Chemistry: natural resins or derivatives; peptides or proteins; – Peptides of 3 to 100 amino acid residues – 6 to 7 amino acid residues in defined sequence
Patent
1997-07-21
1999-09-14
Hutzell, Paula K.
Chemistry: natural resins or derivatives; peptides or proteins;
Peptides of 3 to 100 amino acid residues
6 to 7 amino acid residues in defined sequence
530323, 530327, 514 14, 514 16, 424 169, A61K 3804, A61K 3800, A61K 5100
Patent
active
059524642
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to labelled peptide compounds, to a method of preparing these compounds, to a pharmaceutical composition comprising these compounds, to the use of this composition for diagnosis and therapy, and to a kit for preparing a radiopharmaceutical composition.
Neurotensin is a thirteen amino acid peptide, in 1973 isolated from bovine hypothalamus. It has the following structure:
High concentrations of neurotensin are found in discrete regions of the mammalian central nervous system. In addition, neurotensin interacts with specific receptors in the periphery. During the last decade, neurotensin receptors were found in several tumour cells, like small cell lung carcinoma, human colon carcinoma and human meningiomas.
Two radioiodinated neurotensin derivatives are mentioned in the literature. Because of the existence of two tyrosine residues in the neurotensin sequence, iodination of neurotensin yields a complex mixture of radioiodinated peptides, that possess very different biological properties and, moreover, are difficult to purify. Therefore, Mazella et al. (J. Biol. Chem. 1983, 258, 3476-3481) synthesized a neurotensin analogue in !neurotensin. Iodination (with 125-iodide under electrophilic conditions on the aromatic ring of tyrosine-3) results in a mono-iodo derivative showing a K.sub.d of 0.1 nM for binding on rat brain synaptic membranes. Preliminary experiments from the same group of researchers (Sadoul et al.; Biochem. Biophys. Res. Commun. 1984, 120, 812-819) indicated that neurotensin receptors in human brain showed a low affinity for binding experiments. The same group of researchers succeeded later on in preparing a mono-iodo derivative of neurotensin Itself; only tyrosine-3 was iodinated with 125-iodide in this method. This radioiodinated analogue has a K.sub.d of 0.2 nM for binding on rat brain synaptic membranes and a K.sub.d of 0.26 nM for binding to human brain neurotensin receptors.
The labelled natural neurotensin as well as the labelled tryptophan11 neurotensin analogue, however, suffers from an enzymatic breakdown due to cleavage of peptide bonds, resulting in an in vivo half-life of only a few minutes.
Structure-activity studies (Granier et al.; Eur. J. Biochem. 1982, 124, 117-125) revealed that the right-hand part of the neurotensin molecule fulfills the structural requirements for mimicking the entire sequence, provided its .alpha.-amino end group is protected by acetylation. The binding affinities of this analogue are comparable with those of neurotensin in two binding assays, viz. the binding assay on rat brain synaptic membranes and that on HT 29 cells.
This analogue contains one remaining tyrosine residue which can be readily radioiodinated using electrophilic substitution of the hydrogen in the ortho position of the phenolic group. Structure-activity studies revealed, however, that iodination in the 3-position of said tyrosine residue of this analogue results in a remarkable loss of receptor affinity, viz. with a factor of 20 (Mazella et al.; see above).
It is the objective of the present invention to provide a labelled peptide compound which has a selective affinity to neurotensin receptors, comparable with that of neurotensin itself, and which has a sufficient enzymatic resistance to allow its use in diagnosis and therapy.
This objective can be achieved by a labelled peptide compound, wherein the peptide has a selective neurotensin receptor affinity and is represented by the general formula Xdd-.sup.6 Xee-.sup.7 Leu-OH (SEQ ID NO:2) (I) aryl-(C.sub.1 -C.sub.3)alkanoyl group, or a chelating group attached by an amide bond or through a spacing group to the peptide molecule; selected from Pro and Hyp; the group consisting of .sup.99m Tc, .sup.203 Pb, .sup.67 Ga, .sup.68 Ga, .sup.72 As, .sup.111 In, .sup.113m In, .sup.97 Ru, .sup.62 Cu, .sup.64 Cu, .sup.52 Fe, .sup.52m Mn, .sup.51 Cr, .sup.186 Re, .sup.188 Re, .sup.77 As, .sup.90 Y, .sup.67 Cu, .sup.169 Er, .sup.121 Sn, .sup.127 Te, .sup.142 Pr, .sup.143 Pr, .sup.198 Au, .sup.199 Au, .sup.161 Tb, .sup.109 Pd,
Ceusters Marc
Mertens John
Tourwe Dirk
Hutzell Paula K.
Mallinckrodt Inc.
Worrall Timothy A.
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