# Immuno-PET for Glioma Imaging: An Update
## 5 Discussion
It is crucial to note that, while highly aggressive gliomas like GBM lead to significant BBB leakage, facilitating the integration of radiopharmaceuticals into tumors, low-grade gliomas may maintain an intact BBB, obstructing the passage of radiolabeled mAbs. To address challenges associated with BBB permeability, researchers have devised antibody-based carriers that utilize the inherent macromolecule transportation pathway known as receptor-mediated transcytosis (RMT). A substantial portion of existing studies in this area focus on RMT receptors, specifically the transferrin receptor (TfR), insulin receptor (InsR), and FC5 antibody binding receptor [63]. Adopting this approach involves the utilization of bispecific antibodies (BsAbs), whichpossess the capability to bind to RMT-associated receptors with one arm, facilitating BBB crossing. Once within the brain, the other arm of these BsAbs can target tumor-associated biomarkers. In this context, [PERSON] and colleagues developed a BsAb that activates cells, demonstrating promising outcomes in orthotopic patient-derived malignant glioma and syngeneic glioblastoma in mice [64]. This innovative BsAb comprises two single-chain antibody fragments (bi-scFvs) that bind to the mutant epidermal growth factor receptor variant III (EGFRIII), a common mutation GBM, and human CD3\(\varepsilon\) on T cells. Consequently, the BsAb-based approaches hold considerable potential and merit further exploration to address BBB permeability challenges, especially in the case of low-grade gliomas, thereby expanding the range of applications for immuno-PET in clinical settings. Another potential critique of immuno-PET in gliomas is associated with the mechanisms through which various tracers are assimilated [65]. There is a hypothesis that their incorporation may be more indicative of BBB disruption than relying on specific biomarker-mediated processes. This aspect warrants further investigation in future studies. Shaping the future of immuno-PET in gliomas will depend significantly on the synergy between technology and radiopharmaceutical research. For instance, aptamers, single-stranded oligonucleotide DNA or RNA sequences, exhibit extremely high specificity toward tumor-associated biomarkers without inducing immunogenicity [66]. However, despite their promise, radiolabeled aptamers have seen limited application in PET imaging. Other noteworthy advancements include the incorporation of glioma-associated biomarkers for functionalizing nanoparticles, paving the way for radiotheranostic-based approaches [67; 68]. In the near future, the significance and potential integration of immuno-PET in the diagnostic evaluation of gliomas will be enhanced through a comparative analysis with alternative non-radionuclide-based imaging techniques, including fluorescence and bioluminescent imaging. Regarding fluorescence imaging, particularly Near-Infrared Fluorescence (NIRF) has garnered increasing attention due to its safety, detection sensitivity, and resolution [69]. This makes it a valuable tool for the early diagnosis and visualization of various cancer types, given its convenience. Cyanine and its derivatives have been developed to emit visible light when excited by a specific wavelength, rendering them valuable tools for biological imaging [70]. In this context, it is noteworthy to highlight the significance of tumor specific Heptamethine Cyanine Dyes (HMCDs). Originally recognized for their fluorescent and mitochondria-targeting properties, these compounds have demonstrated a distinct preference for tumor up-take both in vitro and in animal models. Furthermore, their ability to cross the BBB positions HMCDs as an appealing platform for drug delivery systems. However, as of now, only indocyanine green (ICG) and methylene blue have received approval from the Food and Drug Administration for use in medical diagnostics as near-infrared fluorescent (NIRF) compounds.