Press Release
Developing a new strategy to selectively deliver
therapies to the brain
Turning the problem into the solution: exploiting the impermeabilityof the brain vasculature to target nano-vehicles to the brain
Summary:
Therapy-loaded nanoparticles may be directed to the brain by functionalization with ligands
targeting BBB-associated proteins. However, such targeting strategies have inherent brainspecificity limitations, as the target proteins are also significantly expressed in peripheralorgans, thereby limiting the clinical application of such strategies. We have developed acounterintuitive targeting strategy which exploits the high impermeability of the BBB itself toselectively retain molecular labels (i.e. targets) on the surface of brain endothelium.
Nanoparticles capable of binding the displayed targets are consequently directed
specifically to the brain microvasculature with minimal targeting to peripheral organs. This
two-step targeting strategy therefore paves the way to overcome the peripheral ‘off-target’
nanoparticle accumulation, increasing the clinical translation of nanoparticle-based
therapies. The results have been published in the July 23 issue of Proceedings of theNational Academy of Science (Impact Factor = 9.5804).
July 27, 2020 – Kawasaki / Japan: The Innovation Center of NanoMedicine (Director: Prof.
Kazunori Kataoka, Location: Kawasaki-City, Abbreviation: iCONM) announced that a new
strategy to specifically target to the brain was discovered in collaboration with theDepartment of Bioengineering, Graduate School of Engineering, University of Tokyo. The
details are published in the Proceedings of the National Academy of Science (Impact factor= 9.350 in 2019) issued on July 23. (Note 1)
Treatment of neurological diseases is severely hindered by the poor delivery of therapies tothe brain due to the presence of the blood-brain barrier (BBB), a highly impermeable cellularbarrier composed primarily by the specialized endothelial cells lining the brain
microvasculature. Nanotechnology-based strategies have achieved modest success indelivering therapeutics to the brain by loading them onto nanomachines (Note 2) decorated
with ligands which bind to proteins associated with the BBB (Note 3). However, suchtargeting strategies have inherent brain-specificity limitations, as the target proteins are alsosignificantly expressed in peripheral organs, leading to increased accumulation ofnanomachines for instance in the lung and heart. Therefore, the clinical translation of current
strategies is hampered by detrimental peripheral side-effects and reduced effective
therapeutic doses reaching the brain. Hence, new strategies which exploit alternative
features of the BBB need to be developed to overcome ‘off-target’ accumulation ofnanomachines.
The group of Prof. Kataoka have developed a simple, yet counterintuitive strategy whichturns the problem of therapy delivery to the brain, that is, the high impermeability of brain
endothelial cells, into the solution to achieve specific brain targeting of nanomachines withminimal accumulation increase in peripheral organs.
The high impermeability of brain endothelial cells is in large part due to a markedly reduced
level of endocytosis compared to peripheral endothelial cells. This feature may therefore be
exploited to promote free, unconjugated molecular labels to be selectively retained on thesurface of brain endothelial cells while being quickly removed (endocytosed) from thesurface of endothelial cells of other organs in the body. In this way, nanomachines capableof efficiently recognizing the displayed molecular labels are specifically targeted to the brain
with minimal targeting into other organs.
The feasibility of such an approach has been demonstrated by employing biotin-containing
antibodies against the protein Platelet Endothelial Cell Adhesion Molecule (PECAM)-1,
which is expressed in the vasculature of most organs. The authors demonstrated that if
nanomachines decorated with the protein avidin (capable of very strongly binding to biotin)
are injected into mice a short time-period after injection of biotin-PECAM-1 antibodies, thenanomachines accumulate preferentially in the lung, with accumulation also seen in thebrain, heart and pancreas (note 4). However, if the time-interval between antibody andnanomachine injection is increased to allow removal of the antibody from the surface of
peripheral endothelial cells, the ability of the nanomachines to accumulate in the lung,heart and pancreas steadily decreases, while accumulation in the brain remains constant.
Hence, after an 8 hr time-interval, the nanomachines were only targeted to the brain, withno increase in accumulation seen in any peripheral organ.
This novel two-step targeting strategy therefore paves the way to overcome the limitation ofperipheral “off-target” nanomachine accumulation, thereby increasing the clinical translationof nanomachine-based therapies.
(Note 1) Daniel Gonzalez-Carter, Xueying Liu, Theofilus A. Tockary, Anjaneyulu Dirisala,Kazuko Toh, Yasutaka Anraku and Kazunori Kataoka, “Targeting nanoparticles to the brain
by exploiting the blood-brain barrier impermeability to selectively label the brainendothelium”, Proc. Natl. Acad. Sci., 2020 in press. (doi.org/10.1073/pnas.2002016117)(Note 2) Smart Nanomachine: Spherical or rod-shaped molecular assembly (nanomicelles)with a size of tens of nm formed by associating amphipathic polymers with various functional
molecules in water. Horacio Cabral, Keijiro Miyata, Kensuke Osada and Kazunori Kataoka,“Block copolymer micelles in nanomedicine applications” Chem. Rev.118 (14) 6844-6892(2018) (doi.org/10.1021/acs.chemrev.8b00199)(Note 3) Jinbing Xie, Daniel Gonzalez-Carter, Theofilus Tockary, Noriko Nakamura, YongerXue, Makoto Nakakido, Hiroki Akiba, Anjaneyulu Dirisala, Xuying Liu, Kazuko Toh, Tao Yang,Zengtao Wang, Shigeto Fukushima, Junjie Li, Sabina Quader, Kouhei Tsumoto, Takanori
Yokota, Yasutaka Anraku and Kazunori Kataoka, “Dual-Sensitive Nanomicelles Enhancing
Systemic Delivery of Therapeutically Active Antibodies Specifically into the Brain”, ACS
Nano, 2020, 14 (6), 6729-6742.
https://pubs.acs.org/doi/abs/10.1021/acsnano.9b09991(Note 4) Biotin-conjugated anti-PECAM1 antibody (biotin-α-PECAM1) was injected throughthe tail vein of mice, and after a predetermined time (15 minutes, 2 hours, 4 hours, or 8hours), avidin-decorated nanomachines (avidin-NM) were intravenously injected. After 16hours, the mice were anesthetized and perfused with D-PBS before the lung, brain, heart,and pancreas were collected to quantify avidin-NM accumulation. The results shown in Fig.
1 were obtained by evaluating the targeting of the nanomicelles to each organ.
Innovation Center of NanoMedicine (iCONM):
The Innovation Center of NanoMedicine (iCONM) is a leading facility of King Skyfront, thatis a biotech and healthtech innovation cluster in Kawasaki City. iCONM started theoperation in April 2015 with Kawasaki Institute of Industrial Promotion in order to drive"Center of Open Innovation Network for Smart Health (COINS)" as a part of Japanese
governmental research program "Center of Innovation (COI) Stream". Designed for thepurpose of promoting "open innovation" through industry-academia-government andmedicine-engineering collaborations with state-of-the-art facilities and experimental
equipment capable of conducting the R&D from organic synthesis and micro-processing topreclinical studies. This is a very unique research center that is hardly found in the world.
https://iconm.kawasaki-net.ne.jp/en/index.html
Department of Bioengineering, Graduate School of Engineering, University ofTokyo:
In a society where the population ages and the birth rate declines with the sustainable
development being longed for, the Department of Bioengineering aims to contribute to thepromotion of health and well-being of the humanity. To achieve this goal, we promote theeducation and research of bioengineering, which is the multidisciplinary academic fieldintegrating the existing disciplines of engineering and those of life sciences at theirinterface. The key features of bioengineering are to establish its theoretical basis byunderstanding and clarifying the interactions of materials and systems with living bodies,and to develop fundamental technologies that control these interactions based on thetheory. The control of the interactions with living bodies renders materials and systems far
more useful and compatible, promising the birth of groundbreaking medical technologies.
http://www.bioeng.t.u-tokyo.ac.jp/en/overview/index.html

Fig. 1. Short time-intervals (15 mins) between injection of biotin-PECAM1 antibody andinjection of avidin-decorated nanomachines (avidin-NM) results in avidin-NM targeting to
the lung (yellow), brain (blue), heart (red), and pancreas (purple) (a). However, targeting toperipheral organs decreases as a function of time-interval length, while targeting to thebrain remains constant (b, c). Consequently, an 8h time-interval results in specific targetingof avidin-NM to the brain, with no targeting seen in peripheral organs (d). Avidin-NM
accumulation was visualized in freshly excised brains (e) and fixed brain tissue (f).