Antibody-Drug Conjugates:
Modes of Toxicity
Nonclinical safety evaluation
of immunoconjuates
Melissa M. Schutten, DVM, PhD, DACVP
Safety Assessment Pathology
Melissa M Schutten, D
NorCal Society of Toxicology Meeting
September 27, 2012
Overview
• Introduction to Antibody Drug Conjugates (ADCs)
• Modes of ADC toxicity
• Challenges associated with nonclinical safety
evaluation of ADCs
• Summary
2
Anatomy of an Antibody-Drug Conjugate (ADC)
Linker stable in
circulation
Antibody targeted
to tumor
• Humanized monoclonal
Ab (IgG1)
• mAb with Fc modifications
(modulate ADCC, CDC
activity)
• Other mAb fragments
• Linker biochemistry
• Acid labile (hydrazone)
• Enzyme dipeptides (cleavable)
• Thioether (uncleavable)
• Hindered disulfide (uncleavable)
• Site of conjugation
• Fc, HC, LC
Very potent
chemotherapeutic drug
• Tubulin polymerization inhibitors
• Maytansines (DM1, DM4)
• Auristatins (MMAE, MMAF)
• DNA damaging agents
• Calicheamicins
• Duocarmycins
• Anthracyclines (doxorubicin)
Genentech Confidential—Internal Use Only
3
Improving the Therapeutic Window
• ADCs can selectively deliver a potent cytotoxic drug to tumor cells via tumorspecific and/or over-expressed antigens
• Increase drug delivery to tumor
• Reduce normal tissue drug exposure
Chemotherapy
ADC
DRUG DOSE
TOXIC DOSE (MTD)
TOXIC DOSE (MTD)
Therapeutic Window
Therapeutic Window
EFFICACIOUS DOSE (MED)
EFFICACIOUS DOSE (MED)
MTD: Maximum tolerated dose; MED: Minimum Efficacious Dose
4
ADC More Efficacious than Free Cytotoxin in Mice
MMTV-HER2 Fo5 mammary tumor
(HER2-positive, trastuzumab-insensitive)
1500
Vehicle
Mean Tumor Volume (mm3 )
+/- SEM
DM1
Trastuzumab-mertansine
15 mg/kg, 817 µg/m 2
Trastuzumab 15 mg/kg
Trastuzumab 15 mg/kg + Free DM1 817 µg/m2
1000
Free DM1 817 µg/m2
Free DM1 (near MTD) 1947 µg/m2
500
Free DM1
(cytotoxin)
T-DM1 (ADC)
0
0
IV Dosing
5
10
15
20
25
30
Day
Parsons et al, AACR (2007); Modified from S. Spencer
ADC Better Tolerated than Free Cytotoxin in Rats
Single IV dose; rats
Body Weight
(% change from baseline)
T-DM1 (2040 µg DM1/m²)
Free DM1 (2400 µg DM1/m²)
Early mortality (100%)
Time (Day)
T-DM1: Trastuzumab emtansine
6
ADC Better Tolerated than Free Cytotoxin in Monkeys
White Blood Cells
6 mg/kg ADC (~750 μg MMAE/m2)
0.063 mg/kg MMAE (~750 μg MMAE/m2)
• No neutrophil decreases when cytotoxic drug delivered linked to an antibody
• ~2-3 times more cytotoxic drug can be given as an ADC
A. Kim, D. Danilenko, N. Dybdal, K. Flagella, K. Achilles-Poon
Modes of Anti-tumor Activity of ADCs
Tumor
Cell
Tumor cytotoxicity is target-directed
ADC-Ag binding → internalization in
lysosomes → ADC degradation → release
of toxin intracellularly → tumor cell death
Genentech Confidential—Internal Use Only
Tumor
Cells
Tumor cytotoxicity is target-enhanced
(bystander effect)
ADC-Ag binding → extracellular cleavage of
toxin → release of toxin in local tumor
environment → diffusion of toxin intracellularly
to neighboring tumor cells → tumor cell death
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Tissue Antigen Characteristics Are Key in ADCs
Careful selection of target antigens are an important
criterion for both the safety and efficacy of an ADC
•The ‘ideal’ tissue antigen should have:
–
–
–
–
–
High level of target expression in cancer cells
Little to no expression in normal cells
Expressed on the cell surface
Readily internalized
No shedding into the blood by cleavage of the antigen from cancer cell
surface
•The number of antigen molecules and antibody binding affinity for the
antigen may affect the potency of the ADC
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Modes of Toxicity of ADCs
+
Normal Cell
Systemic release of toxin
Unwanted ADC-mediated cytotoxicity
• Instability of linker
• Catabolism of ADC
• Targeted binding to normal tissues
expressing antigen
• Off-target (cross reactive) binding to normal
tissues
• Non-antigen-mediated ADC uptake (e.g., Fcmediated uptake, pinocytosis)
Genentech Confidential—Internal Use Only
10
Modes of Toxicity of ADCs
+
Normal Cell
Systemic release of toxin
Unwanted ADC-mediated cytotoxicity
• Instability of linker
• Catabolism of ADC
• Targeted binding to normal tissues expressing
antigen
• Off-target (cross reactive) binding to normal
tissues
• Non-antigen-mediated ADC uptake (e.g., Fcmediated uptake, pinocytosis)
Genentech Confidential—Internal Use Only
11
Slower Drug Deconjugation With Uncleavable Linker
Concentration (µg/ml)
Single IV dose 20 mg/kg ADC
Total Ab
Uncleavable
linker
Cleavable linker
Days post dose
Polson, et al., Cancer Res., 69(6), 2009
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More Stable Linker Reduces Systemic Toxicity of ADC in Rats
Change in bodyweight (grams)
Single IV dose given on Day 1 :


CD22-DM1 with
cleavable
linker
Days post dose
Polson, et al., Cancer Res., 69(6), 2009
13
More Stable Linker Reduces Systemic Toxicity of ADC in Rats
Single IV dose given on Day 1 :
Polson, et al., Cancer Res., 69(6), 2009
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Modes of Toxicity of ADCs
+
Normal Cell
Systemic release of toxin
Unwanted ADC-mediated cytotoxicity
• Instability of linker
• Catabolism of ADC
• DAR
• Targeted binding to normal tissues
expressing antigen
• Off-target (cross reactive) binding to normal
tissues
• Non-antigen-mediated ADC uptake (e.g., Fcmediated uptake, pinocytosis)
Genentech Confidential—Internal Use Only
15
Early Observation: Highly Drugged ADCs More Toxic
DAR: Drug-to-Antibody Ratio
1500
1300
AST (U/L)
1100
900
DAR 6
Study Day 0
Study Day 3
Study Day 5
700
DAR 4
DAR 4
DAR 2
500
DAR 2
DAR 6
300
100
-100
Vehicle Control
840 ug/m2
840 ug/m2
840 ug/m2
Herceptin-MC-vc- Herceptin-MC-vc- Herceptin-MC-vcPAB-MMAF (2P) PAB-MMAF (4P) PAB-MMAF (6P)
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ADC
Proportion
ThioMAb Technology: Controlling Heterogeneity
TDC
Proportion
DAR
DAR
•Engineered ThioMAb backbone allows more homogenous drug load (MMAE)
•Efficacy of TDC  ADC (mg/kg basis) and  2 x ADC (ug MMAE/m2 basis)
Junutula, et al., Nat. Biotech., 26(8), 2008
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Catabolism and Deconjugation of TDC is Slower than ADC in Rats
Single dose I.V. PK study: ADC or TDC with matched cytotoxin (MMAE) doses
Catabolism of the Antibody
Junutula, et al., Nat. Biotech., 26(8), 2008
Deconjugation of the Antibody
MMAE TDC is Better Tolerated Than ADC in Monkeys
Repeat IV doses of ADC or TDC, Days 1 and 23:
• No neutrophil decreases with TDC compared to equivalent ug/m2 dose of ADC
Junutula, et al., Nat. Biotech., 26(8), 2008
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Modes of Toxicity of ADCs
+
Normal Cell
Systemic release of toxin
Unwanted ADC-mediated cytotoxicity
• Instability of linker
• Catabolism of ADC
• DAR
• Site of conjugation
• Targeted binding to normal tissues
expressing antigen
• Off-target (cross reactive) binding to normal
tissues
• Non-antigen-mediated ADC uptake (e.g., Fcmediated uptake, pinocytosis)
Genentech Confidential—Internal Use Only
20
Modes of Toxicity of ADCs
+
Normal Cell
Systemic release of toxin
Unwanted ADC-mediated cytotoxicity
• Instability of linker
• Catabolism of ADC
• Targeted binding to normal tissues
expressing antigen
• Off-target (cross reactive) binding to normal
tissues
• Non-antigen-mediated ADC uptake (e.g., Fcmediated uptake, pinocytosis)
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Target Antigen Binding Causes “On-Target” Lymphoid Depletion
B-cell target depletion in splenic follicles: An example of “exaggerated pharmacology”
Vehicle
Anti-cyCD79b
CD20
Ki-67
Polson, et. al, Mol Cancer Ther 8(10), 2009
Anti-cyCD79b MCC DM1
Target Toxicity to Normal Tissues
Results: Seven patients received a total of 23 weekly doses of bivatuzumab
mertansine. One patient at the 100 mg/m2 and one at the 120 mg/m2 level
experienced stable disease during treatment phase but also developed grade 1
skin toxicity (desquamation). One of them received a second treatment course. At
the highest dose level achieved in this study (140 mg/m2), one patient developed
toxic epidermal necrolysis after two infusions and died. Massive apoptosis of skin
keratinocytes had occurred, whereas only symptomatic therapy for skin toxicity was
available. The risk-benefit assessment of all patients treated in the total phase I
program (4 clinical trials, 70 patients) turned out to be negative after consideration
of this case of a toxic epidermal necrolysis and the skin-related adverse events
observed in the other trials. Therefore, development of the conjugate was
Modes of Toxicity of ADCs
+
Normal Cell
Systemic release of toxin
Unwanted ADC-mediated cytotoxicity
• Instability of linker
• Catabolism of ADC
• Targeted binding to normal tissues
expressing antigen
• Off-target (cross reactive) binding to
normal tissues
• Non-antigen-mediated ADC uptake (e.g.,
Fc-mediated uptake, pinocytosis)
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Summary
• An ADC is both a “large molecule” and a “small molecule”.
• ADCs hold great promise for improving current oncology therapies.
– Highly potent cytotoxic agents are delivered directly to cancer cells, sparing normal
tissues.
– ADCs tend to be better tolerated than standard chemotherapy.
– Increased therapeutic window allows for better balance between safety/efficacy.
• There is a fine balance between efficacy and toxicity.
─ Choice of linker, cytotoxic drug and mAb are all important determinants of safety,
PK, and efficacy.
─ Toxicity is usually antigen-independent, ADC/drug-dependent.
─ Linker stability, DAR, and site of drug conjugation impacts toxicity.
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Acknowledgements
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Reina Fuji
Kelly Flagella
Willy Solis
Kirsten Achilles-Poon
Jacqueline Tarrant
Rama Pai
Ning Ma
Joe Beyer
Trung Nguyen
Nghi La
Fiona Zhong
Michelle McDowell
Noel Dybdal
Donna Dambach
Theresa Reynolds
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Angela Hendricks
Amy Oldendorp
Surinder Kaur
Ben Shen
Jay Tibbitts
Joo-Hee Yi
Kedan Lin
Doug Leipold
Ola Saad
Montserrat Carrasco-Triguero
Keyang Xu
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Luna Liu
Andy Boswell
Helen Davis
Margaret Kenrick
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Susan Spencer
Paul Polakis
Bonnee Rubinfeld
Jagath Junutula
Shang-Fan Yu
David Kan
Ivan Inigo
Wai Lee Wong
Kathy Kozak
Elaine Mai
Jeff Gorrell
Michael Mamounas
Andrew Polson
Seattle Genetics
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