Gene targeting as a therapeutic avenue in diseases mediated by the complement alternative pathway.

The complement alternative pathway (AP) is implicated in numerous diseases affecting many organs, ranging from the rare hematological disease paroxysmal nocturnal hemoglobinuria (PNH), to the common blinding disease age-related macular degeneration (AMD). Critically, the AP amplifies any activating trigger driving a downstream inflammatory response; thus, components of the pathway have become targets for drugs of varying modality. Recent validation from clinical trials using drug modalities such as inhibitory antibodies has paved the path for gene targeting of the AP or downstream effectors. Gene targeting in the complement field currently focuses on supplementation or suppression of complement regulators in AMD and PNH, largely because the eye and liver are highly amenable to drug delivery through local (eye) or systemic (liver) routes. Targeting the liver could facilitate treatment of numerous diseases as this organ generates most of the systemic complement pool. This review explains key concepts of RNA and DNA targeting and discusses assets in clinical development for the treatment of diseases driven by the alternative pathway, including the RNA-targeting therapeutics ALN-CC5, ARO-C3, and IONIS-FB-LRX, and the gene therapies GT005 and HMR59. These therapies are but the spearhead of potential drug candidates that might revolutionize the field in coming years.

Episomal Nonviral Gene Therapy Vectors Slow Progression of Atherosclerosis in a Model of Familial Hypercholesterolemia.

Familial hypercholesterolemia (FH) is a life-threatening genetic disorder characterized by elevated levels of plasma low-density lipoprotein cholesterol (LDL-cholesterol). Current attempts at gene therapy for FH have been limited by the use of strong heterologous promoters which lack genomic DNA elements essential for regulated expression. Here, we have combined a mini-gene vector expressing the human LDLR cDNA from a 10 kb native human LDLR locus genomic DNA promoter element, with an efficient miRNA targeting 3-hydroxy-3-methylgutaryl-coenzyme A reductase (Hmgcr), to further enhance LDLR expression. We show that the combined vector suppresses endogenous Hmgcr transcripts in vivo, leading to an increase in LDLR transgene expression. In a diet-induced Ldlr-/- mouse model of FH, we show that administration of the combined vector reduces atherogenic plasma lipids by ~32%. Finally, we demonstrate that our episomal nonviral vectors are able to reduce atherosclerosis by ~40% after 12 weeks in vivo. Taken together, the vector system we describe exploits the normal cellular regulation of the LDLR to provide prolonged expression of LDLR through targeted knockdown of Hmgcr. This novel gene therapy system could act alone, or in synergy with current therapies that modulate intracellular cholesterol, such as statins, greatly enhancing its therapeutic application for FH.