Sherry Wu

Publications (4)10.67 Total impact

• Article: Lipidic systems for in vivo siRNA delivery.

  Sherry Y Wu, Nigel A J McMillan
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  ABSTRACT: The ability of small-interfering RNA (siRNA) to silence specific target genes not only offers a tool to study gene function but also represents a novel approach for the treatment of various human diseases. Its clinical use, however, has been severely hampered by the lack of delivery of these molecules to target cell populations in vivo due to their instability, inefficient cell entry, and poor pharmacokinetic profile. Various delivery vectors including liposomes, polymers, and nanoparticles have thus been developed in order to circumvent these problems. This review presents a comprehensive overview of the barriers and recent progress for both local and systemic delivery of therapeutic siRNA using lipidic vectors. Different strategies for formulating these siRNA-loaded lipid particles as well as the general concern about their safe use in vivo will also be discussed. Finally, current advances in the targeted delivery of siRNA and their impacts on the field of RNA interference (RNAi)-based therapy will be presented.
  The AAPS Journal 09/2009; 11(4):639-52. · 5.09 Impact Factor
• Article: Development of a novel method for formulating stable siRNA-loaded lipid particles for in vivo use.

  Sherry Y Wu, Lisa N Putral, Mingtao Liang, Hsin-I Chang, Nigel M Davies, Nigel A J McMillan
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  ABSTRACT: A simple yet novel method was developed to prepare stable PEGylated siRNA-loaded lipid particles which are suitable for in vivo use. PEGylated siRNA-loaded lipid particles were formulated by hydration of a freeze-dried matrix. The effect of various formulation parameters on the size and homogeneity of resulting particles was studied. Particles prepared using this method were compared to those prepared using an established post-insertion procedure for the entrapment efficiency, stability, in vitro biological activity as well as in vivo biodistribution. Using this hydration method, a particle size of less than 200 nm can be obtained with high siRNA entrapment efficiency (>90%) and high gene-silencing efficiency. Following intravenous administration into mice, these particles achieved a similar degree of accumulation in subcutaneous tumours but displayed less liver uptake compared to the post-insertion formulations. Importantly, in contrast to post-insertion preparations, particles made by hydration method retained 100% of their gene-silencing efficiency after storage at room temperature for 1 month. This paper describes a simple method of formulating PEGylated siRNA-loaded lipid particles. Given the ease of preparation, long term stability and favourable characteristics for in vivo delivery, our work represents an advance in lipid formulation of siRNA for in vivo use.
  Pharmaceutical Research 12/2008; 26(3):512-22. · 4.09 Impact Factor
• Article: Investigation of the route of absorption of lipid and sugar modified leu-enkephalin analogues and their enzymatic stability using the caco-2 cell monolayer system.

  Sherry Wu, Christopher Campbell, Yasuko Koda, Joanne T Blanchfield, Istvan Toth
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  ABSTRACT: It has been demonstrated that conjugation of lipoamino acids or glucose units to the endogenous opioid peptide, Leu-enkephalin can significantly improve the peptide's metabolic stability and absorption across biological barriers. The purpose of this study was to investigate the possible involvement of specific carrier proteins in the absorption of these peptide conjugates. A series of lipo- glycol- and liposaccharide peptide conjugates were synthesised and examined using the Caco-2 monolayer assay for evidence of interaction with the human H(+)-coupled oligopeptide transporter (hPepT1), glucose transporters and the multidrug resistance efflux pump, p-glycoprotein. The investigation involved determining the apparent permeability of each compound in the absence of any inhibitors and comparing this to the apparent permeabilities of each compound in the presence of glycylsarcosine, glucose or vinblastine, respective inhibitors of the above mentioned transporters. None of the peptide conjugates were found to be substrates for p-glycoprotein. Of the six peptide conjugates examined, only the C-terminus glucose conjugate of Leu-enkephalin (Enk-glu) showed evidence of transport by both glucose transporters and hPepT1. In contrast, N-terminus conjugation of both lipids and sugars appeared to provide the greatest protection against enzymatic degradation.
  Medicinal Chemistry 04/2006; 2(2):203-11. · 1.50 Impact Factor
• Article: DELIVERY OF SMALL INTERFERING RNA FOR CANCER TREATMENT

  Sherry Wu
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  ABSTRACT: The ability of small interfering RNA (siRNA) to silence specific target genes offers not only a tool to study gene function but also represents a novel approach for the treatment of various human diseases, including cancers. The clinical use of siRNA, however, has been severely hampered by the inefficient delivery of these molecules to target cell populations due to their instability, inefficient cell entry, and poor pharmacokinetic profile. Much effort has therefore been devoted to the development of efficient in vivo siRNA delivery systems, with liposomes being the most widely employed vector. The traditional methods of packaging siRNA into liposomes, however, are often quite complex and labour-intensive, with the resulting products also being unstable at room temperature which limits their wide spread application in the clinic. The main aim of this research was to develop a simple, yet efficient, formulation technique to prepare stable siRNA-loaded liposomes which could be utilized as an efficient therapy for cancer treatment. Throughout this study, cervical cancer was used as the model system to assess the efficiency of various delivery systems. It is an ideal disease for siRNA therapy due to the cancer’s reliance on the expression of a single messenger RNA sequence which encodes two essential viral oncogenes, E6 and E7. Previous research has shown that targeting E6 and E7 by siRNA in cervical cancer cells in vitro results in either cell senescence or apoptosis. This thesis investigates the feasibility of applying E6/7 siRNA both intravaginally and intravenously to model the treatment of early-stage and end-stage cervical cancer, respectively. The practicability of applying E6/7 siRNA intravaginally for the treatment of localised cervical cancer tumours was firstly evaluated by administrating liposome-complexed siRNAs directly into the vaginal cavity of transgenic E7 mice. As no knockdown of E7 in cervical epithelium was observed for mice which received repeated treatments of E6/7 siRNA, the vaginal delivery efficiency of liposomes was further examined using fluorescently-labelled oligonucleotides. Contrary to previous reports, no delivery of lipoplexes into cervicovaginal tissues was detected irrespective of the dosage, type of lipid vector used, or the mouse estrus state at the time of administration. This lack of delivery was likely due to the poor retention of lipoplexes in the vaginal cavity as well as the inefficient penetration of lipoplexes across the mucosal layer lining the cervicovaginal epithelium. Overall, these findings indicated the necessity of developing more suitable and clinically acceptable vaginal siRNA delivery systems to enable this treatment strategy to become a reality. Despite the challenges of using liposomes to deliver siRNA via vaginal administration, their successful use in delivering siRNA intravenously to tumours was demonstrated in a subcutaneous cervical cancer mouse model. These experiments were carried out using PEGylated siRNA-loaded liposomes which were formulated using a novel Hydration-of-Freeze-Dried-Matrix (HFDM) technique. Compared to the existing formulation strategies, this method of preparation is less labour-intensive and the end product is also freeze-dried, ensuring product stability. It was found that the liposomes prepared using the HFDM method were stable in the presence of serum and they also possessed high siRNA entrapment and gene-silencing efficiencies. Following intravenous administration to mice, these particles were also found to accumulate in subcutaneous tumours to a similar degree compared to formulations prepared using a previously established technique. Importantly, these HFDM-formulated preparations showed superior stability over ones prepared using the traditional formulation method, with the particles still retaining 100% of their gene-silencing ability after storage for one month at room temperature. Using HFDM-formulated liposomes loaded with siRNA against Green Fluorescence Protein (GFP), a 50% knockdown of the GFP expression was achieved in tumours following intravenous administration. Additionally, the use of E6/7-targeted siRNA also resulted in a 50% reduction in tumour size when the siRNAs were delivered using HFDM-formulated liposomes. Importantly, this level of tumour growth suppression was comparable to that achieved from cisplatin, a clinically used chemotherapeutic for cervical cancer, at the clinically used dose. Overall, this research demonstrated that while there are still some challenges to overcome for siRNA to be used vaginally for cervical cancer treatment, HFDM-formulated PEGylated liposomes showed promise in bringing E6/7 siRNA forward as a treatment option for end-stage cervical cancer. In addition, the simplicity of preparation procedure along with superior product stability obtained from the HFDM method developed in this thesis will likely facilitate the translation of siRNA technology from laboratory to clinics for a range of other medical applications.