pH-responsive stearic acid-O-carboxymethyl chitosan assemblies as carriers delivering small molecular drug for chemotherapy

Acid-sensitive prodrugs; a promising approach for site-specific and targeted drug release

Drugs administered through conventional formulations are devoid of targeting and often spread to various undesired sites, leading to sub-lethal concentrations at the site of action and the emergence of undesired effects. Hence, therapeutic agents should be delivered in a controlled manner at target sites. Currently, stimuli-based drug delivery systems have demonstrated a remarkable potential for the site-specific delivery of therapeutic moieties. pH is one of the widely exploited stimuli for drug delivery as several pathogenic conditions such as tumor cells, infectious and inflammatory sites are characterized by a low pH environment. This review article aims to demonstrate various strategies employed in the design of acid-sensitive prodrugs, providing an overview of commercially available acid-sensitive prodrugs. Furthermore, we have compiled the progress made for the development of new acid-sensitive prodrugs currently undergoing clinical trials. These prodrugs include albumin-binding prodrugs (Aldoxorubicin and DK049), polymeric micelle (NC-6300), polymer conjugates (ProLindac™), and an immunoconjugate (IMMU-110). The article encompasses a broad spectrum of studies focused on the development of acid-sensitive prodrugs for anticancer, antibacterial, and anti-inflammatory agents. Finally, the challenges associated with the acid-sensitive prodrug strategy are discussed, along with future directions.

O-carboxymethyl chitosan in biomedicine: A review

O-carboxymethyl chitosan (O-CMC) is a chitosan derivative produced through the substitution of hydroxyl (-OH) functional groups in glucosamine units with carboxymethyl (-CH2COOH) substituents, effectively addressing the inherent solubility issues of chitosan in aqueous solutions. O-CMC has garnered significant interest due to its enhanced solubility, elevated viscosity, minimal toxicity, and advantageous biocompatibility properties. Furthermore, O-CMC demonstrates antibacterial, antifungal, and antioxidant characteristics, rendering it a promising candidate for various biomedical uses such as wound healing, tissue engineering, anti-tumor therapies, biosensors, and bioimaging. Additionally, O-CMC is well-suited for the fabrication of nanoparticles, hydrogels, films, microcapsules, and tablets, offering opportunities for effective drug delivery systems. This review outlines the distinctive features of O-CMC, offers analyses of advancements and future potential based on current research, examines significant obstacles for clinical implementation, and foresees its ongoing significant impacts in the realm of biomedicine.

pH-responsive self-assembled nanoparticles for tumor-targeted drug delivery

Recent advances in the field of drug delivery have opened new avenues for the development of novel nanodrug delivery systems (NDDS) in cancer therapy. Self-assembled nanoparticles (SANPs) based on tumour microenvironment have great advantages in improving antitumor effect, and pH-responsive SANPs prepared by the combination of pH-responsive nanomaterials and self-assembly technology can effectively improve the efficacy and reduce the systemic toxicity of antitumor drugs. In this review, we describe the characteristics of self-assembly and its driving force, the mechanism of pH-responsive NDDS, and the nanomaterials for pH-responsive SANPs type. A series of pH-responsive SANPs for tumour-targeted drug delivery are discussed, with an emphasis on the relation between structural features and theranostic performance.

Construction of glutathione-responsive paclitaxel prodrug nanoparticles for image-guided targeted delivery and breast cancer therapy

Paclitaxel (PTX) remains an essential drug in the treatment of breast cancer. To improve metabolic stability and real-time monitoring of drug location, we develop a visualized nano-prodrug. Novel hyaluronic acid (HA)-coated glutathione (GSH)-sensitive chitosan (CS)-based nano-prodrug (HA/TPE-CS-SS-PTX NPs) with aggregation-induced emission effects (AIE) were accomplished. The prodrug NPs (drug loading 29.32%, particle size 105 nm, regular sphericity) exhibit excellent fluorescence stability. The prodrug NPs could target tumor cells with high expression of CD44 and decompose in the presence of high concentrations of glutathione. In vitro evaluations revealed that the prodrug NPs have significant cytotoxicity on 4T1 cells, and due to their excellent AIE characteristics, their position in cells can be tracked. Moreover, the prodrug NPs also shown superior anti-tumor effects in vivo experimental. Overall, the HA/TPE-CS-SS-PTX NPs we constructed have excellent bio-imaging capabilities and can be served as a potential nanomedicine for PTX delivery against breast cancer.

N-lauric-O-carboxymethyl chitosan: Synthesis, characterization and application as a pH-responsive carrier for curcumin particles

A pH-responsive amphiphilic chitosan derivative, N-lauric-O-carboxymethyl chitosan (LA-CMCh), is synthesized. Its molecular structures are characterized by FTIR, 1H NMR, and XRD methods. The influencing factors are investigated, including the amount of lauric acid (LA), carboxymethyl chitosan (CMCh), N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS), and their molar ratio, reaction time, and reaction temperature on the substitution. The degrees of substitution (DS) of the lauric groups on the -NH2 groups are calculated based on the integrated data of 1H NMR spectra. The optimum reaction condition is obtained as a reaction time of 6 h, a reaction temperature of 80 °C, and a molar ratio of lauric acid to O-carboxymethyl chitosan to N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide of 1:3:4.5:4.5, respectively. The crystallinity and initial decomposition temperature of LA-CMCh decrease, but the maximum decomposition temperature increases. The crystallinity is reduced due to the introduction of LA and the degree of hydrogen bonding among LA-CMCh molecules. LA-CMCh could self-aggregate into particles, which size and critical aggregation concentration depend on the degree of substitution and medium pH. LA-CMCh aggregates could load curcumin up to 21.70 %, and continuously release curcumin for >200 min. LA-CMCh shows nontoxicity to fibroblast HFF-1 cells and good antibacterial activity against S. aureus and E. coli, indicating that it could be used as an oil-soluble-drug carrier.

Recent developments in natural biopolymer based drug delivery systems

Targeted delivery of drug molecules to diseased sites is a great challenge in pharmaceutical and biomedical sciences. Fabrication of drug delivery systems (DDS) to target and/or diagnose sick cells is an effective means to achieve good therapeutic results along with a minimal toxicological impact on healthy cells. Biopolymers are becoming an important class of materials owing to their biodegradability, good compatibility, non-toxicity, non-immunogenicity, and long blood circulation time and high drug loading ratio for both macros as well as micro-sized drug molecules. This review summarizes the recent trends in biopolymer-based DDS, forecasting their broad future clinical applications. Cellulose chitosan, starch, silk fibroins, collagen, albumin, gelatin, alginate, agar, proteins and peptides have shown potential applications in DDS. A range of synthetic techniques have been reported to design the DDS and are discussed in the current study which is being successfully employed in ocular, dental, transdermal and intranasal delivery systems. Different formulations of DDS are also overviewed in this review article along with synthesis techniques employed for designing the DDS. The possibility of these biopolymer applications points to a new route for creating unique DDS with enhanced therapeutic qualities for scaling up creative formulations up to the clinical level.

A multi-crosslinking strategy of organic and inorganic compound bio-adhesive polysaccharide-based hydrogel for wound hemostasis

Polysaccharides are naturally occurring polymers with exceptional biodegradable and biocompatible qualities that are used as hemostatic agents. In this study, photoinduced CC bond network and dynamic bond network binding was used to give polysaccharide-based hydrogels the requisite mechanical strength and tissue adhesion. The designed hydrogel was composed of modified carboxymethyl chitosan (CMCS-MA) and oxidized dextran (OD), and introduced hydrogen bond network through tannic acid (TA) doping. Halloysite nanotubes (HNTs) were also added, and the effects of various doping amount on the performance of the hydrogel were examined, in order to enhance the hemostatic property of hydrogel. Experiments on vitro degradation and swelling demonstrated the strong structural stability of hydrogels. The hydrogel has improved tissue adhesion strength, with a maximum adhesion strength of 157.9 kPa, and demonstrated improved compressive strength, with a maximum compressive strength of 80.9 kPa. Meanwhile, the hydrogel had a low hemolysis rate and had no inhibition on cell proliferation. The created hydrogel exhibited a significant aggregation effect on platelets and a reduced blood clotting index (BCI). Importantly, the hydrogel can quickly adhere to seal the wound and has good hemostatic effect in vivo. Our work successfully prepared a polysaccharide-based bio-adhesive hydrogel dressing with stable structure, appropriate mechanical strength, and good hemostatic properties.

Covalent Organic Frameworks as Nanocarriers for Improved Delivery of Chemotherapeutic Agents

Cancer has become one of the main causes of death worldwide. Chemotherapy as one of the main therapy modalities is very unsatisfactory. The various nanocarriers have brought new opportunities for effective tumor treatment. However, most of the current nanocarriers still suffer from low efficiency and confront significant challenges in overcoming multiple biological barriers. Compared with conventional nanocarriers, covalent organic frameworks (COFs) with unique and attractive features exhibited great potential to serve as a promising platform for anticancer drug delivery. In this review, we first summarize the strategies and challenges of nanocarriers for cancer chemotherapy and then highlight the recent advances in COF-based nanocarriers for improved delivery of chemotherapeutic agents. Finally, the challenges remaining for COF-based nanocarriers for clinical applications are outlined.

Fabricating hydrophilic fatty acid-protein particles to encapsulate fucoxanthin: Fatty acid screening, structural characterization, and thermal stability analysis

Biomacromolecules are used to encapsulate carotenoids, but their poor absorption-enhancing ability restricts their application. This study integrated dietary fatty acids (FAs) into the protein-based encapsulation of fucoxanthin (FUCO) due to its positive role in carotenoid absorption. The results showed that of the 14 tested FAs, only myristic, palmitic, stearic, oleic, linoleic, and docosahexaenoic acid obviously promoted FUCO absorption. FAs were employed for FUCO encapsulation using bovine serum albumin (BSA) to fabricate FUCO-FA-BSA systems, with an encapsulation efficiency of > 98%, a particle size ranging from 113.1 nm to 193.5 nm, and a Zeta-potential between -32.8 mV and -38.3 mV. Electron microscopy and Fourier transform infrared spectroscopy revealed complete FUCO encapsulation, while the FUCO-loading particles exhibited a "core-shell" structure. The retention rate of the encapsulated FUCO increased 2.16-4.06 times when heated at 80.0 °C for 200 min. These results suggested that FA-BSA complexes might provide a promising strategy for embedding carotenoids.

pH-Responsive Polymer Nanomaterials for Tumor Therapy

The complexity of the tumor microenvironment presents significant challenges to cancer therapy, while providing opportunities for targeted drug delivery. Using characteristic signals of the tumor microenvironment, various stimuli-responsive drug delivery systems can be constructed for targeted drug delivery to tumor sites. Among these, the pH is frequently utilized, owing to the pH of the tumor microenvironment being lower than that of blood and healthy tissues. pH-responsive polymer carriers can improve the efficiency of drug delivery in vivo, allow targeted drug delivery, and reduce adverse drug reactions, enabling multifunctional and personalized treatment. pH-responsive polymers have gained increasing interest due to their advantageous properties and potential for applicability in tumor therapy. In this review, recent advances in, and common applications of, pH-responsive polymer nanomaterials for drug delivery in cancer therapy are summarized, with a focus on the different types of pH-responsive polymers. Moreover, the challenges and future applications in this field are prospected.

Structure-Based Varieties of Polymeric Nanocarriers and Influences of Their Physicochemical Properties on Drug Delivery Profiles

Carriers are equally important as drugs. They can substantially improve bioavailability of cargos and safeguard healthy cells from toxic effects of certain therapeutics. Recently, polymeric nanocarriers (PNCs) have achieved significant success in delivering drugs not only to cells but also to subcellular organelles. Variety of natural sources, availability of different synthetic routes, versatile molecular architectures, exploitable physicochemical properties, biocompatibility, and biodegradability have presented polymers as one of the most desired materials for nanocarrier design. Recent innovative concepts and advances in PNC-associated nanotechnology are providing unprecedented opportunities to engineer nanocarriers and their functions. The efficiency of therapeutic loading has got considerably increased. Structural design-based varieties of PNCs are widely employed for the delivery of small therapeutic molecules to genes, and proteins. PNCs have gained ever-increasing attention and certainly paves the way to develop advanced nanomedicines. This article presents a comprehensive investigation of structural design-based varieties of PNCs and the influences of their physicochemical properties on drug delivery profiles with perspectives highlighting the inevitability of incorporating both the multi-stimuli-responsive and multi-drug delivery properties in a single carrier to design intelligent PNCs as new and emerging research directions in this rapidly developing area.

Strategies and applications of covalent organic frameworks as promising nanoplatforms in cancer therapy

Cancer nanomedicine is the best option to face the limits of conventional chemotherapy and phototherapy methods, and thus the intensive quest for new nanomaterials to improve therapeutic efficacy and safety is still underway. Owing to their low density, well-defined structures, large surface area, finely tunable pore size, and metal ion free features, covalent organic frameworks (COFs) have been extensively studied in many research fields. The recent great interest in nanoscale COFs to improve the properties of bulk COFs has led to broadening of their applicability in the biomedical field, such as nanocarriers with an outstanding loading capacity and efficient delivery of therapeutic agents, smart theranostic nanoplatforms with excellent stability, high ROS generation, light-to-heat conversion capabilities, and different response and diagnostic characteristics. The COFs and related nanoplatforms with a wide variety of designability and functionalization have opened up a new avenue for exciting opportunities in cancer therapy. Herein we review the state-of-the-art technical and scientific developments in this emerging field, focusing on the overall progress addressed so far in building versatile COF-based nanoplatforms to enhance chemotherapy, photodynamic/photothermal therapy, and combination. Future perspectives for achieving the synergistic effect of cancer elimination and clinical translation are further discussed to motivate future contributions and explore new possibilities.

A core-shell structured alginate hydrogel beads with tunable thickness of carboxymethyl cellulose coating for pH responsive drug delivery

pH-responsive core-shell structured composite hydrogel beads, composed of a alginate (ALG) core coated with carboxymethyl cellulose (CMC) shell (ALG@CMC), were prepared by using in-situ gel preparation technology as a drug delivery system. An anti-inflammatory drug, indomethacin was loaded into the formed hydrogels as a model drug. The resulting gel samples were characterized by Fourier transforms infrared (FTIR) spectroscopy, thermo-gravimetric (TG) analysis, and scanning electron microscopy (SEM). The mechanical stability of all samples in phosphate buffered solution (PBS, pH 7.4) was approximately measured through oscillation experiments. Swelling and controlled drug release behaviors of ALG@CMC beads compared with ALG were studied in simulating gastric fluid of pH 1.2 or intestinal fluid of pH 7.4 at 37 °C. Oscillation experiments proved that the mechanical stability of ALG@CMC beads could be significantly improved by the CMC shell layer. The swelling and drug release behaviors revealed that the swelling and drug release rate of ALG@CMC beads were obviously slower than that of simple-ALG and both have significant pH responsiveness. The cumulative drug release from ALG, ALG@CMC-1, ALG@CMC-2 and ALG@CMC-3 was about 100%, 67%, 46% and 37% in simulated intestinal fluid of pH 7.4, respectively, while the drug release reached only about 2.0% in simulating gastric fluid of pH 1.2 within 720 min. These developed materials could potentially be employed as a pH-responsive drug delivery device in vivo.[Formula: see text].

A self-activating nanovesicle with oxygen-depleting capability for efficient hypoxia-responsive chemo-thermo cancer therapy

Hypoxia-activated prodrugs (HAPs) promise to mitigate side effects of conventional chemotherapy and to enable precise medication treatment. One challenge facing HAPs-based chemotherapy is prodrug failure in normoxic tumor region. However, current strategies to enhance tumor hypoxia rely on delivery of oxygen-consuming agents and external stimulation, which can impede the optimal application of HAPs. Herein, a novel self-activating nanovesicle, TH-302@BR-Chitosan NPs, is constructed by assembling bilirubin-chitosan conjugate (named as BR-Chitosan) with a HAP, TH-302. It is interesting to find that the BR-Chitosan shows the inherent oxygen-depleting performance, especially in the presence of over expressed H₂O₂ in tumor area, during which the BR-Chitosan can facily transform into biliverdin-chitosan (BV-Chitosan) and subsequently result in the disassembly of nanovesicles to release and activate the prodrug. Thus, this in situ strengthening hypoxia level of tumor can greatly promote the chemotherapy efficacy of HAPs. Moreover, as the oxidation derivatives of BR-Chitosan, BV-Chitosan exhibits intense absorbance at the range from long wavelength of visible region to near-infrared region, which can be acted as an effective photothermal agent for photothermal therapy (PTT). This biodegradable and self-activating nanovesicle with concise formulation demonstrates greatly enhanced synergistic therapeutic outcome in the activatable chemo-thermo combined therapy, showing much promising in future clinical transformation.

Stimuli-Responsive Polymeric Nanocarriers for Drug Delivery, Imaging, and Theragnosis

In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers could be further modified as stimuli-responsive systems based on the mechanism of triggered release, i.e., response to a specific stimulus, either endogenous (pH, enzymes, temperature, redox values, hypoxia, glucose levels) or exogenous (light, magnetism, ultrasound, electrical pulses) for the effective biodistribution and controlled release of drugs or genes at specific sites. Various nanoparticles (NPs) have been functionalized and used as templates for imaging systems in the form of metallic NPs, dendrimers, polymeric NPs, quantum dots, and liposomes. The use of polymeric nanocarriers for imaging and to deliver active compounds has attracted considerable interest in various cancer therapy fields. So-called smart nanopolymer systems are built to respond to certain stimuli such as temperature, pH, light intensity and wavelength, and electrical, magnetic and ultrasonic fields. Many imaging techniques have been explored including optical imaging, magnetic resonance imaging (MRI), nuclear imaging, ultrasound, photoacoustic imaging (PAI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). This review reports on the most recent developments in imaging methods by analyzing examples of smart nanopolymers that can be imaged using one or more imaging techniques. Unique features, including nontoxicity, water solubility, biocompatibility, and the presence of multiple functional groups, designate polymeric nanocues as attractive nanomedicine candidates. In this context, we summarize various classes of multifunctional, polymeric, nano-sized formulations such as liposomes, micelles, nanogels, and dendrimers.