Citations

Abstract BACKGROUND Radiotherapy, combined with surgical resection and chemotherapy, remains a first-line treatment for infiltrative gliomas. However, these tumors are not surgically curable, and often recur, even within the prior radiation field, and may demonstrate a more aggressive phenotype. Importantly, high grade gliomas display diverse molecular phenotypes, and whether this genetic variability leads to divergent behaviour in the radiated tumor microenvironment is unknown. Herein, we characterize the effects of the irradiated brain microenvinroment on nine additional unique GBM cell lines to better understand the nuances of how tumor molecular phenotypes influence cellular dynamics. METHODS Female athymic nude mice were randomly divided into cranial radiation (15 Gy) and non-radiated groups. Mice then underwent intracranial implantation with one of the selected patient-derived xenograft (PDX) GBM cell lines (GBM 6, 10, 12, 39, 46, 76, 123, 164, 196; total n=8-15, per group, per line). Kaplan-Meyer (K-M) and log-rank tests were performed to compare the survival between irradiated and non-irradiated groups. RESULT Of nine previously untested human GBM lines, we found that five demonstrated shorter survival in the pre-radiated brain (GBM 6, 46, 76, 164, 196). However, two lines yielded prolonged survival in the pre-radiated brain (GBM 10, 12); GBM 39, 123 whose rate of growth was not impacted by the radiated brain. CONCLUSION These results highlight the likely critical impact of the irradiated microenvironment on tumor behaviour, yet illustrate that different tumors may exhibit opposing responses. Although further evaluation will be needed to understand mechanisms of divergent behavior, our data suggest the increased rate of growth in the radiated microenvironment may not apply to the fastest-growing tumor lines, which could instead demonstrate a paradoxical response.

Abstract BACKGROUND Despite best current therapies, median survival for glioblastoma remains little more than a year. There remains an urgent need for improved treatment strategies. Current therapies, including radiation and temozolomide, are known to induce senescence in tumor cells. Advances in aging research have identified drugs with “senolytic” properties to kill senescent cells. This work tests the hypothesis that induction of senescence pathways following radiation can provide a window of opportunity to eliminate residual glioblastoma cells using drugs that block senescent cell-associated pathways (SCAPs). METHODS Human glioblastoma cells were radiated with 10, 15, or 20 Gy and maintained in culture for 3 to 4 weeks to facilitate maturation of a senescent phenotype. Given existence of multiple SCAPs, we evaluated the IC50 for several senolytic candidates including Dasatinib, Quercetin, Fisetin, AMG-232, Onalespib, A1331852, and Navitoclax in radiated vs non-radiated cells. RESULTS Among these, the Bcl-XL inhibitors A1331852 and Navitoclax both selectively killed multiple lines of radiated, senescent tumor cells at lower concentrations as compared to unirradiated, non-senescent tumor cells. Across multiple GBM cell line, the average IC50 for senescent cells was 12.88 nM (95%CI= 9.068–18.58 nM), as compared to the IC50 of non-senescent cells of 103.2 nM (95%CI= 74.24–143.9 nM; p< 0.005). Such differential sensitivity to Bcl-XL inhibition after radiation was not observed in the non-GBM control cells evaluated to date. CONCLUSION Our findings suggest that blocking the anti-apoptotic pathway Bcl-XL in GBM cells rendered at least transiently senescent following radiation may provide an avenue to selectively ablate residual glioblastoma cells following radiation. Our data provide proof of principle that senolytic therapy may represent a previously untapped window of opportunity to increase extent of tumor ablation following completion of standard cytotoxic therapies.