Search

TTField (Tumor-treating field) therapy utilizes low intensity intermediate frequency AC electric fields to reduce the spread of cancer. While it has attained FDA approval for the treatment of recurrent glioblastoma multiforme, the exact molecular targets of TTField therapy are not well understood. Microtubules are pipe-like polymers of the highly charged (–31 e) and strongly dipolar (dipole moment 1666 D) protein, α, β- tubulin. Studies on the electrical properties of microtubules have recently gained interest, with them being modelled as molecular targets of TTFields. Here, we experimentally show that while tubulin polymerized into microtubules leads to an increase in solution capacitance, unpolymerized tubulin has no appreciable effect. To the best of our knowledge, we present the first experimental quantification of the capacitance of a 20 μm-long microtubule. Using these results, we calculate the resonant frequency of a microtubule meshwork in a cell-like environment to be in the TTField regime. Our results utilize high ionic strength solutions and cell-like concentrations of tubulin to show the potential of microtubules as the targets of TTField action and as intracellular charge-storage devices. We conclude with a hypothesis of an electrically-tunable cell, where the dielectric properties of the cytoskeleton alter local and global charge storage and transport.

BACKGROUND Investigation of mitochondrial DNA (mtDNA) content in glioblastoma has gathered speed in recent years. Our study focusses on the effect of mtDNA content depletion on treatment response in glioblastoma. MATERIALS AND METHODS The study consists of a survival cohort (n=130), a recurrent cohort (32 pairs) and 35 non neoplastic control brain tissues. Malignant glioma cell lines, U87 and LN229 were utilized for radiation biology experiments. Patient tumor tissue was molecularly characterized for IDH, ATRX and TERT promoter mutations, MGMT promoter methylation and EGFR amplification using established methods. Relative quantification of mtDNA content was performed using quantitative real time PCR. Ethidium bromide was used to deplete mtDNA in U87 and LN229 cells. Clonogenic assay and MTT assay were performed to assess sensitivity to radiation and chemotherapy. RESULTS mtDNA content was lower in glioblastoma than in controls. Lower range of mtDNA copy number was associated with poor overall survival (p=0.033) and with markers of tumor aggressiveness like wild type IDH (p=0.02), unmethylated MGMT promoter, amplified EFGR and mutated TERT promoter. Out of 32 recurrent GBM patients, only 19 had received radiation treatment (RT) between the two surgeries and in these patients, mtDNA content was significantly higher in the recurrent tumor when compared to the primary tumor(p=0.01). U87 and LN229 cells showed a higher mtDNA copy number post irradiation (p=0.002). mtDNA depleted U87 and LN229 cells showed higher survival fraction post radiation exposure when compared to parent lines. The IC50 of TMZ was also higher for mtDNA depleted U87 and LN229 cells. CONCLUSION Low mtDNA content is associated with poor survival and aggressive tumor markers in glioblastoma. Lowering the mtDNA content in GBM cells induces radiation resistance as well as resistance to chemotherapy. Irradiation leads to increase in mitochondrial DNA content in both patient samples as well as malignant glioma cell lines.

BACKGROUND Chronotherapy is the optimally timed administration of treatment based on the circadian clock. In non-CNS cancers, circadian rhythms (CR) drive the expression of mechanisms responsible for radiation sensitivity and associated toxicity. Our previous work has shown that cranial irradiation in GBM patients produces a high incidence of hypersomnolence and susceptibility is linked to circadian clock gene polymorphisms. This study determined if CR can be demonstrated using in vitro GBM and CNS cells and then if sensitivity to radiation is circadian time and tissue dependent. METHODS Rat GBM, fibroblasts, and suprachiasmatic nucleus (SCN) cells were used and compared to human U251 GBM cells. Cells were synchronized using the serum shook method; protein levels for PER2 expression over 24 hr in 4 hr intervals were quantified to confirm CR. Colony formation and 3D invasion assays after radiation (0-8Gy or 8Gy, respectively) 8 and 20 hrs after synchronization were evaluated. RESULTS All cell types demonstrated CR by PER2 expression (trough ~8hr post (CT8); peak ~20hrs post (CT20)). In rat, GBM (LD50 = 4Gy) and SCN cells (LD50 =5 Gy) showed lower sensitivity than fibroblasts (LD50= 2 Gy). Human U251 GBM cells had similar radiation sensitivity to rat GBM. Time-of-day effects were dependent on tissue type with both rat and human GBM cell lines more affected by radiation at CT20, with less invasion (CT20:-35488.5±2622.1 vs CT8:-23160.5±3273.4µm) and survival in the colony assay (F(1,71)=4.105,p< 0.05). Conversely, SCN cells which drive sleep-wake, showed the converse with greater effect at the 8hr compared with 20hr (F(1, 35)=19.93,p< 0.001). CONCLUSIONS These data suggest that timing of radiation could be optimized to improve detrimental effects on healthy tissue, while still providing effective intra-tumor doses. In future studies, we will interrogate the mechanisms driving time-of-day effects in cells and test radiation chronotherapy in our radiation-induced hypersomnolence mouse model.

SB28 is a new luciferase expressing murine glioblastoma (GBM) cell line whose morphology, growth pattern, mutational burden immune infiltrate more closely resembles human GBM and is unresponsive to immunotherapy (OncoImmunology, 7:12, e1501137). Radiation therapy (RT) has the potential to improve response to combinations by multiple means: cell kill that may activate an immune response, effects on vascular system may improve drug access, induction of DNA damage that can be augmented by targeted or chemotherapy, and modulation of the tumor microenvironment. High transforming growth factor β (TGFβ) activity in most GBM, which increases with radiation, likely opposes effective therapy by endorsing an effective DNA damage response and being immunosuppressive. Here evaluated the response of SB28 to radiation in combination with PD-L1 checkpoint blockade or neutralizing TGFβ. Establishment of intracranial tumors was monitored by bioluminescence. We determined that SB28 endogenously activate TGFβ as evaluated by biomarkers. We used radiolabeled antibodies and PET-CT to demonstrate access to intracranial tumors, indicative of a compromised blood-brain barrier. TGFβ neutralizing antibody, 1D11, had little effect on tumor growth compared to mice receiving IgG control antibody (median survival control: 19 days vs 1D11: 20.5 days). A single dose of radiation of 10 Gy delivered to the tumor site increased median survival to 21 day, which was increased to 31 days in mice treated with 1D11. In a second experiment in which the radiation dose was 6 Gy, 1D11 provided no benefit. In contrast, median survival of mice treated with PD-L1 neutralizing antibodies 3 days after being irradiated with 6 Gy demonstrated increased median survival (Control: 18 day; anti-PD-L1 20.5; RT: 25 days; RT + anti- PD-L1: 28 days). Double treatment resulted in 1/7 long term survival and loss of bioluminescence indicative of tumor elimination. Thus, radiation can prime SB28 GBM for response to biological agents.

BACKGROUND Glioblastoma is the most aggressive brain tumor with poor prognosis despite the best available treatment. MicroRNAs (miRNAs) are emerging as promising, novel prognostic biomarkers and therapeutic targets in glioblastoma. In a previous study, we demonstrated that miR-4516 predicts poor prognosis and functions as an oncogene in glioblastoma. Aim of the current study is to examine the role miR-4516 in radiation resistance and identify downstream targets contributing to this phenotype METHODS Radiosensitization was evaluated by cell viability and clonogenic assays. Cell apoptosis was evaluated using flow cytometry and immunoblotting. Potential targets of miR-4516 were identified using bioinformatic analysis (Targetscan and miRDB) and confirmed by luciferase reporter assays. Results were validated using immunoblotting. miR-4516 expression in glioblastoma cell lines after radiation treatment was quantified by qRT-PCR. RESULTS Expression of miR-4516 was increased up to 15 fold following radiation treatment, peaking at around 15min-60 min in primary and established glioblastoma cell lines including GBM 08-387, GBM 30 and U87-MG. Furthermore, inhibition of miR-4516 sensitized GBM 08-387, GBM30 and U87-MG cells to radiation in comparison to control groups as determined by cell viability and clonogenic assays. Further, miR-4516 inhibition induced apoptosis in these cell lines following radiation treatment. While conducting mechanistic studies, we found that the tumor-promoting function of miR-4516 was, in part, mediated by inhibition of p21 and PTPN14, two direct targets of miR-4516 CONCLUSION Our data suggest that radiation induces the expression of miR-4516 in glioblastoma cell lines. This miRNA plays a critical role in radio-resistance and promotes aggressive phenotypes in glioblastoma and therefore, functional analyses of its target pathways may uncover novel therapeutically vulnerable target(s) in glioblastoma. FUNDING: R01CA108633, R01CA169368, RC2CA148190, U10CA180850-01(NCI), Brain Tumor Funders Collaborative Grant, and OSU-CCC (all to AC). The Ton and Patricia Bohnenn Fund for Neuro_Oncology Research (to PR).

Treatment resistance in glioblastoma is underpinned by highly interconnected DNA damage response (DDR) processes. The FA-pathway is a fundamental DDR process required for the resolution of replication fork impeding lesions, and we have previously shown that it is inactive in normal brain, but is re-activated in glioblastoma, providing a cancer-specific target for combination DDR therapies. Here, we find that elevated FA-pathway gene expression in gliomas is associated with poor survival (-17.1% 5-year OS, p< 0.0001, n=329–REMBRANT). Furthermore, patient-derived glioblastoma stem cell (GSC) populations, which drive therapeutic resistance, display high FA-pathway expression relative to paired bulk tumour cell populations (mean 2.3-fold higher across genes, p=0.0073). We further show that inhibition of a single DDR process (FA-pathway, PARP, ATR or ATM) increases the susceptibility of glioblastoma cell lines and patient-derived GSCs to current adjuvant therapy. Importantly, clinically approved PARP inhibitor (PARPi) monotherapy stimulates robust FANCD2 mono-ubiquitination, supporting a role of FA-pathway activation in response to current DDR-targeted therapy. In clinically-relevant 3D GSC models, simultaneous inhibition of the FA-pathway (FAPi) and PARP or ATR enhanced temozolomide sensitisation compared to a single DDR inhibitor (DDRi). Furthermore, combined FAPi+PARPi consistently conferred radiosensitisation whilst combined FAPi+ATRi led to a profoundly radiosensitising effect; e.g. sensitizer enhancement ratio (SER0.37) of 3.23 (3.03–3.49, 95% CI). Furthermore, comparison of α/β ratio enhancement suggests dual-DDRi strategies fundamentally alter the response of GSCs, whilst single cell gel electrophoresis & immunofluorescence studies suggest FA-pathway based DDRi combinations profoundly delay the resolution of IR-induced DNA strand breaks at 6 hours post-treatment, with increased persistent DNA double strand breaks at 24 hours. In conclusion, simultaneously targeting the FA-pathway and interconnected DDR processes represents an appealing therapeutic strategy. Additionally, constitutive lack of FA pathway function in some tumours, could serve as a novel predictive biomarker for patient response to PARPi and ATRi currently in clinical trials.