Biologics B - mAbs recycling Flashcards
What receptor mediates recycling of albumin and IgG.?
Neonatal Fc Receptor (FcRn)
Steps in mAbs recycling:
• Fc region binds to FcRn (FcRn is one of the critical quality attributes)
• IgG binds at at acidic pH (endosomal, pH 6), low affinity at pH 7-7.4.
• IgG taken up by monocytes or endothelial cells through endocytic mechanisms
• IgG not bound will be sorted to lysosomes for degradation
- Fv region may also bind to FcRn and alter interactions
- Antibody and antigen complexes are also recycled through FcRn pathway
How can you modify FcRn binding affinity?
by changing AA sequence
Different types of IgG’s and their half lives:
IgG types 1, 2 and 4 have an average 21days half life
IgG type 3 has an average 7 days half life.
Glycosylation impact on mAbs PK:
- All IgGs (natural and recombinant) are glycosylated. Need to ensure that this is characterised
- Glycosylation is not required for an IgG antibody’s long half- life
- However for Fc fusion proteins, The shorter half-life of an Fc-fusion molecule in comparison to the whole IgG has been attributed to the lower binding affinity to FcRn, the glycan mediated disposition and the receptor (of fusion partner) mediated disposition
Charge and PI (isoelectric point) impact on mAbs PK?
- The charge is important as often the surface of a cell/receptors are negatively charged so it is something that you may modulate. I.e. something that is positively charged may bind more easily.
- Changing the pI of mAbs is powerful way to improve KP.
- Charges variation can arise from manufacturing processes
- Charges differences may impact on both PK and PD
Administration of therapeutic mAb may result in the formation of:
anti-drug antibodies (ADA)
What do ADA’s do?
- ADA bind to the mAb, form immune complexes impacting on PK, PD, safety and efficacy of mAbs.
• May cause hypersensitivity responses such as anaphylaxis and infusion reactions, and accelerated clearance of drug
• ADA can be neutralizing or non-neutralizing (bind to the epitopes not needed for activity)
• Immunogenicity of mAb varies across species
• Drop of mAb concentration in blood: ensure to provide sufficiently high dose levels to achieve the desired exposure.
Summarise the attributes and their effect on mAB characteristics:
1) Binding - binding very specific for target antigen. Binding to FcRn and recycling contributes to half life.
2) PK/PD - PK usually dependent on biology of target antigen and PD
3) Dose proportionality - non linear PK at low doses. Linear PK at high doses after saturation of target
4) Distribution - distribution usually limited to blood and interstitial spaced
5) Metabolism - catabolism by proteolytic degradation into amino acids
6) Excretion - no renal clearance of intact antibody
7) immunogenicity - formation of ADA against mAb could occur. ADA will impact on PK, PD, efficacy and safety.
Immunogenicity in animals not predictive of humans
Novel antibody formats can be clustered in:
▫ Antibody fragments,
▫ Fusion protein – different parts and try to create something that works
▫ Antibody drug conjugates – antibody, cytotoxic, mab???
▫ Bispecific – modified igg’s to which a second variable region has been attached therefore two targets making them much more specific. However, complex to produce.
▫ Multispecific antibodies possessing multiple antigen binding sites
Novel format are more complex than mAbs e.g.:
▫ Different antigen-binding domain in the same molecule,
▫ Different molecular domains linked through flexible linkers – pick and choose what you want in structure and discard what you don’t want
▫ Heterogeneous product through conjugation, synthesis, physical chemical attributes.
▫ Overall decrease of conformational stability (form aggregates which are likely to result in loss of dose), decreased solubility
What are antibody fragments:
▫ Skip the Fc part of the mAb
▫ Most prominent is the fragment antibody binding part (Fab)
▫ Others scFv, single domain antibodies (sdAbs)
▫ ScFv made of VH flexibly linked to VL
What are fusion proteins?
▫ Major class of new products ▫ Comprise a protein, peptide or receptor exodomain fused to the Fc region of the mAb ▫ Fc portion typically contains the hinge region usually along with the conserved N-glycosylation site in the CH2 domain ▫ Half-life extended
What are ADC’s?
▫ mAb employed as drug delivery agents with chemotherapeutic drugs, immunotoxins, radioisotopes or cytokines.
▫ Cleavable linker in either Lys or Cys residues allowing release of payload
What are multifunctional antibodies?
▫ Bispecific or multispecific antibodies contain two or more variable domains with specific affinity to bind to different antigens
▫ Bispecific formats comprise IgG like and Fab fragment based constructs.
