title: The antitumor mechanism of progesterone antagonists is a receptor mediated antiproliferative effect by induction of terminal cell death.
abstract: The antiprogesterones Onapristone, ZK 112.993 (Schering AG), and Mifepristone (Roussel-Uclaf) proved to possess progesterone receptor-mediated antiproliferative effects in experimental mammary carcinomas. In this study, the potency and mechanism of the antitumor action of Onapristone and ZK 112.993 is characterized by ovariectomized, progestagen and/or estradiol substituted mice bearing hormone-dependent MXT(+) mammary tumours. Medroxyprogesterone acetate (MPA, 0.8 mg/mouse, 3 times weekly, s.c.) could only induce a poor stimulation of tumour growth (% T/C = 40; intact control % T/C = 100), which was only marginally inhibited (% T/C = 21) by Onapristone (0.2 mg/mouse, 6 times weekly, s.c.) during a 6-week therapy. Therefore, the antitumor mechanism of antiprogesterones cannot preferably depend on a classical progesterone antagonism. In contrary, the pronounced stimulation of tumor growth (% T/C = 152) by estradiol benzoate (EB, 0.33 microgram/mouse, 3 times weekly, s.c.) was completely inhibited (% T/C = 7) by the antiprogesterones. An even more stimulated tumour growth was achieved by a combination of EB and MPA (% T/C = 365 using 0.17 mg; % T/C = 225 using 0.8 mg MPA). Onapristone dramatically blocked tumor growth (% T/C = 7) at the lower dose of MPA; no inhibition (% T/C = 203), however, was detected at the higher dose of MPA. These data and a morphological analysis indicate that the potent antitumor activity of the progesterone antagonists depends on the binding to a number of available progesterone receptors high enough to trigger an antiproliferative effect via the induction of terminal differentiation associated with terminal cell death.
authors.affiliation: Research Laboratories of Schering AG, Berlin, F.R.G.
authors.forename: H
authors.initials: H
authors.lastname: Michna
authors.forename: M R
authors.initials: MR
authors.lastname: Schneider
authors.forename: Y
authors.initials: Y
authors.lastname: Nishino
authors.forename: M F
authors.initials: MF
authors.lastname: el Etreby
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects*; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006067:Gonanes / Q000627:therapeutic use*; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D008815:Mice, Inbred Strains; D015735:Mifepristone / Q000031:analogs & derivatives* / Q000627:therapeutic use*; D010052:Ovariectomy; D011374:Progesterone / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects*
chemical_list: D000970:Antineoplastic Agents; D006067:Gonanes; C064879:ZK 112993; D015735:Mifepristone; D011374:Progesterone; D004958:Estradiol; C053238:onapristone