BBB 3 Flashcards
brain tumours and current treatments?
80% of primary malignant brain tumours = gliomas
- gliomablastoma
- astrocytoma
- ependymoma
25% are metastases from peripheral tumours - originate from skin, lung, breast
- tumour cells can secrete enzymes that can break down tight junction proteins holding cells together - breaks down BBB
current treatment - targets tumour molecular targets to inhibit glioma growth and proliferation
- growth factor receptors
- intracellular signalling to activate p53 gene - induces apoptosis
- inhibit cell division/mitosis
what is the current treatments for peripheral tumors and why don’t they work for CNS tumours?
1) gene modifiers e.g. siRNA, cDNA
- induce p53 - apoptosis
- knockdown growth factor receptors - inhibits glioma growth
physical barrier - RNA, DNA are large hydrophilic compounds - cannot get through TJs
metabolic barrier - nucleases in endothelial cells degrade RNA and DNA
2) chemotherapeutics e.g. vincristine, vinblastine, doxorubicin
- prevent cell division
- disrupt DNA synthesis
transport barrier - large lipophilic drugs are substrates for BBB efflux transporters P-gp, BCRP, MRP
whats an additional problem chemotherapeutics face?
have to overcome efflux transporters on BBB
but also efflux transporters on tumour cells
- known as brain tumour barrier
- another barrier getting chemotherapy drugs into the tumour cells
evaluate the use of nanoparticles to deliver drugs across the BBB to brain tumours
advantages:
- encapsulation of drug protects it from metabolic barrier and efflux transporters
- enhanced penetration
- can deliver high drug load to brain
- can carry almost any type of drug - lipid soluble drugs can sit in phospholipid bilayer and hydrophlic core can carry water soluble drugs
- high MW drugs can be delivered
- controlled release
- targeted deliver
disadvantages:
- toxicity of nanoparticle may induce immune response
- costly - clinical trials needed for both drug + nanoparticle
- accumulation of nanoparticle by liver and spleen
- may target other organs
what are the major types of nanoparticles
1) polymeric NPs- clusters of long chains of polyesters, polysaccharides, amino acids
- allow drug to be carried along long chain - drug conjugated onto side arms - not going in the middle
2) Dendrimers
3) phospholipid based NPs - liposomes
4) inorganic NPs
5) carbon based NPs
what are the nanoparticle features?
changing NP features can enhance function
SIZE
SHAPE
CHARGE
COMPOSITION
DRUG
LIGANDS
compare composition of nanoparticles
SYNTHETIC - removed quickly by kidney liver clearance
- polymers - easy to manufacture but few interavtion sites and drug loading areas
- dendrimers - large SA for drug attachment
NATURAL - avoids immune system and kidney liver clearance. esp phospholipids - like normal cell walls
- liposomes - good flexible drug loading, lipid soluble drugs in shell, hydrophilic drugs in core
- but large NP size
INORGANIC - stable and easy to manufacture
- S.E. - disrupt BBB structure, induce inflammation, clearance issues
size and shape of NPs
SIZE:
- smaller NPs penetrate BBB best
- ideal range of NP diameter 50-100nm
- <20nm - drug released quickly, quickly cleared by kidneys, limited capacity to carry drug
SHAPE:
- spherical NPs easiest to prepare
- rod shaped NPs have higher brain accumulation
protein adsorption of NPs
most NPs adsorb proteins on to their surface once in blood
- this attracts WBCs to engulf it
- increases clearance by WBCs
to get rid of this problem
- NPs coated in PEG polyethylene glycol
- stops proteins sticking onto NP and reduces clearance so it can stay in blood longer and is biocompatible
charge and ligands in NPs
CHARGE:
- neutral or negative charged NPs - more stable, longer half life, low rate of non-specific cellular uptake
- positively charged NPs more easily penetrate BBB but other cell membranes which are negative - more toxic
- for low toxicity + non-specific cellular uptake - neutral or negative NPs preferred
LIGANDS:
- ligands added to outside of NP and PEG coating so BBB can recognise it and want to transport it inside
- ligands improve BBB targeting and transport
give 2 examples of NP formulations trialed for brain tumours
ONYVIDE MM-398:
liposome NP +PEG
100nm diameter
drug load - irinotecan
first use - pancreatic cancer
CAELYX:
liposome NP + PEG
180nm diameter
drug load - doxorubicin
first use - ovarian cancer
BOTH THESE NPs didn’t have specific targeting for BBB
- would go to anywhere in body not just brain
describe trojan horse technology
attaching molecules to NP that are recognised by BBB uptake transporters
tricking the BBB into uptake of whole NP
most successful mechanism targeting BBB uptake is RMT - receptor mediated transcytosis
RMT - specific uptake of larger molecules
- specific to particular compounds as BBB has receptors on its surface that recognise the compound then undergoes endocytosis
- transcytosis avoid metabolic barrier and goes around physical barrier
How can you increase BBB targeting?
BBB has many receptors that if activated can start transcytosis process
BBB has high levels of transferrin (TFR) and lipoprotein (LRP) receptor - can get more drug into brain if using these receptors
give 2 examples of NP formulations using trojan technology to target brain tumours
SCL-P53
- composition - liposome
- charge neutral
- size 100nm
- drug - plasmid p53 - by putting it in NP - avoids metabolic barrier - enzyme degradation
trojan recognised by BBB TFR - undergoes RMT
- NP delivers p53 gene plasmid to brain to stop cell division
ANG
- targets LRP RMT
- to deliver paclitaxel chemotherapy to brain which would normally be effluxed by BBB
- paclitaxel enclosed in NP - avoids efflux transporters
These strategies are more effective at reducing tumour size compared to giving drugs alone
what are some other NP modifications in the pipeline to deliver more drug across BBB
1) NP taken up by 2 BBB uptake systems - RMT & AMT
using LRP trojan ligand (ANG)
1 - NP taken up by RMT using LRP trojan ANG
2 - NP taken up by AMT - PEG is removed by endothelial enzymes (MMPs), charge changes from -7mv to +2mv - now taken up by AMT
- NP uses metabolic barrier enzymes to remove PEG
2) NPs that move around faster - chemotaxis to improve uptake
- use glucose metabolism to generate an oxygen jet
enzymes in the liposome NP oxidise glucose to produce oxygen - oxygen escapes through the thin wall of liposome - comes out of one place so propels the NP along - creating a jet
