Quantitative analysis of gene regulation by seven clinically relevant progestins suggests a highly similar mechanism of action through progesterone receptors in T47D breast cancer cells.

Progesterone (P4) is an essential reproductive steroid hormone required for many aspects of female reproductive physiology. Progestins are compounds that demonstrate progesterone-like activity and are used in oral contraception, hormone therapy, and treatment of some reproductive disorders, but differ widely in their chemical structures, potency, and pharmacokinetics. While numerous studies have assessed progestins on specific endpoints, little is known about the activation of global gene expression by progestins. We used Affymetrix GeneChip U133A expression arrays to examine the action of P4 and six clinically relevant synthetic progestins (3-ketodesogestrel, drospirenone, levonorgestrel, medroxyprogesterone acetate, norethindrone acetate, and trimegestone) on the progesterone receptor (PR)-positive T47Dco and the PR-negative T47D-Y breast cancer cell lines. Excluding drospirenone, one or more of the progestins-regulated 329 genes, with 30 genes regulated by at least 2.0-fold by all progestins in the T47Dco cells. The synthetic progestins show a high degree of similarity in their transcriptional responses, and each progestin regulates between 77 and 91% of the genes regulated by P4. Independent quantitative RT-PCR analysis confirmed a similar regulation for S100P, PPL, IL20RA, NET1, ATP1A1, HIG2, and CXCL12 (SDF-1) by all seven progestins. Attempts to find differentially regulated genes by any progestin compared to all other treatments failed, suggesting any differences are quantitative, not qualitative. This analysis demonstrates a high degree of similarity among these progestins on PR-regulated gene expression in T47D cells, suggesting a similar and fairly specific mode of action.

The progestational and androgenic properties of medroxyprogesterone acetate: gene regulatory overlap with dihydrotestosterone in breast cancer cells.

INTRODUCTION: Medroxyprogesterone acetate (MPA), the major progestin used for oral contraception and hormone replacement therapy, has been implicated in increased breast cancer risk. Is this risk due to its progestational or androgenic properties? To address this, we assessed the transcriptional effects of MPA as compared with those of progesterone and dihydrotestosterone (DHT) in human breast cancer cells. METHOD: A new progesterone receptor-negative, androgen receptor-positive human breast cancer cell line, designated Y-AR, was engineered and characterized. Transcription assays using a synthetic promoter/reporter construct, as well as endogenous gene expression profiling comparing progesterone, MPA and DHT, were performed in cells either lacking or containing progesterone receptor and/or androgen receptor. RESULTS: In progesterone receptor-positive cells, MPA was found to be an effective progestin through both progesterone receptor isoforms in transient transcription assays. Interestingly, DHT signaled through progesterone receptor type B. Expression profiling of endogenous progesterone receptor-regulated genes comparing progesterone and MPA suggested that although MPA may be a somewhat more potent progestin than progesterone, it is qualitatively similar to progesterone. To address effects of MPA through androgen receptor, expression profiling was performed comparing progesterone, MPA and DHT using Y-AR cells. These studies showed extensive gene regulatory overlap between DHT and MPA through androgen receptor and none with progesterone. Interestingly, there was no difference between pharmacological MPA and physiological MPA, suggesting that high-dose therapeutic MPA may be superfluous. CONCLUSION: Our comparison of the gene regulatory profiles of MPA and progesterone suggests that, for physiologic hormone replacement therapy, the actions of MPA do not mimic those of endogenous progesterone alone. Clinically, the complex pharmacology of MPA not only influences its side-effect profile; but it is also possible that the increased breast cancer risk and/or the therapeutic efficacy of MPA in cancer treatment is in part mediated by androgen receptor.