Sensitive Parental Lines Research Articles

The combination of APR-246 and carboplatin in olaparib-resistant high grade serous ovarian cancer (HGSOC) and triple negative breast cancer (TNBC) cell lines.

e17504 Background: PARP inhibitors (PARPi), as Olaparib (OLA), have changed the therapeutic landscape in HGSOC and TNBC. However, most patients will develop resistance to PARPi. Although resistance mechanisms are poorly understood, it is suggested that BRCA mutations reversions or cell cycle alterations could be involved. APR-246 is a new targeted agent that restores p53 in TP53-mutated cells. The aim of our study was to assess the potential synergism of the combination of carboplatin (carbo) plus APR-246 in both OLA-sensitive and OLA-resistant HGSOC and TNBC cell lines. Methods: We selected two HGSOC (PEO1-S and Kuramochi-S) and one TNBC TP53 mutant cell lines (MDA-MB-231-S). Resistance to OLA was generated by pulse doses with IC75 OLA for 24 hours and recovered for two weeks during a period of 6 months (PEO1-R) and to increased concentrations of OLA for 72 hours during a period of 1 year (Kuramochi-R, MDA-MB-231-R). Next-generation sequencing was performed in order to assess mutations. IC50 of APR-246 and Carbo and the combination of both (combo) were calculated for Kura-S/R, PEO1-S/R and 231-S/R cell lines. Synergism between both drugs was assessed with Chou-Talalay method for combination index (CI) at Fa50. DNA damage was assessed by gamma-H2AX expression by western-blot (WB). Results: 231-S harboured a TP53 mutation (mut) (missense R280K) and BRCA wildtype (wt), in PEO1-S BRCA2 mut p.Y1655* and TP53 mut was detectable. Kuramochi-S was TP53 mut (missense D816Y) and BRCA2 mut. BRCA and p53 mutation remained unchanged in the resistant lines generated.The mutation profile of each line and the IC50 of APR-246, carbo and combo are shown in the table. IC50 of carboplatin is superior in all 3 resistant cell lines when compared to their sensitive parental line, suggesting a potential cross-resistance to platinum in OLA-resistance. The combination of carbo and APR-246 is synergistic even in OLA-resistant cell lines, in fact in those cross-resistant lines values of synergism by Chou-Talalay are improved by the combo suggesting a potential role of this combination in PARPi resistant cell lines. WB showed an increased DNA damage with the combo when compared to either single agent, with an increase in H2AX in all lines either sensitive or resistant. Conclusions: The combination of APR246 and carboplatin is synergistic in all 3 studied cell lines but also in the OLA resistant ones. The combo increased its synergistic effect suggesting a potential role of combo in OLA-resistant tumors. [Table: see text]

Abstract 3956: MYC inhibition overcomes IMiD resistance in heterogeneous multiple myeloma populations

Abstract Introduction: Multiple myeloma (MM) is a plasma cell malignancy that remains incurable, with patients enduring multiple relapses and development of drug resistance. Immunomodulatory drugs (IMiDs) are critical anti-MM agents. IMiDs act by inducing CRBN-dependent proteasomal degradation of the transcription factors IKZF1 and IKZF3, which leads to IRF4 and MYC downregulation (collectively termed the “Ikaros axis”). Although CRBN aberrations occur, whether they are a functional mechanism of resistance in patients remains unclear. Based on the importance of CRBN in IMiD response, we hypothesized that IMiD treatment fails to downregulate the Ikaros axis in IMiD-resistant MM cells. Methods: To measure IMiD-induced Ikaros axis downregulation, we designed an intracellular flow cytometry assay that measured relative IKZF1, IKZF3, IRF4 and MYC protein levels in MM cells following ex vivo pomalidomide (Pom) treatment. We established this assay using IMiD-sensitive parental and dose-escalated Pom resistant MM1S and H929 cell lines before utilizing it in patient samples (isolated mononuclear cells). To assess the Ikaros axis in the context of MM intratumoral heterogeneity, we used mass cytometry to simultaneously characterize MM subpopulations in patient samples. Lastly, we determined ex vivo drug sensitivity in patient samples via flow cytometry. Results: Our hypothesis was supported in MM cell lines, as sensitive parental lines showed a significant decrease in all Ikaros axis protein levels following Pom treatment, while resistant lines showed no IMiD-induced decrease in any Ikaros axis protein. However, when assessed in CD38+CD138+ cells from patient samples, Pom treatment caused a significant decrease in IKZF1, IKZF3 and IRF4 regardless of IMiD sensitivity. Mass cytometry in patient samples revealed that individual Ikaros axis proteins were differentially expressed between subpopulations. When correlating this with ex vivo Pom sensitivity of MM subpopulations, we observed that low IKZF1 and IKZF3 corresponded to Pom resistance. Interestingly, most of these resistant populations still expressed MYC. We therefore assessed whether IMiD resistant MM was MYC dependent by treating Pom resistant MM cells with MYCi975. In 88% (7/8) of patient samples tested, IMiD resistant MM cells were sensitive to MYC inhibition. Conclusions: Our findings did not support our initial hypothesis, as IMiD-induced IKZF1 and IKZF3 degradation remains intact in IMiD resistant MM cells from patient samples. However, our data support a mechanism where the Ikaros axis no longer drives MYC expression in IMiD-resistant MM. Therefore, we propose that the critical mediator of IMiD resistance is conversion to a cell state where MYC expression is Ikaros axis independent. This suggests targeting MYC directly or via the as yet uncharacterized mechanism controlling MYC may be an effective strategy to eradicate IMiD resistant MM. Citation Format: Lorraine N. Davis, Zachary J. Walker, Denis Ohlstrom, Brett M. Stevens, Peter A. Forsberg, Tomer M. Mark, Craig T. Jordan, Daniel W. Sherbenou. MYC inhibition overcomes IMiD resistance in heterogeneous multiple myeloma populations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3956.

Characterization and inheritance of dicamba resistance in a multiple-resistant waterhemp (Amaranthus tuberculatus) population from Illinois

AbstractWaterhemp [Amaranthus tuberculatus (Moq.) Sauer] is one of the most troublesome agronomic weeds in the midwestern United States. The rapid evolution and selection of herbicide-resistance traits in A. tuberculatus is a major challenge in managing this species. An A. tuberculatus population, designated CHR, was identified in 2012 in Champaign County, IL, and previously characterized as resistant to herbicides from six site-of-action groups: 2,4-D (Group 4), acetolactate synthase inhibitors (Group 2), protoporphyrinogen oxidase inhibitors (Group 14), 4-hydroxyphenylpyruvate dioxygenase inhibitors (Group 27), photosystem II inhibitors (Group 5), and very-long-chain fatty-acid synthesis inhibitors (Group 15). Recently, ineffective control of CHR was observed in the field after dicamba application. Therefore, this research was initiated to confirm dicamba resistance, quantify the resistance level, and investigate its inheritance in CHR. Multiple field trials were conducted at the CHR location to confirm poor control with dicamba and compare dicamba treatments with other herbicides. Greenhouse trials were conducted to quantify the resistance level in CHR and confirm genetic inheritance of the resistance. In field trials, dicamba did not provide more than 65% control, while glyphosate and glufosinate provided at least 90% control. Multiple accessions were generated from controlled crosses and evaluated in greenhouse trials. Greenhouse dicamba dose–response experiments indicated a resistance level of 5- to 10-fold relative to a sensitive parental line. Dose–response experiments using F1 lines indicated that dicamba resistance was an incompletely dominant trait. Segregation analysis with F2 and backcross populations indicated that dicamba resistance had moderate heritability and was potentially a multigenic trait. Although dicamba resistance was predominantly inherited as a nuclear trait, minor maternal inheritance was not completely ruled out. To our knowledge, CHR is one of the first cases of dicamba resistance in A. tuberculatus. Further studies will focus on elucidating the genes involved in dicamba resistance.

Genomic Adaption and Mutational Patterns in a HaCaT Subline Resistant to Alkylating Agents and Ionizing Radiation.

Sulfur mustard (SM) is a chemical warfare agent that can damage DNA via alkylation and oxidative stress. Because of its genotoxicity, SM is cancerogenic and the progenitor of many chemotherapeutics. Previously, we developed an SM-resistant cell line via chronic exposure of the popular keratinocyte cell line HaCaT to increasing doses of SM over a period of 40 months. In this study, we compared the genomic landscape of the SM-resistant cell line HaCaT/SM to its sensitive parental line HaCaT in order to gain insights into genetic changes associated with continuous alkylation and oxidative stress. We established chromosome numbers by cytogenetics, analyzed DNA copy number changes by means of array Comparative Genomic Hybridization (array CGH), employed the genome-wide chromosome conformation capture technique Hi-C to detect chromosomal translocations, and derived mutational signatures by whole-genome sequencing. We observed that chronic SM exposure eliminated the initially prevailing hypotetraploid cell population in favor of a hyperdiploid one, which contrasts with previous observations that link polyploidization to increased tolerance and adaptability toward genotoxic stress. Furthermore, we observed an accumulation of chromosomal translocations, frequently flanked by DNA copy number changes, which indicates a high rate of DNA double-strand breaks and their misrepair. HaCaT/SM-specific single-nucleotide variants showed enrichment of C > A and T > A transversions and a lower rate of deaminated cytosines in the CpG dinucleotide context. Given the frequent use of HaCaT in toxicology, this study provides a valuable data source with respect to the original genotype of HaCaT and the mutational signatures associated with chronic alkylation and oxidative stress.

DDRE-24. ACQUIRED RESISTANCE TO TARGETED INHIBITORS IN EGFR-DRIVEN GLIOBLASTOMA: IDENTIFICATION OF DUAL KINASE TARGETS

Abstract Glioblastoma (GBM) is a devastating primary brain tumor with 5-year survival < 5%. CDKN2A deletion (~60%) and EGFR amplification (55–60%) mutations frequently co-occur in these tumors. EGFR is an attractive therapeutic target due to its mutational frequency and availability of multiple brain-penetrant tyrosine kinase inhibitors (TKI). Several EGFR TKI have failed clinically, due in part to acquired resistance. To mechanistically examine this type of resistance, we used genetically engineered mouse astrocytes harboring Cdkn2a deletion and EGFRvIII, a common (35%) activating mutation. Resistant cells were generated via chronic exposure to gefitinib or erlotinib, either in vitro or in vivo. Resistance to these first-generation EGFR TKI conferred cross resistance (up to 36-fold ΔIC50) to a panel of second- and third-generation TKI relative to sensitive parental lines. Moreover, integrated RNA sequencing (RNA-seq) and chemical proteomics (multiplexed inhibitor beads and mass spectrometry (MIB-MS)) showed that the kinase transcriptome and proteome were rewired in resistant cells: 113 of ~300 detected kinases were differentially expressed (p< 0.05). We then used these techniques to examine acute (≤ 48 h) kinome changes in both sensitive and resistant cells upon treatment with a CNS-penetrant, second-generation EGFR TKI, afatinib. Whereas exposure of treatment-naïve, sensitive cells to afatinib significantly rewired the kinome (120 differentially expressed kinases), the response of resistant cells to drug re-challenge was significantly blunted (13 differentially expressed kinases). A subset of expressed kinases (35 of 263) dynamically responded to afatinib in both sensitive and resistant cells. Overall, upregulated kinases include those implicated in the biology of gliomas (Bmx, Fgfr2) and of other cancers (Pdgfrb, Mapk3/4, Ddr1/2, Pdk2). These kinases thus represent putative druggable targets for dual inhibition therapy. Integrated kinome profiling using MIB-MS and RNA-seq in GBM models with defined mutational profiles provides a powerful framework to identify novel therapeutic targets that could significantly alter current treatment paradigms.

Kinome Profiling to Predict Sensitivity to MAPK Inhibition in Melanoma and to Provide New Insights into Intrinsic and Acquired Mechanism of Resistance.

Mitogen-activated protein kinase (MAPK) inhibition with the combination of BRAF (Rapidly Accelerated Fibrosarcoma) and MEK (Mitogen-activated protein kinase kinase) inhibitors has become the standard of first-line therapy of metastatic melanoma harbouring BRAF V600 mutations. However, about half of the patients present with primary resistance while the remaining develop secondary resistance under prolonged treatment. Thus, there is a need for predictive biomarkers for sensitivity and/or resistance to further refine the patient population likely to benefit from MAPK inhibitors. In this study, we explored a top-down approach using a multiplex kinase assay, first, to discover a kinome signature predicting sensitivity, intrinsic and acquired resistance to MAPK inhibitors in melanoma, and second, to understand the mechanism of resistance using cell lines. Pre-dose tissues from patients (four responders and three non-responders to BRAFi monotherapy) were profiled for phosphotyrosine kinase (PTK) and serine-threonine kinase (STK) activities on a PamChip® peptide microarray in the presence and absence of ex vivo BRAFi. In addition, molecular studies were conducted on four sensitive parental lines, their offspring with acquired resistance to BRAFi and two lines with intrinsic resistance. PTK and STK activities in cell lysates were measured in the presence and absence of ex vivo BRAFi and/or MEKi. In tissue lysates, concentration-dependent ex vivo inhibition of STK and PTK activities with dabrafenib was stronger in responders than in non-responders. This difference was confirmed in cell lines comparing sensitive and resistant ones. Interestingly, common features of resistance were increased activity of receptor tyrosine kinases, Proto-oncogene tyrosine-protein kinase Src (Src) family kinases and protein kinase B (PKB, AKT) signalling. These latter results were confirmed by Western blots. While dabrafenib alone showed an inhibition of STK and PTK activities in both tissues and cell lines, the combination of dabrafenib and trametinib showed an antagonism on the STK activities and a synergism on PTK activities, resulting in stronger inhibitions of overall tyrosine kinase activities. Altogether; these data reveal that resistance of tumours and cell lines to MAPK inhibitors can be predicted using a multiplex kinase assay and is associated with an increase in specific tyrosine kinase activities and globally to AKT signalling in the patient’s tissue. Thus, such a predictive kinome signature would help to identify patients with innate resistance to MAPK double inhibition in order to propose other therapies.

Overcoming Resistance of Human Non-Hodgkin's Lymphoma to CD19-CAR CTL Therapy by Celecoxib and Histone Deacetylase Inhibitors.

Patients with B-cell non-Hodgkin’s lymphoma (B-NHL) who fail to respond to first-line treatment regimens or develop resistance, exhibit poor prognosis. This signifies the need to develop alternative treatment strategies. CD19-chimeric antigen receptor (CAR) T cell-redirected immunotherapy is an attractive and novel option, which has shown encouraging outcomes in phase I clinical trials of relapsed/refractory NHL. However, the underlying mechanisms of, and approaches to overcome, acquired anti-CD19CAR CD8+ T cells (CTL)-resistance in NHL remain elusive. CD19CAR transduced primary human CTLs kill CD19+ human NHLs in a CD19- and caspase-dependent manner, mainly via the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) apoptotic pathway. To understand the dynamics of the development of resistance, we analyzed several anti-CD19CAR CTL-resistant NHL sublines (R-NHL) derived by serial exposure of sensitive parental lines to excessive numbers of anti-CD19CAR CTLs followed by a limiting dilution analysis. The R-NHLs retained surface CD19 expression and were efficiently recognized by CD19CAR CTLs. However, R-NHLs developed cross-resistance to CD19CAR transduced human primary CTLs and the Jurkat human T cell line, activated Jurkat, and lymphokine activated killer (LAK) cells, suggesting the acquisition of resistance is independent of CD19-loss and might be due to aberrant apoptotic machinery. We hypothesize that the R-NHL refractoriness to CD19CAR CTL killing could be partially rescued by small molecule sensitizers with apoptotic-gene regulatory effects. Chromatin modifiers and Celecoxib partially reversed the resistance of R-NHL cells to the cytotoxic effects of anti-CD19CAR CTLs and rhTRAIL. These in vitro results, though they require further examination, may provide a rational biological basis for combination treatment in the management of CD19CAR CTL-based therapy of NHL.

Abstract P4-07-06: MicroRNAs associated with acquired taxane resistance in a breast cancer cell line model

Abstract Background: Acquired chemoresistance remains the major cause of therapeutic failure in the treatment of breast cancer. Improved knowledge of the transition from drug sensitive to resistant breast cancer will pave the way for novel preventative and therapeutic strategies. MicroRNAs (miRNA) are endogenous, small non-coding RNAs that regulate gene expression by targeting the 3'UTR region of messenger RNAs. There is a growing body of evidence to suggest miRNAs may be involved in the development of chemoresistance and may play a role in the regulation of drug resistance pathways. Methods: An in vitro model of paclitaxel resistance was developed through the generation of resistant MDA-MB-231 cell lines by serial culture in escalating doses of taxane until resistance was achieved. The chemoresistant model was used to compare differential miRNA expression with the sensitive, parental line using the Nanostring® platform, analysing 800 human miRNAs. Confirmation of differential expression was performed by QRT-PCR. Results: This analysis resulted in 30 significantly altered miRNA (1.5 fold, p value < 0.05) at 25nM paclitaxel and 48 significantly altered miRNA at 50nM paclitaxel. The top up-regulated miRNA cluster in MDA-MB-231 25PACR is hsa-miR-548l (fold change: 2.89, p value: 0.016) and top down-regulated was hsa-miR-449a (fold change: -4.1. p value: 0.001). In MDA-MB-231 50PACR the top up-regulated miRNA cluster is hsa-miR-193a-5p (fold change: 3.746, p value: 0.008) and the top down-regulated miRNA cluster is hsa-miR-135a (fold change: -4.085, p value: 0.001). To explore the molecular mechanisms of the differentially expressed miRNAs in paclitaxel resistance, targets were predicted by in silico analysis. Pathways and networks designated by miRNA targets included the cell cycle, PI3K/Akt pathways and focal adhesion. Conclusion: In this study we identified candidate resistance-associated miRNAs which were differentially expressed between in vitro derived paclitaxel resistant MDA-MB-231 and the sensitive parental line. Further validation to ascertain their role in the transition to a chemoresistant phenotype is currently ongoing. Citation Format: Taylor KJ, Chong T, D'Costa A, Yao C, Gourley C, Cameron DA, Bartlett JMS, Spears M. MicroRNAs associated with acquired taxane resistance in a breast cancer cell line model [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-07-06.

Using genome-wide CRISPR library screening with library resistant DCK to find new sources of Ara-C drug resistance in AML.

Acute myeloid leukemia (AML) can display de novo or acquired resistance to cytosine arabinoside (Ara-C), a primary component of induction chemotherapy. To identify genes capable of independently imposing Ara-C resistance, we applied a genome-wide CRISPR library to human U937 cells and exposed to them to Ara-C. Interestingly, all drug resistant clones contained guide RNAs for DCK. To avoid DCK gene modification, gRNA resistant DCK cDNA was created by the introduction of silent mutations. The CRISPR screening was repeated using the gRNA resistant DCK, and loss of SLC29A was identified as also being capable of conveying Ara-C drug resistance. To determine if loss of Dck results in increased sensitivity to other drugs, we conducted a screen of 446 FDA approved drugs using two Dck-defective BXH-2 derived murine AML cell lines and their Ara-C sensitive parental lines. Both cell lines showed an increase in sensitivity to prednisolone. Guide RNA resistant cDNA rescue was a legitimate strategy and multiple DCK or SLC29A deficient human cell clones were established with one clone becoming prednisolone sensitive. Dck-defective leukemic cells may become prednisolone sensitive indicating prednisolone may be an effective adjuvant therapy in some cases of DCK-negative AML.

Abstract 324: Targeting RNA-polymerase I using CX-5461 as a mechanism for treating chemotherapy resistant epithelial ovarian cancer

Abstract BACKGROUND: One of the first identified hallmarks of neoplastic transformation was an increased rate of ribosome biogenesis, and increased activity of RNA polymerase I (RNA pol I) is observed in most human cancers. Ribosome biogenesis is an energy intensive and tightly regulated process, and recent studies have shown that CX-5461, a potent and specific RNA pol I inhibitor, has selective toxicity to cancer cells. Here we demonstrate that CX-5461 is an effective anti-proliferative agent in epithelial ovarian carcinoma cells with an increased efficacy in chemoresistant ovarian cancer cells compared to their sensitive parental lines. METHODS AND RESULTS: Ovarian cancer cells were demonstrated to be highly sensitive to RNA pol I inhibition by MTT assay, with an IC50 range from 25nM to 2uM in 13 different ovarian cancer cell lines, and an IC50 of 3uM in the nontransformed immortalized normal surface epithelial line HIO-180. Notably, chemoresistant cell populations were generally more sensitive to CX-5461, compared to matched chemosensitive lines. IC50 in HeyA8MDR was 80nM compared to 2000nM in parental HeyA8, and was 100nM in SKOV3TRip2 compared to 400nM in SKOV3ip1. CX-5461 induces G2/M arrest (averaging 52.7% in G2 compared to 32.5% in controls), primarily through mitotic catastrophe, inducing an accumulation of multinucleated senescent cells. DNA damage pathways are activated, operating through ATM/ATR, as demonstrated by rescue with caffeine and ATR specific inhibitors. In an effort to identify why chemoresistant cells might be more susceptible, ribosomal synthesis processes were examined. Chemoresistant cells were found to have 2-4-fold increased Pol I occupancy on rDNA by ChIP, and increased rRNA synthesis by isotopic incorporation, while ribosome abundance and overall translation efficiency, measured by sucrose gradient fractionation, were unchanged. Treatment of five separate patient-derived xenograft models (PDX) with CX-5461 showed a complete response in one model, partial 55% reduction in tumor size in a second, stable disease in a 3rd, and progression in two models. CONCLUSIONS: CX-5461 shows high activity in ovarian cancer cell lines and patient-derived xenograft models, with a preferential effect on chemoresistant cells. Enhanced sensitivity to the compound is due at least in part to cancer cells’ increased demand for rRNA synthesis. RNA pol I inhibitors represent an exciting new treatment option that may have preferential effect on the chemoresistant population. Citation Format: Robert Cornelison, Zachary C. Dobbin, Ashwini A. Katre, Dae Hoon Jeong, Yulia Petrova, Danielle C. Llaneza, Adam D. Steg, Yinfeng Zhang, David A. Schneider, Charles N. Landen. Targeting RNA-polymerase I using CX-5461 as a mechanism for treating chemotherapy resistant epithelial ovarian cancer. [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 324.

Relationship between therapeutic efficacy of doxorubicin-transferrin conjugate and expression of P-glycoprotein in chronic erythromyeloblastoid leukemia cells sensitive and resistant to doxorubicin.

BackgroundConjugation of anti-neoplastic agents with human proteins is a strategy to diminish the toxic side effects of anthracycline antibiotics. We have developed a novel doxorubicin-transferrin (DOX-TRF) conjugate aimed to direct anticancer drugs against therapeutic targets that display altered levels of expression in malignant versus normal cells. Our previous work has shown that the cellular bio-distribution of the conjugate is dependent on a dynamic balance between influx and efflux processes. Here, we set out to investigate whether P-glycoprotein (P-gp) expression may affect DOX-TRF conjugate-induced cellular drug accumulation and cytotoxicity.ResultsAll experiments were carried out on human erythromyeloblastoid cells exhibiting P-gp over-expression (K562/DOX) and its drug sensitive parental line (K562). MTT cytotoxicity, flow cytometry, fluorescence microscopy and RT-PCR assessments revealed that the investigated conjugate (DOX-TRF) possesses a greater cytotoxic potential than free DOX.ConclusionOur data suggest that the newly developed DOX-TRF conjugate is a less P-gp dependent substrate than free DOX and, consequently, may be used in a clinical setting to increase treatment efficacy in resistant human tumors.

MicroRNA-449a reduces cell survival and enhances cisplatin-induced cytotoxicity via downregulation of NOTCH1 in ovarian cancer cells.

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecologic malignancies. Platinum-based chemotherapy is the first-line treatment for the advanced ovarian cancer, but resistance to cisplatin remains a major obstacle to successful treatment. MicroRNAs (miRNAs) are a class of non-coding RNAs that play important roles in disease processes, including the development of drug resistance. In this study, we found miR-449a were significantly downregulated in the cisplatin-resistant ovarian cell lines SKOV3/DDP and A2780/DDP, compared with their sensitive parent line SKOV3 and A2780, respectively. The overexpression of miR-449a increased cisplatin sensitivity of SKOV3/DDP and A2780/DDP cells by inhibiting proliferation and promoting apoptosis. The luciferase assay confirmed that miR-449a functioned through suppressing NOTCH1 directly. Concordantly, BALB/c nude mice that were injected intraperitoneally with SKOV3/DDP cells transfected with miR-449a mimics exhibited enhanced cisplatin sensitivity in vivo. Taken together, these results suggest that the ectopic expression of miR-449a may be a promising therapeutic strategy for the management of cisplatin resistance in ovarian cancer.

Adoptively transferred TCR-engineered cytotoxic human T lymphocytes use TRAIL apoptotic pathway in killing melanomas: Pivotal role of DR5 and regulation of resistance by SAHA (P2124)

Abstract Adoptive transfer of ex vivo engineered autologous lymphocytes encoding high-affinity MART-1/ A*0201-specific TCRα/β chains (F5 CTL), densely infiltrate into metastatic sites, mediating dramatic but partial responses in metastatic melanoma patients. We hypothesized that down-modulation of death receptors and aberrant apoptotic signaling confer resistance to F5 CTLs. To test this, we established a preclinical model of resistance from sensitive parental lines under serial F5 CTL-selective pressure. While surface peptide/MHC complex remains intact (F5 CTLs efficiently recognize and engage melanomas), R lines downregulate surface DR5 expression, exhibit constitutive NF-κB activation and overexpress resistant factors. The HDACi SAHA blocked antiapoptotic pathway, reduced expression of resistance factors, restored DR5 expression, and sensitized R lines to F5 CTL. At concentrations used, SAHA didn’t affect functionality and viability of F5 CTLs. Using blocking Abs, rhTRAIL and murine CTL hybridoma line, we found that TCR-engineered F5 CTLs mainly utilize TRAIL apoptosis pathway. Further, using Drozitumab (αDR5 mAb), pivotal role of DR5 and its regulation by SAHA was confirmed. These studies identify molecular determinants of resistance to TCR engineered CTL and suggest that adjuvant therapy with SAHA in immune-resistant tumors imposes a proapoptotic milieu by regulating apoptotic machinery and inducing death-receptor expression, thus, overcoming melanoma immunotherapy resistance.

MiR-152 and miR-185 co-contribute to ovarian cancer cells cisplatin sensitivity by targeting DNMT1 directly: a novel epigenetic therapy independent of decitabine

Epithelial ovarian cancer (EOC) is a highly lethal gynaecological malignancy. Cisplatin is the basal chemotherapeutic agent used to treat EOC, but resistance to cisplatin leads to chemotherapy failure. MicroRNAs are a novel class of regulators that function by controlling gene expression at the post-transcriptional level. Several recent reports have identified some microRNAs that are related to chemotherapy sensitivity. In this study, we found two microRNAs miR-152 and miR-185 that were significantly downregulated in the cisplatin-resistant ovarian cell lines SKOV3/DDP and A2780/DDP, compared with their sensitive parent line SKOV3 and A2780, respectively. Subsequently, the roles of miR-152 and miR-185 were evaluated in vitro and in vivo. The overexpression of miR-152 or miR-185 increased cisplatin sensitivity of SKOV3/DDP and A2780/DDP cells by inhibiting proliferation and promoting apoptosis, then we further confirmed that these miRNAs functioned through suppressing DNA methyltransferase 1 (DNMT1) directly. Concordantly, CD-1/CD-1 nude mice that were injected intraperitoneally with SKOV3/DDP cells transfected with miR-152 mimics exhibited upregulated cisplatin sensitivity in vivo. Interestingly, we found that there were no significant changes in the expression of these two microRNAs after treatment with decitabine (DAC), a traditional epigenetic therapeutic agent, suggesting these miRNAs represented two new regulators independent of DAC. Finally, the survival assay in A549 and HepG2 cells revealed that the two microRNAs involved in cisplatin sensitivity were related to cell types. Our results indicated that miR-152 and miR-185 were involved in ovarian cancer cisplatin resistance in vitro and in vivo by targeting DNMT1 directly. These molecules may serve as potential epigenetic therapeutic targets in other cancers.

Proteasome Inhibition Blocks NF-κB and ERK1/2 Pathways, Restores Antigen Expression, and Sensitizes Resistant Human Melanoma to TCR-Engineered CTLs

Adoptive cell transfer (ACT) of ex vivo engineered autologous lymphocytes encoding high-affinity MART-1/HLA-A*0201-specific T-cell receptor (TCR)α/β chains (F5 CTL), densely infiltrate into sites of metastatic disease, mediating dramatic but partial clinical responses in patients with melanoma. We hypothesized that MART-1 downmodulation in addition to aberrant apoptotic/survival signaling could confer resistance to death signals delivered by transgenic CTLs. To explore this hypothesis, we established an in vitro model of resistant (R) lines from MART-1(+)/HLA-A*0201(+) F5 CTL-sensitive parental (P) lines under serial F5 CTL-selective pressure. We have recently reported that several melanoma R lines, while retaining MART-1 expression, exhibited constitutive NF-κB activation and overexpression of NF-κB-dependent resistance factors. Another established melanoma cell line M244, otherwise sensitive to F5 CTL, yielded R lines after serial F5 CTL-selective pressure, which had both reduced MART-1 expression levels, thus, could not be recognized, and were resistant to CTL-delivered apoptotic death signals. The proteasome inhibitor bortezomib blocked NF-κB activity, decreased phospho-ERK1/2, increased phospho-c-jun-NH(2)-kinase (p-JNK) levels, reduced expression of resistance factors, restored MART-1 expression to sufficient levels, which in combination allowed M244R lines be sensitized to F5 CTL killing. These findings suggest that proteasome inhibition in immune resistant tumors can restore proapoptotic signaling and improve tumor antigen expression.

Abstract 335: Human neuroblastoma cells undergo TGF-beta mediated mesenchymal change in the transition to drug resistance

Abstract Background: Hypoxia inducible factor 1-alpha (HIF1-alpha) is overexpressed in doxorubicin-resistant neuroblastoma cell lines relative to drug sensitive parental cells lines, and has been implicated in inducing epithelial to mesenchymal transition (EMT). We hypothesized that the transition of human neuroblastoma cells from a drug-sensitive to drug-resistant phenotype involves mesenchymal change. Methods: A doxorubicin resistant (DoxR) human neuroblastoma cell line was generated by incubating parental wild type (WT) SK-N-Be(2)C cells in stepwise concentrations of doxorubicin. Cells were deemed resistant after surviving in a concentration of drug approximately 2 Log above the wild type IC50, confirmed by MTT colorimetric survival assay. Cell migration and capacity for invasion were assayed using the scratch test and Matrigel invasion culture system. EMT pathway related genes differentially expressed in the DoxR cells relative to the parental (WT) lines were analyzed using the Ilumina Human HT-12 v4 Expression Beadchip. Genes of interest with a fold change in expression >1.5 and an adjusted p < 0.1 are reported. Quantitative RT-PCR and western blot analysis were used to confirm the results. Results: Western blot confirmed that HIF1-alpha was up-regulated in BE(2)C/DoxR cells relative to WT. DoxR cells also demonstrated increased migration and invasion typical of mesenchymal cells. Up-regulation of TGF-beta dependent induction pathways of EMT via RhoA, PI3K, and ILK and via SMADs was seen on microarray pathway analysis in BE(2)C DoxR cells when compared to WT cells. Genes involved in these EMT pathways that were up-regulated in DoxR cells included TGFBRII, the gene encoding TGF beta-receptor II, TGFB3, the gene for TGF beta 3, as well as other genes implicated in TGF-beta signaling, including PAK1, LEF1, SMAD3, ZEB2, and NET1. EMT markers including vimentin (VIM), and slug (SNAI2) were also up-regulated. Interestingly, CDH2, the gene for N-cadherin, and TWIST1 were down regulated in DoxR cells. CDH1, the gene for E-cadherin, and SNAI1, the gene for Snail-1, were not differentially expressed. Conclusions: As SK-BE(2)C human neuroblastoma cell lines acquire drug-resistance, they undergo mesenchymal change via TGF-beta mediated pathways, displaying increased invasion and migration. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 335. doi:1538-7445.AM2012-335

Abstract 2684: Immunosensitization of apoptosis-resistant MART-1 negative human melanomas by bortezomib

Abstract Adoptive cell transfer (ACT) of ex-vivo engineered autologous lymphocytes encoding high-affinity MART-1+/ HLA A*0210+-specific T-cell receptor α/β (TCRα/β) (F5 CTL) mediates dramatic, but partial, clinical responses in lymphodepleted metastatic melanoma patients. Various mechanisms have been postulated for the limited clinical responses. Selective outgrowth of antigen (MART-1)-loss variants is one potential mechanism of immune-resistance. Our first hypothesis is that development of MART-1-loss variants is due to MART-1 down-modulation upon encountering F5 CTLs. We also hypothesized aberrant apoptotic signaling may contribute to immune-resistance. To test these hypotheses, we established an in vitro model of resistant (R) lines from sensitive parental (P) lines under F5 CTL-selective pressure. Unlike P lines, F5 CTLs failed to recognize and kill R lines. Moreover, R lines exhibited hyper-activation of NF-κB anti-apoptotic signaling pathway and over-expression of NF-κB-dependent resistant-factors. Specific pharmacological inhibition of NF-κB and silencing of resistant-factors (siRNA) were required, but insufficient, to restore sensitivity of R lines. MART-1 peptide pulsing restored recognition (cytokine release) but not killing of R lines by F5 CTLs. However, bortezomib blocked NF-κB activity, reduced expression of resistant-factors, restored MART-1 expression, and immuno-sensitized R lines. Moreover, MART-1 specific CTLs from metastatic melanoma patients were unable to kill the R lines, whereas bortezomib sensitized the R lines to MART-specific CD8 cells. These novel results suggest that bortezomib interferes with both deregulated signaling pathway and restores recognition of poorly-immunogenic resistant-variants by melanoma-reactive CTLs, thus, imposes a pro-apoptotic/MART-1+ phenotype to R cells and reverses their acquired-resistance. Results also imply that immune-resistance is multi-faceted; development of MHC-/Ag-loss variants and perturbed apoptotic signaling pathways are both important contributing factors. Combining targeted therapy with F5 CTL overrides resistance, which may improve clinical responses. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2684. doi:10.1158/1538-7445.AM2011-2684

Abstract 726: Erlotinib overcomes acquired resistance to cetuximab

Abstract The epidermal growth factor receptor (EGFR) is a ubiquitously expressed receptor tyrosine kinase (RTK) and is recognized as a key mediator of proliferation and progression in many human epithelial tumors. Following more than 20 years of preclinical development, five EGFR inhibitors, two monoclonal antibodies and three small molecule tyrosine kinase inhibitors (TKIs), have gained FDA approval in oncology (panitumumab, cetuximab, erlotinib, gefitinib and lapatinib). Both strategies of EGFR inhibition have demonstrated clinical successes. However, many tumors do not show response to EGFR inhibition and some of the responders eventually manifest resistance to the treatment. The underlying mechanisms of intrinsic and acquired resistance to EGFR inhibitors remain an intense area of scientific and clinical investigation. To explore potential molecular mechanisms of acquired resistance to cetuximab we established a series of cetuximab-resistant clones by chronically exposing the NCI-H226 NSCLC cell line to cetuximab. Cetuximab-resistant clones exhibited a dramatic increase in the steady-state expression of EGFR, due to alterations in trafficking and endocytosis as compared to parental controls. This increase in steady-state expression of the EGFR led to constitutive activation of HER2 and HER3 and downstream signals mediated by MAPK and AKT. Cells with acquired resistance to cetuximab remained dependent on EGFR signaling as shown by RNAi studies. This finding prompted investigation on whether or not cells with acquired resistance to cetuximab would be sensitive to erlotinib, an EGFR directed TKI. In vitro, erlotinib was able to decrease AKT and MAPK activation and subsequent cell proliferation measured by BrdU incorporation. Additionally, erlotinib treatment induced apoptosis in cetuximab resistant cells as measured by Annexin V analysis. To determine if erlotinib could have therapeutic benefit in vivo, we treated cetuximab sensitive parental lines, H226, with cetuximab in mouse xenograft studies. Mice harboring tumors were treated for approximately 70-150 days before resistant tumors manifested. At this time a series of mice with resistant tumors were treated with erlotinib for 15-30 days. Mice treated with erlotinib exhibited either a regression or tumor growth delay as compared to controls maintained on cetuximab. Analysis of the erlotinib treated tumors demonstrated a decrease in cell proliferation as measured by Ki67 and higher rates of apoptosis, as measured by TUNEL assays when compared to tumors maintained on cetuximab treatment. The work presented herein suggest that 1) cells with acquired resistance to cetuximab maintain their dependence on EGFR signaling via the MAPK and AKT pathways and 2) tumors developing resistance to cetuximab can be treated with erlotinib. This work may provide data strengthening the rationale for the use of erlotinib to treat patients with cetuximab resistant tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 726. doi:10.1158/1538-7445.AM2011-726

Molecular Mechanism of MART-1+/A*0201+ Human Melanoma Resistance to Specific CTL-Killing Despite Functional Tumor–CTL Interaction

Durable responses in metastatic melanoma patients remain generally difficult to achieve. Adoptive cell therapy (ACT) with ex vivo engineered lymphocytes expressing high affinity T-cell receptors (TCRα/β) for the melanoma antigen MART-1₂₇₋₃₅/HLA-A*0201 [recognized by F5 cytotoxic T lymphocytes (F5 CTL)] has been found to benefit certain patients. However, many other patients are inherently unresponsive and/or relapse for unknown reasons. To analyze the basis for the acquired resistance and strategies to reverse it, we established F5 CTL-resistant (R) human melanoma clones from relatively sensitive parental lines under selective F5 CTL pressure. Surface MART-1₂₇₋₃₅/HLA-A*0201 in these clones was unaltered and F5 CTLs recognized and interacted with them similar to the parental lines. Nevertheless, the R clones were resistant to F5 CTL killing, exhibited hyperactivation of the NF-κB survival pathway, and overexpression of the antiapoptotic genes B cell lymphoma protein 2 (Bcl-2), Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene; Bcl-(xL)), and myeloid cell differentiation 1 (Mcl-1). Sensitivity to F5 CTL-killing could be increased by pharmacological inhibition of the NF-κB pathway, Bcl-2 family members, or the proteasome, the latter of which reduced NF-κB activity and diminished antiapoptotic gene expression. Specific gene-silencing (by siRNA) confirmed the protective role of antiapoptotic factors by reversing R clone resistance. Together, our findings suggest that long-term immunotherapy may impose a selection for the development of resistant cells that are unresponsive to highly avid and specific melanoma-reactive CTLs, despite maintaining expression of functional peptide:MHC complexes, due to activation of antiapoptotic signaling pathways. Though unresponsive to CTL, our results argue that resistant cells can be resensitized to immunotherapy with coadministration of targeted inhibitors to antiapoptotic survival pathways.

The Anti-Malarial Mefloquine Demonstrates Preclinical Activity In Leukemia and Myeloma, and Is Dependent Upon Toll-Like Receptor Signaling for Its Cytotoxicity

AbstractAbstract 290Known drugs with previously unrecognized anti-cancer activity can be rapidly repurposed for this new indication, given their prior safety and toxicity testing. To identify such compounds, we compiled and screened an in-house library of on-patent and off-patent drugs and screened them to identify agents cytotoxic to hematologic malignancies. From this screen, we identified mefloquine, a quinoline licensed for malaria treatment and prophylaxis. In secondary assays, leukemia and myeloma cell lines were treated with mefloquine for 72 hours and cell viability measured by MTS. Mefloquine decreased the viability of 10/10 human and murine leukemia (LD50 <8.0 μM) and 9/9 human myeloma (LD50 <5.0 μM) cell lines; cell death was confirmed by Annexin V staining. Mefloquine also reduced the viability of 6/6 primary AML samples with LD50 < 5 μ M. These concentrations of mefloquine appear pharmacologically achievable based on prior studies conducted in the context of malaria treatment. In contrast to the effects on malignant cells, mefloquine was significantly less cytotoxic to normal hematopoietic cells (LD50 31.83 ± 5.38 μM) and murine monocyte-derived dendritic cells (LD50 17.56 ± 2.69 μM), Given its in vitro activity, we evaluated the effects of oral mefloquine in mouse xenograft models of leukemia and myeloma. Sublethally irradiated SCID mice were injected subcutaneously with OCI-AML2 or K562 human leukemia cells, MDAY-D2 murine leukemia cells, or LP1 human myeloma cells, and treated with 50 mg/kg mefloquine, or vehicle alone, by gavage. Oral mefloquine delayed tumor growth by up to 60% in all 4 mouse models without toxicity at doses that appear pharmacologically relevant to humans based on scaling for body surface area. Mefloquine's mechanism of action as an anti-malarial agent is unknown. Therefore, to determine the mechanism by which mefloquine induced cell death in malignant cells, we performed gene expression oligonucleotide array analysis of mefloquine-treated OCI-AML2 cells. At times preceding cell death, mefloquine altered the expression of genes associated with Toll-like receptor (TLR) signaling. For example, we detected 4.5-fold up-regulation of STAT1 and >10-fold up-regulation of its downstream targets, including OAS1, IFIT3 and TRIM22, by 24 hr after treatment. Upregulation of additional TLR targets IRF1, IRF7 and IL-8 was also noted by 8 hours after treatment. Mefloquine also induced early activation of NF-κB with a 2.5± 0.2-fold increase noted after 1 hr, using an ELISA-based DNA binding assay. In contrast to TLR activation in malignant cells, changes in TLR targets were not detected in mefloquine-resistant normal dendritic cells, suggesting that mefloquine's effects on TLR signaling were specific to malignant cells. We next investigated whether TLR activation was functionally important for mefloquine's cytotoxicity in malignant cells. STAT1 activity was required for mefloquine-mediated cell death, as U4A bladder sarcoma cells lacking JAK1 were resistant to mefloquine (LD50 14.6± 4.9 μM), compared to the mefloquine sensitive parental line (LD50 2.3± 0.4 μM). TLR signaling requires the immediate downstream adapter proteins MyD88 and TRIF1. To assess the functional importance of TLR activation for mefloquine induced cell death, we knocked down MyD88 and TRIF1 with siRNA. Double knockdown of MyD88 and TRIF1 completely abrogated mefloquine-induced cell death in K562 leukemia cells at concentrations where control cells exhibited up to 80% loss of viability. TLR signaling and up-regulation of STAT1 can increase reactive oxygen species (ROS) generation. Therefore, we measured ROS generation in leukemia cells after mefloquine treatment. Mefloquine increased ROS production in leukemia cells in a dose-dependent manner within 24 hr. Co-treatment with the ROS scavenger N-Acetyl-L-Cysteine abrogated mefloquine-induced ROS production and cell death. Mefloquine-induced ROS production was also abrogated in MyD88 and TRIF1 double knockdown cells. Our data suggest that the known anti-malarial mefloquine displays preclinical activity in leukemia and myeloma through a mechanism related to TLR activation. Thus, these results highlight TLR activation as a novel therapeutic strategy for the treatment of leukemia and myeloma. Moreover, given its prior toxicology and pharmacology testing, mefloquine could be rapidly advanced into clinical trial for patients with leukemia and myeloma. Disclosures:No relevant conflicts of interest to declare.