Autophagy inhibition improves the targeted radionuclide therapy efficacy of (131)I-FAP-2286 in pancreatic cancer xenografts.

PURPOSES: Radiotherapy can induce tumor cell autophagy, which might impair the antitumoral effect. This study aims to investigate the effect of autophagy inhibition on the targeted radionuclide therapy (TRT) efficacy of (131)I-FAP-2286 in pancreatic cancer. METHODS: Human pancreatic cancer PANC-1 cells were exposed to (131)I-FAP-2286 radiotherapy alone or with the autophagy inhibitor 3-MA. The autophagy level and proliferative activity of PANC-1 cells were analyzed. The pancreatic cancer xenograft-bearing nude mice were established by the co-injection of PANC-1 cells and pancreatic cancer-associated fibroblasts (CAFs), and then were randomly divided into four groups and treated with saline (control group), 3-MA, (131)I-FAP-2286 and (131)I-FAP-2286 + 3-MA, respectively. SPECT/CT imaging was performed to evaluate the bio-distribution of (131)I-FAP-2286 in pancreatic cancer-bearing mice. The therapeutic effect of tumor was evaluated by (18)F-FDG PET/CT imaging, tumor volume measurements, and the hematoxylin and eosin (H&E) staining, and immunohistochemical staining assay of tumor tissues. RESULTS: (131)I-FAP-2286 inhibited proliferation and increased the autophagy level of PANC-1 cells in a dose-dependent manner. 3-MA promoted (131)I-FAP-2286-induced apoptosis of PANC-1 cells via suppressing autophagy. SPECT/CT imaging of pancreatic cancer xenograft-bearing nude mice showed that (131)I-FAP-2286 can target the tumor effectively. According to (18)F-FDG PET/CT imaging, the tumor growth curves and immunohistochemical analysis, (131)I-FAP-2286 TRT was capable of suppressing the growth of pancreatic tumor accompanying with autophagy induction, but the addition of 3-MA enabled (131)I-FAP-2286 to achieve a better therapeutic effect along with the autophagy inhibition. In addition, 3-MA alone did not inhibit tumor growth. CONCLUSIONS: (131)I-FAP-2286 exposure induces the protective autophagy of pancreatic cancer cells, and the application of autophagy inhibitor is capable of enhancing the TRT therapeutic effect.