Palosuran inhibits binding to primate UT receptors in cell membranes but demonstrates differential activity in intact cells and vascular tissues.
OBJECTIVE
The recent development of the UT ligand palosuran (1-[2-(4-benzyl-4-hydroxy-piperidin-1-yl)-ethyl]-3-(2-methyl-quinolin-4-yl)-urea sulphate salt) has led to the proposition that urotensin-II (U-II) plays a significant pathological role in acute and chronic renal injury in the rat.


METHODS
In the present study, the pharmacological properties of palosuran were investigated further using a series of radioligand binding and functional bioassays.


RESULTS
Palosuran functioned as a 'primate-selective' UT ligand in recombinant cell membranes (monkey and human UT K(i) values of 4 +/- 1 and 5 +/- 1 nM), lacking appreciable affinity at other mammalian UT isoforms (rodent and feline K(i) values >1 microM). Paradoxically, however, palosuran lost significant (10- to 54-fold) affinity for native and recombinant human UT when radioligand binding was performed in intact cells (K(i) values of 50 +/- 3 and 276 +/- 67 nM). In accordance, palosuran also exhibited diminished activity in hUT (human urotensin-II receptor)-CHO (Chinese hamster ovary) cells (IC50 323 +/- 67 nM) and isolated arteries (K(b)>10 microM in rat aorta; K(b)>8.5 microM in cat arteries; K(b)>1.6 microM in monkey arteries; K(b) 2.2 +/- 0.6 microM in hUT transgenic mouse aorta). Relative to recombinant binding K(i) values, palosuran was subjected to a 392- to 690-fold reduction in functional activity in monkey isolated arteries. Such phenomena were peculiar to palosuran and were not apparent with an alternative chemotype, SB-657510 (2-bromo-N-[4-chloro-3-((R)-1-methyl-pyrrolidin-3-yloxy)-phenyl]-4,5-dimethoxybenzenesulphonamide HCl).


CONCLUSIONS
Collectively, such findings suggest that caution should be taken when interpreting data generated using palosuran. The loss of UT affinity/activity observed in intact cells and tissues cf. membranes offers a potential explanation for the disappointing clinical efficacy reported with palosuran in diabetic nephropathy patients. As such, the (patho)physiological significance of U-II in diabetic renal dysfunction remains uncertain.
Behm
D J
DJ
Department of Cardiovascular Pharmacology, GlaxoSmithKline, Metabolic Pathways Center of Excellence for Drug Discovery, King of Prussia, PA 19406-0939, USA. david.j.behm@gsk.com
McAtee
J J
JJ
Dodson
J W
JW
Neeb
M J
MJ
Fries
H E
HE
Evans
C A
CA
Hernandez
R R
RR
Hoffman
K D
KD
Harrison
S M
SM
Lai
J M
JM
Wu
C
C
Aiyar
N V
NV
Ohlstein
E H
EH
Douglas
S A
SA
D000818:Animals; D016466:CHO Cells; D002415:Cats; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D020128:Inhibitory Concentration 50; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D011804:Quinolines / Q000008:administration & dosage / Q000494:pharmacology*; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects* / Q000378:metabolism; D013045:Species Specificity; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D014579:Urotensins / Q000187:drug effects* / Q000378:metabolism
D011804:Quinolines; D043562:Receptors, G-Protein-Coupled; C121697:UTS2R protein, human; D014579:Urotensins; D014508:Urea; C029677:urotensin II; C493249:1-(2-(4-benzyl-4-hydroxypiperidin-1-yl)ethyl)-3-(2-methylquinolin-4-yl)urea