Injectable and biodegradable poly(organophosphazene) hydrogel as a delivery system of docetaxel for cancer treatment

Design and Synthesis of Amphiphilic Graft Polyphosphazene Micelles for Docetaxel Delivery

The structural versatility of polydichlorophosphazene derived from the inestimable possibilities to functionalize the two halogens, attached to each phosphazene main chain unit, attracted increasing attention in the last decade. This uncountable chemical derivatization is doubled by the amphiphilic roleplay demonstrated by polyphosphazenes containing twofold side-chained hydrophilic and hydrophobic moieties. Thus, it is able to encapsulate specific bioactive molecules for various targeted nanomedicine applications. A new amphiphilic graft, polyphosphazenes (PPP/PEG-NH/Hys/MAB), was synthesized via the thermal ring-opening polymerization of hexachlorocyclotriphosphazene, followed by a subsequent two-step substitution reaction of chlorine atoms with hydrophilic methoxypolyethylene glycol amine/histamine dihydrochloride adduct (PEG-NH₂)/(Hys) and hydrophobic methyl-p-aminobenzoate (MAB), respectively. Fourier transform infrared spectroscopy (FTIR) and ¹H and ³¹P-nuclear magnetic resonance spectroscopy (NMR) have been used to validate the expected architectural assembly of the copolymer. Docetaxel loaded micelles based on synthesized PPP/PEG-NH/Hys/MAB were designed by dialysis method. The micelles size was evaluated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The drug release profiles from the PPP/PEG-NH/Hys/MAB micelles were established. In vitro cytotoxicity tests of PPP/PEG-NH/Hys/MAB micelles loaded with Docetaxel revealed that designed polymeric micelles exhibited an increased cytotoxic effect on MCF-7 cells.

Functional Nanoparticles for Enhanced Cancer Therapy

Cancer is the leading cause of death in people worldwide. The conventional therapeutic approach is mainly based on chemotherapy, which has a series of side effects. Compared with traditional chemotherapy drugs, nanoparticle-based delivery of anti-cancer drugs possesses a few attractive features. The application of nanotechnology in an interdisciplinary manner in the biomedical field has led to functional nanoparticles achieving much progress in cancer therapy. Nanoparticles have been involved in the diagnosis and targeted and personalized treatment of cancer. For example, different nano-drug strategies, including endogenous and exogenous stimuli-responsive, surface conjugation, and macromolecular encapsulation for nano-drug systems, have successfully prevented tumor procession. The future for functional nanoparticles is bright and promising due to the fast development of nanotechnology. However, there are still some challenges and limitations that need to be considered. Based on the above contents, the present article analyzes the progress in developing functional nanoparticles in cancer therapy. Research gaps and promising strategies for the clinical application are discussed.

Novel Gellan Gum-Based In Situ Nanovesicle Formulation of Docetaxel for Its Localized Delivery Using Depot Formation

In the present study, different in situ hydrogel formulations of docetaxel (DTX) based on biocompatible polymers such as Hyaluronic Acid (HA), poloxamer-407, chitosan and gellan gum were formulated to increase its therapeutic efficacy and reduce toxicity. DTX was loaded in nanovesicles (20 mg/mL equivalent to commercial strength) and further incorporated into the hydrogel bases to possess a dual rationale of protection against burst release and enhanced solubility of the drug. The optimized hydrogel formulation (NV-TPGS-3-GG-4) showed ideal rheological behavior and in situ characteristics at 37±0.5°C with sustained release of more than 144 h. The optimized formulation had instant in vitro gelation (2.8±0.3 min) with good injectability in comparison to the conventional commercial DTX injectable formulation having instant release (<2 h). Additionally, developed formulation exhibited an improved biodisponibility (25.1±0.2 h) in comparison to the commercially available formulation (1.7±0.1 h). The Solid Tumor Carcinoma model in Swiss albino mice revealed that the optimized formulation (based on gellan gum) showed better tumor reduction (85.7±1.2%) and lower toxicity as compared to the commercial formulation (77.3±1.3%). Pharmacokinetic and biodistribution studies demonstrated 3 to 4 times higher localization of drug in tumors. Our findings suggested that injectable gellan gum-based in situ hydrogel formulation can be an effective delivery system for DTX with enhanced solubility, reduced toxicity, and better targeting to the tumors for improved therapeutics.Graphical abstract.

Recent research progress on polyphosphazene-based drug delivery systems

In recent years, synthetic polymer materials have become a research hotspot in the field of drug delivery. Compared with natural polymer materials, synthetic polymer materials have more flexible structural adjustability, and can be designed to obtain clinically required delivery vehicles. Polyphosphazenes are one of the most promising biomedical materials in the future due to their controllable degradation properties and structural flexibility. These materials can be designed by controlling the hydrophilic and hydrophobic balance, introducing functional groups or drugs to form different forms of administration, such as nanoparticles, polyphosphazene-drug conjugates, injectable hydrogels, coatings, etc. In addition, the flexible backbone of polyphosphazenes and the flexibility of substitution enable them to meet researchers' design requirements in terms of stereochemistry, nanostructures, and topologies. At present, researchers have achieved a lot of successful practices in the field of targeted delivery of anticancer drugs/proteins/genes, bone tissue engineering repair, cell imaging tracking, photothermal therapy, and immunologic preparations. This review provides a summary of the progress of the recent 10 years of polyphosphazene-based drug delivery systems in terms of of chemical structure and functions.

Main-Chain Phosphorus-Containing Polymers for Therapeutic Applications

Polymers in which phosphorus is an integral part of the main chain, including polyphosphazenes and polyphosphoesters, have been widely investigated in recent years for their potential in a number of therapeutic applications. Phosphorus, as the central feature of these polymers, endears the chemical functionalization, and in some cases (bio)degradability, to facilitate their use in such therapeutic formulations. Recent advances in the synthetic polymer chemistry have allowed for controlled synthesis methods in order to prepare the complex macromolecular structures required, alongside the control and reproducibility desired for such medical applications. While the main polymer families described herein, polyphosphazenes and polyphosphoesters and their analogues, as well as phosphorus-based dendrimers, have hitherto predominantly been investigated in isolation from one another, this review aims to highlight and bring together some of this research. In doing so, the focus is placed on the essential, and often mutual, design features and structure-property relationships that allow the preparation of such functional materials. The first part of the review details the relevant features of phosphorus-containing polymers in respect to their use in therapeutic applications, while the second part highlights some recent and innovative applications, offering insights into the most state-of-the-art research on phosphorus-based polymers in a therapeutic context.

Thermoresponsive gating membranes embedded with liquid crystal(s) for pulsatile transdermal drug delivery: An overview and perspectives

Due to the circadian rhythm regulation of almost every biological process in the human body, physiological and biochemical conditions vary considerably over the course of a 24-h period. Thus, optimal drug delivery and therapy should be effectively controlled to achieve the desired therapeutic plasma concentrations and therapeutic drug responses at the required time according to chronopharmacological concepts, rather than continuous maintenance of constant drug concentrations for an extended time period. For many drugs, it is not always necessary to constantly deliver a drug into the human body under disease conditions due to rhythmic variations. Pulsatile drug delivery systems (PDDSs) have been receiving more attention in pharmaceutical development by providing a predetermined lag period, followed by a fast or rate-controlled drug release after application. PDDSs are characterized by a programmed drug release, which may release a drug at repeatable pulses to match the biological and clinical needs of a given disease therapy. This review article focuses on thermoresponsive gating membranes embedded with liquid crystals (LCs) for transdermal drug delivery using PDDS technology. In addition, the principal rationale and the advanced approaches for the use of PDDSs, the marketed products of chronotherapeutic DDSs with pulsatile function designed by various PDDS technologies, pulsatile drug delivery designed with thermoresponsive polymers, challenges and opportunities of transdermal drug delivery, and novel approaches of LC systems for drug delivery are reviewed and discussed. A brief overview of all academic research articles concerning single LC- or binary LC-embedded thermoresponsive membranes with a switchable on-off permeation function through topical application by an external temperature control, which may modulate the dosing interval and administration time according to the therapeutic needs of the human body, is also compiled and presented. In the near future, since thermal-based approaches have become a well-accepted method to enhance transdermal delivery of different water-soluble drugs and macromolecules, a combination of the thermal-assisted approach with thermoresponsive LCs membranes will have the potential to improve PDDS applications but still poses a great challenge.

Injectable Hydrogels for Cancer Therapy over the Last Decade

The interest in injectable hydrogels for cancer treatment has been significantly growing over the last decade, due to the availability of a wide range of starting polymer structures with tailored features and high chemical versatility. Many research groups are working on the development of highly engineered injectable delivery vehicle systems suitable for combined chemo-and radio-therapy, as well as thermal and photo-thermal ablation, with the aim of finding out effective solutions to overcome the current obstacles of conventional therapeutic protocols. Within this work, we have reviewed and discussed the most recent injectable hydrogel systems, focusing on the structure and properties of the starting polymers, which are mainly classified into natural or synthetic sources. Moreover, mapping the research landscape of the fabrication strategies, the main outcome of each system is discussed in light of possible clinical applications.

A Custom Radiopaque Thermoresponsive Chemotherapy-Loaded Hydrogel for Intratumoural Injection: An In Vitro and Ex Vivo Assessment of Imaging Characteristics and Material Properties

PURPOSE

Thermoresponsive hydrogels are gels which have different properties at varying temperatures. The objective of this study was to assess the material characteristics, imaging properties and chemotherapeutic drug release profile of a novel radiopaque thermoresponsive hydrogel in vitro, which is liquid at room temperature but solidifies at body temperature, to determine potential suitability for intratumoural delivery.

MATERIALS AND METHODS

An iodinated radiopaque thermoresponsive hydrogel was formulated using iodixanol at a range of concentrations and assessed for sol-gel transition, radiopacity and imaging using CT and US. A lead formulation containing iodixanol at a concentration of 9.22% weight by weight (w/w, g of iodixanol per g of hydrogel) was evaluated in vitro for injectability, disintegration and dual drug release of cisplatin and paclitaxel from the hydrogel formulation.

RESULTS

Radiopacity of the hydrogel increased in a concentration-dependent manner, but the highest concentration of iodixanol evaluated in this study (13.83% w/w) adversely affected the sol-gel transition of the hydrogel; therefore, 9.22% w/w iodixanol hydrogel was identified as the lead formulation. This formulation was readily visible on both CT and US. The formulation was hand injectable through a range of clinically relevant devices, had a sustained disintegration profile for up to 28 days and was able to deliver a sustained release of chemotherapeutic drug for up to 10 days.

CONCLUSIONS

Favourable in vitro and ex vivo imaging and material characteristics of this thermoresponsive gel are demonstrated, suggesting potential interventional oncology applications for image-guided intratumoural delivery of sustained-release chemotherapy.

Improvement of anti-cancer drug efficacy via thermosensitive hydrogel in peritoneal carcinomatosis in gastric cancer

Peritoneal carcinomatosis (PC) of gastric origin has a poor prognosis with short survival due to lack of effective therapeutic modalities. Here, we evaluated the therapeutic efficacy of an injectable thermosensitive poly (organophosphazene) (PPZ) hydrogel with docetaxel (DTX-gel) to develop an effective therapeutic agent for patient with PC. Three days after inoculation of highly metastatic 44As3Luc cells into peritoneal cavity, the mice were intravenously or intraperitoneally administered with docetaxel alone (DTX-sol IV or IP), and intraperitoneally injected with DTX-gel. The anti-tumor activity was monitored by bioluminescence live imaging system. Compared to DTX-sol IV or IP, the tumor growth was significantly reduced in the DTX-gel treated mice (p<0.0001, p=0.0001). Furthermore, the survival rate was significantly increased in the DTX-gel treated mice compared to DTX-sol IV or IP treated mice (p<0.0001, p=0.0068). Our results demonstrated that DTX-gel suppresses peritoneal metastasis by continuing release of chemotherapy agent, which leads to increase the survival rate in a PC model. Therefore, biodegradable thermosensitive hydrogel with docetaxel system can be a good anti-cancer agent for PC.

Synthesis of polyphosphazenes with different side groups and various tactics for drug delivery

Polyphosphazenes (PPZs) are hybrid polymers comprising a main chain containing nitrogen and phosphorous linked through interchanging single and double bonds, and side chains.

Injectable hydrogel-based drug delivery systems for local cancer therapy

Common chemotherapy is often associated with adverse effects in normal cells and tissues. As an alternative approach, localized chemotherapy can diminish the toxicity of systemic chemotherapy while providing a sustained release of the chemotherapeutics at the target tumor site. Therefore, injectable biodegradable hydrogels as drug delivery systems for chemotherapeutics have become a matter of importance. Here, we review the application of a variety of injectable hydrogel-based drug delivery systems, including thermosensitive, pH-sensitive, photosensitive, dual-sensitive, as well as active targeting hydrogels, for the treatment of different types of cancer. Generally, injectable hydrogel-based drug delivery systems are found to be more efficacious than the conventional systemic chemotherapy in terms of cancer treatment.

Injectable Ternary Nanocomplex Hydrogel for Long-Term Chemical Drug/Gene Dual Delivery

We developed an injectable chemical drug/gene dual delivery platform system for long-term combination therapy. Ternary nanosized thermosensitive polymer/chemical drug/gene-(PCG) complexes showing sol-gel transition were prepared by simple mixing of three components via hydrophobic and ionic interaction. The PCG complex hydrogel showed sustained release of chemical drug and genes for 40 days without denaturalization of genes in vitro. Dual delivery-mediated anticancer effects of PCG complexes were shown in vitro and in an in vivo xenograft model for up to 1 month. Therefore, this dual delivery platform is expected to be a new effective system for treatment of diseases via long-term chemical drug/gene combination therapy.

Temperature-responsive in situ nanoparticle hydrogels based on hydrophilic pendant cyclic ether modified PEG-PCL-PEG

Thermo-sensitive injectable hydrogels based on poly(ε-caprolactone)/poly(ethylene glycol) (PCL/PEG) block copolymers have attracted considerable attention for sustained drug release and tissue engineering applications.

Sustained intravitreal delivery of dexamethasone using an injectable and biodegradable thermogel

Delivery of therapeutic agents to posterior segment of the eyes is challenging due to the anatomy and physiology of ocular barriers and thus long-acting implantable formulations are much desired. In this study, a thermogelling system composed of two poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers was developed as an injectable matrix for intravitreal drug delivery. The thermogel was prepared by mixing a sol and a precipitate of PLGA-PEG-PLGA triblock copolymers with different block ratios, among which a hydrophobic glucocorticoid, dexamethasone (DEX), was incorporated. The DEX-loaded thermogel was a low-viscous liquid at low temperature and formed a non-flowing gel at body temperature. The in vitro release rate of DEX from the thermogel could be conveniently modulated by varying the mixing ratio of the two copolymers. The long-lasting intraocular residence of the thermogel was demonstrated by intravitreal injection of a fluorescence-labeled thermogel to rabbits. Compared with a DEX suspension, the intravitreal retention time of DEX increased from a dozen hours to over 1week when being loaded in the thermogel. Additionally, intravitreal administration of the thermogel did not impair the morphology of retina and cornea. This study reveals that the injectable PLGA-PEG-PLGA thermogel is a biocompatible carrier for sustained delivery of bioactive agents into the eyes, and provides an alternative approach for treatment of posterior segment diseases.

Thermogelling polymer-platinum(IV) conjugates for long-term delivery of cisplatin

In this study, we suggest a novel strategy of constituting an in situ-formed hydrogel composed of polymer-platinum(IV) conjugate to realize a long-term delivery of cisplatin. A unique conjugate was designed and synthesized by covalent linking of Pt(IV) complex to the hydrophobic end of two methoxyl poly(ethylene glycol)-b-poly(d,l-lactide) (mPEG-PLA) copolymer chains, resulting in the formation of Bi(mPEG-PLA)-Pt(IV). The conjugate could self-assemble into micelles in water, and its concentrated solution exhibited a thermoreversible sol-gel transition and formed a semisolid thermogel at body temperature. The incorporation of the cisplatin analogue Pt(IV) prodrug into the conjugate had a significant influence on its thermogelling properties and the conjugate thermogelation was attributed to the micellar aggregation. In vitro release experiments of Pt(IV)-conjugated thermogel showed that the platinum release lasted as long as two months. Furthermore, we demonstrated that the Pt(IV) prodrug was released mainly in the form of micelles and micellar aggregates from the gel depot. Compared with free cisplatin, the formation of conjugate micelles led to the enhanced in vitro cytotoxicity against cancer cells due to the effective accumulation into cells via endocytosis.

Injectable poly(organophosphazene) hydrogel system for effective paclitaxel and doxorubicin combination therapy

Combination therapy is an important option for gastric cancer which is the second leading cause of cancer-related death worldwide. The administration schedule of cell cycle-specific drugs, such as doxorubicin (DOX) and paclitaxel (PTX), is important for therapeutic efficacy. However, to control the schedule is clinically inconvenient. Additionally, in vitro cytotoxicity tests against human gastric cancer cells (SNU-601) showed that the combination indices (CIs) of DOX and PTX were 1.43 (α=0) and 1.90 (α=1), respectively, indicating that the DOX and PTX interaction was antagonistic. Thus, based on the finding that the release rate of drugs from poly(organophosphazene) (PPZ) hydrogel is dependent on the hydrophobicity of the drugs, we used injectable PPZ hydrogel in combination therapy. In vivo anticancer activity test in human gastric cancer cell-xenografted mice showed that intratumoral injection with aqueous PPZ solution, containing DOX (15 mg/kg) and PTX (30 mg/kg), resulted in the highest tumor inhibition and safety (no mortality for approximately 3 months) in the experimental groups. Consequently, PPZ hydrogel is expected to be a promising drug delivery system for cell cycle-specific drugs, facilitating the control of their administration schedule for effective combination therapy.

Efficacy, pharmacokinetics, and biodistribution of thermosensitive chitosan/β-glycerophosphate hydrogel loaded with docetaxel

Docetaxel (DTX) is a widely used anticancer drug for various solid tumors. However, its poor solubility in water and lack of specification are two limitations for clinical use. The aim of the study was to develop a thermosensitive chitosan/β-glycerophosphate (C/GP) hydrogel loaded with DTX for intratumoral delivery. The in vitro release profiles, in vivo antitumor efficacy, pharmacokinetics, and biodistribution of DTX-loaded C/GP hydrogel (DTX-C/GP) were evaluated. The results of in vitro release study demonstrated that DTX-C/GP had the property of controlled delivery for a reasonable time span of 3 weeks and the release period was substantially affected by initial DTX strength. The antitumor efficacy of DTX-C/GP was observed at 20 mg/kg in H22 tumor-bearing mice. It was found that the tumor volume was definitely minimized by intratumoral injection of DTX-C/GP. Compared with saline group, the tumor inhibition rate of blank gel, intravenous DTX solution, intratumoral DTX solution, and DTX-C/GP was 2.3%, 29.8%, 41.9%, and 58.1%, respectively. Further, the in vivo pharmacokinetic characteristics of DTX-C/GP correlated well with the in vitro release. DTX-C/GP significantly prolonged the DTX retention and maintained a high DTX concentration in tumor. The amount of DTX distributed to the normal tissues was minimized so that the toxicity was effectively reduced. In conclusion, DTX-C/GP demonstrated controlled release and significant efficacy and exhibited potential for further clinical development.

Preparation, characterization, and antitumor activities of folate-decorated docetaxel-loaded human serum albumin nanoparticles

CONTEXT

Docetaxel is now a major antitumor drug in clinical use for the treatment of a variety of tumors. The ethanol/Tween 80 solvent required in the formulation to increase the docetaxel solubility is at least partly responsible for the hypersensitivity reaction, decreased uptake by tumor tissue, and increased exposure to other body compartments.

OBJECTIVE

The present study was aimed at developing hydrosoluble DTX-FA-HSANPs targeting tumor cells and to investigate antitumor activities of the nanoparticles.

MATERIALS AND METHODS

The DTX-HSANPs were prepared using a desolvation technique and the carboxylic groups of NHS-folate were conjugated with the amino groups of the human serum albumin nanoparticles, and studied their size and zeta potential, drug loading efficiency, surface morphology, release properties in vitro, and antitumor activities.

RESULTS

The spherical nanoparticles obtained were negatively charged with a zeta potential of about -30 mV and characterized around 150 nm with a narrow size distribution. Drug loading efficiency was approximately 17.2%. The folate-decorated nanoparticles targeted a human hepatoma cell line effectively. The in vitro drug release of DTX-FA-HSANPs in the first 96 h corresponded with the following equation: Q = 18.87851 - 0.13866t + 0.21276t² - 0.00704t³ + 0.0000847854t⁴ - 0.00000034991t⁵ (R² = 0.98155). Moreover, the in vitro antitumor activities of DTX-FA-HSANPs were close to the activities of the positive control (docetaxel). The in vivo inhibition ratios of DTX-FA-HSANPs and docetaxel were 66.2% and 59.5%, respectively, at a dose of 5 mg/kg.

DISCUSSION AND CONCLUSION

In light of the observed antitumor activities, it would be of considerable interest to collect sufficient data for the clinical application of docetaxel-loaded nanoparticles.