Abstract B040: Leader cells mediate tumor engraftment and promote immunosuppression to drive ovarian cancer progression in vivo

Epithelial ovarian cancer (EOC) is most frequently diagnosed at an advanced stage, and is characterized by its high recurrence rate and almost-universal acquisition of chemoresistance. Metastasis of EOC is driven by heterogenous spheroids that passively disseminate throughout the peritoneal cavity, promoting tumor spread and recurrence. We previously identified a sub-population of highly motile and invasive “Leader cells” (LCs) that express the basal epithelial protein KRT14 as an absolute determinant of invasive potential. We demonstrated KRT14 knockout in EOC cells does not impact viability or proliferation, however completely ablates their ability to invade through Matrigel in 2D and 3D format in vitro. Although a role for LCs in mesothelial clearance and invasion has been established, these mechanisms remain poorly understood. Here we show a critical role for KRT14+ LCs in immunosuppression and tumor-immune privilege in vivo. In the ID8 syngeneic EOC mouse model, tumor-specific LC (KRT14) loss (LCKO) impaired ovarian intrabursal primary tumor engraftment and subsequent metastatic spread. Immune phenotyping by flow cytometry revealed that mice bearing LCKO tumors displayed decreased proportions of immunosuppressive tumor-adjacent Tregs and M2 macrophages, and improved CD8+ T-cell/Treg ratios. Conversely, forced LC-overexpression (LCOE) in EOC tumors accelerated metastasis, and promoted tumor-immune evasion via upregulated secretion of suppressive chemokines including CCL22 and CCL5. In addition to their critical role in migration and invasion, the current study provides in vivo evidence that leader cells are mediators of immune suppression in ovarian cancer. This work supports the basis that defining novel strategies to target LCs to promote anti-tumor immunity and limit metastatic progression may be a useful strategy for improved epithelial ovarian cancer therapy.

Citation Format: Amy L. Wilson, Brittany R. Doran, Bashirah Basri, Laura R. Moffitt, Magdalena Plebanski, Andrew N. Stephens, Maree Bilandzic. Leader cells mediate tumor engraftment and promote immunosuppression to drive ovarian cancer progression in vivo [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B040.

DPP4 Inhibitor Sitagliptin Enhances Lymphocyte Recruitment and Prolongs Survival in a Syngeneic Ovarian Cancer Mouse Model

Simple Summary

The role of immunity in the development and progression of epithelial ovarian cancer (EOC) is well established. Poor T-cell infiltration is associated with mortality in EOC patients, and recent evidence has suggested that the enzyme DPP4 plays a role in this process. The aim of our study was to evaluate the potential of the clinically-approved DPP4-inhibitor sitagliptin to improve immune responses in mice with EOC. We showed that sitagliptin improved CD8+ T-cell responses in an EOC mouse model, consequently reducing metastatic burden and prolonging survival. These data provide a rationale for the use of DPP4-inhibitors as a second-line treatment for EOC.

Abstract

Immunity plays a key role in epithelial ovarian cancer (EOC) progression with a well-documented correlation between patient survival and high intratumoral CD8+ to T regulatory cell (Treg) ratios. We previously identified dysregulated DPP4 activity in EOCs as a potentially immune-disruptive influence contributing to a reduction in CXCR3-mediated T-cell infiltration in solid tumours. We therefore hypothesized that inhibition of DPP4 activity by sitagliptin, an FDA-approved inhibitor, would improve T-cell infiltration and function in a syngeneic ID8 mouse model of EOC. Daily oral sitagliptin at 50 mg/kg was provided to mice with established primary EOCs. Sitagliptin treatment decreased metastatic tumour burden and significantly increased overall survival and was associated with significant changes to the immune landscape. Sitagliptin increased overall CXCR3-mediated CD8+ T-cell trafficking to the tumour and enhanced the activation and proliferation of CD8+ T-cells in tumour tissue and the peritoneal cavity. Substantial reductions in suppressive cytokines, including CCL2, CCL17, CCL22 and IL-10, were also noted and were associated with reduced CD4+ CD25+ Foxp3+ Treg recruitment in the tumour. Combination therapy with paclitaxel, however, typical of standard-of-care for patients in palliative care, abolished CXCR3-specific T-cell recruitment stimulated by sitagliptin. Our data suggest that sitagliptin may be suitable as an adjunct therapy for patients between chemotherapy cycles as a novel approach to enhance immunity, optimise T-cell-mediated function and improve overall survival.

Hypoxia Regulates DPP4 Expression, Proteolytic Inactivation, and Shedding from Ovarian Cancer Cells

The treatment of ovarian cancer has not significantly changed in decades and it remains one of the most lethal malignancies in women. The serine protease dipeptidyl peptidase 4 (DPP4) plays key roles in metabolism and immunity, and its expression has been associated with either pro- or anti-tumour effects in multiple tumour types. In this study, we provide the first evidence that DPP4 expression and enzyme activity are uncoupled under hypoxic conditions in ovarian cancer cells. Whilst we identified strong up-regulation of DPP4 mRNA expression under hypoxic growth, the specific activity of secreted DPP4 was paradoxically decreased. Further investigation revealed matrix metalloproteinases (MMP)-dependent inactivation and proteolytic shedding of DPP4 from the cell surface, mediated by at least MMP10 and MMP13. This is the first report of uncoupled DPP4 expression and activity in ovarian cancer cells, and suggests a previously unrecognized, cell- and tissue-type-dependent mechanism for the regulation of DPP4 in solid tumours. Further studies are necessary to identify the functional consequences of DPP4 processing and its potential prognostic or therapeutic value.

Abstract 5547: Synergistic action of sitagliptin and checkpoint inhibition for ovarian cancer therapy

Ovarian cancer is the most lethal gynecological malignancy and treatment options have not improved in decades. Whilst ovarian tumors have an immune-mediated component, emerging immunotherapies (e.g. anti-PD-1, anti-PD-L1) have failed to achieve robust clinical response for ovarian cancer patients. There is an urgent need to develop new therapeutic strategies to improve survival rates in women, particularly those with recurrent, chemoresistant disease. In an ongoing study we are investigating the repurposing of sitagliptin, an anti-diabetes drug, as a novel immunomodulatory therapy in ovarian cancer. Ovarian tumors were generated in C57BL/6 wild-type mice by intrabursal implantation of ID8 murine ovarian cancer cells. Following the formation of primary tumors (~2 weeks), mice received a daily oral dose of sitagliptin (50mg/kg) until ethical endpoint. Anti-tumor immune responses were examined by flow cytometry and immunohistochemical staining according to tumor stage. Mice were assessed for overall survival compared to paclitaxel chemotherapy as standard-of-care. Daily sitagliptin treatment increased circulating Teff:Treg cell ratios in the blood, peritoneal fluid and tumor tissue at an early stage, and this was sustained throughout disease. Sitagliptin also enhanced T effector cell activation and proliferation, indicating that increased Teff:Treg ratios were a positive indicator of the anti-tumor immune response. Treatment with sitagliptin alone increased median survival time by 27% compared to both untreated controls and paclitaxel as standard-of-care, suggesting a beneficial effect mediated by anti-tumor immune responses. Of particular interest, sitagliptin treatment specifically increased the percentage of CXCR3+ T effector cells in the peritoneal cavity. Recent data has suggested that CXCR3+ T cells are functionally required for immune checkpoint inhibitors to exert efficacy. Thus, we hypothesize that sitagliptin may enhance the efficacy of immune checkpoint inhibitor therapies in ovarian cancers. Our ongoing studies are investigating the combination of sitagliptin with anti-PD-1 and anti-PD-L1 antibodies, as a rational approach to improving their efficacy in ovarian cancers. These studies will identify a clinically relevant and directly translatable approach to improve prognosis for ovarian cancer patients.

Citation Format: Laura R. Moffitt, Amy L. Wilson, Bashirah Basri, Kirsty L. Wilson, Magdalena Plebanski, Andrew N. Stephens. Synergistic action of sitagliptin and checkpoint inhibition for ovarian cancer therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5547.

Abstract B69: Noninvasive tumor tracking and characterization of stage-specific immunity in a syngeneic mouse model of ovarian cancer

Ovarian cancers are the most lethal gynecologic malignancy, with high levels of relapse and acquired chemoresistance. Immunity clearly plays a role in ovarian tumor growth, but the inability to accurately correlate progression with stage-specific changes in immunity—both over time and in response to therapy—has hampered our understanding of antitumor immune responses. There is a clear need for improved methods to accurately model and monitor ovarian cancer progression and study its interplay with immunity in vivo. We have generated and characterized an ovarian cancer mouse model allowing noninvasive, real-time tumor imaging with stage-specific tracking of progression over time. Using CRISPR, we integrated the near infra-red phytochrome iRFP720 into the ROSA26 locus of ID8 mouse ovarian cancer cells, and intrabursally implanted these into syngeneic C57BL/6 mice. Noninvasive fluorescence imaging was correlated with post-mortem tumor deposition, and immune populations were assessed at each stage to link immune status with disease progression. Finally, we tested whether this model could be used to monitor therapeutic responses in vivo in real time. Fluorescence imaging accurately identified four distinct stages of cancer progression; (i) primary tumor establishment and growth over 3 weeks; (ii) initial dissemination; (iii) development and expansion of multiple metastases; and (iv) end-stage accumulation of peritoneal ascites. These observations were validated post-mortem. Weight and circumference increase, the standard parameters for tumor burden, did not occur until extensive disease dissemination (week 8), demonstrating their inadequacy for early tumor monitoring. There were no significant differences in immune populations between wild-type and iRFP+ tumor-bearing mice by flow cytometry, indicating iRFP expression by itself does not alter immune profiles. Tumor progression, by contrast, was clearly correlated with decreased frequencies of T-helper 1 (Th1) cells, increased Th2 cells, and a stage-specific decrease in Teff:Treg cell ratios in the peritoneal cavity. Treatment with paclitaxel reduced the tumor volume detected by fluorescence, with tumor recurrence over time. Moreover, paclitaxel depleted peritoneal CD8+ Teff cells, dendritic cells and Th1 cells. Our data demonstrate the effective use of noninvasive fluorescence imaging to discretely stage and quantify ovarian tumor progression, and to correlate therapeutic responses in real time. Moreover, the model mimics the progression of human disease, despite lacking genetic equivalence to human ovarian cancer, and hence has utility for the stage-specific analysis of immune-mediated function.

Citation Format: Amy L. Wilson, Kirsty L. Wilson, Maree Bilandzic, Laura R. Moffitt, Magdalena Plebanski, Andrew N. Stephens. Noninvasive tumor tracking and characterization of stage-specific immunity in a syngeneic mouse model of ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B69.

Autoantibodies against HSF1 and CCDC155 as Biomarkers of Early-Stage, High-Grade Serous Ovarian Cancer

Background: Tumor-directed circulating autoantibodies (AAb) are a well-established feature of many solid tumor types, and are often observed prior to clinical disease manifestation. As such, they may provide a good indicator of early disease development. We have conducted a pilot study to identify novel AAbs as markers of early-stage HGSOCs.Methods: A rare cohort of patients with early (FIGO stage Ia-c) HGSOCs for IgG, IgA, and IgM-mediated AAb reactivity using high-content protein arrays (containing 9,184 individual proteins). AAb reactivity against selected antigens was validated by ELISA in a second, independent cohort of individual patients.Results: A total of 184 antigens were differentially detected in early-stage HGSOC patients compared with all other patient groups assessed. Among the six most highly detected "early-stage" antigens, anti-IgA AAbs against HSF1 and anti-IgG AAbs CCDC155 (KASH5; nesprin 5) were significantly elevated in patients with early-stage malignancy. Receiver operating characteristic (ROC) analysis suggested that AAbs against HSF1 provided better detection of early-stage malignancy than CA125 alone. Combined measurement of anti-HSF1, anti-CCDC155, and CA125 also improved efficacy at higher sensitivity.Conclusions: The combined measurement of anti-HSF1, anti-CCDC155, and CA125 may be useful for early-stage HGSOC detection.Impact: This is the first study to specifically identify AAbs associated with early-stage HGSOC. The presence and high frequency of specific AAbs in early-stage cancer patients warrants a larger scale examination to define their value for early disease detection at primary diagnosis and/or recurrence. Cancer Epidemiol Biomarkers Prev; 27(2); 183-92. ©2017 AACR.