Inhibition of Hamster Melanoma Growth by Estrogen1

A malignant hamster melanoma cell line Il.M-l derived from the heterogenous malignant hamster melanoma MMI contains a specific, high affinity binding protein for estrogens. Partial purification of the binding protein with ammonium sulfate (40% saturation) increased mean binding content (3.1 ±1.2 (SD) fmol/mg protein) 15-fold without any change in affinity (IO10M~'). The binding protein sedimented at 8-9S on 10-30% low salt sucrose gradients and 9-10S in the presence of 20 HIMmolybdate ion. Addition of 0.4 M KC1shifted the SS peak to 4S. Binding was specific, saturable, and indicative of a single class of high affinity sites over a concentration range of 0.01-10.0 UM[3H]estradiol. Estradiol produced a dose related inhibition of 11M-I growth in vitro without altering the growth of an additional line (HM-2) which did not bind estrogen. The antiestrogen tamoxifen (Id"1 M) also significantly inhibited IIM-1 melanoma growth in vitro, which was reversed by the addition of estradici (IO"9 M). IIM1 xenografts grew faster in female BALB/c-nu/nu mice than male mice while there was no sex difference in HM-2 growth. Pharmacological doses of estradici and the antiestrogen nafoxidine significantly inhibited HM-1 growth without altering tumor incidence or latency. Our observations suggest that HM-1 cell lines bind estrogens specifi cally and with high affinity and that hamster melanoma cells positive for this binding protein respond to estrogen.