Region-specific DNA hydroxymethylation along the malignant progression of IDH-mutant gliomas

The majority of low-grade isocitrate dehydrogenase-mutant (IDHmt) gliomas undergo malignant progression (MP), but their underlying mechanism remains unclear. IDHmt gliomas exhibit global DNA methylation, and our previous report suggested that MP could be partly attributed to passive demethylation caused by accelerated cell cycles. However, during MP, there is also active demethylation mediated by ten-eleven translocation, such as DNA hydroxymethylation. Hydroxymethylation is reported to potentially contribute to gene expression regulation, but its role in MP remains under investigation. Therefore, we conducted a comprehensive analysis of hydroxymethylation during MP of IDHmt astrocytoma. Five primary/malignantly progressed IDHmt astrocytoma pairs were analyzed with oxidative bisulfite and the Infinium EPIC methylation array, detecting 5-hydroxymethyl cytosine at over 850,000 locations for region-specific hydroxymethylation assessment. Notably, we observed significant sharing of hydroxymethylated genomic regions during MP across the samples. Hydroxymethylated CpGs were enriched in open sea and intergenic regions (p < 0.001), and genes undergoing hydroxymethylation were significantly associated with cancer-related signaling pathways. RNA sequencing data integration identified 91 genes with significant positive/negative hydroxymethylation-expression correlations. Functional analysis suggested that positively correlated genes are involved in cell-cycle promotion, while negatively correlated ones are associated with antineoplastic functions. Analyses of The Cancer Genome Atlas clinical data on glioma were in line with these findings. Motif-enrichment analysis suggested the potential involvement of the transcription factor KLF4 in hydroxymethylation-based gene regulation. Our findings shed light on the significance of region-specific DNA hydroxymethylation in glioma MP and suggest its potential role in cancer-related gene expression and IDHmt glioma malignancy.

Transcriptomic and epigenetic dissection of spinal ependymoma (SP-EPN) identifies clinically relevant subtypes enriched for tumors with and without NF2 mutation

Ependymomas encompass multiple clinically relevant tumor types based on localization and molecular profiles. Tumors of the methylation class "spinal ependymoma" (SP-EPN) represent the most common intramedullary neoplasms in children and adults. However, their developmental origin is ill-defined, molecular data are scarce, and the potential heterogeneity within SP-EPN remains unexplored. The only known recurrent genetic events in SP-EPN are loss of chromosome 22q and NF2 mutations, but neither types and frequency of these alterations nor their clinical relevance have been described in a large, epigenetically defined series. Transcriptomic (n = 72), epigenetic (n = 225), genetic (n = 134), and clinical data (n = 112) were integrated for a detailed molecular overview on SP-EPN. Additionally, we mapped SP-EPN transcriptomes to developmental atlases of the developing and adult spinal cord to uncover potential developmental origins of these tumors. The integration of transcriptomic ependymoma data with single-cell atlases of the spinal cord revealed that SP-EPN display the highest similarities to mature adult ependymal cells. Unsupervised hierarchical clustering of transcriptomic data together with integrated analysis of methylation profiles identified two molecular SP-EPN subtypes. Subtype A tumors primarily carried previously known germline or sporadic NF2 mutations together with 22q loss (bi-allelic NF2 loss), resulting in decreased NF2 expression. Furthermore, they more often presented as multilocular disease and demonstrated a significantly reduced progression-free survival as compared to SP-EP subtype B. In contrast, subtype B predominantly contained samples without NF2 mutation detected in sequencing together with 22q loss (monoallelic NF2 loss). These tumors showed regular NF2 expression but more extensive global copy number alterations. Based on integrated molecular profiling of a large multi-center cohort, we identified two distinct SP-EPN subtypes with important implications for genetic counseling, patient surveillance, and drug development priorities.

Glioblastoma with high O6-methyl-guanine DNA methyltransferase expression are more immunologically active than tumors with low MGMT expression

Background

Glioblastoma (GBM) is a highly lethal brain tumor. The effectiveness of temozolomide (TMZ) treatment in GBM is linked to the methylation status of O6-methyl-guanine DNA methyltransferase (MGMT) promoter. Patients with unmethylated MGMT promoter have limited treatment options available. Consequently, there is a pressing need for alternative therapeutic strategies for such patients.

Methods

Data, including transcriptomic and clinical information, as well as information on MGMT promoter methylation status in primary GBM, were obtained from The Cancer Genome Atlas (TCGA) (n=121) and Chinese Glioma Genome Atlas (CGGA) (n=83) datasets. Samples were categorized into high and low MGMT expression groups, MGMT-high (MGMT-H) and MGMT-low (MGMT-L) tumors. A comprehensive transcriptome analysis was conducted to explore the tumor-immune microenvironment. Furthermore, we integrated transcriptome data from 13 GBM patients operated at our institution with findings from tumor-infiltrating lymphocyte (TIL) cultures, specifically investigating their response to autologous tumors.

Results

Gene signatures associated with various immune cells, including CD8 T cells, helper T cells, B cells, and macrophages, were noted in MGMT-H tumors. Pathway analysis confirmed the enrichment of immune cell-related pathways. Additionally, biological processes involved in the activation of monocytes and lymphocytes were observed in MGMT-H tumors. Furthermore, TIL culture experiments showed a greater presence of tumor-reactive T cells in MGMT-H tumors compared to MGMT-L tumors. These findings suggest that MGMT-H tumors has a potential for enhanced immune response against tumors mediated by CD8 T cells.

Conclusion

Our study provides novel insights into the immune cell composition of MGMT-H tumors, which is characterized by the infiltration of type 1 helper T cells and activated B cells, and also the presence of tumor-reactive T cells evidenced by TIL culture. These findings contribute to a better understanding of the immune response in MGMT-H tumors, emphasizing their potential for immunotherapy. Further studies are warranted to investigate on the mechanisms of MGMT expression and antitumor immunity.

Principal component analysis of early immune cell dynamics during pembrolizumab treatment of advanced urothelial carcinoma

Immune checkpoint inhibitors have been approved as second-line therapy for patients with advanced urothelial carcinoma (UC). However, which patients will obtain clinical benefit remains to be determined. To identify predictive biomarkers for the pembrolizumab (PEM) response early during treatment, the present study investigated 31 patients with chemotherapy-resistant recurrent or metastatic UC who received 200 mg PEM intravenously every 3 weeks. Blood was taken just before the first dose and again before the second dose, and the peripheral blood mononuclear cells of all 31 pairs of blood samples were immune phenotyped by flow cytometry. Data were assessed by principal component analysis (PCA), correlation analysis and Cox proportional hazards modeling in order to comprehensively determine the effects of PEM on peripheral mononuclear immune cells. Absolute counts of CD45RA+CD27-CCR7- terminally differentiated CD8+ T cells and KLRG1+CD57+ senescent CD8+ T cells were significantly increased after PEM administration (P=0.042 and P=0.043, respectively). Senescent and exhausted CD4⁺ and CD8⁺ T cell dynamics were strongly associated with each other. By contrast, counts of monocytic myeloid-derived suppressor cells (mMDSCs) were not associated with other immune cell phenotypes. The results of PCA and non-hierarchical clustering of patients suggested that excessive T cell senescence and differentiation early during treatment were not necessarily associated with a survival benefit. However, decreased mMDSC counts after PEM were associated with improved overall survival. In conclusion, early on-treatment peripheral T cell status was associated with response to PEM; however, it was not associated with clinical benefit. By contrast, decreased peripheral mMDSC counts did predict improved overall survival.

Selection of RNA-based evaluation methods for tumor microenvironment by comparing with histochemical and flow cytometric analyses in gastric cancer

Understanding the tumor microenvironment (TME) and anti-tumor immune responses in gastric cancer are required for precision immune-oncology. Taking advantage of next-generation sequencing technology, the feasibility and reliability of transcriptome-based TME analysis were investigated. TME of 30 surgically resected gastric cancer tissues was analyzed by RNA-Seq, immunohistochemistry (IHC) and flow cytometry (FCM). RNA-Seq of bulk gastric cancer tissues was computationally analyzed to evaluate TME. Computationally analyzed immune cell composition was validated by comparison with cell densities established by IHC and FCM from the same tumor tissue. Immune cell infiltration and cellular function were also validated with IHC and FCM. Cell proliferation and cell death in the tumor as assessed by RNA-Seq and IHC were compared. Computational tools and gene set analysis for quantifying CD8⁺ T cells, regulatory T cells and B cells, T cell infiltration and functional status, and cell proliferation and cell death status yielded an excellent correlation with IHC and FCM data. Using these validated transcriptome-based analyses, the immunological status of gastric cancer could be classified into immune-rich and immune-poor subtypes. Transcriptome-based TME analysis is feasible and is valuable for further understanding the immunological status of gastric cancer.

Genetic Characteristics of Mismatch Repair-deficient Glioblastoma

Mismatch repair (MMR) gene deficiency is rarely observed in gliomas, a constitutional defect is associated with tumorigenesis in Lynch syndrome, and an acquired defect is associated with hypermutation after temozolomide treatment. However, the meaning of MMR gene deficiency in gliomas is unclear. Two cases of MMR-deficient glioblastomas are reported, and mutational status of oncogenes was compared between primary and recurrent tumor samples in a glioblastoma patient with Lynch syndrome. Additionally, the characteristics of MMR-deficient glioblastomas were analyzed using public glioma datasets to determine the meaning of MMR deficiency in gliomas. Case 1 was a glioblastoma patient with Lynch syndrome, and treatment with pembrolizumab for the recurrent tumor was temporarily effective for a short period. Comparison of mutational changes between primary and recurrent tumor samples showed many additional mutated genes associated with multiple signaling pathways in the recurrent tumor. Tumor recurrence and chemoresistance could be associated with intratumoral heterogeneity and accelerated tumor progression due to defects of multiple signaling pathways. Case 2 was a glioblastoma patient with acquired MMR gene deficiency, and she died of rapid progression of bone marrow metastases. This rare clinical course was considered to be associated with gene expression changes and heterogeneity that resulted from MMR gene deficiency. Two cases of MMR gene-deficient glioblastomas were presented, and their genetic characteristics suggested that their clinical courses could be associated with MMR gene deficiency.

IM-2 Possibility of immunotherapy for the glioblastoma patients with O6-methyl-guanine DNA methyltransferase (MGMT) expression or promoter unmethylated

Background: MGMT is a DNA repair protein that removes the cytotoxic O6-methylguanine (O6MG) DNA lesions generated by TMZ; thereby, MGMT expression is mechanistically linked to TMZ resistance. However, thus far, there is no effective treatment for these patients with MGMT promoter unmethylated. Therefore, a new treatment for GBM patients with MGMT expression is urgently needed. To this end, we examined the tumor microenvironment in GBM with or without MGMT expression. Methods: Based on The Cancer Genome Atlas (TCGA) primary GBM cohort, the tumor-infiltrating lymphocytes (TILs) expression level was calculated using the CIBERSORTx algorithms and the single-sample Gene Set Enrichment Analysis (ssGSEA) method. Furthermore, the differential expression gene analysis was conducted and pathway analysis was performed using Ingenuity Pathway Analysis (IPA). The results were validated using the GBM cohort from the Chinese Glioma Genome Atlas (CGGA) database. In addition, TILs were isolated from 13 surgically removed primary GBM tumors in our institution. Their responses to autologous tumors were evaluated by IFNγ ELISA. Results: T cells CD8 score by CIBERSORTx was significantly higher in the MGMT-high tumor. Similarly, ssGSEA scores for activated CD8 T cell, Macrophage, activated B cell, and Type 1 T helper cell were significantly higher in the MGMT-high tumor. Conversely, T cells CD4 naive was significantly higher in the MGMT-low tumor. Consistently, tumor-reactive TILs were detected in the MGMT-high tumor. Pathway analysis showed that Rictor was highly enriched in the MGMT-high tumor and Rictor inhibited lymphocyte activation. Coclusion: In this study, we demonstrated that macrophage was highly activated in the MGMT-high tumors. Thus, CSF-1R inhibitor can be combined with immunotherapy in these MGMT-high tumors to enhance anti-tumor immune responses. In addition, TMZ + mTOR2 inhibitors + PD-1 inhibitors may be effective against the MGMT-L group.

SURG-10. DEVELOPMENT OF NOVEL TOPICAL FLUORESCENT PROBE FOR INTRAOPERATIVE RAPID DETECTION OF GLIOMA

PURPOSE

Fluorescence imaging is an important surgical adjunct in malignant glioma surgery. 5-aminolevulinic acid (5-ALA) has been proven effective for radical tumor resection and extended progression-free survival in a phase III randomized trial and therefore integrated into surgery for malignant glioma. Importantly, however, some limitations still exist in its use, which include false positivity and false negativity as well as inability of re-administration. In this study, we aimed to develop a novel, spray-type fluorescent probe using hydroxymethyl rhodamine green (HMRG) as a fluorescent scaffold.

METHODS

We have previously established a fluorescent probe library comprised of more than 320 kinds of HMRG probes. They have HMRG as a fluorescent scaffold with various types of dipeptides attached to it. Primary probe screening was performed using the homogenized tumor samples from patients with glioblastoma operated at our institution. Secondary screening followed using the selected probes and fresh tumor samples obtained from patients with glioblastoma operated from 2016 until 2018. Diced electrophoresis gel (DEG) assay, two-dimensional gel electrophoresis followed by a multi-well plate-based fluorometric assay, was performed to identify responsible enzymes for the selected probe. Further experiments with inhibitors, real-time PCR, immunohistochemistry, and western blotting were performed for confirmation.

RESULTS

Proline-arginine-HMRG (PR-HMRG) was selected as a candidate probe based upon the above two-step screenings. It achieved 79.4% accuracy in receiver operating characteristic curve analysis. Calpain-1 was found to be responsible to cleave PR-HMRG probe by DEG-proteome analysis. Calpain-1 protein was expressed at significantly higher level in tumors that were fluoresced by PR-HMRG than in those that were not.

CONCLUSIONS

Our innovative screening method was able to find PR-HMRG as a novel fluorescent probe effective for rapid detection of glioblastoma. A preclinical study is planned to assess the efficacy and safety of the selected probe.

EPCO-01. MOLECULAR PROFILING OF SPINAL CORD EPENDYMOMA

BACKGROUND

Ependymomas are currently classified into 9 subgroups by DNA methylation profiles. Although spinal cord ependymoma (SP-EPN) is distinct from other tumors, diversity within SP-EPN is still unclear. Here, we used transcriptomic and epigenomic profiles to investigate the diversity among Japanese SP-EPN cases.

MATERIALS AND METHODS

We analyzed 57 SP-EPN patients (32 males and 25 females, aged from 18 to 78 years, median: 52), including two cases of neurofibromatosis type 2, five cases of grade 3 (WHO grade). We obtained transcriptome (RNA-seq) and DNA methylation (Infinium Methylation EPIC array) data from fresh frozen specimens of SP-EPN resected at the University of Tokyo Hospital and our collaborative groups.

RESULTS

Three cases had a previous intracranial ependymoma operation. Hierarchical clustering of the DNA methylation data showed that these three cases of intracranial origin as a different cluster from spinal origin. The 45 grade 2 spinal ependymoma showed a relatively homogenous methylation pattern. However, the methylation status of HOX gene cluster regions is compatible with the segment of origin, which reflects the cells of origins are derived after the determination of segment identity. RNA sequencing of 57 cases revealed two subgroups within grade 2. Gene ontology analysis of differentially expressed genes suggested the difference in metabolic state such as rRNA translation and mitochondrial respiration between the two expression subgroups.

CONCLUSION

Epigenetic analysis indicated the accurate body segment origin of SP-EPN. We observed that metabolic states could divide grade 2 spinal cord ependymoma into 2 subgroups and will present the relationship to clinicopathological information.

647 Possibility of immunotherapy for the glioblastoma patients with O6-methyl-guanine DNA methyltransferase (MGMT) expression or promoter unmethylated

Background

It has been widely accepted that O6-methyl-guanine DNA methyltransferase (MGMT) promoter methylation in glioblastoma is associated with a benefit from temozolomide (TMZ) treatment. MGMT is a DNA repair protein that removes the cytotoxic O6-methylguanine (O6MG) DNA lesions generated by TMZ; thereby, MGMT expression is mechanistically linked to TMZ resistance. However, thus far, there is no effective treatment for these patients with MGMT promoter unmethylated. Therefore, a new treatment for GBM patients with MGMT expression is urgently needed.1 2 To this end, we examined the tumor microenvironment in GBM with or without MGMT expression.

Methods

Based on The Cancer Genome Atlas (TCGA) primary GBM cohort, the tumor-infiltrating lymphocyte expression level was calculated using the CIBERSORTx algorithms and the single-sample Gene Set Enrichment Analysis (ssGSEA) method. Furthermore, the differential expression gene analysis was conducted and pathway analysis was performed using Ingenuity Pathway Analysis (IPA). The results were validated using the GBM cohort from the Chinese Glioma Genome Atlas (CGGA) database. In addition, tumor-infiltrating lymphocytes (TILs) were isolated from 13 surgically removed primary GBM tumors in our institution. Their responses to autologous tumors were evaluated by IFNγ ELISA.

Results

T cells CD8 score by CIBERSORTx was significantly higher in the MGMT-high tumor. Similarly, ssGSEA scores for activated CD8 T cell, Macrophage, activated B cell, and Type 1 T helper cell were significantly higher in the MGMT-high tumor. Conversely, T cells CD4 naive was significantly higher in the MGMT-low tumor. These results indicate that more immune cell infiltration is associated with MGMT-high tumors. Consistently, tumor-reactive TILs were detected in the MGMT-high tumor. Pathway analysis showed that oxidative phosphorylation (OXPHOS) was highly enriched in the MGMT-high tumor.There were many CD8 T cells and tumor-reactive T cells in the MGMT-high tumors. However, it has been reported that anti-PD-1/PD-L1 monotherapy was not effective in glioblastoma. In this study, we demonstrated that OXPHOS was highly activated in the MGMT-high tumors. Thus, metabolic therapy can be combined with immunotherapy in these MGMT-high tumors to enhance anti-tumor immune responses.

Conclusions

Although MGMT-high tumors are resistant to TMZ, the existence of immune cell infiltration in the tumor microenvironment of MGMT-high tumors suggest the potential of immunotherapy in these patients.

References

Stupp R, Hegi ME, Mason WP, van den Bent MJ, Taphoorn MJB, Janzer RC, Ludwin SK, Allgeier A, Fisher B, Belanger K, Hau P, Brandes AA, Gijtenbeek J, Marosi C, Vecht CJ, Mokhtari K, Wesseling P, Villa S, Eisenhauer E, Gorlia T, Weller M, Lacombe D, Cairncross Jy, Mirimanoff R-O, European Organisation for Research and Treatment of Cancer Brain Tumour and Radiation Oncology Groups; National Cancer Institute of Canada Clinical Trials Group. Lancet Oncol 2009;10(5):459–66.

Wick W, Weller M, van den Bent M, Sanson M, Weiler M, von Deimling A, Plass C, Hegi M, Platten M, Reifenberger G. Nat Rev Neurol 2014;;10(7):372–85.

Ethics Approval

G3545-(26)

Consent

Written informed consent was obtained from the patient for publication of this abstract and any accompanying images. A copy of the written consent is available for review by the Editor of this journal.

A Novel Topical Fluorescent Probe for Detection of Glioblastoma

PURPOSE

Five-aminolevulinic acid (5-ALA) is widely used as an intraoperative fluorescent probe for radical resection of high-grade glioma, and thus aids in extending progression-free survival of patients. However, there exist some cases where 5-ALA fails to fluoresce. In some other cases, it may undergo fluorescence quenching but cannot be orally readministered during surgery. This study aimed to develop a novel hydroxymethyl rhodamine green (HMRG)-based fluorescence labeling system that can be repeatedly administered as a topical spray during surgery for the detection of glioblastoma.

EXPERIMENTAL DESIGN

We performed a three-stage probe screening using tumor lysates and fresh tumor tissues with our probe library consisting of a variety of HMRG probes with different dipeptides. We then performed proteome and transcript expression analyses to detect candidate enzymes responsible for cleaving the probe. Moreover, in vitro and ex vivo studies using U87 glioblastoma cell line were conducted to validate the findings.

RESULTS

The probe screening identified proline-arginine-HMRG (PR-HMRG) as the optimal probe that distinguished tumors from peritumoral tissues. Proteome analysis identified calpain-1 (CAPN1) to be responsible for cleaving the probe. CAPN1 was highly expressed in tumor tissues which reacted to the PR-HMRG probe. Knockdown of this enzyme suppressed fluorescence intensity in U87 glioblastoma cells. In situ assay using a mouse U87 xenograft model demonstrated marked contrast of fluorescence with the probe between the tumor and peritumoral tissues.

CONCLUSIONS

The novel fluorescent probe PR-HMRG is effective in detecting glioblastoma when applied topically. Further investigations are warranted to assess the efficacy and safety of its clinical use.

Utility of monitoring the serum levetiracetam concentration for intraoperative seizure control during awake craniotomy

Awake craniotomy is an established procedure for resecting brain tumors in eloquent lesions, and intraoperative seizure is one of the most important complications. Phenytoin is normally used to control intraoperative seizures. Recently, phenytoin was replaced with levetiracetam at our institution because the latter has fewer side effects. While the phenytoin dose is calibrated in accordance with the serum concentration, there is currently no consensus on a method of monitoring the serum concentration of levetiracetam or the effective concentration range needed to control intraoperative seizures during awake craniotomy. The present study therefore aimed to determine whether monitoring the serum levetiracetam concentration is useful for controlling intraoperative seizures during awake craniotomy. The intraoperative serum concentration of levetiracetam during awake craniotomy was measured in 34 patients and compared with that of phenytoin in 33 patients undergoing the same procedure. The levetiracetam concentration inversely correlated with body surface area (BSA) and estimated glomerular filtration rate (eGFR). Levetiracetam was superior to phenytoin in terms of the correlation between the serum concentration and the dose adjusted for BSA and eGFR (correlation coefficient, 0.49 vs 0.21). Furthermore, the serum levetiracetam concentration in patients with intraoperative seizures was below the 95% confidence interval (CI) of the regression line whereas the serum phenytoin concentration of two patients with seizures was within the 95% CI, indicating that evaluating the serum levetiracetam concentration against the BSA and eGFR-adjusted dosage may be useful in preventing intraoperative seizures during awake craniotomy by allowing prediction of the seizure risk and enabling more accurate dosage calibration.

A novel scoring method based on RNA-Seq immunograms describing individual cancer-immunity interactions

Because of the complexity of cancer‐immune system interactions, combinations of biomarkers will be required for predicting individual patient responses to treatment and for monitoring combination strategies to overcome treatment resistance. To this end, the “immunogram” has been proposed as a comprehensive framework to capture all relevant immunological variables. Here, we developed a method to convert transcriptomic data into immunogram scores (IGS). This immunogram includes 10 molecular profiles, consisting of innate immunity, priming and activation, T cell response, interferon γ (IFNG) response, inhibitory molecules, regulatory T cells, myeloid‐derived suppressor cells (MDSCs), recognition of tumor cells, proliferation, and glycolysis. Using genes related to these 10 parameters, we applied single‐sample gene set enrichment analysis (ssGSEA) to 9417 bulk RNA‐Seq data from 9362 cancer patients with 29 different solid cancers in The Cancer Genome Atlas (TCGA). Enrichment scores were z‐score normalized (Z) for each cancer type or the entire TCGA cohort. The IGS was defined by the formula IGS = 3 + 1.5 × Z so that patients would be well distributed over a range of scores from 1 to 5. The immunograms constructed in this way for all individual patients in the entire TCGA cohort can be accessed at “The RNA‐Seq based Cancer Immunogram Web” (https://yamashige33.shinyapps.io/immunogram/).

RARE-16. A NOVEL RADIOMICS MODEL DIFFERENTIATING CHORDOMA AND CHONDROSARCOMA

BACKGROUND

Chordoma and chondrosarcoma account for the majority of skull base tumors affecting the petroclival region. Chondrosarcoma has better prognosis than chordoma; heavy particle therapy is often indicated for residual/recurrent chordoma. Preoperative, precise diagnosis of the tumor would be desirable, as it can potentially impact on the choice of a surgical approach and the aggressiveness of surgery.

METHODS

We conducted a radiomics study to create a machine learning model distinguishing chondrosarcoma from chordoma. We collected DICOM T2-weighted images and T1-weighted images with gadolinium (GdT1) enhancement in the consective patients of chordoma or chondrosarcoma who underwent surgery at The University of Tokyo Hospital from September of 2012 to January of 2019. We selected patients with uniform MRI images. VOI (volume of interest) was set using Monaco (https://www.elekta.com/software-solutions/treatment-management/external-beam-planning/monaco.html). Not only sematic features but also agnostic features were calculated. The original images and 8 wavelet transformed images were calculated for texture agnostic features such as Gray-Level Co-occurrence Matrix (GLCM). Features were selected by recursive feature elimination (RFE). The final model evaluation was performed by average area under the curve (AUC).

RESULTS

The study population included 17 chordomas and 22 chondrosarcomas in a total of 39 patients. 476 features were obtained per image sequence. The number of features per case was 476 × 2 = 952 The most accurate machine learning model was created using the extracted three features from only T2. The best AUC was 0.77 ± 0.11 in logistic regression (dataset was divided randomly into halves, average value of AUC calculated six times).

CONCLUSIONS

This novel machine learning model can differentiate chordoma and chondrosarcoma reasonably well. A validation study with a larger number of patients is warranted.

DDIS-02. DEVELOPMENT OF NOVEL SPRAY-TYPE FLUORESCENT PROBES FOR GLIOBLASTOMA DETECTION

PURPOSE: ALA is commonly used as an intraoperative tool in malignant glioma surgery, which has been proven effective for radical tumor resection and extended progression-free survival. However, there are some limitations in its use, such as false positivity, false negativity, and inability of re-administration. We aim to develop a novel fluorescent labeling system which can be repeatedly administered by spray during surgery, using hydroxymethyl rhodamine green (HMRG) as fluorescent scaffold originally designed at our university for cancer detection. [Methods]Primary probe screening was performed using the homogenized glioblastoma (GBM) samples with the fluorescent probe library comprised of more than 320 kinds of HMRG fluorescent scaffold combined with various types of dipeptides. Second probe screening was performed using fresh GBM specimens and the selected probes in primary screening. To identify the responsible enzymes, diced electrophoresis gel (DEG) assay was performed. This method utilizes the combination of two dimensional electrophoresis (isoelectric point and molecular weight) and a multiwell-plate-based fluorometric assay to find protein spots with the specified activities. [Results] The prominent probes were selected based upon the above two-step screenings. We identified two enzymes by proteome analysis and experiments using inhibitors, which was further confirmed with real-time PCR and western blotting. [Discussion] This screening methodology is innovative in that it is based on selecting probes from the probe library that respond to clinical samples rather than creating probes from the responsible enzymes. Practical fluorescent probes can be established even for low-grade gliomas, which would be a breakthrough for rapid intraoperative diagnosis in glioma surgery. [Conclusion] HMRG-based aminopeptidase fluorescent probes may be effective for GBM detection.

COMP-02. MINING-GUIDED MACHINE LEARNING ANALYSES SUPPORTS GRASPING THE LATEST TRENDS ON NEURO-ONCOLOGY

The systems that can objectively predict the future trends of a particular research field are always anticipated while conducting medical research. Such systems also provide a considerable aid to researchers while determining and acquiring appropriate research budgets. This study intended to establish a novel and versatile algorithm that can predict the latest trends in neuro-oncology. Seventy-nine neuro-oncological research fields were selected using computational sorting methods, such as text-mining analyses, along with 30 journals that represent the recent trends in the neuro-oncology field. Further, the annual impact (AI) for each year with respect to each journal and field (number of articles published in the journal × the impact factor of the journal) was calculated as a novel concept. Subsequently, the AI index (AII) for the year was defined as the sum of the AIs for the aforementioned 30 journals. With respect to the aforementioned neuro-oncological research fields, the AII trends from 2008 to 2017 were subjected to machine learning predicting analyses. The prediction accuracy of the latest trends in neuro-oncology was validated using actual data obtained from previous studies. In particular, the linear prediction model achieved a relatively good accuracy. The most notable and latest predicted fields in neuro-oncology included some interesting emerging fields, such as microenvironment and anti-mitosis, as well as the already renowned fields, such as immunology and epigenetics. Furthermore, we retrospectively attempted an analysis of the fields different from neuro-oncology. Interestingly, as of 2008, the future emergence of the CRISPR-Cas9 gene editing system has been predicted using this system. Overall, the presented algorithm displays potential to be an effective and versatile tool for the prediction of future trends in a particular medical field.

Continuous intrathecal injection therapy of methotrexate is a therapeutic option in primary CNS lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare subtype of non-Hodgkin's lymphoma, and its prognosis is still very poor despite the conventional therapy of high-dose methotrexate (HD-MTX) followed by whole-brain radiation therapy (WBRT). The purpose of the present study was to evaluate the survival benefit of continuous intrathecal injection therapy of methotrexate (CIT-MTX) combined with the conventional therapy. A total of 26 PCNSL patients treated with CIT-MTX were analyzed. Ten mg of methotrexate were continuously injected into the lateral ventricle via a subcutaneous port over 5 days biweekly for 5 cycles. CIT-MTX was performed with WBRT in addition to HD-MTX in 15 cases, and 11 cases with high risk for HD-MTX were treated with CIT-MTX and WBRT. The response rate of all patients was 92.3%, and median progression-free survival and median overall survival (mOS) were 59.4 months and 93.8 months, respectively. Median OS of patients treated with CIT-MTX in addition to HD-MTX and WBRT was longer than the previously reported mOS with HD-MTX and WBRT (95 vs 33 months). In cases that could not tolerate HD-MTX, mOS of patients treated with CIT-MTX and WBRT was longer than the previously reported mOS with WBRT alone (36.7 vs 18 months). There was no difference in OS between patients with cerebrospinal fluid dissemination and patients without (p = 0.83). Better prognosis in patients treated with CIT-MTX may be derived from stable concentration of methotrexate in the cerebrospinal fluid. CIT-MTX was an effective additional therapeutic option for PCNSL.