Kej. Dickinson et al., BMS-180560, AN INSURMOUNTABLE INHIBITOR OF ANGIOTENSIN II-STIMULATED RESPONSES - COMPARISON WITH LOSARTAN AND EXP3174, British Journal of Pharmacology, 113(1), 1994, pp. 179-189
1 This study compares the activity of BMS-180560 utyl-4-chloro-1-[[1-[
2-(2H-tetrazol-5-yl)phenyl]-1 H-indol-4-yl]methyl]-1H-imidazole-5-carb
oxylic acid), an insurmountable angiotensin II (AII) receptor antagoni
st, with that of losartan and EXP3174 in functional and biochemical mo
dels of AII-receptor activation. 2 BMS-180560 selectively inhibited [I
-125]-Sar(1)Ile(8)AII ([I-125]SI-AII) binding to rat aortic smooth mus
cle (RASM) cell and rat adrenal cortical AT(1) receptors (K-i = 7.6 +/
- 1.2 and 18.4 +/- 3.9 nM respectively) compared to adrenal cortical A
T(2) receptors (K-i = 37.6 +/- 1.3 mu M). The K-i values of BMS-180560
and EXP3174, but not losartan, varied as a function of the BSA concen
tration used in the assays, indicating that the diacid drugs bound to
albumin. 3 BMS-180560 (3-300 nM) increased the K-D of SI-AII for RASM
cell AT(1) receptors. Only at high concentrations of BMS-180560 (300 n
M) were B-max values decreased. 4 BMS-180560 inhibited AII-stimulated
contraction of rabbit aorta with a calculated K-B = 0.068 +/- 0.048 nM
and decreased maximal AII-stimulated contraction at 1 nM BMS-180560 b
y 75%. In the presence of 0.1% BSA, a higher K-B value (5.2 +/- 0.92 n
M) was obtained. Losartan behaved as a competitive antagonist with a K
-B = 2.6 +/- 0.13 nM. Contraction stimulated by endothelin-1, noradren
aline, KCl, or the TXA(2) receptor agonist U-46619 were unaffected by
BMS-180560 (1 nM). 5 AII stimulated the acidification rates of RASM ce
lls as measured by a Cytosensor microphysiometer with an EC(50) of 18
nM. Losartan (30 nM) shifted the AII concentration-effect curves in a
competitive manner whereas BMS-180560 (0.01 and 0.1 nM) decreased the
maximum responses by 60 and 75% respectively. Inhibition by losartan a
nd BMS-180560 could be reversed following washout although recovery to
ok longer for BMS-180560. 6 In [H-3]-myoinositol-labelled RASM cells,
losartan (30 and 200 nM), shifted the EC(50)) for AII-stimulated [H-3]
-inositol monophosphate formation to higher values, with no change in
the maximal response. By contrast, EXP3174 (0.1 to 1 nM) decreased the
maximal response in a concentration-dependent manner (17-55%). BMS-18
0560 (3 and 10 nM) increased the EC(50) for AII and decreased the maxi
mum response by 30 and 80% respectively. The inhibition by EXP3174 and
BMS-180560 could be reversed by inclusion of losartan (200 nM) indica
ting that the inhibition was not irreversible. 7 In conclusion, BMS-18
0560 is a potent, specific, predominantly competitive, reversible AII
receptor antagonist, which displays insurmountable receptor antagonism
. At concentrations of BMS-180560 which have no effect on receptor num
ber, BMS-180560 produced insurmountable antagonism of AII-stimulated s
econd messenger formation, extracellular acidification, and smooth mus
cle contraction.