The blood–brain barrier acts as a physical barrier that prevents free entry of blood-derived substances, including those intended for therapeutic applications. The development of molecular Trojan horses is a promising drug targeting technology that allows for non-invasive delivery of therapeutics into the brain. This concept relies on the application of natural or genetically engineered proteins or small peptides, capable of specifically ferrying a drug-payload that is either directly coupled or encapsulated in an appropriate nanocarrier, across the blood–brain barrier via receptor-mediated transcytosis. Specifically, in this process the nanocarrier–drug system (“Trojan horse complex”) is transported transcellularly across the brain endothelium, from the blood to the brain interface, essentially trailed by a native receptor. Naturally, only certain properties would favor a receptor to serve as a transporter for nanocarriers, coated with appropriate ligands. Here we briefly discuss brain microvascular endothelial receptors that have been explored until now, highlighting molecular features that govern the efficiency of nanocarrier-mediated drug delivery into the brain.

A polarized layer of endothelial cells that comprises the blood-brain barrier (BBB) precludes access of systemically administered medicines to brain tissue. Consequently, there is a need for drug delivery vehicles that mediate transendothelial transport of such medicines. Endothelial cells use a variety of endocytotic pathways for the internalization of exogenous materials, including clathrin-mediated endocytosis, caveolar endocytosis, and macropinocytosis. The different modes of endocytosis result in the delivery of endocytosed material to distinctive intracellular compartments and therewith correlated differential processing. To obtain insight into the properties of drug delivery vehicles that direct their intracellular processing in brain endothelial cells, we investigated the intracellular processing of fixed-size nanoparticles in an in vitro BBB model as a function of distinct nanoparticle surface modifications. Caveolar endocytosis, adsorptive-mediated endocytosis, and receptor-mediated endocytosis were promoted by the use of uncoated 500-nm particles, attachment of the cationic polymer polyethyleneimine (PEI), and attachment of prion proteins, respectively. We demonstrate that surface modifications of nanoparticles, including charge and protein ligands, affect their mode of internalization by brain endothelial cells and thereby their subcellular fate and transcytotic potential.

Aims-The regulation of cell proliferation is a key event in normal development, pathophysiological responses to injury, and tumorigenesis. The orderly progression of cells through the cell cycle depends on a finely tuned balance between the concentrations of activated cyclins and cyclin dependent kinases. This study was undertaken to compare the expression of cell cycle regulators in benign and malignant melanocytic lesions during tumour progression. Methods-Immunohistochemistry was used to analyse 49 primary cutaneous malignant melanomas, 18 metastatic melanomas, and 12 histologically confirmed naevus cell naevi for their expression of cyclins (A, B1, D1, D2, D3, and E) and cyclin dependent kinases (CDK1, CDK2, and CDK4). Results-Cyclin E and CDK2 had the highest expression patterns in human cutaneous melanomas and metastases and correlated positively with histological type and tumour stage. Cyclins B1, D2, and D3 had significantly increased expression in metastases, but normal or even decreased expression in primary melanomas. However, cyclins A and D1, and CDK1 and CDK4 were expressed very weakly in situ with no significant diVerences between naevi, melanomas, or metastases, and there was no correlation with histopathological staging. The specificity of recognition by the antibodies used was confirmed by western blotting on a panel of seven human melanoma cell lines. Cyclins A, B, and E were expressed by all seven, whereas cyclin D1 was detectable in six of seven and CDK2 and cdc2 were present in five of seven lines analysed. Conclusions-Taken together, this study demonstrated a significant increase of cyclin E and CDK2 expression during tumour progression in malignant melanomas. (J Clin Pathol 2001;54:229-235)