Development of substituted benzimidazoles as inhibitors of human aldehyde dehydrogenase 1A isoenzymes

Aldehyde dehydrogenase 1A (ALDH1A) isoforms may be a useful target for overcoming chemotherapy resistance in high-grade serous ovarian cancer (HGSOC) and other solid tumor cancers. However, as different cancers express different ALDH1A isoforms, isoform selective inhibitors may have a limited therapeutic scope. Furthermore, resistance to an ALDH1A isoform selective inhibitor could arise via induction of expression of other ALDH1A isoforms. As such, we have focused on the development of pan-ALDH1A inhibitors, rather than on ALDH1A isoform selective compounds. Herein, we report the development of a new group of pan-ALDH1A inhibitors to assess whether broad spectrum ALDH1A inhibition is an effective adjunct to chemotherapy in HGSOC. Optimization of the CM10 scaffold, aided by ALDH1A1 crystal structures, led to improved biochemical potencies, improved cellular efficacy as demonstrated by reduction in ALDEFLUOR signal in HGSOC cells, and substantial improvements in liver microsomal stability. Based on this work we identified two compounds 17 and 25 suitable for future in vivo proof of concept experiments.

EGFL6 promotes endometrial cancer cell migration and proliferation

OBJECTIVE

EGFL6, a growth factor produced by adipocytes, is upregulated in and implicated in the tumorigenesis of multiple tumor types. Given the strong link between obesity and endometrial cancer, we sought to determine the impact of EGFL6 on endometrial cancer.

METHODS

EGFL6 expression in endometrial cancer and correlation with patient outcomes was evaluated in the human protein atlas and TCGA. EGFL6 treatment, expression upregulation, and shRNA knockdown were used to evaluate the impact of EGFL6 on the proliferation and migration of 3 endometrial cancer cell lines in vitro. Similarly, the impact of EGFL6 expression and knockdown on tumor growth was evaluated. Western blotting was used to evaluate the impact of EGFL6 on MAPK phosphorylation.

RESULTS

EGFL6 is upregulated in endometrial cancer, primarily in cony-number high tumors. High tumor endometrial cancer expression of EGFL6 predicts poor patient prognosis. We find that EGFL6 acts to activate the MAPK pathway increasing cellular proliferation and migration. In xenograft models, EGFL6 overexpression increases endometrial cancer tumor growth while EGFL6 knockdown decreases endometrial cancer tumor growth.

CONCLUSIONS

EGFL6 is a marker of poor prognosis endometrial cancers, driving cancer cell proliferation and growth. As such EGFL6 represents a potential therapeutic target in endometrial cancer.

Single-cell analysis reveals the stromal dynamics and tumor-specific characteristics in the microenvironment of ovarian cancer

High-grade serous ovarian carcinoma (HGSOC) is a heterogeneous disease, and a highstromal/desmoplastic tumor microenvironment (TME) is associated with a poor outcome. Stromal cell subtypes, including fibroblasts, myofibroblasts, and cancer-associated mesenchymal stem cells, establish a complex network of paracrine signaling pathways with tumor-infiltrating immune cells that drive effector cell tumor immune exclusion and inhibit the antitumor immune response. In this work, we integrate single-cell transcriptomics of the HGSOC TME from public and in-house datasets (n = 20) and stratify tumors based upon high vs. low stromal cell content. Although our cohort size is small, our analyses suggest a distinct transcriptomic landscape for immune and non-immune cells in high-stromal vs. low-stromal tumors. High-stromal tumors have a lower fraction of certain T cells, natural killer (NK) cells, and macrophages, and increased expression of CXCL12 in epithelial cancer cells and cancer-associated mesenchymal stem cells (CA-MSCs). Analysis of cell-cell communication indicate that epithelial cancer cells and CA-MSCs secrete CXCL12 that interacte with the CXCR4 receptor, which is overexpressed on NK and CD8+ T cells. Dual IHC staining show that tumor infiltrating CD8 T cells localize in proximity of CXCL12+ tumor area. Moreover, CXCL12 and/or CXCR4 antibodies confirm the immunosuppressive role of CXCL12-CXCR4 in high-stromal tumors.

Evaluating the trophic transfer of PCBs from fish to humans: Insights from a synergism of environmental monitoring and physiologically-based pharmacokinetic modeling

Accumulation of polychlorinated biphenyls (PCBs) within fish tissues has prompted many states to issue consumption advisories. In Pennsylvania such advisories suggest one meal per month for most game species harvested from Lake Erie; however, these advisories do not account for the emergent properties of regional PCB mixtures, and the downstream accumulation of PCB congeners into human tissues is poorly documented. This study aimed to demonstrate the utility of pairing environmental monitoring with pharmacokinetic modeling for the purpose of estimating dietary PCB exposure in humans. We qualified and quantified the PCB congeners present in the filets of five Lake Erie fish species and used these data to estimate exposure under consumption scenarios that matched or exceeded the advisories. Physiologically-based pharmacokinetic (PBPK) modeling was then employed to predict PCB accumulation within seven tissue compartments of a hypothetical man and woman over 10 years. Twenty-one congeners were detected between the five fish species at concentrations ranging from 56.0 to 411.7 ng/g. Predicted accumulation in human tissues varied based on tissue type, the species consumed, biological sex, and fish-consumption rate. Notably, steady-state concentrations were higher in fatty tissue compartments ("Fat" and "Liver") and across all tissues in women compared to men. This study serves as a preliminary blueprint for generating predictions of site-specific and tissue-specific exposure through the integration of environmental monitoring and pharmacokinetic modeling. Although the details may vary across applications, this simple approach could complement traditional exposure assessments for vulnerable communities in the Great Lakes region that continue to suffer from legacy contamination.

A putative role for ALDH inhibitors and chemoprevention of BRCA-mutation-driven tumors

Aldehyde dehydrogenase (ALDH) enzymatic activity is a marker of cancer-initiating cells (CIC) in many tumor types. Our group and others have found that ALDH1A family inhibitors (ALDHi) can preferentially induce death of ovarian CIC in established ovarian cancer. We sought to determine if ALDHi, by targeting CIC at the time of tumor initiation, could function as a chemopreventive for ovarian cancer. As BRCA1/2 mutation carriers represent a population who could benefit from an ovarian cancer chemopreventive, we focused on BRCA mutation-associated tumor cell lines and murine tumor models. We found that, compared to BRCA wild-type cells, BRCA mutant ovarian cancer cells are more sensitive to the ALDHi673A. Similarly, while 673A treatment of wild-type fallopian tube epithelial (FTE) cells is non-toxic, 673A induces death in FTE cells with BRCA1 knockdown. Using a murine fallopian tube organoid model of ovarian carcinogenesis, we show that 673A reduced organoid complexity and significantly reduce colony formation of BRCA-mutant cells. Organoids that persisted after 673A treatment were predominantly BRCA1wt, but NF1 mutant, suggesting a resistance mechanism. Finally, using the BPRN (Brca1, Trp53, Rb1, Nf1 inactivated) mouse model of tubo-ovarian cancer, we evaluated the impact of intermittent 673A therapy on carcinogenesis. 673A treatment resulted in a significant reduction in serous tubal intraepithelial carcinoma (STIC) lesions and carcinomas. Collectively, the findings suggest that ALDHi, such as 673A, could serve as chemopreventive agents for BRCA1/2 mutation carriers.

Single-cell analysis reveals the stromal dynamics and tumor-specific characteristics in the microenvironment of ovarian cancer

High-grade serous ovarian carcinoma (HGSOC) is a heterogeneous disease, and a high stromal/desmoplastic tumor microenvironment (TME) is associated with a poor outcome. Stromal cell subtypes, including fibroblasts, myofibroblasts, and cancer-associated mesenchymal stem cells, establish a complex network of paracrine signaling pathways with tumor-infiltrating immune cells that drive effector cell tumor immune exclusion and inhibit the antitumor immune response. Single-cell transcriptomics of the HGSOC TME from public and in-house datasets revealed a distinct transcriptomic landscape for immune and non-immune cells in high-stromal vs. low-stromal tumors. High-stromal tumors had a lower fraction of certain T cells, natural killer (NK) cells, and macrophages and increased expression of CXCL12 in epithelial cancer cells and cancer-associated mesenchymal stem cells (CA-MSCs). Analysis of cell-cell communication indicated that epithelial cancer cells and CA-MSCs secreted CXCL12 that interacted with the CXCR4 receptor, which was overexpressed on NK and CD8 + T cells. CXCL12 and/or CXCR4 antibodies confirmed the immunosuppressive role of CXCL12-CXCR4 in high-stromal tumors.

Quiescent Ovarian Cancer Cells Secrete Follistatin to Induce Chemotherapy Resistance in Surrounding Cells in Response to Chemotherapy

PURPOSE

We recently reported that the transcription factor NFATC4, in response to chemotherapy, drives cellular quiescence to increase ovarian cancer chemoresistance. The goal of this work was to better understand the mechanisms of NFATC4-driven ovarian cancer chemoresistance.

EXPERIMENTAL DESIGN

We used RNA sequencing to identify NFATC4-mediated differential gene expression. CRISPR-Cas9 and FST (follistatin)-neutralizing antibodies were used to assess impact of loss of FST function on cell proliferation and chemoresistance. ELISA was used to quantify FST induction in patient samples and in vitro in response to chemotherapy.

RESULTS

We found that NFATC4 upregulates FST mRNA and protein expression predominantly in quiescent cells and FST is further upregulated following chemotherapy treatment. FST acts in at least a paracrine manner to induce a p-ATF2-dependent quiescent phenotype and chemoresistance in non-quiescent cells. Consistent with this, CRISPR knockout (KO) of FST in ovarian cancer cells or antibody-mediated neutralization of FST sensitizes ovarian cancer cells to chemotherapy treatment. Similarly, CRISPR KO of FST in tumors increased chemotherapy-mediated tumor eradication in an otherwise chemotherapy-resistant tumor model. Suggesting a role for FST in chemoresistance in patients, FST protein in the abdominal fluid of patients with ovarian cancer significantly increases within 24 hours of chemotherapy exposure. FST levels decline to baseline levels in patients no longer receiving chemotherapy with no evidence of disease. Furthermore, elevated FST expression in patient tumors is correlated with poor progression-free, post-progression-free, and overall survival.

CONCLUSIONS

FST is a novel therapeutic target to improve ovarian cancer response to chemotherapy and potentially reduce recurrence rates.

Generation and characterization of humanized affinity-matured EGFL6 antibodies for ovarian cancer therapy

OBJECTIVES

Epidermal growth factor EGF-like domain multiple-6 (EGFL6) is highly expressed in high grade serous ovarian cancer and promotes both endothelial cell proliferation/angiogenesis and cancer cell proliferation/metastasis. As such it has been implicated as a therapeutic target. As a secreted factor, EGFL6 is a candidate for antibody therapy. The objectives of this study were to create and validate humanized affinity-matured EGFL6 neutralizing antibodies for clinical development.

METHODS

A selected murine EGFL6 antibody was humanized using CDR grafting to create 26 variant humanized antibodies. These were screened and the lead candidate was affinity matured. Seven humanized affinity-matured EGFL6 antibodies were screened for their ability to block EGFL6 activity on cancer cells in vitro, two of which were selected and tested their therapeutic activity in vivo.

RESULTS

Humanized affinity matured antibodies demonstrated high affinity for EGFL6 (150 pM to 2.67 nM). We found that several humanized affinity-matured EGFL6 antibodies specifically bound to recombinant, and native human EGFL6. Two lead antibodies were able to inhibit EGFL6-mediated (i) cancer cell migration, (ii) proliferation, and (iii) increase in ERK phosphorylation in cancer cells in vitro. Both lead antibodies restricted growth of an EGFL6 expressing ovarian cancer patient derived xenograft. Analysis of treated human tumor xenografts indicated that anti-EGFL6 therapy suppressed angiogenesis, inhibited tumor cell proliferation, and promoted tumor cell apoptosis.

CONCLUSIONS

Our studies confirm the ability of these humanized affinity-matured antibodies to neutralize EGFL6 and acting as a therapeutic to restrict cancer growth. This work supports the development of these antibody for first-in-human clinical trials.

Targeting Therapeutic Resistance and Multinucleate Giant Cells in CCNE1-Amplified HR-Proficient Ovarian Cancer

Approximately 20% of high-grade serous ovarian cancers (HGSOC) have CCNE1 amplification. CCNE1-amplified tumors are homologous recombination (HR) proficient and resistant to standard therapies. Therapy resistance is associated with increased numbers of polyploid giant cancer cells (PGCC). We sought to identify new therapeutic approaches for patients with CCNE1-amplified tumors. Using TCGA data, we find that the mTOR, HR, and DNA checkpoint pathways are enriched in CCNE1-amplified ovarian cancers. Furthermore, Interactome Mapping Analysis linked the mTOR activity with upregulation of HR and DNA checkpoint pathways. Indeed, we find that mTOR inhibitors (mTORi) downregulate HR/checkpoint genes in CCNE1-amplified tumors. As CCNE1-amplified tumors are dependent on the HR pathway for viability, mTORi proved selectively effective in CCNE1-amplified tumors. Similarly, via downregulation of HR genes, mTORi increased CCNE1-amplifed HGSOC response to PARPi. In contrast, overexpression of HR/checkpoint proteins (RAD51 or ATR), induced resistance to mTORi. In vivo, mTORi alone potently reduced CCNE1-amplified tumor growth and the combination of mTORi and PARPi increased response and tumor eradication. Tumors treated with mTORi demonstrated a significant reduction in ALDH+ PGCCs. Finally, as a proof of principle, we identified three patients with CCNE1 amplified tumors who were treated with an mTORi. All three obtained clinical benefits from the therapy. Our studies and clinical experience indicate mTORi are a potential therapeutic approach for patients with CCNE1-amplified tumors.

Abstract 3146: EGFL6 induces immunosuppressive functions of tumor-associated myeloid cells and mediates resistance to anti-PDL1 therapy

Myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) are critical negative regulators of immunity in cancer. Understanding factors which regulate these cells could result in the identification of new approaches to enhance anti-tumor immunotherapy. One such factor is Epidermal growth factor-like 6 (EGFL6). EGFL6 is a secreted factor known to promote cancer stem like cell migration and regulate cancer cell differentiation. Similarly, EGFL6 promotes endothelial cell migration and proliferation. Indicating a potential role for EGFL6 as a myeloid cell regulatory factor, we found that mice which overexpress Egfl6 have an increased numbers of granulocytes and monocytes in both the bone marrow and spleen. In vitro and ex-vivo analysis indicated that EGFL6, via binding with beta integrins and activation of Syk/ERK signaling, (i) acts as a chemotactic factor for human myeloid cells migration and (ii) promotes their differentiation toward a suppressive state. Suggesting an important role in promoting an immunosuppressive tumor microenvironment (TME), using two syngeneic mouse models of ovarian cancer, we found that expression of Egfl6 in tumor cells resulted in increased accumulation of intra-tumoral MDSCs and TAMs and fewer cytotoxic CD8+ T cells. This was associated with increased tumor growth and shortened animal survival. Gene expression profiling and flow cytometry analysis of tumor infiltrating myeloid cells indicated that Egfl6 induced the expression of immunosuppressive factors, including CXCL2, IL-10 and PD-L1. Consistent with Egfl6 driving an immune suppressive TME, EGFL6 expression in an otherwise immune ‘hot’/anti-PD-L1 responsive tumor model completely inhibited response to anti-PD-L-1 therapy. We are currently evaluating the impact of Egfl6 neutralizing antibody on the efficacy of ICI therapy and anti-tumor immunity. Combined our data show that EGFL6 acts as a chemotactic factor to both recruit myeloid cells to the ovarian TME and subsequently promotes their differentiation to an immunosuppressive phenotype. This suggests EGFL6 is a potential novel therapeutic target to ovarian tumor mediated immunosuppression and enhance response to immune therapy in ovarian cancer patients.

Citation Format: Sarah Sinno, Shoumei Bai, Claudia Coronnello, Anda Vlad, Ronald J. Buckanovich, Sandra Cascio. EGFL6 induces immunosuppressive functions of tumor-associated myeloid cells and mediates resistance to anti-PDL1 therapy [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 3146.

A phase I/II study of ruxolitinib with frontline neoadjuvant and post-surgical therapy in patients with advanced epithelial ovarian, Fallopian tube, or primary peritoneal cancer

5501

Background: The Interleukin-6/JAK/STAT3 axis, via an increase in cancer stem-like cell (CSC) survival, is a reported driver of chemotherapy resistance. We hypothesized that addition of the JAK1/2 inhibitor ruxolitinib to standard chemotherapy would be tolerable and, by targeting therapy-resistant cells, improve the progression-free survival (PFS) of ovarian/fallopian tube/primary peritoneal carcinoma (OV/FT/PPC) patients treated in the up-front setting. Methods: Patients with OV/FT/PPC dispositioned to neoadjuvant chemotherapy were eligible for NRG-GY007 (NCT #02713386). In phase I, treatment was with dose-dense paclitaxel (P) 70 or 80 mg/m2 days 1, 8, and 15; carboplatin (C) AUC 5 or 6 day 1; and ruxolitinib (R) 15mg PO BID, every 21 days. In the absence of tumor progression or an inability to tolerate surgery, interval tumor reductive surgery (TRS) was required after cycle 3. After TRS, 3 additional cycles were administered, followed by maintenance ruxolitinib until progression, unacceptable toxicity, or voluntary withdrawal. In phase II, patients were randomized to dose-dense PC (arm 1) or dose-dense PC plus ruxolitinib (arm 2) at the phase I-defined dose of 15mg PO BID. After 3 cycles, TRS was performed, followed by another 3 cycles of the randomized regimen, without maintenance ruxolitinib. The primary phase II endpoint was progression-free survival (PFS). Results: 17 patients were enrolled in phase I. The MTD was P at 70, C at 5, and R at 15, which was chosen as the phase II dose. 130 patients were enrolled in phase II with a median follow-up of 24 months. There were five Grade 5 events in phase II, 2 in arm 1 and 3 in arm 2, with all except one being unrelated to therapy; a G5 febrile neutropenia in arm 2 was considered possibly related. In arm 2 there was potential trend towards higher grade 3-4 anemia (64% v 27% control), grade 3-4 neutropenia (53% v 37%), thromboembolic events (12.6% v 2.4%), and febrile neutropenia (6% v 0%). The HR for PFS was 0.702 (90% 1-sided CI = 0-0.89, log-rank p = 0.059). The median PFS in arm 1 was 11.6 versus 14.6 in arm 2. The overall survival HR = 0.785 (90% CI = 0.44 to 1.39, p = 0.70). There were no differences between rates of total gross resection. Conclusions: Ruxolitinib 15mg PO BID was well-tolerated with acceptable toxicity in combination with dose-dense PC. The primary endpoint of prolongation of PFS was achieved in the experimental arm. Further study of this combination can be considered. This trial also demonstrates the feasibility of early-phase randomized studies with novel agents and biospecimen collection in front line neoadjuvant treatment of ovarian cancer. Clinical trial information: 02713386.

Carcinoma Associated Mesenchymal Stem/Stromal Cells - Architects of the Pro-tumorigenic tumor microenvironment

The interaction between tumor cells and non-malignant hosts cells within the tumor microenvironment (TME) is critical to the pathophysiology of cancer. These non-malignant host cells, consisting of a variety of stromal, immune and endothelial cells, engage in a complex bidirectional crosstalk with the malignant tumor cells. Mesenchymal stem/stromal cells (MSCs) are one of these host cells, and they play a critical role in directing the formation and function of the entire TME. These MSCs are epigenetically reprogrammed by cancer cells to assume a strongly pro-tumorigenic phenotype and are referred to as carcinoma-associated mesenchymal stem/stromal cells (CA-MSCs). Studies over the last decade demonstrate that CA-MSCs not only directly interact with cancer cells to promote tumor growth and metastasis, but also orchestrate the formation of the TME. CA-MSCs can differentiate into virtually all stromal sub-lineages present in the TME, including pro-tumorigenic cancer associated fibroblasts (CAF), myofibroblasts, and adipocytes. CA-MSCs and the CAFs they produce, secrete much of the extracellular matrix in the TME. Furthermore, CA-MSC secreted factors promote angiogenesis, and recruit immunosuppressive myeloid cells effectively driving tumor immune exclusion. Thus CA-MSCs impact nearly every aspect of the TME. Despite their influence on cancer biology, as CA-MSCs represent a heterogenous population without a single definitive marker, significant confusion remains regarding the origin and proper identification CA-MSCs. This review will focus on the impact of CA-MSCs on cancer progression and metastasis and the ongoing work on CA-MSC identification, nomenclature and mechanism of action.

Shifting the Soil: Metformin Treatment Decreases the Protumorigenic Tumor Microenvironment in Epithelial Ovarian Cancer

Controversy persists regarding metformin's role in cancer therapy. Our recent work suggested metformin acts by impacting the tumor microenvironment (TME), normalizing the epigenetic profile of cancer-associated mesenchymal stem cells (CA-MSC). As CA-MSC can negatively impact tumor immune infiltrates, we evaluated metformin's impact on the human TME, focusing on the interplay of stroma and immune infiltrates. Tumor samples from (i) 38 patients treated with metformin and chemotherapy and (ii) 44 non-metformin matched controls were included in a tissue microarray (TMA). The TMA was used to compare the presence of CA-MSC, desmoplasia and immune infiltrates in the TME. In vitro and in vivo models examined metformin's role in alteration of the CA-MSC phenotype. The average percentage of CA-MSC was significantly lower in metformin-treated than in chemotherapy alone-treated tumors (p = 0.006). There were fewer regulatory T-cells in metformin-treated tumors (p = 0.043). Consistent with CA-MSC's role in excluding T-cells from tumor islets, the T-cells were primarily present within the tumor stroma. Evaluation of metformin's impact in vitro suggested that metformin cannot reverse a CA-MSC phenotype; however, the in vivo model where metformin was introduced prior to the establishment of the CA-MSC phenotype supported that metformin can partially prevent the reprogramming of normal MSC into CA-MSC. Metformin treatment led to a decrease in both the presence of protumorigenic CA-MSC and in immune exclusion of T cells, leading to a more immune-permissive environment. This suggests clinical utility in prevention and in treatment for early-stage disease and putatively in immune therapy.

Egfl6 promotes ovarian cancer progression by inducing the immunosuppressive functions of tumor-infiltrating myeloid cells

Myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) are critical negative regulators of immunity in cancer. Understanding factors which regulate these cells could result in the identification of new approaches to enhance anti-tumor immunotherapy. One such factor is epidermal growth factor-like 6 (EGFL6), a secreted factor known to promote cancer stem like cell migration and regulate cancer cell differentiation. We found that mice which overexpress Egfl6 have an increased numbers of granulocytes and monocytes in both the bone marrow and spleen. In vitro and ex-vivo analysis indicated that EGFL6, via binding with beta integrins and activation of SYK and ERK signaling, (i) acts as a chemotactic factor for myeloid cells migration and (ii) promotes their differentiation toward a suppressive state. Suggesting an important role in promoting an immunosuppressive tumor microenvironment (TME), using two syngeneic mouse models of ovarian cancer, we found that expression of Egfl6 in tumor cells resulted in increased accumulation of intra-tumoral MDSCs and TAMs and fewer cytotoxic CD8+ T cells. This was associated with increased tumor growth and shortened animal survival. Gene expression profiling of tumor infiltrating myeloid cells indicated that Egfl6 induced the expression of immunosuppressive factors, including CXCL2, IL-10 and PD-L1. Moreover, in an immune ‘hot’ tumor model, EGFL6 completely inhibited response to a-PD-L-1 therapy. Combined our data show that EGFL6 induces the recruitment of myeloid cells into the ovarian TME and subsequently promotes their immunosuppressive functions. This suggest EGFL6 is a potential novel therapeutic target to enhance response to immune therapy in OvCa patients.

Supported by Ovarian Cancer Research Alliance

Cancer-associated MSC drive tumor immune exclusion and resistance to immunotherapy, which can be overcome by Hedgehog inhibition

We investigated the impact of cancer-associated mesenchymal stem cells (CA-MSCs) on ovarian tumor immunity. In patient samples, CA-MSC presence inversely correlates with the presence of intratumoral CD8+ T cells. Using an immune “hot” mouse ovarian cancer model, we found that CA-MSCs drive CD8+ T cell tumor immune exclusion and reduce response to anti–PD-L1 immune checkpoint inhibitor (ICI) via secretion of numerous chemokines (Ccl2, Cx3cl1, and Tgf-β1), which recruit immune-suppressive CD14+Ly6C+Cx3cr1+ monocytic cells and polarize macrophages to an immune suppressive Ccr2hiF4/80+Cx3cr1+CD206+ phenotype. Both monocytes and macrophages express high levels of transforming growth factor β–induced (Tgfbi) protein, which suppresses NK cell activity. Hedgehog inhibitor (HHi) therapy reversed CA-MSC effects, reducing myeloid cell presence and expression of Tgfbi, increasing intratumoral NK cell numbers, and restoring response to ICI therapy. Thus, CA-MSCs regulate antitumor immunity, and CA-MSC hedgehog signaling is an important target for cancer immunotherapy.

Cost-effectiveness analysis of tumor molecular classification in high-risk early-stage endometrial cancer

PURPOSE

Tumor molecular analyses in endometrial cancer (EC) includes 4 distinct subtypes: (1) POLE-mutated, (2) mismatch repair protein (MMR) deficient, (3) p53 mutant, and (4) no specific molecular profile. Recently, a sub-analysis of PORTEC-3 demonstrated notable differences in treatment response between molecular classification (MC) groups. Cost of testing is one barrier to widespread adoption of MC. Therefore, we sought to determine the cost-effectiveness of MC in patients with stage I and II high-risk EC.

METHODS

A Markov decision model was developed to compare tumor molecular classification (TMC) vs. no testing (NT). A healthcare payor's perspective and 5-year time horizon were used. Base case data were abstracted from PORTEC-3 and the molecular sub-analysis. Cost and utility data were derived from public databases, peer-reviewed literature, and expert input. Strategies were compared using the incremental cost-effectiveness ratio (ICER) with effectiveness in quality-adjusted life years (QALYs) and evaluated with a willingness-to-pay threshold of $100,000 per QALY gained. Sensitivity analyses were performed to test model robustness.

RESULTS

When compared to NT, TMC was cost effective with an ICER of $25,578 per QALY gained; incremental cost was $1780 and incremental effectiveness was 0.070 QALYs. In one-way sensitivity analyses, results were most sensitive to the cost of POLE testing, but TMC remained cost-effective over all parameter ranges.

CONCLUSIONS

TMC in early-stage high-risk EC is cost-effective, and the model results were robust over a range of parameters. Given that MC can be used to guide adjuvant treatment decisions, these findings support adoption of TMC into routine practice.

Abstract 2060: Therapeutic approaches for CCNE1-amplified HR-proficient ovarian cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors have shown great success in ovarian cancer patients that are homologous recombination deficient (HRD). However, approximately 50% of high grade serous ovarian cancer (HGSOC) are HR-proficient. HR-proficient Cancer cells evade lethal DNA damage by triggering HR pathways at the cost of genome stability and evolving of more aggressive cancer cells. Cyclin E1 (CCNE1) amplification is a major subset of known HR-proficient HGSOC. This subset of cancer responds poorly to essentially all available ovarian cancer therapies including PARP inhibitors. Our study showed that the mTOR, HR, and checkpoint pathways were enriched in CCNE1-amplifed ovarian cancer patients. Interactome mapping demonstrated that many of the interactive proteins in the mTOR pathway were also components of HR and DNA checkpoint pathways. mTOR inhibition resulted in downregulation of HR and DNA checkpoint proteins. Downregulation of ATR partly mirrored mTOR inhibition. mTOR inhibitors and ATR inhibitors synergized with PARP inhibitors in vitro and in vivo in CCNE1-amplified HGSOC tumors. This was associated with decrease in cancer stem-like cancer cells and loss of polyploid tumor cells, which are vital for evolving of more aggressive, therapy-resistant cancer cells. These studies will have potential impact on further preclinical validation and clinical applications to cure CCNE1-amplifed HRP ovarian cancer.

Citation Format: Shoumei Bai, Ronald J. Buckanovich. Therapeutic approaches for CCNE1-amplified HR-proficient ovarian 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 2060.

Cost-effectiveness analysis of p53 immunohistochemical testing in stage I and II high-risk endometrial cancer

e18838

Background: PORTEC-3, a phase III clinical trial comparing adjuvant radiation alone (RT) to combined chemoradiation therapy (CTRT) in patients with high-risk endometrial cancer (EC), demonstrated no benefit with CTRT compared to RT for patients with stage I and II EC. However, a subsequent tumor molecular analysis revealed that individuals with stage I and II high-risk EC with p53 mutations had statistically significantly improved progression-free survival (PFS) and clinically significantly improved overall survival (OS) with combined CTRT. As p53 immunohistochemical (IHC) testing and CTRT adds to cost and toxicity, we sought to evaluate the cost-effectiveness of p53 IHC tumor testing in patients with stage I and II high-risk EC. Methods: A Markov decision model was developed to compare two testing strategies in patients with stage I and II high-risk EC: p53 IHC testing vs. no IHC testing. IHC staining for p53 is an accurate and validated surrogate for TP53 mutational status. As a result, p53 IHC testing alone was used in the decision analysis. Data from PORTEC-3 and the subsequent molecular analysis were used for the base case model parameters, including treatment regimen, PFS, OS, and incidence of p53-mutated tumors. Cost and utility data were derived from the Federal Supply Schedule, the Centers for Medicare and Medicaid Services (CMS) Fee Schedules, the Tufts CEA registry, peer-reviewed literature, and expert input. Data analysis was performed using TreeAge Pro Software, 2021. Effectiveness outcomes included quality-adjusted life-years (QALYs) and incremental cost-effectiveness ratios (ICERs). Sensitivity analyses were performed in order to identify the influence of individual variables on the overall model. Results: When compared to no testing, p53 IHC testing resulted in a cost savings of $471 per patient while providing an additional 0.310 QALYs. Therefore, p53 IHC testing was less expensive and more effective than no IHC testing and was a dominant strategy in this model. In one-way sensitivity analyses, CTRT and RT costs, discount rate, and percentage of p53 mutations detected had the most impact on the model; however, p53 IHC testing remained a cost-saving strategy over all parameter ranges examined. Conclusions: For patients with high-risk stage I and II EC, this analysis suggests that p53 IHC testing is cost-effective compared to no testing in determining the costs and benefits of adjuvant chemotherapy. Although additional studies are warranted, this data provides further support for the role of molecular-based treatment decisions for high-risk stage I and II endometrial cancer.

The MEK1/2 Pathway as a Therapeutic Target in High-Grade Serous Ovarian Carcinoma

High-grade serous ovarian carcinoma (HGSOC) is the deadliest of gynecological cancers due to its high recurrence rate and acquired chemoresistance. RAS/MEK/ERK pathway activation is linked to cell proliferation and therapeutic resistance, but the role of MEK1/2-ERK1/2 pathway in HGSOC is poorly investigated. We evaluated MEK1/2 pathway activity in clinical HGSOC samples and ovarian cancer cell lines using immunohistochemistry, immunoblotting, and RT-qPCR. HGSOC cell lines were used to assess immediate and lasting effects of MEK1/2 inhibition with trametinib in vitro. Trametinib effect on tumor growth in vivo was investigated using mouse xenografts. MEK1/2 pathway is hyperactivated in HGSOC and is further stimulated by cisplatin treatment. Trametinib treatment causes cell cycle arrest in G1/0-phase and reduces tumor growth rate in vivo but does not induce cell death or reduce fraction of CD133+ stem-like cells, while increasing expression of stemness-associated genes instead. Transient trametinib treatment causes long-term increase in a subpopulation of cells with high aldehyde dehydrogenase (ALDH)1 activity that can survive and grow in non-adherent conditions. We conclude that MEK1/2 inhibition may be a promising approach to suppress ovarian cancer growth as a maintenance therapy. Promotion of stem-like properties upon MEK1/2 inhibition suggests a possible mechanism of resistance, so a combination with CSC-targeting drugs should be considered.

Aldehyde dehydrogenase inhibitors promote DNA damage in ovarian cancer and synergize with ATM/ATR inhibitors

Rationale: Aldehyde dehydrogenase (ALDH) enzymes are often upregulated in cancer cells and associated with therapeutic resistance. ALDH enzymes protect cells by metabolizing toxic aldehydes which can induce DNA double stand breaks (DSB). We recently identified a novel ALDH1A family inhibitor (ALDHi), 673A. We hypothesized that 673A, via inhibition of ALDH1A family members, could induce intracellular accumulation of genotoxic aldehydes to cause DSB and that ALDHi could synergize with inhibitors of the ATM and ATR, proteins which direct DSB repair.

Methods: We used immunofluorescence to directly assess levels of the aldehyde 4-hydroxynonenal and comet assays to evaluate DSB. Western blot was used to evaluate activation of the DNA damage response pathways. Cell counts were performed in the presence of 673A and additional aldehydes or aldehyde scavengers. ALDH inhibition results were confirmed using ALDH1A3 CRISPR knockout. Synergy between 673A and ATM or ATR inhibitors was evaluated using the Chou-Talalay method and confirmed in vivo using cell line xenograft tumor studies.

Results: The ALDHi 673A cellular accumulation of toxic aldehydes which induce DNA double strand breaks. This is exacerbated by addition of exogenous aldehydes such as vitamin-A (retinaldehyde) and ameliorated by aldehyde scavengers such as metformin and hydralazine. Importantly, ALDH1A3 knockout cells demonstrated increased sensitivity to ATM/ATR inhibitors. And, ALDHi synergized with inhibitors of ATM and ATR, master regulators of the DSB DNA damage response, both in vitro and in vivo. This synergy was evident in homologous recombination (HR) proficient cell lines.

Conclusions: ALDHi can be used to induce DNA DSB in cancer cells and synergize with inhibitors the ATM/ATR pathway. Our data suggest a novel therapeutic approach to target HR proficient ovarian cancer cells.

Immunotherapy Advances for Epithelial Ovarian Cancer

Simple Summary

The overall five-year survival rate in epithelial ovarian cancer is 44% and has only marginally improved in the past two decades. Despite an initial response to standard treatment consisting of chemotherapy and surgical removal of tumor, the lesions invariably recur, and patients ultimately die of chemotherapy resistant disease. New treatment modalities are needed in order to improve the prognosis of women diagnosed with ovarian cancer. One such modality is immunotherapy, which aims to boost the capacity of the patient’s immune system to recognize and attack the tumor cells. We performed a retrospective study to identify some of the most promising immune therapies for epithelial ovarian cancer. Special emphasis was given to immuno-oncology clinical trials.

Abstract

New treatment modalities are needed in order to improve the prognosis of women diagnosed with epithelial ovarian cancer (EOC), the most aggressive gynecologic cancer type. Most ovarian tumors are infiltrated by immune effector cells, providing the rationale for targeted approaches that boost the existing or trigger new anti-tumor immune mechanisms. The field of immuno-oncology has experienced remarkable progress in recent years, although the results seen with single agent immunotherapies in several categories of solid tumors have yet to extend to ovarian cancer. The challenge remains to determine what treatment combinations are most suitable for this disease and which patients are likely to benefit and to identify how immunotherapy should be incorporated into EOC standard of care. We review here some of the most promising immune therapies for EOC and focus on those currently tested in clinical trials.

Epigenomic Reprogramming toward Mesenchymal-Epithelial Transition in Ovarian-Cancer-Associated Mesenchymal Stem Cells Drives Metastasis

A role for cancer cell epithelial-to-mesenchymal transition (EMT) in cancer is well established. Here, we show that, in addition to cancer cell EMT, ovarian cancer cell metastasis relies on an epigenomic mesenchymal-to-epithelial transition (MET) in host mesenchymal stem cells (MSCs). These reprogrammed MSCs, termed carcinoma-associated MSCs (CA-MSCs), acquire pro-tumorigenic functions and directly bind cancer cells to serve as a metastatic driver/chaperone. Cancer cells induce this epigenomic MET characterized by enhancer-enriched DNA hypermethylation, altered chromatin accessibility, and differential histone modifications. This phenomenon appears clinically relevant, as CA-MSC MET is highly correlated with patient survival. Mechanistically, mirroring MET observed in development, MET in CA-MSCs is mediated by WT1 and EZH2. Importantly, EZH2 inhibitors, which are clinically available, significantly inhibited CA-MSC-mediated metastasis in mouse models of ovarian cancer.

Development of 2,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one inhibitors of aldehyde dehydrogenase 1A (ALDH1A) as potential adjuncts to ovarian cancer chemotherapy

There is strong evidence that inhibition of one or more Aldehyde Dehydrogenase 1A (ALDH1A) isoforms may be beneficial in chemotherapy-resistant ovarian cancer and other tumor types. While many previous efforts have focused on development of ALDH1A1 selective inhibitors, the most deadly ovarian cancer subtype, high-grade serous (HGSOC), exhibits elevated expression of ALDH1A3. Herein, we report continued development of pan-ALDH1A inhibitors to assess whether broad spectrum ALDH1A inhibition is an effective adjunct to chemotherapy in this critical tumor subtype. Optimization of the CM39 scaffold, aided by metabolite ID and several new ALDH1A1 crystal structures, led to improved biochemical potencies, improved cellular ALDH inhibition in HGSOC cell lines, and substantial improvements in microsomal stability culminating in orally bioavailable compounds. We demonstrate that two compounds 68 and 69 are able to synergize with chemotherapy in a resistant cell line and patient-derived HGSOC tumor spheroids, indicating their suitability for future in vivo proof of concept experiments.

Regulation and pharmacological targeting of RAD51 in cancer

Regulation of homologous recombination (HR) is central for cancer prevention. However, too little HR can increase cancer incidence, whereas too much HR can drive cancer resistance to therapy. Importantly, therapeutics targeting HR deficiency have demonstrated a profound efficacy in the clinic improving patient outcomes, particularly for breast and ovarian cancer. RAD51 is central to DNA damage repair in the HR pathway. As such, understanding the function and regulation of RAD51 is essential for cancer biology. This review will focus on the role of RAD51 in cancer and beyond and how modulation of its function can be exploited as a cancer therapeutic.

Carcinoma-Associated Mesenchymal Stem Cells Promote Chemoresistance in Ovarian Cancer Stem Cells via PDGF Signaling

Within the ovarian cancer tumor microenvironment, cancer stem-like cells (CSC) interact with carcinoma associated mesenchymal stem/stromal cells (CA-MSC) through multiple secreted cytokines and growth factors. These paracrine interactions have been revealed to cause enrichment of CSC and their chemoprotection; however, it is still not known if platelet-derived growth factor (PDGF) signaling is involved in facilitating these responses. In order to probe this undiscovered bidirectional communication, we created a model of ovarian malignant ascites in the three-dimensional (3D) hanging drop heterospheroid array, with CSC and CA-MSC. We hypothesized that PDGF secretion by CA-MSC increases self-renewal, migration, epithelial to mesenchymal transition (EMT) and chemoresistance in ovarian CSC. Our results indicate that PDGF signaling in the CSC-MSC heterospheroids significantly increased stemness, metastatic potential and chemoresistance of CSC. Knockdown of PDGFB in MSC resulted in abrogation of these phenotypes in the heterospheroids. Our studies also reveal a cross-talk between PDGF and Hedgehog signaling in ovarian cancer. Overall, our data suggest that when the stromal signaling via PDGF to ovarian CSC is blocked in addition to chemotherapy pressure, the tumor cells are significantly more sensitive to chemotherapy. Our results emphasize the importance of disrupting the signals from the microenvironment to the tumor cells, in order to improve response rates. These findings may lead to the development of combination therapies targeting stromal signaling (such as PDGF and Hedgehog) that can abrogate the tumorigenic, metastatic and platinum resistant phenotypes of ovarian CSC through additional investigations.

Abstract A07: A phase II study of metformin therapy in ovarian cancer with translational endpoints

Epidemiologic studies suggest that metformin can improve outcomes for patients with ovarian cancer. Preclinical studies suggest metformin may work in part via effects on cancer stem-like cells (CSCs) to maintain platinum sensitivity. We therefore performed a phase II clinical trial evaluating adjuvant metformin therapy in nondiabetic patients with advanced-stage epithelial ovarian cancer (EOC). The primary aims were translational studies evaluating the impact of metformin on CSC and chemotherapy resistance. Secondary aims included progression-free and overall survival. Thirty-eight patients with confirmed stage IIC (n=1)/III (n=25)/IV (n=12) EOC were treated with either (i) neoadjuvant metformin followed by primary debulking surgery and adjuvant chemotherapy + metformin, or (ii) three cycles of neoadjuvant chemotherapy and metformin, followed by interval debulking surgery, and adjuvant chemotherapy + metformin. Thirty-two patients (84%) completed six cycles metformin + chemotherapy. Metformin was well tolerated with one grade III/IV treatment-related adverse event (3%). Median PFS was 18.0 months (95% CI 14.0-21.6). Median OS was surprisingly long at 57.9 months (95% CI 28.0 – not estimable). For patients with recurred platinum sensitive disease, response to second-line therapy was 85%. Translational studies comparing metformin-treated tumors and historical controls found that metformin-treated tumors had a 2.6-fold decrease in ALDH+/CD133+ CSC (p<0.0001). Consistent with this, metformin-treated tumor cells (i) had an increased sensitivity to cisplatin in vitro, (ii) maintained cisplatin sensitivity over time (p<0.001), and (iii) demonstrated reduced ability to amplify CSC with serial passages (p<0.001). To understand the mechanism of metformin-induced maintenance of platinum response, we evaluated tumor cells and carcinoma-associated mesenchymal stem cells (CA-MSC), cells in the TME we previously reported could increase “stemness” and chemotherapy resistance. While we could not identify significant changes in bulk tumor cells, analysis of DNA methylation in CA-MSC demonstrated metformin treatment resulted in an epigenetic shift. Suggesting CA-MSC alteration drives metformin impact, compared to control CA-MSC, CA-MSC from metformin-treated patients were unable to drive chemotherapy resistance ex vivo. In conclusion, this is the first prospective study of metformin in EOC patients. Metformin therapy was associated with better than expected overall survival, reduction in CSC number, and epigenetic modification of cells in the TME. This was associated with maintenance of platinum sensitivity in vitro and could explain the better than expected median overall survival. This work supports the use of metformin in phase III studies.

Citation Format: Ronald J. Buckanovich, Daniel Chan, Jessica Shank, Kent Griffith, Huihui Fan, Robert Szulawski, Kun Yang, Kevin Reynolds, Carolyn Johnston, Karen McLean, Shitanshu Uppal, Rebecca Liu, Laura Cabrera, Sarah Taylor, Hui Shen, Geeta Mehta, Lan Coffman. A phase II study of metformin therapy in ovarian cancer with translational endpoints [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A07.

Abstract PR05: Patient-derived tumoroids for exploration of the ovarian cancer stem cell regulation, chemoresistance, and tumor heterogeneity

Ovarian cancer is the leading cause of gynecologic malignancy, characterized by a high degree of heterogeneity and relapse leading to poor clinical outcomes. These outcomes are attributed in part to a population of cells termed cancer stem-like cells (CSCs), which are capable of repopulating tumors and are more chemoresistant and tumorigenic. These properties make CSCs a promising target for novel therapies; however, we lack a comprehensive understanding of how they are regulated by the tumor microenvironment. To address this, we have developed a tumoroid culture system wherein patient tumor cells are brought together with controlled ratios of mesenchymal stem cells (MSCs), endothelial cells (ECs), and peripheral blood mononuclear cells (PBMCs) within 384-well hanging drop arrays. This allows for comprehensive analysis of the surrounding cells in the tumor microenvironment and their influence on CSC populations and chemoresistance. The fine control of this culture system over the tumoroid cell composition coupled with the high-throughput nature of 384-well hanging drop also facilitates patient-specific high-throughput analysis of inter- and intrapatient heterogeneity and chemoresistance. Tumoroids were generated from 5 patient samples and characterized using flow cytometry detection of cell type proportions, immunofluorescence evaluation of cell localization, and progressive evaluation of cell localization with fluorescently labeled tumoroids. Patient-derived tumoroids were evaluated by single-cell RNA sequencing. Drug screening was performed on patient-derived tumoroids and control patient-derived spheroids using classic ovarian cancer therapies, carboplatin and paclitaxel, as well as three novel drugs. Additionally, tumor formation assay was performed in immunodeficient mice to compare the rate of tumor formation following injection of tumoroids versus spheroids. Finally, a mathematical model was developed to predict the evolution of cell populations within the tumoroids to facilitate further analysis. Using these methods, we successfully generated and characterized viable tumoroids with primary patient-derived tumor cells, MSCs, ECs, and PBMCs. Within these tumoroids, we observed heterogeneity both between and within patient samples reflective of clinical observations in ovarian cancers. Furthermore, we found increased CSC phenotypes in the tumoroids compared to patient-derived tumor cell-only spheroids. Patient-derived tumoroids also exhibited increased chemoresistance and tumorigenicity compared to spheroids generated with only tumor cells. Through thorough development and characterization of this patient-derived model, we present a novel 3D tumoroid model for comprehensive investigation of CSC regulation, chemoresistance, and heterogeneity in ovarian cancers, with the long-term goal of developing novel CSC targeting therapies and improving clinical outcomes.

This abstract is also being presented as Poster B08.

Citation Format: Micheal E. Bregenzer, Pooja Mehta, Arvind Rao, Karen McLean, Nouri Neamati, Ronald J. Buckanovich, Geeta Mehta. Patient-derived tumoroids for exploration of the ovarian cancer stem cell regulation, chemoresistance, and tumor heterogeneity [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr PR05.

Phase II clinical trial of metformin as a cancer stem cell-targeting agent in ovarian cancer

BACKGROUNDEpidemiologic studies suggest that metformin has antitumor effects. Laboratory studies indicate metformin impacts cancer stem-like cells (CSCs). As part of a phase II trial, we evaluated the impact of metformin on CSC number and on carcinoma-associated mesenchymal stem cells (CA-MSCs) and clinical outcomes in nondiabetic patients with advanced-stage epithelial ovarian cancer (EOC).METHODSThirty-eight patients with stage IIC (n = 1)/III (n = 25)/IV (n = 12) EOC were treated with either (a) neoadjuvant metformin, debulking surgery, and adjuvant chemotherapy plus metformin or (b) neoadjuvant chemotherapy and metformin, interval debulking surgery, and adjuvant chemotherapy plus metformin. Metformin-treated tumors, compared with historical controls, were evaluated for CSC number and chemotherapy response. Primary endpoints were (a) a 2-fold or greater reduction in aldehyde dehydrogenase-positive (ALDH+) CD133+ CSCs and (b) a relapse-free survival at 18 months of more than 50%.RESULTSMetformin was well tolerated. Median progression-free survival was 18.0 months (95% CI 14.0-21.6) with relapse-free survival at 18 months of 59.3% (95% CI 38.6-70.5). Median overall survival was 57.9 months (95% CI 28.0-not estimable). Tumors treated with metformin had a 2.4-fold decrease in ALDH+CD133+ CSCs and increased sensitivity to cisplatin ex vivo. Furthermore, metformin altered the methylation signature in CA-MSCs, which prevented CA-MSC-driven chemoresistance in vitro.CONCLUSIONTranslational studies confirm an impact of metformin on EOC CSCs and suggest epigenetic change in the tumor stroma may drive the platinum sensitivity ex vivo. Consistent with this, metformin therapy was associated with better-than-expected overall survival, supporting the use of metformin in phase III studies.TRIAL REGISTRATIONClinicalTrials.gov NCT01579812.

NFATC4 promotes quiescence and chemotherapy resistance in ovarian cancer

Development of chemotherapy resistance is a major problem in ovarian cancer. One understudied mechanism of chemoresistance is the induction of quiescence, a reversible nonproliferative state. Unfortunately, little is known about regulators of quiescence. Here, we identify the master transcription factor nuclear factor of activated T cells cytoplasmic 4 (NFATC4) as a regulator of quiescence in ovarian cancer. NFATC4 is enriched in ovarian cancer stem-like cells and correlates with decreased proliferation and poor prognosis. Treatment of cancer cells with cisplatin resulted in NFATC4 nuclear translocation and activation of the NFATC4 pathway, while inhibition of the pathway increased chemotherapy response. Induction of NFATC4 activity resulted in a marked decrease in proliferation, G0 cell cycle arrest, and chemotherapy resistance, both in vitro and in vivo. Finally, NFATC4 drove a quiescent phenotype in part via downregulation of MYC. Together, these data identify NFATC4 as a driver of quiescence and a potential new target to combat chemoresistance in ovarian cancer.

An evolving paradigm of cancer stem cell hierarchies: therapeutic implications

Over a decade of research has confirmed the critical role of cancer stem-like cells (CSCs) in tumor initiation, chemoresistance, and metastasis. Increasingly, CSC hierarchies have begun to be defined with some recurring themes. This includes evidence that these hierarchies are 'flexible,' with both cell state transitions and dedifferentiation events possible. These findings pose therapeutic hurdles and opportunities. Here, we review cancer stem cell hierarchies and their interactions with the tumor microenvironment. We also discuss the current therapeutic approaches designed to target CSC hierarchies and initial clinical trial results for CSC targeting agents. While cancer stem cell targeted therapies are still in their infancy, we are beginning to see encouraging results that suggest a positive outlook for CSC-targeting approaches.

Clinicopathological significance of endoplasmic reticulum stress proteins in ovarian carcinoma

Epithelial ovarian cancer (EOC) is a leading cause of cancer-related mortality in the United States due to the late-stage disease at diagnosis. Overexpression of GRP78 and PDI following endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) promote growth and invasion in cancer. To identify novel prognostic biomarkers in EOC, here we determined the expression of ER stress-associated proteins (GRP78, ATF6 and PERK) and correlated with clinical outcome in EOC. Tissue microarray (TMA) samples from 415 tissues collected from three cancer centers (UM, USC, and KCCRI) were used to assess the expression levels of ER-associated proteins using immunohistochemistry (IHC). We observed that the expression levels of GRP78 (p < 0.0001), ATF6 (p < 0.0001), and PERK (p < 0.0001) were significantly increased in specimens of EOC compared to normal tissues, including in the serous subtype (p < 0.0001). Previously we reported that high expression of PDI correlated with poor patient survival in EOC. Here we showed that overexpression of GRP78 and PDI protein expression correlated with poor patient survival (p = 0.03), while low expression of combined GRP78 and PDI correlated with better survival (p = 0.01) in high-grade serous. The increased expression of ER stress-associated proteins in EOC suggests a role for ER stress and the UPR in EOC. More importantly, our results demonstrate that GRP78 and PDI are potential biomarkers for EOC and could be used as dual prognostic markers.

Abstract AP32: THE ROLE OF NFAT3 IN OVARIAN CANCER QUIESCENCE AND CHEMOTHERAPY RESISTANCE

Despite the fact that the majority of patients with ovarian cancer will have a complete clinical remission with combined surgical/chemotherapeutic approaches, Epithelial Ovarian Cancer (EOC) is the fifth most common cause of cancer-related death in American women, with the third highest mortality:incidence ratio. The majority of deaths from ovarian cancer are related to disease recurrence and the subsequent development of ultimately fatal chemotherapy-resistant disease. Elucidating mechanisms of chemoresistance in ovarian cancer cells may identify critical therapeutic targets to prevent or treat relapsed ovarian cancer. One feature that might contribute to the chemotherapy resistance is quiescence.

Quiescence describes a reversible non-proliferative cell state. As such, quiescent cells have reduced susceptibility to chemotherapeutics which target rapidly proliferating cells. Indeed, quiescence is a known mechanism of chemotherapy resistance of normal stem cells. In normal stem cells quiescence is mediated by the NFAT family of transcription factors. Unfortunately, very little is known about the factors that mediate ovarian cancer cell quiescence. Using qRT-PCR, we evaluated the expression of NFAT family members in ovarian cancer cells. We found NFAT3 to be enriched in patient ovarian cancer stem-like cells (CSLC) compared to bulk cancer cells. Treatment of EOC cells with cisplatin chemotherapy resulted in a nuclear translocation of NFAT3 and increase in NFAT3 transcriptional activity. To directly investigate the functional role of NFAT3 in ovarian cancer, we created ovarian cancer cell lines expressing constitutively nuclear/active (cNFAT3) or inducible constitutively active (IcNFAT3) NFAT3. We found that while cNFAT3 expression in ovarian cancer cells did not impact cell viability, senescence or apoptosis, cNFAT3 expression profoundly restricted ovarian cancer cell proliferation, with a 3-fold decreased cell division rates, and cellular arrest in the G0 phase of the cell cycle. Consistent with a quiescent cell phenotype, this was associated with a 10% decrease in cell size, and a 25% decrease in total cellular RNA. Induction of cNFAT3 expression in vivo resulted in tumor growth arrest. This growth arrest resulted in chemotherapy resistance such that cNFAT3 tumors treated with high dose of chemotherapy rapidly expanded after cNFAT3 inactivation. Furthermore, NFAT inhibition with the peptide inhibitor VIVIT enhance chemotherapy response in vitro and in vivo.

Taken together, our data suggests NFAT3 drives a quiescent state in CSLC and thereby mediates chemoresistance. Thus NFAT3 represents a therapeutic target to both overcome chemotherapy resistance in quiescent cancer cells and to restrict the growth of therapy-resistant disease.

Citation Format: Alex J Cole, Mangala Iyengar, Patrick O'Hayer, Kun Yang, Tara Sebastian, Lan Coffman, Ronald J Buckanovich. THE ROLE OF NFAT3 IN OVARIAN CANCER QUIESCENCE AND CHEMOTHERAPY RESISTANCE [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr AP32.

Engineered 3D Model of Cancer Stem Cell Enrichment and Chemoresistance

Intraperitoneal dissemination of ovarian cancers is preceded by the development of chemoresistant tumors with malignant ascites. Despite the high levels of chemoresistance and relapse observed in ovarian cancers, there are no in vitro models to understand the development of chemoresistance in situ. Method: We describe a highly integrated approach to establish an in vitro model of chemoresistance and stemness in ovarian cancer, using the 3D hanging drop spheroid platform. The model was established by serially passaging non-adherent spheroids. At each passage, the effectiveness of the model was evaluated via measures of proliferation, response to treatment with cisplatin and a novel ALDH1A inhibitor. Concomitantly, the expression and tumor initiating capacity of cancer stem-like cells (CSCs) was analyzed. RNA-seq was used to establish gene signatures associated with the evolution of tumorigenicity, and chemoresistance. Lastly, a mathematical model was developed to predict the emergence of CSCs during serial passaging of ovarian cancer spheroids. Results: Our serial passage model demonstrated increased cellular proliferation, enriched CSCs, and emergence of a platinum resistant phenotype. In vivo tumor xenograft assays indicated that later passage spheroids were significantly more tumorigenic with higher CSCs, compared to early passage spheroids. RNA-seq revealed several gene signatures supporting the emergence of CSCs, chemoresistance, and malignant phenotypes, with links to poor clinical prognosis. Our mathematical model predicted the emergence of CSC populations within serially passaged spheroids, concurring with experimentally observed data. Conclusion: Our integrated approach illustrates the utility of the serial passage spheroid model for examining the emergence and development of chemoresistance in ovarian cancer in a controllable and reproducible format.

Wanna Get Away? Maintenance Treatments and Chemotherapy Holidays in Gynecologic Cancers

Epithelial ovarian cancer has a very high rate of relapse after primary therapy; historically approximately 70% of patients with a complete clinical response to surgery and adjuvant chemotherapy will relapse and die of the disease. Although this number has slowly improved, cure rates remain less than 50%. As such, maintenance therapy with the aim of preventing or delaying disease relapse and the goal of improving overall survival has been the subject of intense study. Numerous earlier studies with agents ranging from radioactive phosphorus to extended frontline therapy or to monthly taxol administration demonstrated encouraging improvements in progression-free survival (PFS) only to find, disappointingly, no benefit in overall survival. In addition, the PFS advantage of maintenance therapy was associated with disconcerting side effects such that maintenance therapy was not adapted as standard of care. Studies with bevacizumab and PARP inhibitors have demonstrated a PFS advantage with a manageable side-effect profile. However, an overall survival advantage remains unclear, and the use of these approaches thus remains controversial. Furthermore, in recurrent disease, the length of chemotherapy and benefits of extended chemotherapy is unclear. Thus, additional trials assessing maintenance strategies in ovarian and other gynecologic malignancies are needed.

Overall survival and updated progression-free survival outcomes in a randomized phase II study of combination cediranib and olaparib versus olaparib in relapsed platinum-sensitive ovarian cancer

BACKGROUND

Olaparib is a poly(ADP-ribose) polymerase inhibitor and cediranib is an oral anti-angiogenic. In the primary analysis of this phase II study, combination cediranib/olaparib improved progression-free survival (PFS) compared with olaparib alone in relapsed platinum-sensitive ovarian cancer. This updated analysis was conducted to characterize overall survival (OS) and update PFS outcomes.

PATIENTS AND METHODS

Ninety patients were enrolled to this randomized, open-label, phase II study between October 2011 and June 2013 across nine United States-based academic centers. Data cut-off was 21 December 2016, with a median follow-up of 46 months. Participants had relapsed platinum-sensitive ovarian cancer of high-grade serous or endometrioid histology or had a deleterious germline BRCA1/2 mutation (gBRCAm). Participants were randomized to receive olaparib capsules 400 mg twice daily or cediranib 30 mg daily and olaparib capsules 200 mg twice daily until disease progression.

RESULTS

In this updated analysis, median PFS remained significantly longer with cediranib/olaparib compared with olaparib alone (16.5 versus 8.2 months, hazard ratio 0.50; P = 0.007). Subset analyses within stratum defined by BRCA status demonstrated statistically significant improvement in PFS (23.7 versus 5.7 months, P = 0.002) and OS (37.8 versus 23.0 months, P = 0.047) in gBRCA wild-type/unknown patients, although OS was not statistically different in the overall study population (44.2 versus 33.3 months, hazard ratio 0.64; P = 0.11). PFS and OS appeared similar between the two arms in gBRCAm patients. The most common CTCAE grade 3/4 adverse events with cediranib/olaparib remained fatigue, diarrhea, and hypertension.

CONCLUSIONS

Combination cediranib/olaparib significantly extends PFS compared with olaparib alone in relapsed platinum-sensitive ovarian cancer. Subset analyses suggest this margin of benefit is driven by PFS prolongation in patients without gBRCAm. OS was also significantly increased by the cediranib/olaparib combination in this subset of patients. Additional studies of this combination are ongoing and should incorporate analyses based upon BRCA status.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier NCT0111648.

A Pan-ALDH1A Inhibitor Induces Necroptosis in Ovarian Cancer Stem-like Cells

Ovarian cancer is typified by the development of chemotherapy resistance. Chemotherapy resistance is associated with high aldehyde dehydrogenase (ALDH) enzymatic activity, increased cancer "stemness," and expression of the stem cell marker CD133. As such, ALDH activity has been proposed as a therapeutic target. Although it remains controversial which of the 19 ALDH family members drive chemotherapy resistance, ALDH1A family members have been primarily linked with chemotherapy resistant and stemness. We identified two ALDH1A family selective inhibitors (ALDH1Ai). ALDH1Ai preferentially kills CD133+ ovarian cancer stem-like cells (CSCs). ALDH1Ai induce necroptotic CSC death, mediated, in part, by the induction of mitochondrial uncoupling proteins and reduction in oxidative phosphorylation. ALDH1Ai is highly synergistic with chemotherapy, reducing tumor initiation capacity and increasing tumor eradication in vivo. These studies link ALDH1A with necroptosis and confirm the family as a critical therapeutic target to overcome chemotherapy resistance and improve patient outcomes.

Ovarian Carcinoma-Associated Mesenchymal Stem Cells Arise from Tissue-Specific Normal Stroma

Carcinoma-associated mesenchymal stem cells (CA-MSCs) are critical stromal progenitor cells within the tumor microenvironment (TME). We previously demonstrated that CA-MSCs differentially express bone morphogenetic protein family members, promote tumor cell growth, increase cancer "stemness," and chemotherapy resistance. Here, we use RNA sequencing of normal omental MSCs and ovarian CA-MSCs to demonstrate global changes in CA-MSC gene expression. Using these expression profiles, we create a unique predictive algorithm to classify CA-MSCs. Our classifier accurately distinguishes normal omental, ovary, and bone marrow MSCs from ovarian cancer CA-MSCs. Suggesting broad applicability, the model correctly classifies pancreatic and endometrial cancer CA-MSCs and distinguishes cancer associated fibroblasts from CA-MSCs. Using this classifier, we definitively demonstrate ovarian CA-MSCs arise from tumor mediated reprograming of local tissue MSCs. Although cancer cells alone cannot induce a CA-MSC phenotype, the in vivo ovarian TME can reprogram omental or ovary MSCs to protumorigenic CA-MSCs (classifier score of >0.96). In vitro studies suggest that both tumor secreted factors and hypoxia are critical to induce the CA-MSC phenotype. Interestingly, although the breast cancer TME can reprogram bone marrow MSCs into CA-MSCs, the ovarian TME cannot, demonstrating for the first time that tumor mediated CA-MSC conversion is tissue and cancer type dependent. Together these findings (a) provide a critical tool to define CA-MSCs and (b) highlight cancer cell influence on distinct normal tissues providing powerful insights into the mechanisms underlying cancer specific metastatic niche formation. Stem Cells 2019;37:257-269.

Leukemia inhibitory factor functions in parallel with interleukin-6 to promote ovarian cancer growth

Ovarian carcinoma-associated mesenchymal stem cells (CA-MSC) produce not only high levels of IL6 but also the related cytokine leukemia inhibitory factor (LIF). Interleukin 6 (IL6) mediated activation of STAT3 is implicated as a critical therapeutic target for cancer therapy. Less is known about the role of LIF, which can similarly activate STAT3, in ovarian cancer. We therefore sought to evaluate the tumorigenic effects of CA-MSC paracrine LIF signaling and the redundancy of IL6 and LIF in activating ovarian cancer STAT3 mediated cancer growth. As expected, we found that both IL6 and LIF induce STAT3 phosphorylation in tumor cells. In addition, both IL6 and LIF increased the percentage of ALDH+ ovarian cancer stem-like cells (CSC). Supporting redundancy of function by the two cytokines, CA-MSC induced STAT3 phosphorylation and increased cancer cell ‘stemness’. This effect was not inhibited by LIF or IL6 blocking antibodies alone, but was prevented by dual IL6/LIF blockade or JAK2 inhibition. Similarly, small hairpin RNA (shRNA)-mediated reduction of IL6 or LIF in CA-MSC partially decreased but could not completely abrograte the ability of CA-MSC to induce STAT3 phosphorylation and stemness. Importantly, the in vivo pro-tumorigenic effect of CA-MSC is abrogated by dual blockade with the JAK2 inhibitor ruxolitinib to a much greater extent than treatment with anti-IL6 or anti-LIF antibody alone. Ruxolitinib treatment also improves survival in the immunocompetent ovarian cancer mouse model system with ID8 tumor cells plus MSC. Ruxolitinib-treated tumors in both the immunocompromised and immunocompetent animal models demonstrate decreased phospho-STAT3, indicating on-target activity. In conclusion, CA-MSC activate ovarian cancer cell STAT3 signaling via IL6 and LIF and increase tumorigenesis cancer stemness. This functional redundancy suggests that therapeutic targeting of a single cytokine may be less effective than strategies such as dual inhibitor therapy or targeting shared downstream factors of the JAK/STAT pathway.

Structure-Based Optimization of a Novel Class of Aldehyde Dehydrogenase 1A (ALDH1A) Subfamily-Selective Inhibitors as Potential Adjuncts to Ovarian Cancer Chemotherapy

Aldehyde dehydrogenase (ALDH) activity is commonly used as a marker to identify cancer stem-like cells. The three ALDH1A isoforms have all been individually implicated in cancer stem-like cells and in chemoresistance; however, which isoform is preferentially expressed varies between cell lines. We sought to explore the structural determinants of ALDH1A isoform selectivity in a series of small-molecule inhibitors in support of research into the role of ALDH1A in cancer stem cells. An SAR campaign guided by a cocrystal structure of the HTS hit CM39 (7) with ALDH1A1 afforded first-in-class inhibitors of the ALDH1A subfamily with excellent selectivity over the homologous ALDH2 isoform. We also discovered the first reported modestly selective single isoform 1A2 and 1A3 inhibitors. Two compounds, 13g and 13h, depleted the CD133⁺ putative cancer stem cell pool, synergized with cisplatin, and achieved efficacious concentrations in vivo following IP administration. Compound 13h additionally synergized with cisplatin in a patient-derived ovarian cancer spheroid model.

CDK4/6 inhibition as maintenance and combination therapy for high grade serous ovarian cancer

High grade serous ovarian cancer (HGSOC) is a disease with a high relapse rate and poor overall survival despite good initial responses to platinum-based therapy. Cell cycle inhibition with targeted CDK4/6 inhibitors is a new therapeutic approach showing promise as a maintenance therapy in cancer. As multiple genes in the CDK4/6 pathway are commonly mutated or dysregulated in ovarian cancer, we evaluated the efficacy of the CDK4/6 inhibitor Ribociclib alone, in combination with chemotherapy, and as maintenance therapy in several models of HGSOC. Ribociclib restricted cellular proliferation in multiple ovarian cancer cell lines. Restricted proliferation was associated with a pseudo-senescent cellular phenotype; Ribociclib-treated cells expressed markers of senescence, but could rapidly re-enter the cell cycle with discontinuation of therapy. Surprisingly, concurrent Ribociclib and cisplatin therapy followed by Ribociclib maintenance was synergistic. Evaluation of the cell cycle suggested that Ribociclib may also act at the G2/M check point via dephosphorylation of ATR and CHK1. Consistent with this mechanism, Ribociclib demonstrated clear activity in both platinum-resistant and platinum-sensitive tumor models in vivo. This work supports clinical trials using Ribociclib in combination with cisplatin and as a maintenance therapy in ovarian cancer.

Therapeutic Impact of Nanoparticle Therapy Targeting Tumor-Associated Macrophages

Antiangiogenic therapies, despite initial encouragement, have demonstrated a limited benefit in ovarian cancer. Laboratory studies suggest antiangiogenic therapy-induced hypoxia can induce tumor "stemness" as resistance to antiangiogenic therapy develops and limits the therapeutic benefit. Resistance to antiangiogenic therapy and an induction of tumor stemness may be mediated by proangiogenic tumor-associated macrophages (TAM). As such, TAMs have been proposed as a therapeutic target. We demonstrate here that ovarian TAMs express high levels of the folate receptor-2 (FOLR2) and can be selectively targeted using G5-dendrimer nanoparticles using methotrexate as both a ligand and a toxin. G5-methotrexate (G5-MTX) nanoparticles deplete TAMs in both solid tumor and ascites models of ovarian cancer. As a therapeutic agent, these nanoparticles are more effective than cisplatin. Importantly, these nanoparticles could (i) overcome resistance to antiangiogenic therapy, (ii) prevent antiangiogenic therapy-induced increases in cancer stem-like cells in both murine and human tumor cell models, (iii) prevent antiangiogenic therapy-induced increases in VEGF-C, and (iv) prevent antiangiogenic therapy-induced BRCA1 gene expression. Combined, this work strongly supports the development of TAM-targeted nanoparticle therapy. Mol Cancer Ther; 17(1); 96-106. ©2017 AACR.

Expression of protein disulfide isomerase family members correlates with tumor progression and patient survival in ovarian cancer

Objective

Protein disulfide isomerase (PDI) is an oxidoreductase that is overexpressed in several cancers. PDI family members (PDIs) play a role in various diseases including cancer. Select PDIs were reported as useful markers in other cancers but their expression in ovarian cancer has not been thoroughly assessed. We sought to evaluate the expression of PDI, PDIA6, PDIR, ERp57, ERp72 and AGR3 in ovarian cancer patient samples and examine their prognostic significance.

Methods

TMA samples from 415 tissues collected from three cancer centers (UM, USC, and KCCRI) were used to assess the expression levels of PDI family proteins using IHC.

Results

We observed significant increases in PDI (p = 9.16E-36), PDIA6 (p = 5.51E-33), PDIR (p = 1.81E-12), ERp57 (p = 9.13E-07), ERp72 (p = 3.65E-22), and AGR3 (p = 4.56E-24) expression in ovarian cancers compared to normal tissues. Expression of PDI family members also increases during disease progression (p <0.001). All PDI family members are overexpressed in serous ovarian cancer (p<0.001). However, PDI, PDIA6, PDIR, ERp72 and AGR3 are more significantly overexpressed (p<0.001) than ERp57 (p<0.05) in clear cell ovarian carcinoma. Importantly, overexpression of PDI family members is associated with poor survival in ovarian cancer (p = 0.045 for PDI, p = 0.047 for PDIR, p = 0.037 for ERp57, p = 0.046 for ERp72, p = 0.040 for AGR3) with the exception of PDIA6 (p = 0.381).

Conclusions

Our findings demonstrate that select PDI family members (PDI, PDIR, ERp72, ERp57 and AGR3) are potential prognostic markers for ovarian cancer.

Personalized Medicine-Based Approach to Model Patterns of Chemoresistance and Tumor Recurrence Using Ovarian Cancer Stem Cell Spheroids

Purpose: Chemoresistant ovarian cancers grow in suspension within the ascites fluid. To screen the effect of chemotherapeutics and biologics on resistant ovarian cancers with a personalized basis, we developed a 3D hanging drop spheroid platform.Experimental Design: We initiated spheroids with primary aldehyde dehydrogenase-positive (ALDH⁺) CD133⁺ ovarian cancer stem cells (OvCSC) from different patient samples and demonstrated that stem cell progeny from harvested spheroids was similar to the primary tumor. OvCSC spheroids were utilized to initiate tumors in immunodeficient mice. Drug responses to cisplatin and ALDH-targeting compound or JAK2 inhibitor determined whether the OvCSC population within the spheroids could be targeted. Cells that escaped therapy were isolated and used to initiate new spheroids and model tumor reemergence in a personalized manner.Results: OvCSC spheroids from different patients exhibited varying and personalized responses to chemotherapeutics. Xenografts were established from OvCSC spheroids, even with a single spheroid. Distinct responses to therapy were observed in distinct primary tumor xenografts similar to those observed in spheroids. Spheroids resistant to cisplatin/ALDH inhibitor therapy had persistent, albeit lower ALDH expression and complete loss of CD133 expression, whereas those resistant to cisplatin/JAK2 inhibitor therapy were enriched for ALDH⁺ cells.Conclusions: Our 3D hanging drop suspension platform can be used to propagate primary OvCSCs that represent individual patient tumors effectively by differentiating in vitro and initiating tumors in mice. Therefore, our platform can be used to study cancer stem cell biology and model tumor reemergence to identify new targeted therapeutics from an effective personalized medicine standpoint. Clin Cancer Res; 23(22); 6934-45. ©2017 AACR.

EGFL6 Regulates the Asymmetric Division, Maintenance, and Metastasis of ALDH+ Ovarian Cancer Cells

Little is known about the factors that regulate the asymmetric division of cancer stem-like cells (CSC). Here, we demonstrate that EGFL6, a stem cell regulatory factor expressed in ovarian tumor cells and vasculature, regulates ALDH⁺ ovarian CSC. EGFL6 signaled at least in part via the oncoprotein SHP2 with concomitant activation of ERK. EGFL6 signaling promoted the migration and asymmetric division of ALDH⁺ ovarian CSC. As such, EGFL6 increased not only tumor growth but also metastasis. Silencing of EGFL6 or SHP2 limited numbers of ALDH⁺ cells and reduced tumor growth, supporting a critical role for EGFL6/SHP2 in ALDH⁺ cell maintenance. Notably, systemic administration of an EGFL6-neutralizing antibody we generated restricted tumor growth and metastasis, specifically blocking ovarian cancer cell recruitment to the ovary. Together, our results offer a preclinical proof of concept for EGFL6 as a novel therapeutic target for the treatment of ovarian cancer. Cancer Res; 76(21); 6396-409. ©2016 AACR.

Local endothelial complement activation reverses endothelial quiescence, enabling t-cell homing, and tumor control during t-cell immunotherapy

Cancer immunotherapy relies upon the ability of T cells to infiltrate tumors. The endothelium constitutes a barrier between the tumor and effector T cells, and the ability to manipulate local vascular permeability could be translated into effective immunotherapy. Here, we show that in the context of adoptive T cell therapy, antitumor T cells, delivered at high enough doses, can overcome the endothelial barrier and infiltrate tumors, a process that requires local production of C3, complement activation on tumor endothelium and release of C5a. C5a, in turn, acts on endothelial cells promoting the upregulation of adhesion molecules and T-cell homing. Genetic deletion of C3 or the C5a receptor 1 (C5aR1), and pharmacological blockade of C5aR1, impaired the ability of T cells to overcome the endothelial barrier, infiltrate tumors, and control tumor progression in vivo, while genetic chimera mice demonstrated that C3 and C5aR1 expression by tumor stroma, and not leukocytes, governs T cell homing, acting on the local endothelium. In vitro, endothelial C3 and C5a expressions were required for endothelial activation by type 1 cytokines. Our data indicate that effective immunotherapy is a consequence of successful homing of T cells in response to local complement activation, which disrupts the tumor endothelial barrier.

Abstract AP22: CHEMORESISTANCE, TUMOR INITIATION AND TUMOR RE–EMERGENCE TRENDS IN MALIGNANT ASCITES–DERIVED OVARIAN CANCER STEM CELL SPHEROIDS

Due to the rarity of ovarian cancer stem cells (OvCSC; &lt;0.2% total population), we developed a 3D hanging drop array model, in which as few as 10 OvCSCs (isolated from primary malignant ascites based on ALDH+ CD133+) can be stably incorporated into spheroids for study of drug sensitivity and tumor biology. Our platform can be utilized to: i) quantify drug sensitivity of chemotherapeutic agents in the context of OvCSCs; ii) distinguish drug responses for the same drugs between several patient samples; thereby uniquely suited for the development of personalized therapeutics including the context of OvCSCs. Three patient samples were evaluated (stage IIIcstage IV). Robust proliferation rates were observed in spheroids, ranging from 5.3 fold (progressive Pt.259++) to 6.5 fold(resistant Pt224++) to 8.4 fold(recurrent Pt152++). Examination of OvCSC populations by Day 7 indicated that ALDH+ CD133+ cells had differentiated within spheroids to form progenies of ALDH- CD133-, ALDH+ CD133-, and CD133+ ALDH- cells. Maintenance of the ALDH+ CD133+ pool was also observed (0.04-0.7%). Composition of progenies was different between the three different patient samples: In Pt259, &lt;1% CD133+ and &lt;5% ALDH+; Pt224 with ~25% ALDH+ progeny; and Pt152 with ~20% CD133+ progeny. OvCSC spheroids had differing responses to drug treatments (cisplatin, ALDH targeting compound 673A, and JAK1/2 inhibitor Ruxolitinib). Combination of cisplatin/673A targeted ALDH+ and CD133+ in all patient samples. Progressive Pt259 samples were maximally sensitive to Cisplatin/673A, while Pt224 and Pt152 were more resistant to drug(20-40% higher viability). Combination dose of Cisplatin/Ruxolitinib targeted CD133+ populations, but also resulted in increased ALDH+ cells, indicating a potential differentiation of CD133+ cells into ALDH+ cells to escape cell-death. By isolating cells that escape chemotherapy, we created a spheroid model to study tumor re-emergence. ALDH+ populations re-emerged to a lower extent compared to original OvCSC spheroids, while CD133+ populations did not recover at all. Lastly, OvCSC spheroids (10 cells/drop) initiated tumors in immunodeficient mice (2 spheroids – 80% success rate; 10 spheroids – 100% success rate).

Conclusions: We have developed a hanging drop array model that incorporates primary ovarian cancer stem cells into a 3D spheroid, capable of initiating tumors in immuno-deficient mice. OvCSCs differentiate into heterogeneous progenies within spheroids, correlating with differing responses to conventional and stem cell targeting drug treatments, providing a platform for personalized therapeutics. We also developed a spheroid model that can mimic tumor re-emergence using cells that escape first line chemotherapy. This platform can be utilized to study spheroid and cancer stem cell biology, and model tumor re-emergence to identify new targeted therapeutics.

This work was supported by the DOD OCRP Early Career Investigator Award W81XWH-13-1- 0134 (GM).

Citation Format: Shreya Raghavan PhD, Maria Ward BS, Pooja Mehta MSc, Ronald J Buckanovich MD PhD, Geeta Mehta PhD. CHEMORESISTANCE, TUMOR INITIATION AND TUMOR RE–EMERGENCE TRENDS IN MALIGNANT ASCITES–DERIVED OVARIAN CANCER STEM CELL SPHEROIDS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr AP22.

Abstract TMEM-019: NEW OVARIAN CANCER METASTASIS MODELS DEMONSTRATE PREFERENTIAL HEMATOGENOUS SPREAD OF OVARIAN CANCER CELLS TO THE OVARY AND A REQUIREMENT FOR THE OVARY FOR ABDOMINAL DISSEMINATION

BACKGROUND: Mounting evidence suggests that many high grade serous ‘ovarian’ cancers (HGSOC) start in the fallopian tube. Cancer cells are then recruited to the ovary and subsequently spread diffusely through the abdomen. The mechanism of ovarian cancer spread has long been thought to be largely due to direct shedding of tumor cells into the peritoneal cavity with vascular spread being of limited importance. Recent work challenges this dogma, suggesting hematogenous spread of ovarian cancer may play a larger role in ovarian cancer cell metastasis than previously thought. One reason the role of vascular spread of ovarian cancer has not been fully elucidated is the lack of easily accessible models of vascular ovarian cancer metastasis.

METHODS: We developed three metastatic models of ovarian cancer which confirm the ability of ovarian cancer to hematogenously spread. A murine tail vein injection model using human ovarian cancer cell lines was used to observe the general pattern of hematogenous spread when cells are directly introduced into the vasculature. A subcutaneous murine ovarian tumor model was developed to investigate patterns of metastasis in the setting of a fully murine tumor microenvironment. Finally, a human subcutaneous xenograft model using primary patient derived ovarian cancer cells, human carcinoma-associated mesenchymal stem cells and human endothelial cells was developed to investigate patterns of metastasis in the setting of a humanized microenvironment.

RESULTS: In all three models, we demonstrate the formation of distant metastasis via vascular spread. Strikingly, we observe a high rate of metastasis to the ovary (40-100%) in all three models representing a disproportionately large fraction of total metastatic burden. Mice which developed ovarian metastatic disease also developed further intra-abdominal metastatic disease and ascites. Interestingly, in the tail vein injection model, oophorectomy prior to ovarian cancer cell injection resulted in a complete loss of peritoneal metastases, ascites and decreased burden of liver metastasis. This ovary tropism appears to be unique to ovarian cancer cells as intravenous tail vein injection of breast cancer and lung cancer cell lines, while resulting in typical sites of disease in the lung and bone, did not result in ovary involvement.

CONCLUSIONS: Taken together our data indicates that hematogenously disseminated high grade serous ovarian cancer cells have a unique tropism for the ovary and that hematogenous spread in ovarian cancer may be more common than previously appreciated. Furthermore our studies support a critical role for the ovary in promoting high grade serous ovarian cancer cell metastasis to the abdomen. The models developed here represent important new tools to evaluate both the mechanism of cancer cell recruitment to the ovary and to understand and target key steps in ovarian cancer metastasis.

Citation Format: Lan G Coffman, Daniela Burgos-Ojeda, Rong Wu, Kathleen Cho, Shoumei Bai, and Ronald J Buckanovich. NEW OVARIAN CANCER METASTASIS MODELS DEMONSTRATE PREFERENTIAL HEMATOGENOUS SPREAD OF OVARIAN CANCER CELLS TO THE OVARY AND A REQUIREMENT FOR THE OVARY FOR ABDOMINAL DISSEMINATION [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr TMEM-019.

Abstract TMEM-030: INTERLEUKIN–6 (IL6) AND LEUKEMIA INHIBITORY FACTOR (LIF) ARE FUNCTIONALLY REDUNDANT IN PROMOTING OVARIAN CANCER GROWTH AND REQUIRE DUAL BLOCKADE FOR THERAPEUTIC EFFECT

PURPOSE: We have previously isolated mesenchymal stem cells from the microenvironment of tumors from ovarian cancer patients (cancer-associated MSC, CA-MSC). We found that CA-MSC promote tumorigenesis in vitro and in vivo by increasing cancer stem cells (CSC) in the epithelial tumor cells. Microarray analysis demonstrates the upregulation of the cytokines IL6 and LIF in CA-MSC versus control MSC. The purpose of this work is to characterize the role of cytokines interleukin-6 (IL6) and leukemia inhibitory factor (LIF) secreted by CA-MSC in ovarian cancer tumorigenesis.

EXPERIMENTAL PROCEDURES: We have isolated and established cultures of CA-MSC. Healthy donor adipose-derived MSC were used as controls (Invitrogen). Ovarian cancer cells were treated with MSC-conditioned media or recombinant IL6 and/or LIF (EBioscience). Cytokine function was inhibited with IL6 blocking antibody, LIF blocking antibody, both antibodies or the JAK2 inhibitor ruxolitinib for dual blockade. Phosphorylated STAT3 and total STAT3 immunoblotting was performed by standard methods. Sphere assays were performed using low-adherence plates and X-Vivo20 serum free media (Lonza). Flow cytometry was carried out using the Aldefluor assay for aldehyde dehydrogenase activity (Stem Cell Technologies). For in vivo studies, NSG mice were injected with OVCAR3 ovarian cancer cells without or with CA-MSC, and then either mock treated or treated with IL6 blocking antibody (tocilizumab, Genentech), LIF blocking antibody or ruxolitinib. Tumor size was monitored both during treatment and at sacrifice, and tumors were analyzed.

RESULTS: Treatment of ovarian cancer cells with either recombinant IL6 or LIF alone leads to STAT3 phosphorylation, suggesting functional redundancy in stimulation of this pathway. Neither LIF nor IL6 blocking antibodies alone can prevent upregulation of phospho-STAT3, but combined therapy with both LIF and IL6 blocking antibodies prevents STAT3 phosphorylation. The JAK2 inhibitor ruxolitinib inhibits cytokine-mediated upregulation of phospho-STAT3. Either LIF or IL6 treatment results in an increase the percentage of cancer stem cells in ovarian cancer cell lines, as measured using both sphere assays and aldehyde dehydrogenase activity. Ruxolitinib blocks both LIF and IL6 mediated increase in cancer stem cells. In vivo, the pro-tumorigenic effect of CA-MSC is abrogated by dual blockade with ruxolitinib but not by treatment with anti-IL6 antibody alone or anti-LIF antibody alone. Ruxolitinib treated tumors demonstrate decreased phospho-STAT3, indicating on-target activity.

CONCLUSIONS: IL6 and LIF are secreted by CA-MSC in the ovarian cancer tumor microenvironment. Both cytokines upregulate phospho-STAT3 and increase the percentage of cancer stem cells in epithelial tumor cells. Functional inhibition of these effects cannot be achieved in vitro or in vivo with blockade of either cytokine individually; dual blockade with compounds such as the JAK2 inhibitor ruxolitinib is necessary. Thus the shared downstream signaling molecules of the JAK/STAT pathway may be preferred targets for novel anticancer therapeutics for ovarian cancer.

Citation Format: Karen McLean, Lijun Tan and Ronald J. Buckanovich. INTERLEUKIN–6 (IL6) AND LEUKEMIA INHIBITORY FACTOR (LIF) ARE FUNCTIONALLY REDUNDANT IN PROMOTING OVARIAN CANCER GROWTH AND REQUIRE DUAL BLOCKADE FOR THERAPEUTIC EFFECT [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr TMEM-030.