Affinity-controlled protein encapsulation into sub-30 nm telodendrimer nanocarriers by multivalent and synergistic interactions

Unveiling cytokine charge disparity as a potential mechanism for immune regulation

Cytokines are small signaling proteins that regulate the immune responses to infection and tissue damage. Surface charges of cytokines determine their in vivo fate in immune regulation, e.g., half-life and distribution. The overall negative charges in the extracellular microenvironment and the acidosis during inflammation and infection may differentially impact cytokines with different surface charges for fine-tuned immune regulation via controlling tissue residential properties. However, the trend and role of cytokine surface charges has yet to be elucidated in the literature. Interestingly, we have observed that most pro-inflammatory cytokines have a negative charge, while most anti-inflammatory cytokines and chemokines have a positive charge. In this review, we extensively examined the surface charges of all cytokines and chemokines, summarized the pharmacokinetics and tissue adhesion of major cytokines, and analyzed the link of surface charge with cytokine biodistribution, activation, and function in immune regulation. Additionally, we identified that the general trend of charge disparity between pro- and anti-inflammatory cytokines represents a unique opportunity to develop precise immune modulation approaches, which can be applied to many inflammation-associated diseases including solid tumors, chronic wounds, infection, and sepsis.

Telodendrimer functionalized hydrogel platform for sustained antibiotics release in infection control

Wound infection commonly causes delayed healing, especially in the setting of chronic wounds. Local release of antibiotics is considered a viable approach to treat chronic wounds. We have developed a versatile telodendrimer (TD) platform for efficient loading of charged antibiotic molecules via a combination of multivalent and synergistic charge and hydrophobic interactions. The conjugation of TD in biocompatible hydrogel allows for topical application to provide sustained antibiotic release. Notably, a drug loading capacity as high as 20 % of the drug-to-resin dry weight ratio can be achieved. The payload content (PC) and release profile of the various antibiotics can be optimized by fine-tuning TD density and valency in hydrogel based on the charge and hydrophobic features of the drug, e.g., polymyxin B (PMB), gentamycin (GM), and daptomycin (Dap), for effective infection control. We have shown that hydrogel with moderately reduced TD density demonstrates a more favorable release profile than hydrogel with higher TD density. Antibiotics loaded in TD hydrogel have comparable antimicrobial potency and reduced cytotoxicity compared to the free antibiotics due to a prolonged, controlled drug release profile. In a mouse model of skin and soft tissue infection, the subcutaneous administration of PMB-loaded TD hydrogel effectively eliminated the bacterial burden. Overall, these results suggest that engineerable TD hydrogels have great potential as a topical treatment to control infection for wound healing. STATEMENT OF SIGNIFICANCE: Wound infection causes a significant delay in the wound healing process, which results in a significant financial and resource burden to the healthcare system. PEGA-telodendrimer (TD) resin hydrogel is an innovative and versatile platform that can be fine-tuned to efficiently encapsulate different antibiotics by altering charged and hydrophobic structural moieties. Additionally, this platform is advantageous as the TD density in the resin can also be fine-tuned to provide the desired antibiotic payload release profile. Sustained antibiotics release through optimization of TD density provides a prolonged therapeutic window and reduces burst release-induced cytotoxicity compared to conventional antibiotics application. Studies in a preclinical mouse model of bacteria-induced skin and soft tissue infection demonstrated promising therapeutic efficacy as evidenced by effective infection control and prolonged antibacterial efficacy of antibiotics-loaded PEGA-TD resin. In conclusion, the PEGA-TD resin platform provides a highly customizable approach for effective antibiotics release with significant potential for topical application to treat various bacterial wound infections to promote wound healing.

Carbosilane Dendritic Amphiphiles from Cholesterol or Vitamin E for Micelle Formation

Cationic dendritic amphiphiles were prepared through the linkage of interesting hydrophobic molecules such as cholesterol or vitamin E to the focal point of carbosilane dendrons. These new dendritic systems self-assembled in saline, producing micellar aggregates with hydrodynamic diameters ranging from 6.5 to 9.2 nm, and critical micelle concentrations of approximately 5 and 10 μM for second- and third-generation systems, respectively. The assemblies were able to encapsulate drugs of different charges (anionic, neutral, and cationic). Surprisingly, a 92% encapsulation efficiency for diclofenac was achieved in micelles prepared from second-generation dendrons. Toxicity measurements on peripheral blood mononuclear cells indicated different behavior depending on the generation, corresponding to the micellar regime. In contrast to the third-generation system, the second-generation system was non-toxic up to 20 μM, opening a window for its use in a micellar regimen, thereby operating as a drug delivery system for different biomedical applications.

Engineering Nanotrap Hydrogel for Immune Modulation in Wound Healing

Imbalanced immune regulation leads to the abnormal wound healing process, e.g., chronic unhealing wound or hypertrophic scar formation. Thus, the attenuation of the overflowing inflammatory factors is a viable approach to maintain the homeostatic immune regulation to facilitate normal wound healing. A versatile telodendrimer (TD) nanotrap (NT) platform is developed for efficient biomolecular protein binding. The conjugation of TD NT in size-exclusive biocompatible hydrogel resin allows for topical application for cytokine scavenging. Fine-tuning the TD NT density/valency in hydrogel resin controls resin swelling, optimizes molecular diffusion, and improves cytokine capture for effective immune modulation. The hydrogel with reduced TD NT density allows for higher protein/cytokine adsorption capacity with faster kinetics, due to the reduced barrier of TD NT nano-assembly. The positively charged TD NT hydrogel exhibits superior removal of negatively charged proinflammatory cytokines from the lipopolysaccharide (LPS, a potent endotoxin) primed immune cell culture medium. The negatively charged TD NT hydrogel removes positively charged anti-inflammatory cytokines efficiently from cell culture medium. TD NT hydrogel effectively constrains the local inflammation induced by subcutaneous LPS injection in mice. These results indicate the great potential applications of the engineered TD NT hydrogel as topical immune modulatory treatments to attenuate local inflammation.

Quantifying and Modulating Protein Encapsulation in Guanosine-Based Supramolecular Particles

The encapsulation of proteins is an effective way to preserve their structure and enhance their function. One exciting possibility is adjusting the protective agent to match the specific protein's characteristics to influence its properties. In a recent study, we developed a flow cytometry-based method to quantify the encapsulation of small-molecule dyes in colloidal particles made from guanosine derivatives (supramolecular hacky sacks (SHS) particles). We aimed to determine whether this method could quantify protein encapsulation and track changes and if the particles could be tuned to bind to specific proteins. Our results showed that fluorescein isothiocyanate (FITC)-labeled proteins had apparent association constants in the micromolar range with hydrophobicity as the dominant factor enhancing the affinities. Confocal laser scanning microscopy (CLSM) imaging supported these results and provided additional information about the protein distribution within the particles. We also tested the feasibility of tuning the avidin affinity (AVI) for SHS particles with a biotin ligand. We found that increasing the amount of biotin initially enhanced AVI binding, but then reached saturation, which we hypothesize results from noncovalent cross-linking caused by strong biotin/AVI interactions. CLSM images showed that the linker also impacted the AVI distribution within the particles. Our strategy provides an advantage over other methods for quantifying protein encapsulation by being suitable for high-throughput analysis with high reproducibility. We anticipate that future efforts to use lower-affinity ligands would result in better strategies for modulating protein affinity for drug delivery applications.

Noncovalent PEGylation of protein and peptide therapeutics

Clinical applications of protein therapeutics-an advanced generation of drugs characterized by high biological specificity-are rapidly expanding. However, their development is often impeded by unfavorable pharmacokinetic profiles and largely relies on the use of drug delivery systems to prolong their in vivo half-life and suppress undesirable immunogenicity. Although a commercially established PEGylation technology based on protein conjugation with poly(ethylene glycol) (PEG)-protective steric shield resolves some of the challenges, the search for alternatives continues. Noncovalent PEGylation, which mainly relies on multivalent (cooperative) interactions and high affinity (host-guest) complexes formed between protein and PEG offers a number of potential advantages. Among them are dynamic or reversible protection of the protein with minimal loss of biological activity, drastically lower manufacturing costs, "mix-and-match" formulations approaches, and expanded scope of PEGylation targets. While a great number of innovative chemical approaches have been proposed in recent years, the ability to effectively control the stability of noncovalently assembled protein-PEG complexes under physiological conditions presents a serious challenge for the commercial development of the technology. In an attempt to identify critical factors affecting pharmacological behavior of noncovalently linked complexes, this Review follows a hierarchical analysis of various experimental techniques and resulting supramolecular architectures. The importance of in vivo administration routes, degradation patterns of PEGylating agents, and a multitude of potential exchange reactions with constituents of physiological compartments are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Functionalized core-shell nanogel scavenger for immune modulation therapy in sepsis

Sepsis is a complex, life-threatening hyperinflammatory syndrome associated with organ failure and high mortality due to lack of effective treatment options. Here we report a core-shell hydrogel nanoparticle with the core functionalized with telodendrimer (TD) nanotrap (NT) to control hyperinflammation in sepsis. The combination of multi-valent charged and hydrophobic moieties in TD enables effective binding with biomolecules in NT. The higher crosslinking in the shell structure of nanogel excludes the abundant large serum proteins and allows for size-selectivity in scavenging the medium-sized septic molecules (10-30 kDa), e.g., lipopolysaccharides (LPS, a potent endotoxin in sepsis), thus reducing cytokine production. At the same time, the core-shell TD NT nanogel captures the over-flowing proinflammatory cytokines effectively both in vitro and in vivo from biological fluids to further control hyperinflammation. Intraperitoneal injection of core-shell TD NT nanogel effectively attenuates NF-κB activation and cytokine production in LPS-induced septic mouse models. These results indicate the potential applications of the injectable TD NT core-shell nanogel to attenuate local or systemic inflammation.

Nano-chemically Modified Tetracycline-3 (nCMT-3) Attenuates Acute Lung Injury via Blocking sTREM-1 Release and NLRP3 Inflammasome Activation

BACKGROUND

Intratracheal (IT) lipopolysaccharide (LPS) causes severe acute lung injury (ALI) and systemic inflammation. CMT-3 has pleiotropic anti-inflammatory effects including matrix metalloproteinase (MMP) inhibition, attenuation of neutrophil (PMN) activation, and elastase release. CMT-3's poor water solubility limits its bioavailability when administered orally for treating ALI. We developed a nano-formulation of CMT-3 (nCMT-3) to test the hypothesis that the pleiotropic anti-inflammatory activities of IT nCMT-3 can attenuate LPS-induced ALI.

METHODS

C57BL/6 mice were treated with aerosolized IT nCMT-3 or saline, then had IT LPS or saline administered 2 h later. Tissues were harvested at 24 h. The effects of LPS and nCMT-3 on ALI were assessed by lung histology, MMP level/activity (zymography), NLRP3 protein, and activated caspase-1 levels. Blood and bronchoalveolar lavage fluid (BALF) cell counts, PMN elastase, and soluble triggering receptor expressed on myelocytes-1 (sTREM-1) levels, TNF-α, IL-1β, IL-6, IL-18, and BALF protein levels were also measured.

RESULTS

LPS-induced ALI was characterized by histologic lung injury (PMN infiltration, alveolar thickening, edema, and consolidation) elevated proMMP-2, -9 levels and activity, increased NLRP-3 protein and activated caspase-1 levels in lung tissue. LPS-induced increases in plasma and BALF levels of sTREM-1, TNF-α, IL-1β, IL-6, IL-18, PMN elastase and BALF protein levels demonstrate significant lung/systemic inflammation and capillary leak. nCMT-3 significantly ameliorated all of these LPS-induced inflammatory markers to control levels, and decreased the incidence of ALI.

CONCLUSIONS

Pre-treatment with nCMT3 significantly attenuates LPS-induced lung injury/inflammation by multiple mechanisms including: MMP activation, PMN elastase, sTREM-1 release, and NLRP3 inflammasome/caspase-1 activation.

Nanotraps based on multifunctional materials for trapping and enrichment

Many biomarkers for early diagnosis of cancer and other diseases are difficult to detect because they often exist in body fluids in very low concentrations and are masked by high-abundance proteins such as albumin and immunoglobulins. At the same time, water pollution is one of the most serious environmental problems, but the existing adsorption materials have many shortcomings such as slow kinetics, small adsorption capacity and low adsorption efficiency. Nanotraps, mixed with gases or liquids, can capture and concentrate target substances, such as biomolecules, metal ions and oxoanions. Using nanotraps is a versatile sample pre-processing approach and it can improve the sensitivity of downstream analysis techniques. Herein, the preparations and applications of different types of nanotraps are mainly introduced. What's more, the shortcomings of using nanotraps in practical applications are also discussed. Using nanotraps is a promising sample pre-processing technology, which is of great significance for biomarkers discovery, diseases diagnosis, sewage purification and valuable ions recovery. STATEMENT OF SIGNIFICANCE: This review collates and summarizes the preparations and applications of different types of nanotraps, and discusses the shortcomings of using nanotraps in practical applications. Nanotraps, mixed with gases or liquids, can capture and concentrate target materials, such as biomolecules, metal ions and oxoanions. Using nanotraps is a versatile sample pre-processing approach and it can improve the sensitivity of downstream analysis techniques. During the COVID-19 pandemic, hydrogel nanotraps were successfully utilized for RT-PCR analysis with the FDA Emergency Used Authorization for COVID-19. Using nanotraps is a promising sample pre-processing technology, which is of great significance for biomarkers discovery, diseases diagnosis, sewage purification and valuable ions recovery.

Advances in Non-Animal Testing Approaches towards Accelerated Clinical Translation of Novel Nanotheranostic Therapeutics for Central Nervous System Disorders

Nanotheranostics constitute a novel drug delivery system approach to improving systemic, brain-targeted delivery of diagnostic imaging agents and pharmacological moieties in one rational carrier platform. While there have been notable successes in this field, currently, the clinical translation of such delivery systems for the treatment of neurological disorders has been limited by the inadequacy of correlating in vitro and in vivo data on blood-brain barrier (BBB) permeation and biocompatibility of nanomaterials. This review aims to identify the most contemporary non-invasive approaches for BBB crossing using nanotheranostics as a novel drug delivery strategy and current non-animal-based models for assessing the safety and efficiency of such formulations. This review will also address current and future directions of select in vitro models for reducing the cumbersome and laborious mandate for testing exclusively in animals. It is hoped these non-animal-based modelling approaches will facilitate researchers in optimising promising multifunctional nanocarriers with a view to accelerating clinical testing and authorisation applications. By rational design and appropriate selection of characterised and validated models, ranging from monolayer cell cultures to organ-on-chip microfluidics, promising nanotheranostic particles with modular and rational design can be screened in high-throughput models with robust predictive power. Thus, this article serves to highlight abbreviated research and development possibilities with clinical translational relevance for developing novel nanomaterial-based neuropharmaceuticals for therapy in CNS disorders. By generating predictive data for prospective nanomedicines using validated in vitro models for supporting clinical applications in lieu of requiring extensive use of in vivo animal models that have notable limitations, it is hoped that there will be a burgeoning in the nanotherapy of CNS disorders by virtue of accelerated lead identification through screening, optimisation through rational design for brain-targeted delivery across the BBB and clinical testing and approval using fewer animals. Additionally, by using models with tissue of human origin, reproducible therapeutically relevant nanomedicine delivery and individualised therapy can be realised.

Recent advancements of nanomaterial-based therapeutic strategies toward sepsis: bacterial eradication, anti-inflammation, and immunomodulation

Sepsis is a life threatening disease that is caused by a dysregulated host immune response to infection, resulting in tissue damage and organ dysfunction, which account for a high in-hospital mortality (approximately 20%). However, there are still no effective and specific therapeutics for clinical sepsis management. Nanomaterial-based strategies have emerged as promising tools for improving the therapeutic efficacy of sepsis by combating lethal bacterial infection, modulating systemic inflammatory response, preventing multiple organ failure, etc. This review has comprehensively summarized the recent advancements in nanomaterial-based strategies for the management of sepsis and severe complications, in which those nanosystems act either as inherent therapeutics or as nanocarriers for the precise delivery of agents. These formulations mechanically possess antibacterial, anti-inflammatory, immunomodulatory, and anti-oxidative effects, achieving multifunctional synergistic treatment efficacy against sepsis. Furthermore, several cell membrane-derived biomimetic nanoplatforms have been used as decoys to trap and neutralize the pathogenic toxins. The critical role of other adjuvant therapies in sepsis management, including the combination of nanotechnology and stem cell therapy, is also highlighted. Overall, this review provides insights into innovative nanotechnology-based strategies applied in sepsis treatment.

Telodendrimers: Promising Architectural Polymers for Drug Delivery

Architectural complexity has played a key role in enhancing the efficacy of nanocarriers for a variety of applications, including those in the biomedical field. With the continued evolution in designing macromolecules-based nanoparticles for drug delivery, the combination approach of using important features of linear polymers with dendrimers has offered an advantageous and viable platform. Such nanostructures, which are commonly referred to as telodendrimers, are hybrids of linear polymers covalently linked with different dendrimer generations and backbones. There is considerable variety in selection from widely studied linear polymers and dendrimers, which can help tune the overall composition of the resulting hybrid structures. This review highlights the advances in articulating syntheses of these macromolecules, and the contributions these are making in facilitating therapeutic administration. Limited progress has been made in the design and synthesis of these hybrid macromolecules, and it is through an understanding of their physicochemical properties and aqueous self-assembly that one can expect to fully exploit their potential in drug delivery.

A Rationally Designed Micellar Nanocarrier for the Delivery of Hydrophilic Methotrexate in Psoriasis Treatment

Methotrexate (MTX) is broadly applied in the clinic for the treatments of cancers and autoimmune diseases. Targeted delivery of MTX is attractive to improve its efficacy and reduce off-target toxicity. However, MTX encapsulation in nanoparticle is challenging due to its high water solubility. We rationally designed a well-defined telodendrimer (TD) nanocarrier based on MTX structure to sequester it in nanoparticles. Riboflavin (Rf) and positive charges groups were precisely conjugated on TD to form multivalent hydrogen bonds, π-π stacking and electrostatic interactions with MTX. A reverse micelle approach was developed to preset MTX and TD interactions in the core of micelles, which ensures the effective MTX loading upon dispersion into aqueous solution. As results, MTX loading capacity reaches over 20% (w/w) in the optimized nanocarrier with the particle size of 20-30 nm. The nanoformulations sustain the release of MTX in a controlled manner and exhibit excellent hemocompatibility. The in vitro cellular uptake of MTX was significantly improved by the nanoformulations. The potency of MTX nanoformulations is comparable to the free MTX in cytotoxicity. A psoriasis-like skin inflammation model was induced in mouse by imiquimod (IMQ) stimulation. MTX nanoformulations improved the psoriasis targeting and exhibited a superior long-lasting efficacy in reducing skin inflammation compared with the free MTX in psoriasis treatment.

A nanotrap improves survival in severe sepsis by attenuating hyperinflammation

Targeting single mediators has failed to reduce the mortality of sepsis. We developed a telodendrimer (TD) nanotrap (NT) to capture various biomolecules via multivalent, hybrid and synergistic interactions. Here, we report that the immobilization of TD-NTs in size-exclusive hydrogel resins simultaneously adsorbs septic molecules, e.g. lipopolysaccharides (LPS), cytokines and damage- or pathogen-associated molecular patterns (DAMPs/PAMPs) from blood with high efficiency (92-99%). Distinct surface charges displayed on the majority of pro-inflammatory cytokines (negative) and anti-inflammatory cytokines (positive) allow for the selective capture via TD NTs with different charge moieties. The efficacy of NT therapies in murine sepsis is both time-dependent and charge-dependent. The combination of the optimized NT therapy with a moderate antibiotic treatment results in a 100% survival in severe septic mice by controlling both infection and hyperinflammation, whereas survival are only 50-60% with the individual therapies. Cytokine analysis, inflammatory gene activation and tissue histopathology strongly support the survival benefits of treatments.

Electrostatically Driven Guanidinium Interaction Domains that Control Hydrogel-Mediated Protein Delivery In Vivo

Protein biologics are an important class of drugs, but the necessity for frequent parenteral administration is a major limitation. Drug-delivery materials offer a potential solution, but protein-material adsorption can cause denaturation, which reduces their effectiveness. Here, we describe a new protein delivery platform that limits direct contact between globular protein domains and material matrix, yet from a single subcutaneous administration can be tuned for long-term drug release. The strategy utilizes complementary electrostatic interactions made between a suite of designed interaction domains (IDs), installed onto the terminus of a protein of interest, and a negatively charged self-assembled fibrillar hydrogel. These intermolecular interactions can be easily modulated by choice of ID to control material interaction and desorption energies, which allows regulation of protein release kinetics to fit desired release profiles. Molecular dynamics studies provided a molecular-level understanding of the mechanisms that govern release and identified optimal binding zones on the gel fibrils that facilitate strong ID-material interactions, which are crucial for sustained release of protein. This delivery platform can be easily loaded with cargo, is shear-thin syringe implantable, provides improved protein stability, is capable of a diverse range of in vitro release rates, and most importantly, can accomplish long-term control over in vivo protein delivery.

Zwitterionic Janus Dendrimer with distinct functional disparity for enhanced protein delivery

The development of a facile protein delivery vehicle is challenging and remains an unmet demand for clinical applications. The well-defined structure and functionality of a nanocarrier are highly desirable for the reproducibility and regulatory compliance. Herein, we report for the first time a novel Janus dendrimer (JD) system, comprised of two distinct dendrons with superior protein binding and protein repelling properties, respectively, for efficient spontaneous protein loading and enhanced in vivo protein delivery. Core-forming dendron is tethered with a combination of charged and hydrophobic moieties, which coat protein surface efficiently via the multivalent and synergistic interactions. Zwitterionic peripheries on the counter dendron endow the nanoparticle (<20 nm) with a highly hydrophilic and antifouling surface, which efficiently prevents serum protein adsorption and exchange as demonstrated in biolayer interferometry assay, therefore, reducing premature protein release. Surprisingly, JD nanocarriers containing biomimicking glycerylphosphorylcholine (GPC) surface significantly enhanced the intracellular uptake of protein therapeutics specifically in cancer cells, compared with zwitterionic carboxybetain (CB)-JD and PEGylated nanocarriers. The zwitterionic JD nanocarriers greatly prolonged the in vivo pharmacokinetic profiles of payloads relative to the PEGylated nanocarriers. Janus nanocarrier controlled the in vivo release of insulin and improved the blood sugar control in mice.

Liver-targeted delivery of insulin-loaded nanoparticles via enterohepatic circulation of bile acids

Liver is the primary acting site of insulin. In this study, we developed innovative nanoparticles for oral and liver-targeted delivery of insulin by using enterohepatic circulation of bile acids. The nanoparticles were produced from cholic acid and quaternary ammonium modified chitosan derivative and hydroxypropyl methylcellulose phthalate (HPMCP). The nanoparticles had a diameter of 239 nm, an insulin loading efficiency of 90.9%, and a loading capacity of 18.2%. Cell culture studies revealed that the cholic acid groups effectively enhanced the transport of the nanoparticles through Caco-2 cell monolayer and greatly increased the absorption of the nanoparticles in HepG-2 cells via bile acid transporter mechanism. Ex vivo fluorescence images of ileum section, gastrointestinal tract, and liver demonstrated that the HPMCP increased the mucoadhesion of the nanoparticles in ileum, and the cholic acid groups facilitated the absorptions of the nanoparticles in both ileum and liver by use of bile acid transporters via enterohepatic circulation of bile acids. The therapy for diabetic mice displayed that the oral nanoparticle group could maintain hypoglycemic effect for more than 24 h and its pharmacological availability was about 30% compared with the insulin injection group. For the first time, this study demonstrates that using enterohepatic circulation of bile acids is an effective strategy for oral delivery of insulin.

Combinatorial approaches in post-polymerization modification for rational development of therapeutic delivery systems

The combinatorial polymer library approach has been proven to be effective for the optimization of therapeutic delivery systems. The library of polymers with chemical diversity has been synthesized by (i) polymerization of functionalized monomers or (ii) post-polymerization modification of reactive polymers. Most scientists have followed the first approach so far, and the second method has emerged as a versatile approach for combinatorial biomaterials discovery. This review focuses on the second approach, especially discussing the post-modifications that employ reactive polymers as templates for combinatorial synthesis of a library of functional polymers with distinct structural diversity or a combination of different functionalities. In this way, the functional polymers have a consistent chain length and distribution, which allows for systematic optimization of therapeutic delivery polymers for the efficient delivery of genes, small-molecule drugs, and protein therapeutics. In this review, the modification of representative reactive polymers for the delivery of different therapeutic payloads are summarized. The recent advances in rational design and optimization of therapeutic delivery systems based on reactive polymers are highlighted. This review ends with a summary of the current achievements and the prospect on future directions in applying the approach of post-polymerization modification of polymers to accelerate the development of therapeutic delivery systems.

STATEMENT OF SIGNIFICANCE

A strategy to rationally design and systematically optimize polymers for the efficient delivery of specific therapeutics is highly needed. The combinatorial polymer library approach could be an effective way to this end. The post-polymerization modification of reactive polymer precursors is applicable for the combinatorial synthesis of a library of functional polymers with distinct structural diversity across a consistent degree of polymerization. This allows for parallel comparison and systematic evaluation/optimization of functional polymers for efficient therapeutic delivery. This review summarizes the key elements of this combinatorial polymer synthesis approach realized by post-polymerization modification of reactive polymer precursors towards the development and identification of optimal polymers for the efficient delivery of therapeutic agents.

Polycation-telodendrimer nanocomplexes for intracellular protein delivery

Intracellular delivery of protein therapeutics by cationic polymer vehicles is an emerging technique that is, however, encountering poor stability, high cytotoxicity and non-specific cell uptake. Herein, we present a facile strategy to optimize the protein-polycation complexes by encapsulating with linear-dendritic telodendrimers. The telodendrimers with well-defined structures enable the rational design and integration of multiple functionalities for efficient encapsulation of the protein-polycation complexes by multivalent and hybrid supramolecular interactions to produce sub-20 nm nanoparticles. This strategy not only reduces the polycation-associated cytotoxicity and hemolytic activity, but also eliminates the aggregation and non-specific binding of polycations to other biomacromolecules. Moreover, the telodendrimers dissociate readily from the complexes during the cellular uptake process, which restores the capability of polycations for intracellular protein delivery. This strategy overcomes the limitations of polycationic vectors for intracellular delivery of protein therapeutics.

Riboflavin-containing telodendrimer nanocarriers for efficient doxorubicin delivery: High loading capacity, increased stability, and improved anticancer efficacy

We have developed two linear-dendritic telodendrimers (TDs) with rational design using amphiphilic riboflavin (Rf) as building blocks for efficient doxorubicin (DOX) delivery. Micellar TD nanoparticles (NPs) are composed of a hydrophilic polyethylene glycol (PEG) shell and a Rf-containing affinitive core for DOX encapsulation. Strong DOX-Rf interactions and amphiphilic Rf structure render these nanocarriers with an ultra-high DOX loading capacity (>1/1, DOX/TD, w/w), ∼100% loading efficiency, the sustained drug release and the optimal particle sizes (20-40 nm) for efficient tumor-targeted drug delivery. These nanoformulations significantly prolonged DOX circulation time in the blood without the accelerated clearance observed after multiple injections. DOX-TDs target several types of tumors efficiently in vivo, e.g. Raji lymphoma, MDA-MB-231 breast cancer, and SKOV-3 ovarian cancer. In vivo maximum tolerated dose (MTD) of DOX was increased by 2-2.5 folds for the nanoformulations in mice relative to those of free DOX and Doxil^®. These nanoformulations significantly inhibited tumor growth and prolonged survival of mice bearing SKOV-3 ovarian cancer xenografts. In summary, Rf-containing nanoformulations with high DOX loading capacity, improved stability and efficient tumor targeting lead to superior antitumor efficacy, which merit the further development for clinical application.

Multifunctional Telodendrimer Nanocarriers Restore Synergy of Bortezomib and Doxorubicin in Ovarian Cancer Treatment

We have developed multifunctional nanoparticles for codelivery of bortezomib and doxorubicin to synchronize their pharmacokinetic profiles and synergize their activities in solid tumor treatment, a need still unmet in the clinic. Micellar nanoparticles were formed by a spatially segregated, linear-dendritic telodendrimer containing three segments: a hydrophilic polyethylene glycol (PEG), a bortezomib-conjugating intermediate, and a dendritic doxorubicin-affinitive interior. Bortezomib-conjugated telodendrimers, together with doxorubicin, self-assembled into monodispersed micelles [NP(BTZ-DOX)] with small particle sizes (20-30 nm) for dual drug delivery. NP(BTZ-DOX) displayed excellent drug-loading capacity and stability, which minimized premature drug leakage and synchronized drug release profiles. Bortezomib release was accelerated significantly by acidic pH, facilitating drug availability in the acidic tumor microenvironment. Synergistic anticancer effects of combined bortezomib and doxorubicin were observed in vitro against both multiple myeloma and ovarian cancer cells. NP(BTZ-DOX) prolonged payload circulation and targeted tumors in vivo efficiently with superior signal ratios of tumor to normal organs. In vitro and in vivo proteasome inhibition analysis and biodistribution studies revealed decreased toxicity and efficient intratumoral bortezomib and doxorubicin delivery by nanoformulation. NP(BTZ-DOX) exhibited significantly improved ovarian cancer treatment in SKOV-3 xenograft mouse models in comparison with free drugs and their combinations, including bortezomib and Doxil. In summary, tumor-targeted and synchronized delivery system elicits enhanced anticancer effects and merits further development in the clinical setting. Cancer Res; 77(12); 3293-305. ©2017 AACR.

Structure-Based Nanocarrier Design for Protein Delivery

Structure-based nanocarrier design for protein delivery remains challenging and has rarely been documented in the literature. We herein present a facile computer-aided approach for rational and customized design of a unique linear-dendritic telodendrimer that self-assembles into a nanocarrier for therapeutic protein delivery, e.g., insulin. Virtual screening of a small-molecule library was performed to identify optimal protein binding moieties, which were conjugated precisely in the telodendrimer backbone preinstalled with charged moieties. We systematically tested our hypothesis and obtained significant correlations between the computational predictions and experimental results. The d-α-tocopherol (vitamin E)-containing nanocarrier showed strong binding affinity for insulin in both computational prediction and experiments, which led to improved blood glucose control. This study affirms the concept and validates the approach of structure-based nanocarrier design for protein delivery.

Charge-reversible and pH-responsive biodegradable micelles and vesicles from linear-dendritic supramolecular amphiphiles for anticancer drug delivery

The linear-dendritic supramolecular amphiphiles could assemble into charge-reversible and pH-responsive biodegradable micelles and vesicles.