Arrowhead Research Corporation (NASDAQ:ARWR), a targeted therapeutics company, today announced the publication of data demonstrating that high level target gene knockdown with low doses of cholesterol-siRNA is possible in non-human primates using the company’s Dynamic Polyconjugate (DPC) delivery system and a novel co-injection strategy. This new delivery approach dramatically increases the efficacy of cholesterol-siRNA and, together with the co-injection strategy, simplifies the manufacturing process to enable a commercially scalable delivery vehicle for RNAi therapeutics. The company is using this strategy and a next generation DPC polymer in ARC-520, its hepatitis B clinical candidate. The paper titled, “Co-injection of a targeted, reversibly masked endosomolytic polymer dramatically improves the efficacy of cholesterol-conjugated siRNAs in vivo,” was published online ahead of print in the journal Nucleic Acid Therapeutics to be featured in the December issue ( Nucleic Acid Therapeutics. December 2012, 22(6): 380-390).
The publication describes an important advance in DPC technology. Specifically, the requirement for siRNA attachment to the DPC polymer is replaced by conjugating a cholesterol to the siRNA and co-injecting it with the DPC polymer. Uptake of the DPC in the target cells and subsequent unmasking of the polymer’s endosomolytic properties enables release of the cholesterol-siRNA from the endosome to the cell’s cytoplasm where it can elicit RNAi. This delivery strategy produces over 500-fold increase in efficiency in mice compared to injection of cholesterol-siRNA alone and is the first delivery system to demonstrate cholesterol-siRNA mediated gene knockdown in monkeys. Long duration silencing was observed after administration of a single dose with maximal protein reduction sustained until day 30. Further, unlike other siRNA delivery platforms, the co-injection method does not require complex formation of the siRNA to the delivery vehicle, which eliminates potentially complicated and costly manufacturing steps. This represents a seminal advance in the siRNA delivery field.