Advanced drug delivery 3 - PPC and PEGylated Proteins Flashcards
What is a polymer protein conjugate? (PPC)
Drug delivery system where there is a polymer covalently conjugated to a protein
- The protein is the API
- Single protein has one or more polymeric chains attached (usually multiple).
Polymer drug conjugate (PDC)
Drug delivery system where there is a polymer covalent conjugated to the drug
- The drug is the API
- API is typically low MW molecules like traditional anticancer drugs e.g. dox, paclitaxel
- Each polymeric chain carries several drug molecules
Similarity between PDC and PPC
Both have covalent conjugation between API and polymer
Problems with using proteins as therapeutic agents
- Rapid renal excretion
- Proteolytic degradation
- Immunogenicity
- Aggregation
- Solubility
- Difficulty in formulation
Rapid renal excretion
- Smaller proteins are rapidly excreted
- Too quick = insufficient therapeutic action
Aggregation
Occurs before or after administration
Solubility
Needs to be soluble in blood - some proteins arent.
Advantages of PPC
- Protection
- Increased hydrodynamic volume, therefore reduced renal clearance.
- Reduced protein aggregation
PPC: Protection
- Polymeric chains protect proteins from proteolytic degradation
- Also protects the body from unwanted characteristics of the protein e.g. immunogeneicity
Increased hydrodynamic volume and reduced renal clearance
Conjugated protein vs Native protein:
Conjugated protein = increased hydrodyanmic volume = slower renal excretion because of the larger size
Reduced protein aggregation
- Attaching polymeric chains prevents protein aggregation
- Because of steric hindrence.
- Conjugate polymer in areas that are not key to the binding site to prevent interaction with molecular target
General structure of protein
- Amine group
- Alpha carbon
- Variable R group (side chain)
- Carboxylic acid
What does the polymer bind to in a protien
- The side chain: either C terminus or N terminius
Lysine
- Use lysine with a polymer with an activate carboxyl group
- Side chain of lysine has an amino group that the polymer can bind to
- Available in 2 forms: NH2, NH3+
Lysine group
- Use lysine with a polymer with an activated carboxyl group
- Side chain of lysine has an amino group that the polymer can bind to
- Available in 2 forms: NH2, NH3+
pH when conjugating lysine
- Must be used at a pH above pKa (>9.3-9.5) so that it is in the unprotonated form
- The unprotonated (NH2) form is suitable for conjugation
- Participates in a nucleophilic attack reaction, lone pair reacts with COOH
- pH ~10, not too high to denature protein
Monofunctional polymer
Polymer with only one reactive group per monomer unit
Polyfunctional polymer
More than one reactive group in side chain. So it has multiple sites for reaction
Which type of polymer is best for PPC
- Monofunctional
- Polyfunctional can end up cross-linking with several proteins and form a very heterogeneous mixture
Which type of polymer is best for PDC
- Polyfunctional
Why multifunctional polymers are not used in PPC
- High variability
- Too large conjugates form cross linking with several proteins = very homogenous mixture
- Difficult characterisation
What enzyme is ideal for protein conjugation
- PEG, in its methoxy form (mPEG)
Why should PEG be in its methoxy form?
- Only one reactive group (OH) - monofunctional
- Water soluble
- Soluble in some organic solvents
- Non-toxic
- Broadly non-immunogenic (although research is now indicating some immunogenecity)
Which enzyme is most stable
- mPEG2-trypsin
- It is PEGylated with branched PEG - mPEG-trypsin
- Native trypsin
- Not stable
- Very fast degdradation
