The development of acid degradable linkers that rapidly hydrolyze at endosomal pHs is a central problem in the field of drug delivery. Acid degradable linkages are challenging to develop because of their instability. In this report we present a new acid degradable linker based on an azide-acetal, which rapidly hydrolyzes at endosomal pHs but has exceptional stability at pH 7.4. The azide-acetal linkage hydrolyzes via a two-step mechanism that requires reduction and acid hydrolysis and has a unique combination of stability and rapid triggerable hydrolysis. The azide-acetal has a hydrolysis half-life of days at pH 7.4 and can be conveniently synthesized and incorporated into delivery vectors, however after in situ reduction with DTT it hydrolyzes with a t1/2<15 minutes at pH 6.0. We used the azide-acetal linker to synthesize acid degradable analogs of the lipid components of lipid nanoparticles and demonstrate that these new lipids are significantly better at delivering mRNA to mice than traditional lipids. Lipid nanoparticles containing acid degradable lipids transfected multiple non-liver organs after an intravenous injection and efficiently transfected brain tissue after an intracranial injection. The azide-acetal linkage has the potential to solve the instability problems associated with acid degradable linkers and has numerous applications in drug delivery.

Learninf Objectives:

• Identify the advantages of using azide-acetal linkers for acid degradable lipid nanoparticles in drug delivery
• Compare the stability and hydrolysis rates of azide-acetal linkers at different pH levels
• Analyze the efficacy of acid degradable lipid nanoparticles in mRNA delivery across various tissues in animal models.