Significant effort has been applied to discover and develop vehicles which can guide small interfering siRNA through the many barriers guarding the interior of target cells. Improvements in delivery efficacy were required to fulfill the broadest potential of RNA interference therapeutics. Through the combinatorial synthesis and screening of a different class of materials, a formulation has been identified that enables siRNA-directed liver gene silencing in mice at doses below 0.01 mg∕kg. The potential of this formulation was further validated in non-human primates, where high levels of knockdown of the clinically relevant gene transthyretin were observed at doses as low as 0.03 mg∕kg.
A screening of different tails and amine groups was evaluated, reporting interesting structure-activity results. With respect to tail length, most of the top performing structures possessed tails consisting of 14-carbons in length. Additionally, no compounds with tails less than 12-carbons in length mediated silencing greater than 30%.
Regarding amine head groups, a tertiary amine was present in the top performing compounds. With the top 3 lipids, an in vivo delivery of siRNA to hepatocytes in mice was conducted and a dose dependent gene silencing was obtained. One compound in particular, C12-200, demonstrated over two orders-of-magnitude higher potency when compared to LNP01.
We developed a manufacturing process for C12 200, which is now ready for evaluation by potential customers looking for a breakthrough in LNP and IP free lipid vehicles. C12 200 is available with high purity and a process robust enough to allow for a GMP campaign.