EXP3174, A METABOLITE OF LOSARTAN (MK-954, DUP-753) IS MORE POTENT THAN LOSARTAN IN BLOCKING THE ANGIOTENSIN-II-INDUCED RESPONSES IN VASCULAR SMOOTH-MUSCLE CELLS

Objective: EXP3174 is a metabolite of losartan (previous name DuP753), which is a non-peptide angiotensin II receptor antagonist. Design: The inhibitory potency of these two antagonists on the angiotensin II-induced responses in vascular smooth muscle cells (VSMC) was investigated. Methods: The effect of angiotensin II on cell growth was determined by [H-3]-thymidine incorporation into cell DNA and by cellular protein measurements. Intracellular cytosolic Ca2+ concentration was measured by the fura-2 method. Inositolphosphates were determined by high-performance liquid chromatography after cell labelling with myo-[2-H-3]-inositol. The early growth response gene-1 (Egr-1) messenger RNA (mRNA) expression was determined by the Northern blotting method. Binding and displacement studies of the antagonists were performed using [I-125]-angiotensin II. Results: An apparent dissociation constant (K(d)) Of 5.9 nmol/I for [I-125]-angiotensin II (maximal binding coefficient 69 fmol/10(6) cells) was found. The specific binding of [I-125]-angiotensin II to VSMC was inhibited by losartan, EXP3174 and saralasin with a half-maximal inhibitory concentration (IC50) of 1.0 x 10(-8), 1.1 x 10(-9) and 1.8 x 10(-9) mol/l, respectively. EXP3174 and losartan abolished the angiotensin II-induced formation of inositolphosphates in VSMC. EXP3174 and losartan inhibited the angiotensin II-induced elevation of intracellular cytosolic Ca2+ concentration with an IC50 of 5 x 10(-9) and 5 x 10(-8) mol/l, respectively. EXP3174 was more effective than losartan in blocking the angiotensin II-induced increase in Egr-1 mRNA. EXP3174 and losartan inhibited the angiotensin II-induced cell protein synthesis with an IC50 of 3 x 10(-9) and 4 x 10(-8) mol/l, respectively. Conclusions: These results indicate that EXP3174 is significantly more potent than losartan in blocking angiotensin II-induced cellular responses.