Abstract 3471: Comparative assessment of in vitro activity and aactivated progesterone receptor (APR) biomarker predictivity for multiple antiprogestins

Abstract

Abstract Background: In absence of ligand, PRA and PRB are evenly distributed in nuclei in cell lines. Upon ligand binding, PRA and PRB dimerizes and form discrete focal subnuclear distribution patterns, which are associated with transcriptional activation of PR. This pattern corresponds to the transcriptionally active form of PR and serves as an APR biomarker. The expression of APR in cell lines was demonstrated to be predictive of onapristone antiproliferative effects (Serin, Abs # 473, NCI-AACR-EORTC 2012). In this study the correlation of APR to the antiproliferative effects of different antiprogestins (Type I & type II, and steroidal/non-steroidal chemical structures) is examined. Method: T47D and CAMA-1, two PR expressing breast cancer cell lines, were grown in either FBS or Steroid Free FBS (SFFBS). In FBS, single agent anti-progestins were studied; in SFFBS, cell lines were stimulated with estradiol (E2) or progesterone (P4) and antiprogestins tested. All experiments were performed in duplicate. APR was analyzed at 6h and 30h using paraffin embedded cellular pellets, and processed with standard IHC techniques. Cellular viability was measured by the MTS assay at 30h, 4d and 7d. Antiprogestin drugs tested included: Aglepristone, Mifepristone, Onapristone, PF02413873, ZK230211, and ZM150271. Results: In the T47D cell line, in FBS between zero and ∼ 40% antiproliferative activity was observed from D1 to D7 for all antiprogestins. In SFFBS, T47D proliferation at D7 was increased >300% by E2 and >200% by P4. All antiprogestins opposed P4 and E2 proliferative effects at D7, with a max of 80% inhibition relative to control. In the CAMA-1 cell line, in FBS weak antiprogestin antiproliferative effect was observed (<20% inhibition); with SFFBS, P4 and E2 were weakly stimulatory and antiprogestins had an inconsistent and weak treatment effect. The effect of antiprogestins were not dose dependent. APR: in T47D and FBS, APR was observed at 6h consistently for PR A and PR B. At 30h, controls were APR positive, and with Aglepristone, Mifepristone and Onapristone treatment, the surviving cells were APR neg; PF02413873, ZK230211and ZM150271 APR effect was inconsistent. Specimens from SFFBS are under evaluation. For CAMA-1, in FBS PRA and PRB were weakly expressed i.e. in 5% of the cells; APR was always negative. Specimens from SFFBS are under evaluation. Conclusion: The cell line expressing APR, T47D, is sensitive to direct antiprogestins effect in FBS, to E2 and P4 growth stimulation in SFFBS. In T47D, there was an antagonism by all antiprogestins at D7 and APR status was reversed at 30 h completely in 3/6 cases and incompletely in 3/6. CAMA-1 does not express APR, is weakly stimulated by E2 and P4, and antiprogestins have inconsistent effects in this cell line. APR status is a predictor of antiprogestin action. Citation Format: Alexander Zukiwski, Erard Gilles, Guillaume Serin, Jacques Bosq, Charline Alleaume. Comparative assessment of in vitro activity and aactivated progesterone receptor (APR) biomarker predictivity for multiple antiprogestins. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3471. doi:10.1158/1538-7445.AM2015-3471