Platinum-resistant Cells Research Articles

Abstract 1608: Pharmacologic screening identifies synthetic lethality interactions with Chk1 inhibitors in basal-like breast and ovarian cancer

Abstract Basal-like breast cancer and ovarian cancer are considered as unmet entities as patient outcome in advanced stages is short, even receiving the most appropriate treatment. These tumors are characterized by a high grade of genetic instability and a notable impairment of DNA repair processes. Thus, in response to DNA damage, they depend on checkpoint arrest proteins, such as Chek1, to stop division. Inactivation of Chk1 permits cell cycle progression without a proper DNA repair, therefore increasing genetic instability and aneuploidy and eventually leading to cell death. Chk1 inhibitors are currently in clinical development and, therefore, the identification of chemotherapies that could be used as clinical partners to potentiate their effect is a main goal. OVCAR3 and IGROV ovarian cancer cells as well as the basal-like MDA-MB-231 and HS578T cell lines were used to screen for agents that may increase the antiproliferative properties of Chk1 inhibitors. Combination of DNA-damaging agents, like platinum compounds or gemcitabine, with the Chk1 inhibitors LY2603618 and SAR020106 had a synergistic effect, not observed when combined with agents targeting mitosis, like taxotere, eribulin or vinorelbine. A similar antiproliferative effect was observed for PARP inhibitors such as olaparib, reinforcing the concept that inhibition of Chk1 allows cells to enter apoptosis when a relevant genetic instability is present. Clonogenic assays and 3D colony formation studies confirmed the effect observed on proliferation also on invasion and long-term survival. Analyses of cell cycle, cell death and intracellular mediators were performed by flow cytometry and Western blot. The effect of the association of LY2603618 with cisplatin and gemcitabine did not change the cell cycle. However, combination of both agents produced a marked induction of apoptosis. Experiments evaluating caspase activity demonstrated that the principal mechanism associated with the induction of apoptosis was caspase dependent. We also explored combination of agents that have a clear translation to the clinics including double combinations with chemotherapies like cisplatin and gemcitabine. We observed that these triple combinations were more effective than double or single agents. Finally, we wanted to evaluate the antiproliferative effect when adding LY2603618 to olaparib in addition to a DNA-damaging agent. Of note, we observed a higher effect than single-agent olaparib or the chemotherapy. Interestingly, inhibition of Chk1 also reverted the effect of cisplatin in platinum-resistant cells. Our findings support the clinical development of Chk1 inhibitors in combination with DNA-damaging agents in basal-like and ovarian cancer. Citation Format: Eva M. Galan-Moya, Ana Alcaraz-Sanabria, Cristina Nieto-Jimenez, Veronica Corrales-Sanchez, Miriam Nuncia-Cantarero, Juan C. Montero, Atanasio Pandiella, Alberto Ocaña. Pharmacologic screening identifies synthetic lethality interactions with Chk1 inhibitors in basal-like breast and ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1608.

Abstract 2322: Ferroptosis induced by erastin in RAS mutant ovarian cancer cells

Abstract Although apoptosis has been thought as the principal mechanism of programed cell death in chemotherapy, other forms of non-apoptotic death also has been noted. The oncogenic RAS-selective lethal small molecule erastin triggers a unique iron-dependent form of cell death termed ferroptosis. This mechanism is expected to induce eradication of chemotherapeutic (e.g. platinum) resistant cancer cells. In this study we demonstrate this new form of cell death in ovarian cancer cells. The clear cell epithelial ovarian cancer cell lines, TOV-21G (KRAS_G13C) and KOC-7C (RAS wild type) were used in this study. Erastin dose-dependently inhibited growth in TOV-21G cells, but not KOC-7C cells. Treatment of TOV-21G cells with erastin resulted in increase of ROS. Iron chelator deferoxamine (DFO) rescued growth inhibition induced by erastin in TOV-21G cells. Although cisplatin inhibited growth in TOV-21G cells, this inhibition was not rescued by DFO. The GSH level was reduced by erastin, but this reduction was not rescued by DFO. In addition, the basal GSH level was higher and the basal ROS level was lower in KOC-7C cells than those in TOV-21G cells. Erastin induced ferroptosis by reducing the GSH level in RAS mutant ovarian cancer cells. Although DFO rescued growth inhibition induced by erastin, the pathway was not on System Xc-. The sensitivity to erastin might depends on the basal level of GSH in cells. Ferroptosis had great potential to become a new approach in anti-tumor therapies in ovarian cancer. Citation Format: Motoki Takenaka, Noriko Suzuki, Minako Mori, Hitomi Aoki, Tasuku Hirayama, Hideko Nagasawa, Ken-ichirou Morishige. Ferroptosis induced by erastin in RAS mutant ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2322.

Abstract 4326: The chromatin context and consequence of cisplatin-adduct DNA damage

Abstract Improvements in survival rates for ovarian cancer lag behind those of other cancers. The combination of paclitaxel and carboplatin, along with debulking surgery, form the primary mode of treatment, however, the majority of patients eventually develop resistance. Epigenetic mechanisms have been implicated in the emergence of drug resistance, with platinum based therapies shown to induce DNA methylation changes at relapse which are associated with overall survival. Using a next generation sequencing approach, including a novel NGS method to map platinum adducts, we sought to investigate the association between platinum-DNA adduct formation and changes to chromatin conformation in the emergence of resistance to platinum therapy. We found chromatin conformation changes at the transcription start sites (TSS) of genes differentially expressed between platinum sensitive and resistant cell lines (p<0.05, n=3 pairs). Furthermore, we found non-TSS associated chromatin conformation changes which distinguish sensitive from resistant lines, and occur primarily in the direction of reduced accessibility in resistant lines (FDR <0.05, log2FC >±1.5). Finally, we found that 2kb windows enriched for platinum-DNA adducts are significantly more accessible than an equal number of random windows on the same chromosome (p<0.05, 1000 permutations). Taken together, these data suggest that platinum treatment may induce epigenetic changes, which reduce chromatin accessibility, rendering cells less susceptible to the formation of platinum-DNA adducts in subsequent treatments, resulting in cells becoming less sensitive to the drug. Citation Format: John Gallon, Erick Loomis, Nicholas Martin, James Flanagan, Robert Brown. The chromatin context and consequence of cisplatin-adduct DNA damage [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4326.

PO-510 XRCC6BP1: a novel role in the DNA repair of platinum resistant NSCLC cells

IntroductionAlterations in the DNA repair capacity of damaged cells are now recognised as an important factor in mediating resistance to chemotherapeutic agents.Material and methodsDNA Repair Pathway RT2 Profiler Arrays were used to elucidate key DNA repair genes implicated in chemoresistant NSCLC cells using cisplatin resistant (CisR) and corresponding parental (PT) NSCLC cell lines generated in our laboratory. DNA repair genes significantly altered in CisR cells were validated at the mRNA and protein level. The translational relevance of differentially expressed genes was examined in a cohort of chemo-naïve matched normal and tumour lung tissues from NSCLC patients. Loss of function studies were carried out using siRNA technology. The effect of XRCC6BP1 gene knockdown on apoptosis was assessed by FACS. Cellular expression and localization of XRCC6BP1 protein and gH2AX foci in response to cisplatin were examined by immunofluorescence (Cytell). To investigate a role for XRCC6BP1 in lung cancer stem cells, Side Population (SP) studies were used to characterise stem-like subpopulations within chemoresistant cells. XRCC6BP1 mRNA analysis was also examined in ALDH1+ and ALDH1- subpopulations. Immunohistochemistry analysis was carried out in resected lung tumour tissues and XRCC6BP1 expression was correlated with survival and other clinicopathological parameters.Results and discussionsWe identified a number of critical DNA repair genes that were differentially expressed between PT and CisR NSCLC cells. XRCC6BP1 mRNA and protein expression was significantly increased in H460 CisR cells relative to their PT counterparts. Relative to matched normal lung tissues, XRCC6BP1 mRNA was significantly increased in lung adenocarcinoma patients. Gene silencing of XRCC6BP1 induced significant apoptosis of chemoresistant cells and reduced their DNA repair capacity. Immunofluorescence studies showed an increase in XRCC6BP1 protein expression and gH2AX foci in CisR cells. SP analysis revealed a significantly higher stem cell population in resistant cells, while XRCC6BP1 mRNA expression was considerably increased in SKMES-1, H460 and H1299 ALDH1+ CisR cells compared to ALDH1- cells. IHC scoring of XRCC6BP1 showed that lung cancer patients with high expression had worse survival outcomes.ConclusionOur data highlight the potential of targeting components of the DNA repair pathway in chemoresistant lung cancer, in particular XRCC6BP1, either alone or in combination with conventional cytotoxic therapies such as cisplatin.

Abstract 1386: Safety and tolerability of guadecitabine (SGI-110) plus cisplatin in patients with platinum refractory germ cell tumors (GCT): A phase 1 study

Abstract BACKGROUND: Guadecitabine (SGI-110) is a novel hypomethylating dinucleotide of decitabine and deoxyguanosine resistant to degradation by cytidine deaminase. Germ cell tumor including platinum-resistant embryonal carcinoma cells lines are extremely sensitive to hypomethylating agents and low dose decitabine can restore cisplatin sensitivity in cell lines. We aimed to assess the safety and clinical activity of guadecitabine in combination with cisplatin in patients with platinum-refractory GCT. METHODS: In this open-label, phase 1 study, patients with GCT refractory to or had relapsed after platinum-based treatment were treated with subcutaneous (SQ) guadecitabine, once-daily for 5 consecutive days, followed by cisplatin on day 8 in a 28-day treatment cycle. A modified toxicity probability interval (mTPI) dose-escalation design was used in which we treated patients with guadecitabine doses of 30-45 mg/m2 plus cisplatin 100 mg/m2 up to 6 cycles until progression or intolerable toxicity. The primary objective was to assess safety and tolerability of guadecitabine in combination with cisplatin, determine the maximum tolerated and identify the recommended phase 2 dose of guadecitabine. Safety analyses included all patients who received at least one dose of guadecitabine. Pharmacodynamic analyses to determine the biologically effective dose included all patients for whom samples were available. This study is registered with ClinicalTrials.gov, number NCT02429466. FINDINGS: Between 2015 and 2017, we enrolled and treated 10 patients. Grade 3 or 4 adverse events were febrile neutropenia, thrombocytopenia, anemia, and diarrhea. The most common serious adverse events were febrile neutropenia and thrombocytopenia. Guadecitabine 45 mg/m2 was associated with prolonged SAE and felt to be unsafe to continue. The maximum tolerated dose was 30 mg/m2 daily × 5. Two patients achieved a complete response to treatment lasting more than 6 months. INTERPRETATION: Guadecitabine SQ at 30 mg/m2 daily × 5 is well tolerated and is clinically and biologically active in patients with platinum-refractory GCT. The study is still ongoing. Citation Format: Costantine Albany, Neda S. Hashemi, Fang Fang, James Lowder, Lawrence Einhorn, Kenneth Nephew. Safety and tolerability of guadecitabine (SGI-110) plus cisplatin in patients with platinum refractory germ cell tumors (GCT): A phase 1 study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1386.

Cisplatin triggers cancer stem cell enrichment in platinum-resistant cells through NF-\u03baB-TNF\u03b1-PIK3CA loop

BackgroundParallel to complex alteration in molecular and cellular events, enrichment of cancer stem cells (CSC) contributes significantly in deliberation and maintenance of cisplatin resistance. Cisplatin mediated CSC enrichment is well established in various cancers, yet the underlying mechanism is largely unknown. Cisplatin also promotes transcriptional upregulation of PIK3CA, hence activating PI3K/AKT signaling in resistant cells. However, such cisplatin-induced transcriptional regulators of PIK3CA and their impact on cancer stem cell population in resistant cells are largely unknown.MethodsDNA-binding protein pulldown using PIK3CA promoter as bait followed by nLCMS was used to identify, cisplatin-induced potential transcriptional regulators of PIK3CA promoter. PIK3CA promoter activity was estimated by luciferase based reporter assay. ChIP was used to assess interaction of NF-κB with PIK3CA promoter. CSC-enriched side-population was sorted using DCV-dye exclusion methods. All the gene expression levels were assessed using qPCR.ResultsUsing a transcription factor pull-down assay with PIK3CA promoter, we identified NF-κB as a prime regulator, which escalates both TNFα and PIK3CA expression only in CSC enriched side-population (SP) but not in non side-population (NSP) in platinum resistant ovarian cancer cells upon cisplatin treatment. This SP-specific NF-κB-TNFα-PIK3CA bi-modal loop, on one hand, maintains persistent activation of NF-κB through TNFα- NF-κB autocrine loop, while NF-κB-PIK3CA loop nurture CSC population under cisplatin treatment. Activation of PI3K/AKT signalling drives SP’s into an undifferentiated, anti-apoptotic stage through upregulating P21, P27,cFLIP expression. Contrarily, lack of active NF-κB-TNFα-PIK3CA loop makes NSPs vulnerable towards cisplatin and undergoes apoptosis. Altogether, cisplatin enriches cancer stem cells properties in SP fraction, which is evident from increased levels of pluripotency gene OCT4/SOX2/NANOG expression. Disruption of PIK3CA-NF-κB loop by Wortamannin reduces SP fraction by 1.4–1.6 fold in control and treated cells.ConclusionTogether, our study signifies an active role of NF-κB-TNFα-PIK3CA bi-modal loop in cisplatin-mediated promotion and maintenance of CSC-like population in platinum-resistant cells.

Overcoming Clear Cell Ovarian Cancer Resistance to Taxol by an Oligo Arginine Transporter Conjugate

Objectives: Taxol remains first line treatment for all epithelial ovarian cancer (EOC). However, it has been shown that ovarian clear cell carcinoma (CCC), a rare histological subtype of EOC, often becomes resistant to platinum based therapy when at advanced stage. This chemo-resistant phenotype has led to a poorer prognosis in patients with CCC than in patients with serous subtypes. While many factors contribute to resistance; a major contributor is the active export of drugs from cells mediated by transmembrane efflux pumps that prevent drugs from reaching their intracellular targets. Our lab has developed a Taxol-oligoarginine conjugate that prevents export of the drug from serous papillary EOC leading to increased cell death. In this study we aim to assess whether this Taxol conjugate is effective in improving Taxol mediated cell death in platinum resistant Clear cell ovarian cancer.

Common biological phenotypes characterize the acquisition of platinum-resistance in epithelial ovarian cancer cells

Standard of care for Epithelial Ovarian Cancer (EOC) patients relies on platinum-based therapy. However, acquired resistance to platinum occurs frequently and predicts poor prognosis. To understand the mechanisms underlying acquired platinum-resistance, we have generated and characterized three platinum-resistant isogenic EOC cell lines. Resistant cells showed 3-to 5- folds increase in platinum IC50. Cross-resistance to other chemotherapeutic agents commonly used in the treatment of EOC patients was variable and dependent on the cell line utilized. Gene expression profiling (GEP) of coding and non-coding RNAs failed to identify a common signature that could collectively explain the mechanism of resistance. However, we observed that all resistant cell lines displayed a decreased level of DNA platination and a faster repair of damaged DNA. Furthermore, all platinum resistant cell lines displayed a change in their morphology and a higher ability to grown on mesothelium. Overall, we have established and characterized three new models of platinum-resistant EOC cell lines that could be exploited to further dissect the molecular mechanisms underlying acquired resistance to platinum. Our work also suggests that GEP studies alone, at least when performed under basal culture condition, do not represent the optimal way to identify molecular alterations linked to DNA repair pathway defects.

Abstract 1197: Endothelin-1 receptor/β-arrestin1 is an actionable node that regulates YAP/TAZ signaling and chemoresistance in high-grade ovarian cancer

Abstract The widespread activation of YAP and TAZ transcriptional regulators has been shown to promote tumor progression and resistance to anti-cancer therapies. Extensive studies have identified different upstream regulators of YAP/TAZ, including G-protein coupled receptor (GPCR). However how GPCR signals regulate YAP/TAZ puzzles have remained elusive. Among the GPCR, we reveal that the endothelin-1 (ET-1) receptor activates YAP/TAZ pathway in high-grade serous ovarian cancer (HG-SOC) sensitive and resistant cell lines and primary cultures. In HG-SOC cells, the aberrant activation of ET-1 receptor (ET-1R), promotes an enhanced nuclear shuttling of dephosphorylated YAP and TAZ in a time-dependent manner, through the scaffold protein β-arrestin1 (β-arr1). Interestingly, ET-1-induced YAP/TAZ nuclear accumulation is further improved in platinum-resistant cells and is prevented by expressing a mutant β-arr1 incapable of nuclear distribution. Moreover, the ET-1/ETAR axis activation induces the co-localization of β-arr1, YAP and TAZ in the nucleus. Mechanistically, in sensitive and to a greater extent in resistant cells, ET-1 induces the formation of a complex β-arr1/Trio, a Rho-Guanine nucleotide exchange factor family member, which dephosphorylates YAP, inducing its nuclear accumulation and the transcription of YAP/TAZ target genes. β-arr1, RhoA or Trio depletion, as well as the treatment with the dual ETAR/ETBR antagonist macitentan, significantly reduces RhoA GTPase activity and YAP nuclear translocation, suggesting that ET-1/ETAR axis regulates YAP/TAZ activity by driving β-arr1/Trio/RhoA pathway. According with these results, the ET-1-induced upregulation of YAP/TEAD target genes, such as CYR61, CTGF, ANKRD1 and EDN1, as well as TEAD transcriptional activity and cell invasion, are inhibited upon β-arr1, Trio, or YAP silencing, or macitentan treatment, demonstrating that β-arr1-mediated intersections are required for ET-1-induced YAP signaling. At the chromatin level, the activation of ET-1 axis promotes the recruitment of YAP, TEAD and β-arr1 on TEAD binding sites of CTGF, ANKRD1 and EDN1 promoters, an effect inhibited by macitentan treatment. These results indicate that β-arr1 can act as a transcription co-activator that bind TEAD thereby activating transcription of EDN1, which in turn, can sustain persistent YAP/TAZ activity through an autocrine loop. In murine orthotopic model of patient-derived xenograft (PDX) of HG-SOC, ET-1R blockade by macitentan, inhibits tumor growth, enhances the sensitivity to chemotherapy and reduces YAP and TEAD transcriptional activity. Altogether our results establish for the first time YAP/TAZ as critical downstream effectors of ET-1R/β-arr1 signaling, providing mechanistic insights that targeting ET-1R signaling overcomes YAP/TAZ driven platinum-based therapy failure in HG-SOC. Citation Format: Piera Tocci, Roberta Cianfrocca, Laura Rosanò, Rosanna Sestito, Valeriana Di Castro, Giovanni Blandino, Anna Bagnato. Endothelin-1 receptor/β-arrestin1 is an actionable node that regulates YAP/TAZ signaling and chemoresistance in high-grade ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1197. doi:10.1158/1538-7445.AM2017-1197

The activity of the conjugated antimetabolite 5-FdU-ECyd against platinum-resistant ovarian cancer.

e17077 Background: Primary or secondary resistance to platinum-based chemotherapy is an important clinical challenge in the treatment of ovarian cancer (OC) and limits survival. Therefore, the development of innovative drugs against platinum resistance is urgently needed. Our therapeutic concept is based on the conjugation of two chemotherapeutic compounds to a monotherapeutic pro-drug, which is taken up by cancer cells and is subsequently cleaved into several active cytostatic metabolites. Our in vitro study evaluates the effects of the conjugated antimetabolite 5-FdU-ECyd, consisting of 2-deoxy-5-fluorouridine (5-FdU) and ethynylcytidine (ECyd), on platinum-resistant OC cells. Methods: In vitro assays and RNA-Seq (Illumina) were applied for characterization of 5-FdU-ECyd treated platinum-sensitive A2780 and isogenic platinum-resistant A2780cis as well as independent platinum-resistant Skov-3-IP OC cells. Results: Nano molar 5-FdU-ECyd concentrations induced a rapid dose-dependent decline of cell viability in platinum-sensitive and platinum-resistant OC cells. The cytotoxicity of 5-FdU-ECyd was accompanied by the formation of DNA double strand breaks and by the induction of apoptosis, indicated by a strong increase of pro-apoptotic molecular markers (caspase-3/7 activation, PARP-cleavage). Moreover, 5-FdU-ECyd efficiently decreased cell migration of platinum-resistant OC cells and inhibited other tumor-associated cellular functions, such as clonogenic or spheroidal growth. Transcriptome analysis indicated that, independently of platinum-resistance status, 5-FdU-ECyd influences distinct cellular pathways, involved in cell cycle regulation, apoptosis, DNA-damage response and RNA/pyrimidine metabolism. Combination treatment of 5-FdU-ECyd and platin did not show a synergistic cellular response, suggesting the potential use of 5-FdU-ECyd as a monotherapeutic agent. Conclusions: Our data provide a rationale to characterize the effect of 5-FdU-ECyd in a pre-clinical in vivo setting. We hypothesize that this conjugate is a promising therapeutic option for OC patients with resistance to conventional platinum-based chemotherapy.

Inhibition of Wnt signaling as therapeutic option in platinum-resistant ovarian cancer.

e17050 Background: New therapeutic approaches for platinum-resistant ovarian cancer patients are urgently needed. In this context, Wnt signaling appears to be a promising target so that inhibition of this pathway in platinum-resistant cell lines was aim of the present study. Methods: The ovarian cancer cell line A2780 and its platinum-resistant clone A2780cis were treated with different concentrations of Wnt singaling inhibitors SB216761, XAV939, and triptolides. Metabolic activity and cell viability was estimated by MTT cell proliferation assays. Immunohistochemistry for ß-Catenin visualized activity of the Wnt pathway. Results: MTT proliferation tests revealed an impaired proliferation following treatment with all three agents. While triptolides already led to significantly reduced metabolic activity after 48h, this effect was seen for SB216761 and XAV939 not before 72h. Immunohistochemistry for ß-Catenin confirmed inhibition of Wnt signaling. Following XAV939 treatment of A2780cis, ß-Catenin signals shifted from the nucleus towards the cell membrane. Conclusions: Re-sensitizing platinum-resistant ovarian cancer cells for platinum-based chemotherapy by inhibition of Wnt signaling seems to be mechanism visualized by the translocation of ß-Catenin from the nucleus towards the cell membrane. In this context, a dose-dependent response was noted for XAV939. Inhibition of Wnt Signaling appears to be a prospective therapeutic approach for platinum-resistant ovarian cancer patients.

Cost-effectiveness of nivolumab for treatment of platinum-resistant recurrent or metastatic squamous cell carcinoma of the head and neck.

6026 Background: The Checkmate 141 randomized trial found that patients with platinum-refractory, recurrent or metastatic (R/M) squamous-cell carcinoma of the head and neck (SCCHN) treated with nivolumab had significantly longer overall survival than those treated with standard, single-agent therapy. However, nivolumab is more expensive than standard treatment. We conducted a cost-effectiveness analysis of nivolumab for the treatment of R/M SCCHN. Methods: We constructed a Markov model to simulate treatment with nivolumab or other single-agent therapy (docetaxel, cetuximab, or methotrexate) for patients with R/M SCCHN. Transition probabilities including disease progression, survival, and toxicity were derived from clinical trial data, while costs (in 2016 US dollars) and health utilities were estimated from the literature. Incremental cost-effectiveness ratios (ICERs), expressed as dollar per quality-adjusted life-year (QALY), were calculated with values less than $100,000/QALY considered cost-effective from a healthcare payer perspective. We conducted one-way and probabilistic sensitivity analyses to examine model uncertainty. Results: Our base-case model found that treatment with nivolumab increased overall cost by $59,000 and improved effectiveness by 0.2443 QALYs compared to single-agent therapy, leading to an ICER of $241,100/QALY. In sensitivity analyses, the model was most sensitive to the cost of nivolumab and assumptions about survival. Nivolumab would become cost-effective if the cost per cycle decreased from $13,432 to $5,716. If we assumed that all patients alive at the end of the Checkmate 141 trial were cured of their disease then nivolumab was still not considered cost-effective (ICER $160,000/QALY). Probabilistic sensitivity analysis also demonstrated relative stability of the cost-effectiveness model and found that treatment with nivolumab was cost-effective 0% of the time at a willingness-to-pay threshold of $100,000/QALY. Conclusions: While nivolumab significantly improves overall survival, at the current cost it would not be considered a cost-effective treatment option for patients with R/M SCCHN.

Exosomes as mediators of platinum resistance in ovarian cancer.

Exosomes have been implicated in the cell-cell transfer of oncogenic proteins and genetic material. We speculated this may be one mechanism by which an intrinsically platinum-resistant population of epithelial ovarian cancer (EOC) cells imparts its influence on surrounding tumor cells. To explore this possibility we utilized a platinum-sensitive cell line, A2780 and exosomes derived from its resistant subclones, and an unselected, platinum-resistant EOC line, OVCAR10. A2780 cells demonstrate a ~2-fold increase in viability upon treatment with carboplatin when pre-exposed to exosomes from platinum-resistant cells as compared to controls. This coincided with increased epithelial to mesenchymal transition (EMT). DNA sequencing of EOC cell lines revealed previously unreported somatic mutations in the Mothers Against Decapentaplegic Homolog 4 (SMAD4) within platinum-resistant cells. A2780 cells engineered to exogenously express these SMAD4 mutations demonstrate up-regulation of EMT markers following carboplatin treatment, are more resistant to carboplatin, and release exosomes which impart a ~1.7-fold increase in resistance in naive A2780 recipient cells as compared to controls. These studies provide the first evidence that acquired SMAD4 mutations enhance the chemo-resistance profile of EOC and present a novel mechanism in which exchange of tumor-derived exosomes perpetuates an EMT phenotype, leading to the development of subpopulations of platinum-refractory cells.

Ovarian Cancer Chemoresistance Relies on the Stem Cell Reprogramming Factor PBX1.

The evolution of chemoresistance is a fundamental characteristic of cancer that ultimately hampers its clinical management. However, it may be possible to improve patient outcomes significantly by a better understanding of resistance mechanisms, which cancers rely upon during the evolution to an untreatable state. Here we report an essential role of the stem cell reprogramming factor, PBX1, in mediating chemoresistance in ovarian carcinomas. In the clinical setting, high levels of PBX1 expression correlated with shorter survival in post-chemotherapy ovarian cancer patients. In tumor cells with low endogenous levels of PBX1, its enforced expression promoted cancer stem cell-like phenotypes, including most notably an increase in resistance to platinum-based therapy used most commonly for treating this disease. Conversely, silencing PBX1 in platinum-resistant cells that overexpressed PBX1 sensitized them to platinum treatment and reduced their stem-like properties. An analysis of published genome-wide chromatin immunoprecipitation data indicated that PBX1 binds directly to promoters of genes involved in stem cell maintenance and the response to tissue injury. We confirmed direct regulation of one of these genes, STAT3, demonstrating that the PBX1 binding motif at its promoter acted to positively regulate STAT3 transcription. We further demonstrated that a STAT3/JAK2 inhibitor could potently sensitize platinum-resistant cells to carboplatin and suppress their growth in vivo Our findings offer a mechanistic rationale to target the PBX1/STAT3 axis to antagonize a key mechanism of chemoresistance in ovarian cancers and possibly other human cancers. Cancer Res; 76(21); 6351-61. ©2016 AACR.

PKC-alpha modulation by miR-483-3p in platinum-resistant ovarian carcinoma cells

The occurrence of drug resistance limits the efficacy of platinum compounds in the cure of ovarian carcinoma. Since microRNAs (miRNAs) may contribute to this phenomenon by regulating different aspects of tumor cell response, the aim of this study was to exploit the analysis of expression of miRNAs in platinum sensitive/resistant cells in an attempt to identify potential regulators of drug response. MiR-483-3p, which may participate in apoptosis and cell proliferation regulation, was found up-regulated in 4 platinum resistant variants, particularly in the IGROV-1/Pt1 subline, versus parental cells. Transfection of a synthetic precursor of miR-483-3p in IGROV-1 parental cells elicited a marked up-regulation of the miRNA levels. Growth-inhibition and colony-forming assays indicated that miR-483-3p over-expression reduced cell growth and conferred mild levels of cisplatin resistance in IGROV-1 cells, by interference with their proliferative potential. Predicted targets of miR-483-3p included PRKCA (encoding PKC-alpha), previously reported to be associated to platinum-resistance in ovarian carcinoma. We found that miR-483-3p directly targeted PRKCA in IGROV-1 cells. In keeping with this finding, cisplatin sensitivity of IGROV-1 cells decreased upon molecular/pharmacological inhibition of PKC-alpha. Overall, our results suggest that overexpression of miR-483-3p by ovarian carcinoma platinum-resistant cells may interfere with their proliferation, thus protecting them from DNA damage induced by platinum compounds and ultimately representing a drug-resistance mechanism. The impairment of cell growth may account for low levels of drug resistance that could be relevant in the clinical setting.

ACE2 overexpression inhibits acquired platinum resistance-induced tumor angiogenesis in NSCLC.

AngiotensinII (AngII) is a multifunctional bioactive peptide in the renin-angiotensin system (RAS). Angiotensin-converting enzyme2 (ACE2) is a newly identified component of RAS. We previously reported that ACE2 overexpression may inhibit cell growth and vascular endothelial growth factor (VEGF) production invitro and invivo. In the present study, we investigated the effect of ACE2 on tumor-associated angiogen-esis after the development of acquired platinum resistance in non-small cell lung cancer (NSCLC). Four NSCLC cell lines, A549, LLC, A549-DDP and LLC-DDP, were used invitro, while A549 and A549-DDP cells were used invivo. A549-DDP and LLC-DDP cells were newly established at our institution as acquired platinum-resistant sublines by culturing the former parent cells in cisplatin (CDDP)-containing conditioned medium for 6months. These platinum-resistant cells showed significantly higher angiotensinII type1 receptor (AT1R), ACE and VEGF production and lower ACE2 expression than their corresponding parent cells. We showed that ACE2 overexpression inhibited the production of VEGF invitro and invivo compared to their corresponding parent cells. We also found that ACE2 overexpression reduced the expression of AT1R and ACE. Additionally, we confirmed that ACE2 overexpres-sion inhibited cell growth and VEGF production while simultaneously suppressing ACE and AT1R expression in human lung cancer xenografts. Our findings indicate that ACE2 overexpression may potentially suppress angiogenesis in NSCLC after the development of acquired platinum resistance.

Abstract 2090: Evaluation of the cytotoxic profile of Metformin and Y15 in platinum resistant ovarian cancer cells

Abstract Platinum resistance remains a major challenge in the chemotherapeutic management of ovarian cancer. The anti-diabetic drug metformin has been previously shown to induce cytotoxicity in platinum resistant ovarian cancer cells and overexpression and increased phosphorylation of a tyrosine kinase called Focal Adhesion Kinase (FAK) has been implicated in the development of this platinum resistance. Therefore, in the present study we evaluated the combined cytotoxic efficacy of Metformin and the focal adhesion kinase inhibitor 1,2,4,5-Benzenetetraamine tetrahydrochloride (Y15) in platinum resistant OVCAR3 ovarian cancer cells. Cells were initially treated with concentrations of Y15 ranging from 10-100 μM, and metformin from 10-100mM to determine 1C50 values. Subsequently, cells were treated with Y15 (80 μM) and metformin (26mM) alone and in combination. All treatments were triplicated with duration of 24hrs and control cells exposed to media only. The cytotoxic profile of each treatment was assessed using the automated trypan blue assay. DNA fragmentation and poly ADP ribose polymerase (PARP) cleavage assays were performed to evaluate the mechanism of cell death and we further evaluated the expression of phosphorylated FAK, p53 and p21 in response to treatments using western blot. Y15 alone produced 48% cell death. In combination, Y15 significantly increased the cytotoxic efficacy of metformin by 22%, when compared to the metformin only treatment. Cell death by apoptosis was confirmed by PARP cleavage and the presence of DNA fragments in Y15, metformin, and metformin +Y15 treatment groups. The Metformin +Y15 combination significantly downregulated the expression of phosphorylated FAK when compared to the individual treatments and control and this confirmed reduced FAK activity. Reduced FAK auto phosphorylation also correlated with increased expression of p53 AND p21 in metformin and Y15 treatment groups. Our findings show that Y15 significantly enhances the cytotoxic profile of metformin in platinum resistant OVCAR-3 cells. Furthermore, a FAK dependent apoptotic mechanism appears to underlie the cytotoxic effect of metformin as well as Y15 as both drugs significantly reduced the phosphorylation of FAK alone, and in combination. Reduced FAK activity also correlated with increased p53 and p21 expression. This study is the first to report a FAK dependent cytotoxic mechanism of metformin in ovarian cancer and in further work we will evaluate the mechanisms why which metformin cooperates with Y15 to inhibit FAK activity in platinum resistant ovarian cancer. Citation Format: Arkene S. Levy, Zara Khan, Samuel Batko, Keerthi Thallapureddy, Robert Smith, Thanigaivelan Kanagasabai, Julie Torruellas Garcia, Appu Rathinavelu. Evaluation of the cytotoxic profile of Metformin and Y15 in platinum resistant ovarian cancer cells. [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 2090.

Abstract 4101: Stromal cell-induced alterations in the response of colorectal cancer cell to demethylating agents

Abstract Epigenetic mechanisms such as DNA hypermethylation, that results in gene silencing, is closely associated with resistance to platinum-based chemotherapy for colorectal cancer (CRC). DNA methyltransferase inhibitors (DNMTi) that reactivate and induce reexpression of silenced gene have the potential to improve the outcome of platinum-based and other therapies in CRC. In fact, non-cytotoxic concentrations of azacitidine, a clinically used DNMTi, has been reported to resensitize platinum-resistant ovarian cells to carboplatin. Hypomethylating agents, such as azacitidine and decitabine have shown significant promise in hematologic malignancies; however, studies on their application to CRC and other solid tumors have yielded ambivalent results potentially due to the complexities of the tumor microenvironment that result from the numerous cell type interactions. In this study, we analyzed the impact of different tumor-stroma ratios on cancer cell response to azacitidine, decitabine, and two lead compounds identified by in vitro screens in two-dimensional (2D) and three-dimensional (3D) co-cultures of colorectal HCT116 carcinoma demethylation reporter cells and adipose-derived mesenchymal stromal cells (MSCs) isolated from healthy individuals undergoing elective lipoaspiration. Each subject provided informed consent. Activity of hypomethylating drugs was examined in 2D and 3D cultures of different tumor-stroma ratios using confocal microscopy, flow cytometry, and MTT analyses. Our preliminary flow cytometry results show an altered response of hypomethylating agents in cocultures of HCT116 and MSCs compared to monocultures of HCT116 cells alone. There was an increase in demethylation of HCT116 cells in 3D cultures containing a higher ratio of stromal cells following treatment with low concentration of decitabine. Furthermore, confocal analysis 3D co-cultures at various z-plane heights revealed increased demethylation at low concentrations of all drugs in cultures with high stromal cell numbers. These results indicate that intratumoral stroma may alter the sensitivity of cancer cells to demethylating agents and warrant further studies. Citation Format: Viswanath Das, Svetlana Skolekova, Khushboo Agrawal, Jan Gursky, Lucia Kučerová, Marián Hajdúch. Stromal cell-induced alterations in the response of colorectal cancer cell to demethylating agents. [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 4101.

Abstract 4835: Targeting the ATR/CHK1 axis in combination with PARP inhibition is more effective than PARP inhibition alone in BRCA mutant models

Abstract Introduction: Approximately 50% of high grade serous ovarian cancers (HGSOC) have defects in genes involved in homologous recombination repair (HR). BRCA1/2 mutant HGSOCs have a deficiency in the repair of double strand DNA breaks by HR. Poly(ADP-ribose) polymerase inhibitors (PARPi) block the repair of single-stranded breaks leading to double strand DNA breaks which cannot be repaired efficiently in BRCA-deficient cancers capitalizing on synthetic lethality. PARPi have a modest clinical response of only ∼40% in recurrent BRCA mutant HGSOCs. We hypothesize that PARPi alone increases reliance on other DNA repair pathways such as ATR/CHK1 in HR deficient cells, and by targeting ATR/CHK1 in combination with PARPi would be more effective in eradicating tumor growth. Experimental Procedures: Effects of PARP inhibitor (PARPi, Olaparib), CHK1 inhibitor (CHK1i, MK8776), and ATR inhibitor (ATRi, AZD6738) on cell cycle, survival, colony formation, genome stability were evaluated in PEO1 (BRCA2 mutant), PEO4 (BRCA wild-type), JHOS4 (BRCA1 mutant), and WO-24 (BRCA wild-type) ovarian cancer cells. A BRCA2 mutant (8945delAA) orthotopic PDX model was used to evaluate PARPi alone or in combination with CHK1/ATRi. Targeted capture massively parallel sequencing, Reverse-Phase Protein Array Analysis (RPPA) and IHC were performed on cells and xenografts to evaluate for biomarkers of response. Results: Monotherapy with PARPi, CHK1i, and ATRi in vitro demonstrated selectivity in mediating cell death and DNA damage in BRCA1/2 mutant cell lines (PEO1, JHOS4) compared to BRCA1/2 wild-type, platinum resistant cell lines (PEO4, WO-24). However, monotherapy only results in ∼40-50% cell death in BRCA1/2 mutant cell lines. PARPi alone resulted in tumor suppression but not tumor eradication in a BRCA2 mutant PDX model. PARPi treatment resulted in an increase in ATR/CHK1 signaling in BRCA1/2 mutant cells. Treatment with ATR/CHK1i in combination with PARPi is synergistic in reducing survival of BRCA1/2 cells. Combination treatment was more effective in targeting cell cycle mediators, and promoting apoptosis. Treatment with either PARPi+ATRi or PARPi+CHK1i combinations was synergistic in causing tumor suppression but PARPi/ATRi combination caused tumor regression in a BRCA2 mutant PDX model. Conclusions: Strategies to optimize approaches capitalizing on synthetic lethality are needed for HR deficient HGSOC. PARPi is effective in BRCA deficient cancers but can potentially be more effective when combined with ATR/CHK1i. Citation Format: Erin George, Hyoung Kim, Janos Tanyi, Ryan Ragland, Rugang Zhang, Patricia Bradford, Clemens Krepler, Katherine Nathanson, Brandon Wenz, Yiling Lu, Gordon Mills, Mark Morgan, Fiona Simpkins. Targeting the ATR/CHK1 axis in combination with PARP inhibition is more effective than PARP inhibition alone in BRCA mutant models. [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 4835.

P53 Loses grip on PIK3CA expression leading to enhanced cell survival during platinum resistance

Tumour suppressor p53, a master transcriptional regulator determines cell fate through preferential activation/repression of a myriad of genes during stress. Till date, activation and preferential binding of p53 on different promoters was reported to be influenced by the nature, strength and duration of stress which mediates its post translational modifications. Cisplatin, a widely used cytotoxic drug represses PIK3CA promoter activity and attenuates PI3K/AKT cell survival pathway through p53 activation in sensitive cells. However, very little is understood about the overall mechanism of p53-PIK3CA interaction and influence of p53 on the transcriptional status of PIK3CA during cisplatin resistance. Here we showed that cisplatin could dynamically alter p53 occupancy between the p53 binding sequences present in PIK3CA promoter in ovarian and breast cancer cells. This altered occupancy is dictated by higher acetylation and hyper-phosphorylation at serine 15, serine 20 and serine 46 residues. Interestingly, cisplatin resistant cells when challenged with cisplatin demonstrated abolished PIK3CA promoter attenuation, low level of p53 binding, and loss of p53 serine 46 phosphorylation. A phosphorylation deficient S46A mutant failed to repress PIK3CA in p53 deficient cells. Elevated expression of Bcl2, P27 and cFLIP indicated a pro-survival state in these resistant cells. Non-invasive real time imaging using two different luciferase reporters showed that cisplatin could simultaneously induce PIK3CA attenuation and p53 activation with growth regression in sensitive tumours but not in the resistant tumours where only low level of p53 activation and sustained growth was observed. This is the first report on phosphorylation of p53 serine 46 as a modulator of p53-PIK3CA promoter interaction which influences altered binding of p53 at different consensus sequences in the same promoter in response to chemotherapeutic stress. Absence of such modulation in resistant cellular milieu influences cellular homoeostasis in platinum-resistant cells probably due to altered post translational modification of p53.