Antibody drug conjugates for cancer

1. Antibody Drug Conjugates
for Cancer
Presented By: Anvita Jadhav
M. Pharm (IP)

2. ♠ Antibody-drug conjugates or ADCs are a new class of
drugs designed as a targeted therapy for the treatment
of cancer.
♠ ADCs are complex molecules composed of
an antibody linked, via a stable linker with labile bonds,
to a cytotoxic (anticancer) drug.
What are ADCs ?????????????????

4. ADC timeline
1958
MTX linked
to an
antibody
directed
toward
leukemia
cells
1972
Noncovalent
linked ADC
tested in
animal
models
1975
Covalent
linked
ADCs
tested in
animal
models
1988
Humanized
mAbs
reported
2000
First FDA
approved
ADC
(Mylotarg®)

5. Schematic illustration
of ADC

6. Mechanism of Action
Binding
ADC binds to
the target
antigen on the
surface of the
tumor cell to
produce an
ADC-antigen
complex
Internalization
Entire
antigen-ADC
complex is
internalized
through
receptor-
mediated
endocytosis
Degradation
ADC is
degraded
inside the a
lysosome to
release the
cytotoxic
drug.
Release
The cytotoxic
drug enters
the
cytoplasm,
where it binds
to its
molecular
target.
Cell Death
The
interaction of
the cytotoxic
drug with
DNA/
microtubules
leading to
apoptosis.
1 2 3 4 5

7. Mechanism of Action

8. Antibody
• Antibodies are
immunoglobulins made up
of:
2 Light Chains (identical)
~25 KDa
2 Heavy Chains (identical)
~50 KDa
FabRegion
FcRegion
Antigen Binding Sites

9. Terminology
MAb: Monoclonal Antibodies

10. From a biology perspective, the design of an effective ADC
relies on
Selection of an
appropriate
target antigen
Tumor
expression
levels
Rates of
antigen
internalization
Antibody Fc
format

11. Target antigens
 A successful ADC should target a well-internalized antigen
with low normal tissue expression and high expression on
tumors.
 Antigen expression on normal tissues can be tolerated if
expression on vital organs is minimal or absent.
Target antigens for ADCs in preclinical & clinical development
Cancer Target Antigens
Breast CD174, GPNMB, CRIPTO & nectin-4 (ASG-22ME)
Ovarian MUC16 (CA125), TIM-1 (CDX-014) & mesothelin
Lung CD56, CD326, CRIPTO, FAP, mesothelin & GD2
Pancreatic CD74, CD227 (MUC-1) & nectin-4 (ASG-22ME)
Prostate PSMA, STEAP-1 & TENB2

12. Antigen expression
 In general, optimal ADC targets are homogeneously
and selectively expressed at high density on the surface
of tumor cells.
 Homogenous tumor expression (although preferred) is
likely not an absolute requirement.

13. Antigen internalization
Ideally, once an ADC binds to a tumor-associated target,
the ADC–antigen complex is internalized in a rapid and
efficient manner.
Factors influencing the rate of internalization, such as -
 Epitope on the chosen target antigen bound by the ADC
 Affinity of the ADC–antigen interaction
 Intracellular trafficking pattern of the ADC complex

14. Impact of format
 The biological activity of an antibody can depend on
the interaction of its Fc portion with cells that express Fc
receptors (FcRs).
 Therefore, selection of the appropriate antibody
format for an ADC is an important consideration.

15. Classification of linkers
Linkers
Cleavable
linkers
Lysosomal
protease
sensitive
linkers
Acid sensitive
linkers
Glutathione
sensitive
linkers
Noncleavable
linkers

16. Cleavable linkers
• This strategy utilizes lysosomal proteases, that recognize and cleave a
dipeptide bond to release the free drug from the conjugate.
• Eg.: Valine - Citrulline linker
• This class of linkers takes advantage of the low pH in the lysosomal
compartment to trigger hydrolysis of an acid labile group within the
linker, & release the drug payload.
• Eg.: Hydrazone linker
Lysosomal protease sensitive linkers
Acid sensitive linkers

17. • This strategy exploits the higher concentration of thiols, such
as glutathione, to release the free drug.
• Eg. Disulphide linker
Glutathione sensitive linkers

18. Noncleavable linkers
• This approach depends on complete degradation of the
antibody after internalization of the ADC, resulting in release
of the free drug with the linker attached to an amino acid
residue from the mAb.
• Noncleavable linkers has greater stability in circulation
compared with cleavable linkers.

20. Cytotoxic drugs
• The drugs being used to construct ADCs generally fall into
two categories:
1) Microtubule inhibitors
2) DNA-damaging agents
• The percent of an injected antibody that localizes to a solid
tumor is very small (0.003–0.08% injected dose per gram of
tumor); therefore, toxic compounds with sub-nanomolar
potency are desirable.

21. ADC Design
Antibody Drug Conjugates
Linker
Antibody
Drug
• Targets a well-
characterized
antigen
• Maintains
binding, stability,
internalization,
etc.
• Minimal
nonspecific
binding
• Cleavable or noncleavable
• Stable in circulation
• Selective intracellular
release of drug
• Highly potent
• Non-immunogenic
• Amenable to
modifications for
linker attachment

22. Conjugation
Strategies
Chemical
Conjugation
Site-specific
conjugation

23. Chemical conjugation
• Traditionally, conjugation of linker-drugs to an antibody
takes place at solvent accessible reactive amino acids such as
lysines or cysteines derived from the reduction of interchain
disulfide bonds in the antibody.
Lysine conjugation
• Results in 0–8 conjugated molecules per antibody
• Conjugation occurs on both the heavy and light chain at ~20
different lysine residues (40 lysines per mAb).
• Greater than one million different ADC species can be
generated.

24. Cysteine conjugation
• Cysteine conjugation occurs after reduction of four inter-
chain disulfide bonds.
• Linker-drugs per antibody can range from 0–8, generating
more than one hundred different ADC species.

25. Drawbacks of
Chemical conjugation
• ADC species differ in
drug load & conjugation
site.
• Therefore, each species
may have differ in in-
vivo PK properties.
• Batch-to-batch
consistency in ADC
production is difficult to
obtain.

26. Site-specific conjugation
• It has three strategies
1
•Insertion of cysteine residues in the antibody
sequence by mutation or insertion
2
•Insertion of an unnatural amino acid
3
•Enzymatic conjugation

27. ADC advantages over
Traditional Chemotherapy
Traditional
Chemotherapy
ADC

28. Merits of ADC
• Selective delivery to tumor cells
• Specific binding to target antigen
• Large therapeutic index
• Reduction of adverse effects
• Extended and prolonged circulation half life

29. Demerits of ADC
• Molecular targets having similar expression may also get exposed
to the drug
• Requires screening of antigen of interest
• Premature release of cytotoxic drug
• Sufficient concentration may not be achieved at target site

30. Characterization of ADC
Drug to Antibody Ratio (DAR)
Drug Distribution
Size Variant Analysis
Charge-Based Separations
Analysis of Unconjugated Drug
Peptide Mapping Analysis

31. Approved ADCs
Agent Status Indication Antigen Cytotoxin Linker
Glembatumumab
vedotin
Ph II Advanced
breast
cancer
GPNMB MMAE Cleavable, Val-Cit
Lorvotuzumab
mertansine
Ph II MM, solid
tumors
CD56 DM1 Cleavable, disulfide
BT-062 Ph I MM CD138 DM4 Cleavable, disulfide
ADCs under Clinical Trials
Agent Indication Antigen Cytotoxin Linker
Adcetris®
(brentuximab
vedotin)
HL, ALCL CD30 MMAE Cleavable
Kadcyla®
(trastuzumab
emtansine)
Her2+ metastatic
breast cancer
HER2 DM1 Non-cleavable

34. ADCs are a new class of
drugs designed as
a targeted therapy for the
treatment of cancer.
ADCs are complex
molecules composed of
an antibody, linker and
drug.
Site-specific conjugation is
preferred over chemical
conjugation due to
decrease heterogeneity.
There are some unresolved
issues such as antibody
affinity, internalization rate
etc
Conclusion

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