We have discovered that p-hydroxyphenyllactic acid (HPLA) and methyl p-hydroxyphenyllactate (MeHPLA) are endogenous ligands for nuclear type II sites. MeHPLA appears to be the most important of these two compounds because it binds to type II sites with a high affinity (Kd, nM) and will inhibit normal (rat uterus) and malignant (MCF-7 cells) cell growth. HPLA does not bind to type II sites with a high binding affinity (Kd, mu M), nor does it inhibit cell proliferation. These results suggest MeHPLA may regulate normal and malignant cell growth via a direct binding interaction with nuclear type II sites, however other mechanisms are possible.
The specific aims of this proposal are to study the effects of MeHPLA and synthetic analogues on normal (rat uterus) and malignant (MCF-7; T47-D; MDA-468) cell growth in vivo and in vitro and assess these compounds as potential anti-tumor agents. In addition, the metabolic fate of (3H)-MeHPLA will be studied in these normal and malignant cells to determine why tumors are deficient in this compound (1,2). If we suspect, MeHPLA may be """"""""inactivated"""""""" to HPLA by esterases in malignant cells, analogues of MeHPLA which are not inactivated in this manner may be very effective cell growth inhibiting agents. Since MeHPLA is the endogenous ligand for nuclear type II sites, we will also develop (3H)-MeHPLA exchange assays, to study this binding interaction, and these data will be correlated with MeHPLA effects (inhibition) on normal and malignant cell growth in vivo and in vitro. (3H)- MeHPLA uptake, retention, and compartmentalization (cytosol, microsomes, mitochondria, nuclei) will also be studied in a variety of normal and malignant tissues in vivo and in vitro. This broad approach will allow us to define potential sites of cell growth regulation by MeHPLA, and intracellular mechanisms which may affect the """"""""availability"""""""" and activity of MeHPLA as a cell growth regulating agent. These baseline studies should facilitate more definitive studies regarding the specific mechanism(s) by which MeHPLA regulates normal and malignant cell hypertrophy and hyperplasia.
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