Tuning the Hydrophilic-Hydrophobic Balance of Molecular Polymer Bottlebrushes Enhances their Tumor Homing Properties

Nanoscale Surface Topography of Polyethylene Glycol-Coated Nanoparticles Composed of Bottlebrush Block Copolymers Prolongs Systemic Circulation and Enhances Tumor Uptake

Improving the performance of nanocarriers remains a major challenge in the clinical translation of nanomedicine. Efforts to optimize nanoparticle formulations typically rely on tuning the surface density and thickness of stealthy polymer coatings, such as poly(ethylene glycol) (PEG). Here, we show that modulating the surface topography of PEGylated nanoparticles using bottlebrush block copolymers (BBCPs) significantly enhances circulation and tumor accumulation, providing an alternative strategy to improve nanoparticle coatings. Specifically, nanoparticles with rough surface topography achieve high tumor cell uptake in vivo due to superior tumor extravasation and distribution compared to conventional smooth-surfaced nanoparticles based on linear block copolymers. Furthermore, surface topography profoundly impacts the interaction with serum proteins, resulting in the adsorption of fundamentally different proteins onto the surface of rough-surfaced nanoparticles formed from BBCPs. We envision that controlling the nanoparticle surface topography of PEGylated nanoparticles will enable the design of improved nanocarriers in various biomedical applications.

Particle Engineering via Supramolecular Assembly of Macroscopic Hydrophobic Building Blocks

Tailoring the hydrophobicity of supramolecular assembly building blocks enables the fabrication of well-defined functional materials. However, the selection of building blocks used in the assembly of metal-phenolic networks (MPNs), an emerging supramolecular assembly platform for particle engineering, has been essentially limited to hydrophilic molecules. Herein, we synthesized and applied biscatechol-functionalized hydrophobic polymers (poly(methyl acrylate) (PMA) and poly(butyl acrylate) (PBA)) as building blocks to engineer MPN particle systems (particles and capsules). Our method allowed control over the shell thickness (e.g., between 10 and 21 nm), stiffness (e.g., from 10 to 126 mN m-1 ), and permeability (e.g., 28-72 % capsules were permeable to 500 kDa fluorescein isothiocyanate-dextran) of the MPN capsules by selection of the hydrophobic polymer building blocks (PMA or PBA) and by controlling the polymer concentration in the MPN assembly solution (0.25-2.0 mM) without additional/engineered assembly processes. Molecular dynamics simulations provided insights into the structural states of the hydrophobic building blocks during assembly and mechanism of film formation. Furthermore, the hydrophobic MPNs facilitated the preparation of fluorescent-labeled and bioactive capsules through postfunctionalization and also particle-cell association engineering by controlling the hydrophobicity of the building blocks. Engineering MPN particle systems via building block hydrophobicity is expected to expand their use.

Multicompartment Micro- and Nanoparticles Using Supramolecular Assembly of Core-Shell Bottlebrush Polymers

Multicompartment particles have been produced to date by the self-assembly of linear multiblock polymers. Besides the large diversity of structures that can be obtained with this approach, these are highly sensitive to dilution and environmental factors. Here we show that using core-shell bottlebrush polymers with a hydrophobic polyester core as starting materials it is possible to create compartmentalized particles from the micrometer size down to the molecular scale. These polymers can be used as building blocks to create multicompartment particles and networks via a self-assembly process. The polymers can encapsulate active compounds and slowly degrade in water into polymeric micelles, making them promising materials for drug delivery applications.

Recent Advances in Nanomaterials-Based Targeted Drug Delivery for Preclinical Cancer Diagnosis and Therapeutics

Nano-oncology is a branch of biomedical research and engineering that focuses on using nanotechnology in cancer diagnosis and treatment. Nanomaterials are extensively employed in the field of oncology because of their minute size and ultra-specificity. A wide range of nanocarriers, such as dendrimers, micelles, PEGylated liposomes, and polymeric nanoparticles are used to facilitate the efficient transport of anti-cancer drugs at the target tumor site. Real-time labeling and monitoring of cancer cells using quantum dots is essential for determining the level of therapy needed for treatment. The drug is targeted to the tumor site either by passive or active means. Passive targeting makes use of the tumor microenvironment and enhanced permeability and retention effect, while active targeting involves the use of ligand-coated nanoparticles. Nanotechnology is being used to diagnose the early stage of cancer by detecting cancer-specific biomarkers using tumor imaging. The implication of nanotechnology in cancer therapy employs photoinduced nanosensitizers, reverse multidrug resistance, and enabling efficient delivery of CRISPR/Cas9 and RNA molecules for therapeutic applications. However, despite recent advancements in nano-oncology, there is a need to delve deeper into the domain of designing and applying nanoparticles for improved cancer diagnostics.

Impact of the polymer backbone chemistry on interactions of amino-acid-derived zwitterionic polymers with cells

Zwitterionic polymers are known to interact with cells and have been shown to reveal cancer cell specificity. In this work, the importance of the chemistry of the polymer backbone for the cellular specificity of amino-acid-derived polyzwitterions is demonstrated. A series of glutamic acid (Glu)-based vinyl monomers (i.e., an acrylate, a methacrylate, an acrylamide, and a methacrylamide) were prepared and used for reversible addition-fragmentation chain-transfer (RAFT) polymerisation, yielding defined polymers with narrow size distribution (Р< 1.3). All Glu-functionalised, zwitterionic polymers revealed high cytocompatibility; however, differences in cellular association and specificity were observed. In particular, the methacrylamide-derived polymers showed high association with both, breast cancer cells and non-cancerous dendritic cells and, consequently, lack specificity. In contrast, high specificity to only breast cancer cells was observed for polyacrylates, -methacrylates, and -acrylamides. Detailed analysis of the polymers revealed differences in hydrophobicity, zeta potential, and potential side chain hydrolysis, which are impacted by the polymer backbone and might be responsible for the altered the cell association of these polymers. It is shown that a slightly negative net charge is preferred over a neutral charge to retain cell specificity. This was also confirmed by association experiments in the presence of competitive amino acid transporter substrates. The affinity of slightly negatively charged Glu-derived polymers to the xCT Glu/cystine cell membrane antiporter was found to be higher than that of neutrally charged polymers. Our results emphasise the importance of the polymer backbone for the design of cell-specific polymers. This study further highlights the potential to tailor amino-acid-derived zwitterionic materials beyond their side chain functionality.

Mechanistic insights and importance of hydrophobicity in cationic polymers for cancer therapy

Development of molecules that can be effectively used for killing cancer cells remains a research topic of interest in drug discovery. However, various limitations of small molecules and nanotechnology-based drug-delivery systems hinder the development of chemotherapeutics. To resolve this issue, this study describes the potential application of polymeric molecules as anticancer drug candidates. We describe the design and synthesis of novel anticancer polymers containing hydrophobic groups. We established the fact that the cationic homopolymer (PAMPTMA) does not show any anticancer activity on its own; however, the insertion of hydrophobic moieties in copolymers (PAMPTMA-r-BuMA, PAMPTMA-r-HexMA, and PAMPTMA-r-OctMA) enhances their anticancer activity with a very low IC₅₀ value (60 μg mL^-1 for HepG2 cells). Mechanistic investigations were carried out using LDH leakage assay, cellular uptake, DOSY NMR and molecular dynamics to study the interaction between the polymer and the cell membrane as well as the role of hydrophobicity in enhancing this interaction. The results demonstrated that polymers are attracted by the anionic cancer cell membrane, which then leads to the insertion of hydrophobic groups inside the cell membrane, causing its disruption and ultimate lysis of the cell. This study demonstrates a novel and better approach for the rational design and discovery of new polymeric anticancer agents with improved efficacy.

Probing the Biocompatibility and Immune Cell Association of Chiral, Water-Soluble, Bottlebrush Poly(2-oxazoline)s

Poly(2-oxazoline)s (POx) have received substantial attention as poly(ethylene glycol) (PEG) alternatives in the biomedical field due to their biocompatibility, high functionality, and ease of synthesis. While POx have demonstrated strong potential as biomaterial constituents, the larger family of poly(cyclic imino ether)s (PCIE) to which POx belongs remains widely underexplored. One highly interesting sub-class of PCIE is poly(2,4-disubstituted-2-oxazoline)s (PdOx), which bear an additional substituent on the backbone of the polymers' repeating units. This allows fine-tuning of the hydrophilic/hydrophobic balance and renders the PdOx chiral when enantiopure 2-oxazoline monomers are used. Herein, we synthesize new water-soluble (R-/S-/RS-) poly(oligo(2-ethyl-4-methyl-2-oxazoline) methacrylate) (P(OEtMeOxMA)) bottlebrushes and compare them to well-established PEtOx- and PEG-based bottlebrush controls in terms of their physical properties, hydrophilicity, and biological behavior. We reveal that the P(OEtMeOxMA) bottlebrushes show a lower critical solution temperature behavior at a physiologically relevant temperature (∼44 °C) and that the enantiopure (R-/S-) variants display a chiral secondary structure. Importantly, we demonstrate the biocompatibility of the chiral P(OEtMeOxMA) bottlebrushes through cellular association and mouse biodistribution studies and show that these systems display higher immune cell association and organ accumulation than the two control polymers. These novel materials possess properties that hold promise for applications in the field of nanomedicine and may be beneficial carriers for therapeutics that require enhanced cellular association and immune cell interaction.

Cisplatin-Loaded Tobacco Mosaic Virus for Ovarian Cancer Treatment

Ovarian cancer is the foremost cause of gynecological cancer and a major cause of cancer death in women. Treatment for advanced stage is surgical debulking followed by chemotherapy; however, most patients relapse with more aggressive and therapy-resistant tumors. There is a need to develop drug delivery approaches to deliver platinum therapies to tumors to increase efficacy while maintaining safety. Toward this goal, we utilized the protein nanotubes from the plant virus, tobacco mosaic virus (TMV), as a drug carrier. Specifically, the nanochannel of TMV was loaded with the active dication form of cisplatin (cisPt²⁺), making use of the negatively charged Glu acid side chains that line the interior channel of TMV. We achieved a loading efficiency with ∼2700 cisPt²⁺ per TMV; formulation stability was established with drug complexes stably loaded into the carrier for 2 months under refrigerated storage. TMV-cisPt maintained its efficacy against ovarian tumor cells with an IC₅₀ of ∼40 μM. TMV-cisPt exhibited superior efficacy vs free cisPt in ovarian tumor mouse models using intraperitoneal ID8-Defb29/Vegf-a-Luc (mouse) tumors and subcutaneous A2780 (human) xenografts. TMV-cisPt treatment led to reduced tumor burden and increased survival. Using ID8-Defb29/Vegf-a-Luc-bearing C57BL/6 mice, we also noted reduced tumor growth when animals were treated with TMV alone, which may indicate antitumor immunity induced by the immunomodulatory nature of the plant virus nanoparticle. Biodistribution studies supported the efficacy data, showing increased cisPt accumulation within tumors when delivered via the TMV carrier vs free cisPt administration. Finally, good safety profiles were noted. The study highlights the potential of TMV as a drug carrier against cancer and points to the opportunity to explore plant viruses as chemo-immuno combination cancer therapeutics.

Impact of Zwitterionic Polymers on the Tumor Permeability of Molecular Bottlebrush-Based Nanoparticles

Biocompatible polymers possessing antifouling properties for biomolecules are necessary to be combined with nanoparticles for cancer chemotherapy to improve their retention in blood and subsequent tumor accumulation. However, these properties simultaneously lead to poor affinity to cells, and low tumor tissue permeability subsequently, which is one of the major barriers in achieving efficient anticancer efficacy. To address this, we try to elucidate the tumor permeability of nanoparticles using molecular bottlebrushes (MBs) as model polymeric nanoparticles composed of various biocompatible polymers. An MB comprising nonionic poly[(ethylene glycol) methyl ether methacrylate] (PEGMA) shows no tumor permeability at all, whereas zwitterionic MBs composed of poly(phosphobetaine methacrylate), poly(sulfobetaine methacrylate), or poly(carboxybetaine methacrylate) penetrate deeply into tumor tissues. The carboxybetaine-based MBs showed an efficient cellular uptake into cancer cells while the other MBs did not, which enable them to penetrate into tumor tissues via the transcytosis pathway. Additionally, their permeability is based on intercellular or intracellular pathways, which might be related to the zwitterionic betaine properties that recognize protein transporters on cancer cells. Surprisingly, incorporating only 10 mol % of the zwitterionic betaine polymers into PEGMA-based MBs significantly enhances their tissue permeability. This platform technology enables us to redesign the PEG-based nanoparticles developed for cancer chemotherapy in clinical applications.

Molecular polymer bottlebrushes in nanomedicine: therapeutic and diagnostic applications

Molecular polymer bottlebrushes are densely grafted, individual macromolecules with nanoscale proportions. The last decade has seen an increased focus on this material class, especially in nanomedicine and for biomedical applications. This Feature Article provides an overview of major developments in this area to highlight the many opportunities that these polymer architectures bring to nano-bio research. The article covers aspects of bottlebrush synthesis and summarises their use in drug and gene delivery, imaging, as theranostics and as prototype materials to correlate nanoparticle structure and composition to biological function and behaviour. Areas for future research in this area are discussed.

Radical–radical coupling effects in the direct-growth grafting-through synthesis of bottlebrush polymers using RAFT and ROMP

The direct-growth technique was used to synthesize macromonomers from four classes of vinyl monomers, and the influence of monomer type and conversion on coupling reactions was followed in grafting-through ring-opening metathesis polymerization.

Exosome-based drug delivery systems and their therapeutic applications

In the past few decades, scientists have actively worked on developing effective drug delivery systems (DDSs) as means to control life-threatening diseases and challenging illnesses.