Abstract P6-07-09: Attenuation of progesterone driven mammary stem cell expansion by telapristone acetate

Abstract

Abstract Purpose: The interplay of the ovarian hormones estradiol (E2) and progesterone (P4) contributes to the development of breast cancer, potentially aided by P4-induced expansion in mammary stem cells as observed in diestrous phase in mice, as well as the luteal phase and during pregnancy in women. Telapristone Acetate (TPA), a selective progesterone receptor modulator (SPRM), exhibits a protective effect against mammary carcinogenesis in rodents. TPA has been shown to display a more specific PR blockade and less toxicity when compared to RU486. We have examined the mammary stem cell pool expansion upon exposure to E2+P4 in mice and compared its attenuation by both TPA and RU486. Methods: 8 week old female ovariectomized FVB mice weighing above 20g, were randomized into 4 treatment groups: sham (skin incision only, no pellets), E2+P4, E2+P4+Telapristone Acetate (TPA), E2P4+ Mifepristone (RU486). Eight experimental replicates were performed. At age 10 weeks, the mice were implanted with subcutaneous 30-day release pellets of E2 and P4 (0.3 mg E2 & 30.0 mg P4), E2P4+TPA (30.0 mg) and E2P4+RU486 (30.3 mg) in either flank. The mice were euthanized at day 15 of treatment. Single cell suspensions of the 4th inguinal mammary gland pair and one thoracic gland were prepared and labeled with cell surface markers. Lineage negative mammary gland cells were sorted into luminal and basal population subsets. The basal cell niche was identified as CD24+CD49fhi, the mammary stem cells (MaSC) within this niche are identified by CD61+CD49fhi. The cells were sorted on BD FACSAria 5-Laser and the data was analyzed using BD FACSDIVA.The D'Agostino-Pearson test was performed to determine the normal distribution and once normal distribution was confirmed one-way ANOVA (repeated measures) was performed to examine differences in percent cell populations with Tukey test for post-hoc analysis. Results: The mammary stem cells (MaSC, CD61+CD49fhi) within the basal cell (CD24+CD49fhi) niche showed significant expansion at day 15 in mice implanted with Estrogen and Progesterone 30-day release pellet compared to sham (64.2%, 45.07% respectively; p=0.0392). This expansion was significantly attenuated in both TPA (-38.21%, p=0.011) and RU486 (-34.30%, p=0.002) treated mice compared to MaSC in mice treated with E2+P4 alone (+45.07%). Simultaneously, luminal progenitor cells (CD61+CD49flo) show a marked reduction in E2+P4 treated mice compared to sham (17.77%, 45.54%, respectively; p=0.0375). Luminal mature cells (CD61-CD49flo) show an expansion in E2+P4 treated mice compared to sham (82.23%, 54.41% respectively; %, p=0.0371). TPA significantly (58.40 %, p=0.061) suppresses LM cells expansion observed in the E2+P4 group. TPA and RU486 show significant suppression of the MaSC population in mouse mammary gland compared to the EP-treated mice. Conclusion: TPA and RU486 alter the P4 driven changes in mammary gland cellular composition and in a manner consistent with the hypothesis that they will inhibit hormone-induced tumorigenesis in the mammary gland. To gain a better insight into this phenomenon, a high throughput transcriptomic profiling (RNASeq) of mammary stem cells isolated from the treatment groups is being performed. Citation Format: Ranjan M, Lee O, Sun L, Karavites L, Clare S, Khan SA. Attenuation of progesterone driven mammary stem cell expansion by telapristone acetate [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-07-09.