In ovarian carcinomas, recurrence and acquired chemoresistance are the first leading causes of therapeutic failure and are responsible for the poor overall survival rate. Cisplatin exposure of sensitive cells has been previously associated with a down-regulation of Bcl-x L expression and apoptosis, whereas recurrence was systematically observed when Bcl-x L expression was maintained. Bcl-x L down-regulation could thus constitute an interesting chemosensitizing strategy. We showed that a Bclx L targeted RNA interference strategy efficiently sensitized chemoresistant ovarian carcinoma cells to cisplatin, but some of them were still able to re-proliferate. Considering the possible cooperation between Bcl-x L and MCL-1, we investigated the possibility to avoid recurrence in vitro using a multi-targeted RNAi strategy directed against these two anti-apoptotic proteins. We showed that their concomitant inhibition lead to massive apoptosis in absence of cisplatin, this multi-targeted RNAi approach being much more efficient than conventional chemotherapy. We thus demonstrated that Bcl-x L and MCL-1 cooperate to constitute together a strong molecular ''bolt'', which elimination could be sufficient to allow chemoresistant ovarian carcinoma cells apoptosis. Moreover, we demonstrated that in presence of a low concentration of cisplatin, the concomitant down-regulation of Bcl-x L and MCL-1 allowed a complete annihilation of tumour cells population thus avoiding subsequent recurrence in vitro in cell lines highly refractory to any type of conventional chemotherapy. Therefore, Bcl-x L and MCL-1 targeted strategies could constitute an efficient therapeutic tool for the treatment of chemoresistant ovarian carcinoma, in association with conventional chemotherapy.Ovarian cancer is the leading cause of death from gynecological malignancies worldwide and the fifth most common cause of cancer death in women. 1 Early diagnosis is difficult owing to the asymptomatic character of this disease in early stages, and more than 70% of these cancers are diagnosed in an advanced stage (FIGO stages III or IV). Patients with advanced ovarian cancer are treated initially with optimal debulking surgery and standard chemotherapy (platinumdrugs usually associated to taxanes). 2 Despite an initial 70-80% response rate, most patients will relapse within 1-2 years and develop resistance to chemotherapy 3 and the overall 5-year survival is less than 30%. The identification of new drugs or novel therapeutic strategies able to (re)sensitize ovarian carcinoma cells to existing chemotherapy thus appear as a major challenge.Cisplatin, a DNA-damaging agent that forms DNA adducts, is commonly used for the treatment of advanced ovarian cancers. It is widely accepted that these adducts lead to a cell cycle arrest followed by the induction of apoptotic cell death. 4 However, it should be considered that in resistant cells, a strong protection against apoptosis exist when the DNA damages reach their maximum level, to allow the reparation of these injuries and the r...

The synthesis of oligonucleotides carrying nuclear localization peptide sequences is described using two strategies: first, oligonucleotides carrying a thiol group at the 5' end were reacted with maleimido peptides; second, peptide and oligonucleotide were prepared stepwise on the same support, yielding oligonucleotide-3'-peptide conjugates. This second approach was thoroughly studied. Using amino acids and small peptides as model compounds, some side reactions were analyzed, detected, and minimized. Oligonucleotides complementary to Ha-ras gene and carrying nuclear localization peptides at the 3' and 5' ends were prepared. Melting temperature studies showed that duplexes containing nuclear localization peptides were more stable than duplexes with unmodified oligonucleotides. Moreover, oligonucleotide-peptide conjugates maintain a good mismatch discrimination when they bind to their target RNA.

Lipofectin, which is a mixture of neutral lipid with a cationic lipid, has been widely used to enhance cellular delivery of phosphorothioate, 2'-sugar-modified, and chimeric antisense oligonucleotides. Phosphodiester oligonucleotides delivered with Lipofectin usually do not elicit antisense activity probably because cationic lipid formulations do not sufficiently protect unmodified oligonucleotides from nuclease degradation. We show that a cationic polymer, polyethylenimine (PEI), improves the uptake and antisense activity of 3'-capped 20-mer and 12-mer antisense phosphodiester oligonucleotides (PO-ODN) targeted to different regions of Ha-ras mRNA and to the 3'-untranslated region (3'-UTR) of C-raf kinase. In contrast, PEI, which forms a very stable complex with the 20-mer phosphorothioate oligonucleotide (PS-ODN), does not enhance its antisense activity. Using fluorescently labeled carriers and ODN, we show that PEI-PS-ODN particles are very efficiently taken up by cells but PS-ODN is not dissociated from the carrier. Our results indicate that carrier-ODN particle size and stability and ODN release kinetics vary with the chemical nature of the ODN and the carrier being transfected into the cells. The very low cost of PEI compared with cytofectins and the increased affinity for target mRNA and decreased affinity for proteins of PO-ODN compared with PS-ODN make the use of PEI-PO-ODN very attractive.

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Oligonucleotides covalently attached to a cholesteryl moiety are more stable in biological media and better taken up by eukaryotic cells. However, their anchoring in hydrophobic cellular membranes and endosomes after endocytosis restricts their access to cellular nucleic acids. New methods of cellular delivery and the biological activity of the conjugates were studied. The cholesteryl residue was conjugated via disulfide bond to the 5' or 3' terminal phosphate group of two oligodeoxyribonucleotide dodecamers complementary to the mutated region of Ha-ras oncogene mRNA. The conjugates were able to form complementary duplexes with the mutated 27-b target fragment of mRNA but not with the wild-type sequence. Efficient sequence-specific RNase H cleavage of complementary mRNA was induced with low (< or = 500 nM) concentrations of the conjugates. At higher concentrations, this cleavage was progressively inhibited, probably due to an interaction between RNase H and the cholesterol residue. The hydrophobic conjugates could be adsorbed onto poly(isohexylcyanoacrylate) nanoparticles via their cholesteryl moieties and delivered to eukaryotic cells. Cholesterol-conjugated oligonucleotides were able to sequence-specifically inhibit the proliferation of T24 human bladder carcinoma cells in culture.