TP53 Pathway Alterations Drive Radioresistance in Diffuse Intrinsic Pontine Gliomas (DIPG).

Abstract

Diffuse intrinsic pontine gliomas (DIPG) are the most severe pediatric brain tumors. Although accepted as the standard therapeutic, radiotherapy is only efficient transiently and not even in every patient. The goal of the study was to identify the underlying molecular determinants of response to radiotherapy in DIPG. We assessed <i>in vitro</i> response to ionizing radiations in 13 different DIPG cellular models derived from treatment-naïve stereotactic biopsies reflecting the genotype variability encountered in patients at diagnosis and correlated it to their principal molecular alterations. Clinical and radiologic response to radiotherapy of a large cohort of 73 DIPG was analyzed according to their genotype. Using a kinome-wide synthetic lethality RNAi screen, we further identified target genes that can sensitize DIPG cells to ionizing radiations. We uncover <i>TP53</i> mutation as the main driver of increased radioresistance and validated this finding in four isogenic pairs of <i>TP53^WT</i> DIPG cells with or without <i>TP53</i> knockdown. In an integrated clinical, radiological, and molecular study, we show that <i>TP53^MUT</i> DIPG patients respond less to irradiation, relapse earlier after radiotherapy, and have a worse prognosis than their <i>TP53^WT</i> counterparts. Finally, a kinome-wide synthetic lethality RNAi screen identifies CHK1 as a potential target, whose inhibition increases response to radiation specifically in <i>TP53^MUT</i> cells. Here, we demonstrate that <i>TP53</i> mutations are driving DIPG radioresistance both in patients and corresponding cellular models. We suggest alternative treatment strategies to mitigate radioresistance with CHK1 inhibitors. These findings will allow to consequently refine radiotherapy schedules in DIPG.