Ex-vivo drug screening of surgically resected glioma stem cells to replace murine avatars and provide personalise cancer therapy for glioblastoma patients

Ex Vivo Drug Screening: An Emerging Paradigm in the Treatment of Childhood Cancer

Developing and providing the right therapy for the right patient (or personalized targeted treatments) is key to reducing side-effects and improving survival in childhood cancers. Most efforts aiming to personalize childhood cancer treatment use genomic analysis of malignancies to identify potentially targetable genetic events. But it is becoming clear that not all patients will have an actionable change, and in those that do there is no additional way to determine if treatments will be effective. Ex vivo drug screening is a laboratory technique used to test the effects of various drugs or compounds, on biological tissues or cells that have been removed from an organism. This information is then used to predict which cancer treatments will be most effective based on the therapeutic response in the tissue or cells removed from that individual. Its utility in personalizing treatments in childhood cancer is increasingly recognized. In this review we describe the different methods for ex vivo drug screening and the advantages and disadvantages of each technique. We also present recent evidence that ex vivo screening may have utility in a variety of childhood malignancies including an overview of current clinical trials appraising its use. Finally, we discuss the research questions and hurdles that must be overcome before ex vivo screening can be widely used in pediatric oncology.

Potential of ex vivo organotypic slice cultures in neuro-oncology

Over recent decades, in vitro and in vivo models have significantly advanced brain cancer research; however, each presents distinct challenges for accurately mimicking in situ conditions. In response, organotypic slice cultures have emerged as a promising model recapitulating precisely specific in vivo phenotypes through an ex vivo approach. Ex vivo organotypic brain slice models can integrate biological relevance and patient-specific variability early in drug discovery, thereby aiming for more precise treatment stratification. However, the challenges of obtaining representative fresh brain tissue, ensuring reproducibility, and maintaining essential central nervous system (CNS)-specific conditions reflecting the in situ situation over time have limited the direct application of ex vivo organotypic slice cultures in robust clinical trials. In this review, we explore the benefits and possible limitations of ex vivo organotypic brain slice cultures in neuro-oncological research. Additionally, we share insights from clinical experts in neuro-oncology on how to overcome these current limitations and improve the practical application of organotypic brain slice cultures beyond academic research.

Personalized targeted glioblastoma therapies by ex vivo drug screening: Study protocol of the Advanced brain Tumor TheRApy Clinical Trial (ATTRACT)

Background

Novel approaches to guide personalized treatment in glioblastoma are urgently needed. Given the poor predictive value of genetic biomarkers in glioblastoma, we are conducting a prospective clinical trial to investigate the novel approach of cultivated patient-derived tumor cells (PDCs) for ex vivo drug screening.

Methods

In this randomized phase 2 study, we are testing the ability of PDC-based ex vivo drug screening to formulate a personalized recommendation for maintenance treatment in patients with newly diagnosed glioblastoma with unmethylated MGMT promoter after combined radio-chemotherapy. Based on overall survival as the primary endpoint, we plan to include 240 patients (120 per group) to show with a power of 80% that we can increase the median survival from 12 to 17 months (hazard ratio 0.7). Patients will be randomized 1:1 to either the standard group (no drug screening) or the intervention group (drug screening and personalized recommendation for maintenance treatment). In the intervention group, automated drug screening will be performed on PDCs with 28 drugs used for the treatment of solid tumors and hematological malignancies. Based on the cytotoxic activity of these drugs, as quantified by relative viability based on adenosine triphosphate levels, a molecular tumor board will recommend a personalized treatment regimen.

Results

The first patient was enrolled in July 2024. Interim analysis of the ATTRACT study (NCT06512311) is expected in late 2027, and final results in 2030.

Trial Registration

The ATTRACT trial is registered under the ID NCT06512311 (https://clinicaltrials.gov/study/NCT06512311).

SENP3-FIS1 axis promotes mitophagy and cell survival under hypoxia

SUMOylation, the covalent attachment of the small ubiquitin-like modifier (SUMO) to target proteins, and its reversal, deSUMOylation by SUMO proteases like Sentrin-specific proteases (SENPs), are crucial for initiating cellular responses to hypoxia. However, their roles in subsequent adaptation processes to hypoxia such as mitochondrial autophagy (mitophagy) remain unexplored. Here, we show that general SUMOylation, particularly SUMO2/3 modification, suppresses mitophagy under both normoxia and hypoxia. Furthermore, we identify deSUMO2/3-ylation enzyme SENP3 and mitochondrial Fission protein 1 (FIS1) as key players in hypoxia-induced mitophagy (HIM), with SUMOylatable FIS1 acting as a crucial regulator for SENP3-mediated HIM regulation. Interestingly, we find that hypoxia promotes FIS1 SUMO2/3-ylation and triggers an interaction between SUMOylatable FIS1 and Rab GTPase-activating protein Tre-2/Bub2/Cdc16 domain 1 family member 17 (TBC1D17), which in turn suppresses HIM. Therefore, we propose a novel SUMOylation-dependent pathway where the SENP3-FIS1 axis promotes HIM, with TBC1D17 acting as a fine-tuning regulator. Importantly, the SENP3-FIS1 axis plays a protective role against hypoxia-induced cell death, highlighting its physiological significance, and hypoxia-inducible FIS1-TBC1D17 interaction is detectable in primary glioma stem cell-like (GSC) cultures derived from glioblastoma patients, suggesting its disease relevance. Our findings not only provide new insights into SUMOylation/deSUMOylation regulation of HIM but also suggest the potential of targeting this pathway to enhance cellular resilience under hypoxic stress.

Innovating cancer drug discovery with refined phenotypic screens

Before molecular pathways in cancer were known to a depth that could predict targets, drug development relied on phenotypic screening, where the effectiveness of candidate chemicals is judged from functional readouts without considering the mechanisms of action. The unraveling of tumor-specific pathways has brought targets for molecularly driven drug discovery, but precedents in the field have shown that awareness of pathways does not necessarily predict therapeutic efficacy, and many cancers still lack druggable targets. Phenotypic screening therefore retains a niche in drug development where a targeted approach is not informative. We analyze the unique advantages of phenotypic screens, and how technological advances have improved their discovery power. Notable advances include the use of larger biological panels and refined protocols that address the disease-relevance and increase data content with imaging and omic approaches.

Development and Optimisation of Tumour Treating Fields (TTFields) Delivery within 3D Primary Glioma Stem Cell-like Models of Spatial Heterogeneity

Glioblastoma is an aggressive, incurable brain cancer with poor five-year survival rates of around 13% despite multimodal treatment with surgery, DNA-damaging chemoradiotherapy and the recent addition of Tumour Treating Fields (TTFields). As such, there is an urgent need to improve our current understanding of cellular responses to TTFields using more clinically and surgically relevant models, which reflect the profound spatial heterogeneity within glioblastoma, and leverage these biological insights to inform the rational design of more effective therapeutic strategies incorporating TTFields. We have recently reported the use of preclinical TTFields using the inovitroTM system within 2D glioma stem-like cell (GSC) models and demonstrated significant cytotoxicity enhancement when co-applied with a range of therapeutically approved and preclinical DNA damage response inhibitors (DDRi) and chemoradiotherapy. Here we report the development and optimisation of preclinical TTFields delivery within more clinically relevant 3D scaffold-based primary GSC models of spatial heterogeneity, and highlight some initial enhancement of TTFields potency with temozolomide and clinically approved PARP inhibitors (PARPi). These studies, therefore, represent an important platform for further preclinical assessment of TTFields-based therapeutic strategies within clinically relevant 3D GSC models, aimed towards accelerating clinical trial implementation and the ultimate goal of improving the persistently dire survival rates for these patients.