Predictive Value of [ 18 F]ML-10 PET/CT in Early Response Evaluation of Combination Radiotherapy with Cetuximab on Nasopharyngeal Carcinoma.

PURPOSE: Apoptosis may be an indication of success therapy, and precise detection of apoptosis can provide instructional suggestions in the therapy management of malignant tumors.

PROCEDURES: We used CNE-1 cell lines for in vitro experiments, and colony formation assay, CCK-8 assay, cell apoptosis analysis, and western blotting were performed. For in vivo experiments, subcutaneous xenotransplanted tumor models of CNE-1 in nude mice were established. Then, small animal positron emission tomography/X-ray computed tomography (PET/CT) images were acquired by tail intravenous injection of 2-(5-[18 F]fluoropentyl)-2-methyl-malonic acid ([18 F]ML-10) or 2-deoxy-2-[18 F]fluoro-D-glucose ([18 F]FDG) before and 24 h and 48 h after treatment. Moreover, expression of epidermal growth factor receptor (EGFR), Ki-67, Glut-1, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) was examined by immunohistochemical examination. Tumor volumes of mice were recorded every 2 days.

RESULTS: In the presence of Cetuximab, the number of colonies of CNE-1 cells decreased significantly after irradiation at 1 and 2 Gy. In addition, Cetuximab increased the radiation-induced cytotoxicity and apoptosis of CNE-1 cells. Mechanistic studies demonstrated that Cetuximab enhanced radiosensitivity by suppressing the EGFR/PI3-K/AKT pathway. In PET/CT imaging, the tumors showed clear uptake of [18 F]ML-10 at 24 h and 48 h after combined treatment, and the value of tumor/muscle (T/M) and SUVmax (the max of standard uptake value) was significantly higher than those of the other three groups. The T/M of [18 F]ML-10 uptake showed a positive correlation of 0.926 with the apoptosis index (P < 0.001). However, the uptake of [18 F]FDG in tumors exhibited no trend among the four groups. The T/M of [18 F]FDG revealed a positive correlation of 0.926 with Glut-1 intensity (P < 0.001).

CONCLUSIONS: Our work revealed that Cetuximab could increase the radiosensitivity of CNE-1 cells both in vitro and in vivo. Apoptosis imaging with [18 F]ML-10 PET/CT is a promising modality for application in the response prediction of nasopharyngeal carcinoma.