Detection of glioblastoma intratumor heterogeneity in radiosensitivity using patient-derived neurosphere cultures

Purpose: Glioblastoma (GB) is characterized by extensive clonal diversity suggesting the presence of tumor cells with varying degrees of treatment sensitivity. Radiotherapy is an integral part of glioblastoma treatment. Whether GBs are comprised of spatially distinct cellular populations with uniform or varying degrees of radiosensitivity has not been established.Methods: Spatially distinct regions of three GBs (J3, J7 and J14) were resected and unique cell lines were derived from each region. DNA from cell lines, corresponding tumor fragments, and patient blood was extracted for whole exome sequencing. Variants, clonal composition, and functional implications were compared and analyzed with superFreq and IPA. Limiting dilution assays were performed on cell lines to measure intrinsic radiosensitivity.Results: Based on WES, cell lines generated from different regions of the same tumor were more closely correlated with their tumor of origin than the other GBs. Variant and clonal composition comparisons showed that cell lines from distinct tumors displayed increasing levels of ITH with J3 and J14 having the lowest and highest, respectively. Whereas the radiosensitivity of the cell lines generated from the J3 tumor were similar as were those generated from the J7 tumor, the radiosensitivities of the 2 cell lines generated from the J14 tumor (J14T3 and J14T6) were significantly different with J14T6 being more sensitive than J14T3.Conclusion: Data suggest a tumor dependent ITH in radiosensitivity. The existence of ITH in radiosensitivity may impact not only the initial therapeutic response but also the effectiveness of retreatment protocols.