Recent advances in macromolecular prodrugs

Zero-Order Kinetics Release of Lamivudine from Layer-by-Layer Coated Macromolecular Prodrug Particles

To reduce the risk of side effects and enhance therapeutic efficiency, drug delivery systems that offer precise control over active ingredient release while minimizing burst effects are considered advantageous. In this study, a novel approach for the controlled release of lamivudine (LV) was explored through the fabrication of polyelectrolyte-coated microparticles. LV was covalently attached to poly(ε-caprolactone) via ring-opening polymerization, resulting in a macromolecular prodrug (LV-PCL) with a hydrolytic release mechanism. The LV-PCL particles were subsequently coated using the layer-by-layer (LbL) technique, with polyelectrolyte multilayers assembled to potentially modify the carrier's properties. The LbL assembly process was comprehensively analyzed, including assessments of shell thickness, changes in ζ-potential, and thermodynamic properties, to provide insights into the multilayer structure and interactions. The sustained LV release over 7 weeks was observed, following zero-order kinetics (R2 > 0.99), indicating a controlled and predictable release mechanism. Carriers coated with polyethylene imine/heparin and chitosan/heparin tetralayers exhibited a distinct increase in the release rate after 6 weeks and 10 weeks, respectively, suggesting that this coating can facilitate the autocatalytic degradation of the polyester microparticles. These findings indicate the potential of this system for long-term, localized drug delivery applications, requiring sustained release with minimal burst effects.

Thermosensitive polymer prodrug nanoparticles prepared by an all-aqueous nanoprecipitation process and application to combination therapy

Despite their great versatility and ease of functionalization, most polymer-based nanocarriers intended for use in drug delivery often face serious limitations that can prevent their clinical translation, such as uncontrolled drug release and off-target toxicity, which mainly originate from the burst release phenomenon. In addition, residual solvents from the formulation process can induce toxicity, alter the physico-chemical and biological properties and can strongly impair further pharmaceutical development. To address these issues, we report polymer prodrug nanoparticles, which are prepared without organic solvents via an all-aqueous formulation process, and provide sustained drug release. This was achieved by the "drug-initiated" synthesis of well-defined copolymer prodrugs exhibiting a lower critical solution temperature (LCST) and based on the anticancer drug gemcitabine (Gem). After screening for different structural parameters, prodrugs based on amphiphilic diblock copolymers were formulated into stable nanoparticles by all-aqueous nanoprecipitation, with rather narrow particle size distribution and average diameters in the 50-80 nm range. They exhibited sustained Gem release in human serum and acetate buffer, rapid cellular uptake and significant cytotoxicity on A549 and Mia PaCa-2 cancer cells. We also demonstrated the versatility of this approach by formulating Gem-based polymer prodrug nanoparticles loaded with doxorubicin (Dox) for combination therapy. The dual-drug nanoparticles exhibited sustained release of Gem in human serum and acidic release of Dox under accelerated pathophysiological conditions. Importantly, they also induced a synergistic effect on triple-negative breast cancer line MDA-MB-231, which is a relevant cell line to this combination.

Nanoparticles: Taking a Unique Position in Medicine

The human nature of curiosity, wonder, and ingenuity date back to the age of humankind. In parallel with our history of civilization, interest in scientific approaches to unravel mechanisms underlying natural phenomena has been developing. Recent years have witnessed unprecedented growth in research in the area of pharmaceuticals and medicine. The optimism that nanotechnology (NT) applied to medicine and drugs is taking serious steps to bring about significant advances in diagnosing, treating, and preventing disease-a shift from fantasy to reality. The growing interest in the future medical applications of NT leads to the emergence of a new field for nanomaterials (NMs) and biomedicine. In recent years, NMs have emerged as essential game players in modern medicine, with clinical applications ranging from contrast agents in imaging to carriers for drug and gene delivery into tumors. Indeed, there are instances where nanoparticles (NPs) enable analyses and therapies that cannot be performed otherwise. However, NPs also bring unique environmental and societal challenges, particularly concerning toxicity. Thus, clinical applications of NPs should be revisited, and a deep understanding of the effects of NPs from the pathophysiologic basis of a disease may bring more sophisticated diagnostic opportunities and yield more effective therapies and preventive features. Correspondingly, this review highlights the significant contributions of NPs to modern medicine and drug delivery systems. This study also attempted to glimpse the future impact of NT in medicine and pharmaceuticals.

Regulation of drug release performance using mixed doxorubicin-doxorubicin dimer nanoparticles as a pH-triggered drug self-delivery system

A mixed drug self-delivery system (DSDS) with high drug content (>50%) was developed to regulate pH-triggered drug release, based on two doxorubicin (DOX)-DOX dimmers: D-DOXADH and D-DOXcar conjugated with acid-labile dynamic covalent bonds (hydrazone and carbamate, respectively) and stabilized with PEGylated D-DOXADH (D-DOXADH-PEG). Owing to the different stability of the dynamic covalent bonds in the two dimers and the noncovalent interaction between them, pH-triggered drug release could be easily regulated by adjusting the feeding ratios of the two DOX-DOX dimers in the mixed DSDS. Similar in vitro cellular toxicity was achieved with the mixed DSDS nanoparticles prepared with different feeding ratios. The mixed DSDS nanoparticles had a similar DOX content and diameter but different drug releasing rates. The MTT assays revealed that a high anti-tumor efficacy could be achieved with the slow-release mixed DSDS nanoparticles.

Facile Preparation of Macromolecular Prodrugs for Hypoxia-Specific Chemotherapy

Hypoxia-activated prodrugs (HAPs) have emerged as important candidates for chemotherapy due to their efficient killing of hypoxic cancer cells. Traditional small molecule agents, such as tirapazamine (TPZ) and its derivatives, have shown unsatisfactory therapeutic effect in clinical trials due to poor bioavailability in hypoxic tumor regions. Herein, an amphiphilic macromolecular prodrug with hypoxia-specific activity, named as hypoxia-activated macromolecular prodrug (HAMP), is prepared from poly{[poly(ethylene glycol) methacrylate]-st-(methacrylic acid)} [poly(PEGMA-st-MAA)], containing pendant TPZ residues. This polymer can self-assemble in an aqueous system into ∼37 nm sized nanoparticles. In vitro experiments indicated that HAMP shows 5× higher cytotoxicity to hypoxic cancer cells as compared to normoxic cancer cells. Therefore, the developed HAMP can be concurrently used with other therapeutic agents as a highly efficient hypoxia-activated agent.

Characterization of a novel polymeric prodrug of an antibacterial agent synthesized by mechanochemical solid-state polymerization

Polycrystalline methacryloyl monomers of the antibacterial drug nalidixic acid with an anhydride bond to the drug carboxyl group were prepared. The physicochemical properties of the synthesized vinyl monomer were characterized using X-ray powder diffraction, thermal analysis, and polarized light microscopy measurements. Mechanochemical solid-state polymerization of the resulting monomers was carried out to yield a novel polymeric prodrug. The in vitro hydrolysis behavior of the polymeric prodrug indicated that the release rate of drug from the polymeric prodrug was clearly dependent on the pH value of the hydrolysis solution. Moreover, sustained release of the drug at an almost constant rate for more than 10 hr was shown in both neutral and alkaline solutions. The results suggest that anhydride-based polymeric prodrugs could be potentially useful in colon targeted drug delivery systems.

Synthesis of Acid-Labile Poly(Doxazolidine) as a Polyprodrug with an Ultra-High Drug Content for Self-Delivery of High-Performance Chemotherapeutics

Drug self-delivery systems (DSDSs) have attracted intense attention due to their high drug content. However, their practical application still suffers from their premature drug leakage, slow drug release, and/or low antitumor efficacy of the released small molecular drugs. Here, acid-labile poly(Doxazolidine) (P(Doxaz)) is designed as a polyprodrug for the self-delivery of high antitumor chemotherapeutics (Doxazolidine (Doxaz)), with an ultrahigh Doxaz content of 92.45%. The P(Doxaz) nanoparticles could completely degrade into Doxaz within 10 h in the simulated tumor intracellular microenvironment, with a low drug leakage of 12.9% over 12 h in the normal physiological media. Owing to the ultrahigh drug content, fast acid-triggered degradation and drug release, and high antitumor efficacy of Doxaz, the proposed DSDS possesses an enhanced antiproliferation efficacy compared to the free DOX, demonstrating its potential in future tumor treatments.

One-Pot Synthesis of Chicken-Feather-Keratin-Based Prodrug Nanoparticles with High Drug Content for Tumor Intracellular DOX Delivery

pH/reduction dual-triggered chicken-feather-keratin-based prodrug nanoparticles (C-PK/- SS-Hy-D NPs) were designed via a facile one-pot oxidation coupling reaction between the thiol-functional acid-labile prodrug M-Hy-D and the PEGylated keratin (PK) graft copolymer, for tumor intracellular doxorubicin (DOX) delivery. Due to the encapsulation of the pH and the reduction of the dual-responsive small prodrug D-Hy- SS-Hy-D, a high drug content of 45.8% was obtained in the proposed prodrug nanoparticles. They exhibited excellent pH and reduction of dual-triggered drug release, with cumulative drug release of 88.6% within 51 h in the simulated tumor intracellular microenvironment, while the premature drug leakage was only 13.7% in the simulated normal physiological medium. The in vitro experiments revealed the enhanced antitumor efficacy of the C-PK/- SS-Hy-D NPs than the free DOX at a higher dosage of >10 μg/mL.

Polymeric Nanoparticles in Gene Therapy: New Avenues of Design and Optimization for Delivery Applications

The field of polymeric nanoparticles is quickly expanding and playing a pivotal role in a wide spectrum of areas ranging from electronics, photonics, conducting materials, and sensors to medicine, pollution control, and environmental technology. Among the applications of polymers in medicine, gene therapy has emerged as one of the most advanced, with the capability to tackle disorders from the modern era. However, there are several barriers associated with the delivery of genes in the living system that need to be mitigated by polymer engineering. One of the most crucial challenges is the effectiveness of the delivery vehicle or vector. In last few decades, non-viral delivery systems have gained attention because of their low toxicity, potential for targeted delivery, long-term stability, lack of immunogenicity, and relatively low production cost. In 1987, Felgner et al. used the cationic lipid based non-viral gene delivery system for the very first time. This breakthrough opened the opportunity for other non-viral vectors, such as polymers. Cationic polymers have emerged as promising candidates for non-viral gene delivery systems because of their facile synthesis and flexible properties. These polymers can be conjugated with genetic material via electrostatic attraction at physiological pH, thereby facilitating gene delivery. Many factors influence the gene transfection efficiency of cationic polymers, including their structure, molecular weight, and surface charge. Outstanding representatives of polymers that have emerged over the last decade to be used in gene therapy are synthetic polymers such as poly(l-lysine), poly(l-ornithine), linear and branched polyethyleneimine, diethylaminoethyl-dextran, poly(amidoamine) dendrimers, and poly(dimethylaminoethyl methacrylate). Natural polymers, such as chitosan, dextran, gelatin, pullulan, and synthetic analogs, with sophisticated features like guanidinylated bio-reducible polymers were also explored. This review outlines the introduction of polymers in medicine, discusses the methods of polymer synthesis, addressing top down and bottom up techniques. Evaluation of functionalization strategies for therapeutic and formulation stability are also highlighted. The overview of the properties, challenges, and functionalization approaches and, finally, the applications of the polymeric delivery systems in gene therapy marks this review as a unique one-stop summary of developments in this field.

Glutathione responsive poly(HPMA) conjugate nanoparticles for efficient 6-MP delivery

GSH-sensitive poly(HPMA)–PTA was developed and its antitumor effect on HepG2 cells was evaluated.

Non-covalent hitchhiking on endogenous carriers as a protraction mechanism for antiviral macromolecular prodrugs

Albumin is a highly successful tool of drug delivery providing drastically extended body and blood residence time for the associated cargo, but it only traffics single drug copies at a time. In turn, macromolecular prodrugs (MP) are advantaged in carrying a high drug payload but offering only a modest extension of residence time to the conjugated drugs. In this work, we engineer MP to contain terminal groups that bind to albumin via non-covalent association and reveal that this facile measure affords a significant protraction for the associated polymers. This methodology is applied to MP of acyclovir, a successful drug against herpes simplex virus infection but with poor pharmacokinetics. Resulting albumin-affine MP were efficacious agents against herpes simplex virus type 2 (HSV-2) both in vitro and in vivo. In the latter case, sub-cutaneous administration of MP resulted in local (vaginal) antiviral effects and a systemic protection. Presented benefits of non-covalent association with albumin are readily transferrable to a wide variety of MP in development for drug delivery as anticancer, anti-inflammatory, and anti-viral measures.

The benefits of macromolecular hydrogen sulfide prodrugs

Hydrogen sulfide has significant therapeutic potential that is continually being implicated in a variety of biochemical processes. This highlight article will present the benefits and opportunities in designing macromolecule based H₂S donors. Emphasis will be on how design of polymer systems can help drive the development of H₂S therapeutics. With a better range of donor systems this field will progress rapidly and new applications for H₂S therapeutics will be discovered.

Long-Acting, Potent Delivery of Combination Antiretroviral Therapy

Antiretroviral therapy (ART) has revolutionized HIV treatment, yet grand challenges remain: (i) short blood and body residence time of the antiviral drugs, (ii) relative poor antiretroviral drug penetrance into key tissue reservoirs of viral infection, namely, the spleen and lymph nodes, and (iii) obstacles in different pharmacokinetics of the necessary combination drugs. We present a novel drug delivery approach that simultaneously overcomes these limitations. We designed albumin-polymer-drug conjugates where albumin ensures long body residence time as well as lymphatic accumulation of the conjugate. The polymer enabled the delivery of combinations of drugs in precise ratios affording potency superior to the individual antiretroviral drugs and strong protection from HIV infection in primary human T cells.