Immunoliposome labeling: a sensitive and specific method for cell surface labeling

Strategies for Delivering Nanoparticles across Tumor Blood Vessels

Nanoparticle transport across tumor blood vessels is a key step in nanoparticle delivery to solid tumors. However, the specific pathways and mechanisms of this nanoparticle delivery process are not fully understood. Here, the biological and physical characteristics of the tumor vasculature and the tumor microenvironment are explored and how these features affect nanoparticle transport across tumor blood vessels is discussed. The biological and physical methods to deliver nanoparticles into tumors are reviewed and paracellular and transcellular nanoparticle transport pathways are explored. Understanding the underlying pathways and mechanisms of nanoparticle tumor delivery will inform the engineering of safer and more effective nanomedicines for clinical translation.

Nanostructure-based drug delivery systems for brain targeting

CONTEXT

It is well-known fact that blood brain barrier (BBB) hinders the penetrance and access of many pharmacotherapeutic agents to central nervous system (CNS). Many diseases of the CNS remain undertreated and the inability to treat most CNS disorders is not due to the lack of effective CNS drug discovery, rather, it is due to the ineffective CNS delivery. Therefore, a number of nanostructured drug delivery carriers have been developed and explored over the past couple of years to transport the drugs to brain.

OBJECTIVE

The present review will give comprehensive details of extensive research being done in field of nanostructured carriers to transport the drugs through the BBB in a safe and effective manner.

METHODS

The method includes both the polymeric- and lipid-based nanocarriers with emphasis on their utility, methodology, advantages, and the drugs which have been worked on using a particular approach to provide a noninvasive method to improve the drug transport through BBB.

RESULTS

Polymeric- and lipid-based nanocarriers enter brain capillaries before reaching the surface of the brain microvascular endothelial cells without the disruption of BBB. These systems are further modified with specific ligands vectors and pegylation aiming to target and enhance their binding with surface receptors of the specific tissues inside brain and increase long circulatory time which favors interaction and penetration into brain endothelial cells.

CONCLUSION

This review would give an insight to the researchers working on neurodegenerative and non-neurodegenerative diseases of the CNS including brain tumor.

Target: ligand interactions of the vascular endothelium. Implications for molecular imaging in inflammation

Molecular imaging refers to the non-invasive visualisation of biological processes at the molecular and cellular levels within a living organism, and offers a wide range of potential benefits to both clinical medicine and research into novel therapeutic agents. Inflammation plays an important role in a wide variety of pathological processes and imaging the molecular and cellular machinery that underlies chronic inflammation is attractive and feasible. In this review, we present an overview of molecular imaging of inflammation. We start by characterising molecular and cellular events in early inflammation, identifying current and potential future imaging targets. We focus on the imaging of endothelial cells, which mediate the important first steps in inflammation in any tissue, are readily accessible to imaging probes and which present an approach that can be applied across multiple modalities. We then review the generic requirements for imaging contrast agents and focus on the important considerations in respect of ligands, ligand-target interactions and contrast vehicles. We aim to provide an integrated view of current progress with a focus on promising recent developments in experimental and translational molecular imaging.

New systems for delivery of drugs to the brain in neurological disease

The restricted or regulated entry of most blood-borne substances into the brain has been recognised for more than a century. The blood-brain barrier (BBB)-shielding function provided by endothelial cells is important in the treatment of neurological diseases because this exclusion of foreign substances also restricts entry of many potentially therapeutic agents into the brain. The recent identification of several neuroactive proteins of potential therapeutic value has highlighted the crucial need for effective and safe transcapillary delivery methods to the brain. One promising method is delivery through brain capillaries by augmentation of pinocytotic vesicles delivery systems that use this cellular mechanism are in development. Recent investigations in animal models show that large molecules of neurotherapeutic potential can be conjugated to peptidomimetic ligands, which bind to selected peptide receptors, and are then internalised and transported in small vesicles across the cytoplasmic brain capillary barrier. These conjugates have been shown to remain functionally active and effective in animal models of neurological disease.

Discrepancy between transcriptional products and cell surface expression of MHC class I antigens in metastatic and non-metastatic Lewis lung tumor cells

Major histocompatibility complex class I transcriptional products and cell surface expression of their corresponding proteins were measured in tumorigenic Lewis lung carcinoma cells with either high metastatic activity (G4 cells) or with no metastatic activity (G2 cells). The transcriptional products were measured by hybridization to gene-specific oligonucleotide probes for H-2Kb and H-2Db respectively. The cell surface density of the corresponding H-2 glycoproteins was determined by FACS cell sorter analysis and by radioimmunoassay using anti-H-2Kb and anti-H-2Db specific monoclonal antibodies. The analyses revealed that the cell surface density of both Kb and Db was reduced 4-9 fold in G4 cells compared to G2 cells. However, this reduction of G4 cell surface expression of MHC class I molecules was not reflected at the mRNA level since both subclones had similar low levels of detectable Kb and Db specific mRNA. beta 2-microglobulin was analysed at the mRNA and protein level and found not to be the rate-limiting factor in the MHC class I expression of the metastatic G4 cells. Thus, the cell surface expression of H-2Kb and H-2Db by the two Lewis lung carcinoma subclones did not correlate with the amount of specific mRNA. Other regulatory mechanisms of gene expression acting at the levels between transcription and the appearance of the gene product at the cell surface must therefore account for the observed difference in the cell surface expression of MHC class I molecules of the two Lewis lung carcinoma cells. The potential importance of MHC class I expression in the metastatic capacity of the tumor cells is discussed.

Stability and fusion of lipid vesicles containing headgroup-modified analogues of phosphatidylethanolamine

We have used lipid mixing, contents mixing and contents-leakage assays to characterize the divalent cation-mediated interactions of vesicles composed of various headgroup-modified analogues of phosphatidylethanolamine, PE (N- and C-2-alkylated derivatives, and analogues with increased separations of the phosphoryl and amino groups) together with a low mole percentage of phosphatidylserine (PS). Vesicles containing different structural analogues of PE exhibit marked differences, both in the threshold divalent cation concentrations that are required to initiate vesicle-vesicle interactions and in the rates of contents mixing and leakage observed at suprathresholds divalent cation concentrations. The efficiencies of divalent cation-promoted contents leakage, and to a slightly lesser extent those of contents mixing, for PS/PE (analogue) vesicles show a marked inverse correlation with the lamellar-to-hexagonal II transition temperature (TH) of the PE (analogue) component. However, the destabilization kinetics for such vesicles show no abrupt changes over the temperature range around the equilibrium TH value measured for the vesicle lipids. Vesicles combining PS with different PE analogues exhibit divalent cation thresholds for aggregation that are not correlated with the TH values of the PE (analogue) components but appear instead to be correlated with the equilibrium interbilayer separations measured in multilamellar dispersions of these species. We have identified headgroup-modified analogues of PE that can be used to prepare vesicles that fuse more rapidly under a given set of conditions, or that show a bette ratio of fusion-to-contents-leakage rates, than do PE-containing vesicles. These results may be useful both for understanding better the bases for the high fusion-supporting ability of PE and for the preparation of lipid vesicles 'tailored' for particular practical applications.

A sensitive method to introduce membrane-bound proteins into recipient cells based on affinity enrichment of lipid vesicles to the recipient cell prior to fusion

A sensitive analytical procedure for studying membrane-bound structures has been developed. Membrane glycoproteins inserted into liposomes were transferred to recipient cells by use of a lectin, concanavalin A, bound to the cells as a bridge to generate proximity between the recipient cell and the glycoprotein-containing liposome, prior to exposure to the fusing agent, poly(ethylene glycol). Partially purified histocompatibility antigen from rats was introduced into the membrane of human lymphocytes. After treating the cells with poly(ethylene glycol) under fusion conditions, some of the antigen present in the preparation could not be eluted with alpha-methyl mannoside and EDTA, indicating that incorporation in the cell membrane had taken place. This antigen remained exposed on the lymphocyte surface for approximately 1 h as demonstrated by sensitivity of the lymphocytes to the lytic effect of an antiserum to the histocompatibility antigen in the presence of complement. Some of the lectin molecules seemed to be internalized in the cells but no induction of cell mitosis was observed. The described method gives an opportunity to work with small amounts of membrane proteins inserted into liposomes, introducing them into recipient cells for analysis of their biological activities.

Binding of antibodies in liposomes to extracellular matrix antigens

We have incorporated antibodies against fibronectin or laminin into liposomes and studied their interaction with insoluble forms of these antigens. The antibodies, after modification by palmitoylchloride, were incorporated into the lipid bilayer by the cholate dialysis method. The antibodies in the liposomes recognized their specific antigen with little reaction to the alternative attachment protein or to albumin (less than 2%). The binding of antibody-containing liposomes to insoluble antigen was inhibited by soluble antibodies to the respective antigens but not by antibodies to other antigens. The affinity constant of the liposome-antibody complex with the antigen was estimated at 1-10 X 10(-9) M liposomes. Thus, antibodies in liposomes retain their reactivity and specificity, and the reaction constant is comparable to that observed for immune complexes.

Lectin-mediated binding of liposome-inserted membrane proteins to red blood cells. A method to detect binding of antibodies to purified rat histocompatibility antigen or binding of insulin to the insulin receptor

Partially purified membrane proteins such as the rat RT-1 histocompatibility antigen or the insulin receptor of porcine liver were inserted into liposomes. These liposomes then bound efficiently to Con A-coated red blood cells. After attachment of the liposomes to the cells, cell-liposome conjugates could be separated from free liposomes by centrifugation. Binding of FITC-labeled specific antibodies or insulin to membrane proteins inserted into the liposomes could then be analyzed with a cell flow cytofluorometer. The amount of RT-1 antigen that became associated with the cells depended on the composition and concentration of phospholipids during liposome formation. No association of RT-1 antigen to the cells was obtained in the presence of 50 mM alpha-methyl mannoside. The technique allows detection of micrograms amounts of the histocompatibility antigen associated with the red blood cells. It was possible to detect binding of insulin to cells to which approximately 9 ng (3 X 10(-14) mol) insulin receptor/10(6) cells had been attached. This amount of membrane protein was close to the detection limit of the method.