Improved radiotracing of oxytocin receptor-expressing tumours using the new [111In]-DOTA-Lys8-deamino-vasotocin analogue.

Oxytocin receptors (OTR) have been described in a number of tumours of different origin, and represent a new target for specific radiolabelled oxytocin (OT) analogues in cancer diagnosis and therapy. By linking the DOTA chelating agent to position 8 of the deamino derivative of Lys(8)-vasotocin (dLVT), we obtained a new compound (DOTA-dLVT) with the following characteristics: (1) it forms a monomeric and stable compound that binds to OTR with an affinity comparable to that of the endogenous OT ligand; (2) it is characterised by a very good selectivity profile for the human OTR, with a low affinity binding to the closely related V1a, V1b and V2 vasopressin receptor subtypes; (3) it induces rapid and persistent receptor internalisation and (4) when radiolabelled, [(111)In]-DOTA-dLVT is efficiently and selectively taken up by OTR-positive tumours grown in mice. These features makes radiolabelled DOTA-dLVT a very good candidate for the radiotargeting of OTR-expressing tumours.