[⁶⁸Ga]Ga-NODAGA-RGD post MI reflects activated fibroblasts rather than angiogenesis

Angiogenesis is crucial in myocardial healing after myocardial infarction (MI). The α_vβ₃-integrin, a key regulator of angiogenesis, is targeted by RGD-based PET tracers like [⁶⁸Ga]Ga-NODAGA-RGD. Yet, angiogenesis imaging using RGD-based tracers is seriously hampered by the lack of true specificity of the α_vβ₃-integrin for angiogenic cells. Therefore, our study aimed to identify the cell type with the highest α_vβ₃-integrin expression in the process of myocardial healing in order to determine the actual value of the PET tracer [⁶⁸Ga]Ga-NODAGA-RGD for imaging post-MI angiogenesis.

Cardiac magnetic resonance imaging (CMR) was used to assess cardiac function and morphology after 28 days in two groups: permanent ligation (PL) of the left anterior descending coronary artery and transient occlusion for 30 min (I/R). Following these measurements, hearts were excised for histological and immunohistological examinations to evaluate scar formation, capillary density, and cellular composition. PET imaging with [⁶⁸Ga]Ga-NODAGA-RGD was conducted on day 5 and day 7 post-MI. Single-nucleus transcriptomics were performed to identify cell clusters expressing α_vβ₃-integrin.

Both infarct models induced scar formation, with the PL group developing large infarcts accompanied by massive left ventricular dilation and hypertrophy of cardiomyocytes, while the I/R group exhibited small intramural scars without significant changes in LV geometry or function. PET imaging revealed significantly higher tracer accumulation in the infarct area of the PL group compared to the I/R group. Single-nucleus transcriptomics performed 5 days post-MI revealed that angiogenesis markers were enriched in the I/R group, while the highest α_vβ₃-integrin mRNA expression was identified in the fibroblast cluster, indicating an activated phenotype.

Activated fibroblasts are the primary target cells of [⁶⁸Ga]Ga-NODAGA-RGD, rather than angiogenic cells. In this regard, [⁶⁸Ga]Ga-NODAGA-RGD is most probably not a valid tracer for imaging angiogenesis during the first days post-MI.