CBIO-13. THOC1 DRIVES GBM AGGRESSION THROUGH MODULATION OF R-LOOPS AND GENOMIC STABILITY

Abstract Glioblastoma (GBM) is the most aggressive and common type of adult malignant brain tumor, with a median survival of only 21 months. To identify which genes drive its highly aggressive phenotype, we performed a genome-wide CRISPR-Cas9 knockout screen. Results showed substantial enrichment of ~160 novel essential oncogenic driver genes and pathways, including a previously unstudied gene THOC1—involved in RNA processing—that showed significant elevations in expression at RNA and protein levels (p< 0.05) in GBM, as well as a significant survival benefit in patient datasets when downregulated (p< 0.05). Knocking out THOC1 resulted in cell death in multiple GBM patient-derived xenograft (PDX) lines and extended survival compared to the controls (p< 0.01) in vivo. Overexpression of THOC1 in neural stem cells resulted in transformation to a cancerous phenotype, as evidenced by sphere formation in a soft agar assay (p< 0.01) and in vivo tumor engraftment assays. Further investigation of THOC1 through immunoprecipitation in neural stem cells and multiple GBM lines showed significant interaction in GBM with histone deacetylase complex SIN3A, involved in recruiting major histone deacetylases in order to close the DNA and prevent the accumulation of R-loops, RNA:DNA hybrids that pose a threat to genomic stability. Additional investigation revealed that THOC1-knockdowns in vitro induced R-loop formation and DNA damage, while THOC1-overexpression in vitro resulted in an untenable decrease in R-loops and DNA damage, suggesting that the THOC1-SIN3A axis is elevated in GBM in order to prevent the accumulation of genotoxic R-loops. Additionally, histone deacetylase activity was shown to be elevated in THOC1-overexpression conditions and reduced in THOC1-knockdown conditions, confirming that the THOC1-SIN3A axis functions to prevent R-loop accumulation through the epigenetic regulation. In summary, our whole-genome CRISPR-Cas9 knockout screen has identified a promising therapeutic target for GBM—a disease desperately in need of therapeutic innovations.

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EXTH-07. TUMOR-HOMING INDUCED NEURAL STEM CELLS SECRETING A CYTOTOXIC PAYLOAD AS AN ADJUVANT TREATMENT FOR NON-SMALL CELL LUNG CANCER BRAIN METASTASES

Neuro-Oncology ◽

10.1093/neuonc/noaa215.361 ◽

2020 ◽

Vol 22 (Supplement_2) ◽

pp. ii88-ii88

Author(s):

Alison Mercer-Smith ◽

Wulin Jiang ◽

Alain Valdivia ◽

Juli Bago ◽

Scott Floyd ◽

...

Keyword(s):

Stem Cells ◽

Brain Metastases ◽

Neural Stem Cells ◽

Adjuvant Treatment ◽

Small Cell ◽

Small Cell Lung ◽

Tumor Homing ◽

Induced Neural Stem Cells

Abstract INTRODUCTION Non-small cell lung cancer (NSCLC) is the most common cancer to form brain metastases. Radiation treatment is standard-of-care, but recurrence is still observed in 40% of patients. An adjuvant treatment is desperately needed to track down and kill tumor remnants after radiation. Tumoritropic neural stem cells (NSCs) that can home to and deliver a cytotoxic payload offer potential as such an adjuvant treatment. Here we show the transdifferentiation of human fibroblasts into tumor-homing induced neural stem cells (hiNSCs) that secrete the cytotoxic protein TRAIL (hiNSC-TRAIL) and explore the use of hiNSC-TRAIL to treat NSCLC brain metastases. METHODS To determine the migratory capacity of hiNSCs, hiNSCs were infused intracerebroventricularly (ICV) into mice bearing established bilateral NSCLC H460 brain tumors. hiNSC accumulation at tumor foci was monitored using bioluminescent imaging and post-mortem fluorescent analysis. To determine synergistic effects of radiation with TRAIL on NSCLC, we performed in vitro co-culture assays and isobologram analysis. In vivo, efficacy was determined by tracking the progression and survival of mice bearing intracranial H460 treated with hiNSC-TRAIL alone or in combination with 2 Gy radiation. RESULTS/CONCLUSION Following ICV infusion, hiNSCs persisted in the brain for > 1 week and migrated from the ventricles to colocalize with bilateral tumor foci. In vitro, viability assays and isobologram analysis revealed the combination treatment of hiNSC-TRAIL and 2 Gy radiation induced synergistic killing (combination index=0.64). In vivo, hiNSC-TRAIL/radiation combination therapy reduced tumor volumes > 90% compared to control-treated animals while radiation-only and hiNSC-TRAIL-only treated mice showed 21% and 52% reduced volumes, respectively. Dual-treatment extended survival 40%, increasing survival from a median of 20 days in controls to 28 days in the treatment group. These results suggest hiNSC-TRAIL can improve radiation therapy for NSCLC brain metastases and could potentially improve outcomes for patients suffering from this aggressive form of cancer.

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STEM-20. RADIO-SENSITIZING GLIOBLASTOMA CANCER STEM CELLS BY INHIBITION OF FACT

Neuro-Oncology ◽

10.1093/neuonc/noz175.993 ◽

2019 ◽

Vol 21 (Supplement_6) ◽

pp. vi237-vi238

Author(s):

Miranda Montgomery ◽

Abigail Zalenski ◽

Amanda Deighen ◽

Sherry Mortach ◽

Treg Grubb ◽

...

Keyword(s):

Stem Cells ◽

Dna Damage ◽

Cancer Stem Cells ◽

Combination Therapy ◽

High Rate ◽

Primary Role ◽

Cancer Cell Growth ◽

Treatment Paradigm

Abstract Glioblastoma (GBM) has a particularly high rate of recurrence with a 5-year overall survival rate of approximately 5%. This is in part due to a sub-population of cancer stem cells (CSC), which are both radioresistant and chemotherapeutically resistant to conventional treatments. Here we investigated CBL0137, a small molecule form of curaxin, in combination with radiotherapy as a means to radiosensitize CSCs. CBL0137 sequesters FACT (facilitates chromatin transcription) complex to chromatin, which leads to activation of p53 and inhibition of NF-κB. This sequestering of FACT results in cytotoxicity especially within tumor cells and prevents FACT from performing its primary role as a histone chaperone, as well as inhibits its part in the DNA damage response pathway. We show that when combined with radiotherapy, CBL0137 administration limited the ability of CSCs to identify and repair damaged DNA. CSCs treated in vitro with CBL0137 and irradiation showed an increased inhibition of cancer cell growth and decreased viability compared to irradiation or drug alone. Combination therapy also showed more DNA damage in the CSCs than with either agent alone. Based on our in vitro evidence for the efficacy of combination therapy to target CSCs, we moved forward to test the treatment in vivo. Using a subcutaneous model, we show that the amount of CD133+ cells (a marker for GMB CSCs) was reduced in irradiation plus CBL0137 compared to either treatment alone. Survival studies demonstrated that irradiation plus CBL0137 compared to irradiation alone or CBL0137 alone increase lifespan. Here we show the ability of CBL0137, in combination with irradiation, to target patient GBM CSCs both in vitro and in vivo. This work establishes a new treatment paradigm for GBM that inclusively targets CSCs and may ultimately reduce tumor recurrence.

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PAICS contributes to gastric carcinogenesis and participates in DNA damage response by interacting with histone deacetylase 1/2

Cell Death and Disease ◽

10.1038/s41419-020-2708-5 ◽

2020 ◽

Vol 11 (7) ◽

Author(s):

Nan Huang ◽

Chang Xu ◽

Liang Deng ◽

Xue Li ◽

Zhixuan Bian ◽

...

Keyword(s):

Dna Damage ◽

Histone Deacetylase ◽

Dna Damage Response ◽

De Novo ◽

Dna Damage Repair ◽

Histone Deacetylase 1 ◽

Damage Repair ◽

Damage Response

AbstractPhosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS), an essential enzyme involved in de novo purine biosynthesis, is connected with formation of various tumors. However, the specific biological roles and related mechanisms of PAICS in gastric cancer (GC) remain unclear. In the present study, we identified for the first time that PAICS was significantly upregulated in GC and high expression of PAICS was correlated with poor prognosis of patients with GC. In addition, knockdown of PAICS significantly induced cell apoptosis, and inhibited GC cell growth both in vitro and in vivo. Mechanistic studies first found that PAICS was engaged in DNA damage response, and knockdown of PAICS in GC cell lines induced DNA damage and impaired DNA damage repair efficiency. Further explorations revealed that PAICS interacted with histone deacetylase HDAC1 and HDAC2, and PAICS deficiency decreased the expression of DAD51 and inhibited its recruitment to DNA damage sites by impairing HDAC1/2 deacetylase activity, eventually preventing DNA damage repair. Consistently, PAICS deficiency enhanced the sensitivity of GC cells to DNA damage agent, cisplatin (CDDP), both in vitro and in vivo. Altogether, our findings demonstrate that PAICS plays an oncogenic role in GC, which act as a novel diagnosis and prognostic biomarker for patients with GC.

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