Advanced drug delivery 3 - PPC Flashcards
What is a polymer protein conjugate?
Drug delivery system where there is a polymer covalently conjugated to a protein
Protein polymer conjugate
- The protein is the API
- Single protein has one or more polymeric chains attached (usually multiple).
Polymer drug conjugate
- 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
- Aggregation
- Difficulty in formulation
- Immunogenicity
- Proteolytic degradation
- Rapid renal excretion
- Solubility
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 hydrodynamic volume = slower renal excretion because of the larger size
Reduced protein aggregation
- Attaching polymeric chains prevents protein aggregation because of steric hindrence.
- However they may interfere with interaction with molecular target
- To avoid this, conjugate polymer in areas that are not key to the binding site
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 group
- Use to conjugate polymers with a carboxyl group
- Side chain of lysine has an amino group that the polymer can bind to.
- Available in 2 forms:
NH2
NH3+
pH of Lysine
- Must be used at a pH above the pKa, so that it is in the unprotonated form.
- Above 9.3-9.5
- 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 one site for possible reaction in its chain.
Polyfunctional polymer
Polymer with several functional groups in its side chain so has several points for potential 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 polyfunctional polymers are not used in PPC
- High variability
- Form large conjugates from cross linking with several proteins
- 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
Example of PEGylated protein for cancer
Pegaspargase (Oncospar)
- Acute lymphoblastic leukemia
- Increases half life of L-Asparginase in body
3 catgeories of proteins used for therapeutic applications
- Enzymes
- Singalling proteins
- Antibodies
What is the advantage of using branched PEG compared to linear PEG?
More protection of the protein from enzyme degradation
Mention one point in the protein where you can have polymer-conjugation
Amino terminus, carboxylic acid terminus
What is pKa
Shows the strength of an acid
Lysine group
- Use to conjugate polymer with carboxyl group
