Behavior of glioblastoma brain tumor stem cells following a suborbital rocket flight: reaching the "edge" of outer space

Space exploration presents unique opportunities to study cancer cell biology under conditions of microgravity and hypergravity. Previous research on the International Space Station (ISS) has shown that altered gravity can influence cancer cell behavior, affecting apoptosis, proliferation, and migration. However, the effects of rocket flight on patient-derived glioblastoma (GBM) cells, particularly brain tumor initiating cells (BTICs), remain largely unknown. GBM is a highly aggressive brain tumor with a poor prognosis, and BTICs are a subpopulation of cells responsible for tumor recurrence and resistance to therapy. This study aimed to investigate how the conditions experienced during a suborbital rocket flight – including microgravity, hypergravity, and ionizing radiation – affect the tumorigenic capacity of BTICs isolated from a GBM patient sample. Understanding these effects is crucial for future long-duration space missions and may provide insights into GBM biology and treatment strategies. Simulated microgravity studies have yielded conflicting results regarding GBM cell behavior, with some indicating a reduction in malignancy. Therefore, investigating the real effects of a rocket flight offers valuable information.

The literature review section summarized existing research on the effects of microgravity and hypergravity on various cancer cell lines. Studies conducted on the ISS and during rocket flights demonstrated alterations in cell proliferation, migration, and apoptosis in thyroid and breast cancer cells. These studies indicated that altered gravity conditions can influence cytoskeletal dynamics, potentially affecting cellular behavior through biomechanical signaling. While some simulated microgravity studies suggested that microgravity could reduce the malignancy of GBM cells, the effects of actual rocket flight conditions remained largely unexplored.

Patient-derived QNS108 BTICs were cultured in Origen cell culture bags. One bag served as a ground control (GC), while the other was launched on a suborbital rocket flight (RF). The rocket flight generated periods of hypergravity and microgravity, reaching a maximum altitude of 25.74 km. Post-flight, both GC and RF cells were expanded in vitro and assessed for migration, stemness (using a limiting dilution assay), and proliferation (using Alamar blue and CellCyte technology). In vivo studies involved intracranial injection of both cell groups into male nude mice (n=5 per group). Tumor growth, cystic lesion area (measured on H&E stained brain slices), and survival were compared between the groups. Statistical analysis was performed using GraphPad Prism and R Studio.

The QNS108 RF cells demonstrated significantly higher migration (p<0.0001) and stemness (p<0.001) compared to GC cells in vitro. There was no significant difference in proliferation between the groups. In vivo, mice implanted with RF cells developed larger cystic lesions (p=0.00029) and exhibited significantly decreased survival (p=0.0172) compared to mice implanted with GC cells. The median survival time was 97 days for the RF group and 130 days for the GC group.

The results indicate that brief exposure to altered gravity conditions during a suborbital rocket flight significantly altered the phenotype of QNS108 BTICs, leading to increased aggressiveness. The increased migration and stemness, along with larger cystic lesions and reduced survival in vivo, suggest a selection for a more aggressive subpopulation of cells. These findings contrast with some in vitro studies using simulated microgravity, highlighting the importance of studying the actual effects of space travel. The observed changes might be due to altered cytoskeletal dynamics or other cellular responses to the combined stress of hypergravity, microgravity, and potentially increased ionizing radiation. While other environmental stressors during transport might have played a role, the persistence of the phenotypic changes post-flight suggests a more profound effect of spaceflight conditions on the BTICs. The enhanced aggressiveness of the surviving cells post-flight parallels the characteristics of treatment-resistant cells observed in clinical settings following chemo/radiation therapy. This observation has significant implications for understanding tumor recurrence and developing more effective treatment strategies.

This study demonstrates that a suborbital rocket flight induces a more aggressive phenotype in glioblastoma brain tumor initiating cells. The increased migration, stemness, and tumorigenicity in vivo highlight the potential impact of space travel on cancer biology. Future research should explore the underlying molecular mechanisms of these changes, investigate the effects of sex differences, and conduct similar experiments aboard the ISS or on future suborbital flights to further elucidate these observations. The findings contribute to a better understanding of GBM biology and offer potential insights into the development of novel cancer therapies.

Limitations of the study include the lack of direct measurement of ionizing radiation exposure during the flight and the lack of temperature and gas regulation in the BRIC container used for transporting cells. Additionally, the study used a single patient-derived cell line, limiting the generalizability of the findings. Future studies should address these limitations to provide a more comprehensive understanding of the effects of spaceflight on GBM cells.