Abstract P2-20-11: Progesterone impacts the growth and immune cell infiltration of murine mammary gland tumors

Clinical studies have linked usage of progestins (synthetic progesterone) to breast cancer risk. However, little is understood regarding the role of native progesterone (P4), signaling through the progesterone receptor (PR), in breast tumor formation. Recently, we demonstrated that P4 treatment or PR overexpression can drive changes in immune cell populations in the murine mammary gland and that PR overexpression leads to increased development of mammary gland tumors in mice. Given these findings, we sought to investigate whether P4 impacts tumor growth and immune cell infiltration of mammary gland tumors. We utilized syngeneic mammary gland tumor models to evaluate the effect of P4 on PR+ mammary gland tumor growth, which revealed that P4 promoted tumor growth and impacted immune cell infiltration of PR+ mammary gland tumors. Of note, numbers of tumor-infiltrating dendritic cells were decreased and exhausted T cells and regulatory T cells were increased with P4 treatment in PR+ tumors. To determine if anti-progestin therapies could reverse the growth-promoting effect of P4 on mammary gland tumors, mice bearing PR+ mammary gland tumors were treated with the anti-progestin onapristone. Onapristone treatment led to significantly decreased tumor volumes in two syngeneic mammary gland tumor models and reversed the effect that P4 had on tumor-infiltrating regulatory T cells. To determine if inhibition of tumor growth by onapristone was immunologically mediated, SCID mice bearing PR+ mammary gland tumors were treated with onapristone. Results revealed a decreased ability of onapristone to inhibit tumor growth in SCID mice compared to immunocompetent mice, suggesting that inhibition of tumor growth is, in part, immunologically mediated. These findings offer a novel mechanism of P4-driven mammary gland tumor development and provide rationale in investigating the usage of anti-progestin therapies to promote immune-mediated elimination of mammary gland tumors.

Citation Format: Lauryn R Werner, Dominika E. Helm, Julio Tinoco, Eilidh I Chowanec, Sean M Holloran, Richard C Hastings, Junping Wei, Gangjun Lei, Xiao-Yi Yang, Mary A Markiewicz, Prabhakar Chalise, Justin Balko, Zachary C Hartman, Christy R Hagan. Progesterone impacts the growth and immune cell infiltration of murine mammary gland tumors [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-20-11.

Abstract 1351: Lauryn Werner

Clinical studies have linked usage of progestins (synthetic progesterone) to breast cancer risk. However, little is understood regarding the role of native progesterone (P4), signaling through the progesterone receptor (PR), in breast tumor formation. Recently, we reported a link between PR and immune signaling pathways, showing that P4/PR can repress type I interferon signaling pathways. Given these findings, we sought to investigate whether P4/PR drive immunomodulation in the mammary gland and promote tumor formation. To determine the effect of P4 on immune cell populations in the murine mammary gland, mice were treated with P4 or placebo pellets for 21 days. We found that mice treated with P4 exhibited changes in the mammary gland indicative of an inhibited immune response compared to placebo-treated mice. To assess the effect of PR overexpression on mammary gland tumor development as well as immune cell populations in the mammary gland, a transgenic mouse model was used in which PR is overexpressed throughout the entire mouse. Immune cell populations were assessed in the mammary glands by flow cytometry, which revealed decreased numbers of various immune cell populations. Transgenic mice were also monitored for mammary gland tumor development over a 2-year timespan. Following development of mammary gland tumors, immune cell populations in the tumors and spleens of transgenic and control mice were analyzed by flow cytometry. Upon long-term monitoring, we determined that multi-parous PR overexpressing mice developed significantly more mammary gland tumors than control mice. Additionally, tumors from PR overexpressing mice contained fewer infiltrating immune cells, and RNA sequencing analysis of tumor samples revealed that immune-related gene signatures were lower in tumors from PR overexpressing mice as compared to control mice. Finally, we utilized syngeneic mammary gland tumor models to evaluate the effect of P4 on the growth of PR+ mammary gland tumors in vivo, which revealed that P4 promoted tumor growth and decreased immune cell infiltration of PR+ mammary gland tumors. Together, these findings offer a novel mechanism of P4-driven mammary gland tumor development and provide rationale in investigating the usage of anti-progestin therapies to promote immune-mediated elimination of mammary gland tumors.

Citation Format: Lauryn Rose Werner, Katelin A. Gibson, Merit L. Goodman, Dominika E. Helm, Katherine R. Walter, Sean M. Holloran, Gloria M. Trinca, Richard C. Hastings, Howard H. Yang, Ying Hu, Junping Wei, Gangjun Lei, Xiao-Yi Yang, Rashna Madan, Alfredo A. Molinolo, Mary A. Markiewicz, Prabhakar Chalise, Margaret L. Axelrod, Justin M. Balko, Kent W. Hunter, Zachary C. Hartman, Carol A. Lange, Christy R. Hagan. Lauryn Werner [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1351.

Abstract P4-04-07: Progesterone promotes immunomodulation and tumor development in the murine mammary gland

Clinical studies have linked usage of progestins (synthetic progesterone) to breast cancer risk. However, little is understood regarding the role of native progesterone (P4), signaling through the progesterone receptor (PR), in breast tumor formation. Recently, we reported a link between PR and immune signaling pathways, showing that P4/PR can repress type I interferon signaling pathways. Given these findings, we sought to investigate whether P4/PR drive immunomodulation in the mammary gland and promote tumor formation. To determine the effect of P4 on immune cell populations in the murine mammary gland, mice were treated with P4 or placebo pellets for 21 days. We found that mice treated with P4 exhibited changes in the mammary gland indicative of an inhibited immune response compared to placebo-treated mice. To assess the effect of PR overexpression on mammary gland tumor development as well as immune cell populations in the mammary gland, a transgenic mouse model was used in which PR is overexpressed throughout the entire mouse. Immune cell populations were assessed in the mammary glands by flow cytometry, which revealed decreased numbers of various immune cell populations. Transgenic mice were also monitored for mammary gland tumor development over a 2-year timespan. Following development of mammary gland tumors, immune cell populations in the tumors and spleens of transgenic and control mice were analyzed by flow cytometry. Upon long-term monitoring, we determined that multi-parous PR overexpressing mice developed significantly more mammary gland tumors than control mice. Additionally, tumors from PR overexpressing mice contained fewer infiltrating immune cells, and RNA sequencing analysis of tumor samples revealed that immune-related gene signatures were lower in tumors from PR overexpressing mice as compared to control mice. Finally, we utilized syngeneic mammary gland tumor models to evaluate the effect of P4 on the growth of PR+ mammary gland tumors in vivo, which revealed that P4 promoted tumor growth and decreased immune cell infiltration of PR+ mammary gland tumors. Together, these findings offer a novel mechanism of P4-driven mammary gland tumor development and provide rationale in investigating the usage of anti-progestin therapies to promote immune-mediated elimination of mammary gland tumors.

Citation Format: Lauryn R Werner, Katelin A Gibson, Merit L Goodman, Dominika E Helm, Katherine R Walter, Sean M Holloran, Gloria M Trinca, Richard C Hastings, Howard H Yang, Ying Hu, Junping Wei, Gangjun Lei, Xiao-Yi Yang, Rashna Madan, Alfred A Molinolo, Mary A Markiewicz, Prabhakar Chalise, Margaret L Axelrod, Justin M Balko, Kent W Hunter, Zachary C Hartman, Carol A Lange, Christy R Hagan. Progesterone promotes immunomodulation and tumor development in the murine mammary gland [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-04-07.

Disrupting interferon-alpha and NF-kappaB crosstalk suppresses IFITM1 expression attenuating triple-negative breast cancer progression

Overexpression of interferon induced transmembrane protein-1 (IFITM1) enhances tumor progression in multiple cancers, but its role in triple-negative breast cancer (TNBC) is unknown. Here, we explore the functional significance and regulation of IFITM1 in TNBC and strategies to target its expression. Immunohistochemistry staining of a tissue microarray demonstrates that IFITM1 is overexpressed in TNBC samples which is confirmed by TCGA analysis. Targeting IFITM1 by siRNA or CRISPR/Cas9 in TNBC cell lines significantly inhibits proliferation, colony formation, and wound healing in vitro. Orthotopic mammary fat pad and mammary intraductal studies reveal that loss of IFITM1 reduces TNBC tumor growth and invasion in vivo. RNA-seq analysis of IFITM1/KO cells reveals significant downregulation of several genes involved in proliferation, migration, and invasion and functional studies identified NF-κB as an important downstream target of IFITM1. Notably, siRNA knockdown of p65 reduces IFITM1 expression and a drug-repurposing screen of FDA approved compounds identified parthenolide, an NFκB inhibitor, as a cytotoxic agent for TNBC and an inhibitor of IFITM1 in vitro and in vivo. Overall, our findings suggest that targeting IFITM1 by suppressing interferon-alpha/NFκB signaling represents a novel therapeutic strategy for TNBC treatment.

Progesterone promotes immunomodulation and tumor development in the murine mammary gland

BACKGROUND

Clinical studies have linked usage of progestins (synthetic progesterone [P4]) to breast cancer risk. However, little is understood regarding the role of native P4, signaling through the progesterone receptor (PR), in breast tumor formation. Recently, we reported a link between PR and immune signaling pathways, showing that P4/PR can repress type I interferon signaling pathways. Given these findings, we sought to investigate whether P4/PR drive immunomodulation in the mammary gland and promote tumor formation.

METHODS

To determine the effect of P4 on immune cell populations in the murine mammary gland, mice were treated with P4 or placebo pellets for 21 days. Immune cell populations in the mammary gland, spleen, and inguinal lymph nodes were subsequently analyzed by flow cytometry. To assess the effect of PR overexpression on mammary gland tumor development as well as immune cell populations in the mammary gland, a transgenic mouse model was used in which PR was overexpressed throughout the entire mouse. Immune cell populations were assessed in the mammary glands, spleens, and inguinal lymph nodes of 6-month-old transgenic and control mice by flow cytometry. Transgenic mice were also monitored for mammary gland tumor development over a 2-year time span. Following development of mammary gland tumors, immune cell populations in the tumors and spleens of transgenic and control mice were analyzed by flow cytometry.

RESULTS

We found that mice treated with P4 exhibited changes in the mammary gland indicative of an inhibited immune response compared with placebo-treated mice. Furthermore, transgenic mice with PR overexpression demonstrated decreased numbers of immune cell populations in their mammary glands, lymph nodes, and spleens. On long-term monitoring, we determined that multiparous PR-overexpressing mice developed significantly more mammary gland tumors than control mice. Additionally, tumors from PR-overexpressing mice contained fewer infiltrating immune cells. Finally, RNA sequencing analysis of tumor samples revealed that immune-related gene signatures were lower in tumors from PR-overexpressing mice as compared with control mice.

CONCLUSION

Together, these findings offer a novel mechanism of P4-driven mammary gland tumor development and provide rationale in investigating the usage of antiprogestin therapies to promote immune-mediated elimination of mammary gland tumors.

Reciprocal fine-tuning of progesterone and prolactin-regulated gene expression in breast cancer cells

Progesterone and prolactin are two key hormones involved in development and remodeling of the mammary gland. As such, both hormones have been linked to breast cancer. Despite the overlap between biological processes ascribed to these two hormones, little is known about how co-expression of both hormones affects their individual actions. Progesterone and prolactin exert many of their effects on the mammary gland through activation of gene expression, either directly (progesterone, binding to the progesterone receptor [PR]) or indirectly (multiple transcription factors being activated downstream of prolactin, most notably STAT5). Using RNA-seq in T47D breast cancer cells, we characterized the gene expression programs regulated by progestin and prolactin, either alone or in combination. We found significant crosstalk and fine-tuning between the transcriptional programs executed by each hormone independently and in combination. We divided and characterized the transcriptional programs into four broad categories. All crosstalk/fine-tuning shown to be modulated by progesterone was dependent upon the expression of PR. Moreover, PR was recruited to enhancer regions of all regulated genes. Interestingly, despite the canonical role for STAT5 in transducing prolactin-signaling in the normal and lactating mammary gland, very few of the prolactin-regulated transcriptional programs fine-tuned by progesterone in this breast cancer cell line model system were in fact dependent upon STAT5. Cumulatively, these data suggest that the interplay of progesterone and prolactin in breast cancer impacts gene expression in a more complex and nuanced manner than previously thought, and likely through different transcriptional regulators than those observed in the normal mammary gland. Studying gene regulation when both hormones are present is most clinically relevant, particularly in the context of breast cancer.

Structures of a DNA Polymerase Inserting Therapeutic Nucleotide Analogues

Members of the nucleoside analogue class of cancer therapeutics compete with canonical nucleotides to disrupt numerous cellular processes, including nucleotide homeostasis, DNA and RNA synthesis, and nucleotide metabolism. Nucleoside analogues are triphosphorylated and subsequently inserted into genomic DNA, contributing to the efficacy of therapeutic nucleosides in multiple ways. In some cases, the altered base acts as a mutagen, altering the DNA sequence to promote cellular death; in others, insertion of the altered nucleotide triggers DNA repair pathways, which produce lethal levels of cytotoxic intermediates such as single and double stranded DNA breaks. As a prerequisite to many of these biological outcomes, the modified nucleotide must be accommodated in the DNA polymerase active site during nucleotide insertion. Currently, the molecular contacts that mediate DNA polymerase insertion of modified nucleotides remain unknown for multiple therapeutic compounds, despite decades of clinical use. To determine how modified bases are inserted into duplex DNA, we used mammalian DNA polymerase β (pol β) to visualize the structural conformations of four therapeutically relevant modified nucleotides, 6-thio-2'-deoxyguanosine-5'-triphosphate (6-TdGTP), 5-fluoro-2'-deoxyuridine-5'-triphosphate (5-FdUTP), 5-formyl-deoxycytosine-5'-triphosphate (5-FodCTP), and 5-formyl-deoxyuridine-5'-triphosphate (5-FodUTP). Together, the structures reveal a pattern in which the modified nucleotides utilize Watson-Crick base pairing interactions similar to that of unmodified nucleotides. The nucleotide modifications were consistently positioned in the major groove of duplex DNA, accommodated by an open cavity in pol β. These results provide novel information for the rational design of new therapeutic nucleoside analogues and a greater understanding of how modified nucleotides are tolerated by polymerases.

Interferon-Stimulated Genes Are Transcriptionally Repressed by PR in Breast Cancer

The progesterone receptor (PR) regulates transcriptional programs that drive proliferation, survival, and stem cell phenotypes. Although the role of native progesterone in the development of breast cancer remains controversial, PR clearly alters the transcriptome in breast tumors. This study identifies a class of genes, Interferon (IFN)-stimulated genes (ISGs), potently downregulated by ligand-activated PR which have not been previously shown to be regulated by PR. Progestin-dependent transcriptional repression of ISGs was observed in breast cancer cell line models and human breast tumors. Ligand-independent regulation of ISGs was also observed, as basal transcript levels were markedly higher in cells with PR knockdown. PR repressed ISG transcription in response to IFN treatment, the canonical mechanism through which these genes are activated. Liganded PR is robustly recruited to enhancer regions of ISGs, and ISG transcriptional repression is dependent upon PR's ability to bind DNA. In response to PR activation, key regulatory transcription factors that are required for IFN-activated ISG transcription, STAT2 and IRF9, exhibit impaired recruitment to ISG promoter regions, correlating with PR/ligand-dependent ISG transcriptional repression. IFN activation is a critical early step in nascent tumor recognition and destruction through immunosurveillance. As the large majority of breast tumors are PR positive at the time of diagnosis, PR-dependent downregulation of IFN signaling may be a mechanism through which early PR-positive breast tumors evade the immune system and develop into clinically relevant tumors.Implications: This study highlights a novel transcriptional mechanism through which PR drives breast cancer development and potentially evades the immune system. Mol Cancer Res; 15(10); 1331-40. ©2017 AACR.