Journal Article TASP0434299: A novel pyridopyrimidin-4-one derivative as a radioligand for vasopressin V1B receptor

Koga, Kazumi  ,  Yoshinaga, Mitsukane  ,  Uematsu, Yoshikatsu  ,  Nagai, Yuji  ,  Miyakoshi, Naoki  ,  Shimoda, Yoko  ,  Fujinaga, Masayuki  ,  Minamimoto, Takafumi  ,  Ming-Rong, Zhang  ,  Higuchi, Makoto  ,  Ohtake, Norikazu  ,  Suhara, Tetsuya  ,  Chaki, Shigeyuki

357 ( 3 )  , pp.495 - 508 , 2016-03 , The American Society for Pharmacology and Experimental Therapeutics
A novel pyridopyrimidin-4-one derivative, N-tert-butyl-2-[2-(3-methoxyphenyl)-6-[3-(morpholin-4-yl)propoxy]-4-oxopyrido[2,3-d]pyrimidin-3(4H)-yl]acetamide (TASP0434299), was characterized as a radioligand candidate for arginine vasopressin receptor 1B (V1B receptor). TASP0434299 exhibited high binding affinities for human and rat V1B receptors with IC50 values of 0.526 and 0.641 nM, respectively, and a potent antagonistic activity at human V1B receptor with an IC50 value of 0.639 nM without apparent binding affinities for other molecules at 1 μM. [3H]TASP0434299 bound to membranes expressing human V1B receptor as well as those prepared from the rat anterior pituitary in a saturable manner. The binding of [3H]TASP0434299 to the membranes was dose-dependently displaced by several ligands for V1B receptor. In addition, the intravenous administration of [3H]TASP0434299 to rats produced a saturable radioactive accumulation in the anterior pituitary where V1B receptor is enriched, and it was dose-dependently blocked by the oral administration of 2-[2-(3-chloro-4-fluorophenyl)-6-[3-(morpholin-4-yl)propoxy]-4-oxopyrido[2,3-d]pyrimidin-3(4H)-yl]-N-isopropylacetamide hydrochloride (TASP0390325), a V1B receptor antagonist, indicating that [3H]TASP0434299 can be used as an in vivo radiotracer to measure the occupancy of V1B receptor. Finally, the intravenous administration of [11C]TASP0434299 provided positron emission tomographic images of V1B receptor in the pituitary in an anesthetized monkey, and the signal was blocked by pretreatment with an excess of unlabeled TASP0434299. These results indicate that radiolabeled TASP0434299 is the first radioligand to be capable of quantifying V1B receptor selectively in both in vitro and in vivo studies and will provide clinical biomarker for determining the occupancy of V1B receptor during drug development or for monitoring the levels of V1B receptor in diseased conditions.

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