Impact of the radiated brain microenvironment on a panel of human patient-derived xenografts.

ObjectiveRadiotherapy, combined with surgical resection and chemotherapy, remains a first-line treatment for infiltrative gliomas. However, these tumor are not surgically curable, and often recur, even within the prior radiation field, and may demonstrate a more aggressive phenotype. We recently demonstrated that the radiated brain tumor microenvironment promotes tumor aggressiveness in an orthotopic patient-derived xenograft (PDX) model of glioblastoma (Mayo GBM 143). 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. MethodsFemale 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 PDX GBM cell lines (GBM 6, 10, 12, 39, 46, 76, 123, 164, 196; total n=8-15, per group, per line). GBM 6 cells were additionally implanted 6 months after completion of fractionated radiation (4Gy x 10 fractions or 2Gy x 30 fractions) vs sham radiation. Kaplan-Meyer (K-M) and log-rank tests were performed to compare the survival between irradiated and non-irradiated groups. ResultOf nine previously untested human GBM lines, we found that five demonstrated shorter survival in the pre-radiated brain (GBM 6, 46, 76, 164, 196); similar to previous observations with GBM 143. GBM 6 was also evaluated 6 months after fractionated radiation yielding similar results. However, two lines yielded prolonged survival in the pre-radiated brain (GBM 10, 12); GBM12 and 10 demonstrated the fastest baseline growth in the non-radiated brain; GBM 39, 123 whose rate of growth was not impacted by the radiated brain, demonstrated a an intermediate baseline growth rate between that of those positively and negatively impacted by the radiated brain microenvironment. No other clinical or molecular phenotype was found to consistently correlate with response to the radiated microenvironment. ConclusionAmong a total of 10 total human GBM lines evaluated to date, 60% induce faster mortality in a radiated microenvironment, and 20% induce slower mortality. 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.