Matrix Metalloproteinase-Targeted SPECT/CT Imaging for Evaluation of Therapeutic Hydrogels for the Early Modulation of Post-Infarct Myocardial Remodeling.

Following myocardial infarction (MI), maladaptive upregulation of matrix metalloproteinase (MMP) alters extracellular matrix leading to cardiac remodeling. Intramyocardial hydrogel delivery provides a vehicle for local delivery of MMP tissue inhibitors (rTIMP-3) for MMP activity modulation. We evaluated swine 10-14 days following MI randomized to intramyocardial delivery of saline, degradable hyaluronic acid (HA) hydrogel, or rTIMP-3 releasing hydrogel with an MMP-targeted radiotracer (99mTc-RP805), 201Tl, and CT. Significant left ventricle (LV) wall thinning, increased wall stress, reduced circumferential wall strain occurred in the MI region of MI-Saline group along with left atrial (LA) dilation, while these changes were modulated in both hydrogel groups. 99mTc-RP805 activity increased twofold in MI-Saline group and attenuated in hydrogel animals. Infarct size significantly reduced only in rTIMP-3 hydrogel group. Hybrid SPECT/CT imaging demonstrated a therapeutic benefit of intramyocardial delivery of hydrogels post-MI and reduced remodeling of LA and LV in association with a reduction in MMP activation.