Abstract Pediatric-type diffuse high-grade gliomas (pHGG) are the most frequent malignant brain tumors in children. Current treatment options, including radiotherapy (RT), are mostly limited to palliative benefits. Modulating the efficacy of RT by identifying pHGG-specific mediators of inherent and acquired radioresistance, including RT-induced microenvironmental changes, might reveal novel treatment strategies. We are generating a comprehensive collection of untreated, X-ray irradiated and radioresistant pHGG samples in vitro and in vivo. Therefore, we utilize our unique portfolio of syngeneic autochthonous and orthotopic allograft models driven by distinct receptor tyrosine kinase alterations providing an otherwise homogenous genetic background. In vitro radiation dose-response screening on these models (n = 15) revealed broad differences in radiosensitivity, largely dependent on the respective tumor suppressor knockout (Cdkn2a or Trp53). Comparison with in vivo dose-response data from pHGG allografts (n = 7) showed unexpected discrepancies. Some models displayed a high sensitivity in vitro but low sensitivity in vivo, or vice versa. These inconsistencies suggest a modulatory role of the tumor microenvironment that outweighs cell-intrinsic resistance mechanisms. To further investigate this interplay, we are currently characterizing these models on a single-cell level and are performing competition assays in vitro and in vivo. In parallel, we are treating one of our models with a total of eight cycles of RT and treatment pause over multiple allograft passages. Tumor samples are collected at defined time points throughout all in vivo passages allowing us to closely follow the potential acquisition of radioresistance. Samples receive a maximum of 48 x 2Gy fractions, including clinically-relevant RT exposures, in contrast to commonly used 10-20Gy total dose regimens in mice. Single-cell RNA sequencing will enable the identification of RT related changes in the tumor microenvironment, tumor cell composition and tumor cell identities. Based on the outcome of our studies, we will test rationale combination therapies in a preclinical setting.
Parzer et al. (Tue,) studied this question.