Transforming Growth Factor- Its Relation to Reduction of Estrogen Receptor and Conjugate (KM2210) in Human Breast Cancer Cell Line MCF-7: Growth-inhibitory Action of an Estrogen-Chlorambucil

We investigated the effects of a benzoate of an estradiol-chlorambucil conjugate (KM2210) and chlorambucil on growth, estrogen receptor, and secretion of transforming growth factor (TGF)-a in the hormone-depend ent human breast cancer cell line MCF-7. In the presence of 10"'°-10~' M KM2210, the estrogen-induced growth of MCF-7 was completely inhibited. Inhibited growth of MCF-7 treated with 10"" or 10"* M KM2210 for 4 days was not rescued by removal of the drug and the addition of estradiol. By treatment of MCF-7 with KM2210 for 4 days, estrogen receptor-binding sites were decreased at 1(1* M and were not detected at 10~*Mbut were unaltered by IO"8Mchlorambucil. Moreover, estrogen receptor immunoreactivity and the level of estrogen receptor niKN'A were decreased through treatment with II)"" M KM2210 for 4 days. These suppressions occurred prior to the onset of inhibitory action on MCF-7 growth. Secretion of TGF-a from MCF-7 was decreased by 4 days of treatment with 10"* and 10"* M KM2210 but not with chloram bucil. The addition of exogenous TGF-a generally restored the growth of MCF-7 treated with IO"8 M KM2210. We concluded that KM2210 has irreversible or at least long-standing inhibitory effect on estrogen-dependent growth of MCF-7. It is conceiv able that the decrease of estrogen receptor renders the cell unable to respond to estrogen with increased TGF-a secretion and succeeding cell growth.