In vivo fate of systemically administered encapsulin protein nanocages and implications for their use in targeted drug delivery

Encapsulins, self-assembling protein nanocages derived from prokaryotes, are promising nanoparticle-based drug delivery systems (NDDS). However, the in vivo behavior and fate of encapsulins are poorly understood. In this pre-clinical study, we probe the interactions between the model encapsulin from Thermotoga maritima (TmEnc) and key biological barriers encountered by NDDS. Here, a purified TmEnc formulation that exhibited colloidal stability, storability, and blood compatibility was intravenously injected into BALB/c mice. TmEnc had an excellent nanosafety profile, with no abnormal weight loss or gross pathology observed, and only temporary alterations in toxicity biomarkers detected. Notably, TmEnc demonstrated immunogenic properties, inducing the generation of nanocage-specific IgM and IgG antibodies, but without any prolonged pro-inflammatory effects. An absence of antibody cross-reactivity also suggested immune-orthogonality among encapsulins systems. Moreover, TmEnc formed a serum-derived protein corona on its surface which changed dynamically and appeared to play a role in immune recognition. TmEncs biodistribution profile further revealed its sequestration from the blood circulation by the liver and then biodegraded within Kupffer cells, thus indicating clearance via the mononuclear phagocyte system. Collectively, these findings provide critical insights into how encapsulins behave in vivo, thereby informing their future design, modification, and application in targeted drug delivery. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=187 SRC="FIGDIR/small/549228v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1691ecaorg.highwire.dtl.DTLVardef@647c31org.highwire.dtl.DTLVardef@115a146org.highwire.dtl.DTLVardef@10f2b6f_HPS_FORMAT_FIGEXP M_FIG C_FIG