M. Sato et al., LY353381.HCL - A NOVEL RALOXIFENE ANALOG WITH IMPROVED SERM POTENCY AND EFFICACY IN-VIVO, The Journal of pharmacology and experimental therapeutics, 287(1), 1998, pp. 1-7
Body weight, uteri, serum cholesterol and bones were shown previously
in vivo to be sensitive to circulating levels of estrogen, as well as
to synthetic, nonsteroidal ligands termed selective estrogen receptor
modulators(SERM). In this study, we examined the in vivo effects of a
new potent SERM on these tissues in 6-month-old, ovariectomized rats t
hat were orally dosed with 0.0001-10 mg/kg/day LY353381.HCl for 5 week
s. LY353381.HCl prevented the ovariectomy-induced increase in body wei
ght and serum cholesterol levels of treated rats and lowered them to b
elow sham levels in a dose dependent manner, with maximum efficacy sim
ilar to estrogen or raloxifene. However, LY353381.HCl was consistently
more potent than raloxifene, with a half maximal efficacious dose of
0.001 mg/kg for the reduction of body weight and cholesterol. In the u
terus, LY353381.HCl had marginal effects on uterine weight compared to
ovariectomized controls (OVX) like raloxifene, but unlike estrogen. H
istological examination of uterine epithelial cell height showed littl
e to no stimulatory effect of LY353381.HCl on the endometrium. Quantit
ative computed tomographic analyses (pQCT) of tibiae showed that LY353
381.HCl prevented loss of bone due to ovariectomy with an ED50 of abou
t 0.01 mg/kg with maximal efficacy observed at 0.1-1 mg/kg/day. Maxima
lly attainable bone mineral density and content with LY353381.HCl were
not significantly different from Sham or ovariectomized rats treated
with estrogen or raloxifene. Interestingly, assessment of bone quality
by biomechanical analyses showed that LY353381.HCl preserved the stre
ngth of the femora neck and midshaft, while improving the Young's modu
lus of cortical bone to beyond estrogen, raloxifene or sham levels. In
uteri of immature rats treated with estrogen, LY353381.HCl antagonize
d the estrogen-induced elevation in uterine weight down to vehicle-dos
ed control levels with ED50 of 0.03 mg/kg/day. Therefore, LY353381.HCl
was 30-100 times more potent than raloxifene in preventing ovariectom
y effects on body weight, serum cholesterol and bone, while maintainin
g estrogen antagonist effects on the uterus. These animal data suggest
that LY353381.HCl may have advantages over estrogen or raloxifene in
the prevention of bone loss and treatment of other, tissues in postmen
opausal women.