AR-2 is specifically activated by ATX <i>in vivo</i> with fluorescence attenuated by addition of an ATX inhibitor.

<p>(<b>a</b>) Mice bearing MDA-MB-231 xenografts were treated with vehicle or the ATX inhibitor PF-8380. Twenty minutes later, AR-2 was injected <i>i.v.</i>, and the mice were subsequently imaged with NIRF. (<b>b</b>) Tumors from (a) were imaged <i>ex vivo</i>. (<b>c</b>) <i>Ex vivo</i> tumor fluorescence was normalized to total protein levels (*** denotes p<0.001).