Design and Synthesis of 68Ga-Labeled Peptide-Based Heterodimers for Dual Targeting of NTS1 and GRPR

Abstract

Tumor heterogeneity remains one of the main obstacles for cancer diagnosis and treatment. The simultaneous targeting of several cancer biomarkers is an appealing approach for improved diagnostic procedures. Neurotensin receptor 1 (NTS₁) and Gastrin-Releasing Peptide Receptor (GRPR) are both G-protein coupled receptors with complementary profile of expression in several cancer types. This work proposes the design, the synthesis and the in vitro radiopharmaceutical characterization of three heterodimers, based on GRP/NT modified peptides, radiolabeled with gallium-68. Two NTS₁/GRPR targeting pharmacophores containing linear hybrids that differ in the C-terminus were synthesized (i. e., JMV 7110 and JMV 7253). The branched analogue of the silicon-containing heterodimer JMV 7110, namely JMV 7266, was also synthesized. After radiolabeling with ⁶⁸Ga, saturation binding studies performed on HT29 (NTS₁ ⁺/GRPR^-) and PC3 (NTS₁ ⁺/GRPR⁺) cells demonstrated a significant loss in NTS₁ and GRPR affinity compared to the reference monomers with the exception of the NTS₁ affinity of [⁶⁸Ga]Ga-JMV 7266 which was preserved. Considering cellular processing, NTS₁-internalization at 1 h was the highest with [⁶⁸Ga]Ga-JMV 7266 and was similar to the reference compound. Interestingly [⁶⁸Ga]Ga-JMV 7266 demonstrated lower efflux than the other linear heterodimers but also than its NT reference compound. The branched structure of [⁶⁸Ga]Ga-JMV 7266 seems beneficial for dual NTS₁/GRPR targeting.

Keywords: Bombesin; GRPR; Heterodimers; NTS1; Neurotensin; PET imaging.

Figure 1

Saturation binding curves of the ⁶⁸Ga‐heterodimers performed on HT29 and PC3 cells.

Figure 2

Intracellular distribution of the newly developed ⁶⁸Ga‐heterodimers on HT29 and PC3 cells. Values from reference compounds are reported in dashed lines at 60 min only for easier reading.

Figure 3

Efflux of [⁶⁸Ga]Ga‐heterodimers on HT29 and PC3 cells. Values from reference compounds are reported in dashed lines at 45 min only for easier reading.

Scheme 1

Reagents and conditions: a) 20 % piperidine in DMF (5 min×3), rt; b) Appropriate amino acid, HATU, DIPEA, DMF, appropriate time/cycle, rt; c) DCM/TFE/AcOH 8 : 1 : 1, 12 h, rt; d) HATU, DIPEA, DMF, rt, on; e) 20 % piperidine in DMF, rt, 1 h; f) NaOH, CaCl₂, iPrOH/H₂O (7 : 3), 7 h, rt. All reactions and conditions are detailed reported in the Supporting Information.