Angiogenesis Imaging of Myocardial Infarction Using 68Ga-RGD PET: Characterization and Application to Therapeutic Efficacy Monitoring

Abstract

목적: 최근 개발된 68Ga-RGD PET은 혈관신생을 표적으로 하는 분자영상법으로서, 심근경색에서 발현되는 혈관신생이나 최근 각광 받는 혈관신생치료 등의 모니터링에 유용할 것으로 기대되고 있다. 이 연구에서는 심근경색에서68Ga-RGD의 섭취 양상의 시간경과를 조사하고, 경색심근 영상 및 혈관신생치료 후 모니터링 영상법으로서의 가능성을 평가하고자 한다.

방법: 7주령 암컷 Sprague-Dawley 쥐를 실험대상으로 하여 좌전하행관상동맥을 결찰하여 심근경색 모델을 만들었다. 심근경색 섭취양상 조사를 위해 6마리 경색모델과 4마리 위수술 시행 동물들에게서 시술 후 1일, 7일, 14일째 68Ga-RGD, 15일째 68Ga-BAPEN, 16일째 18F-FDG를 주사하고 PET/CT를 촬영하였다. 68Ga-RGD PET/CT에서 경색심근-정상심근의 섭취 비율(LNR)을 구하여 정량비교를 하였다. 혈관신생치료 평가를 위해 네 마리에서 관상동맥 결찰 후 recombinant human basic fibroblast growth factor (bFGF)를 심근에 주입하였다. 세 마리는 bFGF대신 생리식염수를 대신 주입하였고 다른 세 마리는 위수술을 실시하였다. 이들에게서 시술 후 1일, 7일, 14일째에 68Ga-RGD PET/CT를 촬영하였고 2일, 15일째에 18F-FDG PET/CT를 촬영하였다. 68Ga-RGD PET에서 LNR을 측정하고 18F-FDG PET/CT영상에서 경색범위를 측정하여 비교하였다. 모든 개체에서 마지막 촬영이 끝난 후 68Ga-RGD를 이용한 자가방사촬영과 H&E, TTC 염색, CD68항체, VEGF항체를 이용한 면역병리염색을 실시하였다.

결과: 경색심근 쥐의 경색영역에서18F-FDG와 68Ga-BAPEN 섭취 감소가 동반되어 성공적인 경색 유발을 확인하였고, 해당 부위에서 68Ga-RGD 섭취 증가가 경색유발 후 1일에서 14일의 전 기간에 걸쳐서 나타났다 (p = 0.010, 0.019). 자가방사촬영에서 경색심근에 68Ga-RGD 섭취가 확인되었으며 해당 부위는 VEGF와 CD68발현증가가 나타났다. 경색심근영역에서 bFGF를 투여하여 혈관신생치료를 시행한 군들에서는 술후 1일째의 RGD섭취증가가 다른 군에 비해 유의하게 높았다. 그러나 이 외에 RGD섭취, 경색심근의 크기와 그 변화, 자가방사촬영 및 면역병리염색결과에서 bFGF치료군과 생리식염수 주입군 사이에 유의한 차이는 보이지 않았다.

결론: 68Ga-RGD는 경색심근에 섭취가 증가함으로써 심근경색영상화의 가능성을 보여 주었다. 심근 내에 bFGF 일회 투여가 단기간의 혈관신생 증가에 도움이 되는 것을68Ga-RGD PET 으로 확인할 수 있었으나 장기적인 효과는 없어 장기적인 예후에는 도움이 크지 않을 것임을 시사하였다. 68Ga-RGD는 심근경색 영상과 혈관신생치료 효과를 평가하는 영상 추적자로 유용할 것으로 기대된다.

Purpose: 68Ga-RGD PET is a recentl developed molecular imaging modality that visualizes angiogenesis. In myocardial infarction (MI), angiogenesis is one of the key processes for understanding pathophysiology and implementing therapeutic interventions. In this study, 68Ga-RGD PET was used to investigate imaging characteristics in a rat MI model, as well as to monitor experimental angiogenesis induction therapy. Materials and methods: To assess imaging characteristics, 6 female Sprague-Dawley rats with MI induced by ligation of the left anterior descending artery (LAD) and 4 sham-operated rats were used. 68Ga-RGD PET was performed on post-operative days (POD) 1, 7, and 14. 68Ga-BAPEN PET and 18F-FDG PET were also performed to evaluate perfusion and glucose metabolism, respectively. Results from 68Ga-BAPEN PET and 18F-FDG PET were also directly compared with those from 68Ga-RGD PET. Quantitative analyses were performed by measuring the lesion-to-normal ratio (LNR) by drawing regions of interest for the LAD territory and normal remote myocardium on 68Ga-RGD PET. Autoradiography for 68Ga-RGD and immunohistochemical (IHC) staining for VEGF and CD68 were performed to assess the mechanism of RGD accumulation. In order to monitor experimental angiogenesis induction therapy, an additional 7 rats underwent LAD ligation

4 were injected with recombinant human basic fibroblast growth factor (rhbFGF), and the remaining 3 were injected with saline. 68Ga-RGD PET was performed on POD 1, 7, and 14, and 18F-FDG PET was performed on POD 2 and 15. PET images were compared with those of the 3 sham-operated rats. Results: On PET images, 68Ga-RGD uptake in the LAD territory was significantly increased in MI-induced rats compared with sham-operated rats from POD 1 (LNR 1.47±0.16 versus 1.13±0.14, P=0.010) through POD 14 (LNR 1.31±0.14 versus 1.06±0.07, P=0.019), and this uptake gradually decreased over time. The areas with increased 68Ga-RGD uptake on POD 14 corresponded with the final infarct lesions that demonstrated metabolic defects on 18F-FDG PET and perfusion defects on 68Ga-BAPEN PET. Autoradiography also demonstrated 68Ga-RGD uptake in the infarcted tissue. On IHC staining, 68Ga-RGD uptake corresponded with VEGF expression and macrophage accumulation in the infarcted tissue. In monitoring angiogenesis induction therapy, the LNR on 68Ga-RGD PET was 1.61±0.15 in the rhbFGF group on POD 1, which was significantly higher than that of saline-injected and sham-operated groups (1.37±0.06 and 1.17±0.14, respectively

P=0.018). However, no significant differences were observed at subsequent time points. Additionally, no significant differences were found between the rhbFGF and saline-injected groups with respect to final infarct size, degree of infarct change, autoradiography, or IHC results. Conclusion: This study demonstrated the characteristics of 68Ga-RGD PET as an angiogenesis imaging modality post-MI. In the monitoring of therapeutic efficacy of single injections of rhbFGF using 68Ga-RGD PET, rhbFGF was effective for induction of short-term angiogenesis, though it had limited long-term effects. Thus, 68Ga-RGD PET would be a useful angiogenesis imaging modality in MI for assessment of pathophysiology and monitoring of therapeutic efficacy.