Impact of Polymer Excipient Molar Mass and End Groups on Hydrophobic Drug Solubility Enhancement

Defining Structure-Function Relationships of Amphiphilic Excipients Enables Rational Design of Ultra-Stable Biopharmaceuticals

Biopharmaceuticals are the fastest-growing class of drugs in the healthcare industry, but their global reach is severely limited by their propensity for rapid aggregation. Currently, surfactant excipients such as polysorbates and poloxamers are used to prevent protein aggregation, which significantly extends shelf-life. Unfortunately, these excipients are themselves unstable, oxidizing rapidly into 100s of distinct compounds, some of which cause severe adverse events in patients. Here, the highly stable, well-defined, and modular nature of amphiphilic polyacrylamide-derived excipients is leveraged to isolate the key mechanisms responsible for excipient-mediated protein stabilization. With a library of compositionally identical but structurally distinct amphiphilic excipients, a new property is quantified, compositional dispersity, that is key to excipient performance and utilized this property to rationally design new ultra-stable surfactant excipients that increase the stability of a notoriously unstable biopharmaceutical, monomeric insulin, by an order of magnitude. This comprehensive and generalizable understanding of excipient structure-function relationships represents a paradigm shift for the formulation of biopharmaceuticals, moving away from trial-and-error screening approaches toward rational design.

Impact of a poly(ethylene glycol) corona block on drug encapsulation during polymerization induced self-assembly

Polymerization induced self-assembly (PISA) provides a facile platform for encapsulating therapeutics within block copolymer nanoparticles. Performing PISA in the presence of a hydrophobic drug alters both the nanoparticle shape and encapsulation efficiency. While previous studies primarily examined the interactions between the drug and hydrophobic core block, this work explores the impact of the hydrophilic corona block on encapsulation. Poly(ethylene glycol) (PEG) and poly(2-hydroxypropyl methacrylate) (PHPMA) are used as the model corona and core blocks, respectively, and phenylacetic acid (PA) is employed as the model drug. Attachment of a dithiobenzoate end group to the PEG homopolymer - transforming it into a macroscopic reversible addition-fragmentation chain transfer agent - causes the polymer to form a small number of nanoscopic aggregates in solution. Adding PA to the PEG solution encourages further aggregation and macroscopic phase separation. During the PISA of PEG-PHPMA block copolymers, inclusion of PA in the reaction mixture promotes faster nucleation of spherical micelles. Although increasing the targeted PA loading from 0 to 20 mg mL-1 does not affect the micelle size or shape, it alters the drug spatial distribution within the PISA microenvironment. PA partitions into either PEG-PHPMA micelles, deuterium oxide, or other polymeric species - including PEG aggregates and unimer chains. Increasing the targeted PA loading changes the fraction of drug within each encapsulation site. This work indicates that the corona block plays a critical role in dictating drug encapsulation during PISA.

Drug-Polymer Nanodroplet Formation and Morphology Drive Solubility Enhancement of GDC-0810

Nanodroplet formation is important to achieve supersaturation of active pharmaceutical ingredients (APIs) in an amorphous solid dispersion. The aim of the current study was to explore how polymer composition, architecture, molar mass, and surfactant concentration affect polymer-drug nanodroplet morphology with the breast cancer API, GDC-0810. The impact of nanodroplet size and morphology on dissolution efficacy and drug loading capacity was explored using polarized light microscopy, dynamic light scattering, and cryogenic transmission electron microscopy. Poly(N-isopropylacrylamide-stat-N,N-dimethylacrylamide) (PND) was synthesized as two linear derivatives and two bottlebrush derivatives with carboxylated or PEGylated end-groups. Hydroxypropyl methylcellulose acetate succinate grade MF (HPMCAS-MF) and poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) were included as commercial polymer controls. We report the first copolymerization synthesis of a PVPVA bottlebrush copolymer, which was the highest performing excipient in this study, maintaining 688 μg/mL GDC-0810 concentration at 60 wt % drug loading. This is likely due to strong polymer-drug noncovalent interactions and the compaction of GDC-0810 along the PVPVA bottlebrush backbone. Overall, it was observed that the most effective formulations had a hydrodynamic radius less than 25 nm with tightly compacted nanodroplet morphologies.

Hydrogen Bonding Principle-Based Molecular Design of a Polymer Excipient and Impacts on Hydrophobic Drug Properties: Molecular Simulation and Experiment

Although some commercial excipients for improving the solubility of highly crystalline drugs are widely used, they still cannot cover all types of hydrophobic drugs. In this regard, with phenytoin as the target drug, related molecular structures of polymer excipients were designed. The optimal repeating units of NiPAm and HEAm were screened out through quantum mechanical simulation and Monte Carlo simulation methods, and the copolymerization ratio was also determined. Using molecular dynamics simulation technology, it was confirmed that the dispersibility and intermolecular hydrogen bonds of phenytoin in the designed copolymer were better than those in the commercial PVP materials. At the same time, the designed copolymers and solid dispersions were also prepared during the experiment, and the improvement of their solubility was confirmed, which is in accordance with the simulation predictions. The new ideas and simulation technology may be used for drug modification and development.

Labeling Assembly of Hydrophilic Methionine into Nanoparticle for Mild-Heat Mediated Immunometabolic Therapy

Methionine metabolism has a significant impact on T cells' survival and activation even in comparison to arginine, a well-documented amino acid in metabolic therapy. However, hydrophilic methionine is hardly delivered into TME due to difficult loading and rapid diffusion. Herein, the labeling assembly of methionine into nanoparticle is developed to overcome high hydrophilicity for mild-heat mediated immunometabolic therapy. The strategy is to first label methionine with protocatechualdehyde (as the tag) via reversible Schiff-base bond, and then drive nanoassembly of methionine (MPC@Fe) mediated by iron ions. In this fashion, a loading efficiency of 40% and assembly induced photothermal characteristics can be achieved. MPC@Fe can accumulate persistently in tumor up to 36 h due to tumor-selective aggregation in acidic TME. A mild heat of 43 °C on tumor by light irradiation stimulated the immunogenic cell death and effectively generated CD8⁺ T cells. Notably, MPC@Fe assisted by mild heat promoted 4.2-fold of tumor-infiltrating INF-γ⁺ CD8⁺ T cells, leading to an inhibition ratio of 27.3-fold versus the free methionine. Such labeling assembly provides a promising methionine delivery platform to realize mild heat mediated immunometabolic therapy, and is potentially extensible to other amino acids.

Bioavailability Enhancement Techniques for Poorly Aqueous Soluble Drugs and Therapeutics

The low water solubility of pharmacoactive molecules limits their pharmacological potential, but the solubility parameter cannot compromise, and so different approaches are employed to enhance their bioavailability. Pharmaceutically active molecules with low solubility convey a higher risk of failure for drug innovation and development. Pharmacokinetics, pharmacodynamics, and several other parameters, such as drug distribution, protein binding and absorption, are majorly affected by their solubility. Among all pharmaceutical dosage forms, oral dosage forms cover more than 50%, and the drug molecule should be water-soluble. For good therapeutic activity by the drug molecule on the target site, solubility and bioavailability are crucial factors. The pharmaceutical industry’s screening programs identified that around 40% of new chemical entities (NCEs) face various difficulties at the formulation and development stages. These pharmaceuticals demonstrate less solubility and bioavailability. Enhancement of the bioavailability and solubility of drugs is a significant challenge in the area of pharmaceutical formulations. According to the Classification of Biopharmaceutics, Class II and IV drugs (APIs) exhibit poor solubility, lower bioavailability, and less dissolution. Various technologies are discussed in this article to improve the solubility of poorly water-soluble drugs, for example, the complexation of active molecules, the utilization of emulsion formation, micelles, microemulsions, cosolvents, polymeric micelle preparation, particle size reduction technologies, pharmaceutical salts, prodrugs, the solid-state alternation technique, soft gel technology, drug nanocrystals, solid dispersion methods, crystal engineering techniques and nanomorph technology. This review mainly describes several other advanced methodologies for solubility and bioavailability enhancement, such as crystal engineering, micronization, solid dispersions, nano sizing, the use of cyclodextrins, solid lipid nanoparticles, colloidal drug delivery systems and drug conjugates, referring to a number of appropriate research reports.

Study on the Effect of Polymer Excipients on the Dispersibility, Interaction, Solubility, and Scavenging Reactive Oxygen Species of Myricetin Solid Dispersion: Experiment and Molecular Simulation

Although the preparation of amorphous solid dispersions can improve the solubility of crystalline drugs, there is still a lack of guidance on the micromechanism in the screening and evaluation of polymer excipients. In this study, a particular method of experimental characterization combined with molecular simulation was attempted on solubilization of myricetin (MYR) by solid dispersion. According to the analysis of the dispersibility and hydrogen-bond interaction, the effectiveness of the solid dispersion and the predicted sequence of poly(vinyl pyrrolidone) (PVP) > hypromellose (HPMC) > poly(ethylene glycol) (PEG) as the polymer excipient were verified. Through the dissolution, cell viability, and reactive oxygen species (ROS)-level detection, the reliability of simulation and micromechanism analysis was further confirmed. This work not only provided the theoretical guidance and screening basis for the miscibility of solid dispersions from the microscopic level but also served as a reference for the modification of new drugs.

Preparation and Characterization of Stable Amorphous Glassy Solution of BCS II and IV Drugs

The focus of the present investigation was to develop amorphous glassy solutions (AGSs) of BCS Class II and IV drugs using sucrose acetate isobutyrate (SAIB). The drugs studied were rifaximin (RFX), dasatinib (DST), aripiprazole (APZ), dolutegravir (DLT), cyclosporine (CYS), itraconazole (ITZ), tacrolimus (TAC), sirolimus (SRL), aprepitant (APT), and carbamazepine (CBZ). AGSs were prepared by dissolving known quantity of the drug in the SAIB at 120 (TAC and APZ), 140 (CYS) or 150 ^oC (RFX, DST, DLT, ITZ, SRL, APT, and CBZ). They were characterized visually and by NIR, NIR hyperspectroscopy (NIR-H), and XRPD. Stability were determined by exposing open vials to 40 ^oC/75% RH for a week. AGSs behave like a glassy solid at room temperature and liquified above 60 ^oC. The solubility of APT, DLT, SRL, APZ, RFX, CBZ, TAC and CYS in SAIB was 0.4±0.0, 1.7±0.4, 1.9±0.0, 21.6±2.6, 36.4±0.9, 76.5±4.0, 115.1±2.3, and 239.0±12.6 mg/g, respectively. NIR, NIR-H, and XRPD data indicated the amorphous nature of the AGSs. Furthermore, AGSs were stable against devitrification on exposure to high temperature and humidity. In summary, SAIB can be employed to develop stable AGSs of poorly soluble drugs to increase dissolution, and oral bioavailability with the addition of hydrophilic excipients.

Automation and data-driven design of polymer therapeutics

Polymers are uniquely suited for drug delivery and biomaterial applications due to tunable structural parameters such as length, composition, architecture, and valency. To facilitate designs, researchers may explore combinatorial libraries in a high throughput fashion to correlate structure to function. However, traditional polymerization reactions including controlled living radical polymerization (CLRP) and ring-opening polymerization (ROP) require inert reaction conditions and extensive expertise to implement. With the advent of air-tolerance and automation, several polymerization techniques are now compatible with well plates and can be carried out at the benchtop, making high throughput synthesis and high throughput screening (HTS) possible. To avoid HTS pitfalls often described as "fishing expeditions," it is crucial to employ intelligent and big data approaches to maximize experimental efficiency. This is where the disruptive technologies of machine learning (ML) and artificial intelligence (AI) will likely play a role. In fact, ML and AI are already impacting small molecule drug discovery and showing signs of emerging in drug delivery. In this review, we present state-of-the-art research in drug delivery, gene delivery, antimicrobial polymers, and bioactive polymers alongside data-driven developments in drug design and organic synthesis. From this insight, important lessons are revealed for the polymer therapeutics community including the value of a closed loop design-build-test-learn workflow. This is an exciting time as researchers will gain the ability to fully explore the polymer structural landscape and establish quantitative structure-property relationships (QSPRs) with biological significance.

Bottlebrush Polymer Excipients Enhance Drug Solubility: Influence of End-Group Hydrophilicity and Thermoresponsiveness

Bottlebrush polymers have great potential as vehicles to noncovalently sequester, stabilize, and deliver hydrophobic small molecule actives. To this end, we synthesized a poly(N-isopropylacrylamide-stat-N,N-dimethylacrylamide) bottlebrush copolymer using ring-opening metathesis polymerization and developed a facile method to control the thermoresponsive properties using postpolymerization modification. Six increasingly hydrophilic end-groups were installed, yielding cloud point temperature control over a range of 22-42 °C. Solubility enhancement of the antiseizure medication, phenytoin, increased significantly with the hydrophilicity of the end-group moiety. Notably, carboxylated bottlebrush copolymers solubilized formulations with higher drug loadings than linear copolymers because they exist as unimolecular nanoparticles with a synthetically defined density of polymer chains that are more stable in solution. This work provides the first investigation of bottlebrush polymers for hydrophobic noncovalent sequestration and solubilization of pharmaceuticals.

Automated PET-RAFT Polymerization Towards Pharmaceutical Amorphous Solid Dispersion Development

In pharmaceutical oral drug delivery development, about 90% of drugs in the pipeline have poor aqueous solubility leading to severe challenges with oral bioavailability and translation to effective and safe drug products. Amorphous solid dispersions (ASDs) have been utilized to enhance the oral bioavailability of poorly soluble active pharmaceutical ingredients (APIs). However, a limited selection of regulatory-approved polymer excipients exists for the development and further understanding of tailor-made ASDs. Thus, a significant need exists to better understand how polymers can be designed to interact with specific API moieties. Here, we demonstrate how an automated combinatorial library approach can be applied to the synthesis and screening of polymer excipients for the model drug probucol. We synthesized a library of 25 random heteropolymers containing one hydrophilic monomer (2-hydroxypropyl acrylate (HPA)) and four hydrophobic monomers at varied incorporation. The performance of ASDs made by a rapid film casting method was evaluated by dissolution using ultra-performance liquid chromatography (UPLC) sampling at various time points. This combinatorial library and rapid screening strategy enabled us to identify a relationship between polymer hydrophobicity, monomer hydrophobic side group geometry, and API dissolution performance. Remarkably, the most effective synthesized polymers displayed slower drug release kinetics compared to industry standard polymer excipients, showing the ability to modulate the drug release profile. Future coupling of high throughput polymer synthesis, high throughput screening (HTS), and quantitative modeling would enable specification of designer polymer excipients for specific API functionalities.

A mechanistic review on the dissolution phase behavior and supersaturation stabilization of amorphous solid dispersions

Amorphous solid dispersion (ASD) technology is an attractive formulation approach for poorly soluble drugs because of the supersaturated state acquired during its dissolution. The high thermodynamic activity of the supersaturated state of the drug is also a driver for the enhanced absorptive flux across a membrane. However, this advantage can easily be lost due to the inherent instability of supersaturation, causing drug precipitation. Stabilizing the supersaturated state during the dissolution of ASD for the relevant absorption time frame is a challenging area in formulation research. Stabilizing the supersaturated state by using polymeric excipients and understanding the phase behavior of drugs during dissolution are required for the optimal performance of ASD formulations. A number of confounding kinetic, formulation and physiological factors can influence the evolution of supersaturation and phase changes during dissolution of ASDs. The review highlights the complex nature of dissolution of ASDs and the need of biorelevant dissolution for proper risk assessment and optimizing formulation development.

Porous and highly responsive cross-linked β-cyclodextrin based nanomatrices for improvement in drug dissolution and absorption

AIMS

Aim of the study was to enhance the solubility of Chlorthalidone by developing beta-cyclodextrin cross-linked hydrophilic nanomatrices.

MAIN METHODS

Nine different formulations were fabricated by free radical polymerization technique. All formulations were characterized through different studies. FTIR spectroscopy of unloaded and loaded nanomatrices was processed to determine compatibility of constituents and that of the drug with the system. Surface morphology of the nanomatrices was studied by SEM. The size of the optimized formulation was determined by zeta sizer. Swelling, in-vitro release and solubility studies were carried out in different media and results of in-vitro release profiles of nanomatrices and commercially available tablet of Chlorthalidone were compared. For determination of biocompatibility, toxicity studies were proclaimed in rabbits.

KEY FINDINGS

Main peaks of corresponding functional groups of individual constituents and that of drug were depicted in FTIR spectra of unloaded and loaded nanomatrices. Porous and fluffy structure was visualized through SEM images. Particle size of the optimized formulation was in the range of 175 ± 5.27 nm. Percent loading of optimized formulation showed the best result. Comparing the in-vitro drug release profiles of nanomatrices and commercially available tablet, the results of the synthesized nanomatrices were quite satisfactory. Solubility profiles were also high as compared to the drug alone. Moreover, toxicity studies confirmed that nanomatrices were biocompatible and no sign of any toxic effect was found.

SIGNIFICANCE

We concluded that our developed nanomatrices had successfully enhanced the solubility of Chlorthalidone and can also be used for other poorly aqueous soluble drugs.

Role of Polymer Excipients in the Kinetic Stabilization of Drug-Rich Nanoparticles

Amorphous solid dispersions (ASDs) of crystallizable drugs and polymer excipients are attractive for enhancing the solubility and bioavailability of hydrophobic drug molecules. In this study, the solution behavior of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (PND) and poly(vinylpyrrolidone-co-vinylacetate) (PVPVA), as polymer excipients, and nilutamide (NLT), phenytoin (PHY), and itraconazole (ITN) as model drugs, were monitored by an in vitro dissolution assay, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and polarized optical microscopy (POM). High degrees of drug supersaturation were coincident with the formation of amorphous nanoparticles in each system. The difference in particle size and kinetic stability between PND and PVPVA systems suggest a difference in how the polymers interact with the drug-rich phase. A series of scenarios are proposed based on whether the polymer interacts more strongly with the drug-rich nanoparticles or with water. Understanding the contribution of drug-rich nanoparticles to achievable supersaturation and the effect of polymer excipients on these particles will inform the design of future solid dispersion systems through a better understanding of the polymer/drug solution relationship.

Probing the Complex Loading-Dependent Structural Changes in Ultrahigh Drug-Loaded Polymer Micelles by Small-Angle Neutron Scattering

Drug-loaded polymer micelles or nanoparticles are being continuously explored in the fields of drug delivery and nanomedicine. Commonly, a simple core-shell structure is assumed, in which the core incorporates the drug and the corona provides steric shielding, colloidal stability, and prevents protein adsorption. Recently, the interactions of the dissolved drug with the micellar corona have received increasing attention. Here, using small-angle neutron scattering, we provide an in-depth study of the differences in polymer micelle morphology of a small selection of structurally closely related polymer micelles at different loadings with the model compound curcumin. This work supports a previous study using solid-state nuclear magnetic resonance spectroscopy and we confirm that the drug resides predominantly in the core of the micelle at low drug loading. As the drug loading increases, neutron scattering data suggests that an inner shell is formed, which we interpret as the corona also starting to incorporate the drug, whereas the outer shell mainly contains water and the polymer. The presented data clearly shows that a better understanding of the inner morphology and the impact of the hydrophilic block can be important parameters for improved drug loading in polymer micelles as well as provide insights into the structure-property relationship.

An eco-friendly pathway to thermosensitive micellar nanoobjects via photoRAFT PISA: the full guide to poly(N-acryloylpyrrolidin)-block-polystyrene diblock copolymers

Spherical macromolecular assemblies, so-called latexes, consisting of polystyrene (PS) resemble a relevant class of synthetic polymers used for a plethora of applications ranging from coatings or lubricants to biomedical applications. Their synthesis is usually tailored to the respective application where emulsifiers, radical initiators, or other additives still play a major role in achieving the desired properties. Herein, we demonstrate an alternative based on the photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA) of Poly(N-acryloylpyrrolidin)-block-polystyrene (PAPy-b-PS). This approach yields monodisperse nanospheres with tunable sizes based on an aqueous formulation with only two ingredients. These nanospheres are additionally thermosensitive, meaning that they change their hydrodynamic diameter linearly with the temperature in a broad range between 10 °C and 70 °C. Combined with the eco-friendly synthesis in pure water at 40 °C, the herein presented route constitutes an unprecedented pathway to thermosensitive diblock copolymer aggregates in short reaction times without any additives.

Critical Excipient Properties for the Dissolution Enhancement of Phenytoin

Solubility-enhancing amorphous solid dispersions can aid in the oral delivery of hydrophobic, poorly soluble drugs. Effective solid dispersion excipients enable high supersaturation drug concentrations over biologically relevant time scales. The critical characteristics of an excipient that allow it to work well in a solid dispersion system are not well understood. We prepared poly(N-isopropylacrylamide), poly(N,N-dimethylacrylamide), and poly(N-hydroxyethylacrylamide) excipients of varying molar mass and examined their ability to improve the aqueous solubility of phenytoin, a Biopharmaceutical Class System Class II drug. Binary and ternary solid dispersions of phenytoin and these excipients, along with hydroxypropyl methylcellulose acetate succinate and hydroxypropyl methylcellulose, were prepared at 10 wt % drug loading. Dissolution behavior was studied at early time points (<1 min) and over the course of 6 h. Performance of the ternary solid dispersions was largely a function of the concentration of poly(N-isopropylacrylamide) present in micellar structures and the concentration of PNiPAm micelles in the dissolution media. We present several systems that achieved significant improvement of phenytoin solubility over a wide composition range at enhancement factors among the highest seen to date for phenytoin.

Aggregated Solution Morphology of Poly(acrylic acid)-Poly(styrene) Block Copolymers Improves Drug Supersaturation Maintenance and Caco-2 Cell Membrane Permeation

Amorphous solid dispersions of polymers and drugs have been shown to improve supersaturation maintenance of poorly water-soluble drugs. Herein, amorphous spray-dried dispersions (SDDs) of poly(acrylic acid)-polystyrene (PS-b-PAA) diblock copolymers with differing degrees of polymerization were prepared in aggregated and nonaggregated states with the Biopharmaceutical Classification System Class II drug, probucol (PBC). Specifically, PS₉₀-b-PAA₁₅, PS₉₀-b-PAA₈₀, PS₃₈-b-PAA₂₂₀, and PS₃₈-b-PAA₃₂₀ amphiphilic block polymers that covered a compositional range in the area of oral drug delivery were prepared to examine the role of molecular weight and controlled aggregation in promoting drug supersaturation and maintenance. In addition, hydrophilic homopolymers PAA₂₀, PAA₉₆, PAA₂₂₆, and PAA₃₉₂ were prepared as controls to evaluate the role of the block copolymer-based SDDs in PBC solubilization. Characterization such as powder X-ray diffraction, scanning electron microscopy, and dissolution tests under nonsink conditions were then performed to evaluate the SDDs. When comparing the block copolymer systems, polymers that were preaggregated into micellular structures prior to spray drying with the drug promoted higher drug solubility and maintenance than when the drug was formulated with molecularly dissolved PS-PAA block polymer. Interestingly, the aggregated PS₉₀-b-PAA₈₀ SDD with 25 wt % PBC achieved 100% burst release and maintained full supersaturation of PBC at pH 6.5 (physiological pH in the small intestine). Dissolution studies conducted at the pH of the stomach (pH = 1.2) show that a minimal amount of drug (∼10 μg/mL) was released, which could be used for protecting drugs from acidic environments (stomach) before reaching the small intestine. To evaluate drug bioavailability, in vitro Caco-2 cell assays were performed, which reveal that PAA-based excipients do not hinder drug permeation across the epithelial membrane and that PS₉₀-b-PAA₈₀ SDD with 25 wt % PBC achieved the highest membrane permeability coefficient. This work demonstrates that block copolymer-based SDDs capable of preaggregating into nanostructures may be a tunable drug-delivery platform that can improve solubility and supersaturation maintenance of Class II pharmaceutics while also not prohibiting bioavailability through model intestinal membranes. Indeed, this concept may be extended to accommodate a myriad of pharmaceutical and excipient structures.

Polycation Architecture and Assembly Direct Successful Gene Delivery: Micelleplexes Outperform Polyplexes via Optimal DNA Packaging

Cellular delivery of biomacromolecules is vital to medical research and therapeutic development. Cationic polymers are promising and affordable candidate vehicles for these precious payloads. However, the impact of polycation architecture and solution assembly on the biological mechanisms and efficacy of these vehicles has not been clearly defined. In this study, four polymers containing the same cationic poly(2-(dimethylamino)ethyl methacrylate) (D) block but placed in different architectures have been synthesized, characterized, and compared for cargo binding and biological performance. The D homopolymer and its diblock copolymer poly(ethylene glycol)-block-poly(2-(dimethylamino) ethyl methacrylate) (OD) readily encapsulate pDNA to form polyplexes. Two amphiphilic block polymer variants, poly(2-(dimethylamino)ethyl methacrylate)-block-poly(n-butyl methacrylate) (DB) and poly(ethylene glycol)-block-poly(2-(dimethylamino)ethyl methacrylate)-block-poly(n-butyl methacrylate) (ODB), self-assemble into micelles, which template pDNA winding around the cationic corona to form micelleplexes. Micelleplexes were found to have superior delivery efficiency compared to polyplexes and detailed physicochemical and biological characterizations were performed to pinpoint the mechanisms by testing hypotheses related to cellular internalization, intracellular trafficking, and pDNA unpackaging. For the first time, we find that the higher concentration of amines housed in micelleplexes stimulates both cellular internalization and potential endosomal escape, and the physical motif of pDNA winding into micelleplexes, reminiscent of DNA compaction by histones in chromatin, preserves the pDNA secondary structure in its native B form. This likely allows greater payload accessibility for protein expression with micelleplexes compared to polyplexes, which tightly condense pDNA and significantly distort its helicity. This work provides important guidance for the design of successful biomolecular delivery systems via optimizing the physicochemical properties.

Recent Advances in Understanding the Micro- and Nanoscale Phenomena of Amorphous Solid Dispersions

Many pharmaceutical drugs in the marketplace and discovery pipeline suffer from poor aqueous solubility, thereby limiting their effectiveness for oral delivery. The use of an amorphous solid dispersion (ASD), a mixture of an active pharmaceutical ingredient and a polymer excipient, greatly enhances the aqueous dissolution performance of a drug without the need for chemical modification. Although this method is versatile and scalable, deficient understanding of the interactions between drugs and polymers inhibits ASD rational design. This current Review details recent progress in understanding the mechanisms that control ASD performance. In the solid-state, the use of high-resolution theoretical, computational, and experimental tools resolved the influence of drug/polymer phase behavior and dynamics on stability during storage. During dissolution in aqueous media, novel characterization methods revealed that ASDs can form complex nanostructures, which maintain and improve supersaturation of the drug. The studies discussed here illustrate that nanoscale phenomena, which have been directly observed and quantified, strongly affect the stability and bioavailability of ASD systems, and provide a promising direction for optimizing drug/polymer formulations.

Like Dissolves Like? A Comprehensive Evaluation of Partial Solubility Parameters to Predict Polymer-Drug Compatibility in Ultrahigh Drug-Loaded Polymer Micelles

Despite decades of research, our understanding of the molecular interactions between drugs and polymers in drug-loaded polymer micelles does not extend much beyond concepts such as "like-dissolves-like" or hydrophilic/hydrophobic. However, polymer-drug compatibility strongly affects formulation properties and therefore the translation of a formulation into the clinics. Specific interactions such as hydrogen-bonding, π-π stacking, or coordination interactions can be utilized to increase drug loading. This is commonly based on trial and error and eventually leads to an optimized drug carrier. Unfortunately, due to the unique characteristics of each drug, the deduction of advanced general concepts remains challenging. Furthermore, the introduction of complex moieties or specifically modified polymers hampers systematic investigations regarding polymer-drug compatibility as well as clinical translation. In this study, we reduced the complexity to isolate the crucial factors determining drug loading. Therefore, the compatibility of 18 different amphiphilic polymers for five different hydrophobic drugs was determined empirically. Subsequently, the obtained specificities were compared to theoretical compatibilities derived from either the Flory-Huggins interaction parameters or the Hansen solubility parameters. In general, the Flory-Huggins interaction parameters were less suited to correctly estimate the experimental drug solubilization compared to the Hansen solubility parameters. The latter were able to correctly predict some trend regarding good and poor solubilizers, yet the overall predictive strength of Hansen solubility parameters is clearly unsatisfactory.

Paclitaxel interaction with cucurbit [7]uril and acyclic Cucurbit[4]uril nanocontainers: A computational approach

Paclitaxel (PTX) is a natural terpenoid compound that has been broadly studied for its antitumor activities and widely used as a chemotherapy medication. The treatment efficacy of PTX is affected by its low aqueous solubility, thus causing a subject of extensive research. In recent years, synthetic molecular containers such as cucurbit[n]urils (CB[n]s) and their derivatives have been significantly developing because of their remarkable ability to bind hydrophobic and cationic drugs. Recent experimental studies have shown that acyclic CB[n]-type containers (aCB[n]s), as new derivatives of the family of CB[n]s, increase the solubility of insoluble pharmaceuticals. However, the nature by which the drug interacts with carriers remains largely unknown. In this study, molecular docking and molecular dynamics (MD) simulation were performed to understand how CB[7] and aCB[4] nanocontainers interact with PTX which affect its aqueous solubility. The results clarify how the flexibility of containers is influenced by their structure and how this affects their interactions with PTX. Our results reveal that although both CB[7] and aCB[4] are capable of binding to PTX, the affinity to aCB[4] is higher than that of CB[7]. It has also been shown that the binding to both CB[7] and aCB[4] is probably an entropy-driven process. This research supports the potential use of the cucurbit[n]urils and their acyclic derivatives as drug delivery systems.

Polymer Nanogels as Reservoirs To Inhibit Hydrophobic Drug Crystallization

The effects of cross-link density and composition on the loading and in vitro dissolution of the drug phenytoin as amorphous solid dispersions in emulsion polymerized poly( N-isopropylacrylamide) (PNIPAm) and poly( N-isopropylacrylamide- co- N, N-dimethylacrylamide) nanogels were investigated near the lower critical solution temperature (LCST). Nanogel size and particle density in phosphate buffered saline were quantified by dynamic light scattering (DLS) and viscometry experiments, while drug-nanogel interactions were revealed by cross peaks in aqueous-state nuclear Overhauser effect spectroscopy measurements. Spray-dried dispersions (SDDs) of drug-loaded PNIPAm nanogel particles ( R ≈ 43 nm) were directly visualized by cryogenic transmission electron microscopy and further quantified by small-angle X-ray scattering during in vitro dissolution. SDD dissolution profiles were highly dependent on the nanogel cross-link density and directly correlated with the state of dispersion of the drug-loaded nanogel particles. A balance between net particle hydrophobicity and hydrophilicity along with the distance in temperature from the LCST are shown to dictate the in vitro dissolution of the amorphous solid dispersions. Solubility enhancement mechanisms disclosed in this study provide essential guidance for the design of effective nanogels for oral drug delivery applications.

Effect of Polymer Hydrophobicity on the Stability of Amorphous Solid Dispersions and Supersaturated Solutions of a Hydrophobic Pharmaceutical

Amorphous solid dispersions of pharmaceuticals often show improved solubility over crystalline forms. However, the crystallization of amorphous solid dispersions during storage, or from elevated supersaturation once dissolved, compromise the solubility advantage of delivery in the amorphous phase. To combat this phenomenon, polymer additives are often included in solid dispersions to inhibit crystallization; however, the optimal properties for polymer to stabilize against crystallization are not fully understood, and furthermore, it is not known how inhibition of precipitation from solution is related to the propensity of a polymer to inhibit crystallization from the amorphous phase. Here, polymers of varied hydrophobicity are employed as crystallization inhibitors in supersaturated solutions and amorphous solid dispersions of the BCS Class II pharmaceutical ethenzamide to investigate the chemical features of polymer that lead to long-term stability for a hydrophobic pharmaceutical. A postpolymerization functionalization strategy was employed to alter the hydrophobicity of poly( N-hydroxyethyl acrylamide) without changing physical properties such as number-average chain length. It was found that supersaturation maintenance for ethenzamide is improved by increasing the hydrophobicity of dissolved polymer in aqueous solution. Furthermore, amorphous solid dispersions of ethenzamide containing a more hydrophobic polymer showed superior stability compared to those containing a less hydrophobic polymer. This trend of increasing polymer hydrophobicity leading to improved amorphous stability is interpreted by parsing the effects of water absorption in amorphous solid dispersions using intermolecular interaction strengths derived from global structural analysis. By comparing the structure-function relationships, which dictate stability in solution and amorphous solid dispersions, the effect of hydrophobicity can be broadly understood for the design of polymers to impart stability throughout the application of amorphous solid dispersions.

Tuning PNIPAm self-assembly and thermoresponse: roles of hydrophobic end-groups and hydrophilic comonomer

Systematic study of hydrophobic and hydrophilic modifications to poly(N-isopropylacrylamide) elucidates design rules for control over cloud point and aqueous self-assembly.

Advances in Polymer Design for Enhancing Oral Drug Solubility and Delivery

Synthetic polymers have enabled amorphous solid dispersions (ASDs) to emerge as an oral delivery strategy for overcoming poor drug solubility in aqueous environments. Modern ASD products noninvasively treat a range of chronic diseases (for example, hepatitis C, cystic fibrosis, and HIV). In such formulations, polymeric carriers generate and maintain drug supersaturation upon dissolution, increasing the apparent drug solubility to enhance gastrointestinal barrier absorption and oral bioavailability. In this Review, we outline several approaches in designing polymeric excipients to drive interactions with active pharmaceutical ingredients (APIs) in spray-dried ASDs, highlighting polymer-drug formulation guidelines from industrial and academic perspectives. Special attention is given to new commercial and specialized polymer design strategies that can solubilize highly hydrophobic APIs and suppress the propensity for rapid drug recrystallization. These molecularly customized excipients and hierarchical excipient assemblies are promising toward informing early-stage drug-discovery development and reformulating existing API candidates into potentially lifesaving oral medicines for our growing global population.

Metal Free Reversible-Deactivation Radical Polymerizations: Advances, Challenges, and Opportunities

A considerable amount of the worldwide industrial production of synthetic polymers is currently based on radical polymerization methods. The steadily increasing demand on high performance plastics and tailored polymers which serve specialized applications is driven by the development of new techniques to enable control of polymerization reactions on a molecular level. Contrary to conventional radical polymerization, reversible-deactivation radical polymerization (RDRP) techniques provide the possibility to prepare polymers with well-defined structures and functionalities. The review provides a comprehensive summary over the development of the three most important RDRP methods, which are nitroxide mediated radical polymerization, atom transfer radical polymerization and reversible addition fragmentation chain transfer polymerization. The focus thereby is set on the newest developments in transition metal free systems, which allow using these techniques for biological or biomedical applications. After each section selected examples from materials synthesis and application to biomedical materials are summarized.

Surfactant-Free RAFT Emulsion Polymerization of Styrene Using Thermoresponsive macroRAFT Agents: Towards Smart Well-Defined Block Copolymers with High Molecular Weights

The combination of reversible addition⁻fragmentation chain transfer (RAFT) and emulsion polymerization has recently attracted much attention as a synthetic tool for high-molecular-weight block copolymers and their micellar nano-objects. Up to recently, though, the use of thermoresponsive polymers as both macroRAFT agents and latex stabilizers was impossible in aqueous media due to their hydrophobicity at the usually high polymerization temperatures. In this work, we present a straightforward surfactant-free RAFT emulsion polymerization to obtain thermoresponsive styrenic block copolymers with molecular weights of around 100 kDa and their well-defined latexes. The stability of the aqueous latexes is achieved by adding 20 vol % of the cosolvent 1,4-dioxane (DOX), increasing the phase transition temperature (PTT) of the used thermoresponsive poly(N-acryloylpyrrolidine) (PAPy) macroRAFT agents above the polymerization temperature. Furthermore, this cosolvent approach is combined with the use of poly(N,N-dimethylacrylamide)-block-poly(N-acryloylpiperidine-co-N-acryloylpyrrolidine) (PDMA-b-P(APi-co-APy)) as the macroRAFT agent owning a short stabilizing PDMA end block and a widely adjustable PTT of the P(APi-co-APy) block in between 4 and 47 °C. The temperature-induced collapse of the latter under emulsion polymerization conditions leads to the formation of RAFT nanoreactors, which allows for a very fast chain growth of the polystyrene (PS) block. In dynamic light scattering (DLS), as well as cryo-transmission electron microscopy (cryoTEM), moreover, all created latexes indeed reveal a high (temperature) stability and a reversible collapse of the thermoresponsive coronal block upon heating. Hence, this paper pioneers a versatile way towards amphiphilic thermoresponsive high-molecular-weight block copolymers and their nano-objects with tailored corona switchability.

Enhanced Performance of Blended Polymer Excipients in Delivering a Hydrophobic Drug through the Synergistic Action of Micelles and HPMCAS

Blends of hydroxypropyl methylcellulose acetate succinate (HPMCAS) and dodecyl (C₁₂)-tailed poly(N-isopropylacrylamide) (PNIPAm) were systematically explored as a model system to dispense the active ingredient phenytoin by rapid dissolution, followed by the suppression of drug crystallization for an extended period. Dynamic and static light scattering revealed that C₁₂-PNIPAm polymers, synthesized by reversible addition-fragmentation chain-transfer polymerization, self-assembled into micelles with dodecyl cores in phosphate-buffered saline (PBS, pH 6.5). A synergistic effect on drug supersaturation was documented during in vitro dissolution tests by varying the blending ratio, with HPMACS primarily aiding in rapid dissolution and PNIPAm maintaining supersaturation. Polarized light and cryogenic transmission electron microscopy experiments revealed that C₁₂-PNIPAm micelles maintain drug supersaturation by inhibiting both crystal nucleation and growth. Cross-peaks between the phenyl group of phenytoin and the isopropyl group of C₁₂-PNIPAm in 2D ¹H nuclear Overhauser effect (NOESY) spectra confirmed the existence of drug-polymer intermolecular interactions in solution. Phenytoin and polymer diffusion coefficients, measured by diffusion-ordered NMR spectroscopy (DOSY), demonstrated that the drug-polymer association constant increased with increasing local density of the corona chains, coincident with a reduction in C₁₂-PNIPAm molecular weight. These findings demonstrate a new strategy for exploiting the versatility of polymer blends through the use of self-assembled micelles in the design of advanced excipients.