Monoallelic IDH1 R132H mutation mediates glioma cell response to anticancer therapies via induction of senescence

Heterozygous isocitrate dehydrogenase (IDH) R132H mutation (IDH1R132H/WT) is an early event during gliomagenesis. Clinically, patients with glioma carrying mutant IDH1 respond better to antitumor therapies. However, the mechanism by which IDH1 mutations contribute to gliomagenesis and therapeutic response remains elusive. Here we report that senescence is involved in the improved therapeutic responses of mutant IDH1 glioma cells. Knocking-in IDH1R132H/WT in glioma cells significantly enhanced gliomas cell senescence in response to temozolomide and radiation via a DNA-damage mediated mechanism. We further asked if senescence plays a role in IDH1R132H/ WT-induced gliomagenesis. Together with ATRX knockout and p53/RB loss, IDH1R132H/WT transformed nonneoplastic human astroglial cells to form tumors in mouse brains. In-depth characterization revealed that a subset of these precancerous cells underwent senescence-like phenotypic changes, including flat and enlarged-cell morphology, increased senescence marker expression, decreased cell proliferation, and cell-cycle arrest at the G2-M phase. Mechanistic studies indicated that the combination of glioma driver genes (p53/RB/IDH1/ATRX) dramatically increased DNA damage and activated DNAdamage response (DDR) pathways ATR/ATR and Chk1/Chk2 in senescent cells. To determine how senescent cells drive tumor formation, we investigated non-cell-autonomous mechanisms such as senescence-associated secretory phenotype (SASP), a panel of proinflammatory and tissue-remodeling factors implicated in a tumor-permissive microenvironment. We found that astroglial cells carrying p53/RB/ATRX loss and IDH1R132H/WT upregulated key factors in SASP via an epigenetic-mediated mechanism. Our work suggests that drugs that specifically eliminate senescent cells could help kill precancerous cells and senescent tumor cells following antitumor therapies. Implications: The mechanisms by which IDH1 mutations contribute to gliomagenesis and therapeutic responses remain incompletely characterized; this work reveals senescence as a novel mechanism of IDH-mutant-mediated biological impact and describes new therapeutic opportunities concerning IDH1-mutant gliomas.