PowerPoint Presentation

Background

What are liposomes? Lipidic nanoparticles/colloidal vesicles Artificially prepared, closed phospholipid bilayer, fluidic systems First described by Alex Bangham in 1961 Greek: =fat, =bodyLiposome/vesicle typeLipid bilayerSize small unilamellar (SUV)single20nm-100nmlarge unilamellar (LUV)single100nm-400nmgiant unilamellar (GUV)single1m and greaterlarge multilamellar (MLV)multiple200nm-3mmultivesicular (MVV)multiple200nm-3mLiposome productDrug carriedApplicationCaelyx/ Myocet/DoxilDoxorubicinBreast & ovarian cancers, Kaposis sarcomaAmBisomeAmphotericin BFungal infections leishmaniasisDiprivanPropofolAnaestheticEstrasorbEstrogenMenopausal therapyOther applicationsVaccines; anti-inflammatory drugs; gene medicines; nucleic acid polymers; cosmetic ingredients; nutritional & dietary supplements; imaging; biodetoxificationOne of the most recent liposomal drugs (FDA approved, August 2012) is Marqibo carrying Vincristine acute lymphoblastic leukaemia at relapse.On the liposome surface there is: PEGylation masking the liposome from the immune system Cetuximab (a mAb) for improved cell targeting of metastatic colorectal tumour cells. TAT for improved cell penetration. TAT is protected from degradation by further PEGylation which is pH sensitive. The pH in tumour tissue is approximately 5-6. At this reduced pH, the PEG sheds to reveal TAT.

Cholesterol:Phospholipid bilayer

Phospholipids can include phosphatidylcholine, dipalmitoylphosphatidylcholine or phosphatidylethanolamine. Cholesterol maintains fluidity and structural integrity.

As good and important as liposomal drugs are, there are some disadvantages of utilising liposomal drugs. These include: Sterilisation of the liposome during production processStability of the drug Short half life of the drug in the blood stream and at the site of action High production cost

The applications of liposomes can be divided into therapeutic and diagnostic. Their applications in different fields is due to their versatility and compatibility.Bioengineering applications of liposomes is the focusconsidered here and some advantages include: Sustained release drug delivery Site avoidance delivery Site specific targeting Passive and active targeting Improved solubility of lipophilic and amphiphilic drugs Improved transfer of hydrophilic charged molecules

TATThe stability of liposomes can be promoted in several ways: Increasing saturation by using cholesterol Applying lower internal pH environments in the liposomeIncreasing the drug to lipid ratio

PEGylation involves covalent coupling of polyethylene glycol to the phospholipid, which results in a significant increase in circulation half-life by preventing opsonization.Monoclonal antibodies (mAbs) lead liposomes to the specific target site. Attaching mAbs at the end of PEG is preferable, otherwise PEGylation may obstruct them. Cell-penetrating tag further improves intra cellular drug delivery of nanoparticles (e.g TAT peptide).

Engineering liposomes Liposomal Drug DeliveryPreparationOur Liposomal DrugSummaryAt the target site, the liposome loses its pH sensitive shell and the cell-penetrating action of TAT occurs, resulting in intracellular drug delivery.Our designed drug is a small unilamellar liposome containing the cytotoxic drug fluorouracil which is an anti-metabolite used in the treatment of colorectal cancer.

Encapsulation of hydrophilic drugs:Transmembrane pH gradients Proton-generating dissociable saltsEncapsulation of hydrophobic drugs:During the preparation in the subsequent hydration phase, drugs would trap in the hydrophobic bilayer area.Liposomal drug loadingPEG + mAbTATpeptide Applications/Advantages & DisadvantagesLiposomes are artificially prepared nanoparticles which have a multitude of biotechnological applications. The ability to add surface decorations to alter the properties of liposomes makes them a valuable tool in drug design. The addition of PEGylation, mAbs and TAT protein enabled us to design a novel cancer therapy which could potentially be used in the treatment of colorectal and other cancers.

Masoumeh Mansoubi-Hosseini, Michael Oladimeji, Emily Knight and Natalie Karaminas LiposomePEGylationmAbsDissolve phospholipids in solution of organic solvents (e.g. chloroform and methanol). Evaporate to form a thin lipid film. Hydrate by adding aqueous buffer (which can contain drugs) which causes the lipids to swell and peel off to form multilamellar vesicles (MLVs). These can then be sonicated by high frequency sound waves which causes breakdown of MLVs to small unilamellar vesicles (SUVs).

School of Biosciences, University of Kent, CanterburyCetuximabFluorouracilPEGTATAllen TM, Cullis PR. Liposomal drug delivery systems: From concept to clinical applications. Adv Drug Deliv Rev. 2013;65(1):36-48. Brannon-Peppas L, Blanchette JO. Nanoparticle and targeted systems for cancer therapy. Adv Drug Deliv Rev. 2012;64, Supplement(0):206-212.Koren E, Apte A, Jani A, Torchilin VP. Multifunctional PEGylated 2C5-immunoliposomes containing pH-sensitive bonds and TAT peptide for enhanced tumor cell internalization and cytotoxicity. J Controlled Release. 2012;160(2):264-273.Akbarzadeh A, Rezaei-Sadabady R, Davaran S, Joo SW, Zarghami N, HanifehpourY, Nejati-Koshki K. Liposome: classification, preparation, and applications. Nanoscale Research Letters. 2013;8(1):102.

References

1