Encapsulation of therapeutic nucleoside hydrolase in functionalised nanocapsules

Smart nanocarriers for enzyme-activated prodrug therapy

Exogenous enzyme-activated prodrug therapy (EPT) is a potential cancer treatment strategy that delivers non-human enzymes into or on the surface of the cell and subsequently converts a non-toxic prodrug into an active cytotoxic substance at a specific location and time. The development of several pharmacological pairs based on EPT has been the focus of anticancer research for more than three decades. Numerous of these pharmacological pairs have progressed to clinical trials, and a few have achieved application in specific cancer therapies. The current review highlights the potential of enzyme-activated prodrug therapy as a promising anticancer treatment. Different microbial, plant, or viral enzymes and their corresponding prodrugs that advanced to clinical trials have been listed. Additionally, we discuss new trends in the field of enzyme-activated prodrug nanocarriers, including nanobubbles combined with ultrasound (NB/US), mesoscopic-sized polyion complex vesicles (PICsomes), nanoparticles, and extracellular vesicles (EVs), with special emphasis on smart stimuli-triggered drug release, hybrid nanocarriers, and the main application of nanotechnology in improving prodrugs.

Structure-Function Insights into the Dual Role in Nucleobase and Nicotinamide Metabolism and a Possible Use in Cancer Gene Therapy of the URH1p Riboside Hydrolase

The URH1p enzyme from the yeast Saccharomyces cerevisiae has gained significant interest due to its role in nitrogenous base metabolism, particularly involving uracil and nicotinamide salvage. Indeed, URH1p was initially classified as a nucleoside hydrolase (NH) with a pronounced preference for uridine substrate but was later shown to also participate in a Preiss-Handler-dependent pathway for recycling of both endogenous and exogenous nicotinamide riboside (NR) towards NAD+ synthesis. Here, we present the detailed enzymatic and structural characterisation of the yeast URH1p enzyme, a member of the group I NH family of enzymes. We show that the URH1p has similar catalytic efficiencies for hydrolysis of NR and uridine, advocating a dual role of the enzyme in both NAD+ synthesis and nucleobase salvage. We demonstrate that URH1p has a monomeric structure that is unprecedented for members of the NH homology group I, showing that oligomerisation is not strictly required for the N-ribosidic activity in this family of enzymes. The size, thermal stability and activity of URH1p towards the synthetic substrate 5-fluoruridine, a riboside precursor of the antitumoral drug 5-fluorouracil, make the enzyme an attractive tool to be employed in gene-directed enzyme-prodrug activation therapy against solid tumours.

Ribonucleoside Hydrolases-Structure, Functions, Physiological Role and Practical Uses

Ribonucleoside hydrolases are enzymes that catalyze the cleavage of ribonucleosides to nitrogenous bases and ribose. These enzymes are found in many organisms: bacteria, archaea, protozoa, metazoans, yeasts, fungi and plants. Despite the simple reaction catalyzed by these enzymes, their physiological role in most organisms remains unclear. In this review, we compare the structure, kinetic parameters, physiological role, and potential applications of different types of ribonucleoside hydrolases discovered and isolated from different organisms.

Structure, Oligomerization and Activity Modulation in N-Ribohydrolases

Enzymes catalyzing the hydrolysis of the N-glycosidic bond in nucleosides and other ribosides (N-ribohydrolases, NHs) with diverse substrate specificities are found in all kingdoms of life. While the overall NH fold is highly conserved, limited substitutions and insertions can account for differences in substrate selection, catalytic efficiency, and distinct structural features. The NH structural module is also employed in monomeric proteins devoid of enzymatic activity with different physiological roles. The homo-oligomeric quaternary structure of active NHs parallels the different catalytic strategies used by each isozyme, while providing a buttressing effect to maintain the active site geometry and allow the conformational changes required for catalysis. The unique features of the NH catalytic strategy and structure make these proteins attractive targets for diverse therapeutic goals in different diseases.

Horseradish Peroxidase-Functionalized Gold Nanoconjugates for Breast Cancer Treatment Based on Enzyme Prodrug Therapy

Introduction

Breast cancer has the highest mortality rate among cancers in women. Patients suffering from certain breast cancers, such as triple-negative breast cancer (TNBC), lack effective treatments. This represents a clinical concern due to the associated poor prognosis and high mortality. As an approach to succeed over conventional therapy limitations, we present herein the design and evaluation of a novel nanodevice based on enzyme-functionalized gold nanoparticles to efficiently perform enzyme prodrug therapy (EPT) in breast cancer cells.

Results

In particular, the enzyme horseradish peroxidase (HRP) – which oxidizes the prodrug indole-3-acetic acid (IAA) to release toxic oxidative species – is incorporated on gold nanoconjugates (HRP-AuNCs), obtaining an efficient nanoplatform for EPT. The nanodevice is biocompatible and effectively internalized by breast cancer cell lines. Remarkably, co-treatment with HRP-AuNCs and IAA (HRP-AuNCs/IAA) reduces the viability of breast cancer cells below 5%. Interestingly, 3D tumor models (multicellular tumor spheroid-like cultures) co-treated with HRP-AuNCs/IAA exhibit a 74% reduction of cell viability, whereas the free formulated components (HRP, IAA) have no effect.

Conclusion

Altogether, our results demonstrate that the designed HRP-AuNCs nanoformulation shows a remarkable therapeutic performance. These findings might help to bypass the clinical limitations of current tumor enzyme therapies and advance towards the use of nanoformulations for EPT in breast cancer.

Injectable Biocatalytic Nanocomposite Hydrogel Factories for Focal Enzyme-Prodrug Cancer Therapy

Systemic enzyme-prodrug therapy (EPT) using nanofactories, nanoparticles encapsulating prodrug-activating enzymes, is a promising concept for anticancer therapy. However, systemic delivery systems can be problematic. As nanofactories are typically carried by the blood circulation to tissues throughout the body, conversion of anticancer drugs in normal tissues can cause severe side effects. To overcome this problem, we developed a novel focal EPT approach utilizing nanocomposite hydrogels composed of a poly(dl-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(dl-lactide-co-glycolide) (PLGA-PEG-PLGA) copolymer, LAPONITE, and β-galactosidase (β-gal). The nanocomposite gels can be easily injected locally, and the inherent enzyme activity of β-gal can be preserved long-term. Prodrug 5-FU-β-gal readily permeated into the interior space of gels and was converted into the active anticancer drug 5-FU. Importantly, a single local injection of nanocomposite gels and prodrug 5-FU-β-gal provided long-lasting antitumor activity in vivo without observable side effects, demonstrating the potential utility of injectable biocatalytic hydrogel factories for novel focal EPT systems.

Towards feedback-controlled nanomedicines for smart, adaptive delivery

IMPACT STATEMENT

The timing and rate of release of pharmaceuticals from advanced drug delivery systems is an important property that has received considerable attention in the scientific literature. Broadly, these mostly fall into two classes: controlled release with a prolonged release rate or triggered release where the drug is rapidly released in response to an environmental stimulus. This review aims to highlight the potential for developing adaptive release systems that more subtlety modulate the drug release profile through continuous communication with its environment facilitated through feedback control. By reviewing the key elements of this approach in one place (fundamental principles of nanomedicine, enzymatic nanoreactors for medical therapies and feedback-controlled chemical systems) and providing additional motivating case studies in the context of chronobiology, we hope to inspire innovative development of novel "chrononanomedicines."

Biotransporting Biocatalytic Reactors toward Therapeutic Nanofactories

Drug-delivery systems (DDSs), in which drug encapsulation in nanoparticles enables targeted delivery of therapeutic agents and their release at specific disease sites, are important because they improve drug efficacy and help to decrease side effects. Although significant progress has been made in the development of DDSs for the treatment of a wide range of diseases, new approaches that increase the scope and effectiveness of such systems are still needed. Concepts such as nanoreactors and nanofactories are therefore attracting much attention. Nanoreactors, which basically consist of vesicle-encapsulated enzymes, provide prodrug conversion to therapeutic agents rather than simple drug delivery. Nanofactories are an extension of this concept and combine the features of nanoreactors and delivery carriers. Here, the required features of nanofactories are discussed and an overview of current strategies for the design and fabrication of different types of nanoreactors, i.e., systems based on lipid or polymer vesicles, capsules, mesoporous silica, viral capsids, and hydrogels, and their respective advantages and shortcomings, is provided. In vivo applications of biocatalytic reactors in the treatment of cancer, glaucoma, neuropathic pain, and alcohol intoxication are also discussed. Finally, the prospects for further progress in this important and promising field are outlined.

Development of Enzyme Loaded Polyion Complex Vesicle (PICsome): Thermal Stability of Enzyme in PICsome Compartment and Effect of Coencapsulation of Dextran on Enzyme Activity

Applications of enzymes are intensively studied, particularly for biomedical applications. However, encapsulation or immobilization of enzymes without deactivation and long-term use of enzymes are still at issue. This study focuses on the polymeric vesicles "PICsomes" for encapsulation of enzymes to develop a hecto-nanometer-scaled enzyme-loaded reactor. The catalytic activity of a PICsome-based enzyme nanoreactor is carefully examined to clarify the effect of compartmentalization by PICsome. Encapsulation by PICsome provides a stability enhancement of enzymes after 24 h incubation at 37 °C, which is particularly helpful for maintaining the high effective concentration of β-galactosidase. Moreover, to control the microenvironment inside the nanoreactor, a large amount of dextran, a neutral macromolecule, is encapsulated together with β-galactosidase in the PICsome. The resulting dextran-coloaded nanoreactor contributes to the enhancement of enzyme stability, even after exposure to 24 h incubation at -20 °C, mainly due to the antifreezing effect.

Stabilization of peptide vesicles by introducing inter-peptide disulfide bonds

PURPOSE

Previously, we have shown that the amphiphilic oligopeptide SA2 (Ac-Ala-Ala-Val-Val-Leu-Leu-Leu-Trp-Glu-Glu-COOH) spontaneously self-assemble into nano-sized vesicles in aqueous environment. Relative weak individual intermolecular interactions dominate such oligopeptide assemblies. In this study we aimed at improving the stability of such peptide vesicles by covalently crosslinking the oligopeptide vesicles using disulfide bonds. Two and three cysteines were introduced in the SA2 peptide sequence to allow crosslinking (Ac-Ala-Cys-Val-Cys-Leu-(Leu/Cys)-Leu-Trp-Glu-Glu-COOH).

RESULTS

Upon disulfide formation the crosslinked vesicles remained stable under conditions that disrupted the non-crosslinked peptide vesicles. The stabilized vesicles were more closely examined in terms of particle size (distribution) using atomic force microscopy, cryogenic electron microscopy, as well as dynamic light scattering analysis, showing an average particle radius in number between 15 and 20 nm. Using entrapment of calcein it was shown that intermolecular crosslinking of peptides within the vesicles did not affect the permeability for calcein.

CONCLUSION

Introduction of cysteines into the hydrophobic domain of the SA2 amphiphilic oligopeptides is a feasible strategy for crosslinking the peptide vesicles. Such small crosslinked oligopeptide vesicles may hold promise for drug delivery applications.

Assessment of stability, toxicity and immunogenicity of new polymeric nanoreactors for use in enzyme replacement therapy of MNGIE

The lack of a crucial metabolic enzyme can lead to accumulating substrate concentrations in the bloodstream and severe human enzyme deficiency diseases. Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE) is such a fatal genetic disorder, caused by a thymidine phosphorylase deficiency. Enzyme replacement therapy is a strategy where the deficient enzyme is administered intravenously in order to decrease the toxic substrate concentrations. Such a therapy is however not very efficient due to the fast elimination of the native enzyme from the circulation. In this study we evaluate the potential of using polymeric enzyme-loaded nanoparticles to improve the delivery of therapeutic enzymes. We constructed new 200-nanometer PMOXA-PDMS-PMOXA polymeric nanoparticles that encapsulate the enzyme thymidine phosphorylase. These particles are permeabilised for substrates and products by the reconstitution of the nucleoside-specific porin Tsx in their polymeric wall. We show that the obtained 'nanoreactors' are enzymatically active and stable in blood serum at 37 degrees C. Moreover, they do not provoke cytotoxicity when incubated with hepatocytes for 4 days, nor do they induce a macrophage-mediated inflammatory response ex vivo and in vivo. All data highlight the potential of such nanoreactors for their application in enzyme replacement therapy of MNGIE.

Therapeutic nanoreactors: combining chemistry and biology in a novel triblock copolymer drug delivery system

Triblock copolymeric nanoreactors are introduced as an alternative for liposomes as encapsulating carrier for prodrug activating enzymes. Inosine-adenosine-guanosine preferring nucleoside hydrolase of Trypanosoma vivax, a potential prodrug activating enzyme, was encapsulated in nanometer-sized vesicles constructed of poly(2-methyloxazoline)-block-poly(dimethylsiloxane)-block-(2-methyloxazoline) triblock copolymers. The nanoreactor is functionalized by incorporation of bacterial porins, OmpF or Tsx, in the reactor wall. Efficient cleavage of three natural substrates and one prodrug, 2-fluoroadenosine, by the nanoreactors was demonstrated.