INHIBITION OF ESTROGEN-STIMULATED MITOGENESIS BY 3-PHENYLACETYLAMINO-2,6-PIPERIDINEDIONE AND ITS PARA-HYDROXY ANALOG

3-Phenylactetylamino-2,6-piperidinedione (A10) inhibited estradiol sti mulated 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 inh ibit cell proliferation (IC50 = 3 x 10(-3) M in vitro), the compound d emonstrated little toxicity. The effect appeared specific since a hydr olysis product of A10, phenylacetylglutamine, demonstrated no growth i nhibitory activity at similar concentrations in MCF-7 (E3) cells in vi tro. A computer designed analog, p-hydroxy A10, was more potent than A 10 in inhibiting activity in MCF-7 (E3) cells in vitro. The IC50 for p -hydroxy A10 was 7 x 10(6) M which was comparable to that of the antie strogen, tamoxifen (IC50 1 x 10(-7) M). All three compounds caused a d ecline in estrogen receptor levels in a dose-dependent fashion. A10 al so inhibited estradiol induction of progesterone receptors. Examinatio n of protein kinase activity following an acute exposure to a 10(-11) M growth stimulatory dose of estradiol revealed a 168% increase in pro tein kinase activity over that of untreated control cells. A10 in a do se-responsive fashion inhibited the estradiol stimulated increase in p rotein kinase activity. The protein kinase activity was also inhibited by p-hydroxy A10. These activities of A10 and p-hydroxy A10 coupled w ith the low toxicity and novelty of the basic A10 structure provide an exciting possibility of developing a new class of clinically useful a ntineoplastic drugs with minimal side effects.