Abstract 228: A Novel Combinatorial Non-viral Vector to Treat Familial Hypercholesterolaemia

Familial hypercholesterolaemia (FH) is a life-threatening genetic disorder characterised by elevated levels of plasma low density lipoprotein cholesterol (LDL-C). Loss-of-function mutations in the gene encoding the low density lipoprotein receptor (LDLR) are responsible for ~85% of all FH cases. Current attempts at gene therapy for FH have been limited by the use of strong heterologous promoters which lack regulatory elements essential for controlled expression. We have previously generated mini-gene vectors carrying the human LDLR cDNA, driven by 10 kb of genomic DNA from the native human LDLR locus, encompassing a promoter region with all essential elements required for physiologically regulated expression (pLDLR-LDLR). We demonstrated that incorporation of the genomic DNA promoter elements resulted in long-term physiologically-regulated LDLR transgene expression that complemented Ldlr deficiency. Here we further enhance LDLR transgene expression by characterising and cloning in a miRNA, targeting Hmgcr (miR82) generating a combinatorial RNAi-LDLR vector (pLDLR-LDLR-miR82). We show in vivo that the combinatorial vector efficiently suppresses endogenous Hmgcr transcripts, which leads to an increase in LDLR transgene expression through induction of the LDLR promoter. In a preliminary study the pLDLR-LDLR-miR82 vector was able to significantly reduce total and LDL-C, in Ldlr -/- mice fed a 1% cholesterol diet at two and four weeks post vector delivery. We then carried out a longer term study in Ldlr -/- mice fed a 0.25% cholesterol diet, LDLR expression could be detected 12-weeks post-delivery with the plasmid able to be rescued as a functioning episome. LDL-C was significantly lowered throughout the study and this resulted in reduced atherosclerosis in the pLDLR-LDLR-miR82 vector treated mice. Here we demonstrate for the first time, that an episomal non-viral vector is able to significantly reduce LDL-C and the progression of atherosclerosis in a mouse model of FH.