IMG-02. VISUALIZATION OF TIGIT IN THE GLIOMA MICROENVIRONMENT: THE CREATION OF A PET IMAGING TRACER

Pediatric high-grade gliomas (HGGs) are aggressive tumors and are one of the drivers of pediatric brain tumor mortality. Few effective treatment options exist for pediatric HGGs beyond surgery and chemoradiation. Additionally, some HGGs, such as diffuse midline glioma, are often surgically inaccessible and respond poorly to chemotherapy leaving radiotherapy as the only treatment for this disease. While immune checkpoint inhibitors (ICIs) have seen success in treating cancers outside the CNS, ICIs for gliomas have shown limited efficacy. TIGIT is an IC receptor that is expressed on activated T-cells and has a critical role in suppressing T-cell and NK cell function. Prior work by our group has shown TIGIT to be a promising target for adult gliomas. These studies included analysis of transcriptomic data, and preclinical studies in glioma-bearing mice. We therefore assessed pediatric glioma transcriptomic datasets and identified via optimal cutoff analysis that at a specific mRNA threshold, TIGIT expression is associated with worsened survival. As TIGIT expression may be both prognostic and a biomarker for anti-TIGIT ICI therapy, we created a radiolabeled immunoPET tracer capable of binding TIGIT antigen that could be visualized via PET imaging. Referred to as “89Zr-DFO-TIGIT”, we found this tracer bound TIGIT with moderate immunoreactivity (57.7% ± 3.5%) as determined by bead-based immunoreactivity assays. As proof of feasibility, we injected glioma-bearing mice (GL261 cell line) with 89Zr-DFO-TIGIT which enabled the visualization of TIGIT in the tumor microenvironment via PET imaging. Thereafter, we performed biodistribution studies which found there to be significantly increased 89Zr-DFO-TIGIT in mouse tumor-bearing hemispheres as compared to non-tumor-bearing hemispheres. PET imaging also showed tracer-to-tumor uptake increased from day one to day eight. Our findings demonstrate the capability of 89Zr-DFO-TIGIT to visualize and quantify TIGIT in the glioma microenvironment, highlighting how this tracer may be of value in pediatric brain tumor immunotherapy studies.