Advances in Thiopurine Drug Delivery: The Current State-of-the-Art

Thiopurines (mercaptopurine, azathioprine and thioguanine) are well-established maintenance treatments for a wide range of diseases such as leukemia, inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE) and other inflammatory and autoimmune diseases in general. Worldwide, millions of patients are treated with thiopurines. The use of thiopurines has been limited because of off-target effects such as myelotoxicity and hepatotoxicity. Therefore, seeking methods to enhance target-based thiopurine-based treatment is relevant, combined with pharmacogenetic testing. Controlled-release formulations for thiopurines have been clinically tested and have shown promising outcomes in inflammatory bowel disease. Latest developments in nano-formulations for thiopurines have shown encouraging pre-clinical results, but further research and development are needed. This review provides an overview of novel drug delivery strategies for thiopurines, reviewing modified release formulations and with a focus on nano-based formulations.

Preparation of High-Performance Composite Hydrogel Reinforced by Hydrophilic Modified Waste Rubber Powder

In order to reduce the environmental pollution caused by waste rubber and to realize the recycling of resources, we proposed a facile method for the hydrophilic modification of waste rubber powder (HRP) and used it to reinforce a composite hydrogel. In the presence of toluene, dibenzoyl peroxide (BPO) diffused into the waste rubber powder. After the solvent was removed, BPO was adsorbed in the rubber powder, which was used to initiate the grafting polymerization of the acrylamide monomer on the rubber-water interface. As a result, the polyacrylamide (PAM) molecular chains were grafted onto the surface of the rubber powder to realize hydrophilic modification. The success of the grafting modification was confirmed by FTIR, contact angle testing, and thermogravimetric analysis. The hydrophilic modified waste rubber powder was used to reinforce the PAM hydrogel. Mechanical tests showed that the tensile strength and elongation at the break of the composite hydrogel reached 0.46 MPa and 1809%, respectively, which was much higher than those of pure PAM hydrogel. Such a phenomenon indicates that the waste rubber particles had a strengthening effect.

Kinetics control over the Schiff base formation reaction for fabrication of hierarchical porous carbon materials with tunable morphology for high-performance supercapacitors

Schiff base formation reaction is highly dynamic, and the microstructure of Schiff base polymers is greatly affected by reaction kinetics. Herein, a series of Schiff base cross-linked polymers (SPs) with different morphologies are synthesized through adjusting the species and amount of catalysts. Nitrogen/oxygen co-doped hierarchical porous carbon nanoparticles (HPCNs), with tunable morphology, specific surface area (SSA) and porosity, are obtained after one-step carbonization. The optimal sample (HPCN-3) possesses a coral reef-like microstructure, high SSA up to 1003 m²g^-1, and a hierarchical porous structure, exhibiting a remarkable specific capacitance of 359.5 F g^-1(at 0.5 A g^-1), outstanding rate capability and cycle stability in a 1 M H₂SO₄electrolyte. Additionally, the normalized electric double layer capacitance (EDLC) and faradaic capacitance of HPCN-3 are 0.239 F m^-2and 10.24 F g^-1respectively, certifying its superior electrochemical performance deriving from coral reef-like structure, high external surface area and efficient utilization of heteroatoms. The semi-solid-state symmetrical supercapacitor based on HPCN-3 delivers a capacitance of 55 F g^-1at 0.5 A g^-1, good cycle stability of 86.7% after 5000 GCD cycles at 10 A g^-1, and the energy density ranges from 7.64 to 4.86 Wh kg^-1.

Development of 6-Thioguanine conjugated PLGA nanoparticles through thioester bond formation: Benefits of electrospray mediated drug encapsulation and sustained release in cancer therapeutic applications

Polymeric nanoparticle-based successful delivery of hydrophobic drugs is highly desirable for its controlled and sustained release at the disease site, which is a challenge with the current synthesis methods. In the present study, an electrospray mediated facile one-step synthesis approach is explored in which a solution mixture of a hydrophobic drug, 6-thioguanine (Tg) and a biocompatible FDA approved polymer, Poly (d, l-lactide-co-glycolide) (PLGA) is injected in an applied electric field of suitable intensity to prepare drug encapsulated PLGA nanoparticles, PLGA-Tg with high yield. In order to explore the effect of external electric field on Tg loading and delivery applications, the nanoparticles are characterized using EDX, AFM, FESEM, TEM, FTIR, Raman, fluorescence, and mass spectroscopy techniques. The characterization studies indicate that the electric field mediated synthesis exhibits spherical nanoparticles with a homogenous core size distribution of ~60 nm, high encapsulation (~97.22%) and stable conjugation of Tg (via thioester linkages) with PLGA molecules in the presence of the applied electric field. The kinetic study demonstrates the 'anomalous diffusion' (non-Fickian diffusion) release mechanism in which Tg escapes from PLGA matrix with a slow, but steady diffusion rate and the sustained drug release profile continues for 60 days. To check the biological activity of the encapsulated Tg, in-vitro cell studies of the PLGA-Tg are performed on HeLa cells. The MTT assay shows significant cell death after 48 h of treatment, and the cellular internalization of the drug-loaded nanoparticles occurs through pinocytosis mediated uptake, which is established by the AFM analysis. The Raman and mass spectroscopy studies suggest that the PLGA-Tg nanoparticles are rapidly hydrolyzed inside cell cytoplasm to release Tg which initiates apoptosis-mediated cell death confirmed by as DNA fragmentation and membrane blebbing studies. The results clearly emphasize the benefits of electrospray based synthesis of polymeric nanodrug formulation through the formation of chemical bonds between polymer and drug molecules that could be easily implemented in the design and development of an effective nanotherapeutic platform with no typical 'burst effect,' prolonged release profile, and significant toxicity to the cancer cells.

pH-responsive polymeric nanoparticles with tunable sizes for targeted drug delivery

Biodegradable nanoparticles (NPs) have shown great promise as intracellular imaging probes, nanocarriers and drug delivery vehicles. In this study, we designed and prepared amphiphilic cellulose derivatives via Schiff base reactions between 2,3-dialdehyde cellulose (DAC) and amino compounds. Polymeric NPs were facilely fabricated via the self-assembly of the as-synthesized amphiphilic macromolecules. The size distribution of the obtained NPs can be tuned by changing the amount and length of the grafted hydrophobic side-chains. Anticancer drugs (DOX) were encapsulated in the NPs and the drug-loaded NPs based on cellulose derivatives were stable in neutral and alkaline environments for at least a month. They rapidly decomposed with the efficient release of the drug in acidic tumor microenvironments. These drug-loaded NPs have the potential for application in cancer treatment.

Controlled Microfluidic Synthesis of Biological Stimuli-Responsive Polymer Nanoparticles

Microfluidic flow-directed self-assembly of biological stimuli-responsive block copolymers is demonstrated with dual-location cleavable linkages at the junction between hydrophilic and hydrophobic blocks and on pendant group within the hydrophobic blocks. On-chip self-assembly within a two-phase microfluidic reactor forms various "DualM" polymer nanoparticles (PNPs), including cylinders and multicompartment vesicles, with sizes and morphologies that are tunable with manufacturing flow rate. Complex kinetically trapped intermediates between shear-dependent states provide the most detailed mechanism to date of microfluidic PNP formation in the presence of flow-variable high shear. Glutathione (GSH)-triggered changes in PNP size and internal structure depend strongly on the initial flow-directed size and internal structure. Upon incubation in GSH, flow-directed PNPs with smaller average sizes showed a faster hydrodynamic size increase (attributed to junction cleavage) and those with higher excess Gibbs free energy showed faster inner compartment growth (attributed to pendant cleavage). These results demonstrate that the combination of chemical control of the location of biologically responsive linkages with microfluidic shear processing offers promising routes for tunable "smart" polymeric nanomedicines.

Facile fabrication of pH-responsive nanoparticles from cellulose derivatives via Schiff base formation for controlled release

A controllable drug delivery system demonstrates a promising tool for diverse biomedical applications. In this work, a group of amphiphilic macromolecules was designed and prepared via Schiff base reactions between 2,3-dialdehyde cellulose (DAC) with oleylamine and amino-containing compounds. Benefiting from the self-assemble process of these amphiphilic macromolecules in the poor solvent, a group of novel pH-responsive nanoparticles (NPs) were facilely fabricated by using nanoprecipitation dropping technique. The high amount of aldehyde groups on DAC chains enabled immobilization of tunable amounts of amine compounds (up to 1.67 mmol/g) in the NPs. Furthermore, the Schiff base bonds in NPs allowed the efficient release of the drug in acidic tumor microenvironment by cleaving the Schiff base linkages. This study demonstrates the formation of a group of novel pH-sensitive and drug-loadable NPs, which provide a simple and efficient drug delivery system for the potential application for cancer treatment.