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“In the field of gene therapy, efficient gene delivery in vivo based on non-viral methods remains a major challenge, with an overwhelming variety of polymeric and liposomal compounds being tested [1]. A major obstacle has been the fact that extremely efficient methods involving cationic liposomes for gene delivery to cells in vitro, perform very poorly when tested in animals [2]. Although a regime of transfection-potent lipoplexes has been established in vitro [3], in vivo applications require

different physical–chemical properties and only limited information about these have been described. The development of liposomal carriers with enhanced systemic stability has mainly been advanced by the liposomal formulation of chemotherapeutics, i.e. doxorubicin into DOXIL® that is FDA-approved Ribociclib clinical trial for use against several cancers [4]. Here a great advantage of therapeutic efficiency over the naked drugs has been accomplished [5]. A great accumulation in disease area, i.e. tumor tissue due to the so-called enhanced permeability and retention effect (EPR) is a hallmark of these liposomal formulations [6] where the property of long circulation is accomplished by a 5–10% PEG polymers screen on the liposomal surface. Furthermore, efficient encapsulation of plasmid DNA in liposomes can be

achieved using an ethanol-mediated condensation procedure [7] and [8], and this was established in our laboratory [9]. The technology of stabilized plasmid lipo-particles U0126 nmr (SPLPs) has progressed in recent years [10] and we decided to investigate these methods for laboratory scale studies of a gene therapy strategy in mice using conventional lipid reagents, hence

we included a tritium-labeled lipid in the formulation enabling evaluation of systemic circulation and biodistribution of SPLPs [11]. A robust laboratory-scale protocol allows for researchers to perform experiments investigating the biological properties of SPLPs and the interaction with the biological milieu in order to characterize the barriers to successful gene delivery. Aiming at gene therapy of small cell lung carcinoma (SCLC) [12] we have recently showed high and specific effect of a suicide gene therapy system [13]. Phosphoribosylglycinamide formyltransferase At the time of diagnosis SCLC often appears disseminated to various extra-thoracic organs [14], and therefore a systemic distribution of the therapeutic agent is demanded. Hence in the current study we have exploited the potential of transcriptionally targeted suicide gene therapy using SPLPs as a delivery vehicle for systemic treatment of a mouse model of SCLC. All chemicals, e.g. synthetic cholesterol were purchased from Sigma-Aldrich Inc. (Brøndby, Denmark) unless otherwise stated. DDAB: Dimethyl-dioctadecyl-ammonium bromide, DSPC (1,2-distearoyl-sn-glycero-3-phosphocholine) and DSPE-PEG2000 (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000]) were purchased from Avanti Polar Lipids Inc.