Role of transferrin receptors in brain delivery

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Role Of Transferrin Receptors In Brain Targeting Delivery

By : Niketkumar PatelX01801641

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Outline :

Introduction Blood brain barrier Receptor mediated endocytosis Delivery approach Linking strategies Application Limitation and future trends Summary

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Introduction:

Delivery across BBB is difficult. How glucose (nutrient) being a hydrophilic molecule can reach to

the brain?

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Blood brain barrier :

A buffer between body and the brain…keeps environment of the brain constant.

Tight junction between cells

Very limited compounds small and hydrophobic.

Various approaches have developed.

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Approaches for brain delivery :

Invasive : Complicated surgical

process and disruption of BBB

Pharmacological :Small and hydrophobic molecules

Physiological

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Various transport systems…

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Receptor mediated endocytosis :

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A delivery approach…

Vector…OX26…binds specifically to transferrin receptors.

Linker…attach OX 26 to drug.

Drug…unable to cross BBB

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Transferrin receptors :

Transferrin receptor (TfR)] is a glycoprotein mediating the entry of ferric transferrin (Tf) from the extracellular compartment into the cells.

TfR are present on the surface of many cell types but they are most abundant on cells active in hemoglobin synthesis.

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OX 26 monoclonal antibody- a vector.

OX 26 is a monoclonal antibody for transferring receptors of rats.

Due to its high endogenous plasma concentration of 25 micro M…so the transferring receptor are almost saturated under physiological conditions.

The OX26 binds to an extracellular domain on the TfR, distinct from the transferrin binding site, and does not interfere with Tf binding.

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Linker strategies: Drug should remain biologically active after conjugation. Upon cleavage it should release the drugs in unmodified form. Nontransportable therapeutics are linked to the vector in such a

way that bifunctionality of the conjugates are retained. That is, the conjugates must retain a high affinity to both the BBB

vector and the cognate receptor that is attached to the delivery system.

Mainly three approaches has been developed : Chemical linkers Avidin/biotin linkers Genetic engineering.

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Chemical linkers :Amide bonding : Non cleavable type of binding Therapeutic drug is active in conjugate with vector.

Disulfide linking : Cleavable type of binding. Drug is active after reduction of disulfide bond and release. Disulfide reducing activity mainly contained in the cytosol.

PEGylation technology : Long spacer arm of PEG is placed between vector and drug.

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Avidin/Biotin linkers :

Avidin …an egg white protein4 binding sites for biotin

Noncovalent bindingDissociation half life 89 days

Specialized enzymatic reactions…labile to tissue depot site.

Avidin to OX 26Biotinylated drug

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Continue…Biotinylated drug : Biotin moieties are inserted or attaches using –SS- or –XX- linkers.

Avidin : Streptavidin or neutral light avidin is preferred

Cationic avidin shows rapid plasma clearance.

Multivalency of high avidin binding…high molecular mass aggregates…rapidly cleared by RES.

Avidin fusion proteins : Thiolated avidin and activated monoclonal antibody.

Genetic engineering : Solution to immunogenicity

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Applications : Delivery of vasoactive intestinal peptide (vasodilator) :

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Antisense oligonucleotides : Antisense oligodeoxynucleotides (ODN) are potential

neuropharmaceuticals with high degrees of specificity since these molecules, should react in a sequence specific mechanism with target messenger RNA (mRNA) molecules in the cell cytosol.

Two generations of antisense oliginucleotides ODNs were phosphodiester (PO)–ODNs and ODN molecules were phosphorothioate (PS)–ODNs

Since the principle nuclease degrading PO–ODNs in tissue culture is a 3′-exonuclease.

Placement of a biotin residue at the 3′-terminus of the PO–ODN Facilitates attachment and renders degradation.Rapidly degraded by endonucleases.

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Continue… A fully sulfurated PS–ODN is used

Mono-biotinylated and attached to the OX26–SA drug delivery system for efficient brain uptake.

But PS–ODNs are avidly bound by plasma protein such as albumin and by -2-macroglobulin. The molecular mass of -2-macroglobulin is very high…so easily taken up by RES.

Also exhibits neurotoxicity.

Peptide nucelic acids – A class of antisense oligonucleotidesUnconjugated 5500PNA chimeric proteins 200000…too large to permit rapid glomerular filtration.

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Continue…

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Immunoliposomes : Liposomes are vesicles in which an aqueous volume is entirely

enclosed by a membrane composed of lipid molecules, usually phospholipids .

Naturally occurring phospholipids…very high systemic plasma clearance…incorporation of PEG.

Antibody directed liposomes.

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Limitation : For instance in the field of brain targeting, there does not exist an

‘ideal’ brain vector to date. Such a molecule would have to recognize a target which is expressed exclusively at the brain capillary endothelium.

Targeting of immunoliposomes coupled to anti-transferrin receptor antibodies is not confined solely to the brain. Other organs such as the liver or skeletal muscle are recognized as well.

In liverIn brain

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Future trends.. Alternative brain delivery vector would serve the purpose.

(antibody directed at insulin receptors)…would provide high targeting efficiency.

Targeting tumor cells-over expression of transferrin receptors.

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Summary :

Expected advantages of Tf-drug conjugates such as a preferable tissue distribution, prolonged half-life of the drug in the plasma, and controlled drug release from the conjugates make this approach promising for their brain targeting delivery; still some more research is needed.

In perticular the vector based on immunoliposome (antibody-directed liposome), which bring together liposome technology, pegylation technology, BBB-targeting technology, and plasmid-based therapeutic gene technology may have many applications for the diagnosis and therapy of a broad range of central nervous system disorders in the future.

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Thank you…