Antibody affinity and valency impact brain uptake of transferrin receptor-targeted gold nanoparticles

Transcytosis to Cross the Blood Brain Barrier, New Advancements and Challenges

The blood brain barrier (BBB) presents a formidable challenge to the delivery of drugs into the brain. Several strategies aim to overcome this obstacle and promote efficient and specific crossing through BBB of therapeutically relevant agents. One of those strategies uses the physiological process of receptor-mediated transcytosis (RMT) to transport cargo through the brain endothelial cells toward brain parenchyma. Recent developments in our understanding of intracellular trafficking and receptor binding as well as in protein engineering and nanotechnology have potentiated the opportunities for treatment of CNS diseases using RMT. In this mini-review, the current understanding of BBB structure is discussed, and recent findings exemplifying critical advances in RMT-mediated brain drug delivery are briefly presented.

Modulating the antibody density changes the uptake and transport at the blood-brain barrier of both transferrin receptor-targeted gold nanoparticles and liposomal cargo

Transport of the majority of therapeutic molecules to the brain is precluded by the presence of the blood-brain barrier (BBB) rendering efficient treatment of many neurological disorders impossible. This BBB, nonetheless, may be circumvented by targeting receptors and transport proteins expressed on the luminal surface of the brain capillary endothelial cells (BCECs). The transferrin receptor (TfR) has remained a popular target since its original description for this purpose, although clinical progression of TfR-targeted drug constructs or nanomedicines remains unsuccessful. One proposed issue pertaining to the use of TfR-targeting in nanomedicines is the efficient tuning of the ligand density on the nanoparticle surface. We studied the impact of TfR antibody density on the uptake and transport of nanoparticles into the brain, taking a parallel approach to investigate the impact on both antibody-functionalized gold nanoparticles (AuNPs) and cargo-loaded liposomes. We report that among three different low-range mean ligand densities (0.15, 0.3, and 0.6 ∗ 10³ antibodies/μm²), the highest density yielded the highest ability towards both targeting of the BCECs and subsequent transport across the BBB in vivo, and in vitro using primary cultures of the murine BBB. We also find that TfR-targeting on liposomes in the mouse may induce severe adverse effects after intravenous administration.

Quantification of kinetic rate constants for transcytosis of polymeric nanoparticle through blood-brain barrier

BACKGROUND

Polymeric nanoparticles (PNP) have received significant amount of interests for targeted drug delivery across the blood-brain barrier (BBB). Experimental studies have revealed that PNP can transport drug molecules from microvascular blood vessels to brain parenchyma in an efficient and non-invasive way. Despite that, very little attention has been paid to theoretically quantify the transport of such nanoparticles across BBB.

METHODS

In this study, for the first time, we developed a mathematical model for PNP transport through BBB endothelial cells. The mathematical model is developed based on mass-action laws, where kinetic rate parameters are determined by an artificial neural network (ANN) model using experimental data from in-vitro BBB experiments.

RESULTS

The presented ANN model provides a much simpler way to solve the parameter estimation problem by avoiding integration scheme for ordinary differential equations associated with the mass-action laws. Furthermore, this method can efficiently deal with both small and large data set and can approximate highly nonlinear functions. Our results show that the mass-action model, constructed with ANN based rate parameters, can successfully predict the characteristics of the polymeric nanoparticle transport across the BBB.

CONCLUSIONS

Our model results indicate that exocytosis of nanoparticles is seven fold slower to endocytosis suggesting that future studies should focus on enhancing the exocytosis process.

GENERAL SIGNIFICANCE

This mathematical study will assist in designing new drug carriers to overcome the drug delivery problems in brain. Furthermore, we anticipate that this model will form the basis of future comprehensive models for drug transport across BBB.

Effect of flow on targeting and penetration of angiopep-decorated nanoparticles in a microfluidic model blood-brain barrier

The blood-brain barrier (BBB) limits transport of nanoparticles from the circulation to the brain parenchyma. Angiopep-2, a peptide which functions as a brain transport vector, can be coupled to nanoparticles in order to facilitate binding and internalization by brain endothelial cells (ECs), and subsequent BBB penetration. This multi-step process may be affected by blood flow over brain ECs, as flow influences endothelial cell phenotype as well as interactions of nanoparticles with ECs. In the present study a microfluidic BBB model was constructed to evaluate binding and internalization by brain ECs, as well as BBB penetration of Angiopep-2 coupled liposomes (Ang2-Liposomes) in static and flow conditions. Ang2 conjugation to liposomes markedly improved binding relative to unconjugated liposomes. Ang2-Liposomes bound and were internalized efficiently by brain endothelial cells after static incubation or with 1 dyne/cm² of fluid shear stress (FSS), while binding was reduced at a FSS of 6 dyne/cm². Penetration of the model microfluidic BBB by Ang2-Liposomes was higher at a FSS of 1 dyne/cm² and 6 dyne/cm² than with static incubation. Analysis of barrier function and control experiments for receptor-mediated penetration provided insight into the magnitude of transcellular versus paracellular transport at each tested FSS. Overall, the results demonstrate that flow impacted the binding and BBB penetration of Ang2-functionalized nanoparticles. This highlights the relevance of the local flow environment for in vitro modeling of the performance of nanoparticles functionalized with BBB penetrating ligands.