Inhibition of estrogen stimulated mitogenesis by 3-phenylacetylamino-2,6-piperidinedione and its Para-hydroxy analog

Abstract 3-Phenylactetylamino-2,6-piperidinedione (A10) inhibited estradiol stimulated cell growth in the MCF-7 (E3) human breast tumor cell line in vivo and in vitro . While high concentrations of A10 were needed to inhibit cell proliferation (IC 50 = 3 × 10 −3 M in vitro ), the compound demonstrated little toxicity. The effect appeared specific since a hydrolysis product of A10, phenylacetylglutamine, demonstrated no growth inhibitory activity at similar concentrations in MCF-7 (E3) cells in vitro . A computer designed analog, p -hydroxy A10, was more potent than A10 in inhibiting activity in MCF-7 (E3) cells in vitro . The IC 50 for p -hydroxy A10 was 7 × 10 −6 M which was comparable to that of the antiestrogen, tamoxifen (IC 50 1 × 10 −7 M). All three compounds caused a decline in estrogen receptor levels in a dose-dependent fashion. A10 also inhibited estradiol induction of progesterone receptors. Examination of protein kinase activity following an acute exposure to a 10 −11 M growth stimulatory dose of estradiol revealed a 168% increase in protein kinase activity over that of untreated control cells. A10 in a dose-responsive fashion inhibited the estradiol stimulated increase in protein kinase activity. The protein kinase activity was also inhibited by p -hydroxy A10. These activities of A10 and p -hydroxy A10 coupled with the low toxicity and novelty of the basic A10 structure provide an exciting possibility of developing a new class of clinically useful antineoplastic drugs with minimal side effects.