D. PROTEIN DRUG DELIVERY AND CHALLENGES Flashcards
what are biopharmaceuticals
protein drugs
what are the advantages of protein drugs
highly specific and very effective
how do biologic drugs compare to conventional drugs
bigger and more complex
ie - Insulin and Pembrolizumab vs Aspirin and Crestor
how does IgM act
like a small particle, there is is no transit through basement membrane and hence little extravasation
what is the shape of proteins
- globular and packed
- specified by amino acid sequence of polypeptide chain
- flexible polypeptide chain folds into a compact conformation
- side chains help determine conformation in an aqueous solution
- relationship between molecular weight and size depends on shape
what challenges are caused by intrinsic physicochemical properties of proteins
- absorption: proteins are large and hydrophilic
- extra-vascular access is difficult as the drug mightn’t be able to reach target and hence will circulate in blood (phospholipid bilayer is tight)
- poor stability as they are easily denatured
- purity and characterisation of recombinant products
- pharmacological action is complex
what challenges are caused by anatomical and physiological barriers in human body
low MW drugs reach sites of action by diffusion and partition which isn’t possible for proteins
ie - proteins are large and shapely so can’t easily pass through skin
method of delivery proteins to skin
micro knife technique where small needles deliver proteins by puncturing barrier
how long can biopharmaceutical manufacturing take
up to 90 days
what is process of biopharmaceutical manufacturing
- collect cells and raw materials
- create cell bank
- small scale cell culture
- large scale cell culture (DNA recombination)
- recover product
- filter product (and purify)
- formulation
- pool banks
- sterilise and fill vials
- lyophilize
- add lids
- inspect product
- label product
- package product
how many cells are required for 1 dose of medicine
1000 billion cells
what does the amount of protein drug reaching tissues depend on (ie biodistribution)
- ability of proteins to be transported across endothelium
- differences in relative blood flow to different tissues ie - lungs vs cartilage
- rate of excretion by kidneys
- metabolism
how are small molecules removed in the body (peptides, oligonucleotides etc)
by glomerular filtration in glomerulus by passive filtration in kidneys
what is the cut off for glomerular filtration
> 8nm don’t pass through ie - antibodies, albumin (7nm)
why is albumin not removed
due to charge
(pores are -vely charged and so is albumin and 2 like charges repel and won’t pass through)
how does diabetes affect albumin
makes it more positive and therefore it passes through
what is the cut off MW for glomerular filtration
60kDa (proteins)
polysaccharides are 40kDa but pass through
how are proteins mainly eliminated
- metabolism by clearance receptors in liver on parenchymal cells and they are also on macrophages
ie - asialoglycoprotein receptor (ASGPR) - internalisation of galactose then removed for elimination
how does clearance occur
- many proteins have carbohydrate residues (ie - glycoproteins)
- terminal sugar residue is sialic acid but sugars below are different
- sugars are recognised when terminal sugar is cleaved off
- ASGPR recognises D-galactose
what does the ASGP receptor clear
- hormones eg: erythropoietin, FSH, interferon
- carrier molecules eg: thyroglobulin, caeruloplasmin, transferrin
- protease inhibitors eg: α-1 antitrypsin, α-2 macroglobulin
- immunological eg: IgG and IgG antigen complexes
what other important receptors are on liver parenchymal cells
fucose receptor
what other important receptors are on macrophages
N-acetylgalactosamine/ mannose receptor
what happens once the protein binds to a receptor
endocytosis and lysosomal degradation by enzymes
what is the importance of clearance receptors for drug delivery
- protein drugs may be cleared from circulation by normal homeostatic mechanisms
- specific receptors could be used to target drugs to the liver ie: receptor takes up certain proteins then metabolises them inside and potentially release a drug you want to deliver to a liver cell
but cytotoxic drugs (anti-cancer) can cause liver toxicity
