A number of studies from our laboratory and others have shown that synthetic and naturally occurring
bioflavonoids and related compounds have significant antiproliferative activity in the rat uterus and mouse mammary
tumor model systems. This cell regulatory activity is attributed to the fact these compounds mimic
methyl p-hydroxyphenyllactate (
MeHPLA) as
ligands for nuclear type II [3H]
estradiol binding sites. The rodent prostate is also an
estrogen target tissue which contains type II sites (1,2). Therefore, we assessed the effects of 2,6-bis((3-methoxy-4-hydroxyphenyl)-methylene)-cyclohexanone (
BMHPC) on normal and malignant prostatic cell growth and proliferation in vitro and in vivo. This
cyclovalone is designed to bind to type II sites with high affinity and mimic
MeHPLA as a cell growth antagonist.
Oral administration of
BMHPC (9.5-38.0 mg/kg
body weight per day) to intact adult male Balb/c mice for 14 days resulted in a dose dependent reduction (P<0.01) in prostatic weight relative to controls. No significant treatment effects of
BMHPC on seminal vesicular, testicular or
body weights were observed.
BMHPC also competed for [3H]
estradiol binding to type II sites in LNCaP and PC-3 human
prostatic cancer cell lines and this
ligand inhibited the proliferation of these cells in a dose and time dependent fashion. A direct correlation between type II site occupancy by
BMHPC and the inhibition of LNCaP or PC-3 cell proliferation was observed which was reversible (not shown) following removal of
BMHPC from the medium. Flow cytometry studies revealed that the type II site antagonist significantly reduced (p<0.01-p<0.001) the numbers of LNCaP and PC-3 cells in G0/G1 and caused an accumulation (p<0.001) of these cells in S-phase and G2/M (p<0.01). These data suggest that
BMHPC blocks mitosis. This is consistent with the observed
cytostatic activity of
BMHPC in a variety of model systems.
Oral administration of
BMHPC to nude mice bearing subcutaneous PC-3 cell xenografts impeded the growth of these solid
tumors in vivo without significant signs of toxicity. These findings demonstrate that
BMHPC possesses significant anti-proliferative activity in normal and malignant prostatic tissues and cells, and extend our hypothesis that
MeHPLA regulation of cellular proliferation via type II binding site interactions is an important pathway involved in cell growth regulation.