Abstract
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Nanocarriers
(NCs) are promising tools to improve drug delivery
across the blood–brain barrier (BBB) for more effective treatment
of brain disorders, although there is a scarcity of clinical translation
of brain-directed NCs. In order to drive the development of brain-oriented
NCs toward clinical success, it is essential to understand the prerequisites
for nanodelivery to be successful in brain treatment. In this Perspective,
we present how pharmacokinetic/pharmacodynamic (PK/PD), formulation
and nanotoxicity factors impact the therapeutic success of brain-specific
nanodelivery. Properties including high loading efficiency, slow in vivo drug release, long systemic circulation, an increase
in unbound brain-to-plasma concentration/exposure ratio (Kp,uu,brain), high drug potency, and minimal nanotoxicity
are prerequisites that should preferably be combined to maximize the
therapeutic potential of a brain-targeted NC. The PK of brain-directed
NCs needs to be evaluated in a more therapeutically relevant manner,
focusing on the released, unbound drug. It is more crucial to increase
the Kp,uu,brain than to improve the ability
of the NC to cross the BBB in its intact form. Brain-targeted NCs,
which are mostly developed for treating brain tumors, including metastases,
should aim to enhance drug delivery not just to tumor regions with
disrupted BBB, but equally important to regions with intact BBB where
the drugs themselves have problems reaching. This article provides
critical insights into how a brain-targeted nanoformulation needs
to be designed and optimized to achieve therapeutic success in the
brain.
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