Targeting oncogenic KRAS with molecular brush-conjugated antisense oligonucleotides

Tumor-Selective Gene Therapy: Using Hairpin DNA Oligonucleotides to Trigger Cleavage of Target RNA by Endogenous flap endonuclease 1 (FEN 1) Highly Expressed in Tumor Cells

Nucleic acid drugs, which trigger gene silencing by hybridizing with target genes, have shown great potential in targeting those undruggable targets. However, most of the existing nucleic acid drugs are only sequence specific for target genes and lack cellular or tissue selectivity, which challenges their therapeutic safety. Here, the study proposes a tumor cell-specific gene silencing strategy by using hairpin DNA oligonucleotides to trigger target RNA degrading by highly expressed endogenous flap endonuclease 1 (FEN1) in tumor cells, for selective tumor therapy. Using Kirsten rat sarcoma viral oncogene homolog (KRASG12S) and B-cell lymphoma 2 (Bcl-2) genes as targets, it is verified that the hairpin DNA oligonucleotides show cytotoxicity only to tumor cells but very low effects on normal cells. In addition, hairpin DNA oligonucleotides designed for KRAS inhibition, which are encapsulated in lipid nanoparticles, inhibit tumor growth in mice and demonstrate excellent antitumor efficacy in combination with gefitinib, but has little effect on normal tissues, suggesting that the proposed strategy enables highly selective tumor therapy and has the potential to give rise to a new class of nucleic acid drugs.

Molecular Structure of Foldable Bottlebrush Polymers in Melts

A bottlebrush polymer consists of a long linear backbone densely grafted with many relatively short side chains. A widely accepted view is that strong steric repulsion among the highly overlapped side chains prestrains the bottlebrush backbone, resulting in low polymer extensibility. However, we recently discovered that in the melt of bottlebrush polymers with highly incompatible side chains and backbone, the backbone collapses to reduce interfacial free energy, regardless of the strong steric repulsion among side chains. Despite this discovery, the molecular structure of these so-called "foldable" bottlebrush polymers and their assemblies remains poorly understood. Here, we present the deterministic relationships among molecular architecture, mesoscopic conformation, and macroscopic properties of foldable bottlebrush polymers. A combination of scaling theory and experiments reveals that as the side chain grafting density decreases, the bottlebrush diameter increases, whereas the bottlebrush end-to-end distance decreases. These behaviors contradict the existing understanding of bottlebrush polymers, which assumes that the backbone and side chains are compatible. Since foldable bottlebrush polymers store lengths that can be released upon large deformations, they offer a way to decouple the intrinsic stiffness-extensibility trade-off in single-network elastomers. These findings provide foundational insights into using foldable bottlebrush polymers as building blocks for designing soft (bio)materials.

Point Mutation Selective Photo-Cross-Linking Reactions by Diazirine-Derivatized ODNs

Point mutations and single base mutations are the dominant mutations found in the KRAS gene. Systematic knockout of the KRAS gene with these point mutations is still challenging. In this study, we developed novel photo-cross-linking oligonucleotides (pU1-ODN and pU2-ODN) that had a diazirine group at the 5-position of the uridine derivatives. Photo-cross-linking studies of the oligonucleotides with wild-type and mutated RNAs revealed that pU2-ODN efficiently and selectively reacts with the mutated RNAs that contain a cytidine, guanosine, or uridine residue at the frontal position of the pU2 nucleoside. These results suggest that pU2-ODN is a promising candidate for use as a photo-cross-linking ODN to selectively inhibit the activity of mRNAs with a point mutation.

Responsive Degradable Bottlebrush Polymers Enable Drugs With Superior Efficacy and Minimal Systemic Toxicity

Bottlebrush polymers (BBPs) have garnered significant attention as advanced drug delivery systems, capable of transporting a diverse range of therapeutic agents, including both chemical drugs and biologics. Despite their effectiveness, the empty BBP vectors post-drug release may pose long-term safety risks due to their difficult systemic clearance. Here, a responsive degradable BBP platform for cancer therapy is developed, featuring a poly(disulfide) backbone grafted with fluorine-terminated zwitterionic side chains. Anti-cancer drugs are tethered to the backbone via a clinically approved valine-citrulline (VC) linker. This design leverages the tumor's reductive environment and Cathepsin B overexpression for BBP rapid degradation and precise drug release restricted within tumor cells, thereby addressing systemic safety concerns over synthetic BBP and expanding the therapeutic window of anti-cancer drugs simultaneously. Surface fluorination of BBP further enhances tumor accumulation and deep penetration. In vivo studies with monomethyl auristatin E (MMAE)-loaded BBP in tumor-bearing mice demonstrate substantial tumor suppression with minimal side effects. Together, these findings highlight the potential of responsive degradable BBP as a versatile unimolecular platform for cancer drug delivery, addressing existing challenges associated with synthetic BBP nanomedicines.

A Manual for Genome and Transcriptome Engineering

Genome and transcriptome engineering have emerged as powerful tools in modern biotechnology, driving advancements in precision medicine and novel therapeutics. In this review, we provide a comprehensive overview of the current methodologies, applications, and future directions in genome and transcriptome engineering. Through this, we aim to provide a guide for tool selection, critically analyzing the strengths, weaknesses, and best use cases of these tools to provide context on their suitability for various applications. We explore standard and recent developments in genome engineering, such as base editors and prime editing, and provide insight into tool selection for change of function (knockout, deletion, insertion, substitution) and change of expression (repression, activation) contexts. Advancements in transcriptome engineering are also explored, focusing on established technologies like antisense oligonucleotides (ASOs) and RNA interference (RNAi), as well as recent developments such as CRISPR-Cas13 and adenosine deaminases acting on RNA (ADAR). This review offers a comparison of different approaches to achieve similar biological goals, and consideration of high-throughput applications that enable the probing of a variety of targets. This review elucidates the transformative impact of genome and transcriptome engineering on biological research and clinical applications that will pave the way for future innovations in the field.

Multiarm-Assisted Design of Dendron-like Degradable Ionizable Lipids Facilitates Systemic mRNA Delivery to the Spleen

Lipid nanoparticles (LNPs) have emerged as pivotal vehicles for messenger RNA (mRNA) delivery to hepatocytes upon systemic administration and to antigen-presenting cells following intramuscular injection. However, achieving systemic mRNA delivery to non-hepatocytes remains challenging without the incorporation of targeting ligands such as antibodies, peptides, or small molecules. Inspired by comb-like polymeric architecture, here we utilized a multiarm-assisted design to construct a library of 270 dendron-like degradable ionizable lipids by altering the structures of amine heads and multiarmed tails for optimal mRNA delivery. Following in vitro high-throughput screening, a series of top-dendron-like LNPs with high transfection efficacy were identified. These dendron-like ionizable lipids facilitated greater mRNA delivery to the spleen in vivo compared to ionizable lipid analogs lacking dendron-like structure. Proteomic analysis of corona-LNP pellets showed enhancement of key protein clusters, suggesting potential endogenous targeting to the spleen. A lead dendron-like LNP formulation, 18-2-9b2, was further used to encapsulate Cre mRNA and demonstrated excellent genome modification in splenic macrophages, outperforming a spleen-tropic MC3/18PA LNP in the Ai14 mice model. Moreover, 18-2-9b2 LNP encapsulating therapeutic BTB domain and CNC homologue 1 (BACH1) mRNA exhibited proficient BACH1 expression and subsequent Spic downregulation in splenic red pulp macrophages (RPM) in a Spic-GFP transgene model upon intravenous administration. These results underscore the potential of dendron-like LNPs to facilitate mRNA delivery to splenic macrophages, potentially opening avenues for a range of mRNA-LNP therapeutic applications, including regenerative medicine, protein replacement, and gene editing therapies.

Diagnostic and Therapeutic Advances of RNAs in Precision Medicine of Gastrointestinal Tumors

Gastrointestinal tumors present a significant challenge for precision medicine due to their complexity, necessitating the development of more specific diagnostic tools and therapeutic agents. Recent advances have positioned coding and non-coding RNAs as emerging biomarkers for these malignancies, detectable by liquid biopsies, and as innovative therapeutic agents. Many RNA-based therapeutics, such as small interfering RNA (siRNA) and antisense oligonucleotides (ASO), have entered clinical trials or are available on the market. This review provides a narrative examination of the diagnostic and therapeutic potential of RNA in gastrointestinal cancers, with an emphasis on its application in precision medicine. This review discusses the current challenges, such as drug resistance and tumor metastasis, and highlights how RNA molecules can be leveraged for targeted detection and treatment. Additionally, this review categorizes specific diagnostic biomarkers and RNA therapeutic targets based on tissue type, offering a comprehensive analysis of their role in advancing precision medicine for gastrointestinal tumors.

Bottlebrush Polymers with Sequence-Controlled Backbones for Enhanced Oligonucleotide Delivery

The clinical translation of oligonucleotide-based therapeutics continues to encounter challenges in delivery. In this study, we introduce a novel class of delivery vehicles for oligonucleotides that are based on poly(ethylene glycol) (PEG) bottlebrush polymers with sequence-defined backbones. Using solid-phase synthesis and bespoke phosphoramidites, the oligonucleotide and the polymer backbone can be assembled on the solid support. The synthesis allows chemical modifiers such as carbon 18 (C18) units to be incorporated into the backbone in specific patterns to modulate the cell-material interactions. Subsequently, PEG side chains were grafted onto the polymer segment of the resulting polymer-oligonucleotide conjugate, yielding bottlebrush polymers. We report an optimal pattern of the C18 modifier that leads to improved cellular uptake, plasma pharmacokinetics, biodistribution, and antisense activity in vivo. Our results provide valuable insights into the structure-property relationship of polymer-oligonucleotide conjugates and suggest the possibility of tuning the polymer backbone to meet the specific delivery requirements of various diseases.

High-content tailoring strategy to improve the multifunctionality of functional nucleic acids

Functional nucleic acids (FNAs) have attracted increasing attention in recent years due to their diverse physiological functions. The understanding of their conformational recognition mechanisms has advanced through nucleic acid tailoring strategies and sequence optimization. With the development of the FNA tailoring techniques, they have become a methodological guide for nucleic acid repurposing. Therefore, it is necessary to systematize the relationship between FNA tailoring strategies and the development of nucleic acid multifunctionality. This review systematically categorizes eight types of FNA multifunctionality, and introduces the traditional FNA tailoring strategy from five aspects, including deletion, substitution, splitting, fusion and elongation. Based on the current state of FNA modification, a new generation of FNA tailoring strategy, called the high-content tailoring strategy, was unprecedentedly proposed to improve FNA multifunctionality. In addition, the multiple applications of rational tailoring-driven FNA performance enhancement in various fields were comprehensively summarized. The limitations and potential of FNA tailoring and repurposing in the future are also explored in this review. In summary, this review introduces a novel tailoring theory, systematically summarizes eight FNA performance enhancements, and provides a systematic overview of tailoring applications across all categories of FNAs. The high-content tailoring strategy is expected to expand the application scenarios of FNAs in biosensing, biomedicine and materials science, thus promoting the synergistic development of various fields.

Bottlebrush Polyethylene Glycol Nanocarriers Translocate across Human Airway Epithelium via Molecular Architecture-Enhanced Endocytosis

Pulmonary drug delivery is critical for the treatment of respiratory diseases. However, the human airway surface presents multiple barriers to efficient drug delivery. Here, we report a bottlebrush poly(ethylene glycol) (PEG-BB) nanocarrier that can translocate across all barriers within the human airway surface. Guided by a molecular theory, we design a PEG-BB molecule consisting of a linear backbone densely grafted by many (∼1000) low molecular weight (∼1000 g/mol) polyethylene glycol (PEG) chains; this results in a highly anisotropic, wormlike nanocarrier featuring a contour length of ∼250 nm, a cross-section of ∼20 nm, and a hydrodynamic diameter of ∼40 nm. Using the classic air-liquid-interface culture system to recapitulate essential biological features of the human airway surface, we show that PEG-BB rapidly penetrates through endogenous airway mucus and periciliary brush layer (mesh size of 20-40 nm) to be internalized by cells across the whole epithelium. By quantifying the cellular uptake of polymeric carriers of various molecular architectures and manipulating cell proliferation and endocytosis pathways, we show that the translocation of PEG-BB across the epithelium is driven by bottlebrush architecture-enhanced endocytosis. Our results demonstrate that large, wormlike bottlebrush PEG polymers, if properly designed, can be used as a carrier for pulmonary and mucosal drug delivery.

Bottlebrush polyethylene glycol nanocarriers translocate across human airway epithelium via molecular architecture enhanced endocytosis

Pulmonary drug delivery is critical to the treatment of respiratory diseases. However, the human airway surface presents multiscale barriers to efficient drug delivery. Here we report a bottlebrush polyethylene glycol (PEG-BB) nanocarrier that can translocate across all barriers within the human airway surface. Guided by the molecular theory, we design a PEG-BB molecule consisting of a linear backbone densely grafted by many (∼1,000) low molecular weight (∼1000 g/mol) PEG chains; this results in a highly anisotropic, wormlike nanocarrier featuring a contour length of ∼250 nm, a cross-section of ∼20 nm, and a hydrodynamic diameter of ∼40 nm. Using the classic air-liquid-interface culture system to recapitulate essential biological features of the human airway surface, we show that PEG-BB rapidly penetrates through endogenous airway mucus and periciliary brush layer (mesh size of 20-40 nm) to be internalized by cells across the whole epithelium. By quantifying the cellular uptake of polymeric carriers of various molecular architectures and manipulating cell proliferation and endocytosis pathways, we show that the translocation of PEG-BB across the epithelium is driven by bottlebrush architecture enhanced endocytosis. Our results demonstrate that large, wormlike bottlebrush PEG polymers, if properly designed, can be used as a novel carrier for pulmonary and mucosal drug delivery.

Table of Contents

Chemically Modified Platforms for Better RNA Therapeutics

RNA-based therapies have catalyzed a revolutionary transformation in the biomedical landscape, offering unprecedented potential in disease prevention and treatment. However, despite their remarkable achievements, these therapies encounter substantial challenges including low stability, susceptibility to degradation by nucleases, and a prominent negative charge, thereby hindering further development. Chemically modified platforms have emerged as a strategic innovation, focusing on precise alterations either on the RNA moieties or their associated delivery vectors. This comprehensive review delves into these platforms, underscoring their significance in augmenting the performance and translational prospects of RNA-based therapeutics. It encompasses an in-depth analysis of various chemically modified delivery platforms that have been instrumental in propelling RNA therapeutics toward clinical utility. Moreover, the review scrutinizes the rationale behind diverse chemical modification techniques aiming at optimizing the therapeutic efficacy of RNA molecules, thereby facilitating robust disease management. Recent empirical studies corroborating the efficacy enhancement of RNA therapeutics through chemical modifications are highlighted. Conclusively, we offer profound insights into the transformative impact of chemical modifications on RNA drugs and delineates prospective trajectories for their future development and clinical integration.

Organ/Cell-Selective Intracellular Delivery of Biologics via N-Acetylated Galactosamine-Functionalized Polydisulfide Conjugates

Biologics, including proteins and antisense oligonucleotides (ASOs), face significant challenges when it comes to achieving intracellular delivery within specific organs or cells through systemic administrations. In this study, we present a novel approach for delivering proteins and ASOs to liver cells, both in vitro and in vivo, using conjugates that tether N-acetylated galactosamine (GalNAc)-functionalized, cell-penetrating polydisulfides (PDSs). The method involves the thiol-bearing cargo-mediated ring-opening polymerization of GalNAc-functionalized lipoamide monomers through the so-called aggregation-induced polymerization, leading to the formation of site-specific protein/ASO-PDS conjugates with narrow dispersity. The hepatocyte-selective intracellular delivery of the conjugates arises from a combination of factors, including first GalNAc binding with ASGPR receptors on liver cells, leading to cell immobilization, and the subsequent thiol-disulfide exchange occurring on the cell surface, promoting internalization. Our findings emphasize the critical role of the close proximity of the PDS backbone to the cell surface, as it governs the success of thiol-disulfide exchange and, consequently, cell penetration. These conjugates hold tremendous potential in overcoming the various biological barriers encountered during systemic and cell-specific delivery of biomacromolecular cargos, opening up new avenues for the diagnosis and treatment of a range of liver-targeting diseases.

Regulation and Therapeutic Application of Long non-Coding RNA in Tumor Angiogenesis

Tumor growth and metastasis rely on angiogenesis. In recent years, long non-coding RNAs have been shown to play an important role in regulating tumor angiogenesis. Here, we review the multidimensional modes and relevant molecular mechanisms of long non-coding RNAs in regulating tumor angiogenesis. In addition, we summarize new strategies for tumor anti-angiogenesis therapies by targeting long non-coding RNAs. The aim of this study is to provide new diagnostic targets and treatment strategies for anti-angiogenic tumor therapy.

Nucleic Acid-Based Approaches to Tackle KRAS Mutant Cancers

Activating mutations in KRAS are highly relevant to various cancers, driving persistent efforts toward the development of drugs that can effectively inhibit KRAS activity. Previously, KRAS was considered 'undruggable'; however, the recent advances in our understanding of RNA and nucleic acid chemistry and delivery formulations have sparked a paradigm shift in the approach to KRAS inhibition. We are currently witnessing a large wave of next-generation drugs for KRAS mutant cancers-nucleic acid-based therapeutics. In this review, we discuss the current progress in targeting KRAS mutant tumors and outline significant developments in nucleic acid-based strategies. We delve into their mechanisms of action, address existing challenges, and offer insights into the current clinical trial status of these approaches. We aim to provide a thorough understanding of the potential of nucleic acid-based strategies in the field of KRAS mutant cancer therapeutics.

One-pot synthesis of dynamically cross-linked polymers for serum-resistant nucleic acid delivery

Cationic polymers used for nucleic acid delivery often suffer from complicated syntheses, undesired intracellular cargo release and low serum stability. Herein, a series of ternary polymers were synthesized via facile green chemistry to achieve efficient plasmid DNA and mRNA delivery in serum. During the one-pot synthesis of the ternary polymer, acetylphenylboric acid (APBA), polyphenol and low-molecular weight polyethyleneimine (PEI 1.8k) were dynamically cross-linked with each other due to formation of an imine between PEI 1.8k and APBA and formation of a boronate ester between APBA and polyphenol. Series of polyphenols, including ellagic acid (EA), epigallocatechin gallate (EGCG), nordihydroguaiaretic acid (NDGA), rutin (RT) and rosmarinic acid (RA), and APBA molecules, including 2-acetylphenylboric acid (2-APBA), 3-acetylphenylboric acid (3-APBA) and 4-acetylphenylboric acid (4-APBA), were screened and the best-performing ternary polymer, 2-PEI-RT, constructed from RT and 2-APBA, was identified. The ternary polymer featured efficient DNA condensation to favor cellular internalization, and the acidic environment in endolysosomes triggered effective degradation of the polymer to promote cargo release. Thus, 2-PEI-RT showed robust plasmid DNA transfection efficiencies in various tumor cells in serum, outperforming the commercial reagent PEI 25k by 1-3 orders of magnitude. Moreover, 2-PEI-RT mediated efficient cytosolic delivery of Cas9-mRNA/sgRNA to enable pronounced CRISPR-Cas9 genome editing in vitro. Such a facile and robust platform holds great potential for non-viral nucleic acid delivery and gene therapy.

Drug-Grafted DNA for Cancer Therapy

With the development of solid-phase synthesis and DNA nanotechnology, DNA-based drug delivery systems have seen large advancements over the past decades. By combining various drugs (small-molecular drugs, oligonucleotides, peptides, and proteins) with DNA technology, drug-grafted DNA has demonstrated great potential as a promising platform in recent years, in which complementary properties of both components have been discovered; for instance, the synthesis of amphiphilic drug-grafted DNA has enabled the production of DNA nanomedicines for gene therapy and chemotherapy. Through the design of linkages between drug and DNA parts, stimuli-responsiveness can be instilled, which has boosted the application of drug-grafted DNA in various biomedical applications such as cancer therapy. This review discusses the progress of various drug-grafted DNA therapeutic agents, exploring the synthetic techniques and anticancer applications afforded through the combination of drug and nucleic acids.

The Small RNA Landscape in NSCLC: Current Therapeutic Applications and Progresses

Non-small-cell lung cancer (NSCLC) is the second most diagnosed type of malignancy and the first cause of cancer death worldwide. Despite recent advances, the treatment of choice for NSCLC patients remains to be chemotherapy, often showing very limited effectiveness with the frequent occurrence of drug-resistant phenotype and the lack of selectivity for tumor cells. Therefore, new effective and targeted therapeutics are needed. In this context, short RNA-based therapeutics, including Antisense Oligonucleotides (ASOs), microRNAs (miRNAs), short interfering (siRNA) and aptamers, represent a promising class of molecules. ASOs, miRNAs and siRNAs act by targeting and inhibiting specific mRNAs, thus showing an improved specificity compared to traditional anti-cancer drugs. Nucleic acid aptamers target and inhibit specific cancer-associated proteins, such as "nucleic acid antibodies". Aptamers are also able of receptor-mediated cell internalization, and therefore, they can be used as carriers of secondary agents giving the possibility of producing very highly specific and effective therapeutics. This review provides an overview of the proposed applications of small RNAs for NSCLC treatment, highlighting their advantageous features and recent advancements in the field.

A mechanistic study on the cellular uptake, intracellular trafficking, and antisense gene regulation of bottlebrush polymer-conjugated oligonucleotides

We have developed a non-cationic transfection vector in the form of bottlebrush polymer-antisense oligonucleotide (ASO) conjugates. Termed pacDNA (polymer-assisted compaction of DNA), these agents show improved biopharmaceutical characteristics and antisense potency in vivo while suppressing non-antisense side effects. Nonetheless, there still is a lack of the mechanistic understanding of the cellular uptake, subcellular trafficking, and gene knockdown with pacDNA. Here, we show that the pacDNA enters human non-small cell lung cancer cells (NCI-H358) predominantly by scavenger receptor-mediated endocytosis and macropinocytosis and trafficks via the endolysosomal pathway within the cell. The pacDNA significantly reduces a target gene expression (KRAS) in the protein level but not in the mRNA level, despite that the transfection of certain free ASOs causes ribonuclease H1 (RNase H)-dependent degradation of KRAS mRNA. In addition, the antisense activity of pacDNA is independent of ASO chemical modification, suggesting that the pacDNA always functions as a steric blocker.

Synthesis and biophysical properties of tetravalent PEG-conjugated antisense oligonucleotide

This study was aimed at developing a novel platform for tetravalent conjugation of 4-arm polyethylene glycol (PEG) with an antisense oligonucleotide (ASO). The ASO technology has several limitations, such as low cellular uptake, poor nuclease stability, and short half-life. PEG-conjugated ASOs may result in an improvement in the pharmacokinetic behavior of the drug. Moreover, PEGylation can reduce enzymatic degradation and renal excretion of the conjugates, thereby, increasing its blood stability and retention time. In this study, we successfully synthesized PEG-ASO conjugate consisting of 4-arm-PEG and four molecules of ASO (4-arm-PEG-tetra ASO). Its hybridization ability with complementary RNA, enzymatic stability, and in vitro gene silencing ability were evaluated. No significant difference in hybridization ability was observed between 4-arm-PEG-tetra ASO and the parent ASO. In addition, gene silencing activity of the 4-arm-PEG-tetra ASO was observed in vitro. However, the in vitro activity of the 4-arm-PEG-tetra ASO was slightly reduced as that of the parent ASO. Moreover, the 4-arm-PEG-tetra ASO showed appreciable stability in cellular extract, suggesting that it hybridizes with mRNA in its intact form, without being cleaved in the cell, and exhibits ASO activity.

New prospectives on treatment opportunities in RASopathies

The RASopathies are a group of clinically defined developmental syndromes caused by germline variants of the RAS/mitogen-activated protein (MAPK) cascade. The prototypic RASopathy is Noonan syndrome, which has phenotypic overlap with related disorders such as cardiofaciocutaneous syndrome, Costello syndrome, Noonan syndrome with multiple lentigines, and others. In this state-of-the-art review, we summarize current knowledge on unmet therapeutic needs in these diseases and novel treatment approaches informed by insights from RAS/MAPK-associated cancer therapies, in particular through inhibition of MEK1/2 and mTOR in patients with severe disease manifestations. We explore the possibilities of integrating a larger arsenal of molecules currently under development into future care plans. Lastly, we describe both medical and ethical challenges and opportunities for future clinical trials in the field.

A Long-Circulating Vector for Aptamers Based upon Polyphosphodiester-Backboned Molecular Brushes

Aptamers face challenges for use outside the ideal conditions in which they are developed. These difficulties are most palpable in vivo due to nuclease activities, rapid clearance, and off-target binding. Herein, we demonstrate that a polyphosphodiester-backboned molecular brush can suppress enzymatic digestion, reduce non-specific cell uptake, enable long blood circulation, and rescue the bioactivity of a conjugated aptamer in vivo. The backbone along with the aptamer is assembled via solid-phase synthesis, followed by installation of poly(ethylene glycol) (PEG) side chains using a two-step process with near-quantitative efficiency. The synthesis allows for precise control over polymer size and architecture. Consisting entirely of building blocks that are generally recognized as safe for therapeutics, this novel molecular brush is expected to provide a highly translatable route for aptamer-based therapeutics.