PEGylated siRNA lipoplexes for silencing of BLIMP-1 in Primary Effusion Lymphoma: In vitro evidences of antitumoral activity

Silencing of the B lymphocyte-induced maturation protein 1 (Blimp-1), a pivotal transcriptional regulator during terminal differentiation of B cells into plasma cells with siRNAs is under investigation as novel therapeutic approach in Primary Effusion Lymphoma (PEL), a HHV-8 related and aggressive B cell Lymphoma currently lacking of an efficacious therapeutic approach. The clinical application of small interfering RNA (siRNA) in cancer therapy is limited by the lack of an efficient systemic siRNA delivery system. In this study we aim to develop pegylated siRNA lipoplexes formed using the cationic lipid DOTAP and DSPE-PEG2000, capable to effectively stabilize anti-Blimp-1 siRNA and suitable for systemic administration. Two types of pegylated lipoplexes using a classic (C-PEG Lipoplexes) or a post-pegylation method (P-PEG-Lipoplexes) were formulated and compared in their physicochemical properties (size, zeta potential, morphology and structure) and efficiency on PEL cell lines. A stable siRNAs protection was obtained with post pegylation approach (2% molar of DSPE-PEG2000 with respect to lipid) resulting in structures with diameters of 300 nm and a complexation efficiency higher that 80% (0.08 nmol/10 nmol of lipid). In vitro studies on PEL cell lines suggested that empty liposomes were characterized by a low cell toxicity also after PEG modification (cell viability and cell density over 85% after treatment with 10 μM of lipid). We demonstrated that P-PEG-Lipoplexes were able to significantly reduce the levels of BLIMP-1 protein leading to reduction of viability (less that 15% after transfection with 100 nM of complexed siRNAs) and activation of apoptosis. In vitro efficiency encourages us to further test the in vivo potential of P-PEG-Lipoplexes in PEL therapy.