Identification of CXCL10-CXCR3 axes as mediators of radioresistance in diffuse midline glioma (DMG)

Diffuse Midline Gliomas (DMGs) are aggressive, universally fatal brain tumors with a 100% recurrence rate driven by therapeutic resistance. Many molecular therapies target epigenetically driven gene expression changes in DMG H3K27M-altered tumors, but whether they target methylation, acetylation, or downstream vulnerabilities, these treatments have failed to prevent recurrence. Since no recent therapies have prompted long-term responses, radiation remains the standard of care; however, radiotherapy often suppresses an immune response, and when tumors recur, an immune suppressive and tumor promoting microenvironment provides a niche for tumor cells to regrow uncontrollably. In preliminary studies utilizing single-cell RNA sequencing (scRNA-seq) in a murine model of DMG, we uncovered a complex cellular tumor microenvironment that is modulated upon radiotherapy. In fact, radiation therapy significantly increased the expression of pro-tumorigenic genes in both PDGFRA+ DMG cells (e.g., Tgfa, IL133, Fgf2, Pdgfa) and tumor associated-microglial cells (e.g., IL4i1, IL33, Fgf2, Tgfbr1), suggesting a coordinated pro-tumorigenic response. Furthermore, CXCL10 dramatically increased in tumor cells (DMG) in response to radiotherapy, whereas CXCR3 was found to be predominantly expressed in T cells in these tumors. Interestingly, CXCL10 has previously been shown to be associated with macrophage infiltration and cell proliferation, and expression of the chemokine receptor/ligand pair CXCR3/CXCL10 plays an important role in the proliferation of glioma cells (Pessina et al. Oncoimmunology 2015). These findings suggest radiotherapy-induced immunosuppression occurs through the CXCL10-CXCR3 axis, and thus, in ongoing studies, we are evaluating whether blockade of CXCL10-CRCR3 axes can prevent radioresistance. Lastly, as previously hypothesized, we detected an increase in stemness gene expression in radiated tumors, which was prevented when mice were treated with a pan-ALDH inhibitor (CVT-10216). In summary, we have characterized the stromal and immune tumor microenvironment in untreated and radiated DMG and have identified potential targets that may inform future therapeutic strategies to prevent recurrence.