Papers of the Week

Neurotensin receptor 2 (NTS) is a well-known mediator of central opioid-independent analgesia. Seminal studies have highlighted NTS overexpression in a variety of tumors including prostate cancer, pancreas adenocarcinoma, and breast cancer. Herein, we describe the first radiometalated neurotensin analogue targeting NTS. JMV 7488 (DOTA-(βAla)-Lys-Lys-Pro-(D)Trp-Ile-TMSAla-OH) was prepared using solid-phase peptide synthesis, then purified, radiolabeled with Ga and In, and investigated on HT-29 cells and MCF-7 cells, respectively, and on HT-29 xenografts. [Ga]Ga-JMV 7488 and [In]In-JMV 7488 were quite hydrophilic (logD = -3.1 ± 0.2 and -2.7 ± 0.2, respectively, < 0.0001). Saturation binding studies showed good affinity toward NTS ( = 38 ± 17 nM for [Ga]Ga-JMV 7488 on HT-29 and 36 ± 10 nM on MCF-7 cells; = 36 ± 4 nM for [In]In-JMV 7488 on HT-29 and 46 ± 1 nM on MCF-7 cells) and good selectivity (no NTS binding up to 500 nM). On cell-based evaluation, [Ga]Ga-JMV 7488 and [In]In-JMV 7488 showed high and fast NTS-mediated internalization of 24 ± 5 and 25 ± 11% at 1 h for [In]In-JMV 7488, respectively, along with low NTS-membrane binding (<8%). Efflux was as high as 66 ± 9% at 45 min for [Ga]Ga-JMV 7488 on HT-29 and increased for [In]In-JMV 7488 up to 73 ± 16% on HT-29 and 78 ± 9% on MCF-7 cells at 2 h. Maximum intracellular calcium mobilization of JMV 7488 was 91 ± 11% to that of levocabastine, a known NTS agonist on HT-29 cells demonstrating the agonist behavior of JMV 7488. In nude mice bearing HT-29 xenograft, [Ga]Ga-JMV 7488 showed a moderate but promising significant tumor uptake in biodistribution studies that competes well with other nonmetalated radiotracers targeting NTS. Significant uptake was also depicted in lungs. Interestingly, mice prostate also demonstrated [Ga]Ga-JMV 7488 uptake although the mechanism was not NTS-mediated.