Improved radiotracing of oxytocin receptor-expressing tumours using the new [111 In]-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: (I) 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 Via, VIb and V2 vasopressin receptor subtypes; (3) it induces rapid and persistent receptor intemalisation and (4) when radiolabelled, [111In]-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. © 2003 Cancer Research UK.