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Anti-c-myc cholesterol-based lipoplexes: development, characterisation and evaluation as Onconanotherapeutic agents in vitro.

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Strategies aimed at inhibiting the expression of the c-myc oncogene could provide the basis for alternative cancer treatment. In this regard, silencing c-myc expression using small interfering RNA (siRNA) is an attractive option. However, the development of a clinically viable, siRNAbased, c-myc silencing system is largely dependent upon the design of an appropriate siRNA carrier that can be easily prepared. Nanostructures formed by the electrostatic association of siRNA and cationic lipid vesicles represent uncomplicated, well-recognised siRNA delivery systems. Therefore, this study has focused on traditional cationic liposomes as the foundation for the development of a simple, but effective anti-c-myc onconanotherapeutic agent. Novel liposome formulations contained equimolar quantities of the cytofectin, N,Ndimethylaminopropylamidosuccinylcholesterylformylhydrazide (MS09), and cholesterol (Chol); with or without 2 mol % pegylation. Liposomes which contained dioleoylphosphatidylethanolamine (DOPE) as the co-lipid were included for comparative purposes. Pegylated and non-pegylated MS09/Chol (1:1) suspensions were reproducibly prepared by lipid film hydration to give unilamellar vesicles that were stable for at least 10 months at 4 ˚C. Liposomes successfully bound siRNA to form lipoplexes of less than 200 nm in size, with zeta potentials between -16 and -44 mV. These assumed globular and bilamellar structures in which siRNA was partially protected. Although all formulations were well tolerated at ≤14 nM siRNA, pegylation severely inhibited siRNA delivery in cancer cell lines, MCF-7 and HT-29, which overexpress c-myc. The non-pegylated MS09/Chol (1:1) lipoplex, at the MS09:siRNA (w /w) ratio of 16:1, was most effectively taken up by MCF-7 and HT-29 cells, with negligible effect in non-transformed cells when applied at 12 nM siRNA. Lipoplexes directed against the c-myc transcript (anti-c-myc siRNA), mediated a dramatic reduction in c-myc mRNA and protein levels. This was accompanied by a loss of migratory potential and apoptotic cell death. Moreover, oncogene knockdown and anti-cancer effects were superior to that of a commercially available transfection reagent, Lipofectamine™ 3000. Although the DOPE-containing counterpart performed with iii comparable efficacy under standard in vitro conditions, it was incapable of siRNA delivery at physiological serum concentration. Hence, the anti-c-myc MS09/Chol (1:1) lipoplex reported exemplifies a straightforward anti-cancer agent that warrants further investigation in vivo.


Doctoral Degree in (Biochemistry). University of KwaZulu-Natal, Durban.