NTSR1

NTSR1 is the high-affinity class A GPCR for neurotensin (NT) - the 13-aa neuropeptide that modulates dopaminergic circuits, pain, thermoregulation, and feeding behavior, and that is overexpressed as a growth-promoting receptor in ~80% of pancreatic ductal adenocarcinomas, 40–60% of lung adenocarcinomas, and numerous other solid tumors. Its combination of CNS neuromodulatory roles (dopamine, analgesia, satiety) and cancer-specific expression makes NTSR1 a dual-interest target for psychiatric/metabolic peptide research and oncology targeting. Multiple NTSR1-selective agonist and antagonist peptide analogs are in preclinical development; no drug is approved, but radiolabeled NT analogs for tumor imaging are in clinical trials.

NTSR1 (chromosome 20q13.33, 424 aa) is a Gq/11-primary class A GPCR. NT binds with Kd ~0.3 nM via its C-terminal hexapeptide NT(8-13) (Pro-Tyr-Ile-Leu or Arg-Arg-Pro-Tyr-Ile-Leu) - this C-terminal fragment retains full receptor-binding and pharmacological activity. Key contacts: Arg327^{6.54} (TM6) forms a salt bridge with NT Leu13 C-terminus; Tyr11 of NT hydrogen-bonds Thr226 (ECL2); Arg8/Arg9 contact Asp60 (N-terminus) and Gln324^{6.51} (TM6); Pro10-Leu13 hydrophobic core packs against Phe120^{2.57}, Trp339^{7.35}, Tyr341^{7.37}. Signaling: Gq/11 → PLC-β → IP3/DAG → Ca²⁺/PKC → MAPK/ERK (proliferation, migration); secondary Gi/o → ↓cAMP; EGFR transactivation via metalloproteinase-dependent EGF shedding → RhoGTPase/MMP-driven invasion in tumor cells. β-arrestin (GRK5-mediated) → endosomal MAPK/ERK and NF-κB → pro-inflammatory signaling. High sodium concentrations allosterically accelerate NT dissociation 50-fold via Asp113^{2.50} pocket. Cryo-EM structures: NTSR1-Gi (PDB: 6OS9), NTSR1-GRK2-Gαq (PDB: 8JPB). NTSR1 heterodimerizes with dopamine D2R - this complex routes through distinct signaling pathways and underpins NT's functional antagonism of psychostimulant-induced locomotion without D2R occupancy per se.

No NTSR1-targeted drug is approved. SR48692 (a non-peptide antagonist, Ki ~2.6 nM at NTSR1) inhibits tumor growth and sensitizes cells to radiotherapy in xenograft models. [¹⁷⁷Lu]-NT(8-13) and [¹¹¹In]-NT analogs are in Phase 1/2 trials for NTSR1-positive solid tumors (pancreatic cancer, NSCLC) as peptide receptor radionuclide therapy (PRRT). PD 149163 is the selective NTSR1 peptide agonist used as preclinical antipsychotic and analgesic probe. For peptide research, the tractable recipes are: NT(8-13) analogs with D-Tyr¹¹ and N-methylated Leu¹³ substitutions for DPP-4/metalloprotease resistance while preserving sub-nM NTSR1 affinity; constrained cyclic NT(8-13) lactam analogs that lock the active conformation for improved selectivity over NTSR2; NT(8-13) conjugated to radionuclides (⁶⁸Ga, ¹⁷⁷Lu) or cytotoxins via aminocaproic acid linkers for tumor-targeted delivery; and biased NTSR1 agonists that preferentially activate Gq/Ca²⁺ over β-arrestin/EGFR transactivation to preserve analgesic and dopaminergic effects while minimizing tumor-promoting invasion signals.