Scientists claim that encapsulating drugs in exosomes allows their efficient delivery into the brain via intranasal administration. Trials in experimental mouse models of inflammation-mediated brain diseases showed that the intranasally delivered, exosome-encapsulated anti-inflammatory drugs curcumin or JSI-124 (cucurbitacin I; an inhibitor of Stat3) were taken up by and induced apoptosis in microglial cells.
The team, headed by researchers at the University of Louisville James Graham Brown Cancer Center, used the technique to treat three different inflammatory brain disease models in mice: lipopolysaccharide (LPS)-induced inflammation, experimental autoimmune encephalitis (EAE), and a GL26 brain tumor model. The effects of drug administration were significant blockade of LPS-induced brain inflammation, protection from progression of EAE, and delayed brain tumor growth.
Huang-Ge Zhang, Ph.D., and colleagues, report their findings in Molecular Therapy in a paper titled “Treatment of Brain Inflammatory Diseases by Delivering Exosome Encapsulated Anti-inflammatory Drugs From the Nasal Region to the Brain.”
Building on their previous work demonstrating that exosome-encapsulated drugs are taken up selectively by immature myeloid cells including macrophages, the team investigated whether exosome-formulated dugs could also target brain microglial cells after intranasal administration.
Initial studies in normal mice showed that intranasally administered, dye-labeled exosomes were diffusely located in the brain within 30 minutes. The primary location was the olfactory bulb, “suggesting that translocation of exosomes to the brain occurred rapidly,” the researchers explain.
After three hours the exosomes had further distributed throughout the brain, and there was no apparent toxicity associated with intranasal exosome delivery, even after 30 days. Imaging studies located exosomes in the intestines as well as the brain but not in any other organ.
Similar results were obtained following intranasal delivery of EL-4 exosome-encapsulated curcumin (Exo-cur). Curcumin levels peaked one hour after intranasal administration, and the drug was still detectable in the olfactory bulb region within the first 12 hours of a single intranasal administration.
Repeated administration of Exo-cur every 12 hours maintained the curcumin concentration at an average of 2.6 ± 0.4 nmol/g of brain tissue, with no visible abnormality of the nasal mucosal epithelial structure and no loss of body weight or changes in fecal contents. In vivo imaging studies of brain tissue following intanasal delivery of EL-4 exosomes showed the particles were taken up by microglial cells.
To determine whether the exosomes can be used as a vehicle to carry anti-inflammatory drugs and therefore treat brain inflammatory diseases, the researchers used two disease models. Firstly, intranasal administration of exosome-encapsulated curcumin was used to treat mice with LPS-indcued brain inflammation.
The results demonstrated significantly reduced numbers of activated inflammatory microglial cells in the brain. Further fluorescence-activated cell sorting (FACS) analysis showed that exosomes were taken up by nonactivated and activated brain macrophages. Both staining FACS studies suggested that Exo-cur treatment led to an increase in the number of apoptotic cells.
Exo-cur was then delivered intranasally to a mouse model of EAE. In these animals, the treatment significantly reduced disease scores, compared with control mice or those treated using exosomes or curcumin only. Expression of IL-1β by microglial cells was also significantly reduced in treated mice.
Because microglial cells have been shown to play a critical role in the growth of glioblastoma brain tumors, the researchers moved on to test the therapeutic effects of intranasal delivery of the exosome-encapsulated Stat3 inhibitor, JSI-124, into intracerebral tumor-bearing mice. Animals were treated every other day for 15 days beginning on day three after tumor cells were implanted.
The results showed that while the survival time was 20–30 days for mice treated intranasally using either PBS, exosomes, or JSI-124 alone, animals administered with Exo-JSI-124 lived on average for 44.5 days. Two of 10 mice given Exo-JSI-124 were still alive and showed no neurological symptoms at day 90, when they were killed for further analysis, which found no evidence of tumor at the original implantation site.
None of the Exo-JSI-124-treated animals exhibited evidence of toxicity or behavioral abnormalities during and after the 15-day treatment period. Again, quantitative studies showed that Exo-JSI124 treatment led to the selective reduction of pStat3 in microglial cells, which correlated with a decrease in microglial cell expression of both both IL-1β and IL-6.
“These results could generate interest in previously abandoned drug compounds and enable an entirely novel approach to CNS drug delivery,” the authors conclude. “The delivery method demonstrated in this study may be particularly suited for potent therapeutics with adverse effects in the blood or in peripheral tissues, for therapeutic agents that are extensively bound to plasma proteins or degraded in the blood, or for oral drugs that lose their bioavailability or are not readily soluble in the gastrointestinal tract.”