Year 3 Spherical Nucleic Acids for the treatment of pediatric high-grade gliomas

Pediatric high-grade gliomas (p-HGGs), including Glioblastoma multiforme (GBM) and diffuse intrinsic pontine glioma (DIPG) are the most aggressive primary central nervous system (CNS) tumors in children and young adults, and responsible for the majority of cancer-related mortality with a median survival of only 12-16 months. Such dismal prognosis has not changed significantly over the past decades, as effective chemotherapy regimens for p-HGG have yet to be identified. While efforts in the basic sciences have unraveled a plethora of cancer genes implicated in the genesis of p- HGG, they have, however, rarely led to the implementation of gene-specific, i.e., ‘targeted’ therapies, in part, because many cancer genes cannot be targeted by conventional pharmacological means, such as small molecules or biotherapeutic antibodies, and are classified as ‘undruggable’. In addition, brain and brain tumor tissue is separated from circulating blood by the blood-brain-barrier (BBB), which restrict the diffusion of macromolecules, including most therapeutic agents. Consequently, two of the most fundamental questions in p-HGG research and drug development are: How can therapeutic agents be effectively delivered to intracerebral tumor sites to specifically target cancer genes? And how can ‘undruggable’ cancer genes be functionally neutralized? To address these challenges, we propose to characterize an entirely new class of RNA interference (RNAi)-based gene regulation platforms, termed spherical nucleic acids (SNAs) for the treatment of p-HGG. SNAs are composed of gold nanoparticles with a diameter of 13 nm, and are conjugated with small inhibitory (si)RNA sequences to trigger RNAi in tumors. Early studies indicated that RNAi has the potential to silence expression of various cancer genes implicated in growth and cell death, and consequently has motivated myriad preclinical studies to assess the potential of RNAi as anti-cancer therapeutics. Due to the negative charge of the RNA backbone, however, siRNA oligonucleotides do not penetrate negatively charged membranes effectively, cannot silence gene expression robustly and persistently in tissue in vivo, have significant cytotoxic side effects, trigger auto-immune responses, and cannot cross the blood-brain-barrier (BBB). In contrast, our studies indicated that SNAs are able to transverse cellular membranes, do not require the use of toxic auxiliary reagents, and accumulate in cells very effectively. They also exhibit extraordinary stability in physiological environments, are highly resistant to nuclease degradation, and thus, can move through biological fluids and avoid being destroyed as “foreign materials.” We have evaluated this platform for the treatment of adult GBM We could demonstrate that upon systemic, intravenous administration, SNAs selectively accumulated within intracerebral lesions, provoked robust intratumoral target gene knockdown, reduced tumor burden in a GBM mouse models, and consequently represent a fundamentally novel treatment option for adult GBM patients. Here, we propose to evaluate the SNA platform as a therapeutic modality for p-HGG. We propose to decorate particles with siRNAs specifically targeting the expression of histone modifiers, foremost SUZ1, a critical component of the Polycomb repressive complexe 2 (PRC2), which represses transcription through methylation of lysine residues of histone H3. This proposal aims to establish proof-of-concept that SNA-directed targeting of histone modifiers can inhibit p-HGG progression.