Brain delivery and cellular internalization mechanisms for transferrin conjugated biodegradable polymersomes

Precise glioma targeting of and penetration by aptamer and peptide dual-functioned nanoparticles

The treatment of a brain glioma is still one of the most difficult challenges in oncology. To effectively treat brain glioma and reduce the side effects, drugs must be transported across the blood brain barrier (BBB) and then targeted to the brain cancer cells because most anti-tumor drugs are highly toxic to the normal brain tissue. A cascade delivery strategy was developed to perform these two aims and to achieve enhanced and precisely targeted delivery. Herein, we utilize a phage-displayed TGN peptide and an AS1411 aptamer, which are specific targeting ligands of the BBB and cancer cells, respectively and we conjugate them with nanoparticles to establish the brain glioma cascade delivery system (AsTNP). In vitro cell uptake and three-dimensional tumor spheroid penetration studies demonstrated that the system could not only target endothelial and tumor cells but also penetrate the endothelial monolayers and tumor cells to reach the core of the tumor spheroids, which was extremely important but mostly ignored in glioma therapy. In vivo imaging further demonstrated that the AsTNP provided the highest tumor distribution and tumor/normal brain ratio. The distribution was also reconfirmed by fluorescent images of the brain slides. As a result, the docetaxel-loaded AsTNP presents the best anti-glioma effect with improved glioma bearing survival. In conclusion, the AsTNP could precisely target to the brain glioma, which was a valuable target for glioma imaging and therapy.

Impacts of blood-brain barrier in drug delivery and targeting of brain tumors

INTRODUCTION

Entry of blood circulating agents into the brain is highly selectively con-trolled by specific transport machineries at the blood brain barrier (BBB), whose excellent barrier restrictiveness make brain drug delivery and targeting very challenging.

METHODS

Essential information on BBB cellular microenvironment were reviewed and discussed towards impacts of BBB on brain drug delivery and targeting.

RESULTS

Brain capillary endothelial cells (BCECs) form unique biological structure and architecture in association with astrocytes and pericytes, in which microenvironment the BCECs express restrictive tight junctional complexes that block the paracellular inward/outward traverse of biomolecules/compounds. These cells selectively/specifically control the transportation process through carrier and/or receptor mediated transport machineries that can also be exploited for the delivery of pharmaceuticals into the brain. Intelligent molecular therapies should be designed using such transport machineries for the efficient delivery of designated drugs into the brain. For better clinical outcomes, these smart pharmaceuticals should be engineered as seamless nanosystems to provide simultaneous imaging and therapy (multimodal theranostics).

CONCLUSION

The exceptional functional presence of BBB selectively controls inward and outward transportation mechanisms, thus advanced smart multifunctional nanomedicines are needed for the effective brain drug delivery and targeting. Fully understanding the biofunctions of BBB appears to be a central step for engineering of intelligent seamless therapeutics consisting of homing device for targeting, imaging moiety for detecting, and stimuli responsive device for on-demand liberation of therapeutic agent.