Abstract 2043: Effects of 24-h carboplatin pretreatment on olaparib clearance in women's cancers using noncompartmental and population pharmacokinetic analyses

Background: Olaparib (OLA) is a PARP inhibitor approved for use in deleterious germline BRCA mutated recurrent or refractory ovarian cancer. Combining OLA with carboplatin (CARBO) could have additive effects based on platinum-DNA adducts requiring PARP for DNA repair. Preclinical data suggest greater cytotoxicity when CARBO is given prior to OLA. However, the optimal treatment sequence of these agents has not been studied previously in patients. We therefore investigated: 1) the effects of CARBO treatment on the pharmacokinetics (PK) and pharmacodynamics (PD) of OLA; 2) in vitro mechanisms of the interaction between CARBO and OLA.

Methods: Clinical PK and PD data of OLA were obtained from 58 patients with confirmed recurrent or refractory women's cancers participating in a two arm, parallel design, phase 1 trial (NCT01237067). In cycle 1 OLA tablets (200 mg BID) were given for 7 days either followed by CARBO (AUC 4) on day 8 (arm A) or after CARBO on day 1 (Arm B). In cycle 2 the arms received the reversed scheme. PK of OLA were assessed in both cycles by noncompartmental (NCA) and population pharmacokinetic (PPK) analyses. For PK/PD analyses, PAR levels were measured at baseline and 24 h after the first OLA dose. In vitro mechanistic studies were carried out by incubating whole human blood and avian DT40 PARP-1 KO cells with 10 μM CARBO for 24 h, followed by 1h-treatment of isolated PBMCs and PARP-1 KO cells with 10 μM OLA. Intracellular OLA concentrations were determined using UPLC-MS/MS.

Results: Both NCA and PPK analyses showed a ∼50% increase in OLA clearance when CARBO was administered 24-h prior (P<0.02). The PPK model included a lag time parameter (P = 1.1E-18), a second absorption compartment (P = 7.7E-27), a single elimination compartment, and accounted for covariance among the clearance and volume parameters (P = 6.7E-7). Presence of CARBO was the only significant covariate affecting OLA clearance (P = 1.9E-13). Final estimates for clearance and volume of distribution were 6.8 L/h and 33 L, respectively, which were comparable with related reports. There were no trends between PK data and PAR levels, nor did the presence of CARBO affect PAR levels (P = 0.89). PBMC experiments showed that 24-h pretreatment with CARBO significantly increased intracellular OLA concentrations by more than 30% compared with control samples (P = 0.013). PARP-1 KO cells confirmed that intracellular PARP expression was not related to the increased OLA uptake. Possibly, CARBO affects other intracellular targets or transporters leading to increased intracellular uptake of OLA from the bloodstream.

Conclusion: This is the first known PK analysis showing a significant increase in OLA clearance after pretreatment with CARBO, possibly leading to subtherapeutic plasma concentrations of OLA. Preclinical experiments are ongoing to reveal the exact pharmacological mechanisms of this interaction.

Citation Format: Andrew K.L. Goey, Cody J. Peer, Tristan M. Sissung, Jeffrey Roth, Shandiz Shahbazi, Jeffers Nguyen, Christina M. Annunziata, Nicole Houston, Elise C. Kohn, Jung-Min Lee, William D. Figg. Effects of 24-h carboplatin pretreatment on olaparib clearance in women's cancers using noncompartmental and population pharmacokinetic analyses. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2043.

Abstract 1496: Identification of target and cytotoxicity of novel monoclonal antibody NEO-201 in ovarian and uterine cancer subtypes

Objectives: Given the heterogeneity of ovarian cancer, it is imperative to identify subtype-directed treatments. The novel antibody NEO-201 targets a specific tumor-associated antigen (TAA) expressed on some ovarian and uterine malignancies, providing a tumor-directed approach. Here, we aimed to identify the cancer subtypes which express the NEO-201 target and demonstrate its cytotoxic effects in vitro and in mouse models of ovarian cancer.

Methods: NEO-201 is a genetically humanized novel monoclonal antibody developed through vaccines with TAAs. This antibody targets malignant tissues that express tumor-specific epitopes in membrane-anchored protein CEACAM-6. We performed immunohistochemistry (IHC) on tissue microarrays from formalin-fixed paraffin-embedded subtyped ovarian and uterine cancers to estimate the incidence of cancers expressing the NEO-201 target. Ovarian and uterine cell line pellet arrays were stained by IHC to identify in vitro models. We examined the cytotoxicity of NEO-201 in two high- and three low-expressing cell lines using Calcein AM cell viability assays alone and with purified natural killer (NK) cells with and without IL-2 stimulation. Studies of NEO-201 in ovarian cancer mouse models are ongoing.

Results: IHC of NEO-201 in tissue microarrays demonstrated 51% and 12% reactivity in uterine and ovarian samples, respectively. Similar expression patterns were identified in representative cell lines by IHC and Western blot. NEO-201 killed cell lines expressing its target in the range of 0.5-20μg/mL. Over 3 weeks, NEO-201 treatment of tumor-bearing mice demonstrated control of tumor growth with 3 doses of 250μg NEO-201 and tumor regression with 100μg in combination with IL2-stimulated PBMC. Studies are ongoing to further investigate NEO-201 cytotoxicity in ovarian cancer mouse models as well as identify the mechanism of tumor cell death and the target epitope of NEO-201.

Conclusions: NEO-201, a novel monoclonal antibody, specifically targets epithelial malignancies including ovarian and uterine cancer. This potentially therapeutic antibody demonstrates tumor-specific cytotoxicity in cancer cell lines expressing its target in vitro and in xenografts with IL2-stimulated PBMC, suggesting both antibody-dependent cell-mediated cytotoxicity (ADCC) and direct cytotoxicity mechanisms are involved in tumor inhibition and regression. These studies lay the groundwork for future examination of TAA-directed therapy for ovarian or uterine malignancies.

Citation Format: Monica K. Neuman, Lidia Hernandez, Xue­-Ping Wang, Olga Saric, Alex Dubeykovskiy, Philip Arlen, Christina M. Annunziata. Identification of target and cytotoxicity of novel monoclonal antibody NEO-201 in ovarian and uterine cancer subtypes. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1496.

Molecular Pathways: The Balance between Cancer and the Immune System Challenges the Therapeutic Specificity of Targeting Nuclear Factor-κB Signaling for Cancer Treatment

The NF-κB signaling pathway is a complex network linking extracellular stimuli to cell survival and proliferation. Cytoplasmic signaling to activate NF-κB can occur as part of the DNA damage response or in response to a large variety of activators, including viruses, inflammation, and cell death. NF-κB transcription factors play a fundamental role in tumorigenesis and are implicated in the origination and propagation of both hematologic and solid tumor types, including melanoma, breast, prostate, ovarian, pancreatic, colon, lung, and thyroid cancers. On the other hand, NF-κB signaling is key to immune function and is likely necessary for antitumor immunity. This presents a dilemma when designing therapeutic approaches to target NF-κB. There is growing interest in identifying novel modulators to inhibit NF-κB activity as impeding different steps of the NF-κB pathway has potential to slow tumor growth, progression, and resistance to chemotherapy. Despite significant advances in our understanding of this pathway, our ability to effectively clinically block key targets for cancer therapy remains limited due to on-target effects in normal tissues. Tumor specificity is critical to developing therapeutic strategies targeting this antiapoptotic signaling pathway to maintain antitumor immune surveillance when applying such therapy to patients. Clin Cancer Res; 22(17); 4302-8. ©2016 AACR.

Monocyte and interferon based therapy for the treatment of ovarian cancer

Cytokines and cells of the innate immune system have been shown to be critical regulators in the elimination, equilibrium and escape of malignant cells. Despite in vitro and in vivo evidence, components of the innate immune system have shown limited efficacy in the treatment of ovarian cancer. Intraperitoneal immunotherapies are a promising field that has not yet been fully explored in ovarian cancer. Cytokine immunotherapy using interferon alpha (IFN-α) and interferon gamma (IFN-γ) has predominantly been used intraperitoneally in ovarian cancer, with promising results. Early studies also showed that autologous monocytes infused into the peritoneum have anti-tumor properties. Combination therapies have been shown to be more effective in treating cancer than mono-therapies. Based on these observations the combination of cell therapy with cytokine therapy may provide a unique strategy for the treatment of chemotherapy resistant solid cancers.

Characterization of ovarian cancer cell lines as in vivo models for preclinical studies

OBJECTIVE

The value of cell lines for pre-clinical work lies in choosing those with similar characteristics. Selection of cell lines is typically based on patient history, histological subtype at diagnosis, mutation patterns, or signaling pathways. Although recent studies established consensus regarding molecular characteristics of ovarian cancer cell lines, data on in vivo tumorigenicity remains only sporadically available, impeding translation of in vitro work to xenograft models.

METHODS

We introduced 18 ovarian cancer cell lines into athymic nude mice through subcutaneous, intraperitoneal, and ovary intrabursal routes, and observed tumor development over 6weeks. We also profiled cell line gene expression and identified differentially expressed gene sets based on their ability to form tumors in the subcutaneous or intraperitoneal locations. Representative cell lines were further subjected to proteomic analyses.

RESULTS

Ovarian cancer cell lines showed variable ability to grow in mice when implanted subcutaneous, intraperitoneal, or intrabursal. While some cell lines grew well in both SC and IP locations, others showed a strong propensity to grow in one location only. Gene expression profiles suggested that cell lines showing preference for IP growth had gene expression patterns more similar to primary tumors.

CONCLUSIONS

We report the tumorigenicity of 17 human ovarian cancer cell lines and one mouse cell line in three distinct anatomical locations, and associated gene networks. Growth patterns and histopathology, linked to molecular characteristics, provide a valuable resource to the research community, and better guide the choice of cell lines for in vitro studies to translate efficiently into xenograft testing.

Abstract B43: Characterization of ovarian cancer cells as in vivo models for preclinical studies

Women are most often diagnosed with ovarian cancer in late stages of the disease, making this malignancy the most common cause of death from gynecological cancers in the United States. Identification of factors associated with disease subtypes and clinical outcome is critical to enable pathway-targeted therapeutic advances. As with other systems, the value of cell lines for in vitro and pre-clinical work lies in choosing groups of cell lines with similar characteristics. To date, selection of cell lines has been based on criteria such as patient history, histological subtype at diagnosis, mutation patterns, signaling patterns and tumorigenicity in mice. Most available ovarian cancer cell lines were generated decades ago and variable information exists as to these parameters. In recent years, several studies have reported comprehensive data gathered for the most commonly available ovarian cancer cell lines. While these reviews have established greater consensus regarding the molecular characteristics of these cell lines, data on in vivo tumorigenicity of these cell lines is still only sporadically available, making it difficult to translate in vitro work to xenograft models. We have studied the tumorigenicity of 16 commonly used ovarian cancer cell lines introduced through three distinct anatomical locations: subcutaneous, intraperitoneal, and ovary intrabursal injection. We also characterized these cell lines according to gene expression profiles and phospho-proteomics, in order to create an integrated panel of information by which to choose cells logically for specific research questions. Here we report a comprehensive analysis of in vivo growth patterns and histopathology, linked to molecular characteristics. This will provide a valuable resource to the ovarian cancer research community, and better guiding the choice of cell lines for in vitro studies that can be translated efficiently into xenograft testing.

Citation Format: Lidia Hernandez, Marianne K. Kim, L Tiffany Lyle, Patricia S. Steeg, Christina M. Annunziata. Characterization of ovarian cancer cells as in vivo models for preclinical studies. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B43.

Abstract A72: Dissecting the role of NF-kappaB signaling in ovarian cancer tumor-initiating cells

Ovarian cancer is the most lethal gynecological malignancy in the United States with high morbidity and mortality due to recurrence and chemoresistance. Our data suggest tumor-initiating cells (TICs) play an important role in disease biology. We previously showed that a subset of ovarian cancer cells depends on NF-kappaB signaling, and that expression of NF-kappaB proteins is associated with poor survival. To investigate this pathway in TICs, we designed a novel method to enrich for TICs from cell lines and patient samples by culturing non-adherent, floating cells in stem cell conditions. Preliminary data show these cells have higher stem cell marker expression, are chemoresistant, and are more tumorigenic in nude mice compared to their adherent counterparts. Given that NF-kappaB expression correlates with a poor outcome in ovarian cancer, and NF-kappaB activity supports drug resistance and tumorigenicity, we hypothesize that NF-kappaB supports a TIC program responsible for ovarian cancer relapse. Preliminary data show TIC-enriched culture conditions increased NF-kappaB expression and activity in TICs and stimulation of NF-kappaB signaling enhanced chemoresistance and stem cell marker expression. Current studies focus on dissecting the role of individual NF-kappaB proteins in TICs using inducible shRNAs to measure changes in spheroid formation, chemoresistance, tumorigenesis, and disease relapse following chemotherapy in a xenograft model. Future studies will measure system level changes induced by these shRNAs, and identify a gene signature specific to NF-kappaB in ovarian TICs. Clarifying the nuances of NF-kappaB signaling in TICs will increase our understanding of ovarian cancer recurrence and may lead to improved therapeutic strategies.

Citation Format: Carrie D. House, Christina M. Annunziata. Dissecting the role of NF-kappaB signaling in ovarian cancer tumor-initiating cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A72.

A dual role for Caspase8 and NF-κB interactions in regulating apoptosis and necroptosis of ovarian cancer, with correlation to patient survival

Ovarian cancer is a deadly disease characterized by primary and acquired resistance to chemotherapy. We previously associated NF-κB signaling with poor survival in ovarian cancer, and functionally demonstrated this pathway as mediating proliferation, invasion and metastasis. We aimed to identify cooperating pathways in NF-κB-dependent ovarian cancer cells, using genome-wide RNA interference as a loss-of-function screen for key regulators of cell survival with IKKβ inhibition. Functional genomic screen for interactions with NF-κB in ovarian cancer showed that cells depleted of Caspase8 died better with IKKβ inhibition. Overall, low Caspase8 was associated with shorter overall survival in three independent gene expression data sets of ovarian cancers. Conversely, Caspase8 expression was markedly highest in ovarian cancer subtypes characterized by strong T-cell infiltration and better overall prognosis, suggesting that Caspase8 expression increased chemotherapy-induced cell death. We investigated the effects of Caspase8 depletion on apoptosis and necroptosis of TNFα-stimulated ovarian cancer cell lines. Inhibition of NF-κB in ovarian cancer cells switched the effects of TNFα signaling from proliferation to death. Although Caspase8-high cancer cells died by apoptosis, Caspase8 depletion downregulated NF-κB signaling, stabilized RIPK1 and promoted necroptotic cell death. Blockage of NF-κB signaling and depletion of cIAP with SMAC-mimetic further rendered these cells susceptible to killing by necroptosis. These findings have implications for anticancer strategies to improve outcome for women with low Caspase8-expressing ovarian cancer.

The role of reproductive hormones in epithelial ovarian carcinogenesis

Epithelial ovarian cancer comprises ∼85% of all ovarian cancer cases. Despite acceptance regarding the influence of reproductive hormones on ovarian cancer risk and considerable advances in the understanding of epithelial ovarian carcinogenesis on a molecular level, complete understanding of the biologic processes underlying malignant transformation of ovarian surface epithelium is lacking. Various hypotheses have been proposed over the past several decades to explain the etiology of the disease. The role of reproductive hormones in epithelial ovarian carcinogenesis remains a key topic of research. Primary questions in the field of ovarian cancer biology center on its developmental cell of origin, the positive and negative effects of each class of hormones on ovarian cancer initiation and progression, and the role of the immune system in the ovarian cancer microenvironment. The development of the female reproductive tract is dictated by the hormonal milieu during embryogenesis. Intensive research efforts have revealed that ovarian cancer is a heterogenous disease that may develop from multiple extra-ovarian tissues, including both Müllerian (fallopian tubes, endometrium) and non-Müllerian structures (gastrointestinal tissue), contributing to its heterogeneity and distinct histologic subtypes. The mechanism underlying ovarian localization, however, remains unclear. Here, we discuss the role of reproductive hormones in influencing the immune system and tipping the balance against or in favor of developing ovarian cancer. We comment on animal models that are critical for experimentally validating existing hypotheses in key areas of endocrine research and useful for preclinical drug development. Finally, we address emerging therapeutic trends directed against ovarian cancer.

Pharmacodynamic markers and clinical results from the phase 2 study of the SMAC mimetic birinapant in women with relapsed platinum-resistant or -refractory epithelial ovarian cancer

BACKGROUND

Inhibitors of apoptosis proteins (IAPs) are key regulators of apoptosis and are frequently dysregulated in ovarian cancer. It was hypothesized that blocking IAPs with birinapant would increase tumor cell death and result in objective responses for women with platinum-refractory and -resistant ovarian cancer.

METHODS

In this phase 2, Cancer Therapy Evaluation Program-sponsored study, patients received birinapant at 47 mg/m(2) on days 1, 8, and 15 of 28-day cycles. Pharmacokinetics were obtained during cycle 1. Plasma, peripheral blood mononuclear cells (PBMCs), and percutaneous tumor biopsy samples were collected before cycle 1 and after 6 weeks. The primary endpoint was an objective response or progression-free survival lasting greater than 6 months in a mini-max design.

RESULTS

Eleven patients received birinapant; after this, accrual was terminated for lack of a clinical benefit. Birinapant was well tolerated, with predominantly grade 2 adverse events and 1 case of grade 3 lymphopenia. Pretreatment biopsy samples and PBMCs were collected; paired posttreatment biopsy samples and PBMCs were collected from 7 and 10 patients, respectively. There was consistent downregulation of cellular inhibitor of apoptosis protein 1 in tumors (P = .016) and PBMCs (P < .01). Procaspase 3 also decreased in tumors (P = .031) and PBMCs (P < .01); cleaved caspase 3 colocalized with H2A histone family member X (γ-H2AX) in tumors after birinapant exposure. Peripheral T and B cells decreased significantly after treatment, but natural killer cells did not (P = .04, P = .05, and P = .43, respectively).

CONCLUSIONS

Birinapant shows consistent target suppression in vivo without single-agent antitumor activity in this small population. Single-agent pharmacodynamics are necessary to understand the drug's mechanism of action and set the stage for rational combination therapy. Preclinical studies are ongoing to identify optimal synergistic combinations for future clinical trials.

Loss of compensatory pro-survival and anti-apoptotic modulator, IKKε, sensitizes ovarian cancer cells to CHEK1 loss through an increased level of p21

Ovarian cancer (OC) is extremely heterogeneous, implying that therapeutic strategies should be specifically designed based on molecular characteristics of an individual's tumor. Previously, we showed that IKKε promotes invasion and metastasis in a subset of OCs. Here, we identified CHEK1 as an IKKε-dependent lethal gene from shRNA kinome library screen. In subsequent pharmacological intervention studies, the co-inhibition of IKKε and CHEK1 was more effective in killing OC cells than single treatment. At the molecular level, co-inhibition dramatically decreased pro-survival proteins, but increased proteins involved in DNA damage and apoptosis. IKKε-knockdown increased p21 levels, while overexpression of wild-type IKKε, but not a kinase dead IKKε mutant decreased p21 levels. We further demonstrated that the depletion of p21 rendered OC cells more resistant to cell death induced by co-inhibition of IKKε and CHEK1. In conclusion, we revealed a novel interplay between IKKε, CHEK1 and p21 signaling in survival of OC. Our study provides a rationale for the clinical development of specific IKKε inhibitor and for usage of IKKε as an exploratory marker for resistance to CHEK1 inhibitors in the clinic. The interplay provides one potential explanation as to why very few clinical responses were achieved in patients treated with single-agent CHEK1 inhibitors.

A Phase II Trial of AZD6244 (Selumetinib, ARRY-142886), an Oral MEK1/2 Inhibitor, in Relapsed/Refractory Multiple Myeloma

PURPOSE

AZD6244 is a MEK1/2 inhibitor with significant preclinical activity in multiple myeloma cells. This phase II study used a two-stage Simon design to determine the AZD6244 response rate in patients with relapsed or refractory multiple myeloma.

EXPERIMENTAL DESIGN

AZD6244 (75 mg) was administered orally, twice a day, continuously for 28-day cycles. Response was evaluated after three cycles.

RESULTS

Thirty-six patients received therapy. The median age was 65 years (range: 43-81) and the median number of prior therapies was 5 (range: 2-11). The most common grade 3 and 4 toxicities included anemia, neutropenia, thrombocytopenia, diarrhea, and fatigue. Three deaths occurred possibly related to AZD6244 (2 due to sepsis, 1 due to acute kidney injury). After AZD6244 discontinuation, three additional deaths occurred due to disease progression. The response rate (CR + PR) was 5.6% with a mean duration of response of 4.95 months and median progression-free survival time of 3.52 months. One patient had a very good partial response (VGPR), 1 patient had a partial response, 17 patients had stable disease, 13 patients had progressive disease, and 4 patients could not be assessed for response. Pharmacodynamic studies revealed variable effects on bone marrow CD138(+) cell MEK1/2 and ERK1/2 phosphorylation. The best clinical response, a prolonged VGPR, occurred in a patient with an MMSET translocation.

CONCLUSIONS

Single-agent AZD6244 was tolerable and had minimal activity in this heavily pretreated population.

Abstract POSTER-TECH-1102: Caspase 8 cooperates with IKKβ to protect ovarian cancer cells from necroptosis

Ovarian cancer is a leading cause of cancer death in women, and identification of factors determining clinical outcome is essential to enable pathway-directed therapeutic advances. We recently showed that NF-κB signaling is constitutively active in a subset of ovarian cancer patients. Over-expression of the critical IκBα-regulatory kinase IKKβ, and its defined NF-κB gene signature, correlated with poor overall survival in that population. In order to identify cooperating pathways engaging in compensatory signaling in NF-κB-dependent ovarian cancer cells, genome-wide RNA interference was used as a loss-of-function genetic screen for key regulators of cell survival in response to IKKβ inhibition. The pro-apoptotic protease CASPASE 8 was identified. Ovarian cancer cells became more sensitive to killing with IKKb inhibitor when CASPASE 8 was depleted by shRNA. In agreement, co-expression of CASPASE 8 and NF-κB gene signature was observed in two large cohorts of primary ovarian cancer patient samples, and was largely confined to immune-related subtypes. In vitro, TNFα stimulation of Ovcar3 cells required CASPASE 8 for apoptotic cell death induced by IKKβ or cIAP1 inhibition, suggesting that both enzymatic activity of CASPASE 8 and its association with TNFR-induced cIAP protein complexes are mechanistically involved. However, CASPASE 8 depletion combined with IKKβ inhibition and cIAP1 depletion produced additional, CASPASE 8-independent cell death, in a RIP1-dependent manner. The data presented herein demonstrate our novel finding that Caspase 8 signals in conjunction with IKKβ to maintain viability of a subtype ovarian cancer cells, especially in the presence of TNFα stimulation. Ovarian cancer is known to be a heterogeneous disease, prone to developing resistance to chemotherapies designed primarily to induce apoptosis. The NF-kB pathway is one means by which tumors survive. Our findings point towards a new avenue for treatment of this disease, namely that cancers may be therapeutically susceptible to inducers of necroptosis, in addition to IKKβ blockade. The current data link our in vitro findings to primary patient samples, underscoring the relevance of our findings to future clinical application. Therefore, dual therapy with an IKKβ inhibitor and apoptosis- or necroptosis-inducing treatments may add together in molecularly selected ovarian cancer patient subsets.

Citation Format: Lidia Hernandez, Anne M. Noonan, Ethan Sagher, Holger Kohlhammer, George Wright, L. Tiffany Reed, Patricia S. Steeg, Miriam Anver, David D. Bowtell, Christina M. Annunziata. Caspase 8 cooperates with IKKβ to protect ovarian cancer cells from necroptosis [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-TECH-1102.

Abstract POSTER-THER-1422: Development of proteomic biomarkers for the apoptosis pathway in ovarian cancer cell lines and determination of the appropriate sequence of the SMAC-mimetic birinapant (TL32711) and docetaxel for optimal therapeutic effect

Background: The SMAC-mimetic birinapant (TL32711) induces apoptosis of ovarian cancer (OC) cell lines by eliminating the inhibitors of apoptosis (IAPs) and attenuating NFkB signaling. The increase in mitochondrial membrane permeability (MOMP) induced by docetaxel releases cytochrome c, unleashing the caspase cascade, which culminates in apoptosis. In addition, caspase-8 cleavage results in activation of the BH3-only protein BH3-interacting domain death agonist (BID), the product of which (truncated BID; tBID) is required for death receptor-induced apoptosis via BID activation and MOMP. Thus, caspase-8 is at the intersection between the extrinsic and intrinsic apoptosis pathways. We hypothesized that the combination of birinapant and docetaxel would be synergistic augmenting the apoptotic response in OC. Our aim was to determine the most appropriate sequence for optimal therapeutic effect in a cell line model and develop potential proteomic biomarkers.

Methods: Toxicity of the SMAC-mimetic birinapant and docetaxel was assessed in a panel of OC cell lines using XTT assay with specific attention to the order and timing of drug administration. The target protein changes were assessed using Western blot and Simple Western. Similar protein changes are being assessed in mouse model. Cytokine analysis was performed on the secretome of cells treated with drug.

Results: There was variable sensitivity to single-agent exposure to the small molecule SMAC mimetic in OC cell lines. Increased cell death was seen upon administration of both docetaxel and birinapant, with enhanced toxicity when birinapant was administered prior to docetaxel. Degradation of cIAP1, the main pharmacodynamic outcome of brianapant, was seen after one hour of birinapant exposure, and was maintained up to 12 hours. Interestingly, cIAP2 levels increased from 3 hours to 24 hours. Cleavage of caspase-3 began at 3 hours and was maximal at 24 hours. PARP cleavage occurred 24 hours after treatment. Docetaxel induced cleavage of BID. Enhanced caspase-3 and caspase-8 cleavage were seen when both birinapant and doctaxel were administered. Similar protein changes are being examined in ongoing mouse experiment and will be reported at the meeting.

Conclusions: The combination of birinapant and docetaxel results in enhanced cell death in an OC cell line model with evidence of target protein engagement.

Citation Format: Anne M. Noonan, Lidia Hernandez, Michelle Herrmann, Jinqui Chen, Christina M. Annunziata. Development of proteomic biomarkers for the apoptosis pathway in ovarian cancer cell lines and determination of the appropriate sequence of the SMAC-mimetic birinapant (TL32711) and docetaxel for optimal therapeutic effect [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-THER-1422.

Topotecan synergizes with CHEK1 (CHK1) inhibitor to induce apoptosis in ovarian cancer cells

Background

Topotecan (TPT) is a therapeutic option for women with platinum-resistant or -refractory ovarian cancer. However, the dose-limiting toxicity of TPT is myelosuppression. This led us to seek a combination treatment to augment TPT anti-cancer activity in a cancer-targeted manner. Ovarian serous cancers, a major subtype, show dysregulated DNA repair pathway and often display a high level of CHEK1 (CHK1), a cell cycle regulator and DNA damage sensor. CHEK1 inhibitors are a novel approach to treatment, and have been used as single agents or in combination chemotherapy in many cancers.

Methods

We evaluated the cellular effects of TPT in a panel of high grade serous (HGS) and non-HGS ovarian cancer cells. We then determined IC50s of TPT in the absence and presence of CHEK1 inhibitor, PF477736. Synergism between TPT and PF477736 was calculated based on cellular viability assays. Cytotoxic effect of the combined treatment was compared with apoptotic activities by Caspase3/7 activity assay and Western blotting of cleaved-PARP1 and γH2AX.

Results

Non-HGS ovarian cancer cells were generally more sensitive to TPT treatment compared to HGS ovarian cancer cells. When combined with CHEK1 inhibitor, TPT potently and synergistically inhibited the proliferation of HGS ovarian cancer cells. This dramatic synergism in cellular toxicity was consistent with increases in markers of apoptosis.

Conclusions

Our findings suggest that the addition of CHEK1 inhibitor increases the response of ovarian cancer cells to TPT. Furthermore, reduced dosages of both drugs achieved maximal cytotoxic effects by combining TPT with CHEK1 inhibitor. This strategy would potentially minimize side effects of the drugs for extended clinical benefit.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1231-z) contains supplementary material, which is available to authorized users.

In vitro enrichment of ovarian cancer tumor-initiating cells

Evidence suggests that small subpopulations of tumor cells maintain a unique self-renewing and differentiation capacity and may be responsible for tumor initiation and/or relapse. Clarifying the mechanisms by which these tumor-initiating cells (TICs) support tumor formation and progression could lead to the development of clinically favorable therapies. Ovarian cancer is a heterogeneous and highly recurrent disease. Recent studies suggest TICs may play an important role in disease biology. We have identified culture conditions that enrich for TICs from ovarian cancer cell lines. Growing either adherent cells or non-adherent ‘floater’ cells in a low attachment plate with serum free media in the presence of growth factors supports the propagation of ovarian cancer TICs with stem cell markers (CD133 and ALDH activity) and increased tumorigenicity without the need to physically separate the TICs from other cell types within the culture. Although the presence of floater cells is not common for all cell lines, this population of cells with innate low adherence may have high tumorigenic potential.Compared to adherent cells grown in the presence of serum, TICs readily form spheres, are significantly more tumorigenic in mice, and express putative stem cell markers. The conditions are easy to establish in a timely manner and can be used to study signaling pathways important for maintaining stem characteristics, and to identify drugs or combinations of drugs targeting TICs. The culture conditions described herein are applicable for a variety of ovarian cancer cells of epithelial origin and will be critical in providing new information about the role of TICs in tumor initiation, progression, and relapse.

Abstract 5179: Context-specific dependence of ovarian cancer on IKKϵ and CHEK1

Background: The IκB kinase, IKKϵ, was previously identified as an oncogene in breast cancer and was associated with poor clinical outcome in ovarian cancer. Recently, we demonstrated that IKKϵ is a key regulator of invasion and metastasis in ovarian cancer. A highly specific inhibitor of IKKϵ is not readily available for use as a tool compound to study pathway interactions in the preclinical setting. Therefore, we utilized dual shRNA technique to create IKKϵ-matched cell line pairs and performed sensitization screens to identify the key molecular targets influenced by the loss of IKKϵ expression.

Results: We screened a previously established shRNA library targeting the human kinome, and identified 65 genes that further inhibited the survival of ovarian cancer cells in combination with IKKϵ depletion. In order to evaluate potential clinical significance associated with their overexpression, we examined the expression levels of these 65 genes in TCGA ovarian serous cystadenocarcinoma dataset. Strikingly, CHEK1 was overexpressed in 100% of TCGA ovarian cancers with a cut-off of 1.5 fold change compared to normal ovarian surface epithelium. Interestingly, CHEK1 loss also sensitized IKKϵ depleted A2780, a wild-type p53 containing ovarian cancer cell line.

Next, we investigated whether chemical inhibitors could recapitulate the effects of shRNAs, although they are less specific than RNAi and are unable to interrogate kinase-independent functions of cellular proteins. Consistent with the initial screening methodology, inhibition of IKKϵ and CHEK1 activities by BX795 and PF00477736, respectively, in 6 ovarian cancer cell lines was critical to the cooperative decrease in cell viability. Thus, the co-inhibition of IKKϵ and CHEK1 activities, regardless of p53 status, was more effective in killing ovarian cancer cells than single treatment. The inhibition of IKKϵ activity alone induced dramatic G2/M arrest in all 6 cell lines without inducing a DNA damage response, while CHEK1 inhibition resulted in significant DNA damage response with abnormal S phase profile in cell cycle analysis and an increase in gamma-H2A.X level. This combined inhibition dramatically decreased CHEK1 level and further increased apoptosis compared to CHEK1 inhibitor alone.

Conclusion: Our dual shRNA technique efficiently identified CHEK1 as an IKKϵ synthetic lethal gene in ovarian cancer. CHEK1 inhibitor as a single agent has not been successful in clinic, and this may be due to increased pro-survival signaling mediated by IKKϵ, which may contribute to resistance and subsequent relapse. Identification of IKKϵ dependent signaling will lead to development of context-specific therapeutics in the poor prognostic group of patients with a high level of IKKϵ expression.

Citation Format: Marianne K. H. Kim, Dong Joon Min, George Wright, Christina M. Annunziata. Context-specific dependence of ovarian cancer on IKKϵ and CHEK1. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5179. doi:10.1158/1538-7445.AM2014-5179

Abstract 1923: NF-κB signaling supports a sub-population of ovarian cancer tumor-initiating cells

Although most patients respond favorably to first-line chemotherapy, ovarian cancer remains the most lethal gynecological cancer in the United States primarily because of a high incidence of disease recurrence. The inability of traditional chemotherapy to eradicate tumor-initiating cells (TICs) is a plausible explanation for tumor relapse and we have begun to characterize TIC populations in ovarian cancer cell lines. Importantly, we are investigating the role of the NF-κB pathway in regulating this system. We have identified conditions that sustain a highly tumorigenic TIC population. Preliminary data suggest that NF-κB promotes and sustains TICs in ovarian cancer and current efforts are underway to characterize the molecular mechanisms underlying this preference. We will correlate activity of this pathway with expression of ovarian TIC protein markers such as CD133, Sox2, Nanog, and Oct-4 in TIC cell cultures and xenografts. Moreover we will use TICs to investigate effects of inhibiting this pathway on marker expression, proliferation, resistance to chemotherapy, and the ability to form tumors in mice. Clarifying the specific role of the NF-κB network in TIC populations will further our understanding of ovarian cancer initiation, progression, and relapse and may lead to improved therapeutic strategies for women in first remission, to prevent subsequent relapse to incurable disease.

Citation Format: Carrie D. House, Christina M. Annunziata. NF-κB signaling supports a sub-population of ovarian cancer tumor-initiating cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1923. doi:10.1158/1538-7445.AM2014-1923