Poly(ethylene) glycol-based bottlebrush polymers as nanocarriers for oligonucleotide therapeutics: design, synthesis, and applications

Abstract

Oligonucleotide therapeutics hold the promise of yielding treatments for a wide range of diseases while reducing the drug development cost and time. However, this promise has yet to be fully realized, with only 15 oligonucleotide drugs currently approved by FDA in the past two decades. Limitations associated with the intrinsic properties of nucleic acids include low cellular uptake, poor nuclease stability, rapid clearance in vivo, etc. The delivery and tissue targeting of oligonucleotide drugs have long been a key industry focus. Current strategies include chemical modifications and advanced carrier systems, which while effective, still face challenges such as poor non-liver biodistribution and carrier-associated toxicity and immunogenicity. A safe and highly efficient delivery platform for non-liver organs is still very much desired for oligonucleotides. In this dissertation, we develop poly(ethylene) glycol (PEG)-based bottlebrush polymer delivery systems for oligonucleotide therapeutics. The bottlebrush architecture does not significantly hinder the hybridization of an antisense oligonucleotide or the binding affinity of an aptamer that is conjugated to the backbone of the brush, but the local dense PEG environment protects the oligonucleotide payload from enzymatic degradation and rapid renal clearance in vivo. This unique characteristic leads to improved enzymatic stability, enhanced pharmacokinetic properties, and broad biodistribution. In chapter 2 to 4, we investigate the effective delivery of natural and chemically modified oligonucleotides targeting KRASMUT for the treatment of non-small cell lung carcinoma. Our results show that these bioconjugates exhibit effective reduction of KRAS levels both in vitro and in vivo without toxicity or immunological shortcomings. In chapter 5 and 6, we explore the backbone chemistry and develop non-aliphatic-backboned bottlebrushes with distinct biological properties. Two approaches are demonstrated: a DNA-backboned bottlebrush polymer with antisense oligonucleotide overhangs, and a polyphosphodiester-backboned bottlebrush polymer-aptamer conjugate. The DNA-backboned bottlebrush polymers facilitate effective cellular uptake and lead to in vitro phenotypic responses in KRASMUT cancer cells. The polyphosphodiester-backboned bottlebrush polymers maintain the typical characteristics of polynorbornene-backboned bottlebrush polymers, but exhibit suppressed cellular uptake level in several cell lines, making it an ideal delivery platform for aptamers which usually bind with extracellular targets. We demonstrate the in vivo efficacy of polyphosphodiester-backboned bottlebrush polymers conjugated with a thrombin-binding aptamer, which exhibit significantly improved in vivo bioactivity compared to the unmodified aptamer.--Author's abstract