Tritiated JNJ‐63514230 is a novel GluN2B‐selective radioligand with no affinity to sigma receptors

Commonly used GluN2B radioligands exhibit limited selectivity towards GluN2B receptors as they interact with sigma and other off‐target receptors. Here we describe development and characterization of [ 3 H] JNJ‐63514230, a novel radioligand selective for GluN2B‐containing NMDA receptors. Methods The selectivity JNJ 63514230 was determined using functional assays and CEREP panel. Saturation binding and competitive radioligand binding experiments were used to characterize [ 3 H]‐JNJ 63514230 properties. We have also tested utility of [ 3 H]‐JNJ 63514230 as a tracer for ex‐vivo autoradiography in rat brain. Results We confirmed that widely used tracers [3H] Ifenprodil and [3H] Ro 25‐6981 have substantial affinity to sigma receptors as measured in radioligand competition experiments (CEREP). In contrast, new tracer [ 3 H] JNJ‐63514230 exhibits no affinity to sigma 1 and sigma 2 receptors in CEREP assays. Saturation binding in rat brain membranes yielded a K d value of 2.53 nM and B max of 2531 fmol/mg. Association constant K on , dissociation constant K off , and calculated equilibrium binding constant (K on /K off ) were 0.0067±0.001 min −1 nM‐1, 0.021±0.0002 min −1 , and 3.28±0.61 nM, respectively (average of 3 individual experiments each ± SD). Enhanced selectivity for GluN2B‐containing receptors translates to reduced non‐specific binding and better signal to noise ratio in both in vitro radioligand binding assays and ex vivo autoradiography. Conclusions We showed that new radioligand [ 3 H] JNJ 63514230 is superior to previous previously described GluN2B tracers as it permits accurate measurement of affinity to GluN2B‐containing receptors (K i ) without using additional blockers to mask native sigma receptors. Support or Funding Information Authors are full time employees of Janssen Research & Development, LLC. The research was funded by the company.