@article {Wu1394, author = {Wenyu Wu and Fei Yu and Pengjun Zhang and Ting Bu and Jingjing Fu and Shuyue Ai and Qinqin You and Liang Shi and Guoqiang Shao and Feng Wang and Marina Hodolic and Hongqian Guo}, title = {68Ga-DOTA-NT-20.3 Neurotensin Receptor 1 PET Imaging as a Surrogate for Neuroendocrine Differentiation of Prostate Cancer}, volume = {63}, number = {9}, pages = {1394--1400}, year = {2022}, doi = {10.2967/jnumed.121.263132}, publisher = {Society of Nuclear Medicine}, abstract = {Prostate-specific membrane antigen (PSMA){\textendash}negative neuroendocrine prostate cancer (PCa) is a subtype of PCa likely to be lethal, with limited clinical diagnostic and therapeutic options. High expression of neurotensin receptor subtype 1 (NTR1) is associated with neuroendocrine differentiation of PCa, which makes NTR1 a potential target for neuroendocrine PCa. In this study, the NTR1-targeted tracer 68Ga-DOTA-NT-20.3 was synthesized, and its affinity to androgen-dependent (LNCap) and androgen-independent (PC3) xenografts was determined. Methods: 68Ga-DOTA-NT-20.3 was labeled using an automated synthesizer module, and its stability, labeling yield, and radiochemical purity were analyzed by radio{\textendash}high-performance liquid chromatography. Receptor binding affinity was evaluated in NTR1-positive PC3 cells by a competitive binding assay. The biodistribution of 68Ga-DOTA-NT-20.3 in~vivo was evaluated in PC3 and LNCap xenografts by small-animal PET imaging. NTR1 expression was identified by immunohistochemistry and immunofluorescence evaluation. Results: 68Ga-DOTA-NT-20.3 was synthesized successfully, with a yield of 88.07\% {\textpm} 1.26\%, radiochemical purity of at least 99\%, and favorable stability. The NTR1 affinity (half-maximal inhibitory concentration) for 68Ga-DOTA-NT-20.3 was 7.59 {\textpm} 0.41 nM. Small-animal PET/CT of PC3 xenograft animals showed high-contrast images with intense tumor uptake, which revealed specific NTR1 expression. The tumors showed significant radioactivity (4.95 {\textpm} 0.67 percentage injected dose per gram of tissue [\%ID/g]) at 1 h, which fell to 1.95 {\textpm} 0.17 \%ID/g (P \< 0.01, t = 8.72) after specific blockage by neurotensin. LNCap xenografts had no significant accumulation (0.81 {\textpm} 0.06 \%ID/g) of 68Ga-DOTA-NT-20.3 at 1 h. In contrast, 68Ga-PSMA-11 was concentrated mainly in LNCap xenografts (8.60 {\textpm} 2.11 \%ID/g), with no significant uptake in PC3 tumors (0.53 {\textpm} 0.05 \%ID/g), consistent with the in~vitro immunohistochemistry findings. Biodistribution evaluation showed rapid clearance from the blood and main organs (brain, heart, lung, liver, muscle, and bone), with significantly high tumor-to-liver (4.41 {\textpm} 0.73) and tumor-to-muscle (12.34 {\textpm} 1.32) ratios at 60 min after injection. Conclusion: 68Ga-DOTA-NT-20.3 can be efficiently prepared with a high yield and high radiochemical purity. Its favorable biodistribution and prominent NTR1 affinity make 68Ga-DOTA-NT-20.3 a potential radiopharmaceutical for the detection of PSMA-negative PCa and identification of neuroendocrine differentiation.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/63/9/1394}, eprint = {https://jnm.snmjournals.org/content/63/9/1394.full.pdf}, journal = {Journal of Nuclear Medicine} }