Antibody-Drug Conjugates Flashcards
1
Q
Antibody Drug Conjugates
A
- ADCs
- monoclonal antibodies or antibody fragments attached to biologically active molecules through chemical linkers with labile bonds
- deliver highly cytotoxic agents directly to tumour cells without affecting other dividing cells in the body
- while bound to Ab the chemotherapeutic payload is better tolerated
- target antigen higher on a cancer cell vs. a healthy cell
- many approved as treatments
2
Q
Idea of ADC
A
- drug linked to antibody recognizing the cell surface antigen
- internalisation
- release and action leading to cell death
3
Q
ADC Mechanism
A
- ADC binds to antigen on cancer cell surface and internalised via receptor mediated endocytosis
- highly cytotoxic payload molecule released by lysosomal cleavage
- ADC retains selectivity of original monoclonal Ab while being able to release attached cytotoxic payload in high concentrations
4
Q
ADC Components
A
- antibody
- linker: reduction, pH, protease, or non-cleavable
- payload: microtubule, DNA, transcription damage
5
Q
ADC Requirement
A
- ensure sufficient concentration of payload reaches the interior of the cancer cells to guarantee their death
- estimated that if ADC works at 50% efficiency but only 1-2% of the administered payload will reach the tumor cells
- important to choose a payload with sufficient cytotoxicity to exert effect at low concentrations
- able to use highly toxic drugs not able to be used in chemo
6
Q
Challenges designing ADCs
A
Circulation: stable linker needed to minimize premature release of payload
Binding: mAb must retain high affinity
Internalisation: inefficient internalisation due to limited target antigen level may prevent the cytotoxin from reaching its threshold concentration within the cell
Action: potency of payload must be enough
Release: ADC has to efficiently release the cytotoxic payload in its active form
Recycling: excessive binding to FcRns can reduce amount of cytotoxic payload release in cell
7
Q
Linker Design
A
- antigen selection
- cleavable linkers
- noncleavable linkers
- site of conjugation
8
Q
Antigen Selection
A
- need high expression by tumor cells and limited expression by normal tissue cells
- limited number of antigens on tumour cell surface
- amount of drug delivered by ADCs into tumour cells is low
9
Q
Antibody drug linkers
A
- need to consider stability and drug release
- environment factors affect the delivery
- stability refers to retention of drug by the antibody
10
Q
Drug to Antibody Ratio
A
- number of drugs attached to Ab
- the more drugs attached the more foreign and unstable it is
- ratio of 3.5-4 molecules on Ab normally
11
Q
Cleavable Linkers
A
- utilise the differences in conditions between the bloodstream and the cytoplasm within tumour cells
- change in environment once the ADC-antigen complex has internalised triggers cleavage of the linker and release of the active payload
- three categories: acid-labile, reducible disulfide bonds (cancer cells have high glutathione), enzyme-cleavable
12
Q
Acid Labile
A
- acid labile hydrazone linkers remain stable in neutral pH and utilize the low pH within the endosome/lysosomes the cleave the conjugation and release the drug
- however they have been associated with non-specific release of the payload leading to toxicity
13
Q
Reducible
A
- respond to difference in reduction potential between the intracellular compartment of tumour cell versus the blood based on glutathione concentration gradients
- more specific than acid-labile
- disulfides stable at physiological pH are susceptible to nucleophilic attack from thiols
- tumor cells have more thiol molecules as they are involved in growth and survival
- GSH attacks S-S bonds liberating the drug
- see mechanism notes **
14
Q
Enzyme Cleavable
A
- uses hydrolytic enzymes capable of recognising and cleaving particular peptide sequences contained with linkers
- ensures the ADC undergoes cleavage in the lysosomal environment and not in the plasma
- many peptidases in tumour cells
- see mechanism notes **
eg. capthepsin B-cleavable linker targeted by capthepsin B enzyme
- see mechanism notes **
15
Q
B-glucuronide moiety
A
- enzyme cleavable linker based on this enzyme specific moiety
- enzyme cleavable linker is based on B-glucuronide moiety
- B-glucuronidase enzyme releases payloads from B-glucuronide containing linkers
- enzyme present in lysosomes and is over-expressed in some tumor cell types
- these linkers have hydrophilic properties reducing aggregation during conjugation compared with constructs containing dipeptide-based or other linker types
- see notes for mechanism **
