Antiproliferative actions of tamoxifen to human ovarian carcinomas in vitro.

The cytosolic estrogen receptor (ERc) and progestin receptor (PRc) levels were measured in 56 human epithelial ovarian tumors. The maximum ERc content in a tumor sample was 163 fmol/mg cytosolic protein. Forty-six of the tumor samples were evaluable for clonogenic growth in soft agar, and 19 samples produced 15 or more colonies per 10(5) cells plated. Four of the samples that grew had ERc levels of greater than 30 fmol/mg cytosolic protein. No correlation, however, between growth in soft agar and ERc or PRc content was observed. The antiproliferative properties of the antiestrogen, tamoxifen, were studied. Although no decrease in colony formation was observed after a 1-hr exposure to 0.2 or 2 microM tamoxifen, continuous exposure of cells to 2 microM tamoxifen reduced clonogenicity in 8 of 18 solid ovarian carcinomas examined. The maximum diminution in colony formation was approximately 50% of that of the control and was seen in 2 tumor samples. Both tumors that displayed the maximum response to continuous tamoxifen treatment had ERc and PRc levels greater than 30 fmol/mg cytosolic protein. None of the 14 tumors with ERc levels less than or equal to 30 fmol/mg cytosolic protein exhibited a decrease in colony formation of more than 50%. Exposure of cells for 1 hr to the combination of doxorubicin and tamoxifen produced a significant antagonism of the individual doxorubicin or tamoxifen antiproliferative effects in 7 of 9 samples examined. These data suggest that in a subset of human ovarian epithelial carcinomas tamoxifen alone can have some direct antiproliferative action on the clonogenic cells. The maximum antiproliferative effect of tamoxifen observed was related to ERc content in ovarian tumors.