Cell experiment:

ACAT activity is determined in CaCo-2 cells. Cells cultured in 6-well plates are preincubated for 2 hr in 2 mL of Medium 199 supplemented with 10 mM Hepes, pH 7.4, and cholesterol-rich micelles in the presence or absence of RP-64477 that has been initially prepared in neat DMSO. The final concentration of DMSO in the culture medium is 0.2% v/v. Preincubation medium is then replaced with the same medium containing 50 μM [14C] oleic acid complexed with 17 μM bovine serum albumin (fatty acid-free) and cells incubated for a further 2 hr. RP-64477 or vehicle is present during both incubations[1].

Animal experiment:

Hypocholesterolaemic activity of RP-64477 is investigated by administering RP-64477 (0.00l% to 0.03% w/w by diet) to rats maintained for 3 days on powdered laboratory diet supplemented with cholesterol/cholic acid. Animals are then killed by asphyxiation in carbon dioxide, and terminal blood samples taken by cardiac puncture into a heparinised syringe for preparation of plasma. Plasma cholesterol concentrations are determined enzymatically using standard assay kits. Hypocholesterolaemic activity of RP-64477 in rabbits is investigated by administering RP-64477 at doses of 1, 3, 10, and 30 mg/kg b.i.d. for 7 days to animals receiving standard laboratory diet supplemented with cholesterol. Blood samples are obtained from the central ear artery on days 0 (predosing), 4, and 7 of the study[1].

RP-64477 is a potent inhibitor of the cholesterol esterifying enzyme Acyl-coenzyme A:cholesterol O-acyltransferase (ACAT).

RP-64477 is a potent inhibitor of the cholesterol esterifying enzyme Acyl-coenzyme A:cholesterol O-acyltransferase (ACAT). Inhibitory potencies of RP-64477 in vitro in tissue preparations are obtained from a range of species and in human cell cultures. For animal tissues, IC50 values in the range 6 to 283 nM are recorded, with no obvious species/tissue differences apparent. Potent inhibitory activity of RP-64477 is also recorded in human cell lines of hepatic (HepGZ), intestinal (CaCo-2), and monocytic (THP-1) origin with IC50s of 503, 113, and 180 nM, respectively. No inhibitory activity is recorded against rat PCEH or LCAT at test concentrations up to 200 μM and 20 μM, respectively[1].

Administration of RP-64477 (0.01% and 0.03% w/w by diet) reduces significantly plasma cholesterol levels in cholesterol/cholic acid-fed rats by 29% and 61%, respectively. Food consumption is not affected by dietary incorporation of RP-64477. Animals receiving RP-64477 (10 and 30 mg/kg b.i.d.) over this period exhibit significantly lower plasma cholesterol levels on both days 4 and 7 when compare to values recorded from vehicle treated animals fed the cholesterol-containing diet. Compare to cholesterol-fed controls, after 7 days of dosing, plasma cholesterol levels are 35% and 53% lower in animals receiving 10 and 30 mg/kg b.i.d. doses of RP-64477, respectively[1].

[1]. Bello AA, et al. RP 64477: a potent inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase with low systemic bioavailability. Biochem Pharmacol. 1996 Feb 23;51(4):413-21.