RNAi Therapeutic Delivery by Exosomes - RNA Interference from Biology to Therapeutics - page 193

Fig. 9.3 Exosomes and miRNA-mediated silencing. miRNA RISC components associated with
the membrane of late endosomes and are incorporated into intraluminal vesicles and then released
into exosomes

9.4.2 Exosomes as Drug Delivery Vehicles: Proof-of-Concept

Studies

The Wood Laboratory carried out the first study to harness the RNA-transporting
capacity of exosomes and use them for delivery of exogenous RNAi in vivo,
providing first proof-of-concept for biotechnological exploitation of membrane
vesicles [ 78 ] (Fig. 9.4 ).
Immature dendritic cells (DCs) were derived from mouse bone marrow and used
as a source of exosomes, as they are devoid of lymphocyte stimulatory molecules
such as MHCII, CD80, and CD86. These were subsequently loaded by electropora-
tion with exogenous siRNA for delivery, first in vitro then in vivo. The brain was
selected as a target tissue, given the lack of efficient CNS-delivery vectors. To ensure
that systemically injected exosomes targeted the brain in vivo and to reduce exosome
homing to tissues of drug clearance, a novel targeting strategy was devised, utilizing
the exosomal surface protein Lamp2b to display the previously mentioned brain-
specific RVG peptide. By this method, we demonstrated specific delivery of siRNA
to neurons in the brain, with up to 60% RNA and protein knockdown predominantly
in the midbrain, cortex, and striatum. As well as efficient and specific delivery of
siRNA, these exosomes produced little or no toxicity or immunogenicity.
A subsequent study by Zhuang et al. described the use of exosomes to deliver
anti-inflammatory drugs to the brain through a noninvasive intranasal route [ 79 ] .