Inhibition of PCSK9 with polypurine reverse hoogsteen hairpins: A novel gene therapy approach

PCSK9 is a therapeutic target for hypercholesterolemia. Though different strategies to inhibit PCSK9, such as monoclonal antibodies, small molecules, or nucleic acid drugs are available, the need for safer and inexpensive interventions remains. We developed a time-, cost-, and resource- efficient silencing system using Polypurine Reverse Hoogsteen (PPRH) hairpins to target PCSK9. To achieve PCSK9 silencing, we designed two PPRHs targeting PCSK9 at exon 9 (HpE9) and exon 12 (HpE12). The binding capabilities of PPRHs were measured by EMSA: K_d values were 7.86 x 10^-8 M and 7.58 x 10^-7 M for HpE9 and HpE12, respectively. PPRHs were complexed with the cationic polymer jetPEI forming particles of 167 nm as characterized by Dynamic Light Scattering. PCSK9 gene and protein expression was evaluated upon transfections of HepG2 cells with HpE9 and HpE12. PPRHs effectively reduced PCSK9 mRNA levels (63 % and 74 % for HpE9 and HpE12, respectively) and protein (by 76 % and 87 %) at 24 h. Human PCSK9 overexpressing mice receiving a single injection of HpE12 decreased plasma PCSK9 levels by 50 % by day three post injection and levels returned to baseline by day fifteen. Plasma cholesterol levels were reduced by 47 % by day three. Mice receiving the PPRHs did not exhibit changes in body weight, liver enzymes or pro-inflammatory markers when compared to mice injected with jetPEI alone. Therefore, the PPRH technology emerges as an innovative nucleic acid based therapeutic approach that is effective, cost-efficient and easy to develop, for the inhibition of PCSK9.