IDH Targeting Nanoparticles for In Vivo Imaging and Treatment of Diffuse Gliomas

P. Hardy, T. Dziubla, C. Horbinski, and M. Knecht

High-throughput whole genome analyses of gliomas have recently discovered the presence of mutations in genes encoding isocitrate dehydrogenase types 1 and 2 (IDH1 and IDH2). These mutations, which are restricted to the isocitrate-binding sites of each enzyme, are present in 80-90% of grade 2 and 3 astrocytomas, oligodendrogliomas, and secondary glioblastomas (i.e. grade 4 tumors that developed from lower-grade gliomas). Also, recent work has uncovered a novel function for these mutant IDH1 and IDH2 enzymes, wherein alpha-ketoglutarate is reduced to 2-hydroxyglutarate (2- HG). (Figure 1) Of particular significance, IDH1/2-mutated gliomas produce more 2-HG, by one to two orders of magnitude, compared to tumors that are wild-type for IDH1/2.

Figure 1: Mutations in IDH1/2 impart new enzymatic activity. Whereas wild-type IDH1/2 converts isocitrate to alpha-ketoglutarate, mutant IDH1 enzyme converts alpha-ketoglutarate into D-2-HG. This metabolite is present at one to two full orders of magnitude greater concentrations in gliomas carrying IDH1/2 mutations compared to nonneoplastic tissue and wild-type gliomas.

This local accumulation of 2-HG can therefore be exploited as a means of therapeutic and diagnostic targeting. In this project, trainees will learn how to identify IDH1/2-mutant gliomas in the laboratory of Dr. Horbinski, who has recently demonstrated the ability of targeted PCR and direct sequencing to detect IDH1/2 mutations in paraffin-embedded tissue sections. Additionally, trainees will learn adjunct immunohistochemical methods of detecting the most common mutation, R132H IDH1, in Dr. Horbinski’s laboratory. Then, in the laboratories of Knecht and Dziubla, trainees will learn how to develop nanoparticle targeting systems. Using strategies developed for the targeting and binding of small molecule targets (e.g., adenosine, cocaine and ltyrosinamide, trainees will work to develop novel targeting agents (e.g., oligonucleotide aptamers, peptides, and antibodies) which can be used for both imaging and therapeutic targeting. Finally, in the laboratory of Dr. Hardy, trainees will learn to apply these carriers into the central nervous system using convective-enhanced delivery technologies. This would allow for more accurate, real-time imaging of diffuse gliomas, thereby facilitating more extensive surgical resection. To accomplish this, chemically-functionalized gold nanoparticles will be administered near the tumor site. The nanoparticles will be surface-functionalized with the aforementioned targeting agents that recognize and bind 2-HG. Upon exposure to regions of elevated 2-HG, nanoparticles will aggregate, thus inducing a grossly-visible darkening of the glioma. (Figure 2) These color changes would allow the neurosurgeon to more easily distinguish tumor from normal brain tissue. Such aggregation could also help to provide localized delivery of chemotherapeutic agents, thus promoting cancer cell death while reducing damage to normal brain tissue.

Figure 2: Nanoparticle-based detection of gliomas in neurosurgery. (1) Brain tumor is removed from patient during surgery. (2) Tumor is exposed to nanoparticle-based reagent designed to bind 2-HG. (3) If low levels of 2-HG are present, no color change occurs; the tissue could therefore represent a variety of diseases. (4) If tissue has elevated 2-HG, nanoparticles aggregate and color changes from bright red to dark blue. The neurosurgeon thus knows the tissue must contain an IDH1/2 mutation, meaning it is an infiltrative glioma.