SummaryNon-viral gene therapy is based on the use of plasmid expression vectors and chemical or physical plasmid DNA delivery systems. This review discusses the roles of cationic lipids as vectors for gene transfection, reviews different strategies employed to improve cationic lipids for in vivo use, and provides original results on the physicochemistry of lipoplexes. Cationic lipid/DNA delivery vehicles have evolved considerably since their initial gene transfection experiments. Much work has been carried out to investigate their structure/activity relationships, methods of formulation and physicochemical properties. Further work has also focused on enhancing and prolonging their stability in a physiological environment as well as increasing their sitespecific and tissue-specific interactions. Original data presented in this report confirm that cationic lipids associated to DNA form supramolecular lamellar structures, which protect DNA from serum DNAse degradation. The effect of formulation (and hence the size of the particles) on lipoplex in vivo circulation half-life and biodistribution is also discussed. A list of abbreviations can be found at the end of the review. Copyright  2004 John Wiley & Sons, Ltd.Keywords gene therapy; non-viral vectors; cationic lipids; liposomes Cationic lipids-structure/activity relationshipsExtensive reviewing has been focused on the various published structures of cationic lipids, which are composed of a cationic head (titrable amine or quaternary amine, guanidine, etc.), a linker, and a hydrophobic moiety (Figure 1). The hydrophobic moiety provides self-association to form either micelles or liposomes in the presence of a helper lipid such as dioleylphosphatidylethanolamine (DOPE). Much work has been carried out on modifying the different components of cationic lipids for use in gene transfection in order to try to determine if there is a 'best' length of chain (saturated or unsaturated, asymmetric or not), which type of spacer gives the desired function, plus the number and nature of cationic charges present and their molecular shape. Excellent reviews have covered the different aspects of structure/activity relationships of cationic lipids and a very short summary of some of the main points follows [1].The choice of lipid is predominantly between either a two hydrocarbon chain or a cholesterol moiety. Cholesterol has been found to offer rigidity to the lipid bilayer and there are two main examples of cationic lipids containing cholesterol as their lipid [2]; DC-Chol and the more recent BGTC, illustrated in Figure 2, will be described later. Cationic lipids with hydrocarbon chains as their lipid component have been very thoroughly researched. The most common types of chain lengths are C8 : 0 to C18 : 1 and are either linear and saturated or linear and mono-unsaturated. There

Purpose: Irinotecan is a prodrug converted to the active cytotoxic molecule SN38 predominantly by the action of liver carboxylesterases. The efficacy of irinotecan is limited by this hepatic activation that results in a low conversion rate, high interpatient variability, and dose-limiting gastrointestinal toxicity. The purpose of this study was to evaluate a novel peptidic prodrug of SN38 (DTS-108) developed to bypass this hepatic activation and thus reduce the gastrointestinal toxicity and interpatient variability compared with irinotecan. Experimental Design: SN38 was conjugated to a cationic peptide (Vectocell) via an esterase cleavable linker.The preclinical development plan consisted of toxicity and efficacy evaluation in a number of different models and species. Results: The conjugate (DTS-108) is highly soluble, with a human plasma half-life of 400 minutes in vitro. Studies in the dog showed that DTS-108 liberates significantly higher levels of free SN38 than irinotecan without causing gastrointestinal toxicity. In addition, the ratio of the inactive SN38-glucuronide metabolite compared with the active SN38 metabolite is significantly lower following DTS-108 administration, compared with irinotecan, which is consistent with reduced hepatic metabolism. In vivo efficacy studies showed that DTS-108 has improved activity compared with irinotecan. A significant dose-dependent antitumoral efficacy was observed in all models tested and DTS-108 showed synergistic effects in combination with other clinically relevant therapeutic agents. Conclusions: DTS-108 is able to deliver significantly higher levels of SN38 than irinotecan, without the associated toxicity of irinotecan, resulting in an increased therapeutic window for DTS-108 in preclinical models. These encouraging data merit further preclinical and clinical investigation.Irinotecan is an effective chemotherapeutic agent that is widely prescribed for advanced colorectal cancer as a first-or secondline treatment. Irinotecan has also been shown to be active in gastric cancer, non -small cell lung cancer, and small-cell lung cancer, alone or in combination with other cytotoxic agents (1). Currently, irinotecan is used in combination with 5-fluorouracil (5-FU) in first-line treatment for metastatic colorectal cancer (2). Irinotecan is also used with other agents, including the anti -vascular endothelial growth factor antibody bevacizumab (Avastin; refs. 3,4). Following administration of irinotecan, the active metabolite SN38 (7-ethyl-10-hydroxycamptothecin) is formed by the action of carboxylesterases that are predominantly present in the liver (5, 6). SN38 is a topoisomerase I inhibitor with an activity a thousand times greater than irinotecan, but that cannot be administered directly as it is highly insoluble (1).Several limitations to the clinical use of irinotecan arise due to its mechanism of activation, metabolism, and elimination. The first limitation is caused by the complexity of irinotecan metabolism, which results in high interpatient variabil...

We present a neutral lipopolythiourea (DTTU) as a potential DNA-binding agent. Light scattering experiments showed that mixing a lipopolythiourea with dipalmitoylphosphatidylcholine (DPPC/DTTU) led to small particles with sizes ranging from 100 to 150 nm at optimum conditions. Setting a fixed DNA amount, an increasing amount of DTTU/DPPC or DPPC lipids was added. Particle size increased only with DTTU/DPPC, indicating that interaction occurred between the DTTU/DPPC particles and DNA. In the same way, only DTTU/DPPC limited the ethidium bromide accessibility to plasmid DNA. These data suggest that DTTU/DPPC liposomes associate to DNA, which was confirmed by agarose gel experiments. To prove the active part of the DTTU lipid itself in DNA compaction, pegoylated-lipid was used. Cholesterol-PEG(2000) alone was not able to condense DNA. In contrast, DTTU/PEG-cholesterol was able to retain plasmid DNA on an agarose gel. In vivo injection of DTTU/DPPC/complexes was studied. Circulation time increase for noncationic particles as compared to cationic. More obvious was the lack of nonspecific accumulation in the lung, where a gain of 3 to 40 fold was measured.