Radiosensitisation by olaparib through focused ultrasound delivery in a diffuse midline glioma model.

BACKGROUND AND PURPOSE: Diffuse midline glioma H3K27-altered (DMG) is an aggressive, inoperable, predominantly paediatric brain tumour. Treatment strategies are limited, resulting in a median survival of only 11 months. Currently, radiotherapy (RT), often combined with temozolomide, is considered the standard of care but remains palliative, highlighting the urgency for new therapies. Radiosensitisation by olaparib, an inhibitor of PARP1 and subsequently PAR-synthesis, is a promising treatment option. We assessed whether PARP1 inhibition enhances radiosensitivity in vitro and in vivo following focused ultrasound mediated blood-brain barrier opening (FUS-BBBO). METHODS: Effects of PARP1 inhibition were evaluated in vitro using viability, clonogenic, and neurosphere assays. In vivo olaparib extravasation and pharmacokinetic profiling following FUS-BBBO was measured by LC-MS/MS. Survival benefit of FUS-BBBO combined with olaparib and RT was assessed using a patient-derived xenograft (PDX) DMG mouse model. RESULTS: Treatment with olaparib in combination with radiation delayed tumour cell proliferation in vitro through the reduction of PAR. Prolonged exposure of low olaparib concentration was more efficient in delaying cell growth than short exposure of high concentration. FUS-BBBO increased olaparib bioavailability in the pons by 5.36-fold without observable adverse effects. A Cmax of 54.09 µM in blood and 1.39 µM in the pontine region was achieved following administration of 100 mg/kg olaparib. Although RT combined with FUS-BBBO mediated olaparib extravasation delayed local tumour growth, survival benefits were not observed in an in vivo DMG PDX model. CONCLUSIONS: Olaparib effectively radiosensitises DMG cells in vitro and reduces primary tumour growth in vivo when combined with RT. Further studies are needed to investigate the therapeutic benefit of olaparib in suitable preclinical PDX models.

Prevalence and risk factors of hypothalamic-pituitary dysfunction in infant and toddler childhood brain tumor survivors.

OBJECTIVE: Childhood brain tumor survivors (CBTS) are at risk to develop hypothalamic-pituitary (HP) dysfunction (HPD). The risk for HPD may vary between different age groups due to maturation of the brain and differences in oncologic treatment protocols. Specific studies on HPD in infant brain tumor survivors (infant-BTS, 0-1 years at diagnosis) or toddler brain tumor survivors (toddler-BTS, ≥1-3 years) have not been performed. PATIENTS AND METHODS: A retrospective nationwide cohort study in CBTS was performed. Prevalence and risk factors for HPD were compared between infant-, toddler-, and older-BTS. Subgroup analysis was performed for all non-irradiated CBTS (n = 460). RESULTS: In total, 718 CBTS were included, with a median follow-up time of 7.9 years. Overall, despite the less frequent use of radiotherapy (RT) in infants, no differences in the prevalence of HPD were found between the three groups. RT (OR: 16.44; 95% CI: 8.93-30.27), suprasellar tumor location (OR: 44.76; 95% CI: 19.00-105.49), and younger age (OR: 1.11; 95% CI: 1.05-1.18) were associated with HP dysfunction. Infant-BTS and toddler-BTS showed more weight gain (P < 0.0001) and smaller height SDS (P = 0.001) during follow-up. In non-irradiated CBTS, infant-BTS and toddler-BTS were significantly more frequently diagnosed with TSH-, ACTH-, and ADH deficiency, compared to older-BTS. CONCLUSION: Infant and toddler brain tumor survivors seem to be more vulnerable to develop HP dysfunction than older children. These results emphasize the importance of special infant and toddler brain tumor treatment protocols and the need for endocrine surveillance in children treated for a brain tumor at a young age.

Invaders Exposed: Understanding and Targeting Tumor Cell Invasion in Diffuse Intrinsic Pontine Glioma.

Diffuse Intrinsic Pontine Glioma (DIPG) is a rare, highly aggressive pediatric brain tumor that originates in the pons. DIPG is untreatable and universally fatal, with a median life expectancy of less than a year. Resection is not an option, due to the anatomical location of the tumor, radiotherapy has limited effect and no chemotherapeutic or targeted treatment approach has proven to be successful. This poor prognosis is partly attributed to the tumor's highly infiltrative diffuse and invasive spread. Thus, targeting the invasive behavior of DIPG has the potential to be of therapeutic value. In order to target DIPG invasion successfully, detailed mechanistic knowledge on the underlying drivers is required. Here, we review both DIPG tumor cell's intrinsic molecular processes and extrinsic environmental factors contributing to DIPG invasion. Importantly, DIPG represents a heterogenous disease and through advances in whole-genome sequencing, different subtypes of disease based on underlying driver mutations are now being recognized. Recent evidence also demonstrates intra-tumor heterogeneity in terms of invasiveness and implies that highly infiltrative tumor subclones can enhance the migratory behavior of neighboring cells. This might partially be mediated by "tumor microtubes," long membranous extensions through which tumor cells connect and communicate, as well as through the secretion of extracellular vesicles. Some of the described processes involved in invasion are already being targeted in clinical trials. However, more research into the mechanisms of DIPG invasion is urgently needed and might result in the development of an effective therapy for children suffering from this devastating disease. We discuss the implications of newly discovered invasive mechanisms for therapeutic targeting and the challenges therapy development face in light of disease in the developing brain.

Implementation of a multi-institutional diffuse intrinsic pontine glioma autopsy protocol and characterization of a primary cell culture.

AIMS: Diffuse intrinsic pontine glioma (DIPG) is a fatal paediatric malignancy. Tumour resection is not possible without serious morbidity and biopsies are rarely performed. The resulting lack of primary DIPG material has made preclinical research practically impossible and has hindered the development of new therapies for this disease. The aim of the current study was to address the lack of primary DIPG material and preclinical models by developing a multi-institutional autopsy protocol. METHODS: An autopsy protocol was implemented in the Netherlands to obtain tumour material within a brief post mortem interval. A team of neuropathologists and researchers was available at any time to perform the autopsy and process the material harvested. Whole brain autopsy was performed and primary DIPG material and healthy tissue were collected from all affected brain areas. Finally, the study included systematic evaluation by parents. RESULTS: Five autopsies were performed. The mean time interval between death and time of autopsy was 3 h (range 2-4). All tumours were graded as glioblastoma. None of the parents regretted their choice to participate, and they all derived comfort in donating tissue of their child in the hope to help future DIPG patients. In addition, we developed and characterized one of the first DIPG cell cultures from post mortem material. CONCLUSION: Here we show that obtaining post mortem DIPG tumour tissue for research purposes is feasible with short delay, and that the autopsy procedure is satisfying for participating parents and can be suitable for the development of preclinical DIPG models.

Diffuse intrinsic pontine gliomas: a systematic update on clinical trials and biology.

Patients with diffuse intrinsic pontine gliomas (DIPG) have a poor prognosis. Although DIPG constitute only 10-15% of all pediatric brain tumors, they are the main cause of death in this group. Despite 26 clinical trials in newly diagnosed DIPG in the past 5years (including several targeted agents), there is no clear improvement in prognosis. However, knowledge on DIPG biology is increasing, mainly due to the (re)introduction of biopsies and autopsies, the possibility of gene expression profiling, and the development of in vivo models. Translation of this knowledge into clinical trials in combination with improved drug distribution methods may eventually lead to more effective treatment of this devastating disease.