Positron Emission Tomography Imaging of Vessel Wall Matrix Metalloproteinase Activity in Abdominal Aortic Aneurysm

Background: Matrix metalloproteinases (MMPs) play a key role in the pathogenesis of abdominal aortic aneurysm (AAA). Imaging aortic MMP activity, especially using positron emission tomography to access high sensitivity, quantitative data, could potentially improve AAA risk stratification. Here, we describe the design, synthesis, characterization, and evaluation in murine AAA and human aortic tissue of a first-in-class MMP-targeted positron emission tomography radioligand, ⁶⁴Cu-RYM2.

Methods: The broad spectrum MMP inhibitor, RYM2 was synthetized, and its potency as an MMP inhibitor was evaluated by a competitive inhibition assay. Toxicology studies were performed. Tracer biodistribution was evaluated in a murine model of AAA induced by angiotensin II infusion in Apolipoprotein E-deficient mice. ⁶⁴Cu-RYM2 binding to normal and aneurysmal human aortic tissues was assessed by autoradiography.

Results: RYM2 functioned as an MMP inhibitor with nanomolar affinities. Toxicology studies showed no adverse reaction in mice. Upon radiolabeling with Cu-64, the resulting tracer was stable in murine and human blood in vitro. Biodistribution and metabolite analysis in mice showed rapid renal clearance and acceptable in vivo stability. In vivo positron emission tomography/computed tomography in a murine model of AAA showed a specific aortic signal, which correlated with ex vivo measured MMP activity and Cd68 gene expression. ⁶⁴Cu-RYM2 specifically bound to normal and aneurysmal human aortic tissues in correlation with MMP activity.

Conclusions: ⁶⁴Cu-RYM2 is a first-in-class MMP-targeted positron emission tomography tracer with favorable stability, biodistribution, performance in preclinical AAA, and importantly, specific binding to human tissues. These data set the stage for ⁶⁴Cu-RYM2-based translational imaging studies of vessel wall MMP activity, and indirectly, inflammation, in AAA.