Preclinical Models of Craniospinal Irradiation for Medulloblastoma

Feasibility and Safety of Implementing Volumetric Arc Therapy (VMAT) for Pediatric Craniospinal Irradiation in a Low-Middle-Income Region: The Nigerian Experience

Purpose

Volumetric modulated arc therapy (VMAT) is a relatively new treatment technique in sub-Saharan Africa. Although craniospinal irradiation (CSI) in the pediatric population has been practiced in Nigeria for many years, the use of VMAT to deliver this treatment is previously undocumented. We reviewed the first set of patients to undergo CSI at a cancer center in Nigeria, detailing the treatment technique, the progress experienced, dose statistics achieved, treatment toxicities, and cancer outcomes to date.

Methods and Materials

This was a prospective case series of 5 children with histologically diagnosed cancers requiring CSI whose parents consented to the study. They were recruited at evaluation and followed through the process of their therapy. Toxicity was monitored at weekly review appointments using the Common Terminology Criteria for Adverse Events version 5.0. Follow-up of the children will continue in the long-term effects clinic.

Results

Five patients with a median age of 6 were recruited. Diagnoses were intracranial germ cell tumor (n = 2), medulloblastoma (n = 1), pineoblastoma (n = 1), and ependymoma (n = 1). For all patients, a dose of 36.0 Gy in 1.8 Gy daily fractions was prescribed to the entire neuraxis. A subsequent boost of 18 Gy (n = 4) to 19.8 Gy (n = 1) in 10 daily fractions to the primary tumor bed (n = 2) and posterior fossa (n = 2) was delivered. Four patients had chemotherapy before, during, or after radiation therapy. No patient experienced grade 3 or greater toxicity.

Conclusions

Our results indicate great progress has been made in the delivery of CSI in Nigeria, demonstrating tolerable acute side effects using VMAT. This series suggests the feasibility of implementing VMAT technology in low- or middle-income countries. Additional follow-up will be needed to determine whether survival rates and chronic toxicity rates are similar to those reported in the literature.

OLIG2 Is a Determinant for the Relapse of MYC-Amplified Medulloblastoma

PURPOSE

Patients with MYC-amplified medulloblastoma (MB) have poor prognosis and frequently develop recurrence, thus new therapeutic approaches to prevent recurrence are needed.

EXPERIMENTAL DESIGN

We evaluated OLIG2 expression in a panel of mouse Myc-driven MB tumors, patient MB samples, and patient-derived xenograft (PDX) tumors and analyzed radiation sensitivity in OLIG2-high and OLIG2-low tumors in PDX lines. We assessed the effect of inhibition of OLIG2 by OLIG2-CRISPR or the small molecule inhibitor CT-179 combined with radiotherapy on tumor progression in PDX models.

RESULTS

We found that MYC-associated MB can be stratified into OLIG2-high and OLIG2-low tumors based on OLIG2 protein expression. In MYC-amplified MB PDX models, OLIG2-low tumors were sensitive to radiation and rarely relapsed, whereas OLIG2-high tumors were resistant to radiation and consistently developed recurrence. In OLIG2-high tumors, irradiation eliminated the bulk of tumor cells; however, a small number of tumor cells comprising OLIG2- tumor cells and rare OLIG2+ tumor cells remained in the cerebellar tumor bed when examined immediately post-irradiation. All animals harboring residual-resistant tumor cells developed relapse. The relapsed tumors mirrored the cellular composition of the primary tumors with enriched OLIG2 expression. Further studies demonstrated that OLIG2 was essential for recurrence, as OLIG2 disruption with CRISPR-mediated deletion or with the small molecule inhibitor CT-179 prevented recurrence from the residual radioresistant tumor cells.

CONCLUSIONS

Our studies reveal that OLIG2 is a biomarker and an effective therapeutic target in a high-risk subset of MYC-amplified MB, and OLIG2 inhibitor combined with radiotherapy represents a novel effective approach for treating this devastating disease.

Patient-derived orthotopic xenografts of pediatric brain tumors: a St. Jude resource

Pediatric brain tumors are the leading cause of cancer-related death in children. Patient-derived orthotopic xenografts (PDOX) of childhood brain tumors have recently emerged as a biologically faithful vehicle for testing novel and more effective therapies. Herein, we provide the histopathological and molecular analysis of 37 novel PDOX models generated from pediatric brain tumor patients treated at St. Jude Children's Research Hospital. Using a combination of histopathology, whole-genome and whole-exome sequencing, RNA-sequencing, and DNA methylation arrays, we demonstrate the overall fidelity and inter-tumoral molecular heterogeneity of pediatric brain tumor PDOX models. These models represent frequent as well as rare childhood brain tumor entities, including medulloblastoma, ependymoma, atypical teratoid rhabdoid tumor, and embryonal tumor with multi-layer rosettes. PDOX models will be valuable platforms for evaluating novel therapies and conducting pre-clinical trials to accelerate progress in the treatment of brain tumors in children. All described PDOX models and associated datasets can be explored using an interactive web-based portal and will be made freely available to the research community upon request.