Developing Immunotherapy Targeting Immune Suppression Using Spherical Nucleic Acids (SNAs)

Chou, Liyushang

doi:https://doi.org/10.21985/n2-hz2r-6y46

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Developing Immunotherapy Targeting Immune Suppression Using Spherical Nucleic Acids (SNAs)

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Cancer remains a leading cause of death worldwide, necessitating continued study to explore and unravel its complex etiology. For example, there has been a shift of focus in cancer treatment from surgery and radiotherapy to targeted chemo- and immunotherapies as we gain more knowledge on the hallmarks of cancer (e.g., uncontrolled cell proliferation triggered by genetic mutations, rewired cell signaling, dysregulated metabolism, and increased immune evasion mechanisms). Despite the success of combination therapies that involve immune checkpoint inhibitors and therapeutic antibodies, these treatments do not work for all patients; additionally, many people experience significant adverse off-target effects and/or develop complement-dependent cytotoxicity from long-term systemic use. Therefore, exploring alternative approaches to disrupting the interplay between programmed cell death protein 1 (PD-1) and programmed death ligand 1 (PD-L1) within the tumor microenvironment (TME) became another focus in the development of current cancer immunotherapies.Apart from antibody-based blocking of the PD1/PD-L1 pathway, the cascade of downstream inhibitory signaling could also be dampened via gene regulation strategies on PD-L1 expression using nucleic acid-based drugs. However, traditional delivery of such entities for therapeutic purposes suffers from insufficient cellular uptake or compartmental access and rapid nuclease degradation. Spherical nucleic acids (SNAs) consisting of spherical nanoparticle cores with densely packed and highly oriented oligonucleotides on their surfaces have been shown to deliver oligonucleotides via scavenger receptor-mediated endocytosis in biomedical applications with high efficacy. Indeed, compared to linear oligonucleotides of the same sequence, due to its unique three-dimensional architecture, SNAs: are more efficiently and rapidly taken up by cells; are more resistant to nuclease degradation; exhibit minimal cytotoxicity and immunogenicity; have extended circulation half-lives in vivo; show increased binding affinity to complementary mRNA targets (several orders of magnitude). Herein, I explore how immune suppression can be regulated by targeting PD-L1 using the SNA platform, gaining insight into how nucleic acid-nanoparticle constructs and gene silencing can be utilized for immunotherapy. In Chapter 2, I discuss the design principles that must be considered when developing nanoparticles useful for regulating protein expression. Furthermore, I studied the effects of silencing PD-L1 on the genetic level of its expression and presentation. With that knowledge, I then simulated the effects of depleting PD-L1 with SNAs on different types of cells to see how T cell toxicity is influenced (Chapter 3). Finally, I explored an SNA-based approach to treating tumors in animal models, focusing on how SNAs reprogram the TME and influence anti-tumor response. In Chapter 4, I compared PD-L1 levels after treatment with SNA-based or traditional anti-PD-L1 antibody treatments. Through these in vitro and in vivo biological studies, I developed a keen understanding of how regulating a single protein on the genetic level can initiate downstream biological effects in multiple settings. Taken together, this work lays a framework for using new nanomaterials, SNAs in particular, as potent immunotherapeutic agents.

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