Lipid A6 is an ionizable and biodegradable lipid. Lipid A6 has similar structure as Dlin-MC3-DMA but with ester and alkyne bonds to improve its biodegradability and cell membrane fusion ability. Lipid A6 forms lipid-like nanoparticles together with cKK-E12 synergistically to facilitate robust mRNA delivery with improved tolerability. MC3 is the key delivery nanoparticle component of the first siRNA drug Onpattro.