The effect of anti-oestrogens on cell growth and progesterone receptor concentration in human endometrial cancer cells (Ishikawa)

The effect of two anti-oestrogens, 4-OH tamoxifen and ICI 164,384, on growth and progesterone receptor (PR) concentration was investigated in the endometrial carcinoma cell line, Ishikawa. Growth stimulation in response to 4-OH tamoxifen was antagonized by ICI 164,384, the latter having no agonist effect when used as a single agent. Similarly, ICI 164,384 antagonized oestradiol-stimulated cell growth. PR was significantly increased following treatment with 4-OH tamoxifen, this response being antagonized in the presence of ICI 164,384. Oestradiol increased PR, although to a lesser extent than did 4-OH tamoxifen; the effect of oestradiol on PR was also antagonized by ICI 164,384. Used as a single agent, ICI 164,384 induced a moderate but statistically significant increase in PR, thus demonstrating partial agonist activity. This agonist property of ICI 164,384 may provide a mechanism of maintaining PR, which is down-regulated during conventional progestin therapy, without undesirable mitogenic activity.