oligosaccharide glycoform of R2866 contains four heptose and four hexose residues, and the additional D-Gal unit protects the bacterium Received: August 29, 2011 Published: February 22, 2012 Article pubs.acs.org/jmc © 2012 American Chemical Society 2015 dx.doi.org/10.1021/jm201154p | J. Med. Chem. 2012, 55, 2015−2024