Preclinical Models Of Ovarian Cancer Research Articles

Oophorectomy significantly impacts response to immune therapy regimens in preclinical models of ovarian cancer

<h3>Objectives:</h3> We have previously shown that PARP inhibition (PARPi) synergizes with CTLA-4 immune checkpoint blockade, improving survival in syngeneic high grade serous ovarian cancer models. This combination is currently being tested in clinical trials (NCT02571725 and NCT04034927). In the same models, no therapeutic benefit was seen when PARPi was combined with PD-1 blockade. We attribute the selective synergy of CTLA-4 antibody with PARPi to changes in the ovarian tumor microenvironment (TME). An increase in IFNγ production as a result of treatment with PARPi/CTLA-4 antibody was a predictor of improved survival. These results illustrate the importance of establishing cancer models that accurately represent conditions in the ovarian TME. Most preclinical studies are conducted in mice with intact ovarian function, while women with ovarian cancer are postmenopausal or undergo oophorectomy as part of their treatment. Immunotherapy clinical trials have observed differences in outcomes based on sex. Emerging evidence shows that estrogen affects immune function. Therefore, we tested the impact of oophorectomy on the immune microenvironment and its effects on disease outcome. <h3>Methods:</h3> Oophorectomy was performed on five-week-old female FVB mice that were subsequently injected intraperitoneally with BR5-Akt high grade serous ovarian cancer cells. Three days after tumor challenge, mice received a PARP inhibitor (ABT-888) and immune checkpoint inhibitor (anti-PD1 antibody or CTLA-4 antibody). Mice that had undergone laparotomy without oophorectomy (sham) or no surgery served as controls. On day 24, peritoneal T cells were analyzed by flow cytometry for phenotype and IFNγ production. Tumor burden was measured by non-invasive bioluminescence imaging. <h3>Results:</h3> Estrogen depletion through oophorectomy affects T cell phenotypes, increasing the proportion of central memory CD8 T cells compared to controls in the anti-PD1 combination treatment group. In the same group, estrogen depletion is associated with an increase in IFNγ production by both CD4 and CD8 T cells. These changes were associated with a decrease in tumor burden. The same effects were not seen in mice treated with combination PARPi and CTLA-4 antibody. <h3>Conclusions:</h3> The data presented here confirm that estrogen impacts tumor associated lymphocyte phenotype and function, affecting parameters that are associated with improved disease outcomes in combination of PARPi and immune checkpoint blockade. With knowledge of the significant impact of estrogen on anti-tumor immune function, we can develop pre-clinical models that accurately reflect the immune microenvironment established in ovarian cancer. This will facilitate the development of highly effective immunotherapeutic regimens that will enhance their translational potential and ultimately improve patient outcomes.

SPL-108 mediates metastasis and chemoresistance in high-grade serous tubo-ovarian carcinoma

Objectives: Overcoming chemoresistance will improve outcomes for all women with tubo-ovarian carcinomas. Mechanisms of chemoresistance are multifactorial and heterogeneous. ABCB1 (MDR1) represents one common resistance mechanism in tubo-ovarian carcinomas and is under the regulation of CD44. In the present study we examined the effects of a novel CD44 modulator, SPL-108, in a panel of ovarian cancer cell lines. Methods: We assessed chemosensitivity and migration effects of SPL-108 in a panel of ovarian cancer cell lines with (OVCAR5, OVCAR8, OVCAR3) and without (OVCAR4, CAOV3) MDR1 expression. In vitro experiments (cell viability assay, Western blot analysis, Calcein AM fluorescence assay, and migration assay) were carried out to determine the functional effects of SPL-108. Results: Higher expression of CD44 was seen in OVCAR5 and OVCAR8 on Western Blot analysis. In transwell migration assay, treatment with SPL-108 decreased the number of migrating cells compared to control in OVCAR8 (mean ± SEM, 149.1 ± 22.8 vs 89.0 ± 16.5 cells, p=0.04), OVCAR5 (177.7 ± 15.4 vs 134.5 ± 14.7 cells, p=0.04) and OVCAR3 (111.2 ± 12.4 vs 50.5 ± 9.4 cells, p Conclusions: SPL-108 treatment has anti-metastatic properties and suppresses chemoresistance in preclinical models of ovarian cancer. Ongoing studies in animal models will help to guide the further clinical development of SPL-108. Download : Download high-res image (262KB) Download : Download full-size image

Incidence of malignant transformation in the oviductal fimbria in laying hens, a preclinical model of spontaneous ovarian cancer.

Ovarian high grade serous carcinoma (HGSC) is a lethal form of ovarian cancer (OVCA). In most cases it is detected at late stages as the symptoms are non-specific during early stages. Emerging information suggests that the oviductal fimbria is a site of origin of ovarian HGSC. Currently available tests cannot detect ovarian HGSC at early stage. The lack of a preclinical model with oviductal fimbria that develops spontaneous ovarian HGSC is a significant barrier to developing an early detection test for this disease. The goal of this study was to examine if the oviductal fimbria in hens is a site of origin of HGSC and whether it expresses several putative markers expressed in ovarian HGSC in patients. A total of 135 laying hens (4 years old) were selected from a flock using transvaginal ultrasound (TVUS) imaging, followed by euthanasia and gross examination for the presence of solid masses and ascites. Histological types of carcinomas were determined by hematoxylin and eosin staining. Expression of WT-1, mutant p53, CA-125, PAX2 and Ki67 in normal or malignant fimbriae or ovaries were examined using immunohistochemistry, immunoblotting and gene expression assays. This study detected tumors in oviductal fimbriae in hens and routine staining revealed ovarian HGSC-like microscopic features in these tumors. These tumors showed similarities to ovarian HGSC in patients in expressing several markers. Compared with normal fimbriae, intensities of expression of WT-1, mutant p53, CA-125, and Ki67 were significantly (P<0.05) higher in fimbrial tumors. In contrast, expression of PAX2 decreased gradually as the tumor progressed to late stages. The patterns of expression of these markers were similar to those in ovarian HGSC patients. Thus, tumors of the oviductal fimbria in hens may offer a preclinical model to study different aspects of spontaneous ovarian HGSC in women including its early detection.

Docosahexaenoic Acid in the Inhibition of Tumor Cell Growth in Preclinical Models of Ovarian Cancer

There is a strong rationale for investigating nutritional interventions with docosahexaenoic acid (DHA) in cancer prevention and therapy; however, the effects of DHA on ovarian cancer (OC) have not been well studied. Here, we investigated if DHA alone and in combination with carboplatin reduces OC cell growth in vitro. In vivo, we used a high-grade serous OC patient-derived xenograft (PDX) mouse model to investigate if DHA affects OC growth and enhances the anticancer actions of carboplatin. We showed synergistic cell killing by DHA and carboplatin in DHA-resistant Kuramochi and SKOV3 OC cells, which corresponded with increased DHA incorporation into whole-cell membrane phospholipids (P < 0.05). In vivo, feeding mice a diet supplemented with 3.9% (w/w of fat) DHA resulted in a significant reduction in PDX growth with and without carboplatin (P < 0.05). This reduction in tumor growth was accompanied by an increased tumor necrotic region (P < 0.05) and improved survival. Plasma membranes in tumors and livers excised from mice fed a DHA diet had ∼ twofold increase in DHA incorporation as compared with mice fed a control diet. Our findings indicate that DHA supplementation reduces cancer cell growth and enhances the efficacy of carboplatin in preclinical models of OC through increased apoptosis and necrosis. Supplemental data for this article is available online at https://doi.org/10.1080/01635581.2021.1952453

Abstract 968: Focal adhesion kinase (FAK) inhibitor APG-2449 sensitizes ovarian tumors to chemotherapy via CD44 downregulation

Abstract Ovarian cancer is one of the deadliest malignancies in women, and up to 70% of patients with epithelial ovarian cancer have FAK overexpression, amplification, or activation. FAK plays an important role in cellular migration, growth factor signaling, cell cycle progression, cellular survival and chemoresistance. This biomarker is also significantly associated with higher tumor stage, metastasis, and shorter overall survival in patients with ovarian cancer. Inhibition of FAK is therefore emerging as a promising treatment target. APG-2449 is a clinical stage FAK/ALK/ROS1 multi-kinase inhibitor. In this study we investigated antitumor activity of APG-2449 combined with standard-of-care chemotherapeutics in ovarian cancer in the preclinical setting. In a mouse xenograft tumor model derived from ovarian cancer cell line OVCAR-3, which was resistant to platinum-based therapies, APG-2449 combined with paclitaxel, and paclitaxel plus carboplatin, synergistically enhanced antitumor activity, whereas the chemotherapeutics showed no activity. Synergistic antitumor activity was also observed in multiple patient-derived xenograft (PDX) models derived from women with chemoinsensitive ovarian cancer, which also frequently expresses high levels of FAK. By comparing gene expression profiles of PDX tumors obtained from responders and nonresponders to the combined therapy, we identified CD44 (a marker for cancer stem cells) as a potentially predictive biomarker. Western blot analysis confirmed higher protein levels of CD44 in pretreated tumors of responders. Interestingly, downregulation of CD44 levels was observed in combination-treated tumors, suggesting that these combinations reduced cancer stem cell populations in ovarian cancer. Accordingly, in ovarian cancer cells exposed to APG-2449 alone or combined with paclitaxel, numbers of cells positive for CD44 or aldehyde dehydrogenase 1 (ALDH1; another marker for cancer stem cells) decreased in a dose-dependent manner. In summary, our data suggest that FAK inhibition by APG-2449 sensitizes ovarian tumors to chemotherapeutics in preclinical tumor models of ovarian cancer. The synergistic antitumor activity was mediated by downregulation of CD44+ or ALDH1+ cancer stem cell populations. These findings encourage clinical development of APG-2449 in combination with chemotherapies for treatment of ovarian cancer. Citation Format: Ran Tao, Douglas D. Fang, Yuanbao Li, Kaixiang Zhang, Chunhua Xu, Xu Fang, Qixin Wang, Dajun Yang, Yifan Zhai. Focal adhesion kinase (FAK) inhibitor APG-2449 sensitizes ovarian tumors to chemotherapy via CD44 downregulation [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 968.

A prime/boost vaccine platform efficiently identifies CD27 agonism and depletion of myeloid-derived suppressor cells as therapies that rationally combine with checkpoint blockade in ovarian cancer.

Cancer immunotherapies have generated remarkable clinical responses for some patients with advanced/metastatic disease, prompting exploration of rational combination therapies to bolster anti-tumor immunity in patients with limited response or those who experience tumor progression following an initial response to immunotherapy. In contrast to other tumor indications, objective response rates to single-agent PD-1/PD-L1 blockade in ovarian cancer are limited, suggesting a need to identify combinatorial approaches that lead to tumor regression in a setting where checkpoint blockade alone is ineffective. Using a pre-clinical model of aggressive intraperitoneal ovarian cancer, we have previously reported on a heterologous prime/boost cancer vaccine that elicits robust anti-tumor immunity, prolongs survival of tumor-bearing mice, and which is further improved when combined with checkpoint blockade. As tumor control in this model is CD8 + T cell dependent, we reasoned that the prime/boost vaccine platform could be used to explore additional treatment combinations intended to bolster the effects of CD8 + T cells. Using whole tumor transcriptomic data, we identified candidate therapeutic targets anticipated to rationally combine with prime/boost vaccination. In the context of a highly effective cancer vaccine, CD27 agonism or antibody-mediated depletion of granulocytic cells each modestly increased tumor control following vaccination, with anti-PD-1 therapy further improving treatment efficacy. These findings support the use of immunotherapies with well-defined mechanisms(s) of action as a valuable platform for identifying candidate combination approaches for further therapeutic testing in ovarian cancer. Supplementary InformationThe online version contains supplementary material available at 10.1007/s00262-021-02936-1.

Reduced rDNA transcription diminishes skeletal muscle ribosomal capacity and protein synthesis in cancer cachexia.

Muscle wasting in cancer is associated with deficits in protein synthesis, yet, the mechanisms underlying this anabolic impairment remain poorly understood. The capacity for protein synthesis is mainly determined by the abundance of muscle ribosomes, which is in turn regulated by transcription of the ribosomal (r)RNA genes (rDNA). In this study, we investigated whether muscle loss in a preclinical model of ovarian cancer is associated with a reduction in ribosomal capacity and was a consequence of impaired rDNA transcription. Tumor bearing resulted in a significant loss in gastrocnemius muscle weight and protein synthesis capacity, and was consistent with a significant reduction in rDNA transcription and ribosomal capacity. Despite the induction of the ribophagy receptor NUFIP1 mRNA and the loss of NUFIP1 protein, in vitro studies revealed that while inhibition of autophagy rescued NUFIP1, it did not prevent the loss of rRNA. Electrophoretic analysis of rRNA fragmentation from both in vivo and in vitro models showed no evidence of endonucleolytic cleavage, suggesting that rRNA degradation may not play a major role in modulating muscle ribosome abundance. Our results indicate that in this model of ovarian cancer-induced cachexia, the ability of skeletal muscle to synthesize protein is compromised by a reduction in rDNA transcription and consequently a lower ribosomal capacity. Thus, impaired ribosomal production appears to play a key role in the anabolic deficits associated with muscle wasting in cancer cachexia.

A Novel Salt Inducible Kinase 2 Inhibitor, ARN-3261, Sensitizes Ovarian Cancer Cell Lines and Xenografts to Carboplatin.

Simple SummaryCarboplatin and paclitaxel constitute first-line treatment for ovarian cancer, producing tumor shrinkage in 70% of patients, but curing less than 20% with advanced stage disease. Previous studies have shown that treatment with ARN-3261, a small molecule inhibitor of the enzyme salt-induced kinase 2, can improve the response to paclitaxel in human ovarian cancer cells grown in culture and in immunocompromised mice. Here we have found that ARN-3261 also increases carboplatin’s ability to kill ovarian cancer cells grown in culture and in immunocompromised mice, causing additional DNA damage and decreasing levels of survivin, a protein that protects cancer cells from programmed cell death. Our studies encourage clinical evaluation of ARN-3261 and a Phase I clinical trial has been initiated to test the drug in ovarian cancer patients.Salt-induced kinase 2 (SIK2) is a serine-threonine kinase that regulates centrosome splitting, activation of PI3 kinase and phosphorylation of class IIa HDACs, affecting gene expression. Previously, we found that inhibition of SIK2 enhanced sensitivity of ovarian cancer cells to paclitaxel. Carboplatin and paclitaxel constitute first-line therapy for most patients with ovarian carcinoma, producing a 70% clinical response rate, but curing <20% of patients with advanced disease. We have asked whether inhibition of SIK2 with ARN-3261 enhances sensitivity to carboplatin in ovarian cancer cell lines and xenograft models. ARN-3261-induced DNA damage and apoptosis were measured with γ-H2AX accumulation, comet assays, and annexin V. ARN-3261 inhibited growth of eight ovarian cancer cell lines at an IC50 of 0.8 to 3.5 µM. ARN-3261 significantly enhanced sensitivity to carboplatin in seven of eight ovarian cancer cell lines and a carboplatin-resistant cell line tested. Furthermore, ARN-3261 in combination with carboplatin produced greater inhibition of tumor growth than carboplatin alone in SKOv3 and OVCAR8 ovarian cancer xenograft models. ARN-3261 enhanced DNA damage and apoptosis by downregulating expression of survivin. Thus, a SIK2 kinase inhibitor enhanced carboplatin-induced therapy in preclinical models of ovarian cancer and deserves further evaluation in clinical trials.

Manipulating the Wnt/β-catenin signaling pathway to promote anti-tumor immune infiltration into the TME to sensitize ovarian cancer to ICB therapy

ObjectiveImmune checkpoint blockade (ICB) therapy shows limited efficacy in ovarian cancers due to the “cold” immune phenotype surrounding these tumors. Previous studies have shown that in ovarian cancer Wnt/β-catenin pathway activation contributes to this immune phenotype. Here, we evaluated the anti-tumor and immune-enhancing properties of the Wnt inhibitor, CGX-1321, used alone or in combination with either DKN-01 or anti-PD-1 therapy, in pre-clinical ovarian cancer models. MethodsThe parental ID8 murine ovarian cancer model harboring a knock-out of p53 (ID8p53−/−) and MISIIR-Tag spontaneous ovarian cancer models were used to test the effects of CGX-1321 alone or in combination therapies on tumor burden and immune cell landscape in the tumor microenvironment (TME). Flow cytometry and NanoString analyses were used to characterize the changes in tumor-intrinsic signaling and immune-related profiles in the TME of ovarian cancer in response to treatments. ResultsCGX-1321 significantly reduced tumor burden and constrained tumor progression in the ID8p53−/− and MISIIR-Tag models. Furthermore, CGX-1321 increased infiltrating CD8+ T cells in the TME. Combining CGX-1321 with either DKN-01 or anti-PD-1 therapy also decreased tumor burden and increased CD8+ T cell infiltration in the omentum TME but did not do so to a greater extent that CGX-1321 monotherapy. ConclusionsCGX-1321 significantly reduced tumor burden and enhanced CD8+ T cell levels in ovarian cancer, nevertheless the addition of DKN-01 or anti-PD-1 therapies did not enhance these effects of CGX-1321. Further investigation is needed to determine if CGX-1321 + DKN-01 combination treatment sensitizes pre-clinical ovarian cancer to ICB therapy.

Preclinical Development of MGC018, a Duocarmycin-based Antibody–drug Conjugate Targeting B7-H3 for Solid Cancer

B7-H3, also referred to as CD276, is a member of the B7 family of immune regulatory proteins. B7-H3 is overexpressed on many solid cancers, including prostate cancer, renal cell carcinoma, melanoma, squamous cell carcinoma of the head and neck, non-small cell lung cancer, and breast cancer. Overexpression of B7-H3 is associated with disease severity, risk of recurrence and reduced survival. In this article, we report the preclinical development of MGC018, an antibody-drug conjugate targeted against B7-H3. MGC018 is comprised of the cleavable linker-duocarmycin payload, valine-citrulline-seco duocarmycin hydroxybenzamide azaindole (vc-seco-DUBA), conjugated to an anti-B7-H3 humanized IgG1/kappa mAb through reduced interchain disulfides, with an average drug-to-antibody ratio of approximately 2.7. MGC018 exhibited cytotoxicity toward B7-H3-positive human tumor cell lines, and exhibited bystander killing of target-negative tumor cells when cocultured with B7-H3-positive tumor cells. MGC018 displayed potent antitumor activity in preclinical tumor models of breast, ovarian, and lung cancer, as well as melanoma. In addition, antitumor activity was observed toward patient-derived xenograft models of breast, prostate, and head and neck cancer displaying heterogeneous expression of B7-H3. Importantly, MGC018 exhibited a favorable pharmacokinetic and safety profile in cynomolgus monkeys following repeat-dose administration. The antitumor activity observed preclinically with MGC018, together with the positive safety profile, provides evidence of a potentially favorable therapeutic index and supports the continued development of MGC018 for the treatment of solid cancers. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/19/11/2235/F1.large.jpg.

Combination total abdominal ultra-rapid flash irradiation and PD-1 inhibition provides enhanced tumor burden control in a preclinical ovarian cancer model

Objective: Ovarian cancer often presents with advanced-stage disease; however, despite surgery and chemotherapy, recurrence remains inevitable and prognosis poor. Advances in alternative targets including programmed cell death-1 (PD-1) inhibition show promise; however, clinical trials show modest response rates. Ovarian cancer is known to be radiosensitive, but use of total abdominal radiation is not utilized because of high abdominopelvic toxicity. Conventional radiotherapy is delivered at a dose rate of 3–4 Gy/minute, while our ultra-rapid FLASH radiotherapy system uses a linear accelerator to deliver dose rates of 200 Gy/second.

Cisplatin chemotherapy impacts the gut microbiome in a preclinical murine model of epithelial ovarian cancer

Objective: Recent data suggest that the gut microbiome modulates responses to cancer treatment, including platinum chemotherapy. The objective was to understand whether platinum chemotherapy changes the gut microbiome in a preclinical model of epithelial ovarian cancer (EOC).

Abstract 5357: Total abdominal ultra-rapid FLASH irradiation enhances the efficacy of PD-1 inhibition in preclinical models of ovarian cancer

Abstract Objective: Ovarian cancer often presents with advanced stage disease. Despite surgery and chemotherapy, recurrence remains inevitable and prognosis poor. Advances in immunotherapy including programmed cell death-1 (PD-1) inhibition show promise, however clinical trials show modest response rates as a single agent therapy in ovarian cancer patients. Radiation therapy is an attractive strategy to enhance the efficacy of immune checkpoint blockade in ovarian cancer due to its ability to increase tumor-infiltrating lymphocytes and enhance immune activation. While ovarian cancer is known to be radiosensitive, total abdominal radiation is not routinely utilized due to high abdominopelvic toxicity. We have recently shown that ultra-high dose rate FLASH irradiation reduces intestinal radiation-induced toxicity. Importantly, we demonstrated efficient tumor control in preclinical models of ovarian cancer peritoneal metastasis. Here we sought to determine the efficacy and safety of FLASH irradiation combined with PD-1 inhibition in preclinical models of ovarian cancer. Methods: Female C57BL/6 mice were intraperitoneally inoculated with ID8-Asc or UPK10 ovarian cancer cells. Total abdominal FLASH irradiation at 14 Gy was administered 10 days post-inoculation. Anti-PD-1 and isotype control antibodies were injected on days 7, 10, and 13 post-inoculation. Mice were sacrificed 22-27 days post-inoculation for tumor burden and immune cell analysis. Stool count, stool weight, complete blood count, and survival were evaluated to compare acute and chronic toxicity as well as efficacy in the treatment arms. Results: Four cohorts of mice were analyzed: Isotype control antibody (IgG), anti-PD-1 (aPD-1), FLASH + IgG, and FLASH + aPD-1. In the ID8-Asc model, irradiated mice showed a 44% decrease in solid stool production with subsequent recovery to baseline by 14 days post-treatment. There was no evidence of hematopoietic toxicity in any of the treatment arms. Survival analysis is ongoing. Exploratory necropsy demonstrated significant tumor burden control in the FLASH cohorts, and in particular, a 25-fold decrease in tumor number in the FLASH + aPD-1 cohort compared to control (mean tumor weight 1.82 mg vs. 357.2 mg, respectively). FLASH + aPD-1 increased intratumoral CD4+ and CD8+ T cells and correlated with enhanced tumor control compared to FLASH or aPD-1 single agent treatments. Similar results were observed in the UPK10 model. Conclusion: Combination FLASH and PD-1 inhibition enhanced tumor control and recruitment of tumor infiltrating lymphocytes compared to IgG, aPD-1, and FLASH treatments alone, while demonstrating safety and tolerability. Our data identify a new opportunity for FLASH and checkpoint inhibition in the treatment of ovarian cancer. Citation Format: Stephanie Chow, Joshua T. Eggold, Karen Levy, Jinghui Wang, Rakesh Manjappa, Dylan Y. Breitkreutz, Amy S. Yu, Karl Bush, Oliver Dorigo, Billy W. Loo, Erinn B. Rankin. Total abdominal ultra-rapid FLASH irradiation enhances the efficacy of PD-1 inhibition in preclinical models of ovarian cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5357.

Abstract 1237: Biological effects of a FRα-targeting antibody-drug conjugate, IMGN853 (mirvetuximab soravtansine) in high-grade serous ovarian cancer

Abstract Objective: Autophagic cell death is an important mechanism induced by blocking folate receptor (FRα) in inhibiting tumor growth. Here, our objective is to examine the biological effects of IMGN853 (mirvetuximab soravtansine) in preclinical models of ovarian cancer and to identify potential combination therapies. Methods: In vitro, immunoblotting, assays for cell viability, proliferation and cell cycle by fluorescence-activated cell sorting (FACS) were performed in an array of high grade serous carcinoma (HGSC) cell lines. Autophagy flux and activities of autophagy factors were also determined. In vivo, metastasis mouse models were used for testing the therapeutic efficacy of IMGN853 monotherapy or in combination with olaparib or cisplatin. Potential synergy with these drugs was assessed using in vitro assays. The resulting tumors were subjected to immunohistochemistry and reverse phase protein arrays (RPPA). Results: Data from the Cancer Genome Atlas Data (TCGA) revealed that FRα copy-number alterations was significantly correlated with shorter disease-free survival in patients with HGSC. Autophagy marker LC3 was upregulated following monotherapy with IMGN853 as well as in combination of IMGN853 with olaparib or cisplatin in HGSC cell lines such as OVCA8 and OVCA432, which express high-level of FRα. Experiments using metastatic HGSC models showed that IMGN853 monotherapy reduced tumor growth (30% change); the combination of IMGN853 and olaparib was superior to olaparib monotherapy (24% change; p 0.0033). Integrated analysis on RPPA revealed increased expression of ABL1 and PEA15 in the groups treated with IMGN853 monotherapy or in combination with olaparib. We further found reduced FRα expression and increased caspase 3 expression in IMGN853 groups compared with control. Conclusion: Our results point to sustained autophagy in FRα positive cells as a mechanism of effect of IMGN853. These findings could have implications for clinical development of anti-FRα therapies, especially in combination with other drugs such as olaparib. Citation Format: Anca Chelariu-Raicu, Elaine Stur, Cristina Ivan, Robert L. Coleman, Anil K. Sood, Wen Yunfei. Biological effects of a FRα-targeting antibody-drug conjugate, IMGN853 (mirvetuximab soravtansine) in high-grade serous ovarian cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1237.

Therapeutic Efficacy of 213Bi-labeled sdAbs in a Preclinical Model of Ovarian Cancer.

Targeted alpha-particle therapy (TAT) might be a relevant therapeutic strategy to circumvent resistance to conventional therapies in the case of HER2-positive metastatic cancer. Single-domain antibody fragments (sdAb) are promising vehicles for TAT because of their excellent in vivo properties, high target affinity, and fast clearance kinetics. This study combines the cytotoxic α-particle emitter bismuth-213 (213Bi) and HER2-targeting sdAbs. The in vitro specificity, affinity, and cytotoxic potency of the radiolabeled complex were analyzed on HER2pos cells. Its in vivo biodistribution through serial dissections and via Cherenkov and micro-single-photon emission computed tomography (CT)/CT imaging was evaluated. Finally, the therapeutic efficacy and potential associated toxicity of [213Bi]Bi-DTPA-2Rs15d were evaluated in a HER2pos tumor model that manifests peritoneal metastasis. In vitro, [213Bi]Bi-DTPA-2Rs15d bound HER2pos cells in a HER2-specific way. In mice, high tumor uptake was reached already 15 min after injection, and extremely low uptake values were observed in normal tissues. Co-infusion of gelofusine resulted in a 2-fold reduction in kidney uptake. Administration of [213Bi]Bi-DTPA-2Rs15d alone and in combination with trastuzumab resulted in a significant increase in median survival. We describe for the very first time the successful labeling of an HER2-sdAb with the α-emitter 213Bi, and after intravenous administration, revealing high in vivo stability and specific accumulation in target tissue and resulting in an increased median survival of these mice especially in combination with trastuzumab. These results indicate the potential of [213Bi]Bi-DTPA-sdAb as a new radioconjugate for TAT, alone and as an add-on to trastuzumab for the treatment of HER2pos metastatic cancer.

Therapeutic efficacy of liposomal Grb2 antisense oligodeoxynucleotide (L-Grb2) in preclinical models of ovarian and uterine cancer.

Background: Adaptor proteins such as growth factor receptor-bound protein-2 (Grb2) play important roles in cancer cell signaling. In the present study, we examined the biological effects of liposomal antisense oligodeoxynucleotide that blocks Grb2 expression (L-Grb2) in gynecologic cancer models.Materials and Methods: Murine orthotopic models of ovarian (OVCAR5 and SKOV3ip1) and uterine (Hec1a) cancer were used to study the biological effects of L-Grb2 on tumor growth. In vitro experiments (cell viability assay, Western blot analysis, siRNA transfection, and reverse phase protein array) were carried out to elucidate the mechanisms and potential predictors of tumor response to L-Grb2.Findings: Treatment with L-Grb2 decreased tumor growth and metastasis in orthotopic models of ovarian cancer (OVCAR5, SKOV3ip1) by reducing angiogenesis and increasing apoptosis at a dose of 15 mg/kg with no effect on mouse body weight. Treatment with L-Grb2 and paclitaxel led to the greatest decrease in tumor weight (mean ± SEM, 0.17 g ± 0.10 g) compared with that in control mice (0.99 g ± 0.35 g). We also observed a reduction in tumor burden after treatment with L-Grb2 and the anti-VEGF antibody B-20 (86% decrease in tumor weight compared with that in controls). Ovarian cancer cells with ErbB2 amplification (OVCAR8 and SKOV3ip1) were the most sensitive to Grb2 downregulation. Reverse phase protein array analysis identified significant dysregulation of metabolites (LDHA, GAPDH, and TCA intermediates) in ovarian cancer cells after Grb2 downregulation.Interpretation: L-Grb2 has therapeutic efficacy in preclinical models of ovarian and uterine cancer. These findings support further clinical development of L-Grb2.

Repositioning Quinacrine Toward Treatment of Ovarian Cancer by Rational Combination With TRAIL.

Quinacrine has been identified as a potent DR5-inducing agent that sensitizes cancer cells to TRAIL-induced apoptosis. In the current study, we found that quinacrine increased DR5 mRNA levels significantly in ovarian cancer cell lines regardless of p53 status. Further study showed the half-life of DR5 in quinacrine-treated cells was significantly prolonged, indicating that DR5 protein degradation was inhibited by quinacrine. We tested if the combination of TRAIL and quinacrine could be effective in ovarian cancer treatment in vitro and in ovarian cancer xenograft mouse models. We found that quinacrine enhanced TRAIL sensitivity or reversed TRAIL resistance in all the ovarian cancer cell lines tested. Mice treated with quinacrine and TRAIL remained disease-free for up to 20 weeks, however, mice treated with TRAIL or quinacrine alone and in control group died within ~8 weeks after treatment. Intraperitoneal delivery of quinacrine and TRAIL is rational and practical with extraordinary synergistic anti-cancer effects in preclinical models of ovarian cancer. Clinical investigation of combining quinacrine with TRAIL for ovarian cancer treatment is warranted.

EpCAM-Binding DARPins for Targeted Photodynamic Therapy of Ovarian Cancer.

Ovarian cancer is the most lethal gynecological malignancy due to late detection associated with dissemination throughout the abdominal cavity. Targeted photodynamic therapy (tPDT) aimed at epithelial cell adhesion molecule (EpCAM), overexpressed in over 90% of ovarian cancer metastatic lesions, is a promising novel therapeutic modality. Here, we tested the specificity and activity of conjugates of EpCAM-directed designed ankyrin repeat proteins (DARPins) with the photosensitizer IRDye 700DX in in vitro and in vivo ovarian cancer models. EpCAM-binding DARPins (Ec1: Kd = 68 pM; Ac2: Kd = 130 nM) and a control DARPin were site-specifically functionalized with fluorophores or IRDye 700DX. Conjugation of anti-EpCAM DARPins with fluorophores maintained EpCAM-specific binding in cell lines and patient-derived ovarian cancer explants. Penetration of DARPin Ec1 into tumor spheroids was slower than that of Ac2, indicative of a binding site barrier effect for Ec1. DARPin-IRDye 700DX conjugates killed EpCAM-expressing cells in a highly specific and illumination-dependent fashion in 2D and 3D cultures. Furthermore, they effectively homed to EpCAM-expressing subcutaneous OV90 xenografts in mice. In conclusion, the high activity and specificity observed in preclinical ovarian cancer models, combined with a high specificity in patient material, warrant a further investigation of EpCAM-targeted PDT for ovarian cancer.

Abstract A23: Ultrarapid total abdominal FLASH irradiation in a preclinical model of ovarian cancer

Abstract Introduction: Ultrahigh dose-rate irradiation (FLASH RT) is rapidly emerging as new strategy to enhance the therapeutic index of radiotherapy by protecting normal tissues from radiation-induced toxicity while maintaining tumor control. In mice, FLASH has been shown to protect the lung, skin, and brain against radiation-induced toxicity. A recent study has utilized FLASH radiotherapy in preclinical models of lung cancer to demonstrate that FLASH RT radiotherapy achieves similar tumor control to conventional RT. While these findings identify an important role for FLASH RT in the protection of multiple tissues, the role of FLASH in enhancing the therapeutic index of abdominal and pelvic tumors located near the highly radiosensitive intestine is not known. For this purpose, we have developed an experimental platform using a clinical linear accelerator that enables total abdominal FLASH RT where rapid delivery of a single fraction of high-dose radiotherapy is performed in less than one second (200 Gy/sec). Methods: For the tumor model, ID8 cells were injected intraperitoneally into female mice. Radiation was delivered 10 days post-ID8 injection. Tumor burden was assessed at 28 days following tumor injection. Flow cytometry was used to profile infiltrating immune cells. Normal tissue toxicity was assessed through survival, total body weight, solid stool production, complete blood count, and histologic analysis. Results: In ID8 tumor-bearing mice, 14 Gy FLASH promotes GI function with a 2-fold increase in solid stool production at 5 days post-TAI. Both modalities extended median overall survival in the ID8 model by 5 days and reduced tumor burden by 50% relative to unirradiated controls. Irradiated cohorts also demonstrated an increase in the number of proliferating CD8+ and CD4+ T cells present in the ascites. Conclusion: We demonstrate that FLASH RT protects the gastrointestinal (GI) tract from lethal radiation-induced toxicity, improves epithelial integrity and GI function, enhances crypt survival, and provides efficient tumor control in a preclinical model of ovarian peritoneal metastasis. Here we present the first data supporting the potential for tumor control and GI protection using FLASH-TAI in a syngeneic orthotopic preclinical model of ovarian cancer. Citation Format: Karen Levy, Jinghui Wang, Joshua Eggold, Suchitra Natarajan, Peter Maxim, Bill Loo, Erinn Rankin. Ultrarapid total abdominal FLASH irradiation in a preclinical model of ovarian cancer [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 A23.

Abstract A09: SM08502, a novel, small-molecule CDC-like kinase (CLK) inhibitor, demonstrates strong inhibition of the Wnt signaling pathway and antitumor effects in diverse ovarian cancer models

Abstract Aberrant activation of the Wnt signaling pathway is observed in ovarian cancer (OC) and is associated with chemoresistance, immune evasion, and poor prognosis. SM08502 is a novel, oral, small-molecule pan-CLK inhibitor that has been shown to potently inhibit the Wnt signaling pathway in preclinical colorectal cancer models. The purpose of these studies was to test the in vitro and in vivo activity of SM08502 in preclinical models of OC. The effect of SM08502 on cell viability was tested in 10 OC cell lines of various histotypes, including high-grade serous (HGS), serous, endometrioid, clear-cell, and teratocarcinoma lines in vitro. Cell proliferation was impaired in all cell lines by SM08502 regardless of histotype and mutation profile (average EC50=0.123 μM [0.034 – 0.275]). Relative to DMSO, SM08502 (1 μM) also potently inhibited Wnt-related gene expression (TCF7, DVL2, LRP5, and ERBB2), which correlated with inhibition of protein expression in HGSOC, endometrioid, and teratocarcinoma cell lines. Additionally, in cell lines derived from these histotypes, SM08502 strongly inhibited cyclin E1 gene and protein expression, the amplification/overexpression of which has been associated with treatment resistance and poor overall survival in HGSOC. In vivo antitumor effects and tolerability of oral SM08502 (6.25, 12.5 and 25 mg/kg QD for 15-22 days) were assessed in mice bearing OVCAR-3 (HGSOC; TP53mut), PA-1 (teratocarcinoma; N-Ras mut), and TOV-112D (endometrioid; CTNNB1mut) xenografts (n=5 mice per group). In OVCAR-3 xenografts, significant tumor growth inhibition (TGI) vs. vehicle occurred in mice treated with SM08502 12.5 mg/kg (66%, p&amp;lt;0.01) and 25 mg/kg (89%, p&amp;lt;0.001). SM08502 25 mg/kg also induced tumor regression in all mice. Similarly, in PA-1 xenografts, SM08502 induced TGI of 64% (p&amp;lt;0.01) at 12.5 mg/kg and 93% (p&amp;lt;0.01) with 4/5 tumors regressing at 25 mg/kg. SM08502 at 25 mg/kg also induced TGI of 64% (p&amp;lt;0.01) in TOV-112D xenografts. In addition, SM08502 (25 mg/kg QD) was assessed in 5 patient-derived xenograft (PDX) models of metastatic OC with double-hit TP53 and BRCA1/2 mutations (Crown Biosciences). Inhibition of tumor growth was observed in all tested PDXs (average TGI=61% [47-73], p&amp;lt;0.001). SM08502 was well tolerated in all xenograft models tested based on body weight measurements. In summary, SM08502 potently inhibited cell proliferation and expression of Wnt-related genes and cyclin E1 in OC cell lines. SM08502 also demonstrated strong in vivo antitumor effects, including tumor regressions, in different subtypes of OC xenografts and PDX models. These data suggest that SM08502 may provide clinical benefit for OC patients regardless of histotype, BRCA mutation status, or cyclin E1 expression. A phase 1 study assessing safety, tolerability, and pharmacokinetics of SM08502 in advanced solid tumors is ongoing (NCT03355066). Citation Format: Heekyung Chung, Lauren Sitts, Emily Creger, Erica Liao, Brian Eastman, Chi-Ching Mak, K.C. Sunil, Betty Tam, Gail Bucci, Josh Stewart, Carine Bossard, Timothy Phalen, Steven Cha. SM08502, a novel, small-molecule CDC-like kinase (CLK) inhibitor, demonstrates strong inhibition of the Wnt signaling pathway and antitumor effects in diverse ovarian cancer models [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 A09.