Labelling and evaluation of new stabilised neurotensin (8-13) analogues for single photon emission tomography (SPET).

Neurotensin(8-13) analogues were biologically stabilised by replacement of the peptide bond between amino acids 8 and 9 by the reduced psi(CH2-NH) iso stere. Diethylenetriaminepentaacetic acid (DTPA) analogues :for In-ill labe lling and 2-bromo-phenyl-acetyl analogues for radioiodination, showed recep tor affinities in the nanomolar range in combination with a biological half live in human plasma up to 275 minutes. Biodistribution studies in male Wi star rats of metabolically stabilised aid non-stabilised In-III-DTPA-NT(8-1 3) analogues showed a major clearance from the blood through the kidneys. I -125-Labelled neurotensin (8-13) analogues showed accumulation up to 2.2% o f the injected dose per g tissue in the liver which might be an important d isadvantage when diagnosis of tumours in the gut is aimed. Neurotensin(8-13 ) analogues labelled with In-ill or I-123 may act as new potential peptider gic radiopharmaceuticals for SPET diagnosis of neurotensin receptor (NTR) p ositive tumours.