Autotaxin (ATX) or ecto-nucleotide pyrophosphatase/phosphodiesterase-2 (ENPP2) is a secreted lysophospholipase D that generates the lipid mediator lysophosphatidic acid (LPA), a mitogen and chemo-attractant for many cell types. ATX-LPA signaling has roles in various pathologies including tumour progression and inflammation. However, the molecular basis of substrate recognition and catalysis, and the mechanism of interaction with target cells, has been elusive. Here we present the crystal structure of ATX, alone and in complex with a small-molecule inhibitor. We identify a hydrophobic lipid-binding pocket and map key residues required for catalysis and selection between nucleotide and phospholipid substrates. We show that ATX interacts with cell-surface integrins via its N-terminal somatomedin-B-like domains, using an atypical mechanism. Our results define determinants of substrate discrimination by the ENPP family, suggest how ATX promotes localized LPA signaling, and enable new approaches to target ATX with small-molecule therapeutics.

Autotaxin (ATX) is a secreted nucleotide pyrophosphatase/ phosphodiesterase that functions as a lysophospholipase D to produce the lipid mediator lysophosphatidic acid (LPA), a mitogen, chemoattractant, and survival factor for many cell types. The ATX-LPA signaling axis has been implicated in angiogenesis, chronic inflammation, fibrotic diseases and tumor progression, making this system an attractive target for therapy. However, potent and selective nonlipid inhibitors of ATX are currently not available. By screening a chemical library, we have identified thiazolidinediones that selectively inhibit ATX-mediated LPA production both in vitro and in vivo. Inhibitor potency was approximately 100-fold increased (IC 50 ∼ 30 nM) after the incorporation of a boronic acid moiety, designed to target the active-site threonine (T210) in ATX. Intravenous injection of this inhibitor into mice resulted in a surprisingly rapid decrease in plasma LPA levels, indicating that turnover of LPA in the circulation is much more dynamic than previously appreciated. Thus, boronic acid-based small molecules hold promise as candidate drugs to target ATX.A utotaxin (ATX or NPP2) is a secreted nucleotide pyrophosphatase/phosphodiesterase (NPP) originally isolated as an autocrine motility factor from melanoma cells (1). ATX, a ∼120 kDa glycoprotein, is unique amongst the NPPs in that it functions as a lysophospholipase D (lysoPLD) that converts extracellular lysophosphatidylcholine (LPC) into the lipid mediator lysophosphatidic acid (LPA; mono-acyl-sn-glycero-3-phosphate) (2-5). LPA acts on specific G protein-coupled receptors and thereby stimulates the migration, proliferation, and survival of many cell types (6 and 7) (Fig. 1). ATX is produced by various tissues and is the major LPA-producing enzyme in the circulation. Newly produced LPA is subject to degradation by membranebound lipid phosphate phosphatases (LPPs) (8 and 9). However, little is known about the dynamic regulation of steady-state LPA levels in vivo.ATX is essential for vascular development (10 and 11) and is found overexpressed in various human cancers (12). Forced overexpression of ATX or individual LPA receptors promotes tumor progression in mouse models (13-16), while LPA receptor deficiency protects from colon carcinogenesis (17). In addition to its role in cancer, ATX-LPA signaling has been implicated in lymphocyte homing and (chronic) inflammation (18), fibrotic diseases (19 and 20), and thrombosis (21). Therefore, the ATX-LPA axis qualifies as an attractive target for therapies.Potent and selective ATX inhibitors are now needed as a starting point for the development of targeted anti-ATX/LPA therapy. Direct targeting of LPA receptors seems to be a less attractive strategy, since LPA acts on multiple receptors that show overlapping activities (2 and 6). Since the initial finding that ATX is subject to product inhibition by LPA and sphingosine 1-phosphate (S1P) (22), various synthetic phospho-and phosphonate lipids have been explored as ATX inhibitors (23-26). However, s...

Autotaxin (ATX) is an extracellular enzyme that hydrolyzes lysophosphatidylcholine (LPC) to produce the lipid mediator lysophosphatidic acid (LPA). The ATX-LPA signaling axis has been implicated in diverse physiological and pathological processes, including vascular development, inflammation, fibrotic disease, and tumor progression. Therefore, targeting ATX with small molecule inhibitors is an attractive therapeutic strategy. We recently reported that 2,4-thiazolidinediones inhibit ATX activity in the micromolar range. Interestingly, inhibitory potency was dramatically increased by introduction of a boronic acid moiety, designed to target the active site threonine in ATX. Here we report on the discovery and further optimization of boronic acid based ATX inhibitors. The most potent of these compounds inhibits ATX-mediated LPC hydrolysis in the nanomolar range (IC(50) = 6 nM). The finding that ATX can be targeted by boronic acids may aid the development of ATX inhibitors for therapeutic use.