Pharm lecture 7 - antibodie Flashcards
What is the FAB region?
antigen binding region of antibodies. variable regions of heavy and light chains
What is the structure of antibodies?
2 heavy chains and 2 light chains
What is the FC region?
Constant region of heavy chain - immune effector region
What are the types of IgG?
IgG1, IgG2, IgG3, IgG4
What type of antibody are therapeutic antibodies?
IgG
What are the characteristics of monoclonal antibodies? (4)
1) Homogenous for antibody type, amino acid sequence, affinity and specificity
2) High specificity
3) High Affinity
4) long half life in vivo
What are the following characteristics for an antibody administered subcutaneously or intramuscularly?
Bioavailability?
time till peak concentration?
Bioavailability: 24-95%
time till peak concentration: 7-8 days
What are 4 types of monoclonal antibodies and their suffix?
Murine: -o
Chimeric: -xi
Humanized: -zu
Human: -u
How are antibodies administrated subcutaneously or intramuscularly absorbed? What is this route of administration limited by?
Absorbed slowly by convective absorption through lymph vessels and by diffusion into blood vessels
Limited by volume that can be injected at these sites
Where are antibodies distributed? (3)
Extra-cellular distribution
Access restricted across diffusional barriers unless transport is facilitated
Does not cross blood brain barrier so does not enter CNS
What is the function of the Neonatal Fc receptor? (FcRn) (2)
1) Transfers passive immunity across placenta from mother to fetus (IgG antibody)
2) Protects IgG from degradation, prolonging half life in serum
What cells express the Neonatal Fc receptor? (5)
Hepatocytes endothelial cells phagocytic cells APC intestinal epithelium
How does FcRn protect IgG from degradation? (3 steps)
1) IgG undergoes endocytosis into low pH endosomes promoting IgG binding to FcRn (because FcRn only binds IgG at acidic p.H.)
2) FcRn-IgG complex resistant to lysosomal enzymatic degradation - free IgG is degraded
3) GcRn-bound IgG is returned to cell surface where it dissociates at physiological p.H.
What are the half lives for the isotypes of IgG?
IgG1, IgG2, IgG4 = 20-21 days half life
IgG3 = 7 days half life
Why does IgG3 have the lowest half life?
Because it has a single amino acid difference so that it does not bind FcRn
How long is the Murine mAB half life in humans and why?
12-48 hours because it does not bind with FcRn
What is the half life of antibody fragments and why?
11-27 hours - lack Fc region so does not bind FcRn
What are the mechanisms resulting from antigen-antibody binding?
1) Antagonism/neutralization
2) Cell signaling inhibition
3) Antibody dependent cellular cytotoxicity (ADCC)
4) Complement-dependent cytotoxicity (CDC)
5) Selective delivery of toxins or radionuclides
6) Selective imaging
What is antagonism or neutralization?
Antibody acts as a competitive inhibitor blocking interaction of a soluble antigen with its ligand, thus decreasing the concentration of unbound soluble antigen in plasma
What is Cell signaling inhibition?
Antibody binds cell surface signaling molecule such as a receptor or adhesion molecule to inhibit cell activation or a signaling function.
Can inactivate a pathway or activate a pathway and can act as an agonist or competitive inhibitor
can promote ADCC
What is Anti-body dependent cellular cytotoxicity (ADCC)?
Antigen-bound antibody induces lysis of a target cell by an activated NK cell, neutrophl or macrophage
Which antibodies show the greatest activity for ADCC?
IgG1 and IgG3
How does an antibody cause ADCC?
1) Fab region binds cell surface protein on target cell
2) Fc region binds Fc receptor on NK cell or macrophages
3) NK cell releases cytotoxins or macrophage phagocytoses target cell
What is complement-dependent cytotoxicity?
Antigen-bound antibody induces lysis of a target cell by activation of the complement system
What is the mechanism of compliment-dependent cytotoxicity (CDC)?
1) Fab region binds a cell surface protein on the target cell
2) Fc region binds complement protein C1q and activates the complement system resulting in cell lysis
What is the mechanism of the selective delivery of toxins or radionuclides by antibodies? (3 steps)
1) toxins or radionuclides are conjugated to an antibody
2) antibody binds to cell surface protein of target cell and selectively delivers the toxin or radionuclid
3) antibody-toxin complex is internalized and toxin or radionuclid released to kill target cell
How are antibodies used for selective imaging?
1) Radiocontrast agent or radionuclides are conjugated to antibody
2) Antibody binds to cell surface protein on target cell and delivers imaging agent
3) Radiocontrast agent or radionuclid detected or imaged
What is immunogenicity?
Antibodies are foreign proteins so they can promote generation of endogenous antibodies against the therapeutic antibody
What are the factors that influence immunogenicity?
1) Fraction of foreign amino acid sequence in antibody (high for murine, low for human)
2) Increases with duration of therapy
3) More frequent with low doses
4) More likely with subcutaneous then intravenously
