The Olfactory Bulb Provides a Radioresistant Niche for Glioblastoma Cells

Imaging Spectrum of the Developing Glioblastoma: A Cross-Sectional Observation Study

Glioblastoma (GBM) has the typical radiological appearance (TRA) of a centrally necrotic, peripherally enhancing tumor with surrounding edema. The objective of this study was to determine whether the developing GBM displays a spectrum of imaging changes detectable on routine clinical imaging prior to TRA GBM. Patients with pre-operative imaging diagnosed with GBM (1 January 2014-31 March 2022) were identified from a neuroscience center. The imaging was reviewed by an experienced neuroradiologist. Imaging patterns preceding TRA GBM were analyzed. A total of 76 out of 555 (14%) patients had imaging preceding TRA GBM, 57 had solitary lesions, and 19 had multiple lesions (total = 84 lesions). Here, 83% of the lesions had cortical or cortical/subcortical locations. The earliest imaging features for 84 lesions were T2 hyperintensity/CT low density (n = 18), CT hyperdensity (n = 51), and T2 iso-intensity (n = 15). Lesions initially showing T2 hyperintensity/CT low density later showed T2 iso-intensity. When CT and MRI were available, all CT hyperdense lesions showed T2 iso-intensity, reduced diffusivity, and the following enhancement patterns: nodular 35%, solid 29%, none 26%, and patchy peripheral 10%. The mean time to develop TRA GBM from T2 hyperintensity was 140 days and from CT hyperdensity was 69 days. This research suggests that the developing GBM shows a spectrum of imaging features, progressing through T2 hyperintensity to CT hyperdensity, T2 iso-intensity, reduced diffusivity, and variable enhancement to TRA GBM. Red flags for non-TRA GBM lesions are cortical/subcortical CT hyperdense/T2 iso-intense/low ADC. Future research correlating this imaging spectrum with pathophysiology may provide insight into GBM growth patterns.

Glioblastoma cells have increased capacity to repair radiation-induced DNA damage after migration to the olfactory bulb

BACKGROUND

The invasive nature of GBM combined with the diversity of brain microenvironments creates the potential for a topographic heterogeneity in GBM radioresponse. Investigating the mechanisms responsible for a microenvironment-induced differential GBM response to radiation may provide insights into the molecules and processes mediating GBM radioresistance.

METHODS

Using a model system in which human GBM stem-like cells implanted into the right striatum of nude mice migrate throughout the right hemisphere (RH) to the olfactory bulb (OB), the radiation-induced DNA damage response was evaluated in each location according to γH2AX and 53BP1 foci and cell cycle phase distribution as determined by flow cytometry and immunohistochemistry. RNAseq was used to compare transcriptomes of tumor cells growing in the OB and the RH. Protein expression and neuron-tumor interaction were defined by immunohistochemistry and confocal microscopy.

RESULTS

After irradiation, there was a more rapid dispersal of γH2AX and 53BP1 foci in the OB versus in the RH, indicative of increased double strand break repair capacity in the OB and consistent with the OB providing a radioprotective niche. With respect to the cell cycle, by 6 h after irradiation there was a significant loss of mitotic tumor cells in both locations suggesting a similar activation of the G2/M checkpoint. However, by 24 h post-irradiation there was an accumulation of G2 phase cells in the OB, which continued out to at least 96 h. Transcriptome analysis showed that tumor cells in the OB had higher expression levels of DNA repair genes involved in non-homologous end joining and genes related to the spindle assembly checkpoint. Tumor cells in the OB were also found to have an increased frequency of soma-soma contact with neurons.

CONCLUSION

GBM cells that have migrated to the OB have an increased capacity to repair radiation-induced double strand breaks and altered cell cycle regulation. These results correspond to an upregulation of genes involved in DNA damage repair and cell cycle control. Because the murine OB provides a source of radioresistant tumor cells not evident in other experimental systems, it may serve as a model for investigating the mechanisms mediating GBM radioresistance.

Effects of postoperative radiotherapy and docetaxel and PD-1 inhibitors on the survival and safety of glioblastoma patients: a systematic review and meta-analysis

Background

The present standard treatment rarely allows the complete removal of glioblastoma (GBM). So postoperative treatments are provided to prevent or delay tumor recurrence. The overall survival (OS) rate and safety of postoperative chemotherapy alone, or combined with radiotherapy (RT), or programmed cell death-1 (PD-1) inhibitor in GBM is still unclear. The present goal was to explore postoperative treatment's effect on the survival and safety of patients with GBM.

Methods

We searched the mainstream online databases for clinical studies of RT and chemotherapy and PD-1 inhibitors in the treatment of GBM published up to May 2020. The patients in the experimental group accepted an anti-PD-1 drug alone and RT + chemotherapy, whereas the controlled patients were treated with docetaxel alone. The literature qualities were assessed using Cochrane Risk of Bias 2.0, and studies were assigned. The meta-analysis was conducted by RevMan 5.4 software.

Results

A total of 927 articles were identified through the online database search. The articles unable to meet the inclusion criteria were excluded leaving 6 studies for inclusion in the study. Compared with docetaxel-based chemotherapy for GBM, combined RT chemotherapy and PD-1 inhibitor therapy had better OS [mean difference (MD), -1.75; 95% confidence interval (CI): -2.99 to -0.51; P=0.006] and progression-free survival (PFS) and a lower incidence of adverse reactions (MD, -7.03; 95% CI: -7.64 to -6.42; P<0.00001) above grade III.

Conclusions

Postoperative combination of RT and chemotherapy and PD-1 inhibitors had some advantages over docetaxel in terms of effectiveness. More clinical trials are needed to confirm effectiveness.

Histological analysis of sleep and circadian brain circuitry in cranial radiation-induced hypersomnolence (C-RIH) mouse model

Disrupted sleep, including daytime hypersomnolence, is a core symptom reported by primary brain tumor patients and often manifests after radiotherapy. The biological mechanisms driving the onset of sleep disturbances after cranial radiation remains unclear but may result from treatment-induced injury to neural circuits controlling sleep behavior, both circadian and homeostatic. Here, we develop a mouse model of cranial radiation-induced hypersomnolence which recapitulates the human experience. Additionally, we used the model to explore the impact of radiation on the brain. We demonstrated that the DNA damage response following radiation varies across the brain, with homeostatic sleep and cognitive regions expressing higher levels of γH2AX, a marker of DNA damage, than the circadian suprachiasmatic nucleus (SCN). These findings were supported by in vitro studies comparing radiation effects in SCN and cortical astrocytes. Moreover, in our mouse model, MRI identified structural effects in cognitive and homeostatic sleep regions two-months post-treatment. While the findings are preliminary, they suggest that homeostatic sleep and cognitive circuits are vulnerable to radiation and these findings may be relevant to optimizing treatment plans for patients.