Pluronics Project

ALZHEIMER’S DISEASE 

It is a progressive and fatal brain disease.

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Alzheimer's destroys brain cells, causing memory loss and problems with thinking and behavior.

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It is the most common form of dementia, a general term for memory loss and other cognitive abilities.

Hypotheses for Alzheimer’s Disease Cholinergic Hypothesis Amyloid Hypothesis

Cholinergic Hypothesis Proposal  Alzheimer’s is caused by reduced synthesis of an

important neurotransmitter in brain called acetylcholine that plays an important role in memory, learning, etc.

Not able to maintain widespread support

Amyloid Hypothesis  It postulates that amyloid beta (Aβ) deposits are the fundamental cause of the disease which are generated by β-secretase  Support for this postulate comes from the location

of the gene for the amyloid beta precursor protein (APP) on chromosome 21.

Explanation  Secretase are enzymes that snip pieces off a longer protein that is embedded in the cell membrane.

 The aggregation of these peptide fragements in clumps called “plaques” in brain is supposed to be the cause of Alzheimer’s disease.

Present Day Cure There are currently 4 FDA approved medications

available for treating the disease These drugs are acetylcholine esterase inhibitors

The drugs used are Tacrine, Donepezil,

Galantamine, Rivastigmine

Drawbacks of Present Day Cure  One of the major drawback is the inability to effectively

cross the blood brain barrier (BBB)  These drugs essentially increase acetylcholine levels in the brain and they don’t tackle the root cause of the disease

Blood-Brain Barrier Transport Properties Most substances that must cross the blood-brain barrier are not lipid soluble and therefore cross by specific carrier-mediated transport systems

A complex system of polarized transporter proteins and ionic channels determine the specific movement of water-soluble compounds and ions across barrier endothelial cells.

Drawbacks  Increased Dosage  Side Effects such as nausea and vomiting

 Secondary Effects like muscle cramps, decreased heart rate,

decreased appetite etc.  Sometimes antipyschotic drugs are used which are

associated with increased mortality.

Antisense Technology

This type of oligonucleotide is designed to bind to a complementary sequence (referred to as the ‘‘target sequence’’) in a selected mRNA, inhibiting gene expression at the translational level.

Hypothesis The use of antisense technology to treat Alzheimer's Disease

Objective  To develop a delivery system incorporating antisense technology to treat Alzheimer's disease

Aim  To find a material that would be able to deliver the antisense molecule across the BBB.

Poloxamers(Pluronics)  Bifunctional non-ionic triblock copolymers

 Consist of ethylene oxide (EO) and propylene oxide (PO) segments arranged in the basic A–B–A

structure: EOa–POb–Eoa

Reasons for choosing Pluronics  Ability to block P-gp efflux proteins.  Less toxic to cells than.  Display profound membrane Fluidization  The encapsulated material in the core of the micelles formed by

Pluronic results in increased solubility.  Bioavailability of the material is high.  Pluronics have been reported for use in gene therapy.

Unique properties  Molecular size, hydrophilicity and lipophilicity can by varied by changes in the number EO and PO.  Because of their amphiphilic structure, the polymers have surfactant properties.

 Form micellar structures above critical micellar concentration(CMC).  The temperature at which they form micelles is called the critical micelle temperature (CMT)

How Pluronics work?

Fig:Schematic Illustrating Effects of pluronic Block Copolymer on P gp Drug Efflux System

Mechanism Of Delivery

Above CMC the copolymers remain in micelle form but as the concentration decreases/micelles(in body fluid) are diluted below CMC they disintegrate and release the therapeutic agent.

Design  We will be using a combination of F 127(EO97-PO69-EO-97) & L61(EO2PO32-EO2 )

 A polycation poly(N-ethyl-4-vinylpyridinium bromide) is

incorporated in micelle to stabilize Oligodeoxynucleotide  Hydrophobicity will be increased.

Conclusion  This system will be effective as the antisense works

at the translational level.

 Side effects of drugs will be minimized.  Bioavailability of the therapeutic agent will be

increased across the blood brain barrier.

 As antisense oligonucleotides are highly specific,

there are minimal specficity concerns.

Future Work  The effect of Pluronic copolymers on other transport

systems is unknown.  Toxicity issues and development of safety formulations of

Pluronic still have to be addressed.  Micelles may disintegrate as a result of interactions with

blood components, serum proteins.  The cost analysis of the project is to be done.