Pegylation I/II Flashcards
Protein drugs
active substances made up of essential amino acids (>50 AAs)
Peptide drugs
active substances made up of essential amino acids (<50 AAs)
consists of hormones e.g insulin, human growth hormone
2 principals in drug delivery issues
- stability on storage
- in vivo delivery
issue of clearnace - IV route
What is the problem with protein drugs?
rapidly eliminated from blood:
- renal excretion, opsonisation> capture in liver
- generation of neutralising antibodies i.e. immunogenic response, proteolysis
Physiological half-lives (t½) of protein/ peptide drugs can be short
can we hide a drug?
approach 1)
large MW polymer covalently added to protein
approach 2) mutiple lower MW polymer covalently added to protein
what is end result of both approaches?
higher MW macromolecule, but where the protein component is shielded by the polymer
What are the physiological effects of hiding a drug?
Higher MW reduces glomerular filtration rate so reduces renal excretion
Polymer shields protein from proteases in the blood slowing hydrolysis
Opsonisation (adsorption of plasma proteins) is reduced reduced elimination via the liver or macrophages
Polymers employed are non-immunogenic
what polymers are best to use?
Biocompatible, i.e. non-toxic
Lacks immunogenicity
Water soluble (and soluble in other organic solvents)
Mobile and highly hydrated to create a “halo” around the protein
Easy to attach to proteins
Readily cleared from body after metabolism of the attached protein
What is polyethylene glycol (PEG)?
PEG is a synthetic linear homopolymer
Water-soluble, biocompatible, well-tolerated and FDA-approved
PEG has become the gold standard polymer in the bioconjugation of protein drugs
pegylation
- MW protein will require attachment of several PEG molecules (40-50KDa)
- pEG mols. become heavily hydrated - 2 or 3 H2O molecules per monomer unit > effectively ^ MW
- slow renal clearance, proteolysis and opsonisation of many protein drugs
- but PEGylation near active site of protein; reduce the efficacy
Rheumatoid arthritis & TNF-a
Rheumatoid arthritis (RA) is a chronic inflammatory disease
It is an autoimmune disorder, i.e., the immune system mistakenly attacks its own body
The pro-inflammatory cytokine TNF-α has been shown to be important in the pathogenesis of RA
TNF-α inhibitors have been developed and are proving effective in the treatment of RA
To understand TNF-α inhibitors we need tounderstand monoclonal antibodies (MABs)
MABs are made in the laboratory and can bind targets in the body, e.g. TNF-α
Designing a TNF-a inhibitor
- MAB designed to bind TBF-a bnut only use the fab portion - makes biologic molecule less immunogenic
Certolizumab pegol (Cimzia);
PEGylated monoclonal antibody fragment
MAB is expressed in E. coli and then processed to bioconjugate the Fab portion
biological medicine (biologic) binds to TNF-α stopping its involvement in the inflammatory process
Bioconjugation of the PEG moiety increases the half-life of certolizumab pegol to 13 days allowing a fortnightly maintenance dose
Other TNF-a inhibitors
Adalimumab (Humira) – MAB
Biologics are therefore different to generic small molecules which must be identical to the innovator
Other pegylated protein drugs
34 PEGylated drugs approved by the US FDA
Some of the most important ones include:
Filgrastim
Asparaginase
Interferon alpha/ beta
Brain-derived neurotrophic factor (BDNF)
Interleukin-6
Filgrastim is PEGylated at the amino terminusand up to 4 lysine residues
PEGylated filgrastim half-life is up to 4 timeslonger than the non-PEGylated drug
