Cerenkov luminescence tomography of aminopeptidase N (APN/CD13) expression in mice bearing HT1080 tumors

In vivo imaging of aminopeptidase N (APN/CD13) expression is crucial for the early detection of cancer. This study attempted to show that APN/CD13 expression can be imaged and quantified with novel Cerenkov luminescence tomography (CLT). Na¹³¹I with various activities was placed at different depths in a tissue-mimicking phantom, and various porcine tissues and luminescent images were acquired. The binding of ¹³¹I-NGR with human fibrosarcoma HT1080 and human colon cancer HT-29 cells was detected with Cerenkov luminescence imaging (CLI). Nude mice bearing HT-1080 tumors were imaged after injection with ¹³¹I-NGR using both planar and tomographic CLI methods. The penetration depth increased with ascending activity of Na¹³¹I. There was a robust linear correlation between the optical signal intensity and the HT1080 cell numbers (r² 5 .9691), as well as the activity (r² 5 .9860). The three-dimensional visualization CLT results clearly showed that ¹³¹I-NGR uptake in tumor tissues represented a high expression of the APN/CD13 receptor. CLT also allowed quantifying ¹³¹I-NGR uptake in tumor tissues showing an average activity of 0.1388 6 4.6788E-6 MBq in tumor tissues. Our study indicated that ¹³¹I-NGR combined with CLT allowed us to image and quantify tumorassociated APN/CD13 expression noninvasively. The promising CLT technique could be potentially used for sensitively evaluating tumor angiogenesis in vivo.