Stereotactic modulation of blood-brain barrier permeability to enhance drug delivery

Abstract

Drug delivery in the CNS is limited by endothelial tight junctions forming the impermeable blood-brain barrier. The development of new treatment paradigms has previously been hampered by the restrictiveness of the blood-brain barrier to systemically administered therapeutics. With recent advances in stereotactic localization and noninvasive imaging, we have honed the ability to modulate, ablate, and rewire millimetric brain structures to precisely permeate the impregnable barrier. The wide range of focused radiations offers endless possibilities to disrupt endothelial permeability with different patterns and intensity following 3-dimensional coordinates offering a new world of possibilities to access the CNS, as well as to target therapies. We propose a review of the current state of knowledge in targeted drug delivery using noninvasive image-guided approaches. To this end, we focus on strategies currently used in clinics or in clinical trials such as targeted radiotherapy and magnetic resonance guided focused ultrasound, but also on more experimental approaches such as magnetically heated nanoparticles, electric fields, and lasers, techniques which demonstrated remarkable results both in vitro and in vivo. We envision that biodistribution and efficacy of systemically administered drugs will be enhanced with further developments of these promising strategies. Besides therapeutic applications, stereotactic platforms can be highly valuable in clinical applications for interventional strategies that can improve the targetability and efficacy of drugs and macromolecules. It is our hope that by showcasing and reviewing the current state of this field, we can lay the groundwork to guide future research in this realm.

Keywords: electroporation; focused ultrasound; microbubbles; photodynamic therapy; vascular permeability.

Fig. 1.

Schematic illustration of BBB permeability.

Fig. 2.

Schematic illustration of the enhanced permeability and retention effect in and around the tumor site.

Fig. 3.

Schematic illustration of FUS in the context of intravenous MB injection to transiently disrupt BBB permeability.

Fig. 4.

Schematic illustration of NP activation using magnetic fields to induce targeted hyperthermia.

Fig. 5.

Schematic illustration of electric fields across the BBB membrane, regionally disrupting its permeability.

Fig. 6.

Schematic illustration of laser disruption through focal lesions in the BBB.