Interplay between ATRX and IDH1 mutations governs innate immune responses in diffuse gliomas

Stimulating the innate immune system has been explored as a therapeutic option for the treatment of gliomas. Inactivating mutations in ATRX, defining molecular alterations in IDH-mutant astrocytomas, have been implicated in dysfunctional immune signaling. However, little is known about the interplay between ATRX loss and IDH mutation on innate immunity. To explore this, we generated ATRX-deficient glioma models in the presence and absence of the IDH1R132H mutation. ATRX-deficient glioma cells are sensitive to dsRNA-based innate immune agonism and exhibit impaired lethality and increased T-cell infiltration in vivo. However, the presence of IDH1R132H dampens baseline expression of key innate immune genes and cytokines in a manner restored by genetic and pharmacological IDH1R132H inhibition. IDH1R132H co-expression does not interfere with the ATRX deficiency-mediated sensitivity to dsRNA. Thus, ATRX loss primes cells for recognition of dsRNA, while IDH1R132H reversibly masks this priming. This work reveals innate immunity as a therapeutic vulnerability of astrocytomas.

Interplay between ATRX and IDH1 mutations governs innate immune responses in diffuse gliomas

Stimulating the innate immune system has been explored as a therapeutic option for the treatment of gliomas. Inactivating mutations in ATRX , defining molecular alterations in IDH -mutant astrocytomas, have been implicated in dysfunctional immune signaling. However, little is known about the interplay between ATRX loss and IDH mutation on innate immunity. To explore this, we generated ATRX knockout glioma models in the presence and absence of the IDH1 R 132 H mutation. ATRX-deficient glioma cells were sensitive to dsRNA-based innate immune agonism and exhibited impaired lethality and increased T-cell infiltration in vivo . However, the presence of IDH1 R 132 H dampened baseline expression of key innate immune genes and cytokines in a manner restored by genetic and pharmacological IDH1 R132H inhibition. IDH1 R132H co-expression did not interfere with the ATRX KO-mediated sensitivity to dsRNA. Thus, ATRX loss primes cells for recognition of dsRNA, while IDH1 R132H reversibly masks this priming. This work reveals innate immunity as a therapeutic vulnerability of astrocytoma.

IMMU-34. ATRX MUTATIONS PREDICT RESPONSE TO INNATE BASED THERAPY IN GLIOMA

BACKGROUND

Innate based immunotherapies are becoming increasingly important for treating brain tumor patients. Gliomas carry recurrent mutations in regulatory genes that control innate immune signaling responses. About 71% of adult WHO grade II and III gliomas and 57% of secondary glioblastomas also carry a loss-of-function mutation in the ATRX gene. ATRX is a SWI-SNF chromatin remodeling protein that has major roles in processes such as cell cycle regulation and maintenance of genomic stability. Recent studies have implicated ATRX in dysfunctional innate immune signaling in cancer cells. However, the role of ATRX in mediating innate immune responses has not been investigated in gliomas.

METHODS AND RESULTS

Human and mouse glioma cell lines from a variety of genetic contexts have been examined including models which carry IDH/ATRX mutations, IDH 1p-/19q- and ATRX -/- status. Additionally, using Crispr-Cas9 technology and cloning cell lines with ATRX deletions, we have derived a series of immune competent and nude mice models. Treating these cell lines with double-stranded RNA based innate stimuli led to an enhanced early induction in phospho-interferon regulatory factor 3 (IRF3) and late induction in phospho-STAT1 in the ATRX knockout (KO) cell lines. A differential increase in interferon-stimulated gene 15 (ISG15) release was also noted in the ATRX KO cell lines, further suggesting that ATRX deletion may enable a potent activation of type I interferon production. A combination of patient-derived glioma cell lines in xenograft models and syngeneic murine glioma models derived from ATRX KO cell lines and controls confirm a survival advantage in both immuno-competent mice and xenografts. Our models are under evaluation with PVSRIPO and other innate based RNA therapies.

CONCLUSION

Our data suggests that ATRX mutations may confer sensitivity to RNA-based innate immune signaling agonists in gliomas. This potential vulnerability can be targeted in future therapies.