Increased Cytokine And Chemokine Expression In U87mg Glioblastoma Cells After Large Clinically Relevant Single Doses Of Ionizing Radiation

BACKGROUND: Stereotactic radiosurgery is an established treatment option that uses high, single fraction doses of radiation to target tumors. Despite the best clinical strategies to eliminate brain tumors using this technique or others (surgery, chemotherapy and/or other radiotherapy techniques), post-therapy recurrence of brain tumors remains a major challenge in patients. To better understand the radiation response, we investigated how such high doses modulate the molecular signaling within glioblastoma cell populations from several days to months after irradiation. METHODS: The glioblastoma cell line, U87MG, was treated with single doses of ionizing radiation between 0 to 16Gy in vitro followed by: examination of cell proliferation; clonogenic survival; extraction of RNA; and subcutaneous injection into nude mice to monitor tumor growth 24 hours after cell irradiation. Genome-wide expression profiling was run on the Illumina HT-12 bead array platform and analysis for significant expressed genes was performed along with network analysis using Ingenuity Pathway Analysis and GenePattern platforms. RESULTS: As expected, high doses of radiation stunted growth of the U87MG cells from 0 to 14 days. Long term, single cell clonogenic survival of the irradiated cells was approximately 3% and 0.01% following 8Gy or 16Gy, respectively. Genome-wide gene expression at 1, 4 and 6 days after irradiation of 8 or 16Gy has revealed a dose-dependent increase in inflammatory cytokines and chemokines. Increased cytokine expression for IL-6 and IL-8 was validated in vitro using qRT-PCR. In vivo, 100% of the untreated U87MG cells formed tumors, whereas less than half of all irradiated treatment groups failed to form tumors. In those samples that did grow despite irradiation, the average time to tumor formation (volume = 300mm 3 ) was 13, 32, 58 and 88 days for 0, 8, 12, and 16Gy respectively while the exponential fits to tumor growth rate was shown to be accelerated after 8Gy but diminished after 12 and 16Gy. IL-6 gene expression was found to be elevated in tumors formed from irradiated cells versus control. CONCLUSION: The data presented here provides novel insight into the cellular and molecular modulation of glioblastoma cell populations by large, clinically relevant, single doses of ionizing radiation. A salient finding is the expression of inflammatory cytokines as a major player in the radiation response at periods long after the irradiation insult. This study was supported by NIH ICBP 1U54CA149233 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4340. doi:1538-7445.AM2012-4340