RADIOIODINATED L-703,606 - A POTENT, SELECTIVE ANTAGONIST TO THE HUMAN NK(1) RECEPTOR

A new, radioiodinated, NK, selective radiotracer ([I-125]L-703,606) wa s prepared. L-703,606 is an iodinated analog of the NK1 antagonist CP- 96,345 in which the methoxy group has been replaced by an iodine subst ituent. [I-125]L-703,606 was made from the corresponding trimethylsily l compound by treatment with no carrier added (NaI)-I-125 and an Iodob ead(R) in TFA. The tracer was prepared at a specific activity of appro x. 1100 Ci/mmol and preliminary binding studies demonstrated that [I-1 25]L-703,606 binds selectively to NK1 receptors with a k(d) = 0.3 nM. These results suggest that this radioligand will be useful for the bio chemical and pharmacological characterization of the human NK1 recepto r and, if labeled with I-123, may be useful for non-invasive NK1 recep tor imaging via SPECT.