ABTC-0904: targeting glioma stem cells in GBM: a phase 0/II study of hedgehog pathway inhibitor GDC-0449

Current status of precision oncology in adult glioblastoma

The concept of precision oncology, the application of targeted drugs based on comprehensive molecular profiling, has revolutionized treatment strategies in oncology. This review summarizes the current status of precision oncology in glioblastoma (GBM), the most common and aggressive primary brain tumor in adults with a median survival below 2 years. Targeted treatments without prior target verification have consistently failed. Patients with BRAF V600E-mutated GBM benefit from BRAF/MEK-inhibition, whereas targeting EGFR alterations was unsuccessful due to poor tumor penetration, tumor cell heterogeneity, and pathway redundancies. Systematic screening for actionable molecular alterations resulted in low rates (< 10%) of targeted treatments. Efficacy was observed in one-third and currently appears to be limited to BRAF-, VEGFR-, and mTOR-directed treatments. Advancing precision oncology for GBM requires consideration of pathways instead of single alterations, new trial concepts enabling rapid and adaptive drug evaluation, a focus on drugs with sufficient bioavailability in the CNS, and the extension of target discovery and validation to the tumor microenvironment, tumor cell networks, and their interaction with immune cells and neurons.

Novel strategies to overcome chemoresistance in human glioblastoma

Temozolomide (TMZ) is currently the first-line chemotherapeutic agent for the treatment of glioblastoma multiforme (GBM). However, the inherent heterogeneity of GBM often results in suboptimal outcomes, particularly due to varying degrees of resistance to TMZ. Over the past several decades, O6-methylguanine-DNA methyltransferase (MGMT)-mediated DNA repair pathway has been extensively investigated as a target to overcome TMZ resistance. Nonetheless, the combination of small molecule covalent MGMT inhibitors with TMZ and other chemotherapeutic agents has frequently led to adverse clinical effects. Recently, additional mechanisms contributing to TMZ resistance have been identified, including epidermal growth factor receptor (EGFR) mutations, overactivation of intracellular signalling pathways, energy metabolism reprogramming or survival autophagy, and changes in tumor microenvironment (TME). These findings suggest that novel therapeutic strategies targeting these mechanisms hold promise for overcoming TMZ resistance in GBM patients. In this review, we summarize the latest advancements in understanding the mechanisms underlying intrinsic and acquired TMZ resistance. Additionally, we compile various small-molecule compounds with potential to mitigate chemoresistance in GBM. These mechanism-based compounds may enhance the sensitivity of GBM to TMZ and related chemotherapeutic agents, thereby improving overall survival rates in clinical practice.

TRIM37 interacts with EZH2 to epigenetically suppress PTCH1 and regulate stemness in glioma stem cells through sonic hedgehog pathway

BACKGROUND

Glioma stem cells (GSCs), which are known for their therapy resistance, play a substantial role in treatment inefficacy for glioblastoma multiforme (GBM). TRIM37, a member of the tripartite motif (TRIM) protein family initially linked to a rare growth disorder, has been recognized for its oncogenic role. However, the mechanism by which TRIM37 regulates tumor growth in glioma and GSCs is unclear.

METHODS

For the in vitro experiments, gene expression was measured by western blotting, RT-qPCR, and immunofluorescence. Cell viability was detected by CCK-8, and cell apoptosis was detected by flow cytometry. The interaction between Enhancer of Zeste Homolog 2 (EZH2) and TRIM37 was verified by co-immunoprecipitation (Co-IP). The interaction between EZH2 and the PTCH1 promoter was verified using dual-luciferase reporter assay and chromatin immunoprecipitation (ChIP). For the in vivo experiments, an orthotopically implanted glioma mouse model was used to validate tumor growth.

RESULTS

The expression of TRIM37 is higher in GSCs compared with matched non-GSCs. TRIM37 knockdown promotes apoptosis, decreased stemness in GSCs, and reduces tumor growth in GSCs xenografts of nude mice. TRIM37 and EZH2 co-localize in the nucleus and interact with each other. TRIM37 knockdown or EZH2 inhibition downregulates the protein expressions associated with the Sonic Hedgehog (SHH) pathway. EZH2 epigenetically downregulates PTCH1 to activate SHH pathway in GSCs.

CONCLUSIONS

TRIM37 maintains the cell growth and stemness in GSCs through the interaction with EZH2. EZH2 activates SHH stem cell signaling pathway by downregulating the expression of SHH pathway suppressor PTCH1. Our findings suggest that TRIM37 may be a potential therapeutic target for GBM.

Emerging Therapies for Glioblastoma

Glioblastoma is most commonly a primary brain tumor and the utmost malignant one, with a survival rate of approximately 12-18 months. Glioblastoma is highly heterogeneous, demonstrating that different types of cells from the same tumor can manifest distinct gene expression patterns and biological behaviors. Conventional therapies such as temozolomide, radiation, and surgery have limitations. As of now, there is no cure for glioblastoma. Alternative treatment methods to eradicate glioblastoma are discussed in this review, including targeted therapies to PI3K, NFKβ, JAK-STAT, CK2, WNT, NOTCH, Hedgehog, and TGFβ pathways. The highly novel application of oncolytic viruses and nanomaterials in combating glioblastoma are also discussed. Despite scores of clinical trials for glioblastoma, the prognosis remains poor. Progress in breaching the blood-brain barrier with nanomaterials and novel avenues for targeted and combination treatments hold promise for the future development of efficacious glioblastoma therapies.

Biomarkers and targeted therapy for cancer stem cells

Cancer stem cells (CSCs) are a small subpopulation of cancer cells with capabilities of self-renewal, differentiation, and tumorigenicity, and play a critical role in driving tumor heterogeneity that evolves insensitivity to therapeutics. For these reasons, extensive efforts have been made to identify and target CSCs to potentially improve the antitumor efficacy of therapeutics. While progress has been made to uncover certain CSC-associated biomarkers, the identification of CSC-specific markers, especially the targetable ones, remains a significant challenge. Here we provide an overview of the unique signaling and metabolic pathways of CSCs, summarize existing CSC biomarkers and CSC-targeted therapies, and discuss strategies to further differentiate CSCs from non-stem cancer cells and healthy cells for the development of enhanced CSC-targeted therapies.