Ex. 2 L7: PK of Biological drugs Flashcards
What are biologics
Generally derived from living material (human, animal, microorganism)
Complex in structure and this not fully characterized
Biologics examples
Monoclonal antibodies (mAb) for in vivo use
-Monospecific antibody that is identical because they are produced by immune cells of a single type
-They are clones of a single parent cell (identical)
Cytokines, growth factors, enzymes, immunomodulators Proteins intended for therapeutic use that are extracted from animals or microorganisms
Other non-vaccine therapeutic immunotherapies
Vaccine, blood products and gene therapy
Mabs
Many people use MaB injections/drugs
More and more biologics on market
Monoclonal antibodies (mAb)
VERY Target specific
Companies LOVE MAbs – spend a lot of money on them
We do see side effects from exaggerated pharmacological effects = drug works too well, causes effects
Antibodies – Y shaped protein
unit: Nm
Thickness of membrane – it is impossible to diffuse into cell – NO PASSIVE DIFFUSION DUE TO SIZE
Small molecule drugs
Small molecule drugs go everywhere because they can diffuse easily across biological membranes
Many off target/non-target effects
Immunoglobulin as drugs:
antibodies used as drugs belong to immunoglobulin G (igG) class
IgG accounts for 75-80% of naturally occurring antibodies
Second most common protein in plasma (5-13 g/L)’ albumin 35-50 g/L
Structure of IgG
Two heavy chains
Two light chains
Connected by disulfide bonds
Variable region provides the specificity
Variable region contains CDR (complementarity-determining region; not shown here)
Variable recognize antigen – specificity
FAB and Fc
Fraction of antigen binding : Most important region for recognizing antigen
Fraction of crystallizable
IgG action and structure
When it binds to its target through Fab region, it can bring in different cells (NK, etc. -**Relisten
Can also bring in different complement to initiate CDC (Complement dependent cytotoxicity)
FC region is important in initiating activation of immune cells
Fc Receptor types
FcyR
FcRn (neonatal FcR)
FC receptors: FcyR
Crystallized structure
Y shape
L, light, H, heavy, V variable
IMPORTANT: FC region
Contains binding site for Fc receptor expressed on immune cells: Fcy receptor
Also binds to C1Q
Responsible for binding to certain immune cells for cytotoxicity - relisten
Involved in mediating immune responses
Expressed on immune cells
FC receptors: FCRN
Different FC receptor: FcRN
FC
R = receptor
N = neonatal
Expressed on endothelial cells and immune cells
Involved in uptake into cells
mAb function
Targets of mAb are either on the cell membrane or circulating in the blood
mAb function: targeting on cell membrane:
MAB binding to protein called HER2
HER2 – protein expressed on cell membrane
Expressed on breast
Give MAB to a breast cancer patient, bind to HER2, get internalized, and lead to lysosomal degradation = decreased HER expression
OR antibody undergoes antibody dependent cytotoxicity – brings in different immune cells
mAb function: Circulating target
TNF-a
Cytokine mediating inflammation
Once it binds to target – initiates binding that leads to inflammation
Infliximab
Binds to TNFa – falls into it
Decreased level of TNF-a that binds with target = decreased inflammation
mAb: Absorption
Cannot be taken orally due to instability in GI tract and difficult in permeating the intestinal epithelium
Must be given parenterally (e.g. IV, SC, or IM)
Reach systemic circulation by **convective flow of the interstitial fluids into lymphatic capillaries into lymphatic channels **
CANNOT give orally – body will be treated as big protein, used as nutrient source
Out of three methods: subq is preferred because patient can administer themselves
Lymphatic system
One-way transport system for fluid and proteins by collecting them from interstitial space returning them to blood circulation
Lymph flow rate is 100-500 times slower than that of blood
The protein composition of lymph is nearly equivalent to that of interstitial fluid
Serves as a major transport route for immune cells and macromolecules
mAB absorption process
Put drug into interstitial space
Small molecule drug as subq – typically go through lipid bilayer – small, can cross by passive diffusion
Typical route for small molecule absorption
Pass through capillary membrane
Mabs are too thick, cannot go through membrane
Lymphatic system explained
Relatively high blood pressure
Because of that – some liquids squeeze through blood membranes and reach interstitial fluid area
Fluid accumulation – bad
Lymphatic – collects accumulated fluid back to the blood system
Takes care of extra fluid in interstitial space
Flow happens due to differences in pressure = Convective flow (fluid moving down the gradient)
Major pathway for mAb
Convective flow of the interstitial fluid into lymphatic channel
Minor pathway for mAbs
Diffusion through interstitial fluid and transport across blood capilary
(for small proteins (<5kD size)
Vd of mAb range
lies between that of plasma (0.04L/Kg) and extracellular water (0.23 L/kg)
-mAbs too big to cross - stuck in blood and plasma
mAb disposition:
Bioavailability – not 100%
There are _ to take care of Mabs when you inject
Relatively low at injection site: proteolysis at injection site
RESULT: Small protein and _ = become nutrients
Peak time: 3days – 1 week
Much slower time
Only relevant to IM and subq – IV fast
Half life – unit of days, weeks, or sometimes months
Antibodys hang in body for pretty long time due to FCrn recycling
revisit table
FcRn (neonatal Fc receptor)
Originally identified as a receptor for transporting maternal IgG to neonates via maternal milk
Expressed in many tissues including placenta syncytiotrophoblast and vascular endothelium
Serves as trasnport mechanism for IgG from maternal to fetal
IgG salvage by FcRn
The endothelial cells internalize serum IgG which binds to FcRn in an acidic endosomal compartment. FcRn then recycles IgG back into circulation, extending its serum half-life
FcRn in endothelial cells protects IgG from catabolism
IgG salvage by FcRn deeper explanation
Leads to endocytosis
Leads to endosome
LogpH solidifies this interaction between receptor and antibody
FCRN recycles – after getting through cell, go back to cell membrane = BRING ANTIBODIES WITH because binding is strong due to pH
When exposed to blood – binding is weaker because pH is higher – antibody gets released
IgG goes through cycles over and over – leads to half life of IgG
Q: T/F: The absence of FcRn leads to faster elimination of mAb
True
mAb elimination: IgG salvage by FcRn
FcRn gene knockout (KO) significantly decreases mAb half-life
FcRn binding delays mAb elimination and prolongs mAb half life
Revisit graph
mAb: Elimination - Phase I and II
Hepatic metabolism by phase I and II enzymes plays NO ROLE in mAb elimination
Renal elimination and mAb
Renal elimination of mAb is insignificant (glomerular filtration threshold ~60kDa)
mAbs are mainly eliminated through
Proteolytic degradation, resulting in smaller peptides and amino acids
Clearance from circulation is via nonspecific or specific pathway
Nonspecific clearance pathway (proteolysis by reticuloendothelial system, RES)
Specific clearance pathway (target-mediated clearance)
Other (antidrug antibody-mediated clearance)
mAb elimination: Reticuloendothelial system (RES)
Mononuclear phagocyte system (part of immune system)
Consists of the phagocytic cells located in reticular connective tissue (e.g. liver, bone marrow, and lymphoid organs)
Nonspecific uptake by cells via pinocytosis and subsequent protein catabolism
mAb elimination: Nonspecific clearance by RES
mAb bound to circulating antigen or free mAb is eliminated by RES
Slow but large capacity (not saturated at typical mAb doses)
Endogenous IgG half life: 21 days
Dose-independent” (ie, linear PK)
mAb elimination: Target mediated clearance
Elimination of mAbs through its antigen specific interaction
After mAbs bind to a specific antigen, they may be internalized or catabolized through lysosomal degradation as an antibody-antigen complex
More rapid than nonspecific clearance and most prominent for membrane-bound antigen
At high doses of mAb, this pathway is saturated, leading to dose dependent (nonlinear PK)
Example of Target mediated clearance mAb elimination:
Efalizumab:
Binds to CD11a on lymphocyte membrane and inhibits lymphocyte activation
Nonlinearity in mAb PK: High dose
Slow elimination
By RES mainly because target -mediated clearance is saturated
Linear clearance (unpredictable clearance)
Nonlinearity in mAb PK: Low dose
Rapid elimination
By RES + target mediated clearance
Nonlinear clearance (unpredictable clearance)
mAb: immunogenecity
Both neutralizing and non-neutralizing ADA form circulating ADA-mAb immune complex that is cleared by RES
SC admin elicits a higher likelihood compared to IM or IV admin, potentially secondary to aggregate formation at the injection site
mAb: antidrug antibodies
mAbs may trigger an immune response, i.e. formation of antidrug antibodies (ADA), in patients
Increased fraction of nonhuman sequence in the protein molecule leads to more immune response
Immunogenecity: As duration of treatment lengthens, the chances to elicit an immune response
also increases
Immunogenecity: ADA-mAb complex formation may
Increase mAb clearance
Disposition of mAb
Interstitial fluid
(some are lost at the local injection site)
Lymph
Blood
FcRN Mediated recycling
(Extends mAb half-life)
Elimination by RES or binding to membrane targets
