Sie Yon Lau

Towards targeted cancer therapy: Aptamer or oncolytic virus?

&NA; Cancer is a leading cause of global mortality. Whilst anticancer awareness programs have increased significantly over the years, scientific research into the development of efficient and specific drugs to target cancerous cells for enhanced therapeutic effects has not received much clinical success. Chemotherapeutic agents are incapable of acting specifically on cancerous cells, thus causing low therapeutic effects accompanied by toxicity to surrounding normal tissues. The search for smart, highly specific and efficient cancer treatments and delivery systems continues to be a significant research endeavor. Targeted cancer therapy is an evolving treatment approach with great promise in enhancing the efficacy of cancer therapies via the delivery of therapeutic agents specifically to and into desired tumor cells using viral or non‐viral targeting elements. Viral oncotherapy is an advanced cancer therapy based on the use of oncolytic viruses (OV) as elements to specifically target, replicate and kill malignant cancer cells selectively without affecting surrounding healthy cells. Aptamers, on the other hand, are non‐viral targeting elements that are single‐stranded nucleic acids with high specificity, selectivity and binding affinity towards their cognate targets. Aptamers have emerged as a new class of bioaffinity targeting elements can be generated and molecularly engineered to selectively bind to diverse targets including proteins, cells and tissues. This article discusses, comparatively, the potentials and impacts of both viral and aptamer‐mediated targeted cancer therapies in advancing conventional drug delivery systems through enhanced target specificity, therapeutic payload, bioavailability of the therapeutic agents at the target sites whilst minimizing systemic cytotoxicity. This article emphasizes on effective site‐directed targeting mechanisms and efficacy issues that impact on clinical applications. Graphical abstract The killing mechanism of aptamer‐mediated formulations towards tumor cells. Figure. No caption available.

Biophysical characterization of layer‐by‐layer synthesis of aptamer‐drug microparticles for enhanced cell targeting

Targeted delivery of drug molecules to specific cells in mammalian systems demonstrates a great potential to enhance the efficacy of current pharmaceutical therapies. Conventional strategies for pharmaceutical delivery are often associated with poor therapeutic indices and high systemic cytotoxicity, and this result in poor disease suppression, low surviving rates, and potential contraindication of drug formulation. The emergence of aptamers has elicited new research interests into enhanced targeted drug delivery due to their unique characteristics as targeting elements. Aptamers can be engineered to bind to their cognate cellular targets with high affinity and specificity, and this is important to navigate active drug molecules and deliver sufficient dosage to targeted malignant cells. However, the targeting performance of aptamers can be impacted by several factors including endonuclease‐mediated degradation, rapid renal filtration, biochemical complexation, and cell membrane electrostatic repulsion. This has subsequently led to the development of smart aptamer‐immobilized biopolymer systems as delivery vehicles for controlled and sustained drug release to specific cells at effective therapeutic dosage and minimal systemic cytotoxicity. This article reports the synthesis and in vitro characterization of a novel multi‐layer co‐polymeric targeted drug delivery system based on drug‐loaded PLGA‐Aptamer‐PEI (DPAP) formulation with a stage‐wise delivery mechanism. A thrombin‐specific DNA aptamer was used to develop the DPAP system while Bovine Serum Albumin (BSA) was used as a biopharmaceutical drug in the synthesis process by ultrasonication. Biophysical characterization of the DPAP system showed a spherical shaped particulate formulation with a unimodal particle size distribution of average size ∼0.685 µm and a zeta potential of +0.82 mV. The DPAP formulation showed a high encapsulation efficiency of 89.4 ± 3.6%, a loading capacity of 17.89 ± 0.72 mg BSA protein/100 mg PLGA polymeric particles, low cytotoxicity and a controlled drug release characteristics in 43 days. The results demonstrate a great promise in the development of DPAP formulation for enhanced in vivo cell targeting.

Chromatographic characterisation of aptamer-modified poly(EDMA-co-GMA) monolithic disk format for protein binding and separation

ABSTRACT The introduction of aptameric ligands onto disk-monolithic adsorbent, representing a unique strategy for convective isolation of target molecules with high specificity and selectivity, is investigated for the first time. Experimental results showed that the disk monolith possessed a good permeability of 1.67 ± 0.05 × 10–14 m2 (RSD = 3.2%). The aptameric ligand density for the aptamer-modified disk monolith was 480 pmol/uL. Chromatographic analysis of the aptamer disk-monolith efficiency showed an optimum linear velocity of 126 cm/min (≈0.25 mL/min) at room temperatures 25 ± 2°C. The theoretical number of plates corresponding to the optimum linear velocity was 128.2 with an height equivalent to the theoretical plate of 0.022 mm. The disk aptamer-immobilised monolithic system demonstrated good selectivity and isolation of thrombin from non-targets.

Process evaluation and in vitro selectivity analysis of aptamer-drug polymeric formulation for targeted pharmaceutical delivery

Targeted drug delivery is a promising strategy to promote effective delivery of conventional and emerging pharmaceuticals. The emergence of aptamers as superior targeting ligands to direct active drug molecules specifically to desired malignant cells has created new opportunities to enhance disease therapies. The application of biodegradable polymers as delivery carriers to develop aptamer-navigated drug delivery system is a promising approach to effectively deliver desired drug dosages to target cells. This study reports the development of a layer-by-layer aptamer-mediated drug delivery system (DPAP) via a w/o/w double emulsion technique homogenized by ultrasonication or magnetic stirring. Experimental results showed no significant differences in the biophysical characteristics of DPAP nanoparticles generated using the two homogenization techniques. The DPAP formulation demonstrated a strong targeting performance and selectivity towards its target receptor molecules in the presence of non-targets. The DPAP formulation demonstrated a controlled and sustained drug release profile under the conditions of pH 7 and temperature 37 °C. Also, the drug release rate of DPAP formulation was successfully accelerated under an endosomal acidic condition of ∼pH 5.5, indicating the potential to enhance drug delivery within the endosomal micro-environment. The findings from this work are useful to understanding polymer-aptamer-drug relationship and their impact on developing effective targeted delivery systems.

Microalgal-Based Protein By-Products: Extraction, Purification, and Applications

Abstract Microalgal bioprocesses have emerged as sustainable value-adding processes for the development of biochemicals and biomolecules for a wide range of applications to meet vital consumer needs. Microalgae-based proteins, in particular, have gained significant interest from researchers and industries because of their huge potential applications in the development of a wide range of natural products, including food additives, enzymes, nutraceuticals, and probiotics. The development of process technologies covering upstream and downstream operations for the production of intracellular and extracellular proteins from microalgae as main products or by-products is of significant interest. Research efforts are targeted at screening naturally existing microalgae cells to produce specific proteins, genetic modifications of microalgae cells to express recombinant proteins, the design of novel bioreactors with enhanced photon accessibility and hydrodynamics to optimize biomass density and protein metabolism rate, and the development low-energy and environmentally friendly extraction and purification techniques for large-scale production. This chapter reports an overview of the significance of microalgal cultivation systems for protein production as well as recent advances in the development of microalgae proteins. It discusses the bioprocess pipeline for generating proteins from microalgae biomass. This includes microalgae cultivation, harvesting, biomass disruption, and protein extraction and purification techniques to meet commercial scale production. It also presents various biofunctional applications of microalgal proteins in the cosmetic, food, and nutraceutical industries.

Peroxidase extraction from jicama skin peels for phenol removal

Phenol and its derivatives exist in various types of industrial effluents, and are known to be harmful to aquatic lives even at low concentrations. Conventional treatment technologies for phenol removal are challenged with long retention time, high energy consumption and process cost. Enzymatic treatment has emerged as an alternative technology for phenol removal from wastewater. These enzymes interact with aromatic compounds including phenols in the presence of hydrogen peroxide, forming free radicals which polymerize spontaneously to produce insoluble phenolic polymers. This work aims to extract peroxidase from agricultural wastes materials and establish its application for phenol removal. Peroxidase was extracted from jicama skin peels under varying extraction conditions of pH, sample-to-buffer ratio (w/v %) and temperature. Experimental results showed that extraction process conducted at pH 10, 40% w/v and 25oC demonstrated a peroxidase activity of 0.79 U/mL. Elevated temperatures slightly enhanced the peroxidase activities. Jicama peroxidase extracted at optimum extraction conditions demonstrated a phenol removal efficiency of 87.5% at pH 7. Phenol removal efficiency was ~ 97% in the range of 30 - 40oC, and H2O2 dosage has to be kept below 100 mM for maximum removal under phenol concentration tested.

Dynamic Enzymatic Kinetic Resolution of NSAIDS

The optical purity of non-steriodal anti-inflammatory drugs (NSAIDs) is one of the concerns in pharmaceutical industries, since the enantiomers demonstrate distinct physical and chemical characters. The production of single enantiomer of NSAIDs through dynamic enzymatic kinetic resolution (DEKR) has been pinpointed as among the promising approach developed in recent years. The substrate conversion and product enantioselectivity could be improved as compared to the conventional kinetic resolution. A combination of enzymatic kinetic resolution (EKR) and base-catalyzed racemization process can guarantee racemic substrate conversion of more than 80 %. The utilization of hollow-fiber membrane as enzyme-mediated reactor significantly improves the DEKR operation. This chapter describes the DEKR of a racemic ibuprofen in enzymatic membrane reactor (EMR), which system has been intensively investigated. From the experimental work, high conversion of the substrate (>90 %) and opticaly pure product (ee P > 95 %) have been obtained. The kinetic model was integrated with that of the mass transfer in the cylindrical hollow-fiber module in order to simulating the entire system by the interaction between the EKR and racemization reaction. The product ((S)-ibuprofen acid) was crystallized and the preliminary toxicity studies were carried out. In conclusion, DEKR of NSAIDs is a promising technology for the production a single enantiomer of NSAIDs.