Stimuli-sensitive polymer prodrug nanocarriers by reversible-deactivation radical polymerization

Polymer prodrugs are based on the covalent linkage of therapeutic molecules to a polymer structure which avoids the problems and limitations commonly encountered with traditional drug-loaded nanocarriers in which drugs are just physically entrapped (e.g., burst release, poor drug loadings). In the past few years, reversible-deactivation radical polymerization (RDRP) techniques have been extensively used to design tailor-made polymer prodrug nanocarriers. This synthesis strategy has received a lot of attention due to the possibility of fine tuning their structural parameters (e.g., polymer nature and macromolecular characteristics, linker nature, physico-chemical properties, functionalization, etc.), to achieve optimized drug delivery and therapeutic efficacy. In particular, adjusting the nature of the drug-polymer linker has enabled the easy synthesis of stimuli-responsive polymer prodrugs for efficient spatiotemporal drug release. In this context, this review article will give an overview of the different stimuli-sensitive polymer prodrug structures designed by RDRP techniques, with a strong focus on the synthesis strategies, the macromolecular architectures and in particular the drug-polymer linker, which governs the drug release kinetics and eventually the therapeutic effect. Their biological evaluations will also be discussed.

A Single Functionalization Agent for Heterotelechelic ROMP Polymers

Heterotelechelic polymers are an important class of materials finding applications in bioconjugation, imaging, sensing, and synthesis of organic/inorganic hybrid systems with interesting features. However, the synthesis of such polymers is challenging. Here, we report a mechanistically unique and most efficient method based on a single functionalization agent to prepare heterotelechelic polymers by a ring-opening metathesis polymerization. Different functionalization agents can be synthesized in one simple step from inexpensive commercial starting materials. The functionalization agents initially generate a functional initiator from commercial Grubbs' first-generation ruthenium benzylidene catalyst. During this process, a functional dihydrofuran derivative is produced. After functional initiation and propagation of a suitable monomer, the dihydrofuran derivative functionally terminates the polymerization yielding a primary alcohol-terminated heterotelechelic polymer. Molecular weight control is achieved by varying the ratio between monomer and Grubbs' first-generation catalyst. This method may emerge as a popular choice to prepare heterotelechelic polymers due to its simplicity and efficiency.

Direct routes to functional RAFT agents from substituted N-alkyl maleimides

Three different routes are presented for the synthesis of functional RAFT agents from N-substituted maleimides, which are then used to synthesise α,β,ω-functional RAFT polymers.

One-Pot Heterotelechelic Metathesis Polymers via Regioselective Chain Transfer Agents

Single chain transfer agents are used to synthesize narrowly distributed heterotelechelic ROMP polymers in one pot, exploiting a new mechanistic and synthetic approach. The chain transfer agents carrying different functional groups are synthesized in a few straightforward steps. Prefunctionalization of commercially available Grubbs' third-generation catalyst is realized in situ using regioselective chain transfer agents within a short reaction period. After monomer consumption, the excess chain transfer agent in the reaction medium automatically end-functionalizes the polymer chain, yielding a heterotelechelic polymer via a ring-opening-ring-closing sequence. ¹H NMR, MALDI-ToF, and SEC analyses confirmed end-group functionalization as well as excellent control over molecular weight and dispersity. This strategy highlights a new way of synthesizing one-pot heterotelechelic ROMP polymers straightforwardly and efficiently.

Supramolecular Organization of Polymer Prodrug Nanoparticles Revealed by Coarse-Grained Simulations

Drug-polymer conjugates that can self-assemble into nanoparticles are promising drug delivery systems that improve the drug bioavailability and allow their controlled release. However, despite the possibility of reaching high drug loadings, the efficiency of the drug release, mediated by cleavage of the drug-polymer linker, is a key parameter to obtain significant anticancer activity. To overcome the limitations of experimental characterizations and to gain a better understanding of such systems, we conducted a coarse-grained molecular dynamics simulation study on four representative drug-polymer conjugates obtained by the "drug-initiated" method and studied their supramolecular organization upon self-assembly. The prodrugs were composed of either a gemcitabine or a paclitaxel anticancer drug, either a propanoate or a diglycolate linker, and a polyisoprene chain. Our simulations gave crucial information concerning the spatial organization of the different components (e.g., drug, linker, polymer, etc.) into the nanoparticles and revealed that the linkers are not fully accessible to the solvent. Notably, some cleavage sites were either poorly hydrated or partially solvated. These observations might account for the low efficiency of drug release from the nanoparticles, particularly when the linker is too short and/or not hydrophilic/solvated enough. We believe that our theoretical study could be adapted to other types of polymer prodrugs and could guide the design of new polymer prodrug nanoparticles with improved drug release efficiency.

Biodegradable macromers for implant bulk and surface engineering

Macromers, polymeric molecules with at least two functional groups for cross-polymerization, are interesting materials to tailor mechanical, biochemical and degradative bulk and surface properties of implants for tissue regeneration. In this review we focus on macromers with at least one biodegradable building block. Manifold design options, such as choice of polymeric block(s), optional core molecule and reactive groups, as well as cross-co-polymerization with suitable anchor or linker molecules, allow the adaptation of macromer-based biomaterials towards specific application requirements in both hard and soft tissue regeneration. Implants can be manufactured from macromers using additive manufacturing as well as molding and templating approaches. This review summarizes and discusses the overall concept of biodegradable macromers and recent approaches for macromer processing into implants as well as techniques for surface modification directed towards bone regeneration. These aspects are reviewed including a focus on the authors' contributions to the field through research within the collaborative research project Transregio 67.

Synthesis and characterization of benzodioxinone mono-telechelics and their use in block copolymerization

Poly(methyl methacrylate) (PMMA) and poly(ethylene glycol) methyl ether (mPEG)-based monotelechelics were quantitatively prepared by copper (I)-catalyzed azide/alkyne cycloaddition (CuAAC) click reactions using azido-terminated polymers and alkyne functional benzodioxinones. The monotelechelic containing dimethyl moities (2,2-dimethyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) was heat-sensitive, whereas the monotelechelic containing diphenyl moieties (2,2-diphenyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) was UV light sensitive. Based on the FT-IR, 1H-NMR, and GPC investigations, the CuAAC click reactions enable the quantitative syntheses of monotelechelics under mild conditions. Moreover, the photosensitive mPEG-based monotelechelic was further utilized for the block copolymer synthesis upon UV-light irradiation. The photoinduced acylation of mPEG monotelechelic consist of (2,2-diphenyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) in the presence of hydroxy-terminated poly(epsilon caprolactone) enabled the successful block copolymer formation.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Photoresponsive spiro-polymers generated in situ by C-H-activated polyspiroannulation

The development of facile and efficient polymerizations toward functional polymers with unique structures and attractive properties is of great academic and industrial significance. Here we develop a straightforward C-H-activated polyspiroannulation route to in situ generate photoresponsive spiro-polymers with complex structures. The palladium(II)-catalyzed stepwise polyspiroannulations of free naphthols and internal diynes proceed efficiently in dimethylsulfoxide at 120 °C without the constraint of apparent stoichiometric balance in monomers. A series of functional polymers with multisubstituted spiro-segments and absolute molecular weights of up to 39,000 are produced in high yields (up to 99%). The obtained spiro-polymers can be readily fabricated into different well-resolved fluorescent photopatterns with both turn-off and turn-on modes based on their photoinduced fluorescence change. Taking advantage of their photoresponsive refractive index, we successfully apply the polymer thin films in integrated silicon photonics techniques and achieve the permanent modification of resonance wavelengths of microring resonators by UV irradiation.

Protein-functionalized nanoparticles derived from end-functional polymers and polymer prodrugs for crossing the blood-brain barrier

Nanoparticles may provide a viable way for neuroprotective drugs to cross the blood-brain barrier (BBB), which limits the passage of most drugs from the peripheral circulation to the brain. Heterotelechelic polymer prodrugs comprising a neuroprotective model drug (adenosine) and a maleimide functionality were synthesized by the "drug-initiated" approach and subsequent nitroxide exchange reaction. Nanoparticles were obtained by nanoprecipitation and exhibited high colloidal stability with diameters in the 162-185 nm range and narrow size distributions. Nanoparticles were then covalently surface-conjugated to different proteins (albumin, α2-macroglobulin and fetuin A) to test their capability of enhancing BBB translocation. Their performances in terms of endothelial permeability and cellular uptake in an in vitro BBB model were compared to that of similar nanoparticles with surface-adsorbed proteins, functionalized or not with the drug. It was shown that bare NPs (i.e., NPs not surface-functionalized with proteins) without the drug exhibited significant permeability and cellular uptake, which were further enhanced by NP surface functionalization with α2-macroglobulin. However, the presence of the drug at the polymer chain-end prevented efficient passage of all types of NPs through the BBB model, likely due to adecrease in the hydrophobicity of the nanoparticle surface and alteration of the protein binding/coupling, respectively. These results established a new and facile synthetic approach for the surface-functionalization of polymer nanoparticles for brain delivery purposes.

Carborane RAFT agents as tunable and functional molecular probes for polymer materials

Carborane RAFT agents are introduced as tunable multi-purpose tools acting as ¹H NMR spectroscopic handles, Raman probes, and recognition units.

Photo-selective chain end transformation of polyacrylate-iodide using cysteamine and its application to facile single-step preparation of patterned polymer brushes

A novel photo-selective reaction for converting polymer-I to polymer-SH and polymer-H and its application to patterned functional polymer brushes.