FUNCTIONAL-CHARACTERIZATION OF THE NONPEPTIDE NEUROKININ3 (NK3) RECEPTOR ANTAGONIST, SR142801 ON THE HUMAN NK3 RECEPTOR EXPRESSED IN CHINESE-HAMSTER OVARY CELLS

The effects of SR142801, a nonpeptide tachykinin neurokinin (NK3) rece ptor antagonist, were investigated on the functional events linked to NK3 receptor activation by using Chinese hamster ovary (CHO) cells tra nsfected with the human NK3 receptor. Radioligand binding conducted wi th [I-125]iodohistidyl-[MePhe(7)]-NKB revealed a competitive inhibitio n by SR142801 and its (-)-antipode 8R142806 with K-i values of 0.21 +/ - 0.03 and 32.0 +/- 5.0 nM, respectively. NK3 agonists such as [MePhe( 7)]-NKB and senktide stimulated inositol monophosphate formation with EC(50) values of 2.0 +/- 1.4 and 2.1 +/- 0.7 nM, respectively. SR14280 1 antagonized the stimulatory effect of [MePhe(7)]-NKB (10(-8) M) With an IC50 of 14.3 +/- 2.6 nM and of senktide (10(-8) M) with an IC50 of 4.8 +/- 1.5 nM. The [H-3]arachidonic acid release induced by either [ MePhe(7)]-NKB (EC(50) of 2.6 +/- 0.2 nM) or senktide (EC(50) of 4.2 +/ - 2.9 nM) also was inhibited by SR142801 with IC50 values of 16.1 +/- 0.5 and 8.0 +/- 1.7 nM, respectively. The cyclic AMP accumulation indu ced by 10(-7) M [MePhe(7)]-NKB (EC(50) of 54 +/- 2 nM) also was antago nized by SRI42801 with an IC50 value of 4.0 +/- 0.7 nM. These antagoni stic effects were stereospecific and NK3 receptor specific because the (-)-antipode, SR142806, was much less effective than SR142801 in NK3 agonist-evoked responses, whereas the nonpeptide NK1 (SR140333) and NK 2 (8R48968) receptor antagonists were almost inactive, The activity of SR142801 also was evaluated on the [Ca++](i) increase induced by 10(- 9) M [MePhe(7)]-NKB, At concentrations higher than 10(-8) M, SR142801 antagonized intracellular Ca++ mobilization, total inhibition being ob tained at 10(-7) M. In conclusion, SR142801 is the first selective non peptide NK3 antagonist possessing a powerful antagonist activity on a human NK3 receptor model.