Low levels of circulating estrogen sensitize PTEN-null endometrial tumors to PARP inhibition in vivo.

Earlier in vitro work demonstrated that PARP inhibition induces cell death in PTEN-null endometrial cancer cell lines, but the in vivo therapeutic efficacy of these agents against endometrial cancer remains unknown. Here, we test the efficacy of AZD2281 (olaparib), an oral PARP inhibitor, in the therapy of PTEN-null endometrial tumors in a preclinical endometrial cancer mouse model. Primary endometrial tumors were generated by epithelial loss of PTEN using an in vivo model. This model recapitulates epithelial-specific loss of PTEN seen in human tumors, and histologically resembles endometrioid carcinomas, the predominant subtype of human endometrial cancers. Olaparib was administered orally to tumor-bearing mice in two hormonal extremes: high or low estrogen. Olaparib treatment achieved a significant reduction in tumor size in a low estrogenic milieu. In striking contrast, no response to olaparib was seen in tumors exposed to high levels of estrogen. Two key observations were made when estrogen levels were dropped: (i) the serum concentration of olaparib was significantly increased, resulting in sustained PARP inhibition at the tumor bed; and (ii) the homologous recombination pathway was compromised, as evidenced by decreased Rad51 protein expression and function. These two mechanisms may account for the sensitization of PTEN-null tumors to olaparib with estrogen deprivation. Results of this preclinical trial suggest that orally administered PARP inhibitors in a low estrogenic hormonal milieu can effectively target PTEN-null endometrial tumors. Extension of this work to clinical trials could personalize the therapy of women afflicted with advanced endometrial cancer using well-tolerated orally administered therapeutic agents.

Progesterone receptor signaling in the microenvironment of endometrial cancer influences its response to hormonal therapy.

Progesterone, an agonist for the progesterone receptor (PR), can be an efficacious and well-tolerated treatment in endometrial cancer. The clinical use of progesterone is limited because of the lack of biomarkers that predict hormone sensitivity. Despite its efficacy in cancer therapy, mechanisms and site of action for progesterone remain unknown. Using an in vivo endometrial cancer mouse model driven by clinically relevant genetic changes but dichotomous responses to hormonal therapy, we show that signaling through stromal PR is necessary and sufficient for progesterone antitumor effects. Endometrial cancers resulting from epithelial loss of PTEN (PTENKO) were hormone sensitive and had abundant expression of stromal PR. Stromal deletion of PR as a single genetic change in these tumors induced progesterone resistance indicating that paracrine signaling through the stroma is essential for the progesterone therapeutic effects. A hormone-refractory endometrial tumor with low levels of stromal PR developed when activation of KRAS was coupled with PTEN-loss (PTENKO/Kras). The innate progesterone resistance in PTENKO/Kras tumors stemmed from methylation of PR in the tumor microenvironment. Add-back of stromal PR expressed from a constitutively active promoter sensitized these tumors to progesterone therapy. Results show that signaling through stromal PR is sufficient for inducing hormone responsiveness. Our findings suggest that epigenetic derepression of stromal PR could be a potential therapeutic target for sensitizing hormone-refractory endometrial tumors to progesterone therapy. On the basis of these results, stromal expression of PR may emerge as a reliable biomarker in predicting response to hormonal therapy.

Estrogen and progesterone together expand murine endometrial epithelial progenitor cells.

Synchronous with massive shifts in reproductive hormones, the uterus and its lining the endometrium expand to accommodate a growing fetus during pregnancy. In the absence of an embryo the endometrium, composed of epithelium and stroma, undergoes numerous hormonally regulated cycles of breakdown and regeneration. The hormonally mediated regenerative capacity of the endometrium suggests that signals that govern the growth of endometrial progenitors must be regulated by estrogen and progesterone. Here, we report an antigenic profile for isolation of mouse endometrial epithelial progenitors. These cells are EpCAM(+) CD44(+) ITGA6(hi) Thy1(-) PECAM1(-) PTPRC(-) Ter119(-), comprise a minor subpopulation of total endometrial epithelia and possess a gene expression profile that is unique and different from other cells of the endometrium. The epithelial progenitors of the endometrium could regenerate in vivo, undergo multilineage differentiation and proliferate. We show that the number of endometrial epithelial progenitors is regulated by reproductive hormones. Coadministration of estrogen and progesterone dramatically expanded the endometrial epithelial progenitor cell pool. This effect was not observed when estrogen or progesterone was administered alone. Despite the remarkable sensitivity to hormonal signals, endometrial epithelial progenitors do not express estrogen or progesterone receptors. Therefore, their hormonal regulation must be mediated through paracrine signals resulting from binding of steroid hormones to the progenitor cell niche. Discovery of signaling defects in endometrial epithelial progenitors or their niche can lead to development of better therapies in diseases of the endometrium.

Stem-like epithelial cells are concentrated in the distal end of the fallopian tube: a site for injury and serous cancer initiation.

The reproductive role of the fallopian tube is to transport the sperm and egg. The tube is positioned to act as a bridge between the ovary where the egg is released and the uterus where implantation occurs. Throughout reproductive years, the fallopian tube epithelium undergoes repetitive damage and regeneration. Although a reservoir of adult epithelial stem cells must exist to replenish damaged cells, they remain unidentified. Here, we report isolation of a subset of basally located human fallopian tube epithelia (FTE) that lack markers of ciliated (ß-tubulin; TUBB4) or secretory (PAX8) differentiated cells. These undifferentiated cells expressed cell surface antigens: epithelial cell adhesion molecule, CD44, and integrin α 6. This FTE subpopulation was fivefold enriched for cells capable of clonal growth and self-renewal suggesting that they contain the FTE stem-like cells (FTESCs). A twofold enrichment of the FTESC was found in the distal compared to the proximal end of the tube. The distal fimbriated end of the fallopian tube is a well-characterized locus for initiation of serous carcinomas. An expansion of the cells expressing markers of FTESC was detected in tubal intraepithelial carcinomas and in fallopian tubes from patients with invasive serous cancer. These findings suggest that FTESC may play a role in the initiation of serous tumors. Characterization of these stem-like cells will provide new insight into how the FTE regenerate, respond to injury, and may initiate cancer.