[161Tb]-BASED RADIOPEPTIDES

The radiopeptide of any of the preceding claims, wherein the chelator is a tetradentate chelator.

The radiopeptide of any of the preceding claims, wherein the chelator contains four nitrogen atoms.

The radiopeptide of any of the preceding claims, wherein the chelator is a 12-membered tetraaza ring system.

The radiopeptide of any of the preceding claims, wherein the chelator comprises at least one substituent containing at least one carboxy function.

The radiopeptide of any of the preceding claims, wherein the chelator is DOTA or a DOTA derivative.

The radiopeptide of any of the preceding claims, wherein the somatostatin receptor antagonist is covalently coupled to the chelator via an amide linkage.

The radiopeptide of any of the preceding claims, wherein the somatostatin receptor antagonist binds to SSTR-2 (sst2) or is an SSTR-2 (sst2) selective antagonist.

The radiopeptide of any of the preceding claims, wherein less than 20% of the administered somatostatin receptor antagonist is internalized by cells.

The radiopeptide of any of the preceding claims, wherein the somatostatin receptor antagonist is a cyclic peptide.

The radiopeptide of any of the preceding claims, wherein the somatostatin receptor antagonist contains two cysteine residues, which preferably form a disulfide bridge.

The radiopeptide of any of the preceding claims, wherein the somatostatin receptor antagonist comprises 8 to 14 amino acids, preferably 8 to 10, more preferably 8 amino acids.

The radiopeptide of any of the preceding claims, wherein the somatostatin receptor antagonist comprises formula I:

• X1-cyclo[D-Cys-X3-X4-Lys-Thr-Cys]-D-Tyr-NH2, wherein X1, X3, and X4 may selected from a naturally or a non-naturally occurring D- or L-amino acid.

The radiopeptide of any of the preceding claims, wherein terbium-161 is produced by neutron irradiation of gadolinium-160.

The radiopeptide of any of the preceding claims, wherein terbium-161 is a non-carrier-added terbium-161 (n.c.a. terbium-161).

The radiopeptide of any of the preceding claims, wherein the antagonist is preferentially taken up by tumors relative to other tissue.

The radiopeptide of any of the preceding claims, wherein the radiopeptide has the structure of the following formula:

A pharmaceutical composition, comprising the radiopeptide of any of the preceding claims and at least one pharmaceutically acceptable excipient, preferably water.