Abstract
The vault nanoparticle is one of the largest known ribonucleoprotein complexes in the subโ100 nm range. Highly conserved and almost ubiquitously expressed in eukaryotes, vaults form a large nanocapsule with a barrelโshaped morphology surrounding a large hollow interior. These properties make vaults an ideal candidate for development into a drug delivery vehicle. In this study, the first example of using vaults towards this goal is reported. Recombinant vaults are engineered to encapsulate the highly insoluble and toxic hydrophobic compound allโtrans retinoic acid (ATRA) using a vaultโbinding lipoprotein complex that forms a lipid bilayer nanodisk. These recombinant vaults offer protection to the encapsulated ATRA from external elements. Furthermore, a cryoโelectron tomography (cryoโET) reconstruction shows the vaultโbinding lipoprotein complex sequestered within the vault lumen. Finally, these ATRAโloaded vaults show enhanced cytotoxicity against the hepatocellular carcinoma cell line HepG2. The ability to package therapeutic compounds into the vault is an important achievement toward their development into a viable and versatile platform for drug delivery.