Targeting Tryptophan Catabolism in Ovarian Cancer to Attenuate Macrophage Infiltration and PD-L1 Expression

High-grade serous carcinoma (HGSC) of the fallopian tube, ovary, and peritoneum is the most common type of ovarian cancer and is predicted to be immunogenic because the presence of tumor-infiltrating lymphocytes conveys a better prognosis. However, the efficacy of immunotherapies has been limited because of the immune-suppressed tumor microenvironment (TME). Tumor metabolism and immune-suppressive metabolites directly affect immune cell function through the depletion of nutrients and activation of immune-suppressive transcriptional programs. Tryptophan (TRP) catabolism is a contributor to HGSC disease progression. Two structurally distinct rate-limiting TRP catabolizing enzymes, indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2), evolved separately to catabolize TRP. IDO1/TDO2 are aberrantly expressed in carcinomas and metabolize TRP into the immune-suppressive metabolite kynurenine (KYN), which can engage the aryl hydrocarbon receptor to drive immunosuppressive transcriptional programs. To date, IDO inhibitors tested in clinical trials have had limited efficacy, but those inhibitors did not target TDO2, and we find that HGSC cell lines and clinical outcomes are more dependent on TDO2 than IDO1. To identify inflammatory HGSC cancers with poor prognosis, we stratified patient ascites samples by IL6 status, which correlates with poor prognosis. Metabolomics revealed that IL6-high patient samples had enriched KYN. TDO2 knockdown significantly inhibited HGSC growth and TRP catabolism. The orally available dual IDO1/TDO2 inhibitor, AT-0174, significantly inhibited tumor progression, reduced tumor-associated macrophages, and reduced expression of immune-suppressive proteins on immune and tumor cells. These studies demonstrate the importance of TDO2 and the therapeutic potential of AT-0174 to overcome an immune-suppressed TME.

SIGNIFICANCE

Developing strategies to improve response to chemotherapy is essential to extending disease-free intervals for patients with HGSC of the fallopian tube, ovary, and peritoneum. In this article, we demonstrate that targeting TRP catabolism, particularly with dual inhibition of TDO2 and IDO1, attenuates the immune-suppressive microenvironment and, when combined with chemotherapy, extends survival compared with chemotherapy alone.

Beyond αβ T cells: NK, iNKT, and γδT cell biology in leukemic patients and potential for off-the-shelf adoptive cell therapies for AML

Acute myeloid leukemia (AML) remains an elusive disease to treat, let alone cure, even after highly intensive therapies such as stem cell transplants. Adoptive cell therapeutic strategies based on conventional alpha beta (αβ)T cells are an active area of research in myeloid neoplasms given their remarkable success in other hematologic malignancies, particularly B-cell-derived acute lymphoid leukemia, myeloma, and lymphomas. Several limitations have hindered clinical application of adoptive cell therapies in AML including lack of leukemia-specific antigens, on-target-off-leukemic toxicity, immunosuppressive microenvironments, and leukemic stem cell populations elusive to immune recognition and destruction. While there are promising T cell-based therapies including chimeric antigen receptor (CAR)-T designs under development, other cytotoxic lymphocyte cell subsets have unique phenotypes and capabilities that might be of additional benefit in AML treatment. Of particular interest are the natural killer (NK) and unconventional T cells known as invariant natural killer T (iNKT) and gamma delta (γδ) T cells. NK, iNKT, and γδT cells exhibit intrinsic anti-malignant properties, potential for alloreactivity, and human leukocyte-antigen (HLA)-independent function. Here we review the biology of each of these unconventional cytotoxic lymphocyte cell types and compare and contrast their strengths and limitations as the basis for adoptive cell therapies for AML.

Phase II trial of fulvestrant plus enzalutamide in ER+/HER2- advanced breast cancer

This clinical trial combined fulvestrant with the anti-androgen enzalutamide in women with metastatic ER+/HER2- breast cancer (BC). Eligible patients were women with ECOG 0-2, ER+/HER2- measurable or evaluable metastatic BC. Prior fulvestrant was allowed. Fulvestrant was administered at 500 mg IM on days 1, 15, 29, and every 4 weeks thereafter. Enzalutamide was given at 160 mg po daily. Fresh tumor biopsies were required at study entry and after 4 weeks of treatment. The primary efficacy endpoint of the trial was the clinical benefit rate at 24 weeks (CBR24). The median age was 61 years (46-87); PS 1 (0-1); median of 4 prior non-hormonal and 3 prior hormonal therapies for metastatic disease. Twelve had prior fulvestrant, and 91% had visceral disease. CBR24 was 25% (7/28 evaluable). Median progression-free survival (PFS) was 8 weeks (95% CI: 2-52). Adverse events were as expected for hormonal therapy. Significant (p < 0.1) univariate relationships existed between PFS and ER%, AR%, and PIK3CA and/or PTEN mutations. Baseline levels of phospho-proteins in the mTOR pathway were more highly expressed in biopsies of patients with shorter PFS. Fulvestrant plus enzalutamide had manageable side effects. The primary endpoint of CBR24 was 25% in heavily pretreated metastatic ER+/HER2- BC. Short PFS was associated with activation of the mTOR pathway, and PIK3CA and/or PTEN mutations were associated with an increased hazard of progression. Thus, a combination of fulvestrant or other SERD plus AKT/PI3K/mTOR inhibitor with or without AR inhibition warrants investigation in second-line endocrine therapy of metastatic ER+ BC.

Breast cancers co-opt normal mechanisms of tolerance to promote immune evasion and metastasis

Normal developmental processes, such as those seen during embryonic development and postpartum mammary gland involution, can be reactivated by cancer cells to promote immune suppression, tumor growth, and metastatic spread. In mammalian embryos, paternal-derived antigens are at risk of being recognized as foreign by the maternal immune system. Suppression of the maternal immune response toward the fetus, which is mediated in part by the trophoblast, is critical to ensure embryonic survival and development. The postpartum mammary microenvironment also exhibits immunosuppressive mechanisms accompanying the massive cell death and tissue remodeling that occurs during mammary gland involution. These normal immunosuppressive mechanisms are paralleled during malignant transformation, where tumors can develop neoantigens that may be recognized as foreign by the immune system. To circumvent this, tumors can dedifferentiate and co-opt immune-suppressive mechanisms normally utilized during fetal tolerance and postpartum mammary involution. In this review, we discuss those similarities and how they can inform our understanding of cancer progression and metastasis.

NPC1 Confers Metabolic Flexibility in Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) often undergoes at least partial epithelial-to-mesenchymal transition (EMT) to facilitate metastasis. Identifying EMT-associated characteristics can reveal novel dependencies that may serve as therapeutic vulnerabilities in this aggressive breast cancer subtype. We found that NPC1, which encodes the lysosomal cholesterol transporter Niemann-Pick type C1 is highly expressed in TNBC as compared to estrogen receptor-positive (ER+) breast cancer, and is significantly elevated in high-grade disease. We demonstrated that NPC1 is directly targeted by microRNA-200c (miR-200c), a potent suppressor of EMT, providing a mechanism for its differential expression in breast cancer subtypes. The silencing of NPC1 in TNBC causes an accumulation of cholesterol-filled lysosomes, and drives decreased growth in soft agar and invasive capacity. Conversely, overexpression of NPC1 in an ER+ cell line increases invasion and growth in soft agar. We further identified TNBC cell lines as cholesterol auxotrophs, however, they do not solely depend on NPC1 for adequate cholesterol supply. The silencing of NPC1 in TNBC cell lines led to altered mitochondrial function and morphology, suppression of mTOR signaling, and accumulation of autophagosomes. A small molecule inhibitor of NPC1, U18666A, decreased TNBC proliferation and synergized with the chemotherapeutic drug, paclitaxel. This work suggests that NPC1 promotes aggressive characteristics in TNBC, and identifies NPC1 as a potential therapeutic target.

Abstract P4-02-11: A SIM2s/SEMA7A switch drives therapeutic resistance in ER+ breast cancer

BACKGROUND: Estrogen Receptor (ER) + breast cancers (BC) comprise over 70% of BC cases and can be targeted via ER modulated therapies. Despite this, ER+BC patients can experience recurrence within 20 years and the majority of BC related deaths can be attributed to metastatic ER+BC. These distant metastases commonly become diagnosed as endocrine therapy resistant. Thus, there is an unmet need to identify novel biomarkers for treating ER+ patients with metastasis. We have identified a tumor suppressor, Singleminded 2s (SIM2s), expressed in breast epithelial cells that inhibits EMT and metastasis, and is downregulated in the progression of breast disease. Our previous studies found that loss of SIM2s expression results in downregulation of ESR1 and increased basal markers in the MCF7 (ER+BC) cell line. Likewise, Semaphorin 7a (SEMA7A) expression is associated with decreased overall survival in ER+BC patients. Patients with SEMA7Ahi tumors treated with Tamoxifen exhibit shortened relapse free survival. SEMA7A is a downstream target of both NFKB and PTGS2/COX-2; and our previously published results establish a cross-talk between NFKB and SIM2s to regulate PTGS2 via interactions with the AKT pathway. Moreover, COX-2 inhibition is associated with better prognosis for breast cancer patients. Therefore, we are investigating how SIM2s may repress AKT signaling in SEMA7A driven ER resistance and metastasis. Methods: We performed in silico analysis of the SEMA7A promoter using the ConTra web server. For in vitro assays, we examined estrogen dependent differences in SIM2s, ER, and SP1 binding utilizing luciferase reporter assays using intact promoter and SIM2s site deletion mutants (Invitrogen) in MCF7 cells. Using immunoblotting and qPCR analysis we also assessed expression of SEMA7A, ESR1, PI3K/AKT signaling genes and EMT associated genes in Crispr/Cas9 SIM2s knockout (SIM2KO) MCF7 cells. Treatment of MCF7 cells with exogenous SEMA7A was used to observe possible changes in SIM2s expression and SIM2s promoter activity. For in vivo assays, we used immunohistochemistry (IHC) to assess SIM2s in SEMA7A low and high expressing MCF7 xenografts. To examine the relationship between SIM2s and ER, SEMA7A-/- (KO) mice were crossed with C57/BL6 MMTV-PYMT mice. Results: In silico analysis of the SEMA7A promoter via ConTra revealed four potential SIM2 response elements containing the SIM2s central midline elements (CME) binding motif and highly conserved estrogen response element half-sites adjacent to two specificity protein 1 consensus bindings sites. Luciferase reporter assays in MCF7 cells confirmed SIM2s represses basal and estrogen induced-SEMA7A promoter activity. Moreover, SIM2s was unable to repress the SEMA7A promoter activity with CME mutation. MCF7 SIM2KO cells exhibit increased SEMA7A promoter activity, SEMA7A, AKT signaling, EMT signatures and decreased ESR1, CDH1, and PTEN protein and mRNA expression. Both SIM2s expression and SIM2s promoter activity are significantly decreased with the addition of exogenous SEMA7A. Moreover, MCF7 xenografts reveal reciprocal expression of SIM2s and SEMA7A. Additionally in MMTV-PyMT mice, SIM2s expression is lost as tumors transition from pre-malignant to invasive phenotypes, yet we observe maintenance of SIM2s and ER in SEMA7A-/-;PyMT mice. Conclusion: These findings establish a regulatory relationship between SIM2s and SEMA7A in ER+BC. SIM2s functions to downregulate SEMA7A mediated pro-tumor signaling and maintain ER expression, but can be turned off to allow for resistance in ER+BC. Given the observed reciprocal expression, our study suggests a SIM2s/SEMA7A switch which may confer resistance in ER+BC via AKT signaling through downregulation of PTEN. Thus, a SIM2s/SEMA7A switch may act as a prognostic indicator to provide therapeutic advantages in resistant ER+BC metastasis.

Citation Format: Garhett L Wyatt, Lyndsey S Crump, Traci R Lyons, Weston W Porter. A SIM2s/SEMA7A switch drives therapeutic resistance in ER+ breast cancer [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 P4-02-11.

Triple Targeting of Breast Tumors Driven by Hormonal Receptors and HER2

Breast cancers that express hormonal receptors (HR) and HER2 display resistance to targeted therapy. Tumor-promotional signaling from the HER2 and estrogen receptor (ER) pathways converges at the cyclin D1 and cyclin-dependent kinases (CDK) 4 and 6 complex, which drives cell-cycle progression and development of therapeutic resistance. Therefore, we hypothesized that co-targeting of ER, HER2, and CDK4/6 may result in improved tumoricidal activity and suppress drug-resistant subclones that arise on therapy. We tested the activity of the triple targeted combination therapy with tucatinib (HER2 small-molecule inhibitor), palbociclib (CKD4/6 inhibitor), and fulvestrant (selective ER degrader) in HR⁺/HER2⁺ human breast tumor cell lines and xenograft models. In addition, we evaluated whether triple targeted combination prevents growth of tucatinib or palbociclib-resistant subclones in vitro and in vivo Triple targeted combination significantly reduced HR⁺/HER2⁺ tumor cell viability, clonogenic survival, and in vivo growth. Moreover, survival of HR⁺/HER2⁺ cells that were resistant to the third drug in the regimen was reduced by the other two drugs in combination. We propose that a targeted triple combination approach will be clinically effective in the treatment of otherwise drug-resistant tumors, inducing robust responses in patients.

Abstract 1076: Hormonal regulation of SEMA7A promotes therapeutic resistance in ER+ breast cancer

Background: The majority of all breast cancers (BC) are estrogen receptor positive (ER+). While ER-targeting endocrine therapies have improved patient survival, many tumors become drug resistant and recur within 20 years. Thus, novel targets are needed to treat recurrent ER+BC. Previous reports have described tumor-promotional effects of Semaphorin 7A (SEMA7A) in ER- disease; however, the role of SEMA7A in ER+ disease is not well-characterized.

Hypothesis: SEMA7A promotes cell survival and drug resistance in ER+ BC.

Methods: We measured expression of SEMA7A in drug resistant cells via immunoblotting. We then overexpressed SEMA7A and used ER-targeting drugs (fulvestrant and tamoxifen) to test how SEMA7A-expressing cells respond to endocrine therapy. In vitro, we utilized cell proliferation and survival assays. In vivo, we implanted ER+ BC cells, then treated the animals with fulvestrant to assess how SEMA7A affects primary tumor volume and metastasis. We also measured markers of “stemness” and multi-drug resistance via flow cytometry.

Results: We found that SEMA7A expression correlated with decreased relapse free survival in patients who received endocrine therapy for ER+BC (Kmplotter; p=0.042). We also observe that SEMA7A can be hormonally regulated in ER+BC, but expression did not consistently decrease with endocrine therapy. Instead, long term estrogen deprivation and ER-targeting treatments increased SEMA7A expression, likely through signaling via other hormone receptors such as the androgen receptor, which also increases with long term estrogen deprivation. Additionally, overexpression of SEMA7A promoted in vitro growth and survival of ER+ cells during estrogen-deprivation, tamoxifen, or fulvestrant treatments. In vivo, SEMA7A promoted fulvestrant resistance in the primary tumor and also induced lung metastases. Finally, we identified pro-survival signaling as a therapeutic vulnerability of ER+SEMA7A+ tumors.

Conclusion: These studies show that SEMA7A can promote drug resistance in ER+ BC. We suggest that targeting pro-survival signaling may prove efficacious for treating SEMA7A+ tumors, which are less likely be resistant to endocrine therapies.

Citation Format: Lyndsey S. Crump, Garhett L. Wyatt, Taylor R. Rutherford, Jennifer K. Richer, Weston W. Porter, Traci R. Lyons. Hormonal regulation of SEMA7A promotes therapeutic resistance in ER+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1076.

Hormonal Regulation of Semaphorin 7a in ER+ Breast Cancer Drives Therapeutic Resistance

Approximately 70% of all breast cancers are estrogen receptor-positive (ER⁺ breast cancer), and endocrine therapy has improved survival for patients with ER⁺ breast cancer. However, up to half of these tumors recur within 20 years. Recurrent ER⁺ breast cancers develop resistance to endocrine therapy; thus, novel targets are needed to treat recurrent ER⁺ breast cancer. Here we report that semaphorin 7A (SEMA7A) confers significantly decreased patient survival rates in ER⁺ breast cancer. SEMA7A was hormonally regulated in ER⁺ breast cancer, but its expression did not uniformly decrease with antiestrogen treatments. Additionally, overexpression of SEMA7A in ER⁺ cell lines drove increased in vitro growth in the presence of estrogen deprivation, tamoxifen, and fulvestrant. In vivo, SEMA7A conferred primary tumor resistance to fulvestrant and induced lung metastases. Prosurvival signaling was identified as a therapeutic vulnerability of ER⁺SEMA7A⁺ tumors. We therefore propose that targeting this pathway with inhibitors of survival signaling such as venetoclax may prove efficacious for treating SEMA7A⁺ tumors. SIGNIFICANCE: SEMA7A predicts for and likely contributes to poor response to standard-of-care therapies, suggesting that patients with SEMA7A⁺ER⁺ tumors may benefit from alternative therapeutic strategies. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/1/187/F1.large.jpg.

Cross-talk between SIM2s and NFκB regulates cyclooxygenase 2 expression in breast cancer

Background

Breast cancer is a leading cause of cancer-related death for women in the USA. Thus, there is an increasing need to investigate novel prognostic markers and therapeutic methods. Inflammation raises challenges in treating and preventing the spread of breast cancer. Specifically, the nuclear factor kappa b (NFκB) pathway contributes to cancer progression by stimulating proliferation and preventing apoptosis. One target gene of this pathway is PTGS2, which encodes for cyclooxygenase 2 (COX-2) and is upregulated in 40% of human breast carcinomas. COX-2 is an enzyme involved in the production of prostaglandins, which mediate inflammation. Here, we investigate the effect of Singleminded-2s (SIM2s), a transcriptional tumor suppressor that is implicated in inhibition of tumor growth and metastasis, in regulating NFκB signaling and COX-2.

Methods

For in vitro experiments, reporter luciferase assays were utilized in MCF7 cells to investigate promoter activity of NFκB and SIM2. Real-time PCR, immunoblotting, immunohistochemistry, and chromatin immunoprecipitation assays were performed in SUM159 and MCF7 cells. For in vivo experiments, MCF10DCIS.COM cells stably expressing SIM2s-FLAG or shPTGS2 were injected into SCID mice and subsequent tumors harvested for immunostaining and analysis.

Results

Our results reveal that SIM2 attenuates the activation of NFκB as measured using NFκB-luciferase reporter assay. Furthermore, immunostaining of lysates from breast cancer cells overexpressing SIM2s showed reduction in various NFκB signaling proteins, as well as pAkt, whereas knockdown of SIM2 revealed increases in NFκB signaling proteins and pAkt. Additionally, we show that NFκB signaling can act in a reciprocal manner to decrease expression of SIM2s. Likewise, suppressing NFκB translocation in DCIS.COM cells increased SIM2s expression. We also found that NFκB/p65 represses SIM2 in a dose-dependent manner, and when NFκB is suppressed, the effect on the SIM2 is negated. Additionally, our ChIP analysis confirms that NFκB/p65 binds directly to SIM2 promoter site and that the NFκB sites in the SIM2 promoter are required for NFκB-mediated suppression of SIM2s. Finally, overexpression of SIM2s decreases PTGS2 in vitro, and COX-2 staining in vivo while decreasing PTGS2 and/or COX-2 activity results in re-expression of SIM2.

Conclusion

Our findings identify a novel role for SIM2s in NFκB signaling and COX-2 expression.

Studies of postpartum mammary gland involution reveal novel pro-metastatic mechanisms

Postpartum involution is the process by which the lactating mammary gland returns to the pre-pregnant state after weaning. Expression of tumor-promotional collagen, upregulation of matrix metalloproteinases, infiltration of M2 macrophages, and remodeling of blood and lymphatic vasculature are all characteristics shared by the involuting mammary gland and breast tumor microenvironment. The tumor promotional nature of the involuting mammary gland is perhaps best evidenced by cases of postpartum breast cancer (PPBC), or those cases diagnosed within 10 years of most recent childbirth. Women with PPBC experience more aggressive disease and higher risk of metastasis than nulliparous patients and those diagnosed outside the postpartum window. Semaphorin 7a (SEMA7A), cyclooxygenase-2 (COX-2), and collagen are all expressed in the involuting mammary gland and, together, predict for decreased metastasis free survival in breast cancer. Studies investigating the role of these proteins in involution have been important for understanding their contributions to PPBC. Postpartum involution thus represents a valuable model for the identification of novel molecular drivers of PPBC and classical cancer hallmarks. In this review, we will highlight the similarities between involution and cancer in the mammary gland, and further define the contribution of SEMA7A/COX-2/collagen interplay to postpartum involution and breast tumor progression and metastasis.

Semaphorin 7A Promotes Macrophage-Mediated Lymphatic Remodeling during Postpartum Mammary Gland Involution and in Breast Cancer

Postpartum mammary gland involution is a tissue remodeling event that occurs in all mammals in the absence of nursing or after weaning to return the gland to the pre-pregnant state. The tissue microenvironment created by involution has proven to be tumor promotional. Here we report that the GPI-linked protein semaphorin 7A (SEMA7A) is expressed on mammary epithelial cells during involution and use preclinical models to demonstrate that tumors induced during involution express high levels of SEMA7A. Overexpression of SEMA7A promoted the presence of myeloid-derived podoplanin (PDPN)-expressing cells in the tumor microenvironment and during involution. SEMA7A drove the expression of PDPN in macrophages, which led to integrin- and PDPN-dependent motility and adherence to lymphatic endothelial cells to promote lymphangiogenesis. In support of this mechanism, mammary tissue from SEMA7A-knockout mice exhibited decreased myeloid-derived PDPN-expressing cells, PDPN-expressing endothelial cells, and lymphatic vessel density. Furthermore, coexpression of SEMA7A, PDPN, and macrophage marker CD68 predicted for decreased distant metastasis-free survival in a cohort of over 600 cases of breast cancer as well as in ovarian, lung, and gastric cancers. Together, our results indicate that SEMA7A may orchestrate macrophage-mediated lymphatic vessel remodeling, which in turn drives metastasis in breast cancer.Signficance: SEMA7A, which is expressed on mammary cells during glandular involution, alters macrophage biology and lymphangiogenesis to drive breast cancer metastasis. Cancer Res; 78(22); 6473-85. ©2018 AACR.