Nuclear type II sites and malignant cell proliferation: inhibition by 2,6-bis-benzylidenecyclohexanones.
Methyl-p-hydroxyphenyllactate (MeHPLA) is a bioflavonoid and/or tyrosine metabolite which may regulate cellular growth and proliferation through interactions with nuclear type II sites. Our current studies suggest that type II sites may function as MeHPLA receptors which are localized on the nuclear matrix, and occupancy of this binding site by MeHPLA directly correlates with the inhibition of normal and malignant cell proliferation. This ligand is inactivated by MeHPLA esterase in mammary tumors, resulting in a deficiency in MeHPLA, high quantities of unoccupied type II sites, and uncontrolled cellular proliferation. For these reasons we synthesized 2,6-bis((3,4-dihydroxyphenyl)methylene)-cyclohexanone (BDHPC) and 2,6-bis((3-methoxy-4-hydroxyphenyl)-methylene)cyclohexanone (BMHPC) for assessment as nuclear type II site and cell growth antagonists. These two esterase stable cyclohexanone derivatives, which bind to nuclear type II sites with high affinity (Kd 1-7 nM), mimic MeHPLA as cell growth-regulating agents. Dose-dependent occupancy of type II sites in MCF-7 human cells by BDHPC and BMHPC directly correlated with the inhibition of cell proliferation, and administration of BDHPC by silastic implant inhibited mouse mammary tumor growth in vivo. These findings demonstrate that esterase-stable type II antagonists such as BDHPC and BMHPC inhibit mammary cancer cell proliferation in vitro and in vivo and support earlier studies demonstrating that MeHPLA and functionally related compounds may regulate malignant cell proliferation at the level of this binding site.