LINC00883 Promotes Drug Resistance of Glioma Through a microRNA-136/NEK1-Dependent Mechanism

ObjectiveAccumulating evidence has highlighted the roles of long noncoding RNAs (lncRNAs) as competing endogenous RNAs (ceRNAs) of microRNAs (miRNAs) through their binding sites in the progression of glioma. Hereby, we aim to explore the role of LINC00883 as a regulator of miR-136 and its target, NIMA-related kinase 1 (NEK1), thus, its involvement in the drug resistance of glioma cells.Methods and ResultsMechanistic investigations by dual-luciferase reporter, RNA pull-down, and RNA-binding protein immunoprecipitation (RIP) assays indicated that LINC00883 bound to miR-136, thereby blocking miR-136-induced downregulation of NEK1. Through gain-of-function experiments in U251 cells that presented a high drug resistance, we found that ectopic expression of LINC00883 resulted in increased MRP (encoding multidrug resistance-associated protein), limited cell apoptosis, and increased proliferation. Expectedly, depleting LINC00883 yielded tumor-suppressive and anti-chemoresistance effects on U251 cells by increasing miR-136 and inhibiting NEK1. Next, drug-resistant glioma cell line SOWZ1, drug-sensitive glioma cell line SOWZ2, and drug-resistant glioma cell line SOWZ2-BCNU (SOWZ2 cultured in BCNU) were applied to validate the roles of LINC00883 in the regulation of multidrug resistance. LINC00883 knockdown suppressed the viability of SWOZ1, SWOZ2, and SWOZ2-BCNU cells.ConclusionIn conclusion, LINC00883 knockdown reduces drug resistance in glioma. Hence, our study provides a future strategy to prevent drug resistance-induced therapeutic failure in glioma.

Albumin–Methotrexate Prodrug Analogues That Undergo Intracellular Reactivation Following Entrance into Cancerous Glioma Cells

A family of monomodified bovine serum albumin (BSA) linked to methotrexate (MTX) through a variety of spacers was prepared. All analogues were found to be prodrugs having low MTX-inhibitory potencies toward dihydrofolate reductase in a cell-free system. The optimal conjugates regenerated their antiproliferative efficacies following entrance into cancerous glioma cell lines and were significantly superior to MTX in an insensitive glioma cell line. A BSA–MTX conjugate linked through a simple ethylene chain spacer, containing a single peptide bond located 8.7 Å distal to the protein back bone, and apart from the covalently linked MTX by about 12 Å, was most effective. The inclusion of an additional disulfide bond in the spacer neither enhanced nor reduced the killing potency of this analogue. Disrupting the native structure of the carrier protein in the conjugates significantly reduced their antiproliferative activity. In conclusion, we have engineered BSA–MTX prodrug analogues which undergo intracellular reactivation and facilitate antiproliferative activities following their entrance into glioma cells.

Microglial-stimulation of glioma invasion involves the EGFR ligand amphiregulin

High grade glioma is one of the deadliest human cancers with a median survival rate of only one year following diagnosis. The highly motile and invasive nature of high grade glioma makes it difficult to completely remove surgically. Therefore, increasing our knowledge of the mechanisms glioma cells use to invade normal brain is of critical importance in designing novel therapies. It was previously shown by our laboratory that tumor-associated microglia (TAMs) stimulate glioma cell invasion and this process is dependent on CSF-1R signaling. In this study, we seek to identify pro-invasive factors that are upregulated in microglia in a CSF-1R-dependent manner. We assayed cDNA and protein from microglia treated with conditioned media from the murine glioma cell line GL261, and discovered that several EGFR ligands including amphiregulin (AREG) are strongly upregulated. This upregulation is blocked by addition of a pharmacological CSF-1R inhibitor. Using RNA interference, we show that AREG-depleted microglia are less effective at promoting invasion of GL261 cells into Matrigel-coated invasion chambers. In addition, an AREG blocking antibody strongly attenuates the ability of THP-1 macrophages to activate human glioma cell line U87 invasion. Furthermore, we have identified a signaling pathway which involves CSF-1 signaling through ERK to upregulate AREG expression in microglia. Interfering with ERK using pharmacological inhibitors prevents AREG upregulation in microglia and microglia-stimulated GL261 invasion. These data highlight AREG as a key factor in produced by tumor associated microglia in promoting glioma invasion.

Temozolomide sensitivity of malignant glioma cell lines – a systematic review assessing consistencies between in vitro studies

Background Malignant glioma cell line models are integral to pre-clinical testing of novel potential therapies. Accurate prediction of likely efficacy in the clinic requires that these models are reliable and consistent. We assessed this by examining the reporting of experimental conditions and sensitivity to temozolomide in glioma cells lines. Methods We searched Medline and Embase (Jan 1994-Jan 2021) for studies evaluating the effect of temozolomide monotherapy on cell viability of at least one malignant glioma cell line. Key data items included type of cell lines, temozolomide exposure duration in hours (hr), and cell viability measure (IC50). Results We included 212 studies from 2789 non-duplicate records that reported 248 distinct cell lines. The commonest cell line was U87 (60.4%). Only 10.4% studies used a patient-derived cell line. The proportion of studies not reporting each experimental condition ranged from 8.0–27.4%, including base medium (8.0%), serum supplementation (9.9%) and number of replicates (27.4%). In studies reporting IC50, the median value for U87 at 24 h, 48 h and 72 h was 123.9 μM (IQR 75.3–277.7 μM), 223.1 μM (IQR 92.0–590.1 μM) and 230.0 μM (IQR 34.1–650.0 μM), respectively. The median IC50 at 72 h for patient-derived cell lines was 220 μM (IQR 81.1–800.0 μM). Conclusion Temozolomide sensitivity reported in comparable studies was not consistent between or within malignant glioma cell lines. Drug discovery science performed on these models cannot reliably inform clinical translation. A consensus model of reporting can maximise reproducibility and consistency among in vitro studies.

IMMU-31. TUMOR-SPECIFIC ALTERNATIVE SPLICING GENERATES SPATIALLY-CONSERVED HLA-BINDING NEOANTIGEN TARGETS DETECTED THROUGH INTEGRATIVE TRANSCRIPTOMIC AND PROTEOMIC ANALYSES

BACKGROUND While immunotherapy is profoundly efficacious in certain cancers, its success is limited in cancers with lower mutational burden, such as gliomas. Therefore, investigating neoantigens beyond those from somatic mutations can expand the repertoire of immunotherapy targets. Recent studies detected alternative-splicing (AS) events in various cancer types that could potentially translate into tumor-specific proteins. Our study investigates AS within glioma to identify novel MHC-I-presented neoantigen targets through an integrative transcriptomic and proteomic computational pipeline, complemented by an extensive spatiotemporal analysis of the AS candidates. METHODS Bulk RNA-seq of high tumor purity TCGA-GBM/LGG (n=429) were analyzed through a novel systematic pipeline, and tumor-specific splicing junctions (neojunctions) were identified in silico by cross-referencing with bulk RNA-seq of GTEx normal tissue (n=9,166). Two HLA-binding prediction algorithms were subsequently incorporated to predict peptide sequences with high likelihood for HLA-presentation. Investigation of the tumor-wide clonality and temporal stability of the candidates was performed on extensive RNA-seq data from our spatially mapped intratumoral samples and longitudinally collected tumor tissue RNA-seq. Proteomic validation was conducted through mass-spec analysis of the Clinical Proteomic Tumor Analysis Consortium (CPTAC)-GBM repository (n=99). RESULTS Our analysis of TCGA-GBM/LGG bulk RNA-seq identified 249 putative neojunctions that translate into 222 cancer-specific peptide sequences which confer 21,489 tumor-specific n-mers (8-11 amino acids in length). Both prediction algorithms concurrently identified 271 n-mers likely to bind and be presented by HLA*A0101, HLA*A0201, HLA*A0301, HLA*A1101, or HLA*A2402. We confirmed the expression of 15 out of 58 HLA*A0201-binding candidates in HLA*A0201+ patient-derived glioma cell line RNA-seq with a subset of candidates conserved spatially. Analysis of CPTAC-GBM mass-spec data detected 23 tumor-specific peptides with 5 containing detected n-mers highly predicted to be HLA-presented. CONCLUSION Tumor-specific neojunctions identified in our unique integrative pipeline present novel candidate immunotherapy targets for gliomas and offer a new avenue in neoantigen discovery across cancer types.

KS01.3.A Tumoral MHC class II expression in gliomas drives T cell exhaustion

BACKGROUND Neoepitopes are presented on major histocompatibility class II (MHCII) molecules. In glioma, for instance, the recurrent driver mutation IDH1R132H was shown to bear an MHCII-restricted epitope in preclinical and clinical vaccine studies. The general relevance of MHCII expression in glioma for antitumor immunity, however, remains unknown. Here we evaluate stromal and tumoral MHCII expression, functionality, and its association with survival in gliomas. MATERIAL AND METHODS Immunostaining of human glioma tissues was used to identify tumoral, endothelial, and microglial MHCII expression and to enumerate T cell infiltrates. To gain insights into tumoral MHCII expression, bulk transcriptomic data from TCGA and single-cell transcriptomic data from publicly available datasets were analyzed. MHC ligandome analyses of an MHCII+ glioma cell line and human glioma tissues were used to determine the functionality of MHCII in vitro and ex vivo. Functional in vitro co-culture assays with an HLA-DR-matched tetanus toxoid (TT) epitope-overexpressing glioma cell line and in vitro-expanded TT-reactive T cells from healthy donors were used to examine direct target recognition by T helper cells. CRISPR-Cas9-mediated knockout of MHCII in preclinical hypermutant glioblastoma cell line GL261 was employed to further validate the consequences of tumoral MHCII expression and to probe potential clinical intervention with existing therapies. RESULTS MHCII is expressed in the majority of gliomas and associated with increased infiltration of T cells. In 10% of the analyzed glioma tissues and a subset of single cells, tumoral MHCII expression is detected. Clinical and transcriptomic data reveal that tumoral MHCII is associated with poor prognosis, cytokine responses, immune inhibition and T cell differentiation. Ligandome analyses evidence presentation of peptides by MHCII molecules on glioma cells. In in vitro assays, TT-reactive T helper cells specifically produce IFNg when co-cultured with MHCII+ glioma cells upon the presence of co-stimulation. In agreement with the clinical data, preclinical murine models demonstrate that tumoral MHCII expression leads to reduced survival. Co-culture assay shows that tumoral MHCII results in upregulation of PD-1 on T helper cells antigen-specifically. Concordantly, immune checkpoint blockade (ICB) therapy slows the disease progression of mice carrying MHCII+ tumors. CONCLUSION MHCII is expressed in gliomas by a subset of tumor cells. Although tumoral MHCII is functional, it is associated with poor survival in both clinical data and preclinical models. T cell exhaustion induced by tumoral MHCII expression can, in part, be overcome by ICB in vivo. Further experiments are required to decipher tumor cell intrinsic and microenvironmental consequences of tumoral MHCII expression.

Temozolomide sensitivity of malignant glioma cell lines: a systematic review assessing consistencies between in vitro studies

Background: Malignant glioma cell line models are integral to pre-clinical testing of novel potential therapies. Accurate prediction of likely efficacy in the clinic requires that these models are reliable and consistent. We assessed this by examining the reporting of experimental conditions and sensitivity to temozolomide in glioma cells lines. Methods: We searched Medline and Embase (Jan 1994-Jan 2021) for studies that evaluated the effect of temozolomide monotherapy on cell viability of at least one malignant glioma cell line. Studies using a drug-resistant cell line or a modified preparation of temozolomide were excluded. Key data items included type of cell lines, temozolomide exposure duration, and cell viability measure (IC50). Results: We included 212 eligible studies from 2,789 non-duplicate records that reported 248 distinct cell lines. The commonest cell line was U87 (60.4%). Only 10.4% studies used a patient-derived cell line. The proportion of studies not reporting each experimental condition ranged from 8.0-27.4%, including base medium (8.0%), serum supplementation (9.9%) and number of replicates (27.4%). In studies reporting IC50 the median value for U87 cell line at 24 hours, 48 hours and 72 hours was 123.9μM (IQR 75.3-277.7μM), 223.1μM (IQR 92.0-590.1μM) and 230.0μM (IQR 34.1-650.0μM), respectively (Figure 2A). The median IC50 at 72 hours for patient-derived cell lines was 220μM (IQR 81.1-800.0μM). Conclusions: Temozolomide sensitivity reported in comparable studies was not consistent between and within individual malignant glioma cell lines. Drug discovery science performed on these models cannot reliably inform clinical translation. A consensus model of reporting can maximise reproducibility and consistency among in vitro studies.