A Transcriptional Fingerprint Of Carbon Ion Radiotherapy In Patients With Recurrent Glioma Utilizing Peripheral Blood As A Sentinel Organ

Re-irradiation with carbon ions (RiCi) seems to be a promising treatment strategy in patients with recurrent high-grade glioma (rHGG). Studying radiobiological effects of RiCi is limited by the lack of sequential tumor tissue. We hypothesized that blood cells traversing the tumor during irradiation as well as systemic effects of focal tumor irradiation may leave a molecular fingerprint. Patients with rHGG who were treated with RiCi (33 (30-36) GyRBE in 11 (10-12) fractions) underwent repeated blood sampling (total: n=51), starting prior to irradiation (max. 21 days before therapy start) and at three further time-points post RiCi in 3-6-week intervals (up to max. 92 days after start of irradiation). Whole blood, collected in PAXgene Blood RNA Tubes, was used for total-RNA extraction using the PAXgene Blood RNA Kit (Qiagen). Quality of RNA was checked with a NanoDropTM 1000 spectrophotometer and on Bioanalyzer (Agilent) Illumina BeadChip arrays (HumanHT-12 Expression BeadChip). Time (pre- vs. post-RiCi and continuous) as well as dose specific transcriptome alterations were evaluated. A RiCi specific peripheral whole blood transcriptome signature of 47 genes could be identified comparing pre- vs. post-RiCi samples. Pathway enrichment analysis (KEGG) identified TCA cycle (p=0.002), pathways in cancer (p=0.004) and HIF-1 signaling (p=0.002) to be affected by RiCi. A random forest based selection of genes best discriminating between timepoints of analysis followed by cluster analysis revealed the largest differential effects early after irradiation. Most genes return to baseline at later timepoints, however, few candidates show a more pronounced differential effect at the late timepoint (i.e. time point 3 vs. 1 post RiCi). Focal intracranial irradiation with carbon ions leads to a specific blood transcriptome signature. This approach provides a novel mean for establishing peripheral blood as a sentinel organ for longitudinal investigation of particle radiobiology.