Polymer-Albumin Conjugate for the Facilitated Delivery of Macromolecular Platinum Drugs

Novel Development of Nanoparticles-A Promising Direction for Precise Tumor Management

Although the clinical application of nanoparticles is still limited by biological barriers and distribution, with the deepening of our understanding of nanoparticles over the past decades, people are gradually breaking through the previous limitations in the diagnosis and treatment of tumors, providing novel strategies for clinical decision makers. The transition of nanoparticles from passive targeting to active tumor-targeting by abundant surface-modified nanoparticles is also a development process of precision cancer treatment. Different particles can be used as targeted delivery tools of antitumor drugs. The mechanism of gold nanoparticles inducing apoptosis and cycle arrest of tumor cells has been discovered. Moreover, the unique photothermal effect of gold nanoparticles may be widely used in tumor therapy in the future, with less side effects on surrounding tissues. Lipid-based nanoparticles are expected to overcome the blood-brain barrier due to their special characteristics, while polymer-based nanoparticles show better biocompatibility and lower toxicity. In this paper, we discuss the development of nanoparticles in tumor therapy and the challenges that need to be addressed.

Blood Components as Carriers for Small-Molecule Platinum Anticancer Drugs

The efficacy of platinum drugs is limited by severe side effects, drug resistance, and poor pharmacokinetic properties. Utilizing long-lasting blood components as drug carriers is a promising strategy to improve the circulation half-lives and tumor accumulation of platinum drugs. Non-immunogenic blood cells such as erythrocytes and blood proteins such as albumins, which have long lifespans, are suitable for the delivery of platinum drugs. In this concept, we briefly summarize the strategies of applying blood components as promising carriers to deliver small-molecule platinum drugs for cancer treatment. Examples of platinum drugs that are encapsulated, non-covalently attached, and covalently bound to erythrocytes and plasma proteins such as albumin and apoferritin are introduced. The potential methods to increase the stability of platinum-based thiol-maleimide conjugates involved in these delivery systems are also discussed. This concept may enlighten researchers with more ideas on the future development of novel platinum drugs that have excellent pharmacokinetic properties and antitumor performance in vivo.

Dual-Drug Conjugated Glyco-Nanoassemblies for Tumor-Triggered Targeting and Synergistic Cancer Therapy

Drug-conjugated nanoassemblies potentiate the efficiency of anticancer drugs through the advantages of high drug-loading capacity and passive/active targeting ability in cancer therapy. This study describes the synthesis of gemcitabine (Gem) and cisplatin (cisPt) dual-drug-functionalized glyco-nanoassemblies (GNs) for anticancer drug delivery systems. It also investigates the pH-triggered drug delivery of the conventional anticancer drug cisPt. A Gem-functionalized well-defined glycoblock copolymer backbone (P(iprFruMA-b-MAc)-Gem), which consists of fructose and methacrylic acid segments, was synthesized via a reversible addition-fragmentation chain transfer (RAFT) polymerization method. Following the hydrolysis of the protecting groups on the backbone copolymer, cisPt functionalization of P(FruMA-b-MAc)-Gem in aqueous media was carried out during the transformation of glycoblock polymers into self-assembled spherical glyco-nanoassemblies (GN3). Monodrug-functionalized glyco-nanoassemblies were also prepared either with Gem (GN1) or cisPt (GN2) to compare the synergetic effect of dual-drug conjugated glyco-nanoassemblies (GN3). The sizes of glyco-nanoassemblies GN1, GN2, and GN3 were found as 5.76 ± 0.64, 59.80 ± 0.13, and 53.80 ± 3.90 nm and dispersity (Đ) values as 0.476, 0.292, and 0.311 by dynamic light scattering (DLS) measurement, respectively. The in vitro studies revealed that the drug-free glyco-nanoassemblies are biocompatible at concentrations higher than 296 μg/mL. The drug-conjugated glyco-nanoassemblies (GN1 and GN2) exhibited in vitro cytotoxicity against human breast cancer cell lines of MDA-MB-231 comparable to free Gem and cisPt, illustrating an efficient drug release into the tumor environment. Additionally, GNs exhibited higher selectivity and preferential cellular internalization in MDA-MB-231 when compared to healthy cell lines of CCD-1079Sk. These dual-drug conjugated GNs can effectively enhance the killing of cancer cells and increase synergistic chemotherapy.

Chemical Conjugation in Drug Delivery Systems

Cancer is one of the diseases with the highest mortality rate. Treatments to mitigate cancer are usually so intense and invasive that they weaken the patient to cure as dangerous as the own disease. From some time ago until today, to reduce resistance generated by the constant administration of the drug and improve its pharmacokinetics, scientists have been developing drug delivery system (DDS) technology. DDS platforms aim to maximize the drugs’ effectiveness by directing them to reach the affected area by the disease and, therefore, reduce the potential side effects. Erythrocytes, antibodies, and nanoparticles have been used as carriers. Eleven antibody–drug conjugates (ADCs) involving covalent linkage has been commercialized as a promising cancer treatment in the last years. This review describes the general features and applications of DDS focused on the covalent conjugation system that binds the antibody carrier to the cytotoxic drug.

Progress of albumin-polymer conjugates as efficient drug carriers

Albumin is a protein that has garnered wide attention in nanoparticle-based drug delivery of cancer therapeutics due to its natural abundance and unique cancer-targeting ability. The propensity of albumin to naturally accumulate in tumours, further augmented by the incorporation of targeting ligands, has made the field of albumin-polymer conjugate development a much pursued one. Polymerization techniques such as RAFT and ATRP have paved the path to incorporate various polymers in the design of albumin-polymer hybrids, indicating the advancement of the field since the first instance of PEGylated albumin in 1977. The synergistic combination of albumin and polymer endows manifold features to these macromolecular hybrids to evolve as next generation therapeutics. The current review is successive to our previously published review on drug delivery vehicles based on albumin-polymer conjugates and aims to provide an update on the progress of albumin-polymer conjugates. This review also highlights the alternative of exploring albumin-polymer conjugates formed via supramolecular, non-covalent interactions. Albumin-based supramolecular polymer systems provide a versatile platform for functionalization, thereby, holding great potential in enhancing cytotoxicity and controlled delivery of therapeutic agents.

Platinum-based chemotherapy via nanocarriers and co-delivery of multiple drugs

Platinum-based anticancer drugs can inhibit the growth of cancer cells by disrupting DNA replication, which makes them widely applicable in clinics for treating tumors and cancers. However, owing to the intrinsic or acquired drug resistance and severe side effects caused in the treatment, their successful clinical applications have been limited. Various strategies have been used to address these challenges. Nanocarriers have been used for platinum drug delivery because they can be effectively deposited in tumor tissues to reduce the damage to normal organs for an enhanced permeability and retention (EPR) effect. Furthermore, for synergizing the function of platinum-based drugs with different mechanisms to decrease the toxicities, multicomponent chemotherapy has become an imperative strategy in clinical cancer treatments. This review aims to introduce the mechanisms of action and limitations of platinum-based drugs in clinics, followed by providing the current advancement of nanocarriers including lipids, polymers, dendrimers, micelles and albumin for platinum drug delivery in cancer treatments. In addition, multicomponent chemotherapy based on platinum drugs is introduced in detail. Finally, the prospects of multicomponent chemotherapy for cancer treatment are discussed as well.

Albumin conjugates and assemblies as versatile bio-functional additives and carriers for biomedical applications

As the most abundant plasma protein, serum albumin has been extensively studied and employed for therapeutic applications. Despite its direct clinical use for the maintenance of blood homeostasis in various medical conditions, this review exclusively summarizes and discusses albumin-based bio-conjugates and assemblies as versatile bio-functional additives and carriers in biomedical applications. As one of the smallest-sized proteins in the human body, albumin is physiochemically stable and biochemically inert. Moreover, albumin is also endowed with abundant specific binding sites for numerous therapeutic compounds, which also endow it with superior bioactivities. Firstly, due to its small size and binding specificity, albumin alone or its derived assemblies can be utilized as competent drug carriers, which can deliver drugs through the enhanced permeability and retention (EPR) effect or actively target lesion sites through binding with gp60 and secreted protein acidic and rich in cysteine (SPARC) in tumor sites. Furthermore, its biochemical stability and inertness make it a safe and biocompatible coating material for use in biomedical applications. Albumin-based surface modifying additives can be used to functionalize both macro substrates (e.g. surfaces of medical devices or implants) and nanoparticle surfaces (e.g. drug carriers and imaging contrast agents). In this review, we elaborate on the synthesis and applications of albumin-based bio-functional coatings and drug carriers, respectively.

'Dendrimer-Cationized-Albumin' encrusted polymeric nanoparticle improves BBB penetration and anticancer activity of doxorubicin

Glioblastoma is one of the most rapaciously growing cancer within the brain with an average lifespan of 12-15 months (5-year survival <3-4%). Doxorubicin (DOX) is clinically utilized as a first line drug in the treatment of Glioblastoma, however, its restricted entry into the brain via the blood-brain barrier (BBB), limited blood-tumor barrier (BTB) permeability, hemotoxicity, short mean half-life of 1-3 hr as well as rapid body clearance results in tremendously diminished bioactivity in glioblastoma. Dendrimer-Cationized-Albumin (dCatAlb) was synthesized following the carboxyl activation technique and the synthesized biopolymer was characterized by FTIR, MALDI-TOF and zeta potential. The prepared dCatAlb was encrusted on DOX-loaded PLGA nanoparticle core to develop a novel hybrid DOX nanoformulation (dCatAlb-pDNP; particle size: 156 ± 10.85 nm; ƺ: -10.0 ± 2.1 mV surface charge). The formulated dCatAlb-pDNP showed a unique pH-dependent DOX release profile, diminished hemolytic toxicity, higher drug uptake (<0.001) and cytotoxicity in U87MG glioblastoma cells, increase levels of caspase-3 gene in U87MG cells (approximately 5.35-fold higher) inferred that anticancer activity is primarily taking place through caspase-mediated apoptosis mechanism. The developed novel DOX nanoformulation also showed superior trans-epithelial permeation transport across monolayer bEnd.3 cells as well as notable biocompatibility and stability. The dCatAlb-pDNP showed enhanced BBB permeation efficacy as confirmed permeation assay in bEnd.3 cell-based model. The long-term formulation stability of developed nanoformulations was studied by storing them at 5 ± 2 °C and 30 ± 2 °C/60 ± 5% Relative Humidity (% RH) in the stability chamber for a period of 60 days (ICHQ1A (R2)). The outcomes of this investigation evidently indicate that dCatAlb-pDNP offers superior anticancer activity of DOX in glioblastoma cells while significantly improving its BBB permeation. The developed formulation is a biocompatible, safer and commercially viable approach to delivering DOX selectively in sustained manner glioblastoma while countering its hemolytic toxic effect, which is a major ongoing issue with conventional DOX injectable available in the market today.

Synthesis and Assembly of Laccase-Polymer Giant Amphiphiles by Self-Catalyzed CuAAC Click Chemistry

Covalent coupling of hydrophobic polymers to the exterior of hydrophilic proteins would mediate unique macroscopic assembly of bioconjugates to generate amphiphilic superstructures as novel nanoreactors or biocompatible drug delivery systems. The main objective of this study was to develop a novel strategy for the synthesis of protein-polymer giant amphiphiles by the combination of copper-mediated living radical polymerization and azide-alkyne cycloaddition reaction (CuAAC). Azide-functionalized succinimidyl ester was first synthesized for the facile introduction of azide groups to proteins such as albumin from bovine serum (BSA) and laccase from Trametes versicolor. Alkyne-terminal polymers with varied hydrophobicity were synthesized by using commercial copper wire as the activators from a trimethylsilyl protected alkyne-functionalized initiator in DMSO under ambient temperature. The conjugation of alkyne-functionalized polymers to the azide-functionalized laccase could be conducted even without additional copper catalyst, which indicated a successful self-catalyzed CuAAC reaction. The synthesized amphiphiles were found to aggregate into spherical nanoparticles in water and showed strong relevance to the hydrophobicity of coupled polymers. The giant amphiphiles showed decreased enzyme activity yet better stability during storage after chemical modification and self-assembly. These findings will deepen our understanding on protein folding, macroscopic self-assembly, and support potential applications in bionanoreactor, enzyme immobilization, and water purification.

Multicellular Tumor Spheroids (MCTS) as a 3D In Vitro Evaluation Tool of Nanoparticles

Multicellular tumor spheroid models (MCTS) are often coined as 3D in vitro models that can mimic the microenvironment of tissues. MCTS have gained increasing interest in the nano-biotechnology field as they can provide easily accessible information on the performance of nanoparticles without using animal models. Considering that many countries have put restrictions on animals testing, which will only tighten in the future as seen by the recent developments in the Netherlands, 3D models will become an even more valuable tool. Here, an overview on MCTS is provided, focusing on their use in cancer research as most nanoparticles are tested in MCTS for treatment of primary tumors. Thereafter, various types of nanoparticles-from self-assembled block copolymers to inorganic nanoparticles, are discussed. A range of physicochemical parameters including the size, shape, surface chemistry, ligands attachment, stability, and stiffness are found to influence nanoparticles in MCTS. Some of these studies are complemented by animal studies confirming that lessons from MCTS can in part predict the behaviour in vivo. In summary, MCTS are suitable models to gain additional information on nanoparticles. While not being able to replace in vivo studies, they can bridge the gap between traditional 2D in vitro studies and in vivo models.

Entry of nanoparticles into cells: the importance of nanoparticle properties

Knowledge of the interactions between nanoparticles (NPs) and cell membranes is of great importance for the design of safe and efficient nanomedicines.

Efficient Way to Generate Protein-Based Nanoparticles by in-Situ Photoinitiated Polymerization-Induced Self-Assembly

Protein-based nanoparticles with tailored properties by using different functional proteins as building blocks have many actual and potential applications in biomedicine, biotechnology, and nanotechnology. In this study, we demonstrated a facile and efficient way to synthesize protein-based nanoparticles by taking advantage of photoinitiated reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly by using multi-RAFT modified bovine serum albumin (BSA) as a macro-RAFT agent. The growth of the PHPMA chains results in the increase of the hydrophobicity of the star BSA-PHPMA conjugates, and when reaching the critical aggregation concentration in aqueous solution, they will aggregate into nanoparticles via the hydrophobic interaction of PHPMA. The generated nanoparticles also showed excellent encapsulation ability toward both hydrophobic and hydrophilic components, and as a proof of concept, after loading cancer drug DOX or biomacromolecule DNA, the protease-mediated release of the encapsulants was demonstrated. It is anticipated that the described method may open up new opportunities for designing a variety of protein-polymer self-assembled nanostructures tailored to specific applications.

Multi-stimuli-responsive biohybrid nanoparticles with cross-linked albumin coronae self-assembled by a polymer-protein biodynamer

A thermoresponsive polymer-protein biodynamer was prepared via the bioconjugation of an aliphatic aldehyde-functionalized copolymer to hydrazine-modified bovine serum albumin (BSA) through reversible pyridylhydrazone linkages. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC) results indicated that the pyridylhydrazone linkages cleaved in an intracellular-mimicking acidic milieu, thus leading to the release of BSA. The dynamic character of the protein biodynamer was demonstrated by exchange reactions with aldehyde-containing molecules. The biodynamer self-assembled into spherical micelles at a temperature above its lower critical solution temperature (LCST). Subsequently, BSA molecules within the hydrophilic coronae of the micelles were readily cross-linked via reaction with cystamine at 45°C, and multi-stimuli-responsive nanoparticles were generated. The biohybrid nanoparticles reversibly swelled and shrank as the cores of the nanoparticles were solvated below the LCST and desolvated above the LCST. The accessible reversibility of the pyridylhydrazone bonds imparts pH-responsive and dynamic characteristics to the nanoparticles. The nanoparticles displayed glutathione (GSH) responsiveness, and the synergistic effects of pH and GSH resulted in complete disintegration of the nanoparticles under the intracellular-mimicking acidic and reductive conditions. The nanoparticles were also enzyme-responsive and disintegrated rapidly in the presence of protease. In vitro cytotoxicity and cell uptake assays demonstrated that the nanoparticles were highly biocompatible and effectively internalized by HepG2 cells, which make them interesting candidates as vehicles for drug delivery application and biomimetic platforms to investigate the biological process in nature.

SIGNIFICANCE STATEMENT

In this research, we report the synthesis of a temperature and pH dual-responsive polymer-protein biodynamer through reversible pyridylhydrazone formation. The prepared biodynamer can offer a potential platform for intracellular protein delivery. The multi-stimuli-responsive biohybrid nanoparticles containing disulfide functionalities are constructed by cross-linking albumin coronae of the biodynamer micelles. With the combination of a thermoresponsive polymer, protein and reversible covalent bonds, the biohybrid nanoparticles are endowed with highly biocompatible, environmentally responsive and adaptive features. These nanoparticles present the ability to undergo changes in their constitution, hydrodynamic size and nanostructure in response to physical, chemical and biological stimuli, which make them interesting candidates as vehicles for drug delivery application and a biomimetic platform to investigate the biological process in nature.

Opportunities for dual RDRP agents in synthesizing novel polymeric materials

Dual RDRP agents provide access to new polymeric materials by combining ATRP, NMP, and RAFT polymerization without end group transformations.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

Exploiting developments in nanotechnology for the preferential delivery of platinum-based anti-cancer agents to tumours: targeting some of the hallmarks of cancer

Platinum drugs as anti-cancer therapeutics are held in extremely high regard. Despite their success, there are drawbacks associated with their use; their dose-limiting toxicity, their limited activity against an array of common cancers and patient resistance to Pt-based therapeutic regimes. Current investigations in medicinal inorganic chemistry strive to offset these shortcomings through selective targeting of Pt drugs and/or the development of Pt drugs with new or multiple modes of action. A comprehensive overview showcasing how liposomes, nanocapsules, polymers, dendrimers, nanoparticles and nanotubes may be employed as vehicles to selectively deliver cytotoxic Pt payloads to tumour cells is provided.

Metal-containing and related polymers for biomedical applications

A survey of the most recent progress in the biomedical applications of metal-containing polymers is given. Due to the unique optical, electrochemical, and magnetic properties, at least 30 different metal elements, most of them transition metals, are introduced into polymeric frameworks for interactions with biology-relevant substrates via various means. Inspired by the advance of metal-containing small molecular drugs and promoted by the great progress in polymer chemistry, metal-containing polymers have gained momentum during recent decades. According to their different applications, this review summarizes the following biomedical applications: (1) metal-containing polymers as drug delivery vehicles; (2) metal-containing polymeric drugs and biocides, including antimicrobial and antiviral agents, anticancer drugs, photodynamic therapy agents, radiotherapy agents and biocides; (3) metal-containing polymers as biosensors, and (4) metal-containing polymers in bioimaging.