Polyphosphoester nanoparticles as biodegradable platform for delivery of multiple drugs and siRNA

Degradable Polymeric Bio(nano)materials and Their Biomedical Applications: A Comprehensive Overview and Recent Updates

Degradable polymers (both biomacromolecules and several synthetic polymers) for biomedical applications have been promising very much in the recent past due to their low cost, biocompatibility, flexibility, and minimal side effects. Here, we present an overview with updated information on natural and synthetic degradable polymers where a brief account on different polysaccharides, proteins, and synthetic polymers viz. polyesters/polyamino acids/polyanhydrides/polyphosphazenes/polyurethanes relevant to biomedical applications has been provided. The various approaches for the transformation of these polymers by physical/chemical means viz. cross-linking, as polyblends, nanocomposites/hybrid composites, interpenetrating complexes, interpolymer/polyion complexes, functionalization, polymer conjugates, and block and graft copolymers, are described. The degradation mechanism, drug loading profiles, and toxicological aspects of polymeric nanoparticles formed are also defined. Biomedical applications of these degradable polymer-based biomaterials in and as wound dressing/healing, biosensors, drug delivery systems, tissue engineering, and regenerative medicine, etc., are highlighted. In addition, the use of such nano systems to solve current drug delivery problems is briefly reviewed.

Potentiating the Immune Responses of HBsAg-VLP Vaccine Using a Polyphosphoester-Based Cationic Polymer Adjuvant

Virus-like particle (VLP)-based vaccines are required to be associated with a suitable adjuvant to potentiate their immune responses. Herein, we report a novel, biodegradable, and biocompatible polyphosphoester-based amphiphilic cationic polymer, poly(ethylene glycol)-b-poly(aminoethyl ethylene phosphate) (PEG-PAEEP), as a Hepatitis B surface antigen (HBsAg)-VLP vaccine adjuvant. The polymer adjuvant effectively bound with HBsAg-VLP through electrostatic interactions to form a stable vaccine nanoformulation with a net positive surface charge. The nanoformulations exhibited enhanced cellular uptake by macrophages. HBsAg-VLP/PEG-PAEEP induced a significantly higher HBsAg-specific IgG titer in mice than HBsAg-VLP alone after second immunization, indicative of the antigen-dose sparing advantage of PEG-PAEEP. Furthermore, the nanoformulations exhibited a favorable biocompatibility and in vivo tolerability. This work presents the PEG-PAEEP copolymer as a promising vaccine adjuvant and as a potentially effective alternative to aluminum adjuvants.

Effective loading of incompatible drugs into nanosized vesicles: a strategy to allow concurrent administration of furosemide and midazolam in simulated clinical settings

The current study aims to assess the use of nanocarriers to limit drug incompatibilities in clinical settings, and thus eliminating serious clinical consequences (e.g., catheter obstruction and embolism), and enhancing in vivo bioavailability and efficacy. As a proof-of-concept, the impact of loading well-documented physically incompatible drugs (i.e., furosemide and midazolam) into nanosized vesicles on in vitro stability and in vivo bioavailability of the two drugs was investigated. Furosemide and midazolam were loaded into nanosized spherical vesicles at high entrapment efficiency (ca. 62-69%). The drug-loaded vesicles demonstrated a sustained drug release patterns, high physical stability and negligible hemolytic activity. Physical incompatibility was assessed by exploiting microscopic technique coupled with image processing and analysis, dynamic light scattering and laser Doppler anemometry. Incorporation of drugs separately inside the nanosized vesicles dramatically decreased size and number of the precipitated particles. In vivo, the niosomal drug mixture demonstrated a significant improvement in pharmacokinetic profiles of furosemide and midazolam compared to the mixed free drug solutions, as evidenced by their longer circulation half-lives and higher area under the plasma-concentration time curves of both drugs. Nanocarriers could provide an auspicious strategy for circumventing drug incompatibilities, thus reducing adverse reactions, hospitalization period and improving therapeutic outcomes.

The Hitchhiker's Guide to Human Therapeutic Nanoparticle Development

Nanomedicine plays an essential role in developing new therapies through novel drug delivery systems, diagnostic and imaging systems, vaccine development, antibacterial tools, and high-throughput screening. One of the most promising drug delivery systems are nanoparticles, which can be designed with various compositions, sizes, shapes, and surface modifications. These nanosystems have improved therapeutic profiles, increased bioavailability, and reduced the toxicity of the product they carry. However, the clinical translation of nanomedicines requires a thorough understanding of their properties to avoid problems with the most questioned aspect of nanosystems: safety. The particular physicochemical properties of nano-drugs lead to the need for additional safety, quality, and efficacy testing. Consequently, challenges arise during the physicochemical characterization, the production process, in vitro characterization, in vivo characterization, and the clinical stages of development of these biopharmaceuticals. The lack of a specific regulatory framework for nanoformulations has caused significant gaps in the requirements needed to be successful during their approval, especially with tests that demonstrate their safety and efficacy. Researchers face many difficulties in establishing evidence to extrapolate results from one level of development to another, for example, from an in vitro demonstration phase to an in vivo demonstration phase. Additional guidance is required to cover the particularities of this type of product, as some challenges in the regulatory framework do not allow for an accurate assessment of NPs with sufficient evidence of clinical success. This work aims to identify current regulatory issues during the implementation of nanoparticle assays and describe the major challenges that researchers have faced when exposing a new formulation. We further reflect on the current regulatory standards required for the approval of these biopharmaceuticals and the requirements demanded by the regulatory agencies. Our work will provide helpful information to improve the success of nanomedicines by compiling the challenges described in the literature that support the development of this novel encapsulation system. We propose a step-by-step approach through the different stages of the development of nanoformulations, from their design to the clinical stage, exemplifying the different challenges and the measures taken by the regulatory agencies to respond to these challenges.

Accelerating the End-to-end Production of Cyclic Phosphate Monomers with Modular Flow Chemistry

Biocompatibility, tunable degradability, broad functionalities of polyphosphoesters and their potential for biomedical applications stimulated a renewed interest from the Chemistry, Medicinal Chemistry and Polymer Sciences. Commercial applications of polyphosphoesters as...

Degradable polymers via olefin metathesis polymerization

The development of degradable polymers has commanded significant attention over the past half century. Approaches have predominantly relied on ring-opening polymerization of cyclic esters (e.g., lactones, lactides) and N-carboxyanhydrides, as well as radical ring-opening polymerizations of cyclic ketene acetals. In recent years, there has been a significant effort applied to expand the family of degradable polymers accessible via olefin metathesis polymerization. Given the excellent functional group tolerance of olefin metathesis polymerization reactions generally, a broad range of conceivable degradable moieties can be incorporated into appropriate monomers and thus into polymer backbones. This approach has proven particularly versatile in synthesizing a broad spectrum of degradable polymers including poly(ester), poly(amino acid), poly(acetal), poly(carbonate), poly(phosphoester), poly(phosphoramidate), poly(enol ether), poly(azobenzene), poly(disulfide), poly(sulfonate ester), poly(silyl ether), and poly(oxazinone) among others. In this review, we will highlight the main olefin metathesis polymerization strategies that have been used to access degradable polymers, including (i) acyclic diene metathesis polymerization, (ii) entropy-driven and (iii) enthalpy-driven ring-opening metathesis polymerization, as well as (iv) cascade enyne metathesis polymerization. In addition, the livingness or control of polymerization reactions via different strategies are highlighted and compared. Potential applications, challenges and future perspectives of this new library of degradable polyolefins are discussed. It is clear from recent and accelerating developments in this field that olefin metathesis polymerization represents a powerful synthetic tool towards degradable polymers with novel structures and properties inaccessible by other polymerization approaches.

Injectable in situ forming hydrogel gene depot to improve the therapeutic effect of STAT3 shRNA

Down-regulation of the signal transducer and activity of transcription 3 (Stat3) plays a crucial role in suppression of many solid tumors. Intratumoral injection of a gene carrier applying Stat3-small hairpin RNA (St3-shRNA) is a potential therapeutic strategy. To our knowledge, this is the first report of the intratumoral injection of St3-shRNA using a gene carrier. We herein designed biodegradable (methoxy)polyethylene glycol-b-(polycaprolactone-ran-polylactide) copolymer (MP) derivatized with a spermine group with cationic properties at the pendant position of the MP chain (MP-NH2). The designed MP-NH2 can act as a gene carrier of St3-shRNA by forming an electrostatic complex with cationic spermine. This can increase the stability of the complexes because of protection of PEG in biologic environments and can exhibit a sol-gel phase transition around body temperature for the formation of intratumorally injected MP-NH2 hydrogel depot for St3-shRNA. MP-NH2 was observed to completely condense with St3-shRNA to form St3-shRNA/MP-NH2 complexes. These complexes were protected for a relatively long time (≥72 h) from external biologic molecules of the serum, DNase, and heparin. St3-shRNA/MP-NH2 complexes in in vitro tumor cell experiments can enhance transfection of St3-shRNA, correspondingly enhance Stat3 knockdown efficiency, and inhibit tumor cell growth. St3-shRNA/MP-NH2 complexes and St3-shRNA/MP-NH2 complex-loaded hydrogel were intratumorally injected into the tumor as new efficient delivery carriers and depots of St3-shRNA. The intratumoral injection of St3-shRNA/MP-NH2 complexes and St3-shRNA/MP-NH2 complex-loaded hydrogel showed effective anti-tumor effect for an extended period of time due to the effect of Stat3 knockdown. Collectively, the development of MP-NH2 as a carrier and depot of St3-shRNA provides a new strategy for St3-shRNA therapy through intratumoral injection with high efficacy and minimal adverse effects.

Methods for preparation of nanostructured lipid carriers

Construction of nanocarriers of different structures and properties have shown great promise as delivery systems for a wide range of drugs to improve therapeutic effects and reduce side effects. Nanostructured lipid carriers (NLCs) have been introduced as a new generation of solid lipid nanoparticles (SLNs) to overcome several of the limitations associated with the SLNs. NLCs consist of a blend of solid and liquid lipids which result in a partially crystallized lipid system that enables higher drug loading efficiency compared to SLNs. Owing to their biocompatibility, low toxicity, ease of preparation and scaling-up, and high stability, NLCs have been exploited in numerous pharmaceutical applications. Different methods for fabrication of NLCs have been described in the literature. In this article, procedures involved in emulsification-solvent evaporation method, one of the commonly utilized methods for preparation of NLCs, are described in detail. Critical aspects that should be considered throughout preparation process are also highlighted to allow for consistent and reproducible construction of NLCs.

Polymer-Drug Conjugates as Nanotheranostic Agents

Since the last decade, the polymer-drug conjugate (PDC) approach has emerged as one of the most promising drug-delivery technologies owing to several benefits like circumventing premature drug release, offering controlled and targeted drug delivery, improving the stability, safety, and kinetics of conjugated drugs, and so forth. In recent years, PDC technology has advanced with the objective to further enhance the treatment outcomes by integrating nanotechnology and multifunctional characteristics into these systems. One such development is the ability of PDCs to act as theranostic agents, permitting simultaneous diagnosis and treatment options. Theranostic nanocarriers offer the opportunity to track the distribution of PDCs within the body and help to localize the diseased site. This characteristic is of particular interest, especially among those therapeutic approaches where external stimuli are supposed to be applied for abrupt drug release at the target site for localized delivery to avoid systemic side effects (e.g., Visudyne®). Thus, with the help of this review article, we are presenting the most recent updates in the domain of PDCs as nanotheranostic agents. Different methodologies utilized to design PDCs along with imaging characteristics and their applicability in a wide range of diseases, have been summarized in this article.

Polyphosphoester surfactants as general stealth coatings for polymeric nanocarriers

Opsonization of nanocarriers is one of the most important biological barriers for controlled drug delivery. The typical way to prevent such unspecific protein adsorption and thus fast clearance by the immune system is the covalent modification of drug delivery vehicles with poly(ethylene glycol) (PEG), so-called PEGylation. Recently, polyphosphoesters (PPEs) were identified as adequate PEG substitutes, however with the benefits of controllable hydrophilicity, additional chemical functionality, or biodegradability. Here, we present a general strategy by non-covalent adsorption of different nonionic PPE-surfactants to nanocarriers with stealth properties. Polyphosphoester surfactants with different binding motifs were synthesized by anionic ring-opening polymerization of cyclic phosphates or phosphonates and well-defined polymers were obtained. They were evaluated with regard to their cytotoxicity, protein interactions, and corona formation and their cellular uptake. We proved that all PPE-surfactants have lower cytotoxicity as the common PEG-based surfactant (Lutensol® AT 50) and that their hydrolysis is controlled by their chemical structure. Two polymeric nanocarriers, namely polystyrene and poly(methyl methacrylate), and bio-based and potentially biodegradable hydroxyethyl starch nanocarriers were coated with the PPE-surfactants. All nanocarriers exhibited reduced protein adsorption after coating with PPE-surfactants and a strongly reduced interaction with macrophages. This general strategy allows the transformation of polymeric nanocarriers into camouflaged nanocarriers and by the chemical versatility of PPEs will allow the attachment of additional moieties for advanced drug delivery.

Electrospun vancomycin-loaded nanofibers for management of methicillin-resistant Staphylococcus aureus-induced skin infections

Skin damage exposes the underlying layers to bacterial invasion, leading to skin and soft tissue infections. Several pathogens have developed resistance against conventional topical antimicrobial treatments and rendered them less effective. Recently, several nanomedical strategies have emerged as a potential approach to improve therapeutic outcomes of treating bacterial skin infections. In the current study, nanofibers were utilized for topical delivery of the antimicrobial drug vancomycin and evaluated as a promising tool for treatment of topical skin infections. Vancomycin-loaded nanofibers were prepared via electrospinning technique, and vancomycin-loaded nanofibers of the optimal composition exhibited nanosized uniform smooth fibers (ca. 200 nm diameter), high drug entrapment efficiency and sustained drug release patterns over 48 h. In vitro cytotoxicity assays, using several cell lines, revealed the biocompatibility of the drug-loaded nanofibers. In vitro antibacterial studies showed sustained antibacterial activity of the vancomycin-loaded nanofibers against methicillin-resistant Staphylococcus aureus (MRSA), in comparison to the free drug. The nanofibers were then tested in animal model of superficial MRSA skin infection and demonstrated a superior antibacterial efficiency, as compared to animals treated with the free vancomycin solution. Hence, nanofibers might provide an efficient nanodevice to overcome MRSA-induced skin infections and a promising topical delivery vehicle for antimicrobial drugs.

Nanomedicine: a new paradigm to overcome drug incompatibilities

OBJECTIVES

Drug incompatibilities may compromise the safety and effectiveness of combined drugs and result in mild-to-serious clinical complications, such as catheter obstruction, loss of drug efficacy, formation of toxic derivatives and embolism. Various preventive strategies have been implemented to overcome drug incompatibilities with limited success. This review presents an innovative approach to prevent drug incompatibilities via isolating the incompatible drugs into nanostructures.

KEY FINDINGS

Several examples of incompatible drugs may be loaded separately into nanostructures of various types. Physicochemical characteristics and biocompatibility of the nanomaterials that are being utilized to prevent physicochemical incompatibilities should be carefully considered.

CONCLUSIONS

There is a new era of exploiting nanomaterials in overcoming various types of physicochemical incompatibilities, with additional benefits of further improvements in pharmacokinetic profiles and pharmacological actions of the administered drugs.

Hydrophilic polyphosphoester-conjugated fluorinated chlorin as an entirely biodegradable nano-photosensitizer for reliable and efficient photodynamic therapy

An entirely biodegradable nano-photosensitizer platform (PPE-FP2) was fabricated by conjugating the photosensitizer TFPC to hydrophilic polyphosphoesters (PPEs) for efficiently liberating photosensitizers at the tumor site. The complete biodegradability of PPE-FP2 avoided residual nanoparticles in vivo after therapy, realizing reliable and effective photodynamic therapy.

Development and in vivo evaluation of chitosan nanoparticles for the oral delivery of albumin

Albumin is used as a plasma expander in critically ill patients and for several other clinical applications mainly via intravenous infusion. Oral administration of albumin can improve patient compliance although limited oral bioavailability of proteins is still a major challenge. Although nanomaterials have been extensively utilized for improving oral delivery of proteins, albumin has been utilized only as either a model drug or as a carrier for drug delivery. In the current study, for the first time, chitosan nanoparticles have been developed and extensively optimized to improve oral bioavailability of albumin as a therapeutic protein. Several characterizations have been performed for the albumin-loaded nanoparticles (e.g. drug encapsulation efficiency, DSC, FTIR, particle size, zeta potential, morphology, release kinetics, and enzymatic stability). Nanosized spherical particles were prepared and demonstrated high stability over three months either in a powdered form or as suspensions. Sustained release of albumin over time and high enzymatic stability as compared to the free albumin were observed. In vivo, higher serum concentrations of albumin in normal rabbits and cirrhotic rats were attained following oral and intraperitoneal administrations of the albumin-loaded nanoparticles as compared to the free albumin. The nanoparticles developed in the current study might provide efficient nanovehicles for oral administration of therapeutic albumin.

Development of Fully Degradable Phosphonium-Functionalized Amphiphilic Diblock Copolymers for Nucleic Acids Delivery

To expand the range of functional polymer materials to include fully hydrolytically degradable systems that bear bioinspired phosphorus-containing linkages both along the backbone and as cationic side chain moieties for packaging and delivery of nucleic acids, phosphonium-functionalized polyphosphoester- block-poly(l-lactide) copolymers of various compositions were synthesized, fully characterized, and their self-assembly into nanoparticles were studied. First, an alkyne-functionalized polyphosphoester- block-poly(l-lactide) copolymer was synthesized via a one pot sequential ring opening polymerization of an alkyne-functionalized phospholane monomer, followed by the addition of l-lactide to grow the second block. Second, the alkynyl side groups of the polyphosphoester block were functionalized via photoinitiated thiol-yne radical addition of a phosphonium-functionalized free thiol. The polymers of varying phosphonium substitution degrees were self-assembled in aqueous buffers to afford formation of well-defined core-shell assemblies with an average size ranging between 30 and 50 nm, as determined by dynamic light scattering. Intracellular delivery of the nanoparticles and their effects on cell viability and capability at enhancing transfection efficiency of nucleic acids (e.g., siRNA) were investigated. Cell viability assays demonstrated limited toxicity of the assembly to RAW 264.7 mouse macrophages, except at high polymer concentrations, where the polymer of high degree of phosphonium functionalization induced relatively higher cytotoxicity. Transfection efficiency was strongly affected by the phosphonium-to-phosphate (P+/P-) ratios of the polymers and siRNA, respectively. The AllStars Hs Cell Death siRNA complexed to the various copolymers at a P+/P- ratio of 10:1 induced comparable cell death to Lipofectamine. These fully degradable nanoparticles might provide biocompatible nanocarriers for therapeutic nucleic acid delivery.

Design and development of multifunctional polyphosphoester-based nanoparticles for ultrahigh paclitaxel dual loading

Multifunctional polyphosphoester-based nanoparticles capable of loading paclitaxel (PTX) both chemically and physically were prepared, achieving an ultrahigh equivalent PTX aqueous concentration of 25.30 mg mL^-1. The dual-loaded nanoparticles were effective in killing cancer cells, which has the potential to minimize the amount of nanocarriers needed for clinical applications, due to their ultrahigh loading capacity.

Poly(glycerol methacrylate)-based degradable nanoparticles for delivery of small interfering RNA

Nucleic acids therapeutic efficiency is generally limited by their low stability and intracellular bioavailability, and by the toxicity of the carriers used to deliver them to the target sites. Aminated poly(glycerol methacrylate) polymers are biodegradable and pH-sensitive polymers that have been used previously to deliver antisense oligonucleotide and show high transfection efficiency. The purpose of this study is to compare the efficiency and toxicity of aminated linear poly(glycerol methacrylate) (ALT) biodegradable polymer to the most commonly used cationic degradable (i.e. chitosan) and non-degradable (i.e. polyethylenimine (PEI)) polymers for delivery of short interfering RNA (siRNA). ALT, PEI and chitosan polymers were able to form nanosized particles with siRNA. Size, size-distribution and zeta-potential were measured over a wide range of nitrogen-to-phosphate (N/P) ratios, and the stability of the formed nanoparticles in saline and upon freeze-drying was also assessed. No significant cytotoxicity at the range of the tested concentrations of ALT and chitosan nanoparticles was observed, whereas the non-degradable PEI showed significant toxicity in huh-7 hepatocyte-derived carcinoma cell line. The safety profiles of the degradable polymers (ALT and chitosan) over non-degradable PEI were demonstrated in vitro and in vivo. In addition, ALT nanoparticles were able to deliver siRNA in vivo with significantly higher efficiency than chitosan nanoparticles. The results in the present study give evidence of the great implications of ALT nanoparticles in biomedical applications due to their biocompatibility, low cytotoxicity, high stability and simple preparation method.