Should I stay or should I go? Transsulfuration influences invasion and growth in glioblastoma.

A major challenge in treating patients with glioblastoma is the inability to eliminate highly invasive cells with chemotherapy, radiation, or surgical resection. As cancer cells face the issue of replicating or invading neighboring tissue, they rewire their metabolism in a concerted effort to support necessary cellular processes and account for altered nutrient abundance. In this issue of the JCI, Garcia et al. compared an innovative 3D hydrogel-based invasion device to regional patient biopsies through a comprehensive multiomics-based approach paired with a CRISPR knockout screen. Their findings elucidate a role for cystathionine γ-lyase (CTH), an enzyme in the transsulfuration pathway, as a means of regulating the cellular response to oxidative stress. CTH-mediated conversion of cystathionine to cysteine was necessary for regulating reactive oxygen species to support invasion. Meanwhile, inhibition of CTH suppressed the invasive glioblastoma phenotype. However, inhibiting CTH resulted in a larger overall tumor mass. These findings suggest that targeting the transsulfuration pathway may serve as a means of redirecting glioblastoma to proliferate or invade.

Cancer stem cell hypothesis 2.0 in glioblastoma: Where are we now and where are we going?

Over the past 2 decades, the cancer stem cell (CSC) hypothesis has provided insight into many malignant tumors, including glioblastoma (GBM). Cancer stem cells have been identified in patient-derived tumors and in some mouse models, allowing for a deeper understanding of cellular and molecular mechanisms underlying GBM growth and therapeutic resistance. The CSC hypothesis has been the cornerstone of cellular heterogeneity, providing a conceptual and technical framework to explain this longstanding phenotype in GBM. This hypothesis has evolved to fit recent insights into how cellular plasticity drives tumor growth to suggest that CSCs do not represent a distinct population but rather a cellular state with substantial plasticity that can be achieved by non-CSCs under specific conditions. This has further been reinforced by advances in genomics, including single-cell approaches, that have used the CSC hypothesis to identify multiple putative CSC states with unique properties, including specific developmental and metabolic programs. In this review, we provide a historical perspective on the CSC hypothesis and its recent evolution, with a focus on key functional phenotypes, and provide an update on the definition for its use in future genomic studies.

Androgen loss weakens anti-tumor immunity and accelerates brain tumor growth.

Many cancers, including glioblastoma (GBM), have a male-biased sex difference in incidence and outcome. The underlying reasons for this sex bias are unclear but likely involve differences in tumor cell state and immune response. This effect is further amplified by sex hormones, including androgens, which have been shown to inhibit anti-tumor T cell immunity. Here, we show that androgens drive anti-tumor immunity in brain tumors, in contrast to its effect in other tumor types. Upon castration, tumor growth was accelerated with attenuated T cell function in GBM and brain tumor models, but the opposite was observed when tumors were located outside the brain. Activity of the hypothalamus-pituitary-adrenal gland (HPA) axis was increased in castrated mice, particularly in those with brain tumors. Blockade of glucocorticoid receptors reversed the accelerated tumor growth in castrated mice, indicating that the effect of castration was mediated by elevated glucocorticoid signaling. Furthermore, this mechanism was not GBM specific, but brain specific, as hyperactivation of the HPA axis was observed with intracranial implantation of non-GBM tumors in the brain. Together, our findings establish that brain tumors drive distinct endocrine-mediated mechanisms in the androgen-deprived setting and highlight the importance of organ-specific effects on anti-tumor immunity.

Homeostatic iron regulatory protein drives glioblastoma growth via tumor cell-intrinsic and sex-specific responses.

Background: Glioblastoma (GBM) displays alterations in iron that drive proliferation and tumor growth. Iron regulation is complex and involves many regulatory mechanisms, including the homeostatic iron regulator (HFE) gene, which encodes the homeostatic iron regulatory protein. While HFE is upregulated in GBM and correlates with poor survival outcomes, the function of HFE in GBM remains unclear. Methods: We interrogated the impact of cell-intrinsic Hfe expression on proliferation and survival of intracranially implanted animals through genetic gain- and loss-of-function approaches in syngeneic mouse glioma models, along with in vivo immune assessments. We also determined the expression of iron-associated genes and their relationship to survival in GBM using public data sets and used transcriptional profiling to identify differentially expressed pathways in control compared to Hfe-knockdown cells. Results: Overexpression of Hfe accelerated GBM proliferation and reduced animal survival, whereas suppression of Hfe induced apoptotic cell death and extended survival, which was more pronounced in females and associated with attenuation of natural killer cells and CD8+ T cell activity. Analysis of iron gene signatures in Hfe-knockdown cells revealed alterations in the expression of several iron-associated genes, suggesting global disruption of intracellular iron homeostasis. Further analysis of differentially expressed pathways revealed oxidative stress as the top pathway upregulated following Hfe loss. Hfe knockdown indeed resulted in enhanced 55Fe uptake and generation of reactive oxygen species. Conclusions: These findings reveal an essential function for HFE in GBM cell growth and survival, as well as a sex-specific interaction with the immune response.